The Luquillo Mountains:

Forest Resources and Their History

Peter L. Weaver

United States

Department of

Agriculture

Forest Service

International Institute

of Tropical Forestry

General Technical

Report IITF-44
Product Disclaimer

The use of trade or firm names in this publication is for 

reader information and does not imply endorsement by the 

U.S. Department of Agriculture of any product or service.

The Author:

Peter L. Weaver, Research Forester, 

Forest Service, U.S. Department of 

Agriculture, International Institute of 

Tropical Forestry, Jardín Botánico Sur, 

Río Piedras, PR 00926-1119.

November 2012

International Institute of Tropical Forestry

Jardín Botánico Sur

1201 Calle Ceiba

San Juan, PR 00926-1119

Cover Photos 

left: Recreation and Wildlife—The El Yunque hiking trail, one of the 

oldest, is a favorite for viewing flora and fauna. (Photo by Peter L. Weaver)

top right: Historic legacy—The construction of the Baño Grande bath 

house and bathing pool date to the late 1930s. (Photo from IITF files) 

bottom right: Water—Numerous streams provide pristine water supplies 

to surrounding communities. (Photo by Peter L. Weaver)
The Luquillo Mountains: 

Forest Resources and Their History

PETER L. WEAVER
ii

Contents

LIST OF FIGURES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

ABSTRACT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

FOREWORD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

OBJECTIVES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

CHAPTER 1. HISTORICAL PERSPECTIVE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Pre-Colonial Era. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Spanish Arrival, Exploration, and Settlement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Forest Proclamation and Land Acquisition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Opening of the Forest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Management of the Forest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Research and Training in the Forest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

CHAPTER 2. ENVIRONMENTAL SETTING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Geology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Physiography and Hydrology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Soils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Climate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

CHAPTER 3. TREE DISTRIBUTIONS AND MAJOR FOREST TYPES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Tree Species Affinities and Geographic Distribution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Field Sampling and Permanent Plot Monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Lower Montane Forest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Montane Forest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Palm Brake. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Dwarf Forest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

CHAPTER 4. ENVIRONMENTAL GRADIENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Tree Species Ranges in Luquillo Mountains. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Tree Life Cycles and Longevity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

MAJOR TYPES OF DISTURBANCE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

 Treefalls (Background Mortality). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Climatic Disturbances. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Landslides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Human Activities—Settlement and Development. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Accidents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Post-Disturbance Recovery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

CHAPTER 6. OTHER VEGETATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

Tree Plantings and Plantations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

Mahogany Line Planting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

Mahogany Provenance Trial. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Forest Service Arboretum (Caracoles). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

Other Tree Species and Common Herbs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

CHAPTER 7. VERTEBRATE FAUNA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Mammals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Birds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Reptiles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

Amphibians. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Fish. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
iii

Contents

CHAPTER 8. SPECIES DIVERSITY—PLANTS AND ANIMALS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

Plant Diversity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

Animal Diversity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

CHAPTER 9. CLASSIFIED SPECIES OF PLANTS AND ANIMALS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

Classified Plants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

Classified Animals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

CHAPTER 10. OTHER RESOURCES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

Water and Shrimp. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

Recreation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

Scenery and Trails. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

Heritage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

El Yunque Stories—Myth, Legend, and Curious Facts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

CHAPTER 11. DESIGNATED LAND USES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

The Baño de Oro Research Natural Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

Luquillo Experimental Forest Biosphere Reserve. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

Wild and Scenic Rivers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

The El Toro Wilderness Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

Special Use Permits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

CHAPTER 12. MAJOR FOREST RESEARCH SITES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

El Verde Ecological Studies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

Luquillo Forest Dynamics Plot (LFDP) at El Verde. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

Long Term Ecological Research (LTER) at Bisley. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

Riparian Palm Stand. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

Pico del Oeste Dwarf Forest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114

Pico del Este Dwarf Forest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114

CHAPTER 13. FOREST PLANNING AND MANAGEMENT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

Primary Forest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

Demonstration of Sustainable Timber Production. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

Wildlife. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

Wild and Scenic Rivers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

Wilderness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

Recreation and Conservation Education Programs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

Access (Roads, Trails, Acquisitions). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

Research. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

EPILOGUE—QUO VADIS?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

ACKNOWLEDGMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

ENDNOTES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

LITERATURE CITED. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

APPENDIX A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

APPENDIX B. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

APPENDIX C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

APPENDIX D. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

APPENDIX E. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

APPENDIX F. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

v

List of Figures

Figure 1—Location of the Luquillo Experimental Forest in northeastern Puerto Rico. Major cities and towns (21) 

and municipalities (underlined town names) (8) surround the forest. Built up areas are shaded. . . . . . . . . . . . . . . . . . . 2

Figure 2—Ecological Life Zones within the Luquillo Experimental Forest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Figure 3—Forest types within the Luquillo Experimental Forest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Figure 4—Acquisition of properties (tracts) in the Luquillo Experimental Forest. . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 5—Roads and hiking trails in the Luquillo Experimental Forest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 6—Plantation sites in the Luquillo Experimental Forest in 1947. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 7—Proposed timber production areas within the Luquillo Experimental Forest in 1950. . . . . . . . . . . . . . . . . . . 21

Figure 8—Geology of the Luquillo Experimental Forest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Figure 9—Major peaks, rivers, watersheds, flow gages, and water intakes in and around the Luquillo Experimental Forest. . . 25

Figure 10—Soils of the Luquillo Experimental Forest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28

Figure 11—Climatic diagrams for sites within the Luquillo Experimental Forest. . . . . . . . . . . . . . . . . . . . . . . . . . 31

Figure 12—Hurricane trajectories over Puerto Rico since 1700. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

Figure 13—Permanent and temporary plot locations, and major research sites within the Luquillo Experimental Forest. . . . . 42

Figure 14—Mean canopy heights per plot by elevation in the Luquillo Experimental Forest (linear trends for ridge, slope, 

and ravine). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44

Figure 15—Mean density of stems ≥4 cm d.b.h. per plot by elevation in the Luquillo Experimental Forest 

(linear trends for ridge, slope, and ravine). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Figure 16—Aboveground dry weight biomass per plot for stems ≥4 cm d.b.h. by elevation within the Luquillo Experimental 

Forest (linear trends for ridge, slope, and ravine). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45

Figure 17—Number of tree species per plot for stems ≥4 cm d.b.h. by elevation within the Luquillo Experimental Forest 

(linear trends for ridge, slope, and ravine). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Figure 18—Species-area curves for stems ≥4 cm d.b.h. by forest types within the Luquillo Experimental Forest. . . . . . . . . 46

Figure 19—Design of the arboretum in the Luquillo Experimental Forest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

Figure 20—Management areas and structures within the Luquillo Experimental Forest. . . . . . . . . . . . . . . . . . . . . . 79

Figure 21—Major designated areas within the Luquillo Experimental Forest. . . . . . . . . . . . . . . . . . . . . . . . . . . 104
vi

Abstract

This report presents an overview of the El Yunque National Forest, 

which is also designated as Luquillo Experimental Forest, in northeastern 

Puerto Rico. The principal topics include the environmental setting 

(geology, soils, and climate), environmental gradients, arborescent flora, 

vertebrate fauna, and forest management (i.e., plantations, silvicultural 

operations, planning, research, and designated land uses). A chronology 

from the time of European discovery to the present outlines major events 

in the Luquillo Experimental Forest, including an early presence of 

indigenous peoples, exploration for gold, timber extraction, farming, trail 

and road construction, and recreational developments. 

Keywords: Disturbances, forest resources, gradients, history, Luquillo 

Mountains of Puerto Rico, management, research. 
vii

The Luquillo Mountains of Puerto Rico bear a forest that, above all, is attractive. The attraction 

arises from a mysterious, magnificent, complex manifestation of nature: the mischievous laugh of 

a lizard cuckoo announcing forthcoming rain; the approaching roar of a torrent pounding on the 

forest canopy; weather-beaten palo colorados, invincible despite hundreds of hurricanes; deep shade 

beneath emergent tabonucos dripping with transpiration; understory trees obviously contented, 

including palms and ferns; dutiful yagrumos filling gaps; lianas thick with water; epiphytes with 

yellow-eyed lagartos; extended roots holding the mountain; the talkative approach of the San Pedrito; 

species nowhere else; streams of continuous clear forest water; and an incessant nocturnal symphony. 

A world renowned forest ecologist, the late Dr. Leslie Holdridge, as a result of a 10-year introduction 

to the tropics in the Luquillo forest, despite a subsequent career in tropical forests throughout the 

hemisphere and living at a distance, requested that his bodily remains be left in the Luquillo forest. 

So did the late Angelito Torres, a bull-of-the-woods reputedly born within the forest and an 

indefatigable worker in its care during all of a very active life. 

It is this attraction, after 43 years of Dr. Peter Weaver’s study deep in the Luquillo forest, that brought 

an advanced academic degree and led him to bring a comprehensive story of the forest, much of it 

unknown or forgotten, to this book. Not content with a purely historic record, Dr. Weaver describes 

the present condition of the forest and its prospective uses. I am proud to have been a colleague of 

Dr. Weaver’s during his life in the forest and in his preparation of this classic volume. 

Frank H. Wadsworth

FOREWORD

Introduction

The Luquillo Mountains of northeastern Puerto Rico, which 

contain the 11 310 ha El Yunque National Forest (EYNF) also 

administratively designated as the Luquillo Experimental 

Forest (LEF), are in essence an island within an island (fig. 1) 

(table 1). If sea level were to rise about 50 m, the valleys of the 

major rivers surrounding the mountains would flood and form 

an island comparable in size to many of the Lesser Antilles 

(Weaver 2002a). The mountains—steep, wet, and isolated at 

higher elevations—were not traversed by PR route 191 until 

1942. A major landslide in the early 1970s blocked the road, 

which has remained closed for > 40 years. 

The Luquillo Mountains rise abruptly from sea level at Las 

Cabezas de San Juan on the northeastern tip of Puerto Rico 

to 1074 m in elevation at El Toro Peak in the LEF. Over a 

distance of 20 km, annual rainfall increases from 900 mm 

along the coast through 2500 mm at the forest entrance to 

>4500 mm at the summits (Briscoe 1966). The gradient in 

elevation and moisture results in six distinct ecological life 

zones (Ewel and Whitmore 1973, Holdridge 1967). Subtropical 

dry forest grows along the northeastern coast and subtropical 

moist forest just inland. Ascending the mountains, subtropical 

wet forest encircles most of the LEF along the forest border 

(fig. 2). Subtropical rain forest and subtropical lower montane 

rain forest are found to the windward of the mountain divide, 

and subtropical lower montane wet forest mainly to the 

leeward. A patch of subtropical moist forest lies in an isolated 

parcel to the southwest. Wet forest types account for about 

75 percent of the land area within the LEF. 

Four forest types known as lower montane rain forest, 

montane rain forest, dwarf forest, and palm brake occur in 

the Greater Antilles and in the mountainous Lesser Antilles 

between St. Kitts and Grenada (Beard 1949, Little and 

Wadsworth 1964, Seifriz 1943, Smith 1954). These four forest 

types are recognized with local names in the LEF: tabonuco 

forest between 150 and 600 m; colorado forest between 600 

and 900 m; dwarf forest above 900 m; and palm brake on 

steep windward facing slopes and in drainages above 450 m 

(Wadsworth 1951) (fig. 3). The first two types cover about 

80 percent of the LEF. In addition, four major vegetative 

communities have been described for the above forest types 

along the same gradient (1) Dacryodes excelsa-Manilkara 

bidentata, (2) Cyrilla racemiflora-Micropholis garciniifolia, 

INTRODUCTION

The Luquillo Mountains as viewed from PR route 2, which parallels the north coast. Part of the El Toro Wilderness Area extends left to right through the upper 

middle part of the photo. El Yunque rock is visible at the upper right. (Photo by Peter L. Weaver) 
2

Introduction

!.

!.

!.

!.

!.

!.

!.

!.

!.

!.

!.

!. !.

!.

!.

!.

!.

!.

!.

!.

!.

Ceiba

Loíza

Juncos

Gurabo

Cataño

Caguas

Humacao

Naguabo

Fajardo

Bayamón Luquillo

Carolina

San Juan

Guaynabo

Canóvanas Río Grande

Las Piedras

Trujillo Alto

Sabana

Palmer

El Verde

Legend

!. Towns

Primary roads

Secondary roads

LEF boundary

pr_municipalities

Built-up surface

A B A

C

D

E

A

B

C

D

E

Luquillo Experimental Forest

Arroyo tract

Sandoval tract

La Condesa tract

Private inholdings

Cabezas de

San Juan

(3) Tabebuia rigida-Eugenia borinquensis, and (4) Prestoea 

montana-Cecropia schreberiana, respectively (Gould and 

others 2006). Hereafter, Beard’s terminology will be used and 

cited throughout the text as lower montane forest, montane 

forest, palm brake, and dwarf forest; however, Beard’s 

complete terminology will be written out in figures and tables. 

In 1876, the Spanish King Alfonso XII established forest 

reserves in Puerto Rico, including lands in the Luquillo 

Mountains, by means of the “La Ordenanza de Montes.” 

However, it wasn’t until 1880-81 that the lands in the Luquillo 

Mountains became known as the “Sierra de Luquillo.” The 

King’s declaration antedated the 1891 Land Revision Act that 

created the U.S. National Forest System (table 2) (appendix A). 

In 1898, after the Spanish-American War, Spain ceded Crown 

lands to the United States. In 1903, President Theodore 

Roosevelt proclaimed the lands in the Luquillo Mountains 

as the Luquillo Forest Reserve, a name that was retained 

until 1907. Subsequent administrative decisions led to name 

changes for the forest. From 1907 to 1935, the forest was 

called the Luquillo National Forest, the only tropical forest 

within the National Forest System. From 1935 until 2007, it 

was referred to as the Caribbean National Forest to reflect 

lands held elsewhere in Puerto Rico, e.g., the Toro Negro 

Unit in the Central Mountains retained from 1935 until 1970. 

Finally, in 2007, the forest was designated as El Yunque 

National Forest, the traditional name used by island residents. 

Since 1956, the forest has also been designated as the LEF to 

administratively recognize its concurrent research activities. 

The administrative complexity of the forest was succinctly 

stated 60 years ago in the introduction to the forest atlas 

(Upson 1949, see endnotes): 

“The Caribbean Forest in part is actually the oldest Forest 

Reserve, having been established by the Spanish Crown 

in 1876. It started as a Forest Reserve by Presidential 

Proclamation in 1903, took the general changeover in 

designation to a National Forest and then a change in its 

given name to include two Purchase Unit additions, and 

has been built up by purchase, donation, and transfer 

since 1931. It contains lands to which none of the general 

US land laws apply and is subject to special local laws 

Figure 1—Location of the Luquillo Experimental Forest in northeastern Puerto Rico. Major cities and towns (21) and municipalities (underlined town names) 

(8) surround the forest. Built up areas are shaded.

A Luquillo Experimental Forest 

B Arroyo tract 

C Sandoval tract 

D La Condesa tract

E Private inholdings

Legend

 Towns n LEF boundary

 Primary roads n Municipalities 

 Secondary roads n Built-up surface

8 4 0 8 km

4 2 0 4 km

0 2 10 0 40 60 80

km

N
3

Introduction

Table 1—Fascinating trivia about the Luquillo Experimental Foresta

TOPIC EXPLANATION

Forest Reserve Set aside by Spanish Crown, 1876-1898

Spanish-American War Spain passes crown lands in Puerto Rico to United States

National Forest Forest Reserve proclaimed by Theodore Roosevelt in 1903, renamed as a national forest in 1907

Administration Both a national forest and an experimental forest; also, occupies part of eight local municipalities

Sizeb When set aside, 5040 ha; today, 11 310 ha 

Designated Areas Research Natural Area (1949), Biosphere Reserve (1976), Wild and Scenic Rivers (2002), El Toro Wilderness (2005)

Major research sitesc Permanent forest monitoring plots (scattered in LEF), El Verde LTER studies, Luquillo forest ecology and dynamics

plot (El Verde), LTER (Bisley), riparian palm stand plot, dwarf forest (Pico del Este and Pico del Oeste)

Geology Uplifted Cretaceous marine volcanoclastic rocks and Tertiary quartz diorite intrusive rocks

Topography From 120 to 1074 m in elevation; 6 peaks >1000 m

Climate Tropical maritime

Rainfall (mean annual) Increases with elevation, about 3800 mm for the forest

Rainfall (total 1 day) Recorded 485 mm on May 19, 1969 on Pico del Este

Showers per year 1,625 between 1938-1942 at La Mina 

Temperature extremes Minimum = 11 °C and maximum = 32 °C

Hurricanes (major) About 15 passed near or over mountains since 1700

Hail January 1969 for 10 minutes near Pico del Este

Water

Sources Ten watersheds and rivers within the LEF

Largest rivers Headwaters of Río Grande de Loíza and Río Mameyes

River—free flow Río Mameyes, only major LEF stream without a dam

Municipal water 35 intakes on forest streams supply ~750,000 people

Shrimp 11 migratory species live in forest streams

Trees

Native tree species 225 in total; 41 percent shared with continents, 28 percent West Indian but not on continents, and 31 percent 

endemic to Puerto Rico and the U.S. Virgin Islands

Endemic tree species 8 species to the Luquillo Mountains alone; 60 species to Puerto Rico (and the Luquillo Mountains)

Planted tree species 144 (agriculture, arboretum, ornamental, and plantations)

Exotic tree species 113 planted but not all survived

Native conifer Podocarpus coriaceae near El Yunque Peak

Coastal lowland species Pterocarpus officinalis—rare Caribbean island occurrence at 250 m elevation

Most common Prestoea montana from forest border to summits

Rarest Uncertain— one of the dwarf forest endemics, possibly Didymopanax gleasonii or Styrax portoricensis

Range (greatest in LEF) Cecropia schreberiana, Henriettea squamulosa, Micropholis garciniifolia, and Prestoea montana

Range (greatest in the Guarea guidonia—Cuba to Argentina; Cyrilla racemiflora, eastern Virginia to Amazon River in Brazil

Western hemisphere)

Range—also in Africa Andira inermis, Ceiba pentandra, Pterocarpus officinalis

Largest (in diameter) Cyrilla racemiflora previously recorded at 2.65 m in d.b.h.

Tallest (total height) Dacryodes excelsa and Manilkara bidentata at >30 m

Oldest tree species Cyrilla racemiflora and Mangolia splendens at ~1000 years

Densest native wood Clusia clusioides, specific gravity at ~0.9 g cm-3

Lightest native wood Ochroma pyramidale, specific gravity at ~0.22 g cm-3

Vertebratesd

Mammals 16 species, 11 native bats + 5 introduced pests

Birds 107 species (12 endemics, 2 endemic subspecies), 7 exotics 

Reptiles 19 species (1 endemic), 18 natives, 11 lizards, 3 geckos (1 introduced), 5 snakes 

Amphibians 15 species (11 endemics), 13 native, 2 introduced 

Fish 7 species, 6 native and 1 introduced

Recreation About 750,000 visitors annually

Major sites El Portal Rain Forest Center; La Coca falls; Caimitillo, Palo Colorado, Río Cubuy, and Sierra Palm Picnic Areas; 

Baño Grande and Baño de Oro pools

Other sites Quebrada Grande and Río Sabana picnic areas, La Mina falls 

Trails 23 trails, 39 km recreational + 19 km administrative 

Towers El Yunque, Mt. Britton, and Yokahu

Forest vistas El Yunque rock, Los Picachos, Pico del Este, Pico del Oeste, and above towers 

Other vistas Las Cabezas viewpoint, La Mina and El Toro peaks, Río Espíritu Santo bridge 

aSources: Data extracted from text and the literature. 

bSource: U.S. Department of Agriculture, Forest Service (1995), see endnotes.

cLTER = Long term ecological research.

dEndemics to Puerto Rico
4

Introduction

and practices governing surveys, titles, registration, and 

reservations. And it has been under more administrative 

directions regionally, is the smallest separately 

administrated area, and the closest tied to Forest Research, 

of any Forest in the entire National Forest system.” 

Management of national forests involves livestock grazing, 

timber harvest, mining, water resources, wildlife, and 

recreation. All received attention at some time during the 

forest’s first 50 years (U.S. Department of Agriculture Forest 

Service 1997a, 1997b; Wadsworth 1951, 1952a, 1952b, 1970). 

Nearly a century of research in the Luquillo Mountains 

provided much information on tree species composition, 

tree size, growth, regeneration, and ecology (Britton and 

Wilson 1923, 1930, Little and Wadsworth 1964, Little and 

Woodbury 1976, Little and others 1974, Odum and Pigeon 

1970, Wadsworth 1951) as well as hurricane impacts and 

subsequent recovery (Walker and others 1991, 1996). Human 

settlement, including past agriculture and tree planting at 

lower elevations, has imposed changes on the landscape since 

the early 1800s (Aide and others 1996, Marrero 1948, Scatena 

1989, Wadsworth 1970, Weaver 1989a, Weaver and Bauer 

1986, Zimmerman and others 1995). Terrain above 600 m 

in elevation largely escaped human intervention because of 

the inaccessible steep slopes and heavy rainfalls (Lugo 1994; 

Wadsworth 1949, 1950; Weaver 1972). 

Table 2—Chronological designations of areas encompassing all or part of the Luquillo 

Mountains known today as the Luquillo Experimental Forest or El Yunque National Forest 

Land unit designations Year(s)

Size

ha

Forest

percenta

Pre-Columbian

Yukiyú (Luquillo Mountains) <1500 19 600 173.2

Spainb

Forest Reserve 1876-1898 10 058 88.9

USDA Forest Service 

Luquillo Forest Reservec 1903-1907 5040 44.6

Luquillo National Forestc 1907-1935 5040 44.6

Caribbean National Forestd 1935-2007 6184 54.7

Baño de Oro Natural Areae 1949-present 745 6.6

Luquillo Experimenal Forestd,f 1956-present 10 638 94.1

Biosphere Reservef 1976-present 11 274 99.7

LTER—Bisley Watershedsg 1985-present ~363 3.2

LFDP—Ecological Gridg 1990-present 16 0.1

Wild and Scenic Riversh 2002-present 525 6.6

Río Icacos—scenich 2002-present 74 0.6

Río Mameyes—wild/scenich 2002-present 100 0.9

Río de la Mina— scenich 2002-present 38 0.3

El Toro Wilderness 2005-present 4050 35.8

El Yunque National Forestd 2007-present 11 310 100.0

aPercent of current forest area of 11 310 ha. 

bEstimates (Domínguez Cristóbal 1997a).

cU.S. Department of Agriculture, Forest Service (1995), see endnotes.

dFrom 1935 to 1970, the designation Caribbean included land located outside of the Luquillo Mountains. Caribbean 

National Forest and Luquillo Experimental Forest are coterminous, the second name recognizes research activities. 

Caribbean changed to El Yunque, which is the current name.

eProposed expansion of 1835 ha will bring the Baño de Oro to a total 2580 ha (U.S. Department of Agriculture, 

Forest Service 1997a).

f

Areas according to dates listed. Currently, both are 11 310 ha.

gLong-term monitoring areas: LTER = Long Term Ecological Research; LFDP = Luquillo Forest Dynamics Plot.

hEstimate of 525 ha includes wild and scenic river corredors and adjacent recreation areas (U.S. Department 

of Agriculture, Forest Service 1997a). Linear corredor totals for the 3 rivers: Rio Icacos (scenic) = 3.7 km; Rio 

Mameyes (scenic) = 1.6 km and (wild) = 3.4 km; Rio de la Mina (scenic) = 1.9 km. Corredor areas are arbitrarily 

estimated at 100 m on each side of the respective rivers.
5

Introduction

PR 186

PR 966 PR 191

PR 988

Forest type

Lower montane rain forest

Montane rain forest

Palm brake

Dwarf forest

5663

3441

1838

368

Area (ha)

50.1

30.4

16.2

3.3

Legend LEF (%)

Primary roads

Secondary roads

LEF boundary

Forest type Area (ha) LEF (%)

n Lower montane rain forest 5663 50.1

n Montane rain forest 3441 30.4 

n Palm brake 1838 16.2

n Dwarf forest 368 3.3

Legend

 Primary roads

 Secondary roads

 LEF boundary

Figure 3—Forest types within the Luquillo Experimental Forest.

PR 186

PR 966 PR 191

PR 988

Legend

Primary roads

Secondary roads

LEF boundary

Life zones Area (ha) LEF (%)

Lower montane rain forest 1148 10.1

Lower montane wet forest 4338 38.4

Subtropical moist forest 229 2.0

Subtropical rain forest 1387 12.3

Subtropical wet forest 4208 37.2

Life zones Area (ha) LEF (%)

n Lower montane rain forest 1148 10.1

n Lower montane wet forest 4338 38.4 

n Subtropical moist forest 229 2.0

n Subtropical rain forest 1387 12.3

n Subtropical wet forest 4208 37.2

Legend

 Primary roads

 Secondary roads

 LEF boundary

Figure 2—Ecological Life Zones within the Luquillo Experimental Forest.

8 4 0 8 km

4 2 0 4 km

0 2 10 0 40 60 80

km

8 4 0 8 km

4 2 0 4 km

0 2 10 0 40 60 80

km

N

N
6

Objectives

One of the first observations made by foresters at the new 

Tropical Forest Experiment Station in 1941 was that “study 

of the existing literature showed that no works on forestry 

in Puerto Rico had been published, but a few good botanical 

works are available” (Anon. 1941, page 4, see endnotes). 

Since then, a considerable amount of forestry and ecological 

research has been carried out. However, the highlights of 

those efforts have never been conveniently summarized into 

a reference document. The purpose of this report is to provide 

an overview of the LEF’s resources and an orientation to 

research and management activities carried out on the forest, 

especially with regard to forestry:

• A chronology of major past activities or events which had an 

impact on the forest environment since European discovery.

• Background information on geology, physiography, soils, 

climate (hurricanes and recovery), water resources, flora, 

vertebrate fauna, classified plants and animals, scenery, 

recreation, roads, and trails. 

• Detail on tree species composition, growth by forest 

type, and silvicultural activities, with special interest in 

permanent plot monitoring.

• A description of environmental gradients within the 

Luquillo Mountains along with the results of recent 

sampling of tree species by elevation and topography within 

different forest types.

• Information on plantings of native and exotic tree species for 

different purposes.

• General information on major research projects carried out 

at particular locations such as the Baño de Oro Research 

Natural Area, Bisley watersheds, the El Toro Wilderness 

Area, the El Verde field station, Pico del Este, Pico del 

Oeste, and scattered permanent and temporary plots. 

• A concise summary of current planning and management 

issues on the forest. 

• Maps showing the location of places mentioned in text.

• Some little known observations and facts about the LEF. 

Much of the information regarding tree distributions and 

forest types was derived from a system of permanent plots 

established throughout the forest from 1943 to 1956. Figures, 

tables, and photographs illustrate much of this material. 

General ecological observations have also been incorporated 

into the text; however, detailed studies about watersheds and 

aquatic invertebrates, other fauna (i.e., bats, birds, lizards, 

frogs, and fishes), soils, and nutrient cycling are outside of the 

scope of this review. Plant nomenclature is based on relatively 

recent work (Liogier 1985, 1997). Authorities for plant species 

not listed in appendices appear in text.

OBJECTIVES
7

Historical Perspective

The Luquillo Mountains have a long history that involves 

pre-Columbian cultures, Spanish colonization, gold mining 

and timber exploitation, the construction of access roads and 

facilities, and ultimately forest management and research. 

Details and most citations for the following historical section 

appear in the chronology (appendix A).

Pre-Colonial Era

Archaeological finds confirm the presence of pre-Columbian 

cultures in Puerto Rico around 300 B.C. and new discoveries 

possibly date to 2,000 years B.C. or earlier. During the precolonial era, the forests on the lower slopes of the Luquillo 

Mountains provided indigenous cultures with a source of 

food and materials for the construction of shelters and boats. 

However, the impact of these groups on forest resources was 

minimal. Archaeological discoveries—including petroglyphs 

near and within the forest—and pre-Columbian names for 

different sites (e.g., El Cacique, El Yunque, and Cubuy) 

indicate that native peoples were familiar with the mountains. 

The Luquillo Mountain summits, visible for about 100 km 

offshore, were likely used as a geographical reference by 

indigenous sailors; moreover, the mountaintops were probably 

the first lands sighted by Spaniards as they approached the 

island from the southeast.

Spanish Arrival, Exploration, 

and Settlement

Europeans made contact in Puerto Rico during the 1490s 

and by the early 1500s colonization had begun in the river 

valleys flowing out of the Luquillo Mountains. At that time, 

the island’s indigenous peoples were in conflict. Soon, gold 

was found in the sands of Río Blanco, Río Canóvanas, Río 

Espíritu Santo, Río Fajardo, Río Grande, Río Mameyes, Río 

de la Mina, Río Prieto, and Río Sabana. The first discovery 

was in 1509, and placer mining was underway in the Río 

Fajardo and Río Blanco around 1513. Mining was the island’s 

most important economic activity during the early 16th 

century, including the eastern mountains. The period of 

greatest mining activity ended around 1530 when the houses 

of miners were attacked and burned. Forced labor, introduced 

diseases, confrontations, and migrations elsewhere devastated 

the island’s indigenous population by the mid-1500s. As late 

as 1582, colonists reported the mountains as unsafe because 

they were still occupied by hostile groups. Mining continued 

into the 20th century along several streams, including the 

Río Mameyes where gold was sought in the upper watershed 

Chapter 1. HISTORICAL PERSPECTIVE

top: Petroglyphs are found within the Luquillo Experimental Forest (LEF), 

including sites in the Quebrada Jiménez, La Coca, Río Cubuy, Río Icacos, 

Río Comándulas, and Río Sabana watersheds, and near La Mina peak. 

(Photo from IITF files) bottom: A pre-Columbian stone ax probably used 

between 600 and 1500 A.D. was found during survey activities within the 

LEF. (Photo by Iván Vicéns)
8

Historical Perspective

until 1870 and below the bridge referred to as Puente Roto 

until 1946. Locally, mining had an impact in the mountains. 

Mining camps depended on felled trees for the construction 

of tunnels, dikes, canals, shacks for protection, corrals 

for livestock, fuelwood, and the transport of equipment 

(Anderson-Córdova 2005). Throughout this period, the 

Spanish used the resin from Dacryodes excelsa to caulk their 

ship timbers.

During the 1600s, Puerto Rico remained isolated with only 

three populated areas and residents lived through contraband. 

In the 1730s, coffee was introduced and planted on the lower 

slopes of the Luquillo Mountains. Settlement in eight towns 

surrounding the Luquillo Mountains took place between 

1772 and 1890, with the greatest influx after 1820. In 1815, 

the Cédula de Gracias conceded Crown Lands on the island 

for agricultural development, stimulating the local economy 

through new farms and businesses. During the 1830s, some 

of the lands made available were situated in the Luquillo 

Mountains. Between the mid-1830s and the mid-1890s, 

timbers were cut on the lower slopes of the mountains, 

including the Bisley, Jiménez, and Mameyes watersheds, and 

exported through the coastal town of Luquillo. Subsistence 

crops were planted as Spanish Crown lands decreased in area. 

As early as 1839, however, the Spanish expressed concern 

regarding the protection of forests, fish, and wildlife within 

the mountains. In 1853, two Spanish foresters were sent to 

survey and manage Crown Lands, including those of the 

top: Gold placer mining was common along prominent Luquillo 

Mountain streams. Surnames of past miners such as Guzmán, Jiménez, 

and Toro survive on maps of the forest and surrounding areas as do 

the names of streams such as Río de la Mina and Quebrada Baño de 

Oro. (Photo from IITF files) bottom: An olive jar, possibly used during 

exploration for gold during the Spanish colonial period between 1500 

and 1700 A.D. was found at high elevation in the Luquillo Experimental 

Forest. (Photo by Iván Vicéns)
9

Historical Perspective

Luquillo Mountains. The 19th century in Puerto Rico was 

characterized by a rapid increase in population, an increased 

demand for agricultural land, poor farming practices, 

constant political disturbances, a lack of communication 

between metropolitan centers and the rural population, and a 

scarcity of personnel and budget for forestry activities—all of 

which led to the dramatic decline of the island’s forest cover 

(Domínguez Cristóbal 1989). 

Forest Proclamation and Land Acquisition

In 1876, Spanish King Alphonso XII proclaimed forest 

reserves in Puerto Rico, including the 10 000 ha Luquillo 

forest reserve. In 1885, a forest guard was assigned to patrol 

the Luquillo Mountains. At that time, transportation problems 

were a major deterrent to timber exploitation. In 1898, the 

Spanish Crown ceded Puerto Rico to the United States in 

the Treaty of Paris. By then, most of the island’s original 

forests had been cut over. However, the Luquillo Mountains 

still protected about 16 000 ha of forest and shrub land, 

including nearly 2300 ha of virgin forest at higher elevations. 

In July 1898, Puerto Rico was renamed Porto Rico, a Federal 

designation that would remain until May 1932.

 Between 1891 and 1897, two acts (i.e., Land Revision Act and 

Organic Administrative Act) passed by the U.S. Government 

allowed the President to set aside forest lands; subsequently 

in 1903, President Theodore Roosevelt proclaimed the 

transferred Crown lands as the Luquillo Forest Reserve. The 

original proclamation boundary encompassed about 25 650 ha 

classified as public forest as soon as the government might 

acquire the lands; later, the boundary was modified. About 

1200 ha remained as property of the people of Puerto Rico 

until 1916 when the land was legally turned over to the Federal 

government by the local legislative assembly. Between 1903 

and the early 1930s, the national forest contained 21 parcels 

of land totaling 44 percent of today’s LEF (fig. 4). Between 

1933 and 1949, an additional 48 parcels totaling 5625 ha, 

or nearly 50 percent of the current land area, were acquired 

or purchased by the Federal government and added to the 

national forest. In 1970, another 19 parcels amounting to 

about 635 ha, or < 6 percent of the total area, were attained 

through exchange. Toro Negro and St. Just, previously Forest 

Service, U.S. Department of Agriculture, properties in other 

parts of the island, were exchanged for tracts in the Luquillo 

Mountains and added to the forest. Finally, in the early 1990s, 

four more parcels with about 37 ha, or about 0.3 percent, were 

purchased, bringing the grand total to about 11 310 ha. 

The Luquillo Mountains total about 19 660 ha and are 

administratively located within eight municipalities: Ceiba 

(5.4 percent), Fajardo (5 percent), Juncos (4.1 percent), Las 

Piedras (5.6 percent), Loíza (11.5 percent), Luquillo 

(10.8 percent), Naguabo (22.6 percent), and Río Grande (35 

percent) (Wadsworth 1949). Today, the LEF is comprised 

of one major block of forest of about 11 000 ha and several 

small, isolated parcels: three in the southwest (i.e., Arroyo 

with 60.3 ha, La Condesa with 219.7 ha, and Sandoval with 

12.6 ha), one to the south (15.7 ha), and other smaller tracts 

near the northeastern and southeastern borders. Moreover, 

one major inholding, Barrio Mameyes Segundo, occupies 

54 ha and is situated east and west of PR route 191 at km 7.0 

(U.S. Department of Agriculture, Forest Service 1997a) (fig. 

1). Three other smaller inholdings are located in the same 

vicinity, and two others are situated along PR route 186. 

The total area of inholdings is about 70 ha. 

Opening of the Forest 

From 1903 until 1918, the U.S. Government was not able to 

dedicate much attention to the newly acquired national forest. 

Other challenging overseas commitments, including the 

construction of the Panama Canal (1903-14), negotiations for 

the purchase of the U.S. Virgin Islands (pre-1917), and World 

War I (1914-18) assumed center stage. During this period, 

several activities like placer gold mining, timber extraction, 

and charcoal production continued in the mountains. In 

Timber cutting occurred in the lower montane rain forest and the montane 

rain forest from the time of initial settlement through the early 1950s. (Photo 

from IITF files) 
10

Historical Perspective

0 

2000 

4000 

6000 

8000 

10000 

12000 

1880 1900 1920 1940 1960 1980 2000 

Area (ha) 

Year 

Land acquisition 

Figure 4—Acquisition of properties (tracts) in the Luquillo Experimental Forest.

Legend

Primary roads

Secondary roads

Proclamation boundary

LEF boundary

PR 186

PR 966 PR 191

Land Acquisition

National Forest in 1903

Acquisitions by 1940

Acquisitions by 1970

Recent acquisitions

5040

4648

1586

36

Area (ha)

44.6

41.1

14.0

0.3

LEF (%)

Land Acquisition Area (ha) LEF (%)

n National Forest in 1903 5040 44.6

n Acquisitions by 1940 4648 41.1 

n Acquisitions by 1970 1586 14.0

n Recent acquisitions 36 0.3

Legend

Primary roads

Secondary roads

 Proclamation boundary

 LEF boundary

8 4 0 8 km

4 2 0 4 km

0 2 10 0 40 60 80

km

N
11

Historical Perspective

1905, narrow trails existed to El Yunque, sites across the 

mountains to the south, and into the Espíritu Santo and 

Jiménez watersheds. In 1910, a visiting U.S. Department of 

Agriculture official found property ownership records in the 

mountains to be in a state of chaos. Between 1912 and 1916, 

the national forest was surveyed, mapped, and the boundaries 

were monumented. Those farming within the boundaries were 

allowed to continue by permit. 

Between 1912 and 1926, water was diverted from the forest 

borders to supply the needs of communities and towns 

surrounding the Luquillo Mountains. In 1928, construction 

began on the Rio Blanco Hydroelectric plant with intakes on 

the Río Cubuy, Río Icacos, Río Prieto, and Río Sabana. During 

the 1970s, the same system supplied water to the Roosevelt 

Roads Navy Base near Ceiba and the island of Vieques. In 

1950, San Juan began to receive water via the reservoir on the 

Río Grande de Loíza watershed. Today, two new reservoirs are 

planned or under construction; one on the Río Blanco south of 

the forest and the other near the town of Juncos. 

From 1919 to 1926, about 60 km of horse trails were laid out 

to patrol forest boundaries. Several construction projects 

began in the mountains in the 1920s and their development 

continues to the present, with the major efforts taking place 

in the 1930s. Between 1926 and 1929, the first section of PR 

route 191 was built between Palmer and Catalina (fig. 1). 

In 1933, the Emergency Conservation Program began 

extensive reforestation, road construction, and recreational 

improvements within the mountains. Moreover, in 1928, 

a narrow gage cable railway was built in the Río Blanco 

watershed just below the southern boundary of the forest to 

develop water control structures on the Río Icacos and nearby 

streams originating in the Luquillo Mountains. 

U.S. military involvement in the Luquillo Mountains began 

in 1933 when U.S. Army reserve officers briefly supervised 

Puerto Rico’s Emergency Conservation Program; later 

cooperation continued with the Forest Service in Civilian 

Conservation Corps (CCC) projects. In 1942, preparations 

for World War II in the Caribbean basin were initiated by 

army engineers who built a road and laid a telephone line to 

El Yunque peak where the U.S. Army Signal Corps operated 

an early warning radar system to detect enemy aircraft. In 

the 1960s under Forest Service permits, the Atomic Energy 

Commission, as part of the “Atoms for Peace” program, 

initiated the gamma radiation project near El Verde to 

determine the ramifications of using nuclear devices to 

excavate a proposed sea level canal in Panama. In 1963, 

the U.S. Army carried out a 0.4 ha defoliation experiment 

testing the herbicide Agent White (2, 4-D, and Picloram 

without dioxin). In the same year, the U.S. Navy used the 

electronic site at Pico del Este to trace missiles on a target 

range in nearby Vieques. Later in the 1960s, surveillance 

radar was installed for different agencies, among them the 

Federal Aviation Administration (FAA), which monitored 

flights approaching the San Juan airport. In 2003, the U.S. 

Navy departed from the Roosevelt Roads Naval Station and 

discontinued its use of the Pico del Este electronics site.

From 1935 to 1943, the CCC implemented its work program 

in cooperation with the Forest Service, building 100 km of 

roads and 80 km of trails to open the forest for human use. 

At La Mina, CCC workers built two picnic areas, 18 stone 

cabins that were later converted to picnic shelters, two bathing 

pools (i.e., Baño de Oro and Baño Grande), a fish hatchery, 

and the El Yunque pavilion, which later became the Rain 

Forest restaurant. Also built on nearby summits were the 

Mt. Britton tower and El Yunque radar post, and at lower 

elevations barracks and overnight shelters on the El Toro and 

El Yunque trails. Opened to the public in 1934, the La Mina 

recreation area was immediately popular among islanders. 

The recreation area and subsequent improvements remain 

today. However, an attempt to introduce rainbow trout into the 

LEF’s streams failed. In 1935, applications were accepted for 

the construction of eight summer cottages near La Mina. Soon 

after, two spur roads, PR routes 930 and 9938 were built to 

accommodate about 20 additional cottages. Later, all but three 

of the cottages were removed.

In 1937, the Puerto Rico Reconstruction Administration built 

the El Verde field station, which has served as a major research 

site since the early 1960s. In 1949, construction of the El 

Construction of PR route 191 from Palmer to Naguabo started in 

1926 and was completed in 1942. The road traversed the Luquillo 

Mountains and later provided access via tributary roads to the 

summits of El Yunque, Pico de Este, and Pico del Oeste. (Photo from 

IITF files)
12

Historical Perspective

Yunque Peak Electronics Communication Center began, and 

between 1974 and 1995, the facilities were consolidated. In 

1950, the Eliza Colberg Girl Scout Camp was dedicated near 

El Verde. In 1963, the radar facilities at Pico del Este and 

the Yokahú tower along PR route 191 were both opened. In 

1976, the Youth Conservation Corps (YCC) program began 

operating and in 1982 the Catalina Service Center opened as 

the new Forest Service office complex.

PR route 191, the principal forest road, was completed in 

1942 and served the public until 1970 when it was covered by 

major landslides in the Río Icacos watershed. Repairs were 

attempted in the mid-1970s but reconstruction plans were 

abandoned in 1992. Another 16 roads still present today were 

constructed within or along forest borders at different times 

(fig. 5) (table 3). These may be conveniently divided into three 

major groups: 

1. Tributary roads to PR route 191(Mameyes-Río Blanco 

road), which include the PR route 930 (Molindero road), 

PR route 9938 (Mt. Britton road), and FS-10 (El Yunque 

road) were built in the late 1930s. FS-27 (Pico del Este road) 

was built from 1958 to 1962. These roads served to access 

recreation areas or Federal Government observation points.

2. PR route 186 (El Verde Road) was built in stages between 

1945-48 and 1955-57. Its major tributary roads, PR route 946 

(Cubuy road), PR route 956 (Guzmán Arriba road), and PR 

route 9948 (no local name) were constructed between 1935 

and the 1970s to serve settlements within the respective areas. 

The PR 911 (Sonadora link), PR 903 (El Verde station link), 

and PR 963 (Eliza Colberg link) connections with PR route 

186 were built between the late 1930s and late 1940s to access 

Forest Service facilities along the western boundary of the 

LEF. The Youth Conservation Corps link was built in 1973.

3. The last group of roads was located within or near the 

northern boundary of the LEF. PR route 966 (Jiménez 

road), PR route 983 (Sabana-Pitahaya road), and PR route 

988 (Sabana-Catalina road) connected major highways and 

settlements. These roads could also serve for timber extraction 

that was being contemplated along the northern boundary of 

the LEF. Two smaller roads, PR 9915 (Bisley road) and PR 915 

top left: Completed in 1982, the Catalina Service Center houses the administrative offices of Forest Service specialists in wildlife, water 

resources, and forest management. (Photo by Peter L. Weaver) bottom left: Rainbow trout eggs imported from the United States during the 

mid-1930s were introduced into this circular pool along one of the trails within the Luquillo Experimental Forest. (Photo by Iván Vicéns) 

top right: Mt. Britton tower was built in 1938 to commemorate Nathanial Britton, a New York Botanical Garden botanist, who collected 

plants during expeditions to El Yunque from 1913 to 1917. (Photo by Iván Vicéns) bottom right: El Yunque observation tower and storage 

buildings were constructed in 1938 as defense measures. (Photo by Peter L. Weaver)
13

Historical Perspective

Table 3—Major roads and connecting roads within or bordering the Luquillo Experimental Forest

Date(s)a

Route No. 

length (km)a Road name Brief comments: road purpose and notes

PR route 191 and tributary roads

1926-42 PR 191 (18.6) Mameyes-Río Blanco Forest highway dissected the LEF until 1970 landslide blocked road at km 13b

late 1930s PR 930 (1.3) Molindero Summer cottages near the La Mina Recreation Area.

late 1930s PR 9938 (0.8) Mt. Britton Summer cottages; also serves as access to Mt. Britton trail.

late 1930s FS 10 (2.0) El Yunque Military observation post before and during World War II; paved in 1943.

1958-62 FS 27 (5.0) Pico de Este Access to Pico del Este radar dome used by the Federal Aviation Administration; also 

for U.S. Navy maneuvers off Roosevelt Roads and Vieques until 2003.

PR route 186 and tributary roads

1943-57 PR 186 (8.0) El Verde Built in stages to serve the public and access the western part of the forest; rock 

surfaced by 1943; later construction carried out in 1945-48 and 1955-57.

1934-47 PR 956 (0.6) Guzmán Arriba Built in stages to serve the Guzmán Arriba area.

late 1930s PR 911 (0.1) Sonadora link Access to a water station on LEF land.

~1938 PR 903 (0.3) El Verde link Access to the El Verde Field Station; later improved.

~1948 PR 963 (0.5) Scout camp link Access to Eliza Colberg Girl Scout Camp.

~1955 PR 946 (0.7) Cubuy To serve the public near isolated LEF outlier property called La Condesa.

~1973 PR 9948 (1.0) None To serve public living near isolated southwestern corner of the LEF.

~1973 Link (0.2) Job Corps link Access to Youth Conservation Corps (Job Corps) Camp

Routes along or near northern or northwest forest border

late 1960s PR 966 (3.4) Jiménez Originally to export timber from the proposed Jiménez working area.

late 1960s PR 9966 Jiménez (extension) Connect PR 186 and PR 191.

~1962 PR 983 (0.5) Sabana-Pitahaya Serve Sabana and vicinity; later extends south to northeastern forest corner.

1965-72 PR 988 (4.5) Sabana-Catalina Connect highways PR 191 and PR 983 near Sabana.

1942 PR 915 (1.0) Cristal Access timber in upper Cristal valley; never completed; today, a hiking trail.

1943 PR 9915 (1.3) Bisley Originally to export timber; since 1985 to carry out LTER research.c

aDates and road lengths (km) are best estimates based on approved plans or purported construction dates (El Yunque Forest 2009, see endnotes).

bLEF = Luquillo Experimental Forest; Source: U.S. Department of Agriculture, Forest Service (2009), see endnotes.

cLTER = Long term Ecological Research.
14

Historical Perspective

(Cristal road), which served communities in the vicinity, were 

improved in anticipation of logging planned for the late 1950s.

In 1996, the El Portal Rain Forest Center opened to the public. 

More than 60 years had elapsed since the first recreation area 

had been opened at La Mina and about 35 years since the first 

small visitor information center served the public at that site. 

Management of the Forest 

For nearly a century, island foresters have been involved in 

forest planning and management. In the 1920s, sawmills 

began to operate at low elevations near the forest boundary. 

The most valuable timbers for furniture were Dacryodes 

excelsa, Magnolia splendens, Manilkara bidentata, and 

Ocotea moschata. In 1931, the first mahogany plantations were 

established within the forest and by 1949 all tree plantings 

totaled >1500 ha (fig. 6). 

In 1932, the forest supervisor (appendix B) completed a 

policy statement which outlined forest protection and timber 

production. Before 1932, no timber was sold in the national 

forest but the Forest Service allowed the removal of trees 

damaged by Hurricane San Felipe in 1928. Between 1932 

and 1962, four systematic forest surveys were implemented, 

including a timber cruise on 6900 ha, to determine stocking, 

sawtimber, and regeneration. Also, between 1932 and 1949, 

timber sales were carried out on 2150 ha yielding >293 000 m3, 

including sawtimber (11 percent), pole wood (6 percent), and 

fuelwood (83 percent). From 1937 to 1943, a sawmill located 

in Sabana cut lumber for the use of temporary residents (i.e., 

“parceleros” in Spanish) living within the forest. The number 

of parceleros increased from one person in 1919 to about 220 

families by 1940; by 1953, all of the parceleros had departed 

from the forest. Parceleros had a house, cistern, and access to 

land for a period of time. They occupied tracts where they were 

allowed to intercrop foodstuffs with trees (i.e., a system called 

taungya or agroforestry), gradually reforesting Federal lands. 

PR-186

PR-966

PR-191

PR-988

1

3

4

2

5

10

8

7

9

PR-9938

FS-10

PR-930

PR-956

PR-983

PR-915

PR-9915

PR-946

PR-9948

PR-911

PR-903

PR-963

6 12

15

14 13

11

PR-9966

FS-27

PR-988

17

16

Legend

Trails

Primary roads

Secondry roads

LEF boundary

Forest trails (asterisks indicate trails with trailheads)

7

8

9

10

11

12

El Yunque

El Yunque rock

Los Picachos

Mt. Britton*

Mt. Britton tower

Big tree*

13

14

15

16

17

arillo

La oca*

La Mina

Eli a olberg am link

Youth onser ation or s 

am link

1

2

3

4

5

6

ngelito*

El Portal

El Toro

Tradewinds*

Bano de ro

aimitillo

Forest trails (asterisks indicate trails with trailheads)

1 Angelito* 7 El Yunque 13 Carillo

2 El Portal 8 El Yunque rock 14 La Coca* 

3 El Toro 9 Los Picachos 15 La Mina

4 Tradewinds* 10 Mt. Britton* 16 Eliza Colberg Camp link

5 Baño de Oro 11 Mt. Britton tower 17 Youth Conservation Corps Camp link

6 Caimitillo 12 Big tree*

Legend

Trails

 Primary roads

 Secondary roads

 LEF boundary

Figure 5—Roads and hiking trails in the Luquillo Experimental Forest.

8 4 0 8 km

4 2 0 4 km

0 2 10 0 40 60 80

km

N
15

Historical Perspective

In 1945, timber stand improvement was carried out to alleviate 

a post-war energy crisis and provide jobs. Also in 1945, exotic 

bamboo was first introduced to help stabilize soils. In 1949, 

kerosene stoves eliminated the charcoal market but logging for 

furniture quality Magnolia splendens continued into the early 

1950s, reaching lower elevations of montane forest in a couple 

of areas.

In 1950, the Puerto Rico Department of Agriculture set up 

a tree nursery along the northern forest border at Catalina 

where it operated until 1974 (fig. 6). In the early 1950s, a 

multiple use and timber management plan was devised for the 

forest. Among the topics considered were timber production, 

watershed conservation, research, protection of high elevation 

forests, and parrot habitat. Timber production areas were 

divided into working areas (i.e., about 20 percent of the 

forest) based on previous forest inventories (table 4). Tree 

species were classified according to their value based on wood 

properties, size, resistance to pathogens, and availability 

(table 5). In 1955, logging within the forest finally ceased 

when imported mahogany depressed the demand for local 

timber. However, in 1956 the Forest Service began building 

timber access roads to the Bisley, Espíritu Santo, Jiménez, and 

Sabana working areas along the northern and western LEF 

boundaries (fig. 5) (table 4). The roads were in anticipation 

of future forest harvests in areas designated for timber 

management (fig. 7). 

Between 1956 and 1978, pilot forest management was initiated 

on >2800 ha of lands designated for timber production. 

Field activities included the liberation of crop trees and the 

establishment of plantations. In 1961, an arboretum was set 

up at Caracoles along PR route 186 in the driest part of the 

forest. Line planting of mahogany was started in 1963 on 

the lower northern slopes near Sabana and by the mid-1970s 

plantings covered about 1275 ha. In 1965, the Forest Service 

drafted a timber management plan. The plan was based on 

past inventory information and growth data that allowed 

estimates of timber volumes for sustainable harvest. In 1986, 

the Agency developed a more elaborate plan for land use 

and resource management, this time with invited comments 

from the public. The 1986 plan was accompanied by several 

management alternatives, including timber production. There 

was also a record of decision and an environmental impact 

above: A plantation of Cordia alliodora planted in the early 1930s at Del Valle averaged 3 m in height after 1.3 years. above right: From the 

1920s to the 1940s, three sawmills operated in the lower Espíritu Santo and Sabana watersheds supplying lumber from the lower montane rain 

forest. (Photos from IITF files) 
16

Historical Perspective

statement. By the late 1980s, however, the public no longer 

considered logging to be appropriate within the LEF. The plan 

was revised and adopted in 1997 without timber management. 

In 1992, the first interpretative plan for public education 

was completed for the forest. This plan was later revised 

and updated into a more comprehensive interpretative and 

conservation education master plan. In 1999, an environmental 

education program for teachers was developed to complement 

tours within the forest; moreover, in 2002, interpretative guides 

were published in English and Spanish. A severe drought in 

the mid-1990s and increased use of the national forest resulted 

in additional concerns. An emergency plan was devised in 

1994 to supply water from forest streams during periods of 

prolonged drought. Moreover, a forest transportation study 

completed in 2002 concluded that a mass transit system should 

be implemented for PR route 191 to alleviate congestion during 

holidays and other periods of heavy use. 

The entire LEF was proclaimed as a Biosphere Reserve in 

1976 (table 2). Other separate designations within the forest 

include: the Baño de Oro Natural Area in 1949, a long-term 

ecological research (LTER) site in 1985, and a long-term 

ecological grid site (i.e., the Luquillo Forest Dynamics Plot or 

LFDP) in 1990. Also designated were three stretches of rivers 

as scenic and one stretch as a wild river in 2002, and the 

El Toro Wilderness area in 2005. All of the separately 

designated areas total about 70 percent of the forest. 

Research and Training in the Forest

Research began with the earliest field biologists and continues 

today with various ongoing projects. In 1797, Pierre Ledru 

explored northeastern Puerto Rico and collected plant 

specimens. During the 19th and 20th centuries, several 

botanists including the Swiss Heinrich Wydler (1797-98), 

Danish Henrick F.A. von Eggers (1883), German Paul Ernst 

Figure 6—Plantation sites in the Luquillo Experimental Forest in 1947.

!

!

!

!

!

Legend

Primary roads

Secondary roads

LEF boundary

PR 186

PR 966 PR 191

PR 988

4

5

2

3

1

1

2

3

4

Catalina

Guzm n

Harvey

JimÈnez

Planting sites

CiÈnaga Alta

Coca Valley + Sabana

Del Valle and tract 91

El Verde and JimÈnez

Piz

Sabana

618

386

222

73

211

9800

Area (ha)

5.5

3.4

2.0

0.6

1.9

86.6

Plantation tracts LEF (%)

Remainder of forest

Legend

 Primary roads

 Secondary roads

 LEF boundary

Plantation tracts Area (ha) LEF (%)

n Ciénaga Alta 618 5.5

n Coca Valley + Sabana 386 3.4 

n Del Valle and tract 91 222 2.0

n El Verde and Jiménez 73 0.6

n Pizá 211 1.9

n Remainder of forest 9800 86.6

Planting sites

1 Catalina

2 Guzmán

3 Harvey

4 Jiménez 

5 Río Chiquito

8 4 0 8 km

4 2 0 4 km

0 2 10 0 40 60 80

km

N
17

Historical Perspective

top left: Typical forest home. Between 1919 and 1953, forest residents (i.e., parceleros in Spanish) occupied tracts where they were allowed 

to intercrop foodstuffs with trees (i.e., a system called taungya or agroforestry), gradually reforesting parts of the Luquillo Experimental 

Forest. top right: Charcoal production, common in several areas within the Luquillo Mountains, was permitted after hurricanes and during 

silvicultural operations. The practice survived until the introduction of kerosene stoves in 1949. above: Located along the Luquillo Experimental 

Forest border, the Catalina nursery produced seedlings for reforestation projects between 1950 and 1974. (Photos from IITF files) 
18

Historical Perspective

Emil Sintenis (1885), and Puerto Rican Augustín Stahl (1898) 

visited the Luquillo Mountains and collected plants. Americans 

Percy Wilson (1902) and W.A. Evans (1902) also collected 

plants in the mountains, ascending to El Yunque. Although 

the German Ignatz Urban (1903-11) never visited the island, 

he collected plants from the West Indies, including Puerto 

Rico, and later published Flora Portoricensis. Between 1913 

and 1917, Nathanial Britton and coworkers Henry A. Gleason 

and Melville T. Cook of the New York Botanical Garden 

contributed to the scientific survey of Puerto Rico and the 

U.S. Virgin Islands, publishing their detailed observations 

between 1923 and 1930. Between 1905 and 1932, several other 

visiting U.S. scientists provided information regarding the 

mountains, including: John C. Gifford, Louis Murphy, and 

E. Murray Bruner on forest resources; Alexander Wetmore on 

birds; H.E. Anthony on native bats; and W.P. Kramer on forest 

policy. In 1933, Leslie R. Holdridge began a Forest Service 

herbarium, contributing numerous specimens collected from 

the Luquillo Mountains. Also in 1933, Howard Augustus 

Meyerhoff described the geologic resources of the island, 

including those of the Luquillo Mountains. The history of 

mining and the mineral prospects within the mountains were 

summarized 50 years later. Other well-known botanists and 

foresters working in the field from the early 1940s until the 

1990s included Elbert L. Little, Jr., Frank H. Wadsworth, 

and Roy O. Woodbury. They published texts and numerous 

research papers on forest resources, including the trees of 

Puerto Rico. Henri A. Liogier, Luis F. Martorell, and Richard 

A. Howard, all prominent taxonomists active at the same time, 

published texts on the flora of Puerto Rico and the West Indies. 

Between 1935 and 1939, small scale timber stand 

improvement was carried out in forests of the Espíritu Santo 

and Mameyes Valleys. In 1938, study plots were set up on 

55 ha to evaluate the results. In 1939, the Tropical Forestry 

Experiment Station, now the International Institute of Tropical 

Forestry (IITF), was established under the McSweeneyMcNary Act to implement forestry research in Puerto Rico. 

Prior to 1939, field experience guided forestry practices. 

During the Institute’s 70 years, the staff published a forestry 

journal from 1939 until 1964, carried out about 2,600 research 

studies, tested >100 native and 350 introduced tree species, 

and established one of the best libraries on tropical forestry in 

the hemisphere. Many of the research documents and journal 

articles were based work in the Luquillo Mountains.

In 1943, long-term research began on a 0.72 ha permanent 

plot located at El Verde, and at the end of the decade local 

scientists summarized research on forest resources and 

plantations, producing a forest type map for the forest. By 

1956, >400 permanent plots, including the pilot management 

study, had been established in three different forest types to 

determine species composition, stand characteristics, and 

timber production potential. 

Other resource studies were also undertaken over the years. 

In 1942, stream gaging stations were first monitored on the 

Río Espíritu Santo and the Río Icacos. In 1943, topographic 

maps were developed for the mountains, and in 1952 they 

were revised. During the early 1960s, the University of 

Puerto Rico began ecological studies in lower montane forest 

near El Verde and in 1990 the long-term ecological grid 

was established nearby. Dwarf forest research began at Pico 

del Oeste and Pico del Este during the mid-1960s and longterm ecological research started at Bisley in 1986. After the 

mid-1960s, scientific publications increased substantially 

appearing as journal articles, books, and Forest Service 

technical reports. Most of these publications concerned work 

carried out at the aforementioned sites. 

After 1960, continued wildlife research in the Luquillo 

Mountains documented gains, losses, and changes in some 

animal populations. In 1963, Eleuthrodactylus hedricki

(tree-hole coqui) was discovered and Corvus leucognaphallus

(white-necked crow) was last recorded. In 1968, the study 

of the rare and endangered Amazona vittata (Puerto Rican 

parrot) was undertaken. Its population had declined from 200 

to just 13 birds between the mid-1950s and the early 1970s. In 

1968, the parrot recovery program was implemented through 

the cooperation of Federal and Commonwealth of Puerto Rico 

government agencies. In 1975, eight captive birds were placed 

in the La Mina barracks which was converted to a parrot 

aviary. In 1971, at a time when it was believed that all of the 

island’s bird species were known, Dendroica angelae (elfinwoods warbler) was discovered in the LEF’s dwarf forest. 

Table 4—Proposed working areas for timber 

harvest in the Luquillo Experimental Forest 

Working areasa

Area

ha

Cacique 502

Ciénega Alta 808

Cristal 499

Cubuy 289

Espíritu Santo 789

Fajardo 665

Gurabo 510

Icaco 1173

Jiménez 763

La Mina 732

Total 6730

aSource: Wadsworth (1949). 
19

Historical Perspective

Table 5—The classification of timber species in the Luquillo Experimental Foresta

Forest type Rankingc Usesd Woode Termitesf Mean annual increment 

Scientific nameb cm yr-1 (no.)g cm yr-1 (no.)h

Lower montane rain forest

Alchornea latifolia Sw. 37 P L 21 0.21 (6) 0.38 (225)

Alchorneopsis portoricensis Urban 41 P 0.45 (4)

Andira inermis (W. Wright) DC. 24 P L 46

Beilschmiedia pendula (Sw.) Hemsl. 17 C L

Buchanavia tetraphylla (Aublet) R. Howard 4 F L 69 0.19 (7) 0.69 (41)

Byrsonima spicata (Cav.) HBK 26 P L 39 0.17 (9) 0.48 (61)

Chrysophyllum oliviforme L. 18 C

Cinnamomum elongatum (Nees) Kostermans 16 C

Cordia alliodora (Ruiz & Pav.) Oken 7 F L 60

Cupania americana L. 31 P

Dacryodes excelsa Vahl 2 F L 31 0.16 (167) 0.36 (207)

Genipa americana L. 21 C L 34

Guarea guidonia (L.) Slumer 1 F L 70 0.81 (18)

Guazuma ulmifolia Lam. 36 P 33

Hernandia sonora L. 23 C L

Homalium racemosum Jacq. 9 C L 71 0.19 (4) 0.50 (36)

Hymenaea courbaril L. 13 C L 88

Inga laurina (Sw.) Willd. 29 P L 0.14 (6) 0.46 (150)

Laetia procera (Poeppig) Eichler 38 P

Laplacea portoricensis (Krug and Urban) Dyer 28 P 0.11 (5)

Linociera domingensis Lam. 27 P 46 0.37 (20)

Mammea americana L. 15 C L 30

Manilkara bidentata (A. DC.) Chev. 8 C L 58 0.12 (15) 0.55 (49)

Matayba domingensis (DC.) Radlk. 30 P L 0.26 (33) 0.44 (96)

Meliosma herbertii Rolfe 20 C L 0.07 (11)

Ocotea coriacea (Sw.) Britton 40 P L 53?

Ocotea globosa (Aubl.) Schlect & Cham. 19 C 53?

Ocotea leucoxylon (Sw.) Mez. 25 P L 48 0.35 (128)

Ocotea membranaceae (Sw.) Howard 34 P L 53?

Ocotea moschata (Meisn.) Mez. 5 F L 36 0.07 (23)

Ocotea nemodaphne Mez. 22 C

Ocotea patens (Sw.) Nees. 39 P

Ormosia krugii Urban 32 P L 0.37 (21) 0.48 (77)

Petitia domingensis Jacq. 6 F L 51

Phoebe elongata (Vahl) Nees 33 P

Pouteria multiflora (A. DC.) Eyma 10 C L

Schefflera morototoni (Aubl.) Mcguire 42 P L 0.23 (36) 0.35 (193)

Sloanea berteroana Choisy 11 C L 53 0.09 (31) 0.46 (66)

Tabebuia heterophylla (DC.) Britton 14 C L 34 0.19 (10) 0.29 (514)

Tetragastris balsamifera (Sw.) Kuntze 3 F L 45

Vitex divaricata Sw. 12 C L 42

Zanthoxylum martinicense (Lam.) DC. 35 P L 0.39 (5)

Means 0.18 (388) 0.46 (1559)

(table continued on following page)
20

Historical Perspective

Training activities in the Luquillo Mountains have been a part 

of the Forest Service program for nearly 60 years. In 1953, 

the Institute held the first of 16 international tropical forestry 

short courses, which included excursions to the Luquillo 

Mountains. The earliest programs were designed for visiting 

foresters from tropical countries throughout the world and 

included instruction and field training in dendrology, ecology, 

surveying, inventory, aerial photo interpretation, silviculture, 

and forest management, protection, and utilization. In 

addition, exposure to environmental and conservation issues 

was provided through activities at the Eliza Colberg Girl 

Scouts camp starting in 1950, and the Youth Conservation 

Corps camp beginning in 1976. 

In the early 1960s, students from U.S. universities were 

introduced to tropical forestry and silviculture through 

National Science Foundation sponsored programs that had 

field activities in the LEF. Since the mid-1980s, students 

from universities in Puerto Rico and elsewhere have 

pursued undergraduate and graduate programs based on 

ecological studies carried out within the forest. Several major 

publications, some dating back nearly a century, contain 

valuable information on the flora, fauna, related resources and 

management in the Luquillo Mountains, including: 

• The scientific survey of Porto Rico and the Virgin Islands 

(Anthony 1925, 1926; Britton and Wilson 1923, 1930; 

Gleason and Cook 1927). These documents plus others from 

the New York Botanical expeditions in Puerto Rico provide 

some of the earliest observations regarding flora, fauna, 

geology, paleobotany, and archaeology. The survey series 

contains 18 volumes between 1919 and 1953. 

• The 24 volumes of the Caribbean Forester. This journal, 

published between 1939 and 1963, contains a wealth of 

information on tree species, forest types, stand conditions, 

silvicultural research, nursery practices, reforestation 

and forest plantations, herbicides, forest policy and 

legislation, forest insects, wood resistance to termites, wood 

preservation and utilization, climate and hurricane impacts, 

soils, training courses, and annual summaries of work. 

Contributions from elsewhere in the tropics, mainly the 

Caribbean and Latin America, were also included. English 

and Spanish were the principal languages, but articles also 

appeared in French and Portuguese.

Table 5 (continued)—The classification of timber species in the Luquillo Experimental Foresta

Forest type Rankingc Usesd Woode Termitesf Mean annual increment 

Scientific nameb cm yr-1 (no.)g cm yr-1 (no.)h

Montane rain forest

Clusia clusiodes (Griseb.) D’Arcy 8 P 0.35 (5) 0.96 (2)

Eugenia stahlii (Kiaersk.) Krug & Urban 6 P L

Henriettea squamulosa (Cogn.) Judd. 10 P L 0.08 (74) 0.09 (19)

Homalium racemosum Jacq. 2 C L 71

Magnolia splendens Urban 1 F L 40 0.09 (32) 0.24 (1)

Matayba domingensis (DC.) Radlk. 9 P L

Micropholis garciniifolia Pierre 4 C L 0.07 (144) 0.07 (226)

Micropholis guyanensis (A. DC.) Pierre 3 C L 48 0.12 (170) 0.10 (12)

Ocotea spathulata Mez. 7 P L 0.06 (45) 0.06 (7)

Ternstroemia luquillensis Krug & Urban 5 C

Weinmannia pinnata L. 11 P

Means 0.09 (470) 0.08 (267)

aSource: Wadsworth (1952b).

bNomenclature: Liogier (1985-97).

cTentative ranking by forest type: Lower montane rain forest, 1 = best and 42 poorest (i.e., 1 to 7, furniture woods from most to least 

valuable; 8 to 23, construction woods most the least valuable; and 24 to 42, post woods from most to least valuable. Montane rain forest, 

1 = best and 11 = poorest (1, furniture wood; 2 to 5, construction woods from most to least valuable; and 6 to 11, post woods from most to 

least valuable.

dUse: F = furniture; C = construction; P = large post. Uses determined to some extent by availability of large diameter specimens 

(Wadsworth 1952b). See also: Little and Wadsworth 1964; Little and others 1974. 

eL= description of wood characteristics available (Longwood 1955, 1961).

f

Termite resistance index: low = 20, high = 100; Nectandra (Ocotea) spp. = 53? classed as a group (Wolcott 1946, 1950). gSource: Weaver 1983 (i.e., Tabonuco ridge (TR-1), Tabonuco slope (TS-3), Colorado valley (CV-1), Colorado slope (CS-2). Tabonuco is 

Lower montane rain forest and colorado is Montane rain forest.

hSource: Crow and Weaver (1977). Lower montane rain forest plots (i.e., Río Grande, Sabana 4, Sabana 8). Montane rain forest plot (i.e., 

Cutover colorado (CCU).
21

Historical Perspective

• The Caribbean Forest atlas (Upson 1949, see endnotes). The 

atlas contains a chronology of legislation and events relating 

to the creation, enlargement, improvement, and management 

of the national forest between December 10, 1899 and June 

30, 1949. 

• Puerto Rican woods: their machining, seasoning and related 

characteristics of Puerto Rican woods (Longwood 1961). 

This publication describes the wood properties 60 native and 

introduced tree species.

• Trees of Puerto Rico and the Virgin Islands, Volumes I 

and II (Little and Wadsworth 1964, Little and others 1974). 

These two tomes on dendrology describe the island’s 

547 known native trees and 200 introduced species.

• A tropical rain forest: a study of irradiation and ecology 

at El Verde (Odum and Pigeon 1970). This 1,600 page 

compendium contains 9 chapters and 111 research papers on 

tropical flora, fauna, and ecology.

• A descriptive flora of Puerto Rico, Volumes I-V (Liogier 

1985, 1997), Los bejucos de Puerto Rico, Volumen 1 

(Acevedo-Rodríguez and Woodbury 1985), and Vines 

and climbing plants of Puerto Rico and the Virgin Islands 

(Acevedo-Rodríguez 2005). These documents contain 

relatively recent taxonomic updates of the island’s flora.

• History and conservation of the Puerto Rican Parrot (Snyder 

and others 1987). This book summarizes 20 years of work 

and includes the history, ecology, and current efforts to save 

the rare and endangered Puerto Rican parrot.

• Biotropica special issues: (1) Ecosystem, plant, and animal 

responses to hurricanes in the Caribbean; and (2) Long term 

responses of Caribbean ecosystems to disturbance (Walker 

and others 1991, 1996). Most of the post-hurricane studies 

described were carried out within the forest.

• Tropical forests: management and ecology (Lugo and Lowe 

1995). This book commemorates the 50th anniversary of 

the IITF and contains several review chapters on ecological 

research.

• The food web of a tropical rain forest (Reagan and Waide 

1996). This work summarizes past studies of fauna, 

including information on their abundance, food habits, and 

ecological roles in the ecosystem.

Legend

Primary roads

Secondary roads

LEF boundary

PR 186

PR 966 PR 191

PR 988

Timber production areas

Plantations

Secondary and Plantations

Young secondary

Advanced secondary

Remainder of forest

733

451

467

733

8926

Area (ha)

6.5

4.0

4.1

6.5

78.9

LEF (%)

Figure 7—Proposed timber production areas within the Luquillo Experimental Forest in 1950.

Timber production areas Area (ha) LEF (%)

n Plantations 733 6.5

n Secondary and Plantations 451 4.0 

n Young secondary 467 4.1

n Advanced secondary 733 6.5

n Remainder of forest 8926 78.9

Legend

 Primary roads

 Secondary roads

 LEF boundary

8 4 0 8 km

4 2 0 4 km

0 2 10 0 40 60 80

km

N
22

Historical Perspective

• The revised land and resource management plan for 

the Luquillo Forest and the final environmental impact 

statement (U.S. Department of Agriculture, Forest Service 

1997a, 1997b). These documents consider forest resources, 

recreation, access, and research in a proposed 10-year 

management plan.

• Forest biodiversity in North, Central and South America, 

and the Caribbean: research and monitoring (Dallmeier and 

Comiskey 1998). This tome on the neotropics contains five 

chapters on the flora and fauna of the LEF.

• Producción forestal para América Tropical (Wadsworth 

2000). This major effort contains > 600 pages that describe 

forest management practices throughout the tropics with some 

experiences derived from years of research within the LEF.

• The bioecology of native and exotic tree species in Puerto 

Rico (Francis and Lowe 2000). This summary of tree life 

histories contains information on 102 species, including 

many native and introduced trees. 

• Geology, geochemistry, geophysics, mineral occurrences 

and mineral resource assessment for the Commonwealth 

of Puerto Rico (Bawiec 2001). This compendium includes 

information for all of Puerto Rico, with nine geologic 

formations found in the LEF.

• The soil survey of the Luquillo Experimental Forest 

(U.S. Department of Agriculture, Natural Resources 

Conservation Service 2002). This volume updates five 

general and 20 detailed soil map units within the LEF, 

and describes their soil classification, potential use, and 

management.

• Distribution, ecology, and life history of Margarops fuscatus

(Pearly-eyed thrasher) (Arendt 2006). This book summarizes 

observations on an avian supertramp and major competitor 

of the Puerto Rican parrot, a species well adapted to the LEF 

where many of the observations were made.
23

Environmental Setting

Puerto Rico was heavily deforested during the past three 

centuries leaving only 3500 ha (i.e., about 0.4 percent) of 

the island completely undisturbed by human activities 

(Wadsworth 1949, 1950). Today, the forests of the LEF survive 

like a large central park surrounded by San Juan, Fajardo, 

Naguabo, Humacao, Caguas, and other northeastern towns 

where about 40 percent of the island’s population resides 

(CEEPUR 2009, Watlington 2008) (fig. 1). The LEF represents 

about 1.3 percent of Puerto Rico and nearly 15 percent of the 

island’s protected areas held by commonwealth, Federal, and 

nongovernmental agencies (Gould and others 2008).

Geology

Island chains may form through compression, the subduction 

of one oceanic crustal plate under another, causing magma 

generation beneath the upper plate and volcanism on the 

surface of that plate (Donnelly 1996). Before the Cretaceous 

(a period from 145 to 65 million years ago), the geographic 

site that Puerto Rico currently occupies was a deep ocean 

(Meyerhoff 1933, Picó 1974). In the early Cretaceous, the 

site was characterized by submarine volcanic eruptions and 

the gradual appearance of transitory islands. In the Late 

Cretaceous, a chain of islands appeared, growing into a large 

volcanic island that extended from the Dominican Republic 

to the Virgin Islands. Puerto Rico, situated on the northern 

edge of the Caribbean plate, is part of this island arc complex 

(Bawiec 2001).

The Luquillo Mountains were first described as monadnocks 

(i.e., residual isolated peaks or mountains) not because of 

structural resistance or lack of stream erosion but rather due 

to uparching and faulting (Beinroth 1969, Mitchell 1954). 

The mountains are part of a volcanic-plutonic province that 

is underlain by rocks ranging in age from early Cretaceous 

to mid-Eocene (i.e., about 45 million years ago). Marine 

volcanoclastics (i.e., breccia, conglomerate, mudstone, and 

sandstone) underlie about 80 percent of the LEF and intrusive 

rocks (i.e., the quartz-diorite Río Blanco stock) most of the 

remainder (Cox and Briggs 1973, Seiders 1971). A contact 

metamorphic zone surrounds the Río Blanco stock.

A recent geologic summary for Puerto Rico outlined the 

following sequences, four of which account for 96 percent of 

the LEF (Bawiec 2001, Seiders 1971) (fig. 8).

• Augite andesite porphyry (TKap)—Intrusive rocks of the 

late Cretaceous.

• Daguao formation (Kd)—Massive andesitic breccia, 

hyaloclastic breccia, and fine grained volcanoclastic rocks. 

Daguao, the oldest mapped sequence, is assumed to be early 

Cretaceous.

• Figuera lava (Kf)—Pillowed andesitic lava flows. Figuera is 

also assumed to be early Cretaceous.

• Fajardo formation (Kfa)—Tuffaceous sandstone-siltstone, 

and tuff breccia of Albian age (i.e., Cretaceous, about 100 to 

110 million years ago).

• Hato Puerco formation (Kh)—Andesitic to basaltic volcanic 

sandstone, breccia, conglomerate, and basaltic lava flow of 

middle Cenomanian age (i.e., late Cretaceous, about 85 to 

100 million years ago).

• Lomas formation (Klo)—Basaltic to andesitic lava, volcanic 

breccia, and sandstone. Age has not been established.

• Quaternary alluvium (Qa)—Sand deposits and quaternary 

alluvium. The alluvium is found in mountainous river 

valleys and the surrounding lowlands.

• Río Blanco unit (TKh)—A highly magnetic pluton that 

dates to 46 million years ago. The stock intrudes the Fajardo, 

Hato Puerco, Lomas, and Tabonuco formations.

• Tabonuco formation (Kta)—Calcareous and tuffaceous 

sandstone-siltstone and volcanic breccia of Albian age.

Tuffaceous sandstone, siltstone, breccia, conglomerate, and 

quartz diorite parent materials underlie the lower montane 

and montane forests in the LEF (Bogart and others 1964). 

Surveys carried out by forest researchers indicated that 

tree species composition did not change across a line that 

separated parent materials within montane forest (Wadsworth 

and Bonnet 1951).

Two zones of mineral occurrence are found within the Luquillo 

Mountains—a northern zone with gold deposits and a southern 

zone with copper and related iron oxides, sulfur, and traces 

of mercury. A review of early Spanish mining documents 

indicates at least 23 sites associated mainly with gold placer 

mining operations were set up along prominent Luquillo 

Mountain streams (Cardona 1984). Today, the surnames of 

past miners such as Guzmán, Jiménez, and Toro survive on 

U.S. Geological Survey quadrangle maps as part of the forest’s 

legacy (figs. 5 and 6). Gold also played a role in the naming of 

streams such as Río de la Mina and Quebrada Baño de Oro.

Chapter 2. ENVIRONMENTAL SETTING
24

Environmental Setting

Figure 8—Geology of the Luquillo Experimental Forest.

Legend

Primary roads

Secondary road

s

LEF boundary

PR 186

PR 966 PR 191

PR 988

Geology

Augite andesite porphyry

Daguao formation

Figuera lava

Fajardo formation

Hato Puerco formation

Lomas formation

Quaternary alluvium

RÌo Blanco stock unit

Tabonuco formation

5.2

2.8

15.5

3171.8

4206.1

361.4

73.5

2144.6

1329.1

Area (ha)

<0.1

<0.1

0.1

28.0

37.2

3.2

0.6

19.0

11.8

LEF (%)

Legend

 Primary roads

 Secondary roads

 LEF boundary

Geology Area (ha) LEF (%)

n Augite andesite porphyry 5.2 <0.1

n Daguao formation 2.8 <0.1 

n Figuera lava 15.5 0.1

n Fajardo formation 3171.8 28.0

n Hato Puerco formation 4206.1 37.2

n Lomas formation 361.4 3.2

n Quaternary alluvium 73.5 0.6

n Río Blanco stock unit 2144.6 19.0

n Tabonuco formation 1329.1 11.8

Not too distant from the La Mina Recreation Area, a few quartz boulders and numerous quartz 

fragments are exposed on the soil surface. (Photo by Peter L. Weaver)

8 4 0 8 km

4 2 0 4 km

0 2 10 0 40 60 80

km

N
25

Environmental Setting

Physiography and Hydrology

The topography of the Luquillo Mountains is rugged with 

cliffs and exposed rocks at high elevations (Wadsworth 

1951). One-quarter of the LEF lies between 120 and 400 m in 

elevation; nearly one-half between 400 and 600 m; another 

one-quarter between 600 and 900 m; and about 3 percent lies 

above 900 m in elevation (Wadsworth 1951). The lowest point 

is along the northeastern boundary near the town of Sabana. 

Five peaks in the LEF exceed 1000 m in elevation: El Toro 

(1074), El Yunque (1065), Pico del Este (1051), Pico del Oeste 

(1025), and El Cacique (1020). For many years El Yunque was 

thought to be the highest peak but subsequent surveys proved 

otherwise (Wadsworth 1970).

Ten rivers, some with numerous tributaries within the forest, arise 

at some point within the LEF. Four, the Río Blanco, Río Espíritu 

Santo, the Río Grande de Loíza (with its tributaries), and the Río 

Mameyes drain nearly 80 percent of the forest (fig. 9):

• Quebrada Grande—flows southeast from the forest and 

ultimately into the Río Santiago at Naguabo.

• Río Blanco—flows south with LEF tributaries Río Cubuy, 

Quebrada Maizales, Río Icacos, Río Prieto, and Río Sabana.

• Río Canovanillas—flows northwest from the outlying La 

Condesa property, becoming a tributary to the Río Grande 

de Loíza outside of the LEF.

• Río Espíritu Santo—flows northwest with LEF tributaries 

Quebrada Grande, Quebrada Jiménez, and Quebrada 

Sonadora.

Figure 9—Major peaks, rivers, watersheds, flow gages, and water intakes in and around the Luquillo Experimental Forest.

"

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4

2

G B

C

F

D

H

J

I

E

A

*

!

1

2

3

4

5

6

7

Cacique

El Negro

El Toro

El Yunque

La Mina

Los Picachos

Mt.Britton

1020

~750

1074

1065

931

968

941

Mountain peaks Elevation (m)

Quebrada Grande

 (RÌo Santiago)

RÌo Blanco

RÌo Canovanillas

RÌo Espiritu Santo

RÌo Fajardo

RÌo Grande 

A

B

C

D

E

Watersheds (A-J)

219.6

2079.2

209.6

3476.5

1125.9

1.9

18.4

1.8

30.7

10.0

Area (ha) LEF ( )

Legend

# Intakes

" Stream gages

Hydroelectric plant

Rivers

LEF boundary

! atersheds

* alley o the Giants

Legend

s Intakes 

n Stream gages 

Hydroelectric plant

Rivers

LEF boundary

Watersheds

* Valley of the Giants

Watersheds Area (ha) LEF (%)

A Quebrada Grande (RÌo Santiago) 219.6 1.9

B Río Blanco 2079.2 18.4

C Río Canovanillas 209.6 1.8

D Río Espiritu Santo 3476.5 30.7

E Río Fajardo 1125.9 10.0

F Río Grande de Loíza 622.4 5.5

G Río Gurabo 535.6 4.7

H Río Mameyes 2088.3 18.5

 I Río Pitahaya 175.6 1.6

J Río Sabana 777.3 6.9

Mountain peaks Elevation (m)

1 Cacique 1020

2 El Negro ~750

3 El Toro 1074

4 El Yunque 1065

5 La Mina 931

6 Los Picachos 968

7 Mt.Britton 941

8 Pico del Este 1051

9 Pico el Oeste 1025

8 4 0 8 km

4 2 0 4 km

0 2 10 0 40 60 80

km

N
26

Environmental Setting

• Río Fajardo—flows east with LEF tributaries Quebrada 

Grande and Quebrada Sonadora.

• Río Grande de Loíza—flows west with LEF tributaries 

Río Cubuy, Río Gurabo, Quebrada Grande, and Río 

Canovanillas (confined to the La Condesa tract).

• Río Gurabo—flows initially south out of the forest, 

becoming a tributary of the Río Grande de Loíza outside of 

the LEF.

• Río Mameyes—flows north with LEF tributaries Quebrada 

La Coca and Quebrada Juan Diego, Quebrada La Máquina, 

Quebrada Linguete, Quebrada Tabonuco, and Río de la 

Mina.

• Río Pitahaya—flows north without tributaries in the LEF.

• Río Sabana—flows north with LEF tributaries Río 

Camándulas and Río del Cristal.

On the northern slope, rivers descend rapidly at high elevation 

and more gradually below (Wadsworth 1951). The reverse 

happens on the southern exposure where basin-like valleys 

occur at relatively high elevations. Several of the streams and 

rivers have waterfalls and cascades.

One study of the LEF’s water budget shows that rainfall 

averages about 3600 mm yr-1 of which 63 percent is runoff 

and the remainder is evapotranspiration (Crook 2005, Crook 

and others 2007). An earlier study placed the same estimates 

at 60 percent for runoff and 40 percent for evapotranspiration 

(Naumann 1994). The average volume of water extracted from 

forest streams is about 250 mm yr-1, which equals 7 percent 

of the annual rainfall and 11 percent of the annual runoff. 

Although little groundwater exists at high elevations within 

the watersheds, it may become important at lower levels 

(Larsen 1997).

Hydrograph data show that heavy rainfalls cause rapid runoff 

from the LEF landscape (Bogart and others 1964, Larsen and 

Torres Sánchez 1992). Water infiltrates vertically but relatively 

low soil permeability limits the amount that permeates to 

greater depths (Jordan 1970). When denser soil is encountered, 

water flows laterally down slope. Stream hydrographs show 

rapid peaks within a few minutes to hours after rainfalls 

lasting <24 hours. Return to baseflow takes 5 to 10 hours 

(Larsen and Torres Sánchez 1992).

Streamflow in the LEF (e.g., Río Icacos) varies considerably 

due to scattered showers of different intensity (Bogart and 

others 1964). Sediment levels in streams will likely be 

minimal during periods of low flow, but much greater during 

floods. Low flow, derived from ground water, produces 

a greater proportion of dissolved materials. Chemical 

concentrations, however, vary and may remain low if the flow 

is caused largely by storm runoff. In addition, the pH, color, 

temperature, odor, and taste of water may change with the 

amount of flow.

Stream gage records within the Río Icacos watershed “show 

more runoff produced than rainfall” (Crook and others 2007). 

This phenomenon was first observed during the 1940s after 

the installation of a weir on the Río Icacos (Wadsworth 

2009). The anomaly was explained as a possible non-linear 

relationship between basin size and runoff (Crook and 

others 2007). Other factors, however, may be important. The 

upper reaches of the Río Icacos watershed contain dwarf 

forest between Pico del Este and Pico del Oeste. Previous 

monitoring of rainfall and cloud moisture interception on both 

Pico del Este and Pico del Oeste showed that intercepted fog 

increased the amount of water received at ground level by 

10 percent (Baynton 1969, Weaver 1972)—a fact that might 

explain some of the missing rainfall input. Also, rainfall 

records for Pico del Este showed that the amount of rainfall 

just to the leeward of the peak surpassed the amount measured 

to the windward, an orographic phenomenon called spillover 

effect (Linsley and others 1949, Weaver 1972). The Icacos 

watershed lies to the leeward of the northeast-facing saddle 

(<750 m in elevation), which is situated between Pico del 

Oeste and a string of peaks to the west, including El Yunque, 

El Toro, and La Mina (fig. 9). The ridge that extends from Pico 

del Oeste to the PR route 930 gate, or the upper boundary of 

the Mameyes watershed, is occupied by montane forest and is 

the wettest area within the LEF (Ewel and Whitmore 1973). 

Spillover could funnel through the mountain pass adding 

rainfall to the Icacos watershed, particularly during periods of 

high winds and heavy cloud cover.

Soils

The warm climate and heavy rainfalls in the LEF cause deep 

weathering and produce a saprolite (i.e., residual soil zone 

with boulders of parent rock) that averages 11 m deep on 

slopes. This zone is underlain by weathered bedrock, which 

in turn is underlain by bedrock lower in the profile (Simon 

and others 1990). Mass wasting (i.e., downhill movement of 

soil and rock induced by gravity) appears to be the principal 

process responsible for erosion in the Luquillo Mountains.

LEF soils are highly leached inceptisols and ultisols 

comprised of silty clay loams, silty clays, and clays in different 

horizons. Twelve types of soils were recognized during early 

surveys: Los Guineos clay, Rough stony land, Catalina stony 

clay, Catalina clay, Catalina clay (steep phase), Lares silty clay 

loam, Múcara silty clay loam (steep phase), Pandura sandy 

clay loam, Picacho stony clay loam, Sabana silt loam, Sabana 

silty clay loam, and Via silty clay (broken phase) (Roberts 

1942). The first three types were estimated to cover about 

60 percent of the mountains, mainly in the interior 

(Wadsworth 1951). Later, the Los Guineos-Guayabota 

Rock land association and the Los Guineos-Humatas-Lirios 

association were described (Boccheciamp 1977).
27

Environmental Setting

Recently the forest’s soils were surveyed again. Five general 

map units (or associations) and 18 detailed map units were 

located and described (U.S. Department of Agriculture, 

Natural Resources Conservation Service 2002). Three of the 

units cover nearly 50 percent of the land area (fig. 10). The 

general and detailed map units are:

Zarzal-Cristal-Humatas Association—This association 

contains very deep, well drained and somewhat poorly drained 

clayey soils that formed in residuum that weathered from 

volcanic sandstone and mudstone of the Fajardo, Hato Puerco, 

and Tabonuco formations.

• Cristal Zarzal complex (5 to 50 percent slopes)—very 

deep, somewhat poorly drained Cristal soil and very deep, 

well drained Zarzal soil found on mountain side slopes at 

elevations <600 m. Depth to bedrock is >150 cm. The soils 

have medium organic matter content, slow permeability, and 

medium natural fertility.

• Humatas Zarzal complex (5 to 30 percent slopes)—very 

deep, well drained Humatas soil and very deep, well drained 

Zarzal soil. They are found on hill summits, ridge tops, and 

mountain footslopes at elevations <450 m. Depth to bedrock 

is >150 cm. The soils have medium organic matter content, 

moderately slow permeability, and medium natural fertility.

• Zarzal Cristal complex (20 to 60 percent slopes)—very 

deep, well drained Zarzal soil and very deep, somewhat 

poorly drained Cristal soil. They are found on mountain 

slide slopes at elevations <600 m. Depth to bedrock is 

>150 cm. The soils have medium organic matter content, 

moderately slow permeability, and medium natural fertility.

• Zarzal very cobbly clay (40 to 60 percent slopes)—very 

deep, well drained soil found mainly on convex mountain 

side slopes at lower elevations <550 m. Depth to bedrock 

is >150 cm. The soil has medium organic matter content, 

moderately slow permeability, and medium natural fertility.

Sonadora-Caguabo-Prieto Association—This 

association is composed of moderately deep and poorly 

drained clayey soils that formed in residuum that weathered 

from volcanic mudstones and conglomerates of the Fajardo, 

Hato Puerco, and Tabonuco, formations.

• Caguabo gravelly clay loam (8 to 15 percent slopes)—

shallow, well drained soil at lower elevations <550 m on 

side slopes and footslopes of lower hills, and on strongly 

dissected uplands. Depth to bedrock is between 25 and 

50 cm. The soil has low organic matter content, moderate 

permeability, low natural fertility, and is one of the least 

productive soils in the lower montane forest zone.

• Coloso silty clay loam (occasionally flooded)—very deep, 

somewhat poorly drained soil at lower elevations <400 m on 

flood plains and low terraces along mountain streams. Depth 

to bedrock is >150 cm. The soil has medium organic matter 

content, slow permeability, and medium natural fertility.

• Luquillo stony clay loam (occasionally flooded)—very deep, 

well drained soil on flood plains and low stream terraces 

at elevations <400 m. Depth to bedrock is >150 cm. The 

soil has medium organic matter content, moderately slow 

permeability, and medium natural fertility.

• Prieto very cobbly clay loam (25 to 50 percent slopes)—

moderately deep, poorly drained soil in concave positions 

on side slopes and in drainages at elevations <600 m. Depth 

to bedrock is 50 to 100 cm. The soil has medium organic 

matter content, moderate slow permeability, and medium 

natural fertility.

• Sonadora Caguabo complex (25 to 40 percent slopes)—

moderately deep, well drained Sonadora soil and the 

shallow, well drained Caguabo soil situated on mountain 

side slopes at lower elevations <500 m. Depth to bedrock 

is 50 to 100 cm. The soils have medium organic matter 

content, very slow permeability, and medium natural 

fertility.

Yunque-Los Guineos-Moteado Association—This 

association is composed of very deep and deep, moderately 

well drained and poorly drained clayey soils that formed 

in residuum that weathered from volcanic sandstone and 

mudstone of the Fajardo, Hato Puerco, and Tabonuco 

formations.

• Palm Yunque complex (35 to 85 percent slopes, extremely 

stony)—very deep, poorly drained Palm soil and very deep, 

moderately well drained Yunque soil located on mountain 

side slopes at upper elevations (750 to 900 m). Depth to 

bedrock is >150 cm. The soils have high organic matter 

content, moderately slow permeability, and high natural 

fertility.

• Yunque cobbly clay (40 to 80 percent slopes, extremely 

stony)—very deep, moderately well drained soil found in 

canyons and on side slopes at elevations between 600 and 

900 m. Depth top bedrock is >150 cm. The soil has high 

organic matter content, moderate permeability, and medium 

natural fertility.

• Yunque-Los Guineos-Moteado complex (5 to 30 percent 

slopes)—very deep, moderately well drained Yunque soil 

and the very, deep well drained Los Guineos soil, and deep, 

poorly drained Moteado soil. The soils occur on summits, 

ridge tops, and mountain side slopes at elevations from 

600 to 900 m. Depth to bedrock is >150 cm. They have high 

organic matter content, moderate permeability, and medium 

natural fertility.

• Yunque Moteado complex (20 to 65 percent slopes)—very 

deep, moderately well drained Yunque soil and deep, poorly 

drained Moteado soil. They are found on mountain side slopes 

at elevations between 600 and 900 m. Depth to bedrock is 

>150 cm. The soils have medium organic matter content, 

moderate permeability, and medium natural fertility.
28

Environmental Setting

Figure 10—Soils of the Luquillo Experimental Forest.

Legend

Primary roads

Secondary roads

LEF boundary

PR 186

PR 966 PR 191

PR 988

Soils

Caguabo gravelly clay loam

Coloso silty clay loam

Cristal zarzal complex

Dwarf muck windswept

Guayabota Yunque complex

Humatus zarzal complex

Icacos loam

Luquillo stony clay loam

Palm Yunque complex

Picacho Ciales complex

Picacho Utuado complex

Prieto very cobbly clay loam

Sonadora Caguabo complex

Yunque cobbly clay

Yunque los Guineos moteado

Yunque moteado complex

Zarzal cristal complex

Zarzal very cobbly clay

33.6

12.0

73.8

191.3

82.2

376.4

95.7

39.5

478.4

134.8

1842.2

88.8

470.5

912.6

340.4

2391.0

2296.4

789.4

Area (ha)

0.3

0.1

6.5

1.7

0.7

3.3

0.8

0.3

4.2

1.2

16.3

0.8

4.2

8.1

3.0

21.1

20.3

7.0

Legend LEF ( )

 Primary roads

 Secondary roads

 LEF boundary

Soils Area (ha) LEF (%)

n Caguabo gravelly clay loam 33.6 0.3

n Coloso silty clay loam 12.0 0.1

n Cristal zarzal complex 734.8 6.5

n Dwarf muck windswept 191.3 1.7

n Guayabota Yunque complex 82.2 0.7

n Humatus zarzal complex 376.4 3.3

n Icacos loam 95.7 0.8

n Luquillo stony clay loam 39.5 0.3

n Palm Yunque complex 478.4 4.2

n Picacho Ciales complex 134.8 1.2

n Picacho Utuado complex 1842.2 16.3

n Prieto very cobbly clay loam 88.8 0.8

n Sonadora Caguabo complex 470.5 4.2

n Yunque cobbly clay 912.6 8.1

n Yunque los Guineos moteado 340.4 3.0

n Yunque moteado complex 2391.0 21.1

n Zarzal cristal complex 2296.4 20.3

n Zarzal very cobbly clay 789.4 7.0

8 4 0 8 km

4 2 0 4 km

0 2 10 0 40 60 80

km

N
29

Environmental Setting

Picacho-Utuado-Ciales Association—This association 

is composed of very deep, somewhat poorly drained and 

poorly drained loamy soils underlain by granitic saprolite 

and formed in residuum weathering from intrusive rocks of 

the Río Blanco formation in the plutonic uplands.

• Guayabota Yunque complex (30 to 60 percent slopes)—

shallow, poorly drained Guayabota soil and very deep, 

moderately well drained Yunque soil found on mountain 

side slopes at elevations from 600 to 750 m. Depth to 

bedrock is 25 to 50 cm. The soils have medium organic 

matter content, slow permeability, and low natural fertility.

•Icacos loam (occasionally flooded)—very deep, somewhat 

poorly drained soil found on flood plains and low terraces 

along perennial stream valleys at elevations between 600 

and 750 m. Depth to bedrock is >150 cm. The soil has high 

organic matter content, moderate permeability, and high 

natural fertility.

• Picacho Ciales complex (5 to 30 percent slopes) —very deep, 

somewhat poorly drained Picacho soil and very deep, poorly 

drained Ciales soil found on ridge tops and mountain side 

slopes at elevations from 600 to 800 m. Depth to bedrock 

is >150 cm. The soils have low organic matter content, 

moderate permeability, and low natural fertility.

• Picacho Utuado complex (5 to 35 percent slopes) —very 

deep, somewhat poorly drained Picacho and Utuado soils 

found on hills and footslopes in mountain stream valleys at 

elevations from 600 to 850 m. Depth to bedrock is >150 cm. 

The soils have low organic matter content, moderate 

permeability, and low natural fertility.

Dwarf—This association is very deep, poorly drained clayey 

soils that have an organic surface layer, are on summits and 

ridges of mountains, and formed in residuum that weathered 

from metamorphosed andesitic to basaltic, marine-deposited, 

volcanic sandstone of the Hato Puerco, Fajardo, and Tabonuco 

formations.

• Dwarf muck (10 to 65 percent slopes, windswept)—very 

deep, poorly drained soil on both convex and concave slopes 

at elevations >800 m. Depth to bedrock is >150 cm. The 

soil has very high organic matter content, moderately slow 

permeability, and high natural fertility.

Mean surface soil properties within the LEF differ 

significantly among forest types, topographic positions, and 

seasons (Cox and others 2002). Soil differences among forest 

types include those associated with biological processes 

and water inputs such as bulk density, soil moisture, and 

the nutrients Na, P, C, and S. In contrast, differences among 

topographic positions are typically related to geochemical 

processes and involve Ca, Mg, K, and Al.

Soil erosion varies by topographical position (Basnet 1992a). 

Slopes have the highest rates of erosion because of their 

steepness. In contrast, ridges are more stable because they 

are densely covered with trees and are underlain by stable 

geologic substrates. Sedimentation is highest in ravines, which 

receive runoff from other topographic positions and have 

lower tree densities. Also, ravines typically descend at lower 

slope angles.

The status of soils is also affected by past agricultural 

activities and climatic events. Cultivation began on the 

lower slopes of the mountains in the 16th century, with most 

concessions continuing until the 19th century (Wadsworth 

1951). In 1899, Hurricane San Ciriaco heavily impacted the 

forest and caused a subsequent decline in coffee plantings. 

Other storms have similarly affected the forest causing 

landslides (Larson and Torres-Sánchez 1992). By 1943, land 

used for cultivation and livestock grazing had decreased to 

only 160 ha. Soil erosion and degradation from these events 

not only influenced forest recovery and natural succession 

but also subsequent efforts to restore the landscape by tree 

planting (Marrero 1948).

Climate

Puerto Rico, lying in the path of the easterly trade winds, has 

a tropical maritime climate influenced by the surrounding 

ocean. During the year, the island is affected by tropical 

waves, depressions, storms, and hurricanes that normally 

occur from May to October as well as by northerly cold fronts 

during the winter months (Calvesbert 1970, Daly and others 

2003, Larsen 2000, Larsen and Torres-Sánchez 1998, Scatena 

1998a). The elevational gradient within the LEF produces 

differences in rainfall, relative humidity, wind velocity, cloud 

cover, temperature, atmospheric saturation deficit, and solar 

radiation. The first four parameters increase with ascent and 

the last three decrease. Seasonal differences in climate are 

evident during the year. For example, seasonality at El Verde 

on the lower northwestern slopes was generalized as follows 

(Odum and others 1970): “A winter season, December through 

March, could be differentiated from the remainder of the year 

by small average differences: temperature, 2o C less; relative 

humidity, 5 to 10 percent less; 5 to 18 percent of the days 

with westerly and northwesterly winds; 66 percent as much 

rain per month (January to March); 25 percent less insolation 

(November to February); and a higher frequency of almost 

clear days (15 percent).”

Precipitation—Several studies of rainfall have been carried 

out (Lugo 1986, Odum and others 1970, Wadsworth 1970), 

each varying slightly in its estimates. According to one study, 

the entire LEF receives an average of 3860 mm yr-1 during 

a typical year (García-Martinó and others 1996). Rainfall 
30

Environmental Setting

estimates by forest type averaged 3540 mm yr-1 in lower 

montane forest, 4190 in montane forest, 4170 in palm brake, 

and 4850 mm yr-1 in dwarf forest. The average number of days 

with rainfall and the amount of stream runoff increased with 

elevation. Heavier rainfalls occurred during the last 8 months 

of the year, notably in May and from September to November 

(fig. 11).

Mean annual rainfall averaged from 2475 to 4650 mm yr-1 at 

six different sites on the LEF’s northern slopes between 150 

and 1065 m in elevation (Briscoe 1966, Heartsill Scalley 2006, 

National Oceanic and Atmospheric Administration 2002, 

Ramírez and others 2005, Scatena 1998a, Wadsworth 1948) 

(fig. 11). Because the records represent different periods and 

vary considerably in duration, valid comparisons among sites 

are impossible. Mean annual rainfall averaged >4000 mm yr-1

at El Yunque, La Mina, Pico del Este, and Pico del Oeste, sites 

between 715 and 1065 m in elevation (Baynton 1968, Briscoe 

1966, National Oceanic and Atmospheric Administration 

2002, Wadsworth 1948). The highest daily rainfall of 485 mm 

was recorded at Pico del Este on May 20, 1969 (Weaver 1972).

The 9-year period of rainfall observations carried out at La 

Mina beginning in 1935 is of special interest. The mean of 

4650 mm yr-1, with an annual range of values between 3725 

and 6450 mm yr-1 (Wadsworth 1948), is the highest multiyear 

record for the mountains. Rainfall was detected on nearly 

75 percent of the days and averaged 19 minutes in duration. 

Rainfall intensity was nearly 8 mm hr-1 for the 1,625 showers 

recorded annually.

Rainfall that arrives on the forest canopy is distributed 

to the ground by throughfall (i.e., water falling from leaf 

surfaces through the canopy to the ground) or stemflow (i.e., 

water moving via tree branches and trunks to the ground). 

Throughfall estimates for the lower montane forest average 

about 60 percent of the annual rainfall (Odum and others 

1970, Scatena 1998a). These estimates are typically 20 to 

30 percent lower than for many other montane and lowland 

tropical forests (Scatena 1990). The differences are due to 

a high frequency, low intensity rainfall regime rather than 

characteristics of the forest itself.

Despite the heavy rainfall associated with the LEF, droughts 

occur occasionally and their effects are noteworthy. Puerto 

Rico experienced regional droughts from 1966 to 1968, 

1971 to 1974, 1976 to 1978, and from 1993 to 1995. All had 

a profound impact on streamflow and reservoir storage in 

watersheds that supply the island’s major towns (Larsen 2000), 

and all resulted in agricultural losses and water rationing in 

metropolitan areas.

One other climatic phenomenon merits reporting. During 

January 1969, hail fell in the vicinity of Pico del Este, and 

possibly elsewhere in the forest, for about 10 minutes at about 

10 a.m.1 Hail is rare in the LEF and other occurrences have 

not been noted.

Temperature—Temperature varies from about 24 to 27 °C 

at the base of the LEF to 17 to 20 °C at the summits (Baynton 

1968, Briscoe 1966, Brown and others 1983) (fig. 11). Diurnal 

temperature variation and temperature range in any particular 

month are greater at lower elevations than at higher elevations. 

Reported minimum and maximum temperatures were 11 and 

32 °C, respectively. The dew point temperature varies little 

over Puerto Rico, indicating that the overlying air mass is 

relatively constant with regard to moisture content during the 

year (Calvesbert 1970).

Wind chill would seem inappropriate to mention with 

regard to the LEF. However, a notable chilling is felt at the 

summits, especially during the cool winter months when 

wind-driven fog is deposited onto surfaces, including humans. 

One memorable experience was the penetrating cold that 

researchers felt while removing epiphytes from trees near Pico 

del Este during January and February of 1991 and 1997.

Relative humidity and evapotranspiration—Relative 

humidity at El Verde, about 350 m in elevation facing 

northwest, was above 95 percent except during a few hours 

on sunny days, or when air trajectories were unusual (Odum 

and others 1970). At Catalina located at 150 m, it averaged 

88 percent, with regular descents into the high 60s and 70s 

at midday (Briscoe 1966). At the summits of Pico del Este, 

Pico del Oeste, and El Yunque, relative humidity was at or 

near 100 percent most of the time, with the lowest recordings 

between 12:00 noon and 2:00 p.m. (Baynton 1968, Briscoe 

1966, Weaver 1972). Prevailing climatic conditions reduce 

transpiration rates but occasional clear days allow stomates to 

regulate water losses from tree species (Gates 1969, Medina 

and others 1981, Weaver and others 1986).

In the Bisley watersheds at 350 m elevation, 

evapotranspiration estimated by hydrological and 

micrometeorological techniques ranged between 2180 and 

2420 mm yr-1 during 1996 and 1997 (Schellekens and others 

2000). The values were considered high for lowland tropical 

areas and were partially attributed to frequent, low intensity 

rainstorms. Other possible influencing factors were also 

suggested. These were an effective net upward transport of 

evaporated moisture, proximity to the warm waters of the 

Atlantic providing advected energy, an irregular canopy due 

to the recent passage of Hurricane Hugo, and the watershed’s 

location in dissected terrain.

1 Personal observation. 1969, P.L. Weaver, Research Forester, U.S. 

Department of Agriculture Forest Service, International Institute of Tropical 

Forestry, Jardin Botanico Sur, 1201 Calle Ceiba, Rio Piedras, PR 00926-1119.
31

Environmental Setting

0

50

100

150

200

250

300

350

400

1 2 3 4 5 6 7 8 9 10 11 12

Monthly values

Months

Catalina (150 m; 1959-1962)

Annual =2475 mm, 23.9 oC 

Temperature (C)

Rainfall(mm)

0

50

100

150

200

250

300

350

400

450

1 2 3 4 5 6 7 8 9 10 11 12

Monthly values

Months

El Verde ( 350 m; 1975-2003)

Annual = 3535 mm, 23.9 oC 

Temperature (C)

Rainfall(mm)

0

100

200

300

400

500

600

1 2 3 4 5 6 7 8 9 10 11 12

Monthly values

Months

Pico delEste (1050 m; 1969-2005)

Annual =4345 mm, 18.6 oC 

Temperature (C)

Rainfall(mm)

0

50

100

150

200

250

300

350

400

450

1 2 3 4 5 6 7 8 9 10 11 12

Monthly values

Months

Bisley (300 m; 1988-2008)

Annual = 3670 mm, 24.6 oC 

Temperature (C)

Rainfall(mm)

0

100

200

300

400

500

600

1 2 3 4 5 6 7 8 9 10 11 12

Monthly values

Months

LaMina (715 m; 1935-1943)

Annual =4650 mm, 21.2 oC 

Temperature (C)

Rainfall(mm)

0

100

200

300

400

500

600

700

800

1 2 3 4 5 6 7 8 9 10 11 12

Monthly values

Months

El Yunque (1065 m; 1959-1962)

Annual = 3840 mm, 18.4 oC 

Temperature (C)

Rainfall(mm)

Figure 11—Climatic diagrams for sites within the Luquillo Experimental Forest.
32

Environmental Setting

Wind velocity and direction—Consistent trade winds, 

blowing mostly from an easterly direction, are the outstanding 

feature of climate in Puerto Rico (Calvesbert 1970). Wind 

velocity at El Verde averaged about 2 to 6 km hr-1 just above 

the forest, diminishing downward into the canopy (Odum 

and others 1970); similar velocity estimates were recorded 

at Catalina (Brown and others 1983). Wind velocities on the 

summits, strongest at night and weakest during the afternoon, 

averaged from 8 to 18 km hr-1 in any month (Baynton 1968, 

Briscoe 1966), but gusts of 100 km hr-1 were recorded during 

periods of normal winds elsewhere (Wadsworth 1948).

Winds may be tied to aberrant occurrences of insects within 

the forest. One incident involved Polistes americanus (Paper 

wasp) described as follows: “enormous numbers of these 

wasps have been observed on El Yunque rock (April 5, 1939), 

so abundant that one could not approach in safety” (Wolcott 

1948). Updrafts were suggested for the phenomenon. During 

October of 1968, a similar swarm of unidentified wasps was 

observed on the crowns of dwarf forest trees (see footnote 

1). The swarm completely surrounded Mt. Britton tower, 

which lies 1 km south of El Yunque (fig. 9). Indeed, these 

occurrences may be more common than is realized yet go 

unreported. In both cases, observers were able to look down 

on the swarms. The wasps, however, may have gone unnoticed 

by people walking on trails below the canopy.

Cloud cover and solar insolation—Cloud cover 

increases with elevation in the LEF where the summits are 

frequently bathed in clouds while the surrounding lowlands 

remain clear. Above 600 m, the base of trade wind cumulus 

clouds passes through the forest, depositing condensed cloud 

moisture on vegetative surfaces. Cloud moisture deposition 

adds 10 percent more water to the annual moisture balance 

than would result from rainfall alone (Baynton 1969, Weaver 

1972). Runoff from the summits of the dwarf forest is 

estimated to be virtually all of the ~5000 mm of combined 

rainfall and intercepted cloud moisture received by the soil 

surface during the year.

February and March are the months when the peaks are most 

likely to be free of clouds. Cloud cover also affects solar 

radiation. Mean annual solar radiation on El Yunque and Pico 

del Oeste averages about 60 percent of that received on the 

northeastern coast of Puerto Rico (Baynton 1968, Briscoe 1966).

Hurricanes—Hurricanes that traverse Puerto Rico typically 

originate off the coast of Africa and come from the southeast; 

occasionally, other storms originate in the Gulf of Mexico 

and may move northeast towards the Bahamas and Florida. 

Based on existing data, hurricanes may be expected to pass 

directly over the LEF once every 62 years and within 60 

km once every 22 years (Scatena 1989). Since 1738, at least 

33 hurricanes of varying intensity have passed over or near 

Puerto Rico, virtually all of them with trajectories sufficiently 

close to the Luquillo Mountains to have caused some impact 

within the LEF (Neumann and others 1988; Salivia 1972; 

Weaver 1986a, 1989b) (fig. 12).

Hurricane nomenclature in Puerto Rico, borrowing from 

different traditions, has varied over time. The Spanish 

explorers and early settlers named hurricanes according to 

saint’s days on the church calendar (Salivia 1972). In 1941, 

the fictitious “incipient little whorl” —a wind called “Maria” 

in the novel “Storm”—led to a revolution in hurricane 

nomenclature (Stewart 1941, page 18). Apparently, U.S. 

Navy meteorologists adopted Stewart’s innovation during 

World War II, remembering girlfriends back home by giving 

their names to tropical cyclones. It was certainly easier to 

personalize the storms than try to recall their degrees of 

latitude and longitude. In the early 1950s, Atlantic cyclones 

were labeled according to the phonetic alphabet, but in 1953, 

the U.S. Weather Bureau switched to female names. That 

tradition continued until 1979 when male and female names 

were alternated during the year. It is interesting to note that 

the 1956 Hurricane labeled as Betsy by the U.S. Weather 

Bureau was called “Santa Clara” when it traversed Puerto 

Rico (fig. 12). Today, the World Meteorological Organization 

has a procedure to designate the names of tropical storms and 

hurricanes in different regions of the world.

San Janero (1766) and San Augustín (1772) were the only 

recorded 18th century hurricanes that traversed the Luquillo 

mountains. San Jacinto I (1807), a slow moving storm, passed 

just south of the Luquillo Mountains, spending 50 hours over 

some part of Puerto Rico (Salivia 1972). Santa Ana (1825), 

San Jacinto II (1827), and Nuestra Señora de los Angeles 

(1837) all passed a short distance to the south of the Luquillo 

Mountains. In 1867, the island experienced Hurricane Narciso, 

which traversed directly over the Luquillo Mountains; 

moreover, only 3 weeks later, a major earthquake shook the 

island (Salivia 1972).

At least six hurricanes during the 20th century passed over 

Puerto Rico and had varying effects on the forests of the LEF 

(table 6):

• San Felipe (1928), with maximum winds of 240 km hr-1 and 

735 mm of rain, the “the largest, most violent, and most 

destructive” of hurricanes (Salivia 1972), or the island’s 

legendary storm, passed west of the Luquillo Mountains and 

spent 36 hours over the island.

• San Nicolas (1931), with winds of 145 km hr-1 and 125 

mm of rain, traversed the island’s north coast for 40 hours 

(Salivia 1972).

• San Cipriano (1932), with 200 km hr-1 winds and 430 mm of 

rain, passed directly over the LEF and spent 18 hours over 

the island (Crow 1980).
33

Environmental Setting Figure 12—Hurricane trajectories over Puerto Rico since 1700.

. 0 20 40 60 80 10

km

Legend for major hurricanes in Puerto Rico since 17001, 2

1Key: A = hurricane vortex passed over island with hurricane force winds; B = hurricane vortex passed over part of the island or offshore, with hurricane force winds on part of the

island; A/? and B/? = uncertain trajectory (i.e., San Ramón II in 1772 passed northeast of the island). Trajectories in 1899 and later are known; pre-1899 trajectories were sketched

from descriptions except those classed as A/? or B/?. 2Sources: Neumann et al. 1988, Salivia 1972.

32B

22B

26A27A 30A 5A, 25A

10B, 13A, 14B, 15B, 21B

33A

19A 17A 24A

1A, 2A, 3A

20A

11A, 18A

29A

31B

6A

4B

23A

28B

Key10-B11-A12-B/?

13-A14-B15-B16-A/?

17-A

Year

18051807180918131814181618191825

NameSan Vicente IISan Jacinto

San Esteban III

San Liborio II

San Liborio III

San José de CupertinoSan Mateo III

Santa Ana

Key18-A19-A20-A21-B22-B23-A24-A25-A

Year18271835183718511852186718761893

NameSan Jacinto IISan Hipólito

N.S. de los Angeles

San Agapito IISan Lloren o

San NarcisoSan elipe I

San Ro ue III

Key1-A2-A3-A4-B5-A6-A7-B/?

8-B/?

9-B/?

Year173817381751176617661772177217801785

NameSanta Rosa II

San Leoncio III

San Agapito

San Jenaro

San MarcusSan AgustínSan Ramón IISan Antonio

San Lupo

Key26-A27-A28-B29-A30-A31-B32-B33-A

Year18991928193119321956198919961998

NameSan Ciriaco

San elipe II

San Nicol s

San Cipriano IISanta Clara (Betsy)

ugoortense

eorges

z

F

F

á

HH

G q

N
34

Environmental Setting

Table 6—Impacts of 20th century hurricanes on vegetation in the Luquillo Mountains, mainly the Luquillo Experimental 

Forest 

Names and dates of hurricanes

Forest type or area, and brief summary of storm impacts and recovery in the LEF (source)

San Felipe (9/13/28)

Luquillo District: Field surveys showed defoliation, and snapping and uprooting of trunks. Post-storm seed production was 

abnormally high for some species. The time elapsed before recovery varied by species, mainly from 4 to 6 months (Bates 1929).

San Felipe (9/13/28), San Nicolás (9/10/31), and San Cipriano (9/26/32)a

Lower montane rain forest: The 1943-76 record for the El Verde III plot showed two distinct phases in post-hurricane forest 

structure and species composition: in early 1940s, secondary species were common, and stem numbers and biomass increased 

rapidly; in the mid-1970s, fewer stems and species were present, and biomass accumulation slowed. The percentage loss of 

secondary tree species was greater than for primary species (Crow 1980). Also, a 1946-88 record for permanent plot TR-1 showed 

stem density, species numbers, and the rate of biomass accumulation at a maximum 14 years after the last hurricane. Secondary 

species declined in numbers over time and Dacryodes excelsa dominated in stems and biomass throughout the post-hurricane 

recovery period (Weaver 2002b).

Montane rain forest: The 1946-81 combined record for seven stands showed positive changes in diameter and height class 

distributions. Secondary species present initially declined more rapidly in numbers than primary species. The mean specific gravity 

of the forest (i.e., weighted by tree volumes) increased during 30 years by 1.9 percent including palms, and 3.9 percent for broadleaf 

species alone. Both tree diameter growth rates and species diversity (i.e., mixture of secondary and primary species) were greatest 

a few years after the hurricane, declining over time. Stand volumes and biomass increased during the recovery period (Weaver 

1989b).

Santa Clara or Betsy (8/13/56)

LEF: Defoliation, breakage, and uprooting did not appear to increase with elevation. Impacts on ridges were limited to defoliation 

whereas windthrow within the Mameyes Valley was locally severe. More defoliation occurred on east-facing slopes than on westfacing slopes. Breakage was most common on shallow soils whereas uprooting was most pronounced on deep soils. Dominant 

trees in stands suffered more damage than subordinate trees. Forest plantations suffered heavy losses in certain areas. Younger 

plantations survived better than older (i.e., larger trees) plantations. Some tree species were more susceptible to breakage or 

windthrow than others (Wadsworth and Englerth 1959).

Hugo (9/18/89)

Lower rain montane forest: In Bisley, Sabana 4, and Río Grande, large trees were damaged with greater effects closer to the 

trajectory (Parresol and Alemañy 1998). More trees were more severely defoliated at Bisley (closer to Hurricane Hugo trajectory) 

than at El Verde. The proportion of uprooted or snapped stems between sites was not significantly different. Buttressing was not 

a deterrent to uprooting. Specific gravity of snapped trees was significantly negatively correlated with damage at Bisley but not at 

El Verde (Walker and others 1992). Severe defoliation occurred on 56 percent of the trees, with 11 percent of the trees snapped, 

9 percent uprooted, and 7 percent killed. Most damage occurred on north-facing sites. Tall trees with large diameters were the 

most likely to be uprooted (Walker 1991). At Bisley, all trees were defoliated, and 35 percent had broken branches, 5 percent had 

broken trunks, and 48 percent were uprooted and broken. The rate of recovery (resprouting, regeneration, and growth) was high. 

Dacryodes excelsa showed the most resistance to hurricane damage and recovered quickly from injury. The most severe impacts 

were in valleys rather than ridges or slopes. Most introduced tree species, planted in ravines, were severely affected. All palms 

were defoliated, but 46 percent remained standing. Large trees were highly susceptible to damage. No clear pattern of damage was 

evident for tree size classes <50 cm in diameter (Basnet 1993a; Basnet and others 1992). Continued measurement of permanent 

plot TR-1 stand showed an immediate post-hurricane decline in species numbers and biomass along with an explosion of Cecropia 

schreberiana ingrowth (Weaver 2002b). On the Bisley biodiversity plot, species composition was relatively constant before and after 

Hugo except that Cecropia schreberiana replaced Prestoea montana as the most common species. Live standing trees decreased 

by 61 percent and basal area by 64 percent 5 months after the storm (Dallmeier and others 1998). In the Bisley watersheds, total 

vegetative biomass declined by 62 percent from 301 to 113 t ha-1, reducing aboveground nutrient content of the forest by 45 to 48 

percent (Scatena and others 1993). Deposition of fine litterfall (leaves, and small woody and miscellaneous debris) varied from 420 

to 450 times the mean daily pre-storm input (Lodge and others 1991). Litter accumulation inhibited the establishment of seedlings, 

with variability in species responses likely to change tree composition in the forest (Guzmán-Grajales and Walker 1991). At El Verde, 

about 25 percent of the trees suffered impacts and 9 percent died. Pioneer species suffered high breakage and mortality, and 

had low capacity to sprout whereas nonpioneers suffered moderate damage and resprouted. Stem breakage was related to wood 

density and branch damage increased with tree size (Zimmerman and others 1994). Light increased in the post-hurricane understory 

(Fernández and Fetcher 1991). Post-hurricane treefall pits altered the recruitment and mortality of understory species but did not 

change species richness; moreover pit sizes did not affect species seedling or sapling densities (Walker 2000).

(table continued on following page) 
35

Environmental Setting

Table 6 (continued)—Impacts of 20th century hurricanes on vegetation in the Luquillo Mountains, mainly the Luquillo 

Experimental Forest 

Names and dates of hurricanes

Forest type or area, and brief summary of storm impacts and recovery in the LEF (source)

Growth rates of Manilkara bidentata seedlings increased in response to light available at the forest floor (You and Petty 1991). Posthurricane seed rain, coinciding with periods of high seed production, was dominated by shrubs that colonized landslides (Walker 

and Neris 1993). Live fine roots ≤10 cm in depth disappeared 3 months after the storm (Parrotta and Lodge 1991). Herbaceous 

cover was at 55 percent 1 year after the storm when vine cover was at a maximum. The cover and species richness of herbs and 

vines, but not ferns, were significantly reduced after 4 years (Chinea 1999). At El Verde, eight understory tree species showed an 

increase in leaf numbers and a more even seasonal production of leaves than in pre-hurricane conditions; also, herbivory levels 

declined from 16 to 2 pecent (Angulo-Sandoval 2004). The reorganization of aboveground biomass was characterized by an initial 

period of foliage and canopy recovery, followed by a peak of aboveground productivity as successional species grew as saplings 

and pole-size stems. Within stands, nutrient-use-efficiency was very low and aboveground productivity (e.g., 21.6 t ha-1 yr-1) 

was very high (Scatena and others 1995). A summary of recovery at Bisley showed an immediate post-hurricane loss of 50 percent 

of the biomass, and a loss in stem density and species richness followed by a 15-year period when biomasss recovered to prehurricane levels, and tree numbers and species richness exceeded pre-hurricane levels (Heartsill and others 2010).

Montane rain forest: Fine litterfall deposition was 680 times the pre-storm mean daily input (Lodge and others 1991). Rainfall 

caused >400 landslides ranging in size from 18 m2 to 4500 m2 in an area of 6475 ha, or 0.11 percent of the forest area sampled 

(Larsen and Torres-Sanchez 1992).

Palm brake: Thirty percent of the trees suffered impacts with 84 percent of the damage in the canopy. Tree mortality was only 

1 percent of the stems. Recovery was characterized by rapid refoliation, epicormic branching, adventitious root production, 

sprouting, and regeneration from seed in open areas (Frangi and Lugo 1991). Five year post-hurricane stem density, basal area, 

and biomass exceeded pre-hurricane values with 76 percent of the biomass accumulation between 1990 and 1995 due to palms. 

Litter on the forest floor decreased immediately after the hurricane to pre-hurricane values by 1995. Delayed tree mortality between 

1990 and 1995 was twice the instantaneous tree mortality immediately after the hurricane. The regeneration of palms, trees, and 

tree ferms was dependent on a combination of factors, including hydroperiod, light, and space (Frangi and Lugo 1998).

Dwarf forest: The 1990-95 record for six small plots showed that post-hurricane mortality (i.e., delayed mortality) accounted for 

a loss of 20 percent of the stems, notably in the smallest diameter and height classes. Mortality rates varied considerably by tree 

species. Pre- and post-hurricane total litterfall were virtually the same, but the leafy fraction decreased and the woody fraction 

increased. Post-hurricane primary productivity (1991) exceeded pre-hurricane (1981) values when post-hurricane coarse woody 

debris was included (Weaver 1999b, Weaver and Murphy 1990). Stripping of epiphytes from trees was widespread, and varied by 

topography (i.e., exposure to wind) (Weaver, pers. obs.). About one-third of the biomass recovered in 16 months and >40 percent in 

8 years (Weaver 1999).

Forests of the LEF: Profiles of the percent of foliage at different heights above the ground changed dramatically, with upper 

levels decreasing and the ground levels increasing after the storm (Brokaw and Grear 1991). The establishment of woody species 

by seeds is more important to post-hurricane regeneration in Lower montane forest than in Dwarf forest. The recovery of forest 

productivity is less responsive to nutrient availability in Dwarf forest than Lower montane forest. Opportunistic, rapid responses to 

nutrient additions (Cecropia schreberiana and graminoids in Lower montane forest, and graminoids in Dwarf forest) contrast with 

the slow responses of mature trees (Walker and others 1996).

Georges (9/21/98) 

Lower montane rain forest: Continued measurement of permanent plot TR-1 stand revealed a continual decline in species 

numbers along with a proportionately greater dominance of Dacryodes excelsa in both residual stems and biomass (Weaver 

2002b). Basal area explains 61 percent of the post-hurricane mound volume of uprooted trees; also, soil turnover rates based on 

uprooted trees during hurricanes is between 1,600 and 4,800 years, and exceeds turnover rates caused by either background 

treefall or landslides (Lenart and others 2010).

Dwarf forest: Continued measurement of the six small permanent plots on Pico del Este showed that stem numbers and biomass 

declined slightly (Weaver 2008). 

Forests of the LEF: Post-hurricane litterfall deposits for six different forests ranged from 0.55 to 0.93 times the annual rates 

and their decomposition rates varied from 0.74 to 1.09 years. Subsequent decomposition returned litter levels to normal within 

≤1.1 years at all sites (Ostertag and others 2003).

aLong-term data analyses included the combined effects of all three hurricanes (Crow 1980, Weaver 1989b).
36

Environmental Setting

• Santa Clara (1956), with maximum of 145 km hr-1 and 230 

mm of rainfall, crossed the center of the island and caused 

localized damage in the Luquillo Mountains (Wadsworth 

and Englerth 1959).

• Hugo (1989), with maximum sustained winds of 165 km hr-1

and gusts to 194 km hr-1, and >200 mm of rainfall, passed 15 

km northeast of the LEF but lasted only 4 hours (Brennan 

1991, Scatena and Larsen 1991).

• Georges (1998), with maximum sustained winds of 185 km 

hr-1 (gusts to 240 km hr-1) and rainfall between 125 and 150 

mm, passed about 15 km south of the LEF, spending 6 hours 

over the island (Ostertag and others 2003, U.S. Geological 

Survey 1999).

A monthly classification of 102 past hurricanes between 1500 

and 1970 revealed: July with 12; August with 35; September 

with 41; and June, October, and November together with 14 

(Salivia 1972). An oft repeated rhyme of uncertain origin 

conveniently generalizes these results: “June, too soon; July, 

stand by; August, don’t trust; September, to remember; 

October, it’s over.”

Queries are sometimes made regarding the most damaging 

hurricane or the most frequently hit location on the island. 

Hurricane impacts at any site are influenced by numerous 

factors, for example:

• Trajectory: Twenty of the 33 hurricanes that crossed all or 

a part of Puerto Rico entered in the southeastern corner 

of the island and departed in the west or northwest (fig. 

12). From the standpoint of the Luquillo Mountains, San 

Janero, San Augustín, San Narciso, and San Cipriano were 

powerful storms whose trajectories actually crossed over the 

mountains.

•Intensity: San Felipe II (1928) had violent winds with 

a trajectory through the middle of the island causing 

considerable damage to homes, crops, and forests (Salivia 

1970).

• Duration: San Jacinto I (1807), a slow moving storm, 

battered different parts of Puerto Rico for 50 hours (Salivia 

1970).

• Concurrent events: San Narciso (1867) was followed within 

20 days by a major earthquake that shook Puerto Rico and 

the Virgin Islands, causing tidal waves (Lewisohn 1964).

• Human lives: Although its winds over Puerto Rico were 

barely hurricane force and its trajectory was largely south 

of the island, the heavy rainfall that accompanied Hortense 

(1996) killed about 20 persons (Bennett 1996). Hortense 

also caused several landslides within the LEF and closed PR 

route 191 for about 1 month.

• Economic: Georges (1998), the most recent, traversed the 

entire island and caused $1.9 billion in damages to a modern 

Puerto Rico (U.S. Geological Survey 1999).

Hurricanes have other effects as well. After defoliation, 

breakage, and windthrow caused by Hurricane Hugo, clouds 

appeared to be positioned higher on or above the mountains, 

sometimes leaving the summits clear for extended periods 

(Scatena and Larsen 1991). A decrease in the number of brief 

episodes of orographic rainfall at lower elevations was also 

noted. Many factors could contribute to such a phenomenon. 

Forest openings and loss of leaves at lower elevations could 

lead to a temporary increase in heating at ground level (Van 

der Molen and others 2006) and a reduction in transpiration 

rates. Also, runoff could be temporarily increased because 

more rainfall reaches the ground in the absence of intercepting 

leaf surfaces. In comparison, a temporary loss of leaves and 

epiphytes on the summits could reduce the amount of cloud 

moisture interception (Weaver 1999).

Widespread effects on vegetation also influenced the LEF’s 

wildlife populations—birds, reptiles, amphibians, bats, and 

invertebrates. Some birds are killed and others are forced to 

either adapt to new environmental conditions or temporarily 

migrate to new surroundings (Wiley and Wunderle 1993, 

Wunderle 1995). Adult populations of Eleutherodactylus 

coqui, the island’s best known frog, increased sixfold as a 

result of the deposition of canopy branches on the ground 

(Woolbright 1996). Juvenile frogs also increased 1 year later. 

Both hurricanes and droughts also influence the abundances 

and distributions of freshwater shrimp in headwater streams 

by modifying channels and substrates, or temporary drying 

out waterways (Covich and others 1996, 2006).

An attempt was made to associate either distant or shortterm climatic events (e.g., six hurricanes and five droughts 

of varying intensity between 1989 and 1998) with field 

observations in the LEF (Beard and others 2005). Litterfall 

was heavily impacted by the major hurricanes of 1989 and 

1998 (table 6) and fine root biomass by the intense 1994-

95 prolonged drought. The remaining phenomena caused 

minor structural and functional forest responses and could be 

considered as background variation.

•
37

Tree Distributions and Major Forest Types

Tree distributions and major forest types are a product of 

climate, recurrent disturbances, and human activities. With 

reference to the LEF, some have noted that the “ubiquitous 

human activity across this mountainous landscape mandates 

that all research, management decisions, and ecological 

interpretations incorporate an awareness of land use history.” 

They also cautioned that “Despite compelling field and 

historical evidence of land use, there has been tendency to 

interpret forest structure and dynamics largely in natural 

terms” (Foster and others 1999).

Tree Species Affinities and Geographic 

Distribution

The Luquillo Mountains have at least 830 native species of 

plants, including >250 species of trees, and are one of the 

centers of high species richness and endemism in Puerto Rico 

(Figueroa Colón 1996). The LEF, occupying 58 percent of the 

Luquillo Mountains (table 2), has at least 225 species of native 

trees in 144 genera and 59 plant families with the following 

regional distributions: 41 percent are also found in continental 

areas (i.e., South and Central America, Mexico, and Florida); 

28 percent grow elsewhere in the West Indies, but not on the 

continent; and 31 percent are endemic to Puerto Rico and the 

Virgin Islands (Little 1970; Little and Woodbury 1976, 1980). 

Of the 88 tree species classified as either endemic or rare in the 

LEF, 16 were classed as endemic only to the LEF, 52 as endemic 

to Puerto Rico and also found in the LEF, and 20 species as 

rare in Puerto Rico but also native to areas outside of the island. 

Recent work has reduced the number of LEF endemics to 8, 

which means that 60 species are currently classed as endemic to 

Puerto Rico and also found in the LEF (Axelrod 2011).

The results of several surveys and studies provide other 

estimates of tree species by forest type (tables 7 and 8):

• Lower montane, 73 tallied on 4 ha and 168 noted during 

excursions to several sites (Little 1970); also, 69 tallied on 

0.9 ha during gradient sampling (Weaver 2010a).

• Montane, 51 tallied on 4 ha (Little 1970) and 73 on 3.75 ha 

during past sampling (Weaver 1989b).

• Palm brake, 63 recorded on 4 ha (Little 1970) and 36 tallied 

on 0.6 ha in gradient sampling (Weaver, 2012).

• Dwarf, 54 observed on 0.82 ha during gradient sampling 

(Weaver 2008, 2010b).

Although some areas within the LEF have never been 

sampled, it seems improbable that additional surveys could 

add more than a few rare tree species for the forest.

Field Sampling and Permanent Plot 

Monitoring

The Forest Service and collaborators have carried out surveys 

in the Luquillo Mountains for nearly a century and have 

monitored primary and secondary forest plots for nearly 70 

years. Since 1943, at least 618 demarcated plots with >134,000 

trees have been established on 66.75 ha located between 210 

and 1,025 m in elevation (Lugo and Brown 1981, Wadsworth 

1970) (fig. 13) (table 7). Although receiving less attention than 

better known research sites, plot monitoring has contributed 

background information on tree species and forest types, and 

remains an integral part of the Institute’s research program. 

Ideally, sampling would have included more plots near the 

forest border. However, most of those areas were heavily 

impacted by human activities such as agriculture, timber 

harvest, charcoal production, road and trail construction, 

forest plantations, and timber stand improvement (Crow 1980, 

García-Montiel and Scatena 1994, Scatena 1989, Thompson 

and others 2002, Wadsworth 1950, Weaver and Bauer 1986).

The results of plot studies and monitoring reflect study 

objectives, sampling design and replication, and the period of 

time when measurements were carried out, especially with 

regard to previous hurricanes or land use. Many of the studies 

emphasized tree species, timber volumes, or other aspects of 

the vegetation, as follows:

• Timber surveys—Temporary plots were used to: survey 

the stocking of sawtimber species in lower montane forest 

in 1905; estimate standing timber volume in 1918; carry out 

strip surveys of forest stocking in 1930; and conduct linear 

strip timber surveys in areas scheduled for future harvest 

in 1937 and 1948. The data was for used for planning and 

management purposes (Wadsworth 1970) (appendix A).

• Isolated permanent plots—Trees on 24 plots of variable 

size located within representative forest cover were 

permanently tagged and measured (fig. 13) (table 7): in 

1943, a lower montane plot near El Verde; in 1946 and 1951, 

five plots in lower montane forest, nine in montane forest, 

and two in palm brake; in 1980, another palm plot; in 1990, 

six small dwarf forest plots. All trees above a specified 

diameter at breast height (d.b.h.) were identified and 

measured, and height was omitted, measured, or estimated. 

Ingrowth (i.e., recruitment of trees attaining the minimum 

d.b.h. size) and mortality were tallied. All plots were remeasured periodically. The information was initially used 

to determine tree species’ compositions and distributions, 

typical tree sizes, stem densities, basal areas, locally derived 

volume tables, and d.b.h. growth rates by tree species and 

Chapter 3. TREE DISTRIBUTIONS AND MAJOR FOREST TYPES
38

Tree Distributions and Major Forest Types Setting

Table 7—Permanent and temporary tree monitoring plots established in the Luquillo Experimental 

Foresta

Location

Plot name

Dates 

established

Plots

no.

Total area

ha

Elevation

m

Stems

no.

Species

no.

Long-term tree species monitoring plots

Lower montane rain forestb

El Verde III 1943 1 0.72 380 955 46

Tabonuco ridge 1 (TR-1) 1946 1 0.40 400 713 48

Tabonuco slope 2 (TS-2) 1946 1 0.40 500 827 46

Tabonuco slope 3 (TS-3)c 1946 1 0.40 570 949 48

Tabonuco cutover 1 (TCU-1) 1947 1 0.20 470 402 47

Tabonuco cutover 2 (TCU-2) 1947 1 0.20 470 493 42

Montane rain forestd

Colorado slope 1 (CS-1) 1946 1 0.40 700 905 35

Colorado slope 2 (CS-2) 1946 1 0.40 700 725 47

Colorado slope 3 (CS-3) c 1946 1 0.40 880 676 40

Colorado slope 4 (CS-4) c 1946 1 0.40 880 733 33

Colorado valley 1 (CV-1) c 1946 1 0.40 750 662 37

Colorado valley 2 (CV-2) c 1946 1 0.40 740 588 27

Colorado valley 3 (CV-3) c 1946 1 0.40 650 785 58

Colorado valley 4 (CV-4) c 1946 1 0.40 650 805 49

Colorado cut over (CCU) 1947 1 0.40 670 794 24

Palm brakee

Palm slope 1c 1946 1 0.40 500 705 26

Palm slope 2 1946 1 0.40 570 703 33

Riparian palm brake 1980 1 0.25 750 765 27

Dwarf forestf

East Peak (near road)

Ridge 1990 1 0.025 1000 101 6

Slope 1990 1 0.025 970 48 6

Ravine 1990 1 0.025 970 49 7

East Peak (near wreck)

Ridge 1990 1 0.025 900 78 9

Slope 1990 1 0.025 900 89 7

Ravine 1990 1 0.025 900 81 7

Subtotal (long-term plots) 1943-90 24 7.12 380-1000 13,631 NA

(table continued on following page))
39

Tree Distributions and Major Forest Types

Table 7 (continued)—Permanent and temporary tree monitoring plots established in the Luquillo 

Experimental Foresta

Location

Plot name

Dates 

established

Plots

no.

Total area

ha

Elevation

m

Stems

no.

Species

no.

Special research monitoring plots

Lower montane rain forest

Pilot management plotsg

Cubuy 1957 100 8.00 350-550 799 29

Río Grande 1957 104 8.32 420-600 404 14

Sabana 4 1957 106 8.48 210-600 273 8

Sabana 8 1957 107 8.56 180-360 1,332 17

Luquillo Forest dynamics plot h 1990 1 16.00 333-428 86,788 145

Montane rain forest

FIA inventory plotsi 2000 6 0.40 608-808 229 27

Subtotal (special plots) 1957-2000 424 49.76 210-808 89,825 NA

Gradient sampling plots

Lower montane rain forestj 2000-02 18 0.90 380-550 3,619 42

Montane rain forestk 1980-81 69 3.75 600-900 8,183 87

Palm brakel 2000-02 12 0.60 550-850 1,122 35

Dwarf forestm 2000-02 33 0.82 900-1025 3,621 42

Northeastern island gradientn 2001-02 12 1.20 380-1000 1,764 71

Metacommunity studyo 2001-02 26 2.60 300-1000 12,361 99

Subtotal (gradient plots) 1980-2002 170 9.87 300-1025 30,670 NA

Total 1943-2002 618 66.75 210-1025 134,126 NA

aOther small plots were established early within the LEF but not maintained. Minimum d.b.h. for all plots is ≥4 cm unless 

otherwise indicated. Stem and species numbers are from the first tallies made on each plot. NA = Not available.

bSources: Crow (1980); Drew and others (2009); Johnston (1990); Weaver (1983, 1998, 2002b).

cPermanent plots within the El Toro Wilderness Area.

dSources: Weaver (1983, 1986, 1987a, 1987b, 1989b, 2000a).

eSources: Frangi and Lugo (1985, 1991, 1998); Lugo and Frangi (1993); Weaver (1983).

f

Sources: Weaver (1999, 2008).

gSources: Anonymous (1958); Crow and Grigal (1980); Crow and Weaver (1977). Each area contained selected crop trees 

≥10 cm.

hSource: Thompson and others (2002). Minumum d.b.h is ≥1 cm.

i

Source: Brandeis and others (2007). Minimum d.b.h is ≥12.5 cm.

j

Source: Weaver (2010a) (18 plots 50x10 m in size).

kSource: Weaver (1991, 2000, 2001). Also, gradient study (69 plots 50x10 m in size).

l

Source: Weaver (XXX) (12 plots 50x10 m in size).

mSource: Weaver (2010b) (33 plots 25x10 m in size).

nSource: Gould and others (2006) (12 plots 10x10 m in size) . Minimum d.b.h. is ≥2 cm. 

oSource: Barone and others (2008) (26 plots 50x20 m in size). Minimum d.b.h is ≥1 cm. 
40

Tree Distributions and Major Forest Types Setting

Table 8—Comparison of forest structure and dynamics data for the Luquillo Experimental Forest 

gradient

Feature

Forest type

Lower montane

rain forest

Montane

rain forest

Palm

brake

Dwarf

forest

Forest type boundaries, elevation (m) 120-600 600-900 >450 >900

Total tree species per typea 168 88 63 54

Tree species (no. ha-1)b 40-50 35-40 25-30 15-20

Species in gradient sample (no.)c 69 84 36 42

Single most abundant species (%)d 20 19 57 23

Five most abundant species (%)d 47 52 84 72

Ten most abundant species (%)d 65 71 90 91

Structural characteristicsc

Mean density (trees ha-1) 1,557 ± 100 2059 ± 72 1892 ± 93 3,328 ± 242

Ridge topography 1677 ± 144 2385 ± 130 2165 ± 50 3878 ± 386

Slope topography 1623 ± 200 2164 ± 98 1820 ± 225 3843 ± 460

Ravine topography 1370 ± 174 1627 ± 84 1690 ± 31 2263 ± 173

Total range of density values 680-2380 1060-3840 1160-2300 1320-4660

Mean canopy tree height (m) 19.4 ± 0.1 13.0 ± 0.3 12.5 ± 0.5 8.8 ± 0.4

Ridge topography 21.1 ± 1.9 12.4 ± 0.5 11.2 ± 0.6 7.4 ± 0.7

Slope topography 19.3 ± 1.2 12.5 ± 0.4 13.5 ± 0.8 8.3 ± 0.7

Ravine topography 17.9 ± 1.2 14.1 ± 0.5 12.8 ± 0.9 10.7 ± 0.5

Total range of tree height values 14.2-25.9 7.3-17.9 9.9-15.3 4.0-13.5

Mean aboveground woody biomass (t ha-1) 244 ± 28 190 ± 11 105 ± 14 172 ± 12

Ridge topography 361 ± 38 243 ± 23 146 ± 36 181 ± 25

Slope topography 229 ± 29 198 ± 13 90 ± 5 178 ± 17

Ravine topography 142 ± 20 129 ± 11 78 ± 10 148 ± 17

Total range of biomass values 95-512 77-519 59-249 76-356

Additional structural characteristicsb

Typical d.b.h. range; maximum d.b.h. (cm)b 4-50; 120 4-30; 250 4-30; 50 4-15; 40

Typical basal area range (m2 ha-1)b 35-45 35-45 30-35 30-45

Typical mean plot specific gravity (g cm-3)e 0.49 (0.60) 0.56 (0.66) 0.35 (0.52) 0.63 (0.64)

Leaf biomass (t ha-1)b 7.9 5.8 25.1 2.9

Leaf area index (m2 m-2)b 67 35 3.3 33.5

Mean specific leaf area (cm2 g-1)b 127 91 NAf 47

Soil organic matter (t ha-1)b g 420 330 320 550

(table continued on following page))
41

Tree Distributions and Major Forest Types

Table 8 (continued)—Comparison of forest structure and dynamics data for the Luquillo Experimental 

Forest gradient

Feature

Forest type

Lower montane

rain forest

Montane

rain forest

Palm

brake

Dwarf

forest

Dynamic characteristicsb

Ingrowth (stems ha-1 yr-1)h i 13 23 12 32

Mortality (stems ha-1 yr-1)h i 28 18 22 75

Litterfall (t ha-1 yr-1) 8.6 6.8 8.8 3.1

Leaf 4.94 5.05 6.26 2.45

Wood 1.38 1.22 0.86 0.28

Fruit/Flower 0.51 0.23 0.56–1.32 0.07

Miscellaneous 1.78 0.3 0.36 0.37

Loose litter (t ha-1) 6.0 8.76 5.4 4.34

Standing herbivory (%) 7.0 NA 5.0 NA

Herbivory rate (t ha-1 yr-1) 0.38 0.25 NA 0.13

Litterfall/loose litter 1.2 0.78 1.62 0.7

Mean d.b.h. growth (cm yr-1) 0.09-0.14 0.10 0.23 0.03

Woody biomass increment (t ha-1 yr-1) 2.50 0.57 3.30 0.45

Total aboveground NPP (t ha-1 yr-1) 10.5 7.6 19.5 3.7

aSources: Lower montane (Little 1979), Montane (Weaver 1989b), Palm (Little 1970), and Dwarf (Weaver 2008). The entire LEF 

has 225 tree species (Little 1970, Little and Woodbury 1976).

bSources: Lugo and Frangi 1993; Weaver 1983, 1999, 2008; Weaver and Murphy 1990. 

cSource: Species, mean stem density, canopy height, biomass, and values by topography (gradient sampling). All plots had 

closed canopies and measured 500 m2 except for the Dwarf forest plots with 250 m2. All stems >4.0 cm were tallied. d% = percent of total stems.

eSpecific gravities were estimated as the mean of available values weighted by number of stems by forest type. The first 

estimate includes Prestoea montata and the second estimate only broadleaf species (Chudnoff 1981, see endnotes; Little and 

Wadsworth 1964; Little and others 1974; Reyes and others 1992; Smith 1970; Weaver 1992; appendix F). Mean values were 

based on most common species weighted according to their numerical abundance (Table 9).

f

NA = not available.

gSoil depths: Lower montane, 25 cm; Montane and dwarf, 50 cm; Palm, 100 cm.

hLower montane (2), Montane (2), and Palm (1) plots 0.4 ha in size measured for 30 years (Weaver 1983).

i

Dwarf forest plots 0.025 ha in size measured for 15 years, post-hurricanes Hugo and Georges (Weaver 2008).
42

Tree Distributions and Major Forest Types Setting

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Legend Trails Primary roads Secondary roads LEF boundary

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" Forest inventory

# Permanent plots

! Temporary plots

Plot Network

1

2

3

4

5

6

Arboretum

BaÒo de Oro RNA

Bisley - LTER

El Verde field station

El Verde ecological grid

Mahogany provenance trial

Research Sites Research Sites

7

8

9

10

11

12

Pico del Este

Pico del Oeste

Riparian palm

Sabana Research Center

Landslide (PR-191)

Airplane wreck

Pilot Study Areas

A

B

C

D

Cubuy

RÌo Grande 3

Sabana 4

Sabana 8

3 1.5 0 3 km

Figure 13—Permanent and temporary plot locations, and major research sites within the Luquillo Experimental Forest.

Legend

Trails

Primary roads

Secondary roads

LEF boundary

Research Sites

1 Arboretum 7

2 Baño de Oro RNA

3 Bisley - LTER 

4 El Verde field station

5 El Verde ecological grid

6 Mahogany provenance trial

7 Pico del Este 

8 Pico del Oeste

9 Riparian palm

10 Sabana Research Center

11 Landslide (PR-191)

12 Airplane wreck

Pilot Study Areas

A Cubuy

B Río Grande 3

C Sabana 4

D Sabana 8

Plot Network

s Permanent plots 

n Forest Inventory 

l Temporary plots

N
43

Tree Distributions and Major Forest Types

forest type (Wadsworth 1947, 1951, 1953, Weaver 1983) 

(table 8). Later, the datasets were used to determine biomass, 

evaluate hurricane impacts, and to derive estimates of net 

primary productivity, nutrient fluxes, tree ages, and to help 

characterize tree life cycles.

• Pilot management plots—In 1957, the pilot management 

study employed a grid of plots in four areas—in the 

secondary lower montane forests in Cubuy, Río Grande, and 

Sabana 8, and in the mature lower montane forest at Sabana 

4 (figs. 3 and 13) (table 7). Thinnings were carried out within 

the secondary forests and the d.b.h. growth rates of 2,060 

trees were determined.

• Gradient sampling—After 1980, a systematic series of 

temporary closed forest plots (i.e., untagged trees on plots 

marked with corner stakes) was set up along elevational 

gradients throughout the LEF (Weaver 1987a, 1991, 2000b, 

2010a, 2010b) (fig. 13) (table 7) (appendix C). The plots were 

stratified in groups of three by topography (i.e., ridge, slope, 

and ravine). Plot sizes were relatively small yet provided 

good estimates of variation in forest structure and species 

composition (figs. 14, 15, 16, 17, and 18) (tables 9, 10, 11, 

and 12) (appendix C). The total number of species tallied 

was relatively high because the sample plots were limited 

to closed forest conditions and encompassed considerable 

environmental variation.

• Vegetation surveys—After Hurricane Hugo, surveys 

were carried out on disturbed sites (i.e., landslides, areas 

heavily impacted by hurricanes, or roadsides). Sampling 

usually involved relatively small areas with temporary plots 

(appendix D). In these instances, survey results may be 

influenced by local conditions.

• El Verde Ecological Grid (forest dynamics plot)—

Starting in 1990, a complete tree census was carried out on a 

16-ha permanent plot composed of a grid of subplots set up 

at El Verde to explore hurricane recovery and tree species 

dynamics (Thompson and others 2002) (fig. 13) (table 7). 

Large plots may subsequently be divided into subplots for 

particular studies (e.g., nutrient analyses, riparian zone 

species compositions). Their remeasurement requires 

considerable time.

• Forest Inventory and Analysis (FIA) Program—Since 

1980, FIA has surveyed secondary forests throughout 

Puerto Rico. The FIA, first called the Forest Survey, dates to 

McSweeney-McNary Act that also established the research 

branch of the Forest Service (Shaw 2006; U.S. Department 

of Agriculture, Forest Service 1983). Island-wide inventories 

carried out in 1980 and 1990 (Birdsey and Weaver 1982, 

Franco and others 1997), were expanded in 2001 to include 

six plots within the LEF (Brandeis and others 2007) (fig. 13) 

(table 7). Data from the standardized LEF plots are analyzed 

along with other plots in the FIA network for Puerto Rico 

and its offshore islands.

• Northeastern gradient—In 2001-02, several plots were 

established along an elevational gradient between the coastal 

lowland and Pico del Oeste to determine forest structure and 

composition. Twelve were located in the LEF (Gould and 

others 2006) (figs. 1 and 13) (table 7).

• Metacommunity structure—In 2001-02, woody stems 

were sampled on 26 plots along elevational transects in the 

Baño de Oro and Río Sonadora watersheds (Barone and 

others 2008) (fig. 9) (table 7).

• Plantations—Since the 1950s, trees have been planted as 

part of species trials, provenance studies, forest plantations, 

or as additions to the Caracoles arboretum (figs. 6, 7, and 

13). Subsequent surveys of select plots or labeled trees 

were used to determine survival and growth (Francis 1987, 

1995) (appendix E). Study results may be influenced by 

tree species, their genetic attributes, site quality, or field 

techniques, including plot maintenance schedules.

Lower Montane Forest

The lower montane forest, the most diverse in the LEF, 

contains the tallest trees and has the longest history of human 

activity, including mining, logging, subsistence agriculture, 

and temporary settlement in certain areas. Research has 

included tree planting and experimental silviculture in 

secondary stands, permanent plot monitoring, gradient 

sampling, and numerous ecological studies carried out at two 

major sites—Bisley and El Verde.

Stand features and notable tree species—Mature 

lower montane forest contains three layers of trees, mainly 

evergreen. Canopy species reach 30 m in height with 

occasional diameters approaching 1.5 m (Wadsworth 1951). 

The forest type, occupying about one-half of the LEF, 

has the lowest average stem density, and greatest mean 

canopy height and biomass (fig. 3) (table 8). Dacryodes 

excelsa, Prestoea montana, Sloanea berteroana, Cordia 

borinquensis, Manilkara bidentata, Schefflera morototoni, 

Cecropia schreberiana, Micropholis garciniifolia, Henriettea 

squamulosa, and Quararibea turbinata (Sw.) Poir., as listed, 

were the 10 most common of > 80 species that were recorded 

on 4 ha of permanent plots during the 1940s (Briscoe and 

Wadsworth 1970). Cecropia schreberiana is most abundant 

after hurricanes when its dormant seeds germinate in response 

to canopy openings; however, it is uncommon in abandoned 

pastures at lower elevations (Brokaw 1998). During posthurricane recovery of the forest, Cecropia schreberiana and 

Schefflera morototoni declined significantly in numbers. 

Cecropia schreberiana trees persist within the forest along 

road cuts and within riparian areas, ravines, landslides, and 

treefall gaps.
44

Tree Distributions and Major Forest Types Setting

0

5

10

15

20

25

30

0 200 400 600 800 1000 1200

C

a

n

o

p

y

h

eig

h

t (m)

Elevation (m)

Ridge

Slope

Ravine

Ridge

Slope

Ravine

Figure 14—Mean canopy heights per plot by elevation in the Luquillo Experimental Forest (linear trends for ridge, slope, and ravine).

Figure 15—Mean density of stems ≥4 cm d.b.h. per plot by elevation in the Luquillo Experimental Forest (linear trends for ridge, slope, and ravine).

0

1000

2000

3000

4000

5000

6000

7000

0 200 400 600 800 1000 1200

S

t

e

m

s(n

o. h

a-1

)

Elevation (m)

Ridge

Slope

Ravine

Ridge

Slope

Ravine
45

Tree Distributions and Major Forest Types

0

100

200

300

400

500

600

0 200 400 600 800 1000 1200

Bio

m

ass(t h

a-1)

Elevation (m)

Ridge

Slope

Ravine

Ridge

Slope

Ravine

Figure 16—Aboveground dry weight biomass per plot for stems ≥4 cm d.b.h. by elevation within the Luquillo Experimental Forest (linear trends for ridge, 

slope, and ravine).

Figure 17—Number of tree species per plot for stems ≥4 cm d.b.h. by elevation within the Luquillo Experimental Forest (linear trends for ridge, slope, and ravine).

0

5

10

15

20

25

30

0 200 400 600 800 1000 1200

S

p

e

cies p

e

r

plot (n

o.)

Elevation (m)

Ridge

Slope

Ravine

Ridge

Slope

Ravine
46

Tree Distributions and Major Forest Types Setting0102030405060

0 1000 2000 3000 4000

).on(seicepS

Area (m2)

Lower montane rain forest

RidgeSlopeRavine

Figure 18—Species-area curves for stems ≥4 cm d.b.h. by forest types within the Luquillo Experimental Forest.

0

1020304050607080

0 5000 10000 15000

).on(seicepS

Area (m2)

Montane rain forest

RidgeSlopeRavine

50

101520253035

0 500 1000 1500 2000 2500

).on(seicepS

Area (m2)

Palm brake

RidgeSlopeRavine 5

0

101520253035

0 1000 2000 3000

).on(seicepS

Area (m2)

Dwarf forest

RidgeSlopeRavine
47

Tree Distributions and Major Forest Types

Table 9—Lower montane rain forest: occurrence of 31 tree species on 

18 plots each 50 x 10 m in size within the Luquillo Experimental Foresta

Species Occurrence Topographyb

Plots Stems R S V

Stems no.

Prestoea montana 17 285 48 42 195

Dacryodes excelsa 9 150 83 65 2 

Micropholis garciniifolia 9 83 31 49 3

Manilkara bidentata 10 80 31 38 11

Sloanea berteroana 12 60 19 17 24

Drypetes glauca 10 55 16 30 9

Tetragastris balsamifera 8 52 32 17 3 

Croton poecilanthus 7 51 7 4 40

Daphnopsis philippiana 6 49 19 24 6

Cecropia schreberiana 7 48 10 14 24

Cyrilla racemiflora 5 36 17 18 1

Henriettea squamulosa 5 34 4 20 10

Tabebuia rigida 4 32 15 12 5

Cordia borinquensis 12 23 4 10 9

Schefflera morototoni 8 23 13 8 2

Psychotria berteroana 7 21 12 2 7

Ocotea spathulata 5 19 13 6 0

Myrcia leptoclada 4 19 7 12 0

Micropholis guyanensis 4 19 11 8 0

Tetrazygia ubanii 4 17 8 6 3

Matayba domingensis 6 14 10 4 0

Ocotea leucoxylon 9 13 7 2 4

Meliosma herbertii 5 13 5 8 0

Hirtella rugosa 5 13 5 7 1

Guarea glabra 9 12 2 3 7

Inga laurina 4 9 2 5 2

Ormosia krugii 4 9 5 4 0

Alchornea latifolia 5 8 4 4 0

Guatteria caribaea 4 8 6 2 0

Miconia tetrandra 4 8 1 5 2

Ixora ferra 4 8 4 4 0

38 other species – 123 53 34 36

Total 18 1394 504 484 406

— = Not applicable because the number of species varies.

aSource: Gradient study (Weaver 2010a).

bTopography: Six plots apiece on ridge (R), slope (S), and ravine (V) topography.

Listed species ≥8 stems equal 91.2 percent of all stems tallied (summarized from 

appendix C).
48

Tree Distributions and Major Forest Types Setting

Table 10—Montane rain forest: occurrence of 26 tree species on 

69 plots each 50 x 10 m in size within the Luquillo Experimental Foresta

Species Occurrence Topographyb

Plots Stems R S V

Stems no.

Prestoea montana 58 1309 217 254 838

Henriettea squamulosa 60 937 309 454 174

Micropholis garciniifolia 49 643 295 319 29

Tabebuia rigida 35 387 177 190 20

Micropholis guyanensis 27 349 206 122 21

Cordia borinquensis 57 346 135 114 97

Ocotea spathulata 43 337 215 105 17

Croton poecilanthus 36 315 22 74 219

Cyrilla racemiflora 33 206 113 82 11

Haenianthus salicifolius 32 171 82 70 19

Daphnopsis philippiana 37 140 48 74 18

Miconia tetrandra 27 138 73 26 39

Clusia clusioides 27 136 66 69 1

Hirtella rugosa 17 121 84 6 1

Eugenia borinquensis 23 111 63 21 27

Matayba domingensis 19 108 58 44 6

Myrcia fallax 29 97 73 21 3

Cyathea arborea 13 70 30 25 15

Byrsonima wadsworthii 25 69 44 19 6

Ditta myricoides 27 61 10 27 24

Magnolia splendens 27 59 25 28 6

Psychrotia berteroana 22 56 27 10 19

Garcinia portoricensis 6 55 43 10 2

Cecropia schreberiana 24 53 7 9 37

Drypetes glauca 9 48 4 28 16

Ocotea leucoxylon 22 46 34 8 4

47 other species — 662 290 178 194

Totals 69 7030 2750 2417 1863

— = Not applicable because the number of species varies.

aSource: Gradient study (Weaver 1989b).

bTopography: Twenty-three plots each on ridge (R), slope 

(S), and ravine (V) topography. Listed species ≥46 stems 

equal 90.6 percent of all stems tallied (summarized from 

appendix C).
49

Tree Distributions and Major Forest Types

Table 11—Palm brake: occurrence of 11 tree species on 18 plots each 

50 x 10 m in size within the Luquillo Experimental Foresta 

Species Occurrence Topographyb

Plots Stems R S V

Stems no.

Prestoea montana 12 637 203 202 232

Cecropia schreberiana 11 129 47 50 32

Henriettea squamulosa 9 73 34 24 15

Tabebuia rigida 3 40 36 4 0

Cordia borinquensis 9 38 14 16 8

Eugenia borinquensis 4 28 22 0 6

Psychotria berteroana 8 19 9 8 2

Croton poecilanthus 4 16 1 4 11

Sapium laurocerasus 9 14 5 6 3

Clibadeum erosum 4 13 5 2 6

Cyathea portoricensis 4 13 0 8 5

25 other species – 102 70 14 18 

Total 12 1122 446 338 338

— = Not applicable because the number of species varies.

Table 12— Dwarf forest: occurrence of 10 tree species on 33 plots each 

25 x 10 m in size within the Luquillo Experimental Foresta

Species Occurrence Topographyb

Plots Stems R S V

Stems no.

Tabebuia rigida 27 844 378 372 94

Ocotea spathulata 22 566 292 215 59

Eugenia borinquensis 30 432 173 183 76

Cyathea bryophila 21 421 41 176 204

Micropholis garciniifolia 26 362 166 169 27

Henriettea squamulosa 25 357 129 96 132

Prestoea montana 12 135 0 5 130

Clusia clusioides 11 76 24 34 18

Calyptranthes krugii 19 61 30 21 10

Haenianthus salicifolius 10 48 23 12 13

32 other species – 317 120 100 97

Total 33 3619 1376 1383 860

— = Not applicable because the number of species varies.

aSource: Gradient study (Weaver 2010).

bTopography: Four plots each on ridge (R), slope (S), and ravine (V) topography. 

Listed species ≥13 stems equal 90.9 percent of all stems tallied (summarized 

from appendix C).

aSource: Gradient study (Weaver 2008, 2010b).

bTopography: Eleven plots apiece on ridge (R), slope (S), and ravine (V) 

topography. Listed species ≥48 stems equal 91.2 percent of all stems tallied 

(summarized from appendix C).
50

Tree Distributions and Major Forest Types Setting

The best developed stands in lower montane forest are on 

low, well-drained ridges where Dacryodes excelsa, a species 

formerly valued for furniture and general construction, is 

abundant and grows in large sizes (Little and Wadsworth 

1964). Indigenous peoples hollowed out trunks as boats 

and used its resin for torches, as incense in religious 

ceremonies, for caulking boats, and for medicinal purposes. 

Although Dacryodes excelsa is considered the dominant tree 

species within the type, Sloanea berteroana is sometimes 

more abundant in smaller sizes (Basnet 1992b, Lugo and 

Wadsworth 1990). Manilkara bidentata, another stand 

dominant, is one of Puerto Rico’s most attractive commercial 

timbers (Little and Wadsworth 1964). The wood is strong, 

hard, and heavy, and was used for construction locally and 

for furniture and cabinets elsewhere. Two other species, 

Buchenavia tetraphylla and Guarea guidonia, both valued 

as furniture woods, are among the fastest growing in d.b.h. 

(Crow and Weaver 1977, Longwood 1961).

Within the secondary stands of the Bisley watershed, 

Alchorneopsis portoricensis, Casearia arborea, Dacryodes 

excelsa, Inga laurina, and Manilkara bidentata were more 

frequent on ridges and slopes than in ravines. In contrast, 

Guarea guidonia and Prestoea montana were more abundant 

in ravines (Basnet 1992b) (appendix C). The dominance of 

Dacryodes excelsa on ridges has been attributed to better soil 

drainage, better anchorage among boulders, and root grafting, 

which make the trees more resistant to windthrow (Basnet and 

others 1993). Root grafting in Dacryodes excelsa has been 

known since the early 1960s when abundant, healthy, shaded 

saplings were observed growing in the vicinity of larger trees 

(Wadsworth 2009, see endnotes). Grafted trees were taller 

and had smaller crowns than nongrafted neighbors probably 

because they received additional water or nutrients (Basnet 

and others 1993, Wadsworth 2009, see endnotes).

Pterocarpus officinalis, with its sinuous buttresses, is a 

common swamp species in the neotropics. It grows in Puerto 

Rico’s coastal fresh- and brackish-water swamps, and is also 

found along the Río Mameyes and its tributaries (Francis 

and Lowe 2000, Little and Wadsworth 1964). One site is at 

and above the confluence of the Río Mameyes and the Río 

de la Mina. The site floods frequently, a condition similar to 

the seasonal flooding of coastal lowlands. The occurrence 

of Pterocarpus officinalis at elevations above the coastal 

plain, although rare, has been documented elsewhere in the 

Caribbean (Francis and Lowe 2000). Probably coincidental, 

this species, whose buttresses were fashioned into plates for 

panning gold, is only 400 m from the nearest abandoned gold 

mine along the Río de La Mina (Cardona 1984, Weaver 1994).

In the past, Buchenavia tetraphylla, a deciduous species, 

was prevalent in lowland forests surrounding the Luquillo 

Mountains (Gill 1931). Other prominent or common LEF tree 

species found today in lowland forest remnants or abandoned 

pastures and recorded in the gradient sampling include 

Andira inermis, Brysonima spicata, Cecropia schreberiana, 

Dacryodes excelsa, Guarea guidonia, Inga laurina, I. vera, 

Manilkara bidentata, Miconia prasina, Ocotea leucoxylon, 

Schefflera morototoni, Tabebuia heterophylla, Tetragastris 

balsamifera, Trichilia pallida, and Vitex divaricata (Aide 

and others 1996, Gould and others 2006, Wadsworth 1950) 

(appendix C).

Past human activity—Past human involvement in the 

lower montane forest was extensive and has affected the 

structure and composition of the forest to varying degrees. 

Timber extraction occurred along the forest border and in 

river valleys and lower slopes where 42 tree species were 

considered satisfactory for harvest: 7 for furniture, 16 for 

Lower montane rain forest. Dacryodes excelsa (tabonuco tree) is 

the dominant species that grows at elevations <600 m within the 

Luquillo Mountains. Tabonuco favors ridge topography where it 

sometimes exceeds 30 m in height and 1 m in diameter. (Photo by 

Gerald P. Bauer) 
51

Tree Distributions and Major Forest Types

construction, and 19 for large posts (table 5). From the mid1930s to the mid-1940s, about 3500 ha of open land reforested 

naturally, including areas with planting trials (Wadsworth 

1970). In the mid-1990s, researchers studied secondary forest 

stands growing on the lower, northern slopes of the Luquillo 

Mountains (Aide and others 1996). After 40 years of recovery, 

these stands could not be distinguished from undisturbed sites 

in terms of density, basal area, species numbers, or diversity; 

however, centuries would be required before the species 

compositions were similar. Moreover, abandoned pastures 

ranging from about 50 to 80 years old had tree species distinct 

from those on old growth forest sites > 80 years old, again 

suggesting that considerable time would be required for the 

species compositions to converge (Aide and others 2000). On 

another site harvested for timber around 1900 and abandoned 

in the 1930s, the basal area and litterfall rates 50 years later 

were similar to undisturbed lower montane forest in the 

vicinity; the dominant species, however, were successional 

(Zou and others 1995). It appears that secondary forests 

recovering after disturbance on the lower slopes of the LEF 

will carry the signature of past land use for centuries, at least 

with regard to species composition.

Gradient sampling—Gradient sampling within lower 

montane forest was carried out in the Río Mameyes and Río 

Espírtu Santo watersheds. The 18-plot sample disclosed 69 

trees species, 10 of which accounted for 64 percent of the total 

stems (tables 8 and 9). Prestoea montana, with 20 percent 

of the total, was the most common species and Dacryodes 

excelsa followed with 11 percent. Of the remaining species, 

the 38 least common accounted for only 9 percent of the 

tallied stems.

Of the 10 most frequently encountered species, Cecropia 

schreberiana, Croton peocilanthus, and Prestoea montana

were more common in ravines and Dacryodes excelsa and 

Tetragastris balsamifera on ridges (Weaver 2010a) (table 9). 

Moreover, Manilkara bidentata favored slopes and ridges and 

Sloanea berteroana slightly favored ravines although well 

represented on other topographies. Less common species 

such as Cyrilla racemiflora, Matayba domingensis, and 

Schefflera morototoni also grew mainly on ridges and upper 

slopes whereas Cordia borinquensis was more common on 

slopes and ravines. Sampling also revealed differences in 

species composition by watershed: the Río Mameyes faces 

northeast and is wetter and probably cloudier than the Espíritu 

Santo, which faces northwest (Ewel and Whitmore 1973). 

Species such as Clusia clusioides, Eugenia borinquensis, 

Ocotea spathulata, and Tabebuia rigida, all most abundant in 

dwarf forest (appendix C), survive on scattered sites at midelevations within the Río Mameyes watershed. These sites 

are mainly exposed, upper slopes and ridges similar in some 

respects to the summit areas.

Monitoring long-term plots—Four basically undisturbed 

permanent plots were established on slopes and ridges in 

lower montane forest (Wadsworth 1947, 1949, 1952a, 1952b, 

1953, 1970) (fig. 13) (table 7):

• El Verde III, a lightly thinned 0.72 ha plot, in 1943.

• TR-1 (tabonuco ridge) and TS-3 (tabonuco slope), two 

previously undisturbed 0.40 ha plots, both in 1946.

• TS-2 (tabonuco slope), a 0.40 ha undisturbed plot in 1946 

(abandoned in the 1960s after a service road was routed 

through it).

Research on El Verde III plot provided a 33-year posthurricane history for several indicator species: Dacryodes 

excelsa, Manilkara bidentata, and Sloanea berteroana, 

mature forest canopy species; Cecropia schreberiana

and Schefflera morototoni, both common gap species 

regenerating after disturbance; Prestoea montana, the 

ubiquitous understory palm; and Croton poecilanthus, an 

endemic understory species (Crow 1980). The mature species 

Dacryodes excelsa and Manilkara bidentata along with 

Prestoea montana increased in stem numbers and basal area 

during the measurement period and Sloanea berteroana and 

Croton poecilanthus, after initial increases, later declined. 

Gap species were common in the stand during the 1940s, 

when stem numbers and biomass increased rapidly. Later, they 

also declined. In the 1970s, the stand approached steady-state 

for biomass, and had a lower stem density and fewer species 

than during the 1940s.

A thinning carried out at El Verde in 1937, designed to 

minimize impacts in the watershed, was very light and at most 

“extended the period in which youthful stand characteristics 

persisted” (Crow 1980). Another thinning in the late 1950s 

was also light. Virtually all of the stems removed were ≤16 

cm, many of which would likely have succumbed naturally as 

the stand matured. Consequently, the activity had little impact 

on composition, eliminating only Beilschmiedia pendula

and Micropholis garciniifolia, both uncommon. Because 

no control plots were maintained nearby the effects of these 

thinnings on growth rates were uncertain.

Later work at El Verde III confirmed that changes in species 

and stem numbers varied by successional types (Johnston 

1990). Moreover, Dacryodes excelsa grew best on welldrained sites and Prestoea montana was concentrated on 

poorly drained soils. Species diversity and evenness (i.e., 

as determined by the Shannon-Weiner index and Pielou’s 

evenness index) gradually declined from the mid-1940s 

through 2005 with the exception of a slight increase associated 

with Hurricane Hugo in 1989 (Drew and others 2009).
52

Tree Distributions and Major Forest Types Setting

Post-hurricane observations on the TS-3 plot spanning 

30 years showed typical patterns for long-term recovery. 

Between 1946 and 1976, basal area increased by 5 percent 

and stem numbers decreased by 14 percent (Weaver 1983). 

Secondary species like Alchorneopsis portoricensis, Cecropia 

schreberiana, and Schefflera morototoni all declined 

considerably in stem numbers whereas mature forest species 

like Dacryodes excelsa, Manilkara bidentata, and Sloanea 

berteroana maintained or increased their stem numbers. 

Growth rates in d.b.h. for surviving broadleaf species ranged 

between 0.03 and 0.48 cm yr-1 (Weaver 1983). Clusia rosea,

Croton poecilanthus, Matayba domingensis, and Ormosia 

krugii all grew relatively rapidly, averaging >0.25 cm yr-1 in 

increment during the measurement period.

TR-1, a plot located on a steep, exposed ridge at 350 m in 

the Mameyes watershed, is notable because its composition 

is made up of tree species from all four forest types: Cyrilla 

racemiflora, Magnolia splendens, and Matayba domingensis, 

most common in montane forest but present at higher elevations 

in lower montane forest (Weaver 1983, 1998, 2002b); Henriettea 

squamulosa and Micropholis garciniifolia, more common in 

montane and dwarf forests but also present in lower montane 

forest (Wadsworth 1951); Eugenia borinquensis and Ocotea 

spathulata, abundant in dwarf forest and common in montane 

forest but rare in lower montane forest (Weaver 2010a, 2010b); 

and Prestoea montana, dominant in palm brakes above 450 m 

elevation. The presence tree species normally found at higher 

elevations appears related to the very wet and exposed nature of 

the site, and the magnitude of earlier hurricanes (table 6).

TR-1 plot data, spanning >60 years, provide the best long-term 

record in lower montane forest. Measurements encompasses 

a complete disturbance cycle with the initial tally being 

made 14 years after two major hurricanes and the last tally 

2 years after another pair of major hurricanes. Recovery 

included a prolonged period of calm from 1932 to 1989. Initial 

measurements showed that stem density, species numbers, 

and the rate of biomass accumulation were at a maximum 

15 years after the 1932 hurricane. About 50 years later, most 

of the secondary species associated with past disturbance—

Cecropia schreberiana, Psychotria berteroana, and Schefflera 

morototoni—had decreased or disappeared and the rate of 

biomass accumulation for the stand began to level. Cecropia 

schreberiana again regenerated abundantly after hurricanes 

Hugo and Georges (Weaver 2002b). Other species that 

regenerated well after Hugo included Manilkara bidentata, 

Prestoea montana, Psychotria berteroana, and Sloanea 

berteroana. Growth rates of broadleaf species surviving the 

1946 to 1976 measurement period ranged between 0.01 and 

0.51 cm yr-1 (Weaver 1983). Fast growing species such as 

Buchenavia tetraphylla, Cyrilla racemiflora, and Matayba 

domingensis all averaged >0.25 cm yr-1 in d.b.h. increment 

over the measurement period.

Silvicultural research in natural forest—The first 

silvicultural activities carried out within the lower montane 

forest were exploratory in nature and had a minor impact 

on the species composition and forest structure of relatively 

small areas. The earliest timber stand improvements were 

implemented in 1938 and 1939 on 55 ha and involved 

vine cutting, thinning around desirable saplings of timber 

species, pruning, and limited removal of tree species with no 

commercial value (Wadsworth 1970). These procedures, aimed 

at increasing growth rates of select trees in young secondary 

stands, would be ineffective without repeated thinning.

Additional silvicultural activities were carried out on two 

types of permanent plots in lower montane forest (fig. 13) 

(table 7):

•In 1951, two 0.20 ha cutover lower montane forest plots 

(tabonuco cutover plots or, as called in table 7, TCU plots) 

were set up to determine the effects of thinning.

•In 1957, a pilot management project was located in four 

research areas—Cubuy, Sabana 4, Sabana 8, and Río 

Grande. Each area had at least 100 circular plots measuring 

0.08 ha in size. Thinnings were carried out to increase 

forest productivity by eliminating the poorest species and 

providing ample growing space for select trees (Crow and 

Weaver 1977).

The thinning experiment carried out on the TCU plots 

between 1947 and 1975 showed that basal area increased from 

16 to 33 m2 ha-1, averaging 0.64 m2 ha-1 yr-1. Basal area growth 

on similar unthinned, mature forest plots with typical basal 

areas >35 m2 ranged from 0.06 to 0.25 m2 ha-1 yr-1 over the 

same period (Weaver 1983).

By 1957, improvement cuttings had been carried out on 930 

ha in the pilot management project (Anon. 1958). In addition, 

undesirable trees were frilled and herbicides applied. Trees 

were liberated if they measured ≥10 cm in d.b.h. and their 

crowns were in contact. Liberation provided about 2 m of 

crown freedom between trees. In most instances, openings on 

the forest floor were kept to ≤8 m. Trees scheduled for removal 

included: dying, diseased, or insect infested individuals; 

inferior species (i.e., neither pole nor sawtimber species); 

trees of poor form or with heavily damaged crowns; and all 

remaining trees in excess of desired stand density.

The pilot management project showed that d.b.h. increment on 

liberated timber species in young secondary forest averaged 

nearly 0.40 cm yr-1 over 18 years, or approaching twice the 

average for the same species on undisturbed lower montane 

forest plots (Crow and Weaver 1977). The d.b.h. growth 

rate for six mature forest species—Buchenavia tetraphylla, 

Dacryodes excelsa, Manilkara bidentata, Micropholis 

garciniifolia, M. guyanensis, and Sloanea berteroana—nearly 
53

Tree Distributions and Major Forest Types

doubled whereas six typical secondary species—Byrsonima 

coriaceae, Homalium racemosum, Inga laurina, Chionanthus

domingensis, Matayba domingensis, and Ormosia krugii—

increased by about 50 percent. Four pioneer species—

Alchornea latifolia, Cecropia schreberiana, Schefflera 

morototoni, and Tabebuia heterophylla—only increased by 

an average of 10 percent (Weaver 1983). Unfortunately, the 

results are not clear because growth differences between 

thinned and untreated secondary forest stands were never 

evaluated. Regardless, these studies suggest that a single 

liberation of crop trees in secondary lower montane forest 

fosters relatively rapid d.b.h. increment for a period of 

time. Reduction of density also stimulated the regeneration 

of timber species such as Dacryodes excelsa, Manilkara 

bidentata, Ocotea moschata, and Tetragastris balsamifera.

A recent re-evaluation of 1,425 trees of 12 timber species with 

at least 40 replicates within the pilot study showed that the top 

25 percent, those with the highest productivity, were growing 

at a rate double that of the remainder (Wadsworth and others 

2010). With reduced impact logging leaving many cutover 

forests less disturbed, greater interest is being shown in the 

potential of secondary stands. The presence of fast growing 

trees suggests that these forests could serve as an attractive 

start to a second timber crop.

Mean annual d.b.h. increment (MAI), frequently used by 

foresters to characterize tree growth, is influenced by many 

factors including:

• Tree species—Primary species usually have denser or 

heavier woods (i.e., a greater specific gravity) than either 

secondary or gap species. Denser tree species with greater 

investments in wood production generally grow more slowly 

in d.b.h. than pioneer or secondary species (Grubb 1977, 

Lawton 1984).

• Stand conditions—Tree density and stand basal areas 

increase several years after hurricanes and MAI tends to 

slow considerably due to competition among surviving 

stems (Weaver 1986a, 1989b). Growth studies of thinned vs. 

unthinned stands also show the influence of stand density 

or basal area on d.b.h. growth rates (Crow and Weaver 1977, 

Weaver 1983).

• Site variation (site indices)—Tree species situated on 

favorable sites with regard to elevation, topography, rainfall, 

and soil fertility are likely to grow more rapidly in MAI 

than those on poor sites. An example is the gradually 

diminishing MAI for Micropholis garciniifolia with ascent 

in the LEF. The species is found from lower montane forest 

to the summits, but its best d.b.h. growth is at low elevations 

(Weaver 1983).

• Crown classes—Crown size and canopy position (i.e., 

dominant, codominant, intermediate, and suppressed) 

influence MAI for all species (Baker 1950). Crown 

exposure may be altered by silvicultural treatments or past 

disturbances. Large, well-positioned crowns produce the 

most rapid MAI whereas trees in suppressed conditions 

grow the slowest (Wadsworth 1947).

Montane Forest

The montane forest is characterized by dense stands of polesize trees (fig. 3). Isolated by elevation and inclement climate, 

past human disturbance has been limited to the occasional 

extraction of Magnolia splendens near 600 m elevation, and 

the development of roads, trails, and recreational facilities. For 

nearly a century, montane forest has been the last habitat of 

the Puerto Rican parrot (Rodríguez Vidal 1962). Lacking the 

potential for major timber production, past forestry research 

has been limited mainly to permanent plot monitoring, 

gradient sampling, and one plot for experimental silviculture.

Stand features and notable tree species—The 

canopy of montane forest reaches 15 m in height with about 

two-thirds of the tree diameters ranging between 10 and 

15 cm (Wadsworth 1951). Prestoea montana, Micropholis 

garciniifolia, Henriettea squamulosa, Micropholis guyanensis, 

Croton poecilanthus, Cyrilla racemiflora, Ocotea spathulata, 

Cecropia schreberiana, Tabebuia rigida, and Magnolia 

splendens, as listed, accounted for 83 percent of the stems 

Dense, pole-size stems characterize typical stands of montane rain 

forest, which grows between 600 and 900 m elevation within the 

Luquillo Mountains. This stand in the upper Río Mameyes contains 

a blind where field observations of Amazona vittata (Puerto Rican 

parrot) were carried out for many years. (Photo by Peter L. Weaver) 
54

Tree Distributions and Major Forest Types Setting

recorded on 4 ha of permanent plots during the 1940s 

(Wadsworth 1951). Trees are typically short and crooked, and 

crowns consist of heavy branches that emerge low on the trunk. 

Grasses, sedges, and ferns characteristically grow in openings. 

At least 11 species within the type had timber uses: 1 for 

furniture, 4 for construction, and 6 for large posts (table 5).

Among the most interesting tree species are Cyrilla 

racemiflora and Magnolia splendens, which are both longlived, occasionally >1 m in diameter (Weaver 1986b, 1987a). 

Regeneration of both occurs in openings or after disturbance, 

and is largely absent under closed canopy (Weaver 1992). 

Three other species, Henriettea squamulosa, Micropholis 

garciniifolia, and M. guyanensis may also attain large sizes 

(Wadsworth 1951, Weaver 1983).

Cyrilla racemiflora ranges from eastern Virginia through 

the Caribbean islands to the Amazon River Basin in Brazil 

(Francis and Lowe 2000) (table 1); however, it attains its 

greatest size and longevity in Caribbean forests. Its branches 

and trunks commonly decompose with age creating cavities 

that are occupied by forest fauna. During the 20th century, the 

last surviving population of Puerto Rican parrots depended 

heavily on branch cavities in Cyrilla racemiflora for nesting 

sites (Rodríguez-Vidal 1959, 1962; Snyder and others 1987; 

Wunderle and others 2003).

Cyrilla racemiflora shows several adaptations to the 

persistently wet, montane environment. After Hurricane 

Hugo, Cyrilla racemiflora seedlings regenerated on 

overturned root masses (Weaver 1994) and the exposed 

subsoils of landslides (appendix D). Also, Cyrilla racemiflora 

saplings sometimes grow at an angle to exploit small openings 

in the canopy (Snyder and others 1987). On occasion, aerial 

roots grow out of the lower trunk into crotches of the same 

tree, probably helping to absorb water and nutrients (see 

left: Cyrilla racemiflora (palo colorado), often with hollow branches and trunks, is the major nesting tree of Amazona vittata (Puerto Rican 

parrot) in the Luquillo Experimental Forest. The largest known trees form by the coalescence of proximate stems right: Cyrilla racemiflora, 

measuring 2.6 m in d.b.h. Within montane forest, the species may attain ages approaching a millennium. (Photos by Peter L. Weaver)
55

Tree Distributions and Major Forest Types

footnote 1). Finally, uprooted Cyrilla racemiflora trees in both 

the montane and dwarf forests sprout along the fallen trunks. 

The sprouts ultimately develop roots and grow into the canopy 

where they preserve the original tree’s genetic material for 

another generation.

Concern regarding Puerto Rico’s flora led to a preliminary 

classification of plants considered to be rare and possibly 

endangered, including Magnolia splendens (Little and 

Woodbury 1976, Woodbury and others 1975). Magnolia 

splendens, popular as a cabinet wood, was logged in the forest 

until the early 1950s (Weaver 1987b). By the early 1970s, many 

accessible mature specimens of magnolia had already been 

removed from the lower montane forest and a few bordering 

areas of montane forest, thus reducing seed sources. Moreover, 

gradual closing of the forest after the 1928 to 1932 hurricanes 

had eliminated most gaps required for magnolia’s regeneration 

(Weaver 1991, 1992). An early 1980s survey of montane forest 

disclosed several species considered to be rare, including the 

endemics Ardisia luquillensis and Ilex sintenisii, and sensitive 

species such as Marlierea sintenisii, Maytenus elongata (Urban) 

Britton, Ternstroemia heptasephala Krug & Urban,

T. luquillensis, and Xylosma schwaneckeanum (Weaver 1989c).

“Crown shyness,” which manifests itself as channel-like gaps 

between the crowns of adjacent canopy trees, was observed 

in 1981 within groups of Henriettea squamulosa in an area of 

persistent winds on the east-facing slopes of El Yunque (see 

footnote 1). Similar gaps elsewhere have been attributed to 

high winds that result in the abrasion and death of the sensitive 

growing tips of twigs (Walker and Whiteaker 1988).

Gradient sampling—Gradient sampling of montane forest 

was carried out in the upper Río Mameyes and upper Río 

Blanco watersheds, and to the windward and leeward of the 

ridge running from El Yunque to El Toro peaks. The 69-plot 

sample disclosed 65 tree species, 10 of which accounted for 

71 percent of the total stems (tables 8 and 10). Prestoea 

montana with 17 percent of the stems and Henriettea 

squamulosa with 14 percent were the most common species.

Of the 10 most common species, Prestoea montana and 

Croton poecilanthus are more abundant in ravines, and 

Cyrilla racemiflora, Haenianthus salicifolius, Micropholis 

garciniifolia, M. guyanensis, Ocotea spathulata, and 

Tabebuia rigida favor ridges; in comparison, Henriettea 

squamulosa and Cordia borinquensis area better distributed 

topographically (table 10). Understory species such as 

Daphnopsis philippiana and Garcinia portoricensis were 

more common on ridges and upper slopes, and Ditta 

myriocoides on slopes and in ravines (table 10).

An ordination revealed that tree species sort by elevation 

and topography (Weaver 1991). Species commonly found 

in ravines were Citharexylum caudatum at high elevations 

and Sapium laurocerasus at lower elevations. Cecropia 

schreberiana, Croton poecilanthus, and Prestoea montana

also favored ravines but were well-distributed within the 

forest. In comparison, species that favored ridges were: 

Calyptranthes krugii, Clusia clusioides, and Ocotea 

spathulata at high elevations; Byrsonima wadsworthii, Cyrilla 

racemiflora, and Haenianthus salicifolius at midelevations; 

and Dacryodes excelsa, Micropholis guyanensis, and Matayba 

domingensis at lower elevations. Cordia borinquensis and 

Henriettea squamulosa were well distributed with regard to 

topography.

An evaluation of the influence of environmental gradients 

on forest structure showed that tree height decreased with 

elevation on both windward and leeward exposures in the LEF 

(Weaver 2000a). Also, aboveground woody biomass decreased 

significantly with elevation on ridges to the windward and soil 

organic matter with elevation to the leeward. Tree density was 

greatest on ridges and least in ravines. Species-area curves 

showed that the greatest number of species was found on 

ridges and slopes, and the fewest in ravines (Weaver 2000a).

Monitoring of long-term plots—The first observations of 

d.b.h. growth carried out on seven 0.4 ha plots between 1946 

and 1951 showed that mean growth rates in closed stands 

were slow with considerable differences evident among tree 

species and crown classes (Anon. 1957; Wadsworth 1951, 

1952b). Subsequently the plots, located on slopes and in 

valleys, were not revisited until the mid-1970s and early 1980s 

when observations of longer duration were summarized. 

Long-term observations from 1946 to 1981 showed that the 

plots had experienced changes in species composition, forest 

structure, and growth during the post-hurricane recovery 

period (Weaver 1986a, 1989b) (fig. 13) (table 6). Diameters 

and heights on surviving trees increased during the 35-year 

measurement period; moreover, the number of trees in the 

suppressed crown class increased in response to gradual 

canopy closure. One notable observation regarding structure 

was that the mean specific gravity for broadleaf species within 

the montane forest increased by nearly 4 percent (table 6). The 

change in specific gravity reflects the gradual disappearance 

of short-lived secondary trees characterized by low specific 

gravities and the gradual dominance of longer-lived, mature 

forest species with denser woods.

During the 35-year period of observation, small secondary 

species like Hedyosmum arborescens and Psychotria 

berteroana virtually disappeared from the plots (Weaver 

1986a, 1989b). Larger secondary species, Cecropia 

schreberiana, Schefflera morototoni, and Miconia laevigata

also declined considerably in stem numbers although their 

basal areas remained about the same because of continued 

growth on residual stems. Cyrilla racemiflora remained 
56

Tree Distributions and Major Forest Types Setting

constant in stem numbers but declined in basal area due to 

the loss of large trees. Cordia borinquensis, a mature forest 

understory tree, increased in both numbers and basal area. 

Prestoea montana remained relatively constant in stem 

numbers and basal area. Finally, mature forest dominants 

like Micropholis garciniifolia and M. guyanensis increased in 

stem numbers and basal areas to varying degrees. Secondary 

species continue to regenerate in forest gaps many years 

after hurricane passage but in reduced numbers. The gradual 

decline of secondary species combined with the gradual 

dominance of mature forest species are trends associated with 

post-hurricane recovery.

Species richness showed a couple of trends on the seven plots 

during the 35-year recovery period (Weaver 1986a, 1989b). 

First, the total number of species on all plots combined declined 

from 88 in 1946 to 83 in 1981. Valley plots near the transition 

to lower montane forest had the greatest numbers of species. 

Second, species numbers per plot in 1946 varied widely, 

ranging between 33 and 58. By 1981, they had converged, 

ranging from 36 to 49. Species richness on a plot basis appears 

to be greatest and most variable a few years after hurricane 

disturbance with the simultaneous occurrence of secondary and 

mature forest species. With post-hurricane recovery, species 

richness declines. It is also evident that any single plot selected 

to represent species richness within the forest could be seriously 

biased by its location and sampling date.

Mean d.b.h. growth for all stems, regardless of species, 

significantly declined from 0.14 cm yr-1 between 1946 and 

1951 to 0.09 cm yr-1 between 1976 and 1981 (Weaver 1986a, 

1989b). Differences in d.b.h. growth were readily apparent 

by crown classes, with dominant and codominant trees 

growing at significantly more rapid rates. D.b.h. increment 

on montane forest slope and ravine plots both averaged about 

0.09 cm yr-1, with individual broadleaf species varying 

considerably (Weaver 1983). The only species that averaged 

>0.20 cm yr-1 during the measurement period were Clusia 

clusioides, Miconia laevigata, and Ternstroemia luquillensis. 

The mean net increase in aboveground woody biomass during 

the 1946 to 1981 measurement period averaged 0.67 t ha-1 yr-1, 

and woody volume increased by 1.06 m3 ha-1 yr-1. The decline 

in d.b.h. growth reflects a gradual increase in competition 

among surviving stems in a post-hurricane environment.

Silvicultural activities—An experimental 50 percent basal 

area reduction was carried out on a 0.4 ha plot called CCU 

within montane forest during the mid-1940s to determine the 

effect on residual stems (table 7). The thinning yielded no 

noticeable differences in d.b.h. increment after 10 years and 

the study was closed (Anon. 1957). Another visit to the plot 

33 years later showed that the stand had experienced a massive 

influx of Clusia clusioides, Cyrilla racemiflora, and Miconia 

tetrandra (Weaver 2001). Moreover, Micropholis garciniifolia

and Tabebuia rigida also showed gains in stem numbers. 

Thinning had not stimulated an increase in the d.b.h. growth 

rate of the residual stems. Instead, new stems colonized the 

available space within the slow-growing stand.

Silvicultural experience with pines also merits mention. About 

1960, a few seedlings of Mexican pines (species uncertain) 

were planted on an exposed ridge at 750 m near the PR 930 

gate. The trees grew to about 3 or 4 m in height, remained 

stunted for years, and then perished in the early 1990s 

(see footnote 1). Also, Pinus caribaea planted on the large 

landslide at km 21 on PR route 191 during the early 1980s 

have survived, grown, and regenerated. The landslide, located 

at 600 m elevation, is at the transition between montane and 

lower montane forest.

Palm Brake

Palm brake, dominated by Prestoea montana, is relatively 

simple in species composition and has been less studied than 

other forest types in the LEF (fig. 3). Major research has 

included permanent plot monitoring, gradient sampling, and 

ecological studies on a riparian site in the upper Espíritu Santo 

watershed. Palm fruits are a staple in the diet of the Puerto 

Rican parrot (Snyder and others 1987).

Stand features and notable tree species—Palm 

brakes may reach 15 m in canopy height and grow mainly 

in ravines, and on steep, east-facing slopes above 450 m in 

elevation (Wadsworth 1951). Broadleaf species from either 

the lower montane or montane forest are present in palm 

brake, depending on elevation, but typically palms with a 

d.b.h. between 15 and 20 cm dominate the stands. The ground 

sometimes contains a sparse herbaceous layer and, in the case 

of ravines or drainages, it is covered with rocks.

Prestoea montana is ubiquitous in the LEF above 350 m, 

reproducing in forest gaps, on landslides, in openings, and 

under shade. An autecological study of the palm showed that it 

grew slowly, survived for long periods, adapted well to shade, 

and had a high moisture requirement, all suggesting that the 

species was adapted to closed forest (Bannister 1970). Palms 

appear to survive hurricanes well (Weaver 1983). Indeed, one 

immediate impression of post-Hurricane Hugo damage along 

FS-27 was the abundance of palms on slopes above 700 m 

(see footnote 1). This was due in part to its capacity to survive 

hurricanes by shedding leaves and resprouting, and in part to 

storm-caused defoliation and crown damage to surrounding 

broadleaf species.

Palm brake was previously considered as a sub-climax 

community on steep soils subject to landslips or soil 

movement (Beard 1949). The abundance of narrow-crowned 
57

Tree Distributions and Major Forest Types

palms and lower basal areas allow more light to reach the 

understory. When viewing palm brakes from a distance, 

two species are readily detectable in the canopy: Prestoea 

montana because of their dominance, and scattered Cecropia 

schreberiana due to their large leaves with light colored 

undersurfaces. Psychotria berteroana is common in the 

understory. All three regenerate in openings or gaps

Gradient sampling—Palm brakes are frequently situated 

on terrain with little local relief. Slight increases in topography, 

however, occur and support proportionately more broadleaf 

species. The 12-plot palm brake sample, located on steep slopes 

to the windward and leeward of Mt. Britton, showed that 10 

species accounted for 91 percent of the total stems (tables 8 

and 11). Prestoea montana was the most common species with 

57 percent of the stems and Cecropia schreberiana followed 

with 12 percent. Croton poecilanthus was most common in 

ravines and slopes. Eugenia borinquensis and Tabebuia rigida, 

both abundant at higher elevations in dwarf forest, appeared 

to favor ridges along with Psychotria berteroana. Cecropia 

schreberiana, Cordia borinquensis, Henriettea squamulosa, 

and Prestoea montana were fairly well distributed, with the 

broadleaf species more common on ridges and slopes and the 

palm on ravines and slopes.

Monitoring of long-term plots—In 1947 and 1975, 

Prestoea montana accounted for 54 to 63 percent of the 

stems and basal area on permanent palm plot PS-2 (Weaver 

1983) (table 7). In comparison, palms ranged between 6 and 

23 percent of the stems and basal area on four typical lower 

montane and montane forest permanent plots (Weaver 1983). 

Typical basal areas on palm plots average less than on lower 

montane and montane forests plots, where the occasional 

occurrence of large broadleaf trees tends to inflate basal area 

estimates.

Long-term d.b.h. increment for broadleaf trees on palm plots 

averaged double the rates on either lower montane or montane 

forest plots (Weaver 1983). The more rapid d.b.h. growth is 

probably due to lower stem densities, lower basal areas, and 

more open canopies that characterize palm brakes (Weaver 

1983). Many of the broadleaf tree species encountered within 

plot PS-2, such as Alchornea latifolia, Cecropia schreberiana, 

Cordia sulcata, Croton poecilanthus, Henriettea squamulosa,

Inga vera, and I. laurina, are capable of regenerating in 

openings (appendix D). Moreover, they all grow at fairly rapid 

rates over long periods under the favorable light conditions 

found in palm brakes. 

On a 0.25 ha of riparian palm brake plot established in 1980, 

Prestoea montana, Croton poecilanthus, and Henriettea 

squamulosa, accounted for 61 percent of the 3,060 stems 

≥2.5 cm in d.b.h. (Frangi and Lugo 1985). The plot, 

surrounded by montane forest, also contained Cyrilla 

racemiflora, Magnolia splendens, Micropholis garciniifolia, 

and M. guyanensis.

Prestoea montana (Sierra palm), common throughout the Luquillo Experimental Forest, is the dominant species within palm brakes. It grows 

on steep slopes and in ravines between 350 m and the mountain summits. (Photo by Peter L. Weaver)
58

Tree Distributions and Major Forest Types Setting

Dwarf Forest 

In most of the neotropics, ascent to dwarf forest is difficult 

because no roads and few trails exist. The earliest expeditions 

to the Luquillo Mountain summits were done by hiking or 

horseback. After the completion of PR route 191 through the 

forest, El Yunque peak was first made accessible by dirt road 

in 1938, and both Pico del Este and Pico del Oeste by paved 

road nearly 25 years later (figs. 3 and 5) (table 3) (appendix A). 

The roads presented unparalleled opportunities for studies at 

three major sites. Research on El Yunque dealt with climate 

and on Pico de Este with forest recovery after disturbance, 

cloud moisture interception, and permanent plot monitoring. 

Studies on Pico del Oeste were part of a multi-faceted project 

aimed at exploring the phenomenon of dwarf forest.

Dwarf forest, limited in extent, is a critical resource for Puerto 

Rico. It accounts for about one-sixth of the LEF’s pristine 

forest and protects the highest slopes and summits from 

erosion (Murphy 1916). The forest also serves as habitat for 

20 endemic tree species, 15 restricted to the island and five 

to the LEF (Weaver 2008). The summits offer panoramic 

views and runoff provides critical water supplies to growing 

island populations. In many areas of Middle America and the 

Caribbean, cloud forests are being cut for new agricultural 

lands, highlighting the need for their protection (LaBastille 

and Pool 1978, Stadtmuller 1986).

Stand features and notable tree species—Dwarf 

forest is characterized by a single story of trees that commonly 

range from 1 to 6 m or more in height, depending on exposure 

(Wadsworth 1951). The trees are branchy and trunks are 

seldom straight. The upper canopy is uniform in height, and 

leaves are generally small, thick, and concentrated at the ends 

of branches. Mosses, liverworts, and epiphylls are abundant, 

and cover branches, trunks, and leaves. “Nearly every species 

of flowering plant of the forest is found as an epiphyte” 

(Howard 1968, page 394). Roots are generally superficial, 

aerial roots are common, and grasses, sedges, and ferns 

grow in openings. Several genera (e.g., Podocarpus, Ocotea, 

Magnolia, and Ilex), the dominance of relatively few species, 

and the abundance of mosses are similar to temperate rain 

forest habitats (Dansereau 1966). Although no tree species 

is confined to this type, only a few are adapted to survive 

on the exposed summits (Nevling 1971, Wadsworth 1949). 

Earlier observations in the vicinity of El Yunque showed that 

Weinmannia pinnata L. along with Eugenia borinquensis,

Ocotea spathulata, and Tabebuia rigida composed 75 percent 

of the dominant trees in dwarf forest (Gleason and Cook 

1927). On Pico del Oeste, Ocotea spathulata and Tabebuia 

rigida made up 70 percent of the canopy (Howard 1968). 

El Yunque Rock, El Yunque peak, Los Picachos, Pico del 

Oeste, the area surrounding the radar dome on Pico del Este, 

El Toro peak, and the steep east-facing slopes below Mt. 

Dwarf forest. Short, gnarled, epiphyte laden trees composed of 

a few species, many of them endemic to the forest, grow above 

900 m in elevation in the Luquillo Experimental Forest. On rocky 

summits, trees may be limited to 2 or 3 m in height. (Photo by Peter 

L. Weaver)
59

Tree Distributions and Major Forest Types

Britton, where trees are 1 to 3 m in height, are among the most 

accessible examples of stunted, windswept vegetation in the 

LEF (fig. 9).

The high stem density in some areas was attributed to fallen 

trees from which lateral branches or adventitious shoots 

subsequently developed (Howard 1969). Soils on the summit 

are saturated and contain about 50 percent organic matter; 

moreover, tree stems are covered with organic matter and 

blanketed with epiphytes (Lyford 1969). Aerial roots, recorded 

for 22 species of trees and shrubs, probably help stabilize plants 

in an environment where the combined weight of epiphytes, 

water, and eroding soils could topple them (Gill 1969). They 

also shorten the distance that nutrients have to travel.

Dwarf forest is characterized by low tree species richness, 

high stem density, low canopy height, small tree diameter, 

low leaf area index, low specific leaf area, and low amounts 

of aboveground biomass compared to lower forest types 

(table 8). Moreover, dwarf forest dynamics are slow, 

including: tree growth rates (d.b.h., height, and biomass 

accumulation); rates of litterfall, herbivory, and litter 

turnover; aboveground net primary productivity; and 

nutrient recycling. Thick dwarf leaves and dense woods 

represent considerable biological investments that come 

at the expense of growth (Grubb 1977, Lawton 1984). 

Moreover, slow growth on the summits assures that posthurricane biomass recovery would take considerable time 

(Weaver 2008). In summary, “Saturated soils, impeded root 

respiration, high winds, high soil leaching, low nutrient 

availability, low temperatures, high fog incidence, reduced 

solar insolation, high humidity, and reduced transpiration 

have all been suggested as causal agents in stunting, either 

individually or in combination” (Weaver 1995). This 

impoverishment of forests on small, wet, isolated, tropical 

mountains has been attributed to the Massenerhebung 

effect, or the interaction of cool temperatures, frequent fog, 

and heavy precipitation that serves to retard mineralization 

of organic matter (Grubb 1971). The combined effects of 

these environmental conditions may effectively lower the 

elevational level at which a forest composed of shorter trees, 

mainly controlled by temperature, would normally occur.

Numerous visits to and surveys of dwarf forest over a period 

of 43 years have provided a few interesting observations:

• Standing dead trees—Surveys in 1968 showed that 10 

percent of standing stems with a measureable d.b.h. ≥2.5 cm 

near Pico del Este were dead, a phenomenon possibly 

associated with dense post-hurricane regeneration 35 years 

earlier (Weaver 1972).

• Aerial roots—After a rare loss of their trunks, Clusia 

clusioides and Tabebuia rigida may be supported solely by 

aerial roots (Weaver 1994).

• Protected dwarf forest—Surrounding topography may 

protect isolated patches of large trees in dwarf forest from 

recurrent hurricane damage (Weaver 2008). One example 

was a Magnolia splendens with a d.b.h. of 78 cm and four 

large Eugenia borinquensis growing in an east-facing 

El Yunque ravine at 985 m.

• Sedges and grasses—Sedges have survived for about 

50 years along portions of the abandoned 5 km Pico del Este 

trail between the PR route 930 gate and the Pico del Este 

radar domes (see footnote 1). Their presence reflects soil 

compaction by past hikers about 50 years ago.

• Cans, sheds, and decomposition—Two #10 cans used 

to sample throughfall near Pico del Este in the late 1960s 

(Weaver 1972) were deliberately left on an exposed ridge 

near Pico del Este. Their decomposition was nearly complete 

after 35 years. Also, a wooden shed used as a shelter on Pico 

del Oeste in the mid-1960s (Howard 1968) had decomposed 

into a mound of debris by the mid-1980s.

Gradient sampling—Gradient sampling within dwarf forest 

was carried out near El Yunque, Pico del Este, and Pico del 

Oeste. The 33-plot sample showed that four species accounted 

for nearly 70 percent and 10 species for >93 percent of the 

total stems (tables 8 and 12). Cyathea bryophila, Eugenia

borinquensis, Ocotea spathulata, and Tabebuia rigida were 

not only the most abundant species, but also those that 

appeared to favor windward rather than leeward exposures at 

high elevations (Weaver 2010b).

Stratified sampling by topography throughout dwarf forest 

showed that Cyathea bryophila and Prestoea montana were most 

common in ravines and on lower slopes whereas Calyptranthes 

krugii, Eugenia borinquensis, Micropholis garciniifolia, and 

Ocotea spathulata had the majority of their occurrences on 

slopes and ridges (table 12). Clusia clusioides and Henriettea

squamulosa had more equitable distributions by topography. 

Previous stratified sampling of dwarf forest by topography near 

Pico del Este showed similar results (Weaver 1999).

Monitoring of long-term plots—Because dwarf forest 

was not considered a potential source of timber, no permanent 

plots were established in the 1940s and 1950s when other 

forest types were first investigated. Subsequently, two types 

of long-term monitoring plots were established in dwarf 

forest near Pico del Este. The first study was set up to observe 

forest recovery after a 1968 airplane wreck and the second to 

monitor growth after Hurricane Hugo of 1989.

The airplane wreck near Pico del Este created a swath 

about 20 x 60 m (Byer and Weaver 1977). The crash site 

provided a rare opportunity to study forest recovery with 

conditions similar to slash and burn agriculture on lowland 

sites. Monitoring, once per decade, showed that the recovery 

process passed through several stages:
60

Tree Distributions and Major Forest Types Setting

• After 4 or 5 years, grass, ferns, and fern allies dominated 

the site, and woody seedlings were scarce (Byer and Weaver 

1977).

• After 19 years, ferns and broadleaf species dominated with 

nearly the same biomass. Of 20 broadleaf species tallied, 

three were dominant—Eugenia borinquensis, Henriettea 

squamulosa, and Wallenia sp. (Weaver 1990). Cyathea 

bryophila was the abundant fern. At this time, about 90 

percent of the broadleaf trees were endemics (Weaver 

2000b).

• After 30 years, only 31 trees of five species were ≥4 m tall 

(Weaver 2000b). Biomass on the sample plot averaged only a 

third of that found in surrounding mature dwarf forest.

• After 37 years, the largest broadleaf trees were Clusia 

clusioides, Micropholis garciniifolia, and Tabebuia rigida 

(Weaver 2008). Recovery on the wreck site remained patchy, 

with small areas of grasses and ferns still evident. Time for 

complete biomass recovery was estimated at two centuries.

In 1990, after Hurricane Hugo, six small plots were 

established at two sites near Pico del Este and subsequently 

measured at 5-year intervals (table 7). Post-hurricane 

monitoring indicated that about 10 percent of the biomass 

was lost during the storm event and delayed mortality 

(i.e., subsequent mortality of impacted trees that initially 

survived the storm) continued for many years. Tree growth 

and recovery from disturbance in the dwarf forest is slow; 

moreover, endemic tree species are important in the forest, 

notably during recovery (Weaver 2000b). The alpine meadows 

occasionally seen near the summits (Odum and Pigeon 1970) 

may be caused by landslides or major hurricane disturbance, 

which uproot trees and expose the subsoil. Subsequently, grass 

and ferns invade and once established may persist for decades.
61

Environmental Gradients in the Luquillo Mountains

Early botanists in the Caribbean observed that changes in 

forest composition and structure correlated with environmental 

factors such as elevation, aspect, topography, and exposure 

(Beard 1944, 1949; Shreve 1914). Shreve, working in Jamaica, 

justified sampling by topographic features stating that “slope 

forests far exceed the other types, but their characteristics and 

vegetation are intermediate between those of the ravines and 

the ridges, and they do not possess the interest of either of the 

latter habitats” (Shreve 1914). Similarly, numerous visits to 

the mountainous Lesser Antilles revealed that lower montane 

forest grew to higher elevations on leeward aspects than to the 

windward (Beard 1949).

The earliest researchers studying the Luquillo Mountain 

summits noted that dwarf forest was exposed to “four 

environmental conditions which may be of considerable 

importance in determining the peculiar vegetation of the 

mossy forest, low temperature, great wind exposure, a watersoaked soil, and an atmosphere of high humidity, frequent 

fog and mist, and heavy precipitation” (Gleason and Cook 

1926). Some considered the dwarf forest in Puerto Rico to 

be an impoverished “subdivision of the colorado type,” (i.e., 

montane forest) (Wadsworth 1951). By the same measure, 

palm brake could be considered an impoverished version of 

the lower montane or montane forests. Both the palm brake 

and dwarf forests are characterized by saturated soils and 

contain fewer tree species.

Changes in elevation affect climate and influence forest 

structure, species composition, and stand dynamics 

(Wadsworth 1948, 1951; Weaver 1991, 1999, 2000a; Weaver 

and Murphy 1990) (fig. 11) (table 8). Likewise, structure 

and composition vary by aspect, topography, and exposure 

at any particular elevation within the major forest types 

(Weaver 1999, 2000b, 2010a, 2010b). Topography influences 

soil formation, organic matter concentrations, soil moisture 

content, water movement, and erosion. It also affects the 

occurrence of landslides and tree species colonization after 

disturbance (Basnet 1992a, Guariguata 1990, Simon and 

others 1990). The occurrence and abundance of certain 

species in lower montane forest was attributed to local 

geologic and edaphic factors—depth to bedrock or large rocks 

and soil moisture—as well as recurrent disturbances (Basnet 

1992a, 1993b; Crow and Grigal 1979).

The measured plot parameters—tree height, stem density, 

biomass, and species richness— tallied in gradient sampling 

were highly variable partly due to small plot size and partly to 

the variety of habitats sampled. Some relationships, however, 

were apparent. Mean canopy height decreased with an 

increase in elevation, most rapidly for ridges and least rapidly 

for ravines (fig. 14) (table 8). In comparison, stem density 

for all trees >4cm in d.b.h. increased with elevation (fig. 15) 

(table 8). Ridges and slopes showed parallel trends whereas 

stem density in ravines increased at a slower rate. Noteworthy 

variation in stem density is evident above 900 m, where some 

dwarf forest sites contain thickets of small stems. Mean plot 

biomass on ridges and slopes also decreased with elevation but 

with considerable variation; biomass in ravines, in contrast, 

showed no elevational trends (fig. 16) (table 8). Biomass varies 

considerably between 350 and 650 m in lower montane forest 

and montane forest where a few large trees, often Dacryodes 

excelsa or Cyrilla racemiflora, may inflate plot values. The 

number of species per plot also declined with elevation on 

all topographic positions (fig. 17) (table 8). Again, roughly 

parallel trends were apparent on ridges and slopes, but species 

numbers in ravines declined at a slower rate. The number of 

species per plot also varies considerably, with the greatest 

values found between 600 and 750 m.

Gradient sampling also showed that forest structure varied by 

topography. Canopy heights for the four forest types ranged 

between 4 and 26 m, with the tallest trees on ridges in lower 

montane forest and the shortest on ridges in dwarf forest (table 

8). Plot stem densities for the four forest types varied from 

680 ha-1 in lower montane forest to 4660 ha-1 in dwarf forest. 

Moreover, plot stem densities declined from ridge through 

slopes to ravine topography in all forest types. Aboveground 

plot biomass also showed considerable variation, ranging from 

nearly 60 t ha-1 in palm brake ravines to about 520 t ha-1 on 

montane forest ridges. Mean biomass values within all forest 

types declined from ridge through slope to ravine topography. 

Known specific gravities for 87 LEF tree species ranged from 

0.22 to 0.90 with nearly 75 percent between 0.50 and 0.79 g 

cm-3 (Reyes and others1992) (appendix F). Estimates of mean 

specific gravity by forest types (i.e., weighted by number of 

stems per species) varied from 0.49 to 0.63 for all species 

combined, including palm, and from 0.60 to 0.66 for broadleaf 

species alone (i.e., excluding palm) (table 8). Specific gravity 

for all species combined tended to increase slightly from lower 

montane forest to dwarf forest with the exception of palm 

brake. Palm brakes are dominated by Prestoea montana and 

Cecropia schreberiana, woods that are very light in weight 

(appendix F).

Species’ richness also varied by topography (fig. 18) (table 8). 

In lower montane and montane forests, ridges and slopes 

contain more species than ravines (Scatena and Lugo 1995; 

Weaver 1987a, 2000a). These differences may be partially 

due to greater tree density on ridges, a factor that creates 

Chapter 4. ENVIRONMENTAL GRADIENTS
62

Environmental Gradients in the Luquillo Mountains

numerically larger sample sizes. Ridge topography also has 

better access to light and better drainage, both of which may 

favor the survival of rarer species, which are normally smaller 

in stature (Weaver 1989c). Slightly elevated terrain in palm 

brakes showed greater species’ richness than either straight 

slopes or ravines, again reflecting better drainage (fig. 18). In 

dwarf forest, with fewer species and less relief, topographic 

differences are less pronounced, and species richness is 

limited mainly by climatic conditions and exposure.

Other studies in the LEF showed that tree density, tree taper, 

the amount of branch wood, and soil organic matter all 

increased with elevation whereas canopy height, typical d.b.h. 

range, total timber volumes, aboveground woody biomass, leaf 

biomass, leaf area index, specific leaf area, total number of 

tree species, and total aboveground net primary productivity 

(with the notable exception of palm brake) were greater at 

lower elevations (Wadsworth 1949; Waide and others 1998; 

Weaver 1991, 2000; Weaver and Murphy 1990; White 1963) 

(table 8). Moreover, tree biomass equations derived from field 

measurements in lower montane, montane, and dwarf forests 

differed by vegetation type (Weaver and Gillespie 1992). 

Surveys along the LEF’s elevational gradient also showed a 

decreasing trend in stem respiration due to changes in tree 

species composition, a decrease in the surface area of trees, 

and lower temperatures (Harris and others 2008).

Fauna (i.e., birds, amphibians, and reptiles) also show 

preferential distributions according to elevation, forest type, 

and habitat (Joglar 1998, Raffaele 1983, Rivero 1978). Palm 

litter samples were richer in nutrients than broadleaf forest 

samples, significantly so at high elevations (Richardson 

and others 2005). Litter invertebrate abundance and species 

richness paralleled the nutrient pattern, declining with 

elevation in broadleaf forests but not in palm brakes. These 

latter differences were attributed to forest heterogeneity and 

its contribution to the chemical and physical nature of the 

litter rather than the direct effects of temperature and rainfall. 

Also along the gradient from sea level to Luquillo Mountain 

summits, the number of earthworm species increased with 

greater rainfall and lower temperature (González and others 

2007). Differences in earthworm species richness were 

associated with soil pH and with the root length density (i.e., 

root length divided by soil volume at 30 cm depth). Worm 

biomass, however, was greatest at the lowest and highest 

elevations along the gradient.

Tree Species Ranges in Luquillo Mountains

Tree species in the LEF’s different forest types form a mosaic 

in time and space influenced by their inherent biology, 

their capacity to adapt to landscape variables, competition 

with other vegetation, and their response to disturbances. 

Knowledge of species adaptations and their longevity helps 

explain their occurrence and persistence in the landscape. 

Some abundant species are adapted to a variety of sites in the 

LEF whereas others have much narrower habitat preferences.

Gradient sampling showed that the 10 most common species 

within each forest type accounted for 72 percent of the tallied 

stems in lower montane forest, 64 percent in montane forest, 

91 percent in palm brake, and 93 percent in dwarf forest 

(appendix tables 9A–9D). Of the 105 species tallied throughout 

the LEF, the two most abundant, Prestoea montana and 

Henriettea squamulosa, accounted for nearly 29 percent 

of all stems (appendix C). The 25 most common species, 

each tallied ≥ 90 times, accounted for 90 percent of the total 

sample. Of the less common species, eight were recorded only 

once, and 32 were recorded ≤ 5 times. The greatest elevational 

ranges (i.e., ≥600 m) recorded during sampling were for 

Brysonima wadsworthii, Cecropia schreberiana, Cordia 

borinquensis, Croton poecilanthus, Haenianthus salicifolius, 

Henriettea squamulosa, Magnolia splendens, Micropholis 

garciniifolia, Ocotea leucoxylon, O. spathulata, and Prestoea 

montana (appendix C).

Several mature forest species are largely confined to one or 

two forest types (e.g., Dacryodes excelsa, Manilkara bidentata

and Tetragastris balsamifera in lower montane forest; 

Byrsonima wadsworthii, Matayba domingensis, Micropholis 

guyanensis, and Miconia laevigata in montane forest; Cyathea 

bryophila in dwarf forest; and Eugenia borinquensis, Ocotea 

spathulata, and Tabebuia rigida in dwarf forest and higher 

elevations of montane forest) (appendix C). In contrast, some 

species intermediate in size like Henriettea squamulosa, 

Micropholis garciniifolia, and Prestoea montana have ample 

elevational ranges, growing in the second story at lower 

elevations and reaching the canopy at higher elevation. Also, 

secondary tree species such as Cecropia schreberiana and 

Psychotria berteroana have a cosmopolitan distribution 

occupying openings within mature forests at lower elevations 

but are sparsely represented in dwarf forest.

Some tree species show strong topographic preferences 

such as Dacryodes excelsa on ridges, Cyrilla racemiflora

and Micropholis garciniifolia for ridges and upper slopes, 

and Prestoea montana for ravines and lower slopes. The 

best distributed species, Henriettea squamulosa, grows on 

all topographies in all forest types. Cordia borinquensis, 

Croton poecilanthus, and Psychotria berteroana, found on 

ridges and slopes at lower elevations, were not recorded on 

ridges within dwarf forest. Finally, Didymopanax gleasonii

Britton & Wilson, Podocarpus coriaceae L.C. Rich., and 

Styrax portoricensis Krug & Urban and similar rare species 

are largely confined to higher elevations in montane or dwarf 

forests (Little and Wadsworth 1964, Little and others 1974, 

Weaver 1989c) (appendix C).
63

Environmental Gradients in the Luquillo Mountains

Eight native trees were sampled on plots well outside of their 

normal elevational range within the LEF (appendix C):

• Pterocarpus officinalis, common in coastal freshwater 

wetlands and along the Río Mameyes near Puente Roto, also 

in ravine topography at and above the confluence of the Río 

Mameyes and Río de La Mina.

• Dacryodes excelsa, common in lower montane forest, as 

high as 850 m on ravine topography in the Espíritu Santo 

watershed.

• Sloanea berteroana, common in lower montane forest, 

as high as 890 m on slope topography in the Río Blanco 

watershed.

• Sapium laurocerasus, found in lower montane and montane 

forests, as high as 950 m on ravine topography in the 

Espíritu Santo watershed.

• Clusia clusioides, most common in dwarf and montane 

forests, as low as 450 m on ridge topography in the Río 

Mameyes watershed.

• Tabebuia rigida, abundant in dwarf forest, as low as 450 m 

on slope topography in the Río Mameyes watershed.

• Eugenia borinquensis, abundant in dwarf forest, as low as 

350 m on ridge topography in the Río Mameyes watershed.

• Ocotea spathulata, most common in dwarf and montane 

forests, as low as 350 m on ridge topography in the Río 

Mameyes watershed.

Given that the entire gradient sample covered only 5.77 ha 

(0.05 percent of the LEF), more extensive field observations 

would most likely extend the maximum ranges for virtually 

all of the 105 sampled species (appendix C). Past land use has 

obscured the natural distributions of species in lower montane 

forest, some of which also grew in the coastal lowlands.

Tree Life Cycles and Longevity

Tree regeneration and growth follows several pathways 

depending on plant life cycles and environmental conditions 

(Gómez-Pompa and Vázquez-Yanes 1974). Many years of 

research and monitoring, including observations made after 

disturbances, have provided insights regarding the ecological 

roles and longevity of several tree species. Some species 

Pterocarpus officinalis (Bloodwood tree), with sinuous buttressed roots, grows at 120 m elevation along a small forest stream tributary to the 

Río Mameyes. (Photo by Iván Vicéns) 
64

Environmental Gradients in the Luquillo Mountains

surviving today in lower montane forest were most likely 

more abundant in the lowland forests surrounding the LEF 

before human intervention.

Diameter growth rates of several timber species in the lower 

montane forest vary considerably, being comparatively rapid 

under favorable stand conditions (Crow and Weaver 1977, 

Weaver 1983). Some of these data have been used to explore 

population dynamics in life history studies for different species 

(McCormick 1995). In lower montane forest, Dacryodes 

excelsa, with its narrow crown, may reach >1 m in d.b.h. in 

about 500 years (Weaver 2002b). Buchenavia tetraphylla, 

considered to be a “late secondary” species with a spreading 

crown, favors upper slopes and ridges (Sastre-De Jesús 1979). 

Its growth is relatively rapid and trees may approach 1 m in 

d.b.h. within a couple of centuries. Manilkara bidentata, the 

remaining large species in lower montane forest, is a dense, 

shade tolerant tree that attains >1 m in d.b.h. (Little and 

Wadsworth 1964). Seedlings may persist in the understory with 

little growth for 40 years before they are released by openings 

in the canopy (You 1991). Trees 0.6 m in size were estimated 

to be about 250 years old. It is likely that the largest specimens 

>1 m in size harvested in the past approached 500 years in age 

(Weaver 2002b). Inga vera, common in areas like El Verde 

where shade coffee was previously grown, probably attains 

a d.b.h. of 0.5 m in about 65 years (Muñiz-Meléndez 1978). 

One specimen, however, was recorded at 0.9 m in d.b.h. (Little 

and Wadsworth 1964). Cecropia schreberiana, a secondary 

species, grows to largest size in lower montane forest where it 

reaches 30 cm in 30 years (Brokaw 1998, Doyle 1981, Silander 

1979); however, the largest observed specimens reaching 

80 cm probably survived > 60 years. In contrast, Palicourea 

riparia and Schefflera morototoni are small and medium-size 

gap opportunists, respectively, which regenerate and mature 

quickly in disturbed areas of lower montane forest (Lebrón 

1977, Nieves 1979).

Cyrilla racemiflora, most common in the montane forest, 

grows to about 1 m in d.b.h. in 650 years (Weaver 1986b). 

Magnolia splendens, also most common in montane forest, 

appears to reach at least 65 cm in 500 years (Weaver 1987b). 

Prestoea montana dominates the palm brake. The oldest 

palms at one site located at 550 m elevation were estimated 

at 100 years (Lugo and Rivera Batlle 1987). The oldest 

specimens, however, reach 20 m tall and may persist for about 

180 years (Bannister 1970, Van Valen 1975). Because several 

of these species grow along an elevation gradient that becomes 

climatically more rigorous near the summits, it is likely that 

some of the island’s oldest trees may be specimens of Cyrilla

racemiflora or Magnolia splendens growing at high elevations 

within montane or dwarf forest (Weaver 1986b, 1987a). The 

largest specimens of most other tree species in the LEF 

probably do not attain ages more than a century or two, with 

many being comparatively ephemeral within the stands. Life 

history and silvicultural information has been summarized 

for native and exotic trees growing in Puerto Rico, including 

20 species native to the lower forests of the LEF (Francis and 

Lowe 2000).

Most trees growing in dwarf forest are small in stature (table 

8). Of the 10 most common species, Micropholis garciniifolia

and Tabebuia rigida sometimes attain larger sizes (table 

12). D.b.h. growth rates for all tree species combined on a 

small plot in closed dwarf forest near Pico del Este averaged 

only 0.03 cm yr-1 (Weaver 1983, 2008). Saplings of Clusia 

clusioides and Tabebuia rigida growing in openings, however, 

may average 0.15 to 0.35 cm yr-1 for a few years until they 

begin to slow because of competition. Topography and 

exposure may also influence growth rates and the final size 

of dwarf forest trees. Estimating ages given these conditions 

would be tenuous.

Attempts to determine the successional status of tree species 

are influenced by the types of observations made (e.g., 

environmental conditions required for regeneration; or stand 

compositions, dynamics, and growth) and their duration (e.g., 

instantaneous vs. monitoring). Other important variables 

include:

• Location (spatial factors)—such as geographic range, 

and occurrence along gradients (e.g., elevation, aspect, 

topographic position, exposure).

• Forest maturity (temporal factors)—such as the status 

of the forest with regard to past disturbance (e.g., posthurricane, early secondary, late secondary, mature, or 

possibly mixed) and its influence on reproduction and 

growth of species.

Past attempts at classifying the successional status of trees 

within the lower montane and montane forests used similar 

but not identical approaches and showed considerable overlap 

(appendix D). Both developed indices that were based on: the 

ratio of understory trees to canopy trees; the ratio of seedlings 

to canopy trees; seed size; and, wood specific gravity. Lower 

montane forest observations were made on 30 species in 

the mid-1960s, about 30 years after the passage of three 

hurricanes (Smith 1970). Observations in montane forest 

were made on 20 species during the early 1980s, about 50 

years after the same hurricanes (Weaver 1992). Both indices 

ranked Cecropia schreberiana as most secondary (appendix 

D); Tetragastris balsamifera was rated most primary in lower 

montane forest and Eugenia borinquensis in montane forest. 

The use of stand features and autecological characteristics 

offered some assurance that the results would be fairly robust.

At El Verde, sampling along gradients from gaps to surrounding 

forest showed that gap centers, gap margins, and forest below 

canopy are distinct environments for the regeneration of 
65

Environmental Gradients in the Luquillo Mountains

tree species (Devoe 1989). Several observations were made 

with regard to seeds and fruits, including: a greater mass and 

number of seeds fall below closed canopy than in the open; 

animal-dispersed seeds are more likely to be deposited below 

the canopy whereas wind-dispersed seeds are more common 

in openings; and heavier seeds or fruits are more likely to fall 

below the canopy. Thus, late successional or mature forest 

tree species seldom reach the center of gaps. Edge conditions 

along gaps are particularly favorable for the establishment 

of commercial timbers by seed (Devoe 1989). In terms of 

silviculture, clear cutting and seed tree methods, both of 

which clear large areas, were not considered appropriate for 

regenerating timber species in the lower montane forest. In 

contrast, shelterwood and selection methods, both of which 

provide shade, were deemed more likely to be successful. 

Native tree species in the lower montane forest were classified 

according to their capacity to regenerate in different light 

conditions, as follows (Devoe 1989):

• High light—Alchornea latifolia, Alchorneopsis floribunda, 

Casearia arborea, Casearia sylvestris, Cecropia 

schreberiana, Dendropanax arboreus (L.) Decne. & 

Planch., Laetia procera (Poepp. & Endl.) Eichl., Schefflera 

morototoni, Tabebuia heterophylla, Trema micrantha, and 

Zanthoxylum martinicense (Lam.) DC.

• Intermediate light—Buchenavia tetraphylla, Byrsonima 

spicata, Calophyllum calaba, Chionanthus domingensis, 

Croton poecilanthus, Guarea guidonia, Guettarda scabra

(L.) Vent., Ormosia krugii, Prestoea montana, Pterocarpus 

officinalis, and Sapium laurocerasus.

• Low light—Dacryodes excelsa, Drypetes glauca, Inga 

laurina, Manilkara bidentata, Ocotea moschata, Nectandra 

turbacensis (HBK) Nees (formerly Ocotea sintenisii (Mez.) 

Alain, Quararibea turbinata, Sloanea berteroana, and 

Tetragastris balsamifera.

In addition to the above specific observations regarding tree 

growth and regeneration, nearly 100 tree species were recorded 

on numerous landslides of different sizes throughout the LEF 

(appendix D). Although individual site conditions vary, all 

slides have disturbed soils, are exposed to overhead light at 

least temporarily, and are situated at relatively short distances 

from the forest edge. In general, these conditions favor the 

regeneration of pioneer or secondary tree species and shrubs.
66

Major Types of Disturbance

The natural vegetation of the LEF has been affected by 

numerous disturbances, including:

• Background mortality such as sporadic treefalls.

• Climatic disturbances, including heavy rainfalls, tropical 

storms, and hurricanes.

• Landslides and erosion associated with climatic events and 

human activities.

• Human disturbances, including timber cutting, charcoal 

harvest, agriculture, grazing, road construction, and mining.

• Forestry activities such as silvicultural operations and 

planting of native and exotic tree species.

• Accidents, notably plane crashes.

Treefalls (Background Mortality)

Recording a treefall, except during a hurricane, is a rare event. 

While monitoring a permanent plot in lower montane forest in 

1976, a Forest Service field crew mounted a tarp for protection 

during a heavy rainfall. Returning the next day, the tarp was 

found pinned to the ground by a 43-cm Sapium laurocerasus

(see footnote 1). Typical background tree mortality such as 

this event form scattered gaps in the forest.

Mortality rates within the LEF may vary by forest type 

(Weaver 1983). The rates (in trees ha-1 yr-1) for trees >4 cm 

between 1946 and 1976 were: Lower montane forest, 24 to 

32; montane forest, 17 to 20; and palm brake, 22. In contrast, 

mortality rates in previously thinned stands of lower montane 

and montane forest were 37 and 16, respectively. Although the 

data are very limited, it appears that mortality rates may be 

slightly greater in lower montane forest than in either montane 

forest or palm brake. The data may also suggest that postthinning mortality rates differ by forest type.

Background tree mortality rates in the LEF are mainly 

influenced by typical species life cycles, competition among 

trees, the minimum diameters recorded, and the frequency 

of plot remeasurement. The above tree mortality data were 

determined during a post-hurricane recovery period spanning 

15 to 45 years using 4 cm as the minimum d.b.h. Recurrent 

surveys conducted during shorter or longer periods, at 

different times in the life of the stands, and with different 

dimensions should yield different results. Current tree 

mortality rates in the LEF are underestimates because a 

30-year remeasurement cycle invariably fails to record 

numerous small stems (i.e., stems that enter the minimum 

d.b.h. class and die before the next measurement). One typical 

example would be the abundant regeneration of Cecropia 

schreberiana immediately after canopy disturbances, most of 

which succumbs within a few years (Weaver 2002b).

Gap analyses are sometimes employed in lieu of actual tree 

mortality data to estimate tree turnover in the short term. 

In lower montane forest, gaps formed at the rate of 0.8 per 

hectare per year; moreover, they varied by topography, being 

the greatest in riparian valleys, intermediate on ridges, and the 

least on slopes and in upland valleys (Scatena and Lugo 1995). 

Estimates of gap formation for most neotropical lowland 

forests were slightly higher, averaging about one gap per 

hectare per year. It was suggested that the lower rate of gap 

formation in the LEF may reflect the periodic loss of weaker 

stems during recurrent hurricanes.

Other factors, however, are at least as important. Tropical 

mainland trees tend to be larger than those in the LEF, 

perhaps up to one-third or more in height. Some also have 

spreading crowns. Before Hurricane Hugo, the canopy in the 

LEF’s lower montane forest was described as smoother and 

with fewer and smaller treefall gaps than were evident on 

Barro Colorado Island in Panama (Brokaw and others 2004). 

Persistent winds and recurrent hurricane impacts within the 

LEF appear to reduce the canopy size of dominant trees. 

Tree species in Dominica’s lower montane forest, notably 

the dominant Dacryodes excelsa, had comparatively small 

crown-to-bole ratios (Bell 1976). Lower montane forest in the 

Caribbean Basin appears adapted to hurricanes with its “littledeveloped emergent story, small crowns, small crown-to-stem 

ratio, many stems, and small photosynthetic surface per stem, 

accompanied by slow stem growth rates, gradual limb loss, 

and in situ decomposition of standing trunks” (Odum 1970, 

page H-3). The gradual mortality of upright stems (Crow 1980, 

Odum 1970) should produce smaller gaps than those found on 

the mainland.

Climatic Disturbances

Hurricanes regularly impact the forests of the Caribbean 

Islands (Tomblin 1981). They vary in frequency, trajectory, 

forward movement, wind velocity, gust speed, duration, 

rainfall, and associated tornados. Hurricanes may impact 

organisms in the landscape by causing changes in forest 

structure, species composition, and diversity; by increasing 

the heterogeneity of landscapes and variability in ecosystem 

processes; by redirecting succession; and, inducing 

evolutionary change through natural selection (Lugo 2008).

Chapter 5. MAJOR TYPES OF DISTURBANCE
67

Major Types of Disturbance

Tree impacts correlate with hurricane trajectory and gust 

speed (Francis and Gillespie 1993). Defoliation and minor 

branch breakage start near 60 km hr-1 and increase rapidly to 

130 km hr-1 after which they do not worsen. The most severe 

damage is avoided if crown surface area is diminished by 

the loss of leaves. Wood strength in the branches and bole 

contributes little resistance to breakage at high wind speeds. 

Palms, without branches and with leaves that trail in the wind, 

defoliate at high gust speeds and prove more wind resistant 

than broadleaf trees.

Hurricane impacts are a function of pre-storm forest 

composition and structure, including tree size, stem density, 

and root characteristics. Various factors within the LEF 

(i.e., topography, elevation, aspect, exposure, soil depth, soil 

moisture content, and past human activities) may also locally 

influence storm impacts. In addition, mortality rates of tree 

species depend on their inherent capacities to withstand major 

storms and to regenerate vegetatively afterwards. In some 

cases, however, purported differences in storm damage may 

actually be attributable to poor field techniques if live trees are 

prematurely recorded as dead.

Hurricane damage and recovery vary over the landscape. 

Hurricane trajectories near and over the Luquillo Mountains 

are frequent enough so that parts of the LEF are always in 

some stage of recovery from past events (fig. 12) (see table 6 

for hurricane details and most citations). Field observations 

made in northeastern Puerto Rico immediately after the 

passage of Hurricane San Felipe showed defoliation, snapping, 

and uprooting, followed a short time later by refoliation, and 

for some tree species, abnormal seed production. Permanent 

plots established in the 1940s, 11 to 18 years after the 

hurricanes, showed an increase in saplings and pole-size trees 

after 15 years, accompanied by an increase in tree species 

richness and mean d.b.h. growth rates. As the forest closed, 

competition among surviving stems caused heavy mortality 

of secondary species. The survivors, mainly mature forest 

species, gradually dominated the stands. In montane forest, 

and probably in the lower montane forest as well, the mean 

specific gravity for the forest increased during 30 years as 

species composition changed. Forest volume and biomass also 

increased, gradually becoming asymptotic as the respective 

forests approached maturity. At any moment, however, the 

cycle could be renewed locally by treefalls, or throughout 

by new hurricanes (Brokaw 1985). In 1956, Santa Clara, a 

marginal hurricane with a trajectory over the center of the 

island, caused minor impacts within the LEF resulting mainly 

in defoliation, localized breakage, and some windthrow.

Hurricane Hugo, with a trajectory just east of the LEF, was 

the first major hurricane to strike the mountains in nearly 

60 years (fig. 12) (table 6). Aspect and topography within 

the mountains sheltered pockets of trees in some places and 

exposed others to high winds. Hurricane impacts included 

defoliation, breakage, uprooting, and loss of standing biomass, 

with some impacts increasing closer to the storm trajectory. 

Large trees were found susceptible to wind whereas smaller 

trees showed no consistent patterns; moreover, buttresses did 

not appear to protect against uprooting. Light reaching the 

forest floor increased immediately after the storm. Uprooting 

created treefall pits of variable size and vast quantities of 

debris and litter were deposited on the soil surface where 

they had variable effects on seed germination. Within a few 

years, canopy spaces created by broken branches were filled. 

Secondary tree species regenerated in gaps along with ferns 

and grasses. Vines also grew rapidly, often climbing dead and 

surviving stems.

In lower montane forest, post-Hugo observations showed 

an early recovery of foliage and tree crowns along with the 

establishment of herbaceous and woody ground vegetation. 

Comparative foliage profiles showed that the percentage of 

leaves at upper levels decreased after the hurricane and the 

percentage at lower levels increased. Pioneer species suffered 

high breakage and mortality and had a low capacity to 

The effects of Hurricane Hugo (September 1989), the first major 

hurricane to affect the Luquillo Mountains in 57 years, was evident 

throughout the Luquillo Experimental Forest. Coca Falls is in the 

background. (Photo by Peter L. Weaver)
68

Major Types of Disturbance

sprout whereas nonpioneers survived better and resprouted. 

Dacryodes excelsa and Prestoea montana, common in lower 

montane forest, appeared best adapted to recurrent storms. 

In contrast, many introduced species planted in ravines were 

severely affected.

Fine roots in the topsoil died a few months after Hurricane 

Hugo and much of the nutrient uptake was retained in the 

aboveground vegetation. Canopy development was followed 

by peak aboveground productivity as early successional 

trees grew into sapling and pole size trees. At this time, the 

Bisley forest had low within stand nutrient-use efficiency 

and the highest levels of productivity observed in the LEF. 

Subsequently, many of the trees impacted by the storm died. 

A summary of 15 years of recovery showed immediate losses 

of biomass, tree numbers, and species richness followed by 

gradual recovery.

Studies of post-Hurricane Hugo seed rain in the center and 

along the edges of two landslides at 370 and 520 m within 

lower montane forest reflected the presence of local flora 

(i.e., long distance dispersal was not required to explain 

observations). Seed rain peaks coincided with periods of 

high seed production and were dominated by shrubs that 

had increased fruit production in the surrounding forest 

understory.

Heavy rainfall in montane forest caused numerous landslides 

and the deposition of fine litter greatly in excess of pre-storm 

inputs (table 6). On a riparian palm forest plot, stem damage 

was common but mortality was low and recovery rapid. Litter 

deposited on the forest floor immediately after the hurricane 

decreased to pre-hurricane levels after 5 years. Also, posthurricane stem density and biomass exceeded pre-hurricane 

values and delayed tree mortality was twice the normal 

background mortality.

In dwarf forest, about one-quarter of the stems that survived 

the hurricane suffered delayed mortality, with individual 

mortality rates varying by species (table 6). Pre- and posthurricane litterfall were nearly equal, except when coarse 

woody debris was included in the post-hurricane tally. Loss 

of epiphytes in dwarf forest changes the pattern of water 

movement from the canopy to the ground. Hurricane Hugo 

stripped dwarf forest epiphytes in varying amounts depending 

on topography and exposure. Although not associated with 

Hugo, the experimental removal of dwarf forest epiphytes 

two decades earlier showed dramatic changes in the amounts 

of throughfall and stemflow during rainfall events (Weaver 

1972). Before removal, epiphytes served to conduct much of 

the impinging rainfall as throughfall; after epiphyte removal, 

stemflow increased considerably. Hurricanes and the manual 

removal of epiphytes cause similar effects, increasing 

stemflow at the expense of throughfall. In addition, epiphyte 

removal increases the amount of light reaching the soil 

surface, a change that favors immediate increases in grasses 

and ferns.

Hurricane Georges, with a trajectory just south of the LEF, 

had less impact than Hugo and received less attention (fig. 12) 

(table 6). Immediate post-Georges observations on permanent 

plot TR-1 in the lower montane forest showed a decline in tree 

species richness; moreover, Dacryodes excelsa accounted for 

a proportionally greater dominance in both residual stems 

and biomass. A post-hurricane island-wide study of sites 

varying in rainfall, elevation, soil type, topography, and aspect 

indicated high soil turnover rates caused by uprooting. Lower 

montane sites at Bisley and El Verde were part of the study. In 

dwarf forest, delayed mortality further reduced stem numbers 

and biomass adding to losses caused directly by Georges. 

Instantaneous litterfall due to Hurricane Georges ranged from 

about one-half to nearly the entire annual rate at six forest sites 

in the LEF. Subsequent decomposition returned litter levels to 

pre-hurricane values in about 1 year.

In addition to major impacts on the vegetation, hurricanes also 

affect wildlife. The direct impacts on bird populations include 

mortality due to wind, rain, storm surges, and geographic 

displacement of individuals (Wiley and Wunderle 1993, 

Wunderle 1995, Wunderle and Arendt 2011). For example, 

Hurricane Hugo reduced the wild population of Amazona 

vittata by one-half. Indirect effects include post-storm loss 

of food supplies or foraging sites, loss of nest or roosting 

sites, increased vulnerability to predators, and microclimatic 

changes. Birds respond in the short-term through shifts in 

diet, foraging sites or habitats, and changes in reproduction. 

Long-term responses may involve greater use of secondary 

vegetation. Post-hurricane recovery of bird populations 

depends on the amount of vegetation damaged as well as 

inherent species’ characteristics like reproductive rates.

Bat populations are also affected by storm damage 

(Gannon and Willig 1994). The population levels of Artibus 

jamaicensis, Monophyllus redmani, and Stenoderma 

rufum, the latter species listed as sensitive by the Forest 

Service, were affected by the hurricane. The first two 

species recovered within 2 years, but the Stenoderma rufum

population only reached 30 percent of pre-hurricane levels 

after 3 years. Moreover, the size of its foraging and home 

range had expanded by five times implying significant 

increases in time and energy to secure food. A change in 

population age structure was also evident. Juveniles were 

absent after the storm indicating a decline in reproduction. 

Post-hurricane conditions also affected Epicrates inornatus

(Puerto Rican boa constrictor), which wandered more after 

the hurricane than before (Wunderle and others 2004). 

Apparently, less branch density and leaf cover limited their 

use of arboreal sites.
69

Major Types of Disturbance

Lost forest cover temporarily increased the amount of rainfall 

reaching the ground. Landslides and debris blocked stream 

channels altering habitats and food webs for aquatic fauna 

(Covich and others 1996, 2006). Other impacts included 

population changes and migrations of aquatic organisms. 

Hurricanes and tropical storms also affect the abundance, 

dispersion, and colonization of insects (Torres 1988, 1992). 

Outbreaks of 15 species of Lepidoptera were reported during 

the spring and early summer after Hurricane Hugo. All of the 

species fed on early successional vegetation, some of which 

represented new host plants within the LEF.

Landslides

More than one-half of the landslides in Puerto Rico are caused 

by intensive rains and winds associated with disturbances 

such as hurricanes, tropical storms, and tropical depressions, 

waves, or troughs; the remainder result from winter cold 

fronts or convective thunderstorms (Larson and TorresSánchez 1992). The area with the greatest number of slides in 

the LEF lies between 600 and 800 m in elevation. Most occur 

during the June through October hurricane season. Their 

detection is not easy because many are small and are rapidly 

colonized by surrounding vegetation.

Highway construction and maintenance are critical factors 

affecting hillslope erosion and landslides. The lateral extent 

of impact caused by road construction is considerable. A 

survey of Puerto Rican roads in humid mountainous terrain 

showed that the rate of mass wasting increased five to eight 

times within a 170 m swath along road corridors as compared 

to more distant areas (Larsen and Parks 1997). Undercutting 

the foot of a slope is the most common construction-related 

activity that results in landslides. In the Río Blanco area, the 

frequency of landslides increased with (Larsen and TorresSánchez 1992):

• Slope angle, with more slides on precipitous slopes than less 

steep ones.

• Elevation, with more slides on high elevation hillslopes than 

on low elevation hillslopes.

• Aspect, with more slides on windward slopes facing the 

prevailing winds than to the leeward.

Landslides in ravines (cove slopes) are more common than 

those on slopes (side slopes) or ridges (nose slopes) (Simon 

and others 1990). Several observations have been made with 

regard to the growth of tree species on slides and unstable 

soils. In general, regeneration is more vigorous in the lower 

part of a slide, where light-demanding, fast-growing pioneer 

species dominate (Guariguata 1990). Prestoea montana is 

associated with saturated soils and grows on slopes disturbed 

by mass wasting (Guariguata 1990). The distribution of other 

species varies with topographic form: Clusia clusioides, 

Cyrilla racemiflora, Micropholis garciniifolia, Micropholis 

guyanensis, and Tabebuia rigida are least common on cove 

slopes. Fern thickets growing on landslides low in nutrients 

appear to facilitate the germination of tree seedlings but later 

may inhibit their growth, notably on the upper portions of 

slides (Guariguata 1990). Cecropia schreberiana seeds sown 

under fern thickets germinated at a higher rate than those 

sown in adjacent open areas (Walker 1994).

Hurricane Hugo caused more than 400 landslides on nearly 60 

percent of the LEF (Larsen and Torres-Sánchez 1992). Slides 

averaged about 150 m2 and ranged between 18 and 4500 m2. 

Estimates show that landslides are eroding the LEF at a rate 

that equals about 1 percent (about 113 ha) per 1,000 years. 

Long-term landslide estimates are tenuous, however, because 

the proportion of a landscape covered by slides may increase 

dramatically in response to prolonged heavy rainfalls or 

hurricanes.

The largest LEF landslide occurred in 1970 at 600 m elevation 

on the south side of the forest at km 21 along PR route 191 

(Guariguata and Larsen 1990; Larsen 1997; U.S. Department 

of Agriculture, Forest Service 1997b). The ~6 ha 

slide was caused by a 5-day storm with an accumulated 

rainfall of 950 mm. In September 1979, Hurricanes David 

and Frederick caused additional erosion on the large slide 

and smaller landslides about 1.5 km to the north on PR route 

191. Subsequently, the road 0.5 km north and south of the 

main slide has been completely covered by numerous minor 

landslides. In some instances, slump (i.e., mass wasting where 

a coherent mass of loosely consolidated materials slide a 

short distance down slope) has deposited mature trees on the 

road surface. Cecropia schreberiana, Prestoea montana, and 

Psychotria berteroana are well represented on the transported 

soil. Large patches of the popular flowering Impatiens sp. are 

also growing in shaded areas on the road surface.

An October 2005 survey of trees on the major slide showed 

>40 species (appendix D), about the same number that was 

detected on all other landslides within the LEF (Guariguata 

1990). The large landslide shared 19 species with the 

remaining LEF slides, including Cyathea arborea, which was 

the most abundant species in a range of sizes. Other common 

species included Alchornea latifolia, Cecropia schreberiana, 

Cyrilla racemiflora, Inga laurina, I. vera, Miconia racemosa, 

Prestoea montana, Psychotria berteroana, and Tabebuia 

heterophylla. Rare species on the site included Coccoloba 

schwartzii, Roystonea borinquena O.F. Cook, and Sloanea 

berteroana, possibly survivors on an isolated clump of soil 

that remained intact during the slide. Fruit trees, such as 

Psidium guajava and Annona sp., were probably introduced 

by visitors. Pinus caribaea was planted about 20 to 25 years 

earlier, and its regeneration is common along the top and 
70

Major Types of Disturbance

southern fringe of the slide. By 2009, most of the major slide 

was covered by secondary regeneration. The steep slopes 

bordering the slide, however, are continuously eroding and 

several deep crevasses dissect it at lower levels. Because the 

slide is large, the substrate unstable, and rainfall both frequent 

and heavy, complete recovery will require considerable time.

Plant responses to nutrients and light on landslides were 

explored to determine if the availability of nitrogen and 

phosphorus limited the growth of pioneer and nonpioneer 

species differently (Fetcher and others 1996). The amount 

of nitrogen appeared to influence the growth of both pioneer 

and nonpioneer species, whereas the amount of phosphorus 

appeared to affect the growth of pioneers. In the absence of 

nutrient additions, neither pioneer nor nonpioneer species 

appeared to be well adapted to colonize parent material 

because their growth was slow.

An attempt was made to predict landslide vegetation after 

disturbance in the LEF (Myster and others 1997). Age, aspect, 

elevation, and substrate were found to be important variables 

influencing vegetation complexity on slides. More advanced 

succession is found on landslides which are older, leeward 

to hurricane winds (i.e., southeast in the case of Hurricane 

Hugo), at lower elevation within the mountains, and on 

volcanoclastic as opposed to dioritic substrates. Biological 

mechanisms, such as dispersal, predation, and competition, 

are variables of less importance. Tree species which colonize 

treefall gaps within the forest are also found on landslides and 

their sequences are determined by decreasing light availability 

(Myster and Walker 1997). Alchornea latifolia, Cecropia 

schreberiana, Solanum torvum, Tabebuia heterophylla, 

and Trema micrantha are the most light-demanding species 

(appendix D); Miconia spp. and Urera baccifera are 

considered to be light demanding; Piper spp. are rated as 

intermediate with regard to light; and finally Inga laurina, 

I. vera, Ocotea leucoxylon, and Prestoea montana grow in 

gaps with low light. It was suggested that the aforementioned 

sequence might represent the order in which tree species 

would replace each other during the recovery process.

The major landslide at km 21 on PR route 191 closed the 

scenic highway on the south slopes making access to the 

forest interior more difficult. Simultaneously it made the forest 

less environmentally fragmented and gave managers greater 

control over forest resources, especially wildlife. Humans built 

the road on unstable terrain where it served visitors for almost 

30 years. Nature, via heavy rains and a major landslide, has 

kept the road closed for >40 years.

Human Activities—Settlement and 

Development

Forests were the dominant vegetation cover in virtually all of 

Puerto Rico when Columbus arrived (Wadsworth 1950). At 

that time, the lower montane forest probably had an average 

timber volume of about 250 m3 ha-1 (Wadsworth 1949, 1950, 

1951). By the middle of the 20th century, however, timber 

harvest, agriculture, and fuelwood cutting had removed or 

disturbed all but 3500 ha in Puerto Rico, 65 percent of which 

was at higher elevations in the LEF (Wadsworth 1950). The 

upper LEF was always forested and experienced very little 

human disturbance. In contrast, much of the lower part 

was subjected to “the familiar routine of logging, clearing, 

burning, grazing, and farming which constitutes shifting 

agriculture” (Marrero 1948).

This major landslide at 600 m elevation (i.e., km 21 along 

PR route 191) occurred after heavy rains in 1970 and permanently 

closed the highway. top: The slide with little vegetation in 1981 

bottom: The same area with denser cover in 2005. Note the 

abundance of the native Cyathea arborea (tree fern) and the 

presence of introduced Pinus caribaea (Caribbean pine). (Photos by 

Peter L. Weaver)
71

Major Types of Disturbance

In 1936, <50 percent of the LEF had continuous canopy cover 

(i.e., areas with >80 percent of the land area under forest 

canopy) (Foster and others 1999). This was about 100 years 

after major human activity began on the lower slopes and 

only 4 to 8 years after the passage of three major hurricanes, 

including one regarded as the island’s legendary storm and 

another that passed directly over the forest. Subsequently, 

forestry operations like timber stand improvement and 

planting of native and exotic timber species were carried out at 

lower elevations (fig. 6) (table 13). By 1989, >97 percent of the 

LEF was under forest canopy.

Many other human disturbances have occurred since the 

period of discovery and settlement (table 13). Initially, the 

cutting of timber and clearing of trails for mining most likely 

had minor impact on the forest. At least 24 mining claims 

were made in the El Yunque quadrangle (Cardona 1984). Five 

of the sites were worked, 10 were not, and the history of the 

remainder is uncertain. Virtually all of the sites were situated 

in lower montane forest.

The construction of PR routes 186 and 191 as well as secondary 

roads led to the direct loss of forest. By the mid-1990s, nearly 

50 ha of the LEF were occupied by roads (Kharecha 1997). 

Moreover, road construction and maintenance—or the 

extension of long corridors through the forest—has an impact 

on adjacent ecosystems (Heyne 2000). These include changes 

in soil and surface water properties, erosion, landslides, 

leaching of nutrients, and the addition of pollutants from road 

deterioration and use. Canopy openings for the roads change the 

local microclimate, increasing levels of radiation, temperature, 

and evapotranspiration and reducing humidity and water 

infiltration. The net effect is to dry nearby soils and to slow 

organic matter decomposition and nutrient release to the soil. 

The roads and associated landslides also provide routes for the 

entrance of secondary and exotic species. The development 

of administrative sites, recreation areas and hiking trails, and 

communication sites, including towers and transmission lines, 

disturbed at least 630 ha (table 13). These sites have similar 

negative impacts on the environment. In addition, they are a 

source of noise, garbage, and contamination of clean waters.

A case study of past land use carried out in the early 1990s 

disclosed some of the less obvious impacts of past human 

activity. The Spanish began land distribution in the 1800s to 

encourage the settlement of the LEF’s lower slopes (GarcíaMontiel and Scatena 1994). Select removal of timber species 

and the cultivation of coffee and subsistence crops followed, 

and in 1934, when the Forest Service acquired Bisley, forestry 

activities were initiated. Among the forest impacts observed at 

Bisley in the early 1990s were:

• Evidence of skid trails used for timber extraction.

• Shifts in the dominance and age structure of canopy trees.

• Proportional decreases in certain commercial timber species.

• Understory subsistence crops, notably the banana in riparian 

areas.

•Increases in the importance of Guarea guidonia, Inga 

laurina, and I. vera, tree species that were used as coffee 

shade in the mountains.

• Evidence of past charcoal kilns and an increase in Prestoea 

montana in the vicinity of the kilns.

Human impacts similar to those at Bisley most likely 

characterize other sites along the LEF’s border.

Accidents

Several accidents have caused minor disturbances within 

the forests of the Luquillo Mountains. At least six notable 

incidents (i.e., with estimates of site damage and trail clearing 

in parenthesis) have occurred (appendix A):

• An airplane crashed in lower montane forest near the Bisley 

watersheds, possibly during the 1940s or 1950s (0.3 ha). No 

additional information could be found regarding the wreck.

Table 13—Estimated areas of historic and current 

disturbances within the Luquillo Experimental Foresta

Disturbance types

Area

ha

Hurricanesb ~11 310

Agriculture and timberc 6450

Administrative sitesd 82

Communication sitesd 79

Developed recreationd 468

Roadse 50

Landslidesf 113

Miningg 3

Forest management 

Stand improvementh 1620

Plantationsi 1510

Research manipulationj 5

Crashes (airplanes and vehicles)k 5

aSome areas overlap.

bOver the course of centuries, hurricanes would impact virtually all of 

the LEF.

cCrops, grazing, charcoal, and wood harvest (Marrero 1948).

dU.S. Department of Agriculture, Forest Service (1997a). 

eRoads and margins (Kharecha 1997, Scatena 1993).

f

Data expressed in hectares per 1,000 years (Larsen and Torres 

Sánchez 1992).

gMost was placer mining for gold (Cardona 1984). 

hThinning, girdling, tree cutting (Snyder and others 1987).

i

Numerous species (Marrero 1948).

j

Tree cutting, trails, arboretum, and canopy trimming (Byer and Weaver 

1977; Francis 1989; Howard 1968; Sheils and others 2010).

kCrash site plus areas disturbed in clean-up operations.
72

Major Types of Disturbance

• A Fairchild C-119 (Flying boxcar) departed from Roosevelt 

Roads and crashed in dwarf forest near Pico del Este on 

December 14, 1968 (0.3 ha). Subsequently, vegetative 

recovery has been monitored for > 40 years on the site 

(Weaver 2000b, 2008).

• A Havilland Heron DH-114 (Prinair flight) flying between 

St. Thomas and San Juan crashed in montane forest near 

Cacique Peak on March 5, 1969 (1.5 ha) (Rojas Daporta and 

Ortiz Otero 1969).

• A Cessna 441 flying between Culebra and San Juan fell in 

lower montane forest near the roadside restaurants on PR191 on January 5, 2002 (0.3 ha) (Torres 2002).

• A fixed-wing Rockwell International 690B turbo 

commander flying between Tortola and San Juan fell in the 

El Toro Wilderness Area situated in lower montane forest 

near the northern forest border on December 3, 2008 (2.0 ha) 

(Hernández Pérez 2008).

• A crane parked overnight on FS-27 near Pico del Oeste slid 

off the road, clearing a patch of montane forest during the 

early 1980s (0.3 ha). The crane was not removed from the 

forest.

In addition, an unknown number of automobiles and trucks 

have crashed at several points along forest roads causing local 

damage. Some accidents affect considerably more area than 

the accident site. Crash investigations and debris removal 

for airplane wrecks involve trail clearing, intense trampling 

around the accident sites, and soil erosion. They also cause 

changes in herbaceous species and present opportunities for 

the introduction of exotic weeds. The total impact to the six 

forest sites above is estimated cover about 5 ha.

Post-Disturbance Recovery

Forest recovery from past disturbance depends on numerous 

factors. These include: site variables such as elevation, aspect, 

topography, and exposure; the nature of past disturbance (e.g., 

selective logging, agriculture, grazing, hurricane damage, 

or landslides, alone or in combination); size of disturbance 

and distance from seed sources; and duration of disturbance, 

especially with regard to agricultural activities or temporary 

settlement.

At least five airplanes have crashed within the Luquillo Experimental 

Forest since the 1940s, including the 1968 crash of a Fairchild C-119 

(flying boxcar) in dwarf forest near Pico del Este. left: The crash 

site after 9 years is covered by ferns and grasses. (Photo by Peter L. 

Weaver) above: After 35 years, debris at the same site is surrounded 

by many endemic broadleaf species and ferns. (Photo by Iván 

Vicéns)
73

Major Types of Disturbance

Hurricane disturbance and recovery were modeled for the 

LEF’s lower montane forest considering several factors 

(Everham 1995):

• Catastrophic wind intensity—sustained wind, maximum 

gusts, storm duration, total storm rainfall, the storm’s 

proportion of total annual rainfall, and the distance between 

impacted sites and climatic stations.

• Biotic factors—tree species, size, and stand factors as they 

influence the severity of damage during a storm event.

• Abiotic factors—factors as they relate to severity of damage 

such as topography (i.e., channeling wind, site exposure, 

or vegetative preadaptation to chronic wind), soil (i.e., 

root growth as affected by water tables and other factors), 

and previous disturbance (i.e., increase in turbulence by 

canopy opening, the loss of susceptible trees, or shifting 

composition to more wind resistant species).

• Response pathways—regrowth and recruitment, the 

major pathways, along with some release and repression, 

as influenced by mainly the amount of structural and 

compositional damage incurred.

At small spatial scales, damage is controlled mainly by biotic 

factors such as species composition. At larger scales, abiotic 

factors such as topography and storm intensity become more 

important. Post-disturbance recovery is sensitive to gradients 

in light and water (Everham 1995). For example, sheltered 

valleys are humid but receive less light due to shading by 

surrounding slopes; ridges, in comparison, are better drained 

but receive more diffuse light at lower levels, differences 

often reflected in a greater shrub layer. Moreover, two general 

patterns of canopy recovery are possible. Where pioneers 

are recruited, a homogeneous canopy layer grows upward 

shading lower vegetation. Where regrowth of surrounding 

trees dominates, the canopy extends outward creating a more 

heterogeneous profile. Seedling recruitment is also important 

in site recovery (Uriarte and others 2005). Recruitment 

reflects interactions among several factors, including distance 

from local parent trees, parent tree size, seeds from nonlocal 

trees, and density-dependent effects from conspecific 

seedlings.

One might speculate on the time required for complete 

recovery after major disturbance within the LEF’s forests. 

Stand biomass and dynamics should recover relatively rapidly. 

Structure, or the typical size class distribution of trees within 

mature forest, would take longer. Species’ compositions 

similar to those found at the time of discovery, especially with 

regard to rare endemics, could require yet more time. Lower 

montane forest, with the greatest structure and diversity, 

also has the most favorable climate. Dwarf forest at the other 

extreme has the least structure and fewest species but the most 

rigorous climate.

Time required in lower montane and montane forests may 

be in the order of 100 years for biomass, 300 to 400 years for 

structure, and perhaps 1,000 years for species composition. 

Palm brakes and ravines, regardless of elevation, should take 

less time because their total biomass is less and their species 

compositions are not as complex. Prestoea montana matures 

quickly and regenerates well in openings and closed forest. 

Recovery of biomass and structure in dwarf forest may be a 

little longer than for the lower forest types; however, given 

the paucity of total species, and the abundance of endemics 

during succession, recovery of typical species composition 

may be more rapid. Superimposed on all of these estimates are 

the unknown effects of future disturbances, especially global 

warming and probable plant and animal migrations.
74

Other Vegetation

In addition to the four major forest types, the LEF has tree 

plantings, timber plantations, mahogany line plantings, a 

mahogany provenance trial, and the Forest Service arboretum at 

Caracoles (figs. 13 and 19). A total of 144 tree species have been 

planted, including 61 in plantings or in plantations, 75 as species 

blocks within the arboretum, 17 during agricultural activities, 

and 18 as ornamentals (appendix E). Of the total, 120 tree 

species were introduced from elsewhere, including 112 exotics 

and 8 species native to other parts of Puerto Rico (appendix E).

Tree Plantings and Plantations

Beginning in the 1920s, timber and ornamental trees from 

other countries, both tropical and temperate, were introduced, 

propagated, and tested in Puerto Rico (Bates 1927; Francis 

1987, 1995; Kramer 1926, 1927; Wadsworth 1970) (appendix 

E). In 1931, plantings began in the northwest (El Verde) and 

south (Del Valle) sites near the forest border (fig. 6). The major 

reasons for establishing plantations were timber production 

and watershed protection (Marrero 1947). An additional 

goal was the development of a multiaged forest composed of 

sawtimber and other species capable of natural reproduction. 

Local farmers recognized topographic variation (i.e., convex, 

straight, and concave slopes) as a critical factor in the selection 

of sites for agricultural crops. Likewise, topography was 

considered important to the survival and growth of plantation 

species (Marrero 1948, 1950).

The most active period for reforestation was between 1934 and 

1945 when more than 4 million seedlings of 27 species were 

planted at 54 different plantation sites on ~2000 ha of recently 

abandoned farmland (Marrero 1947, 1948) (appendix E). Ten 

species accounted for >94 percent of the planted seedlings: 

Swietenia macrophylla and Swietenia mahagoni totaled 51 

percent; and Casuarina equisetifolia, Cedrela odorata, Cordia

alliodora, Guarea guidonia, Montezuma speciosissima, 

Petitia domingensis, Tabebuia heterophylla, and Tectona 

grandis accounted for >43 percent. The remaining 17 species 

totaled <6 percent. Byrsonima spicata, Calophyllum calaba, 

and Tabebuia heterophylla, tree species that invade degraded 

secondary sites throughout the island were also used (Marrero 

1950) (appendix E). About 60 percent of the plantations were 

well stocked; however, many of the planted species, both 

natives and exotics, were not well adapted to the Luquillo 

Mountains. Previous inexperience with native species, 

misjudgments with regard to species selection, and planting 

on eroded and depleted soils all contributed to failures. Partial 

replanting was carried out on more than one-half of the 

plantations. By 1960, all plantations within the LEF had been 

thinned (Wadsworth 2009, see endnotes).

In the late 1930s, taungya plantings (i.e., interplanting of 

timber species with subsistence crops) using Calophyllum 

calaba, Swietenia macrophylla, and Swietenia hybrid (i.e., 

S. macrophylla x S. mahogoni) were initiated at elevations 

between 250 and 450 m (Holdridge 1940). The purpose was 

to convert abandoned agricultural lands into timberland. 

After 50 years, some plantings that had survived the period 

were measured to determine their mean and current annual 

increments (Weaver 1989a). Swietenia hybrid at 250 m 

elevation on the Harvey site (fig. 6) had grown satisfactorily 

over the entire period, averaging about 400 m3 ha-1 or a 

mean annual increment of 7.5 m3 ha-1 yr-1; moreover, current 

annual increment at 12.0 m3 ha-1 yr-1 was considered excellent. 

Mahogany seedlings and saplings were evident throughout 

the stand. In comparison, Calophyllum calaba at 450 m, like 

many other species in the LEF, grew slowly, averaging 200 m3

ha-1, or 5.0 m3 ha-1 yr-1. Current annual increment was similar. 

Stand densities, including the ingrowth of other species, 

averaged about 1000 ha-1 in the mahogany stand and 1450 

ha-1 in the Calophyllum calaba stand. The latter appeared 

stagnated but its survival demonstrated a capacity to tolerate 

marginal planting sites and competition.

Other studies indicate the performance of introduced species. 

Differences in spacing affected the height and d.b.h. growth 

of Pinus caribaea planted at Guzmán and the Caracoles 

arboretum along the western and southwestern boundaries of 

the LEF (figs. 6 and 13). The different spacings within the LEF 

contained trees that averaged 23 m tall after 20 years, growth 

rates which were slower than for sites in western Puerto Rico 

(Liegel and others 1985). The performance of Anthocephalis 

chinensis in spacing studies at El Verde, line plantings at 

Jiménez, plantations at Catalina, and at sites elsewhere on the 

island showed that it averaged between 16 and 21 m in height 

after 10 to 22 years. The best growth was attained on silty clay, 

nutrient-rich soil (Lugo and Figueroa 1985). Wide spacings 

allow trees to grow rapidly for 10 years and satisfactorily for 

20, usually with excellent form. Anthocephalis chinensis is a 

recommended species for pulp in the wet tropics because of its 

fast growth and desirable wood characteristics.

Hibiscus elatus was surveyed at 34 sites in Puerto Rico, 

including the arboretum and Sabana (Francis and Weaver 

1988) (figs. 6, 13, and 19). Growth rates after 25 and 26 years 

showed basal areas ranging between 20 and 50 m2 ha-1, with 

Chapter 6. OTHER VEGETATION
75

Other Vegetation

77 78 79 80

76 74 73

71 72 69

68

83

70

82

75

59 1 58 2

3

4

5

60

61

6 7 8 9

10

11

12

56

55

52

53

54

46

51

50

48

45

40

44 42

41 34

35

13 14

15 16 17 19

29 31 32

39

38

33 36

24 25

26

87

21

23 28

22

21

85

700

650

186

0 25 50 100

Legend

20

m m m

m

m

P.R.

Trail

Creek

Plots

Figure 19—Design of the arboretum in the Luquillo Experimental Forest.

N
76

Other Vegetation

a mean d.b.h. for dominant stems between 20 and 50 cm. 

Hibiscus elatus appeared to be adapted to a wide range of sites 

in Puerto Rico, including most with rainfalls >1500 mm yr-1.

Tectona grandis was surveyed on 27 plantations in Puerto 

Rico, including a 49-year-old stand at 120 m in Sabana 

(Weaver and Francis 1990) (fig. 6). The merchantable volume 

of Tectona grandis at Sabana, which accounted for one-half 

of the 1400 stems on the plot, was ~110 m3 ha-1. The mean 

height and mean d.b.h. of dominants were 17 m and 28 cm, 

respectively. Teak growth on the island was satisfactory on 

soils varying in texture from sands to heavy clays when 

rainfalls averaged between 1200 and 3400 mm yr-1. Plantings 

of Byrsonima spicata, Cordia alliodora, Guarea guidonia, 

Ocotea moscata, Petitia domingensis, Pouteria multiflora, 

and Tabebuia heterophylla growing in the LEF were also 

evaluated (Wadsworth 2009, see endnotes).

Mahogany Line Planting

Several enrichment techniques, including line planting, 

have been used to establish at least 163 trees species in 

at least 12 countries or territories within the neotropics 

(Weaver 1987c). The objective of enrichment planting is 

to improve the composition and commercial potential of 

secondary forests, rendering them more valuable at maturity. 

Because enrichment plantings require only partial clearing 

of secondary forests, they help conserve the soil, water, and 

wildlife resources during the establishment phase.

Field observations showed that secondary forest regeneration 

in areas with planting trials appeared to have a positive effect 

on the planted trees, especially mahogany (Wadsworth 1970). 

Consequently, line planting (i.e., underplanting or enrichment 

planting) trials were initiated with Swietenia hybrid in 

degraded secondary forest along the northeastern border of 

the LEF (Tropical Forest Experiment Station 1950) (fig. 6). 

Swietenia hybrid line plantings began in the 1960s and by 

1981 they covered about 1275 ha (Weaver and Bauer 1986).

Establishment and tending methods for the mahogany plantings 

varied. In the earliest enrichment plantings, the overstory was 

gradually poisoned and seeds were planted at 3x3 m spacings. 

Weeds were controlled by using herbicides. Seedlings were 

liberated by repeated early thinnings based on tree form and 

spacing. Later plantings employed bare root seedlings with a 

spacing of 2.5 m between trees and 11 m between rows. Tree 

Mahogany plantings. left: Line-planted mahogany hybrid grows on the lower slopes of the Luquillo Experimental Forest after the 

abandonment of agriculture. (Photo by Gerald P. Bauer) right: A 70-year old mahogany plantation at the Harvey site reflects the dedicated 

efforts of earlier foresters. (Photo by Peter L. Weaver)
77

Other Vegetation

survival and growth rates for both techniques were satisfactory. 

Growth differed significantly by topographic position with 

trees on bottomlands and lower slopes averaging about 20 m in 

height after 18 years, and those on mid-slopes and ridges about 

17 and 10 m, respectively (Weaver and Bauer 1986). Plot density 

after 18 years was 370 stems ha-1, basal area 28 m2 ha-1, and 

total aboveground biomass 170 t ha-1.

Seedling survival rates varied between 55 and 65 percent 

and shoot borer infestation between 10 and 60 percent 

(Weaver and Bauer 1986). Better light conditions and lower 

surrounding basal areas positively influenced growth. 

However, no consistent relations were found between shoot 

borer damage and crown class, surrounding basal area, or 

topographic position. Later, volume tables based on 133 trees 

were developed for 16 and 20-year-old plantation-grown 

Swietenia hybrid at the Sabana and nearby Río Chiquito sites 

(Bauer and Gillespie 1990) (figs. 6 and 13).

Although forest plantations are widespread in the tropics and 

common at lower elevations within the LEF, their importance 

and use by avian species has not been well studied. In the early 

1980s, avian community organization and resource use was 

surveyed in the Swietenia hybrid plantings at Río Chiquito 

(Cruz 1987). Frugivores and nectarivores foraged mostly 

in the understory when flowering and fruiting shrubs were 

present. Insectivores (foliage gleaners) were more common 

in the canopy whereas sally-hoverers were concentrated in 

the understory. Later, foraging patterns in Pinus caribaea

plantations were found similar to those in the Swietenia 

hybrid plantings (Cruz 1988). Maintaining or encouraging a 

heterogeneous understory along with scattered native canopy 

species could improve the use of forest plantations by birds.

Enrichment plantings previously used to improve commercial 

timber potential in the LEF (Weaver and Bauer 1986) may 

also be one of the best alternatives available to enhance 

wildlife habitat, particularly for the avifauna. In the latter 

case, foraging or nesting trees, especially natives, could be 

favored in lieu of timber species. Another option might be 

experimental forest thinnings to stimulate the regeneration 

of critical wildlife tree species. Past basal area reductions in 

montane forest increased significantly the regeneration of 

Cyrilla racemiflora (Weaver 2001). Increasing foraging and 

nesting habitats could help all wildlife species survive future 

hurricanes, notably the parrot.

Mahogany Provenance Trial

Swietenia macrophylla and S. humilis seeds collected in the 

mid-1960s from 24 sites in Mexico, Guatemala, El Salvador, 

Honduras, Nicaragua, Costa Rica, and Panama were 

germinated and tested at 11 sites in Puerto Rico, including 

the LEF, and at two sites in St. Croix (Geary and others 1973, 

Glogiewicz 1986, Weaver 2006). Nineteen provenances were 

planted at sites ranging from dry to wet in Puerto Rico and 10 

provenances were planted on dry sites in St. Croix. Seedling 

survival, height, and d.b.h. growth were determined after 

outplanting (Geary 1969, Geary and others 1973) along with 

wood densities from sites in Mexico, Central America, Puerto 

Rico, and the U.S. Virgin islands (Boone and Chudnoff 1970, 

Chudnoff and Geary 1973).

The objectives of the most recent analysis of the Swietenia

spp. (i.e., S. macrophylla, S. mahagoni, and S. humilis Zucc.) 

and provenance plantings, including 20 genetic sources, were 

to determine the amount of phenotypic plasticity and genetic 

variation within and among species and populations, and to 

examine how species and provenance growth characteristics 

change across environments (Ward and Lugo 2003). Relative 

amounts of environmental and genetic variation in growth and 

size traits, survival, and insect susceptibility were estimated. 

Trees were planted at 14 sites in Puerto Rico and St. Croix, 

including two locations within the LEF. The study showed the 

following size and growth traits after 14 years:

• Mahogany species showed about 10 times more genetic 

variation than was apparent among provenances within 

species.

• The mean estimated environmental variance for 

S. macrophylla was 79 percent, the mean estimated genetic 

variance was 11 percent, and the mean interaction was 

8 percent. Similar estimates for S. humilis were 41, 15, and 

29 percent, respectively. Comparisons for S. mahagoni were 

unavailable.

• Significant correlations existed between environmental 

gradients at sites of origin and measures of growth 

suggesting natural selection in differentiating populations.

• S. macrophylla showed the greatest mean growth (i.e., 

height, d.b.h., and biomass) at 14 years across all sites. 

S. mahagoni and S. humilis did not differ in most measured 

variables.

• All species and several populations showed distinct 

responses to different life zones and soil types.

• For both S. macrophylla and S. humilis, 95 percent of the 

variation in shoot borer attack was caused by estimated 

large- and small-scale environmental effects.

• Provenances became more genetically distinct as distance 

increased (i.e., source populations ranged from 160 to 

1600 km apart).

The planting site for the provenance trial represents an ex-situ

preserve that originally contained germplasm for an average 

of 16 trees per 19 provenances (fig. 13). Because many of the 

source areas for seeds may have been logged, the collection 

is critical to conservation biology and strategies to preserve 

genetic variation in mahogany. Without the study, the genotypic 
78

Other Vegetation

information and breeding material itself would have been lost 

(Glogiewicz 1986). Today, the collection provides opportunities 

for new studies, including future genetic, morphological, and 

biochemical analyses. Seed orchard establishment and clonal 

propagation, however, may no longer be feasible.

Forest Service Arboretum (Caracoles)

The arboretum is located between 620 and 690 m in elevation 

on the lower western flank of El Toro Peak (Francis 1989) 

(figs. 13 and 20). In its pristine state, the site was probably 

occupied by transition vegetation between lower montane and 

montane forests. Rainfall averages about 3000 mm yr-1, and the 

soils are clays with a mean pH of 4.7 and an average organic 

matter content of 8.6 percent. The land was first cleared for 

subsistence farming in the 1920s and was partially replanted at 

a later date. Subsequently brush occupied much of the area.

In 1959, a small test plantation was established on the site and 

in 1960, different tree species, mostly exotics, were gradually 

planted in small blocks (fig. 19) (appendix E). Most plantings 

were completed by 1963, but new species were added in plots of 

49 trees (7 x 7 trees) when seedlings were available. During the 

1980s, seven new species were introduced. By 1989, 14 species 

had been lost whereas 68 species, some represented by multiple 

subspecies or provenances, still survived (Francis 1989).

Some of the plots were measured earlier but a complete 

inventory was not finished until 1987. The tallest specimens 

by species ranged from 6 to 46 m and their corresponding 

diameters from 8 to 75 cm. Grouping by height classes for the 

tallest specimens of all species showed that 44 percent were 

<20 m, 45 percent were between 20 and 30 m, and 

11 percent were >30 m tall. Corresponding data for diameters 

showed 16 percent <20 cm, 51 percent between 20 and 40 cm, 

and 33 percent >40 cm (Francis 1989). The species 

represented 26 countries: Africa (Nigeria, Sudan, Uganda, 

Zimbawe); North America (Mexico, United States); Central 

America (Belize, Costa Rica, Guatemala, Honduras); South 

America (Argentina, Brazil, Surinam, Venezuela); the 

Caribbean (Cuba, Jamaica, Puerto Rico, U.S. Virgin Islands); 

Asia and islands (China, India, Iran, Papua New Guinea, the 

Philippines, Sri Lanka, Taiwan); and Australia.

Several of the introduced broadleaf species at the arboretum 

site showed promise for timber production, including: 

Anthocephalis chinensis and Aleuritus moluccana, both 

species with low specific gravities; Eucalyptus grandis, 

E. robusta, and E. saligna; Khaya grandifolia, K. nyasica, 

and K. senagalensis; and Hibiscus elatus, Maeopsis eminii, 

Swietenia macrophylla, and Terminalia ivorensis. Among the 

conifers, Pinus caribaea var. hondurensis (also var. caribaea) 

and P. oocarpa performed well. Some broadleaf species also 

showed potential as ornamentals, including the introduced 

Pterocarpus indicus and Clitoria racemosa, and the native 

Hernandia sonora. Among the conifers with potential as 

ornamentals were Callitris glauca and C. intertropica. 

Other species showed promise for planting or further testing 

as timber species or ornamentals. Today, the arboretum 

continues as an experimental site for species adaptability 

trials; moreover, it is also used for ecological research, seed 

collection, demonstration, and educational purposes.

In 1987 and 1998, species composition and structure in the 

arboretum understory were studied (Lugo and others 1999). 

Of the 83 species tallied, 20 were considered abundant, 

including Maeopsis eminii, Palicourea riparia, Prestoea 

montana, Schefflera morototoni, Syzygium jambos, and 

Ornamentals. Roadside mahogany planted along PR route 988 in 

the 1960s adds some color to the surrounding foliage during the dry 

season. (Photo by Iván Vicéns)
79

Other Vegetation

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16 7

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PR-966 PR-956

PR-186

PR-191

PR-983

PR-915

PR-9948

PR-963

Legend Trails Primary roads Secondary roads LEF boundary

Key

1

2

3

4

2

3

5

6

7

8

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10

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Interpretation

El Portal

Palma de Sierra

Palo Colorado

Picnic Areas

Caimitillo

Palma de Sierra

Palo Colorado

Quebrada Grande

RÌo Sabana (south)

Observation sites

BaÒo de Oro pool

BaÒo Grande pool

Cabezas viewpoint

El Yunque tower

La Coca falls

Key

12

13

14

15

1

16

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3

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Observation sites

Los Picachos

Mt. Britton tower

RÌo EspÌritu Santo

Yokah ̇ tower

Recreation Sites

El Portal

El Toro Wilderness

Caimitillo

La Mina falls

Palma de Sierra

Palo Colorado

Puente Roto (bathing)

Quebrada Grande

Yokah ̇ tower

Key

19

20

10

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Buildings and structures

Catalina Center

Ci nega lta house

El Yunque radar post

Eliza Colberg camp

El Yunque pavillion

ob Corps camp

La Condesa school

La Guaca aviary

La Mina barracks

La Mina fish hatchery

Molindero cottages

Pico del Este radar

PR communications

Stone house

CCC Camp 8 remnants

32

Figure 20—Management areas and structures within the Luquillo Experimental Forest.

Legend

Trails

Primary roads

Secondary roads

LEF boundary

Interpretation

1 El Portal 

2 Palma de Sierra 

3 Palo Colorado

Picnic Areas

4 Caimitillo 

2 Palma de Sierra 

3 Palo Colorado 

5 Quebrada Grande 

6 Río Sabana (south)

Observation sites

7 Baño de Oro pool 

8 Baño Grande pool 

9 Cabezas viewpoint

10 El Yunque tower 

11 La Coca falls

Observation sites

12 Los Picachos 

13 Mt. Britton tower 

14 Río Espíritu Santo 

15 Yokahú ̇ tower

Recreation Sites

1 El Portal 

16 El Toro Wilderness

4 Caimitillo 

17 La Mina falls

2 Palma de Sierra

3 Palo Colorado 

18 Puente Roto (bathing)

5 Quebrada Grande 

15 Yokahú ̇ tower

Buildings and structures

19 Catalina Center 

20 Ciénega Alta house 

10 El Yunque radar post 

21 Eliza Colberg camp 

22 El Yunque pavillion 

23 Job Corps camp 

24 La Condesa school 

25 La Guaca aviary 

26 La Mina barracks 

27 La Mina fish hatchery 

28 Molindero cottages 

29 Pico del Este radar 

30 PR communications 

31 Stone house 

32 CCC Camp 8 remnants

N
80

Other Vegetation

Thespesia grandiflora. Hurricanes of 1989 and 1998 caused a 

decline in species numbers and plant density in the understory.

Other Tree Species and Common Herbs

Ascending PR route 191, Bambusa vulgaris, established 

during the 1930s and 1940s, is visible along the roadside 

and in ravines where it was planted to help stabilize the soil 

(Little and Wadsworth 1964). The species, however, gradually 

spreads along streams where its increase could impact aquatic 

communities that depend on leaf litterfall (O’Conner and others 

2000) (appendix E). The risk of colonization was considered 

sufficient enough during a recent survey to recommend 

monitoring and research (Blundell and others 2003).

During gradient sampling, a few exotic tree species not 

associated with plantations were noted in closed forest. 

Castilla elastica was seen at 730 m above the La Mina 

recreation area. The fruit may have been carried by birds 

from ornamental plantings along the road. Mangifera indica, 

observed in the Mameyes valley near the forest border, 

was most likely introduced as fruit tree during settlement. 

Syzygium jambos, native to Southeast Asia and introduced 

to Puerto Rico nearly 200 years ago, yields edible fruit and 

fuelwood, and is not restricted by topography, soil nutrient 

status, or elevation (Brown and others 2006). The species is 

shade tolerant and gradually spreads along streams and lower 

slopes where it may exclude natives by allelopathy (O’Conner 

and others 2000). Its presence in closed forest is due to past 

human activity, possibly hikers or laborers traversing the 

forest years ago. In addition, Psidium guajava, Pinus 

caribaea, and Annona sp. were recorded during the survey of 

the large landslide at km 21 along PR route 191. The pine was 

planted to help stabilize the soil. The other species, both edible 

fruits, were probably discarded by hikers.

Exotic ornamentals, including shrubs (Hibiscus sp.), herbs 

(Impatiens sp., Heliconia spp., and Zingiber sp.), and several 

grasses also grow along LEF roadsides and in recreation 

areas. After construction of FS-27, the exotic grass Melinis 

minutiflora Beauv. was seeded with fertilizer to reduce erosion 

and sedimentation (Olander and others 1998). Pennisetum 

purpureum Schumach, another exotic grass, also grows along 

the same road. Interestingly, these grasses remained largely 

confined to the roadside. A recent survey carried out in the 

El Toro Wilderness tallied 82 invasive species: 23 vines, 

14 trees, 11 grasses, 11 herbs, 10 shrubs, 8 ferns, 1 orchid, 

1 sedge, and 3 listed as weeds (U.S. Department of 

Agriculture, Forest Service 2009, see endnotes).

At least 41 of the exotic tree species planted in the LEF 

have become naturalized in varying degrees (Francis and 

Liogier 1991) (appendix E). Naturalized species showing the 

highest degree of integration include those that are capable of 

competing in mature or primary forests after escaping from 

their original planting sites. Lesser integration is shown by 

those species that have entered secondary forests. The least 

integration includes species that reproduce infrequently or 

incidentally, and are dependent on human disturbance for 

survival. At least 35 exotic tree species were independently 

rated as adapted to the climate and soils of the LEF (Francis 

1987) (appendix E).
81

Vertebrate Fauna

The LEF has 165 species of vertebrates of which 158 are 

terrestrial and 7 are aquatic (U.S. Department of Agriculture, 

Forest Service 1997a, 1997b). In addition, the forest has 

aquatic macroinvertebrates.

Mammals

The LEF has 16 species of mammals. Eleven are native bats 

and five are introduced species common to Caribbean islands 

(table 14). Of the natives, Artibeus jamaicensis (fruit bat) is the 

most common though not necessarily the most abundant bat 

in Puerto Rico (Joglar 2005). The species feeds on a variety 

of fruits and occupies caves or the lower surfaces of palms 

or dense foliage during the day. Brachyphylla cavernarum

(cave bat) has similar habits, and may displace the fruit bat 

when foraging in the same tree. Eptesicus fuscus (big brown 

bat) is common, nocturnal, and insectivorous, foraging in 

openings in vegetation. It spends days in caves, and has been 

recorded underneath concrete structures used to channel 

streams. Erophylla sezekorni (brown flower bat) is completely 

nocturnal and principally frugivorous, but also consumes 

some insects. During the day it occupies warm caves. 

Lasiurus borealis (red bat) is insectivorous, hiding during the 

day in the foliage of trees. It has been encountered in coastal, 

urban, and very humid areas, and is difficult to capture. 

Molossus molossus (velvety free-tailed bat) is common 

throughout the island and often hides in houses. It is nocturnal 

and insectivorous, frequently feeding on beetles and moths.

Monophyllus redmanii (Greater Antillean long-tongued bat), 

native exclusively to the Greater Antilles, is widespread in 

Puerto Rico. It is nocturnal, nectivorous, and spends the day in 

caves. Mormoops blainvilli (Blainvillee’s leaf-chinned bat) is 

nocturnal and insectivorous, foraging principally on moths in 

the forest understory. Pteronotus quadridens (sooty mustached 

bat) is insectivorous and begins its activity just before sunset. 

It flies in formation, following the same route each night. 

Stenoderma rufum (red fruit bat) is endemic to the Puerto 

Rico and offshore islands. Spending the day in trees, it begins 

activities at sunset, flying short distances to feed on fruits. 

Tadarida brasiliensis (Mexican free-tailed bat) is insectivorous 

and begins foraging in open areas at sunset. During the day, it 

occupies crevices in rocks or caves in dense groups.

Introduced mammals include two species of rats, one mouse, 

the ubiquitous Herpestes auropunctatus (Indian mongoose) 

(table 14), and an occasional feral cat. Rats have been 

implicated in the loss of Puerto Rican parrot eggs (Snyder and 

others 1987). The mongoose, introduced between 1877 and 

1879 to control rats in sugar cane fields, is now Puerto Rico’s 

most detrimental predator on ground-nesting birds and lizards 

(Raffaele 1983). Mongooses also consume frogs, blind snakes, 

and several species of invertebrates, including ants (Danforth 

1926, Wolcott 1953) but apparently do not prey on parrots 

(Snyder and others 1987).

Birds

The LEF avifauna list includes 26 families and 107 species 

of which 61 are resident in Puerto Rico (54 native and 

7 introduced that also reside on the island), and 46 are 

migratory or transient (table 15). The Parulidae with 

27 species, only two of which are migrants, is the best 

represented family. Columbidae with nine species, Falconidae 

with six, and Trochilidae, Vireonidae, and Icteridae each with 

five species, are also well represented. Five families have only 

a single species recorded in the LEF.

Many species have been reported during the Fajardo 

Christmas count, which has been carried out as part of the 

National Audubon Society’s Christmas bird count since 1994. 

The Society of Puerto Rican Ornithologists, the Puerto Rican 

Natural History Society, the Puerto Rican Conservation 

Trust, and the International Institute of Tropical Forestry 

are co-sponsors of the event. Several additional species 

were recorded during monthly point counts and incidental 

observations by Forest Service wildlife biologists (Wayne 

Arendt, see endnotes). Of the total, 25 species are common, 

34 uncommon, and 48 are rare. In addition, 13 species 

and 2 subspecies are Puerto Rican endemics. Corvus 

leucognaphallus, previously reported within the LEF, is 

locally extirpated (Raffaele 1983). It survives, however, on 

other Caribbean islands.

The story of three species—Amazona vittata, Margarops 

fuscatus, and Dendroica angelae—presents interesting 

contrasts with regard to their discovery and adaptation to 

human settlement. During the time of the Tainos, hunting 

parrots was an occupation for youngsters (Alegría 1972). 

In 1493, the parrot occupied most of Puerto Rico, including 

the offshore islands of Vieques and Culebra. The species 

was most likely one of the first to be seen and heard by early 

explorers. Human disturbance—deforestation and habitat 

destruction—during the mid-to-late 19th century reduced the 

population considerably (Snyder and others 1987, Wunderle 

and others 2003). By 1900, parrots lived in only two areas on 

the island, and by the 1930s, only in the Luquillo Mountains 

(Danforth 1936; Gerhart 1936, see endnotes). In 1936, the 

Chapter 7. VERTEBRATE FAUNA
82

Vertebrate Fauna

Table 14—Vertebrate animal species except birds with environmental and status information for the Luquillo 

Experimental Foresta

Group and species English namesb

Status classificationd

Originc USFS Federal Nat. Her. PR

Mammals—native bats (11) and exotic species (5)

Artibeus jamaicensis Fruit bat NA

Brachyphylla cavernarum Cave bat NA

Eptesicus fuscus Big brown bat NA

Erophylla sezekorni Brown flower bat NA

Lasiurus borealis Red bat NA

Molossus molossus Velvety free-tailed bat NA

Monophyllus redmanii Greater Antillean long-tongued bat NA

Mormoops blainvillii Blainvillee’s leaf-chinned bat NA

Pteronotus quadridens Sooty moustached bat NA

Stenoderma rufum Red fruit bat NA S G3,L4

Tadarida brasiliensis Mexican free-tailed bat NA

Felis catis Feral cat EX

Herpestes auropunctatus Indian mongoose EX

Mus muculus House mouse EX

Rattus norvegicus House rat EX

Rattus rattus Roof rat EX

Reptiles—native lizards and geckos (13) and exotic species (1) 

Ameiva exsul Puerto Rican ground lizard EN

Amphisbaena caeca Puerto Rican worm lizard EN

Anolis cristatellus Puerto Rican crested anole NA

Anolis cuvieri Cuvier’s (Green giant) anole NA

Anolis evermanni Everman’s (Emerald) anole NA

Anolis gundlachi Yellow-bearded anole NA M

Anolis krugi Krug’s (Olive bush) anole NA

Anolis occultus Pygmy (Twig) anole EN

Anolis pulchellus Grass anole NA

Anolis stratulus Spotted anole NA

Diploglossus pleei Puerto Rican Galliwasp EN

Hemidactylus brooki Brook’s gecko EX

Sphaerodactylus klauberi Klauber’s least gecko NA

Sphaerodactylus macrolepis Big scale dwarf gecko NA

Reptiles—native snakes (5) 

Alsophis portoricensis Puerto Rican (P.R.) racer EN

Arrhyton exiguum P.R. garden snake EN

Epicrates inornatus P.R. boa EN E E G1,G2,N3 E

Typhlops richardii Richard’s worm snake NA

Typhlops rostellatus P.R. wetland blind snake EN

(table continued on following page))
83

Vertebrate Fauna

Table 14 (continued) —Vertebrate animal species except birds with environmental and status information for the Luquillo 

Experimental Foresta

Group and species English namesb

Status classificationd

Originc USFS Federal Nat. Her. PR

Amphibians—native frogs (14) and exotic species (1) 

Bufo marinus Marine toad EX

Eleutherodactylus antillensis Red-eyed coqui NA

Eleutherodactylus brittoni Grass coqui EN

Eleutherodactylus cochranae Whistling coqui NA

Eleutherodactylus coqui Common coqui EN

Eleutherodactylus eneidae Mottled coqui EN S G2,G3,N3 T

Eleutherodactylus gryllus Green (cricket) coqui EN

Eleutherodactylus hedricki Tree-hole coqui EN M

Eleutherodactylus karlschmidti Web-footed coqui EN S G1,N1 T

Eleutherodactylus locustus Warty coqui EN M,S G2,N?

Eleutherodactylus portoricensis Upland coqui EN

Eleutherodactylus richmondi Bronze (Ground) coqui EN S G3,N?

Eleutherodactylus unicolor Elfin (Burrow) coqui EN M,S G1,G2,N?

Eleutherodactylus wightmanii Melodius coqui EN

Leptodactylus albilabris White-lipped frog NA

Fish—native fishes (6) and exotic species (3)

Agonostomus monticola Mountain mullet NA M

Anguilla rostrata American eel NA

Awaous tajasica Sand fish, River goby NA

Carpinus carpioe Koi (carp) EX

Eleotris pisonis Spinycheek sleeper NA

Gobiomorus dormitor Bigmouth sleeper NA

Oncorhynchus mykisse Rainbow trout EX

Poecilia reticulatae Guppy EX

Sicydium plumieri Rock sucker (goby) NA M

aSources: Brown and others (1983); Gannon and others (2005); Nieves (1998); U.S. Department of Agriculture, Forest Service (1997b); Weaver 

(1994); Willig and Bauman (1984).

bBat common names (Joglar 2005).

cOrigin: EN = endemic; EX = exotic; NA = native.

dStatus classification: EN = endemic; Nat. Her. = Natural Heritage classification system: G = global, N = national, L = taxa formerly listed, 1 = 

critically imperiled, 2 = imperiled, 3 = vulnerable, 4 = apparently secure, 5 = widespread and secure, ? = species not ranked; USFS = Forest 

Service; PR = Puerto Rico; E = endangered; M = management indicator species; S = sensitive; T = threatened.

eIntroduced species: Koi survived in a shallow, excavated area along Pico del Este road for several years; rainbow trout eggs were introduced 

during the mid-1930s but adults failed to reproduce; and, guppies are found in many of the LEF streams.
84

Vertebrate Fauna

Table 15—Bird species with environmental and status information for the Luquillo Experimental Foresta

Status classificationf

Scientific name Common name Typeb Occurc Forestd Sitee Endemic USFS Fed. Nat. Her. PR

ARDEIDAE

Bubulcus ibis Cattle egret R R T E

Butorides striatus Green-backed heron T R T-C R

Egretta caerulea Little blue heron R R T R

Egretta thula Snowy egret R R T R

Nycticorax violaceus Yellow-crowned heron R U T R

SCOLOPACIDAE

Actitis macularia Spotted sandpiper T U T-C-P R

FALCONIDAE

Accipiter striatus Sharp-shinned hawk R U/R T-C ENSS E,M E G5,N2 E

Buteo jamaicensis Red-tailed hawk R C T-C-P-D

Buteo platypterus Broad-winged hawk R C T-C ENSS E,M E G5,N2 E

Falco columbarius Merlin T U T-C-P 

Falco peregrinus Peregrine falcon T U/R T-C-P T T G2,NN T

Falco sparverius American Kestrel R U T-C-PL E

COLUMBIDAE

Columba leucocephala White-crowned pigeon R R T-C

Columba livia Rock pigeon R-I U T-PL E

Columba squamosa Scaly-naped pigeon R C T-C-P-D-PL E

Columbina passerina Common ground-dove R U T-PL E

Geotrygon montana Ruddy Quail-dove R C T-C-P-PL

Patagioenas inornata Plain pigeon R R T-C-P-PL E

Zenaida asiatica White-winged dove R U T-C-PL E

Zenaida aurita Zenaida dove R C PL E

Zenaida macroura Mourning dove R R T-PL E

PSITTACIDAE

Amazona vittata Puerto Rican parrot R R T-C-P EN E,M E G1,N1 E

Aratinga canicularis Orange-fronted parakeet R-I U PL E

Brotogeris versicolurus White-winged parakeet R-I U/R PL E

Myiopsitta monachus Monk parrot R-I R T-PL E

CUCULIDAE

Coccozygus americanus Yellow-billed cuckoo T R T-C-PL E

Coccyzus minor Mangrove cuckoo R U T-PL E

Crotophaga ani Smooth-billed ani R U/R T-PL E

Saurothera vieilloti Puerto Rican lizard-cuckoo R C T-C-P-D-PL E EN 

STRIGIDAE

Megascops nudipes Puerto Rican screech-owl R C T-C-P-D-PL EN

Tyto alba Barn Owl R R T-PL E

CAPRIMULGIDAE

Caprimulgus carolinensis Chuck-will’s widow T R T-C-P

Chordeiles gundlachi Antillian nighthawk R R T-PL E

APODIDAE

Cypseloides niger Black swift R C/U T-C-P-D

TROCHILIDAE

Anthracothorax dominicus Antillean mango R U/R PL-T-C E

Anthracothorax viridis Green mango R U/R T-C-P-D E EN

(table continued on following page)
85

Vertebrate Fauna

Table 15 (continued)—Bird species with environmental and status information for the Luquillo Experimental Foresta

Status classificationf

Scientific name Common name Typeb Occurc Forestd Sitee Endemic USFS Fed. Nat. Her. PR

Chlorostibon maugaeus Puerto Rican emerald R C T-C-P-D-PL E EN

Eulampis holosericeus Green-throated Carib R R T-PL E

Orthorhyncus maugaeus Antillean crested hummingbird R R T-PL E

TODIDAE

Todus mexicanus Puerto Rican tody R C T-C-P-D-PL E-R EN

ALCEDINIDAE

Ceryle alcyon Belted kingfisher T R T R

PICIDAE

Melanerpes portoricensis Puerto Rican woodpecker R C T-C-P-D-PL E-R EN

Sphyrapicus varius Yellow-bellied sapsucker T R T-C-P-D-PL

TYRANNIDAE

Elaenia martinica Caribbean elaenia R R T-PL

Myiarchus antillarum Puerto Rican flycatcher R U T-C-PL E EN

Tyrannus caudifasciatus Loggerhead kingbird R U T-C-PL E

Tyrannus dominicensis Gray kingbird R C T-C-P-D-PL E-R

VIREONIDAE

Vireo altiloquus Black-whiskered vireo R C T-C-P-D-PL E-R

Vireo flavifrons Yellow-throated vireo T R T-C-PL E

Vireo griseus White-eyed vireo T R T-PL E

Vireo latimeri Puerto Rican vireo R R T-C EN

Vireo olivaceus Red-eyed vireo T R T-PL E

HIRUNDINIDAE

Hirundo rustica Barn swallow T U/R T-C-P-D-PL E-R

Pretochelidon fulva Cave swallow R U/R PL E

Progne diminicensis Caribbean martin R R T-C-P-D-PL E-R

TURDIDAE

Catharus bicknelli Bicknell’s thrush T R PL E

Catharus ustulatus Swainson’s thrush T R T-C-PL

Hylocichia mustelina Wood thrush T R T-PL E

Turdus plumbeus Red-legged thrush R C T-C-PL E

MIMIDAE

Dumetella carolinensis Gray catbird T R T-C-PL E

Margarops fuscatus Pearly-eyed thrasher R C T-C-P-D-PL E-R

Mimus ployglottos Northern mockingbird R U/R T-PL E

BOMBYCILLIDAE

Bombycilla cedrorum Cedar waxwing T R T-C-PL

PARULIDAE

Coereba flaveola Bananaquit R C T-C-P-D-PL E-R

Dendroica angelae Elfin-woods warbler R U C-P-D EN M,S G1,G2,N? E

Dendroica caerulescens Black-throated blue warbler T C T-C-P-D-PL M 

Dendroica castanea Bay-breasted warbler T R T-PL E

Dendroica coronata Yellow-rumped warbler T R T-PL E

Dendroica discolor Prairie warbler T U T-C-PL E

Dendroica fusca Blackburnia warbler T R T-PL

Dendroica magnolia Magnolia warbler T U/R T-C-PL E

Dendroica pensylvanica Chestnut-sided warbler T R T-C-PL E

(table continued on following page)
86

Vertebrate Fauna

Table 15 (continued)—Bird species with environmental and status information for the Luquillo Experimental Foresta

Status classificationf

Scientific name Common name Typeb Occurc Forestd Sitee Endemic USFS Fed. Nat. Her. PR

Dendroica petechia Yellow warbler T R D

Dendroica pinus Pine warbler T R C-P

Dendroica striata Blackpoll warbler T U T-C-P-D-PL E-R

Dendroica tigrina Cape May warbler T U/R T-C-PL E

Dendroica virens Black-throated green warbler T R C

Geothlpis trichas Common Yellowthroat T R T-PL E

Helmitheros vermivorus Worm-eating warbler T R T-C-P

Mniotilta varia Black-and-white warbler T U T-C-P-D-PL E-R

Oporornis formosus Kentucky warbler T R T-C-D-PL E

Parula americana Northern parula T C T-C-P-D-PL E-R

Seiurus aurocapillus Ovenbird T U T-C-P-D-PL E-R

Seiurus motacilla Louisiana waterthrush T U T-C-P-PL E-R

Seiurus noveboracensis Northern waterthrush T U T-C-P R

Setophaga ruticilla American redstart T C T-C-P-D-PL E-R

Vermivora chrysotera Golden-winged warbler T U T-C-P

Vermivora peregrina Tenessee warbler T R T-C-PL

Vermivora pinus Blue-winged warbler T R T-C-PL E

Wilsonia citrina Hooded warbler T R T-C-PL E

THRAUPIDAE

Nesospingis speculiferus Puerto Rican tanager R C T-C-P-D-PL E-R EN

Spindalis zena portoricensis Stripe-headed tanager R C T-C-P-D-PL E-R EN

EMBERIZIDAE

Tiaris bicolor Black-faced grassquit R C PL E

Tiaris olivaceus Yellow-faced grassquit R U PL E

Loxigilla portoricensis Puerto Rican bullfinch R C T-C-P-D-PL E-R EN

CARDINALIDAE

Passerina ciris Painted bunting T R C

Passerina cyanea Indigo bunting T U/R T-PL E

Pheucticus ludovicianus Rose-breasted grosbeak T R PL

ICTERIDAE

Icterus dominicensis Black-cowled oriole R C/U T-C-PL E

Icterus galbula Baltimore oriole T R PL E

Icterus icterus Troupial R R PL E

Molothris bonariensis Shiny cowbird R U T-C-PL E

Quiscalus niger Greater Antillian grackle R R PL E

FRINGILLIDAE

Euphonia musica Antillean euphonia R C/U T-C-P-D-PL E-R

ESTRILIDAE

Estrilda melopoda Orange-cheeked waxbill R-I R PL E

Lonchura cucullata Bronze mannikin R-I U PL E

Lonchura punctulata Nutmeg mannikin R-I U PL E

aSources: Kepler and Kepler (1970); Recher and Recher (1966); Snyder and others (1987); U.S. Department of Agriculture, Forest Service 

(1997b); Wiley and Bauer (1985); monthly point counts and incidental observations (Wayne Arendt, see endnotes). White-necked crow (Corvus 

leucognaphalus) was last seen in the LEF in 1963. bType (in Puerto Rico): I = introduced (or exotic); R = resident; T = transient (or migratory).

cOccurrence (in LEF): C = common; U = uncommon; R = rare.

dForest preference: T = Lower montane rain forest; C = Montane rain forest; P = Palm brake; D = Dwarf forest; PL = plantation.

eSite preference: E = forest edge at interface with pastures, cropland, or fallow; R = stream edge.

f

Status classification: EN = endemic species; ENSS = endemic subspecies; USFS = Forest Service; Fed. = Federal; Nat. Her. = Natural Heritage 

classification system: G = global, N = national, 1 = critically imperiled, 2 = imperiled, 3 = vulnerable, 4 = apparently secure, 5 = widespread and 

secure, ? = species not ranked; PR = Puerto Rico; E = endangered; M = mangement indicator species; S = sensitive; T = threatened.
87

Vertebrate Fauna

LEF was recommended as a bird sanctuary. At the same time, 

however, the mountains were being dissected by a major 

highway, which opened the area to the public, including 

hunters and pet seekers. With the decline in population, the 

parrots became more vulnerable to numerous competitors, 

predators, and parasites. Between 1953 and 1956, tallies 

made within the LEF estimated the population at 200 birds 

(Rodríguez Vidal 1959, 1962). At this time, the parrot was 

concentrated in three river valleys—Río Espiritu Santo, Río 

Hicaco, and Río de la Mina, where it consumed the fruits of at 

least 54 species of trees and vines. During the 1960s, about 

50 individuals were estimated and by the early 1970s, a 

complete count revealed only 13 birds (Recher and Recher 

1966, Snyder and others 1987).

In 1968, the parrot was designated as an endangered 

species—one of the 10 most endangered in the world—and 

in 1972 an aviary was established in the La Mina barracks 

on FS 10 (Synder and others 1987) (fig. 20) (table 3). After a 

successful effort to increase the captive and wild populations 

to about 100 birds, Hurricane Hugo eliminated about one-half 

of the wild population (i.e., about one-quarter of the entire 

population) (U.S. Department of Agriculture, Forest Service 

1997b). By the time that Hurricane Georges passed over the 

forest, several birds had been moved to the Río Abajo aviary 

within the commonwealth forest reserve system south of 

Arecibo. Four factors appear responsible for maintaining the 

bottleneck in the recovery of the parrot (Beissinger and others 

2008): reduced hatching success due to inbreeding; failure of 

adults to nest; nest failure; and reduced survival of adults and 

juveniles. Today, many parrot eggs are hatched and fledged in 

captivity both at Río Abajo aviary and the new “La Iguaca” 

aviary built on the lower, northern slopes of El Yunque 

in 2007. Birds are then conditioned for the wild and released. 

Three recent releases totaling 34 birds were carried out 

between 2000 and 2002 (White and others 2005). Slightly less 

than one-half of the released birds survived in the wild, with 

one-fifth being lost to raptors. Today’s parrot population of 

nearly 250 birds is found either in captivity or in the wild.

The pearly-eyed thrasher was relatively scarce and only 

patchily distributed in the lowlands and hills of Puerto Rico 

until the 1920s when biologists noted a steady increase in its 

numbers (Arendt 2006). The spread continued to 600 m in 

the LEF by 1930 and throughout the forest by the early 1950s 

(Snyder and others 1987). The thrasher has superior colonizing 

capabilities and traits characteristic of avian “tramps” (Arendt 

2006). It is a strong flier, disperses well, and occupies all 

available habitats within Puerto Rico and other Caribbean 

islands. It is omnivorous, shows variability in diet and 

foraging, and has several reproductive strategies that facilitate 

its survival and expansion. Moreover, the thrasher is resilient 

to major disturbances such as hurricanes and droughts.

The thrasher, a most remarkable natural enemy of the 

parrot, nests in tree cavities (Snyder and others 1987). It also 

frequently enters parrot nests where it destroys eggs, attacks 

nestlings, and may take control of the nest site. The gradual 

increase of thrashers at higher elevations within the forest 

resulted in encounters with the parrot, especially during 

Amazona vittata (Puerto Rican parrot), once common throughout much of Puerto Rico, is currently classified as rare and endangered. (Photo 

by Gerald P. Bauer)
88

Vertebrate Fauna

their coincident breeding seasons. The thrasher, along with 

predators such as Buteo jamaicensis (red-tailed hawk) and 

rats, and parasites and site competitors like warble flies and 

honey bees, caused a decline in the parrot population to record 

lows during the mid-1970s.

In 1971, long after the island’s native bird species had 

been identified and described, the elfin-woods warbler 

was discovered in the dwarf forest and upper reaches of 

the montane forest in the LEF (Kepler and Parkes 1972). 

Interestingly, the species had been noted a short time earlier 

by another birder working at Roosevelt Roads. Similar to 

Mniotilta varia (black-and-white warbler), the elfin-woods 

warbler required specimens to assure its identification as a 

new species (Kepler 2009). The late discovery of the warbler 

decades after the identification of all other species in Puerto 

Rico is due in part to its limited habitat and distribution 

(Raffaele 1983). Later, other populations were found in the 

Central Mountains. Today the species is protected throughout 

the island.

Reptiles

Of the 19 species of reptiles found in the LEF, 14 are lizards 

or geckos, and 5 are snakes (table 14). Some are restricted 

to particular forest types or habitats whereas others have 

more ample foraging sites or ranges. Nearly a century ago, 

the diets of 11 species (i.e., an iguana, a skink, two geckos, 

and seven lizards), were investigated from the standpoint of 

agricultural economics (Wolcott 1924). Stomach contents 

revealed a variety of insects but no mosquitoes or house flies. 

The samples were based on observations made outside of the 

national forest.

Ameiva exsul (Puerto Rican ground lizard) is found in open 

areas, including roads and trails, at low elevations near the 

border. Anolis cristatellus (Puerto Rican crested anole) and 

Anolis gundlachi (yellow-bearded anole) forage on trunks 

and on the ground (Joglar 2005, Rivero 1978). Anolis cuvieri

(giant green anole), the largest species in Puerto Rico, 

seems to prefer canopies in shady, cool areas at intermediate 

elevations. Anolis evermanii (Everman’s anole) and Anolis 

stratulus (spotted anole) forage in canopies and trunks. Both 

Anolis krugi (Krug’s anole) and the Anolis pulchellus (grass 

anole) frequent grassy areas, herbaceous growth, and bushes, 

whereas the small Anolis occultus (pygmy anole) forages on 

twigs and branches. Amphisbaena caeca (worm lizard) hides 

under vegetative debris, logs, rocks, and in roots, consuming 

coleopteran larvae (Reagan and Waide 1996). Hemidactylus 

brooki (Brook’s gecko), widespread in the tropics, lives in leaf 

litter and among tree roots and buttresses where it eats spiders, 

cockroaches, and other insects.

Diploglossus pleei (Puerto Rican Galliwasp), the only species 

of its genus in Puerto Rico, hides under rocks, logs, and 

decaying ground vegetation where it may consume various 

invertebrates, including insects, and even frogs (Joglar 2005, 

Rivero 1978) (table 14). Sphaerodactlus klauberi (Klauber’s 

least gecko) has been found above 900 m in elevation and 

S. macrolepis (big scale dwarf gecko), the most widespread of 

its genus, to 880 m.

Five nonpoisonous species of snakes are found in the LEF. 

They range from the island’s shorelines to midelevations in 

the mountains. Alsophis portoricensis (Puerto Rican racer) 

is widely distributed, diurnal, and terrestrial, although 

sometimes found in trees. Arrhyton exiguum (Puerto Rican 

garden snake), the most common throughout the island, is 

terrestrial and somewhat secretive, typically being found 

Parrot aviaries. left: La Mina barracks served as the U.S. Department of Agriculture Forest Service’s first parrot aviary from 1972 until after 

2000. right: The new Iguaca aviary opened in 2007 on PR route 9966 along the northern forest border. (Photos by Peter L. Weaver)
89

Vertebrate Fauna

under logs and tree stumps (Joglar 2005, Rivero 1978). Both 

consume lizards, frogs, and frog eggs. Epicrates inornatus,

the largest species, is found on the ground or in trees where it 

feeds on rats, mice, birds, and sometimes bats (Rivero 1978). 

It is apparently less common in the LEF than other locations 

such as the limestone hills. Typhlops richardii (Richard’s 

worm snake) and Typhlops rostellatus (Puerto Rican wetland 

blind snake) are both blind and subterranean in habit. They 

typically feed on termites, ants, and other invertebrates.

Amphibians

The LEF has 15 species of amphibians. All but two species of 

tree frogs (Eleutherodactylus spp., locally called coquis) are 

endemic to Puerto Rico and feed on a large variety of insects 

and snails found in the forest (table 14). Natural predators 

include spiders, notably on young individuals, as well as 

lizards, snakes, birds, rats, and mongooses.

The Eleutherodactylus antillensis (red-eyed coqui), widely 

distributed in open areas and along forest borders, occurs 

most frequently at low to intermediate elevations (Joglar 

1998, Rivero 1978). The species typically hides below rocks, 

herbaceous roots, trunks, and loose bark. E. brittoni (grass 

coqui) is most frequently found at low elevations in fields and 

pastures exposed to the sun, but it also may be found 

in herbaceous growth along roads and forest borders. 

E. cochranae (whistling coqui), with distribution in both dry 

and wet sites on the island, occupies low elevations in the 

LEF where it frequents vegetation near the ground, including 

bushes, trees, and bromeliads. The species waits for prey and 

feeds mainly on arthropods and a variety of insects. The E.

coqui (common coqui), living from the coast to mountain 

summits, is the best known and the best studied of the island’s 

amphibians. During the day, it hides under fallen leaves, in 

bromeliads, and in the axils of palm leaves at intermediate to 

high elevations, and within pastures at low elevations near the 

LEF border.

E. eneidae (mottled coqui) occupies humid forests at 

elevations between 300 and the summits, where it prefers 

slopes along trails and moss-covered trunks near the ground 

(Joglar 1998). E. gryllus (green coqui) also occupies similar 

elevations. At lower elevations, it prefers open areas and forest 

borders whereas at higher elevations it is found in bromeliads 

and under moss on rocks. E. hedricki (tree-hole coqui) is 

arboreal and occupies dense, wet forests between 450 m and 

the summits. Diurnal refuges include cavities in trees up to 

18 m in height. E. karlschmidti (web-footed coqui) is found 

below: Lizard. Anolis evermanni (Emerald anole), one of eight 

native anoles, frequents the deep, wet forests of the Luquillo 

Experimental Forest and humid mountainous sites elsewhere on 

the island. right: Snake. Epicrates inornatus (Puerto Rican boa 

constrictor), which feeds on small mammals, birds, and lizards, 

is the island’s largest snake. The endemic boa, reaching 2.5 m in 

length, remains listed as an endangered species largely because of 

past habitat destruction. (Photos by Iván Vicéns)
90

Vertebrate Fauna

at elevations between 50 and 650 m in rocks along streams, 

and near waterfalls and rocks splashed with water. Recent 

exhaustive searches for both the mottled coqui and the webfooted coqui have been unsuccessful and they are presumed 

to be extinct.

E. locustus (warty coqui) is found in wet, mountainous forest 

above 370 m, including dwarf forest, where it appears to be 

more abundant along forest borders and in open areas (Joglar 

1998). E. portoricensis (upland coqui) is found at elevations 

from 180 m to the summits where it occupies bushes, palms, 

bromeliads, but appears to prefer the soil surface and litter. 

Recent data suggest that both of these species are less 

abundant than formerly (Joglar 1998). E. richmondi (bronze 

coqui) is found in the interior of the island at elevations 

from 40 m to near the summits. However, it appears to have 

declined at elevations above 600 m in the LEF since the early 

1980s. E. unicolor (elfin coqui) is endemic to peaks above 

675 m in the LEF, where it lives in subterranean cavities 

under surface roots, and in mosses growing on the ground. 

E. wightmanii (melodious coqui) is also found in the 

interior of Puerto Rico from 150 m to the summits. It dwells 

principally on or very near to the ground.

The remaining amphibians are in other genera (Rivero 1978) 

(table 14). The native Leptodactyllus albilabris (white-lipped 

frog) is terrestrial but is seldom found away from streams or 

marshy areas. It passes through a tadpole stage and often calls 

from muddy areas. Bufo marinus (marine toad) was imported 

from Jamaica and Barbados during the 1920s to control grubs 

on sugar cane. A few years later, it was abundant.

The apparent extinctions of E. eneidae and E. karlschmidti

in the LEF, and E. jasperi (golden coqui) from the Central 

Mountains near Cayey (Joglar 1998) suggest island-wide 

problems among certain amphibian populations. This trend 

is substantiated by the apparent decline of other species like 

the E. locustus, E. portoricensis, and E. gryllus in the LEF 

(Woolbright 1997). Whether these population declines are 

related to normal fluctuations or migrations is uncertain. 

The LEF remained largely undisturbed by hurricanes from 

1932 until 1989. Recent hurricanes, however, may have 

caused temporary changes in the understory, reducing some 

populations or causing migrations to other sites. More serious 

possibilities involve the amphibian chytridiomycosis fungus 

which has devastated frog populations worldwide (Daszak and 

others 2003).

Fish

Six native fish species were recorded in the headwaters of 

the Río Espíritu Santo and Río Mameyes, including the 

Bisley watersheds (Nieves 1998) (table 14). Three are found 

in the upper portions of streams—Agonostomus monticola

(mountain mullet), Anguilla rostrata (American eel), and 

Sicydium plumieri (rock sucker) and the others, Awaous 

tajasica (sand fish), Eleotris pisonis (spinycheek sleeper) and 

Gobiomorus dormitor (bigmouth sleeper) are found below. 

None of the six is endemic or endangered. All feed on shrimp 

except the rock sucker, which is herbivorous. In addition, at 

least three introduced species have reached the LEF at one 

time or another—the common Poecilia reticulata (guppy), 

Oncorhynchus mykiss (rainbow trout), and a few Carpinus 

carpio (koi or carp). Rainbow trout eggs were introduced into 

the La Mina area nursery in 1934 and 1935 in an attempt to 

provide sport fishing. The effort was unsuccessful because the 

streams were too warm for reproduction (Gerhart 1936, see 

endnotes). During the 1990s, koi were placed into a shallow, 

75 m2 depression scraped out of impermeable soil along 

FS-27. Rainfall, cloud moisture deposition, and possibly runoff 

from the road provide enough water for the koi to survive.

With regard to migrations, the American eel is catadromous 

(i.e., adults live in fresh water and migrate to the sea to spawn) 

whereas the remaining native species are amphidromous 

(i.e., adults spawn in upland streams, larvae are carried 

downstream to sea during rainfalls, and juveniles return 

upstream). The headwaters of LEF streams serve as refugia 

from predators, sites where the fish grow, mature, and 

reproduce. The mountain mullet, the most important game 

fish found in fast flowing upland streams in Puerto Rico, is 

also adapted to sluggish waters (Erdman 1972, Hildebrand 

1935). The rock sucker has the capacity to climb waterfalls 

and obstructions such as low level dams and was recorded at 

elevations of 650 m in the Mameyes watershed (Nieves 1998). 

The species is considered as a biological indicator of the 

ecological health of streams (Erdman 1984).

Frog. Eleutherodactylus coqui (Coqui frog) is 1 of 13 native frogs in 

the genus, 12 of which are also island endemics that live within the 

Luquillo Experimental Forest. The widespread coqui is the island’s 

best known and cherished amphibian. (Photo by Iván Vicéns) 
91

Species Diversity—Plants and Animals

Plant Diversity

The LEF has a diverse plant life. Native trees number 225 

(Little and Wadsworth 1964; Little and Woodbury 1976, 1980; 

Little and others 1974), orchids at least 79 (Ackerman 1992, 

1995; Kasomenakis 1988), and ferns about 150 (Kepler 1975). 

The number of trees exceeds that found on all other national 

forests combined (U.S. Department of Agriculture, Forest 

Service 1997b). In addition, 120 of the 144 tree species planted 

in the LEF were introduced species (i.e., 112 were exotics and 

8 were natives to Puerto Rico that grow outside of the forest). 

Only 24 of the planted species were forest natives (appendix 

E). Although most of these introductions were made for 

forestry purposes, some species were planted for agriculture 

or as ornamentals.

The relative abundances of tree species within the LEF vary 

in time and space. In 1500, before settlement, the forest 

contained native tree species in abundances controlled by life 

cycles, environmental variables, and climatic events. During 

the 19th and 20th centuries, agriculture and tree plantings 

on the lower slopes along with the construction of roads, 

trails, and facilities at higher elevations, introduced exotics 

and secondary species. The long post-hurricane recovery 

period after San Felipe and San Cipriano showed a gradual 

decline in secondary tree species on permanent plots (Crow 

1980, Weaver 1983, 1989b), a trend that was reversed after 

hurricanes Hugo and Georges (Weaver 2002b).

Although the total number of tree species recorded by forest 

type decreases with ascent in the LEF (table 8), gradient 

sampling showed a greater number of species at elevations in 

montane forest rather than lower montane forest (fig. 18) (table 

8) (appendix tables 9A through 9D). This is due partially to 

the forest classification system and partially to the sampling 

procedure. First, forest types are broadly defined by elevation. 

Species distribution in mountainous terrain, however, is also 

influenced by aspect and topography (Weaver 1991, 2010a, 

2010b). The greatest current abundance of species occurs 

in highly dissected terrain in the ecotone between the lower 

montane and montane forest types (fig. 17). Second, more 

plots were sampled in the montane forest and dwarf forest 

types than in lower montane forest or palm brake (appendix 

C). Greater numbers of plots produce larger tree samples 

and a greater likelihood of encountering new species. 

Third, plot size was limited 500 m2 in order to sample on 

topographic features. This plot size may have been inadequate 

to encompass representative samples of the larger stems 

characteristic of lower montane forest. In addition, past human 

activities precluded sampling undisturbed native forest at 

lower elevations near the forest border (i.e., near the ecotone 

between the lowland coastal and lower montane forests). 

Species richness was most likely greatest in this area before 

logging and settlement. Finally, species richness in palm 

brake, regardless of elevation, and dwarf forest is limited by 

environmental conditions.

Animal Diversity

The current vertebrate fauna within the LEF is fairly diverse 

and includes 157 terrestrial and seven aquatic species (tables 

11 and 12): 16 species of mammals; 107 birds, including 

61 residents and 46 migrants; 19 reptiles; 15 amphibians; and 

7 species of freshwater fishes. In addition to the fish, about 

1800 km of rivers and streams in the forest support nine 

species of freshwater shrimp and one freshwater crab (U.S. 

Department of Agriculture, Forest Service 1997a, 1997b). The 

relative abundances of several animal species have varied in 

time and space as a result of human activities. Most notable 

are changes involving populations of Amazona vittata, Buteo 

jamaicensis, and Corvus leucognaphallus.

As with islands elsewhere, the arrival of animals from 

continental land masses to Puerto Rico was restricted. Bird 

species richness in the LEF, although fairly high, is less than 

in Guánica Forest in the dry southwestern part of the island 

(Kepler and Kepler 1970). A plausible explanation is that insect 

populations in the forest are controlled by abundant resident 

populations of lizards and frogs that effectively compete with 

avian species (table 14). Differences in species richness could 

also be partially due to past climatic conditions in Puerto Rico. 

During the Pleistocene, the West Indies were both larger and 

drier than today (Faaborg and Arendt 1990, 1992). Summaries 

of recent bird counts in the southwest showed at least 157 bird 

species in Guánica Forest, substantiating earlier observations 

(Weaver and Schwagerl 2009).

Chapter 8. SPECIES DIVERSITY—PLANTS AND ANIMALS
92

Classified Species of Plants and Animals

The Forest Service and commonwealth agencies use several 

terms to classify the status of plant and animal species (U.S. 

Department of Agriculture, Forest Service 1997b):

• Endemic—the characteristic of being unique to a particular 

geographic region (i.e., an island, a habitat, a forest, or other 

defined area).

• Rare—a species for which population viability is a concern 

because it exists at extremely low numbers within a forest or 

particular habitat.

• Endangered—a species that is in danger of extinction 

throughout or in a significant portion of its range.

• Threatened—a species that is likely to become endangered 

in the foreseeable future throughout or in a significant 

portion of its range.

• Sensitive—a species for which population viability is a 

concern as indicated by downward trends in population 

numbers or density, or in habitat availability that would 

further reduce the distribution of a species.

• Management indicator species—species whose population 

changes may reflect management practices.

Classified Plants

The LEF has 38 classified species of plants, including 24 trees, 

2 shrubs, and 12 herbs (1 liana, 1 grass, 1 fern, 2 lycopodia, 

and 7 others) (table 16). Of these, 30 are endemic to Puerto 

Rico, and 13 are confined to the Luquillo Mountains alone. 

The Forest Service lists 8 as endangered, 30 as sensitive, 

and 11 as management indicator species (U.S. Department 

of Agriculture, Forest Service 1997a). Both the Federal and 

Puerto Rican governments also list 8 as endangered, and the 

Federal Government cites another as threatened and under 

consideration for listing. The Natural Heritage classification 

system ranks 30 of the species either as critically imperiled or 

imperiled either globally or nationally 

Classified Animals

The LEF has 32 endemic animal species, including 

11 amphibians, 8 reptiles, and 13 birds; moreover, there are 

two endemic avian subspecies (tables 11 and 12). In addition, 

13 species of animals are classified, including 1 mammal 

(bat), 1 reptile (snake), 5 amphibians (frogs), and 6 birds. The 

Forest Service lists 5 animals as endangered, 7 as sensitive, 

1 as threatened, and 11 as management indicator species 

(U.S. Department of Agriculture, Forest Service 1997a). 

Both the Federal and Puerto Rican governments also list 

5 as endangered. Moreover, the Federal Government cites 

one species as threatened and the Puerto Rican government 

cites three as threatened. The Natural Heritage classification 

ranks 13 species in various classes. Finally, the Forest Service 

has classified five as a management indicator species (U.S. 

Department of Agriculture, Forest Service 1997b).

Chapter 9. CLASSIFIED SPECIES OF PLANTS AND ANIMALS
93

Classified Species of Plants and Animals

Table 16—Classified plants within the Luquillo Experimental Foresta

Status classificationc

Scientific name Life formb Endemic USFS Fed. Nat. Her. PR

Brachionidium ciliolatum Garay H ENL S G1,N1

Brachionidium sherringii Rolfe H S G1,N1

Brunfelsia portoricensis Krug & Urban T EN S G1,N2

Callicarpa ampla Schauer T EN E,M E G1,N1 E

Calyptranthes luquillensis Alain T ENL S G1,N1

Calyptranthes woodburyi Alain T EN S G1,N2

Coccoloba rugosa Desf. T M,S P,T G2,N2

Conostegia hotteana Urban & Ekman T S G2,N2

Cordia wagnerorum R. Howard S ENL S G1,N1

Cybianthus sintenisii (Urban) Agostini S ENL S G1,N1

Dichanthelium aciculare (Desv. ex Poir) Gould & Clark G S G4,G5,N1

Eugenia eggersii Kiaersk. T EN S G2,N2

Eugenia haematocarpa Alain T EN E,M E G1,N1 E

Ilex sintenisii (Urban) Britton T EN E,M E G1,N1 E

Laplacea portoricensis (Krug & Urban) Dyer T EN S

Lepanthes dodiana Stimson H EN S G1,N2

Lepanthes eltorensis Stimson H EN E,M E G1,N1 E

Lindsaea stricta (Sw.) Dryander var. jamesoniiformis Kramer H S G1,N1

Lycopodium tenuicaule Underw. & Lloyd LY S

Lycopodium wilsonii Underw. & Lloyd LY S

Marliera sintenisii Kiaersk. T ENL S G1,N1

Marsdenia elliptica Decne. LI ENL S

Maytenus elongata (Urban) Britton T EN S G1,N1

Miconia faveolata Cogn. T ENL M,S G1,N1

Miconia pycnoneura Urban T EN S G1,N1

Myrcia holdridgeana Lundell T EN S G2,N2

Pilea multicaulis Urban H ENL S

Pilea yunquensis Urban (Britton & Wilson) H EN S

Pleodendrum macranthum (Baill.) v. Tiegh. T E,M E G1,N1 E

Psidium sintenisii (Kiaersk.) Alain T EN S G1,N1

Ravenia urbanii Engler T EN S

Solanum woodburyi R.A. Howard H EN M,S G1,N1,N2

Styrax portoricensis Krug & Urban T EN E,M E G1,N1 E

Ternstroemia hepatasepala Krug & Urban T ENL S G1,N1

Ternstroemia luquillensis Krug & Urban T EN E,M E G1,N1 E

Ternstroemia subsessilis (Britton) Kobuski T EN E,M E G1,N1 E

Urera chlorocarpa Urban T EN S G2,N2

Xylosma schwaneckeanum (Krug & Urban) Urban T EN S G1,N1

aSource: Liogier (1985, 1997); Little and Wadsworth (1964); Little and others (1974); U.S. Department of Agriculture, Forest Service (1997b).

bLife form: F = fern; G = grass; H = herb; LI = Liana; LY = lycopodium; S = shrub; T = tree.

cStatus classification: EN = Endemic Puerto Rico, ENL = Endemic Luquillo Mountains; USFS = Forest Service; Fed. = Federal; Nat. Her. = 

Natural Hertiage classification system: G = global, N = national, 1 = critically imperiled, 2 = imperiled, 3 = vulnerable, 4 = apparently secure, 

5 = widespread and secure; PR = Puerto Rico; E = endangered; S = sensitive; T = threatened; P = proposed for classification.
94

Other Resources

Water and Shrimp

The LEF’s water resources begin with abundant rainfall and 

intercepted cloud moisture. Seasonal variation and climatic 

phenomena along with dams and intakes in the lower stretches 

of streams all influence the quantities that ultimately reach 

the island’s coastal estuaries. On a typical day, 70 percent of 

the water originating within the LEF is diverted for use before 

reaching the ocean (Crook and others 2007).

Ten streams drain parts of the LEF, seven of them providing 

domestic and commercial water supplies to communities 

surrounding the forest (figs. 1 and 9) (appendix A). Since 1945, 

the U.S. Geological Survey has maintained at one time or 

another 17 flow gages on seven rivers (Crook and others 2007) 

(fig. 9). At the moment, 31 dams and 35 water intakes intercept 

flow at some point between the LEF and the surrounding 

lowlands (Crook 2005, Crook and others 2007):

• Puerto Rican Aqueduct and Sewer Authority, 15

• Private entities, 13

• Puerto Rican Electric Power Authority, 4

• U.S. Department of Agriculture, Forest Service, 1

•Intakes with no record of permission, 2.

In addition, water was also diverted by gravity from four 

streams (Río Cubuy, Río Sabana, Río Icacos, and Río Prieto) 

to a penstock and finally to the Río Blanco hydroelectric plant 

(Naumann 1994) (fig. 9). By the early 1990s, however, water 

removal from the first two intakes had been discontinued 

because of broken pipes. About 225 liters of water is required 

to generate 1 kilowatt hour of energy.

Shrimp are considered to be an integral part of water 

resources because they are the dominant animals accounting 

for most of the aquatic faunal biomass; moreover, shrimp 

range from highest elevations to coastal estuaries where they 

play a key role as regulators of leaf decomposition (Crook 

2005). Shrimp species migrate up and down streams during 

the year, and are vulnerable to water withdrawal during low 

flows, especially on steams with multiple dams (Crook 2005). 

Water intakes reduce shrimp habitat, negatively affecting their 

populations, diversity, and distribution. The migratory nature 

of shrimp highlights the need to protect stream connectivity 

and ecosystem health.

Before 1990, dams had been constructed for water supplies 

on all of the LEF’s major streams except the Río Mameyes 

(Benstead and others 1999). By 1993, however, the Puerto 

Rico Water and Sewer Authority had plans to install a dam on 

the Mameyes (Nieves 1998). Public opposition to the proposal 

resulted in the installation of a series of stainless steel risers 

(i.e., intakes) that allow water to be pumped out of the stream. 

This system alters the river channel and flow less than a lowhead dam and has a minimal impact on migratory species 

(March and others 2003).

In addition to human impacts, the mountain streams are 

regularly affected by natural disturbances, including 

hurricanes, high rainfalls, landslides, and debris accumulation 

such as treefalls and landslides. The abundance of palaemonid 

shrimp (Macrobrachium spp.) measured from 1988 to 2002 

in Quebrada Prieta, a tributary of the Río Espíritu Santo, 

was lowest during the 1994 regional drought. In contrast, 

hurricanes and storm flows had little influence on their 

abundance (Covich and others 2006).

Recreation

Puerto Rico’s population is approaching 4 million 

(U.S. Department of Agriculture, Forest Service 2009). From 

1975 to 1988, visits to the LEF more than doubled, reaching 

an estimated 750,000. About 60 percent of the visits were 

between April and September in either developed recreation 

facilities for concentrated use or dispersed recreation 

activities such as hiking or picnicking (Bauer 1987). The 

most recent surveys are based on a monitoring process that 

provides visitor estimates within 15 percent at the 80 percent 

confidence level (English and others 2002). By 2006, total 

forest visits had increased to about 1.2 million, with guided 

tours in 2007 bringing >110,000 visitors into the forest 

(U.S. Department of Agriculture, Forest Service 2006, 2009). 

Visitor responses showed that 40 percent were from Puerto 

Rico, 5 percent from foreign countries and the U.S. Virgin 

Islands, and the remainder from 44 states and the District of 

Columbia in the United States. Of the latter, 30 percent were 

from five states—New York, Florida, New Jersey, California, 

and Massachusetts—in descending order. About 50 percent of 

the respondents were of Hispanic or Latin origin and nearly 

60 percent between the ages of 20 and 50. Surveys showed 

that visitor use was greater on weekends and holidays than on 

week days, and that most of the visits were for viewing natural 

features or wildlife, hiking, nature activities, driving for 

pleasure, relaxing, or visiting historic sites. Local visitors were 

more common during the summer months and international 

visitors during the winter. Visitors expressed a high level of 

satisfaction with their experience on the forest.

Chapter 10. OTHER RESOURCES
95

Other Resources

Most developed facilities are located in the northern part 

of the LEF along PR route 191. The El Portal Rain Forest 

Center, situated at the forest entrance, has three pavilions 

with >900 m2 of exhibit space, a theater, a gift shop, and a 

short nature trail through secondary forest (fig. 5) (table 17).

The theme of the center is that tropical forests and its people 

are linked in a global community and that cooperative 

efforts can help conserve forests. Visitors are introduced to 

the beauty, diversity, and complexity of tropical forests and 

current activities aimed at their management. Interpretation 

is provided in six areas: an orientation, an introduction to 

tropical forests, displays promoting an understanding of 

the forest, connections (i.e., benefits and relations between 

humans and forests), forest management, and hope for 

conservation in the future.

Ascending PR route 191 toward the summits, two other major 

recreation areas border the road. The Sierra Palm Center, 

located a short distance past Yokahú tower, has picnic shelters, 

restrooms, a food concession, and access to hiking trails 

(fig. 20) (table 17). Slightly farther along the road, the Palo 

Colorado Center has similar facilities and a trail that descends 

to La Mina Falls. Other trails ascend to freshwater swimming 

pools at Baño de Oro, to nearby historic sites such as the stone 

house and trout rearing pools, and ultimately to Mt. Britton 

and El Yunque peak (fig. 20) (table 17). Parking spaces within 

lots is limited to about 200 spaces for the entire forest.

In addition to the developed recreation sites, LEF visitors 

frequent river crossings (Kartchner 2003). Surveys and vehicle 

counts were carried out at bridges over the Río Mameyes 

(i.e., Puente Roto) on PR route 988 and Río Espíritu Santo 

on PR route 186 (figs. 5 and 9). Most visitors enjoyed eating 

near the rivers and bathing. Other bridges used similarly 

were those at Quebrada Juan Diego on PR route 191 and at 

Quebrada Río Grande on PR route 186. In 1995, household 

and recreation surveys estimated the willingness of islanders 

to pay for preserving instream flows in the Río Mameyes and 

the Río Fajardo (González-Caban and Loomis 1999). Survey 

results indicated that visitors were concerned about protecting 

the environment for future generations; moreover, they would 

pay $21 per household per year to avert dams on the rivers. 

Expanded island-wide, that would yield $110 million per year. 

Surveys also showed that heavy withdrawals would reduce 

steam visitations by >90 percent.

Other recreational opportunities include bird watching, stream 

bathing, hiking, and primitive camping. The new El Toro 

wilderness protects the LEF’s only population of Amazona 

vittata and offers both solitude and serenity, rare resources in 

modern Puerto Rico.

Scenery and Trails

The summits of the Luquillo Mountains are well known 

landmarks visible from several parts of the island and 

offshore. In the past, they helped to orient sailors in 

surrounding waters. Today, spectacular views of different 

forest types and panoramas of surrounding coastal shoreline 

can be enjoyed from several accessible vantage points, 

including (figs. 5, 9, and 20) (table 17):

• The 21-m Yokahú observation tower on PR route 191 

has views of the Baño de Oro Natural Area in the upper 

Mameyes watershed, different forest types, and the island’s 

northeast coast.

• Mt. Britton Tower, located along FS-10, provides an 

overview of dwarf forest and vistas north toward El Yunque, 

east toward Pico del Este, and south to El Toro.

• El Yunque Peak at the end of FS-10, where military radar 

facilities were installed in 1942, gives visitors a panorama 

of Puerto Rico’s northeastern coast, and all of the highest 

peaks and major forest types in the LEF.

• El Yunque Rock offers a vista of the Puerto Rico’s 

northeastern coast from San Juan to Fajardo.

• Los Picachos observation point, perched on top of a volcanic 

pinnacle, provides both a rigorous climb and a good view of 

the forest.

• Pico del Oeste overview, located along FS-27, allows clear 

views of El Yunque Peak, patches of palm brake forest, 

Los Picachos, and Puerto Rico’s northeastern shore.

The El Portal Rain Forest Center is the gateway to the Luquillo 

Experimental Forest. The center has numerous informative displays, 

a theater, a souvenir store, a snack bar, and ample parking. (Photo 

by Peter L. Weaver)
96

Other Resources

Table 17—Facilities and structures in the Luquillo Experimental Foresta, b

Major facility or structurec Date(s)d Notes

Interpretation centers

El Portal Rain Forest Center 1993-96 Information center, parking, trail, theater, food concession, book store

Palma de Sierra picnic areae late 1930s Parking, wooden buildings, picnic and bathing access 

1965+ Parking, bathrooms, food concession

Palo colorado information centere late 1930s Parking, wooden buildings, picnic and bathing access 

1965+ Parking, visitor information, interpreters, souvenirs, picnic area

Picnic areas

Caimitillo 1963+ Picnic area, parrot interpretative trail 

Palma de Sierra (locations historic)e 1930s+ Original wooden facilities later replaced; 8 cement overnight cabins later converted 

to picnic shelters

1960-70s Current structures - bathrooms, water systems, picnic areas

1999 Remodelling and repairs

Palo colorado (locations historic)e 1930s+ Original wooden facilities later replaced; 10 cement overnight cabins later converted 

to picnic shelters

1960-70s Current structures - bathrooms, water systems, parking lot

Quebrada Grande 1990s Parking, picnic and day use facilities

Rio Sabana 2009 Parking, picnic and day use facilities

Observation sites

Baño de Oro (bathhouse/bathing pool)f 1935 Dug in area of Spanish gold mining pits; concrete bottom 

Baño Grande (bathhouse/bathing pool)f 1937-38 Larger facility, stone masonry dam, arch bridge 

El Yunque tower 1938 Rock and mortar walls; 360 degree view of mountains

La Coca falls (26-m waterfall) 1933 Small structure at falls built about 1991 after Hurricane Hugo 

Las Cabezas observation point 1930s Roadside parking viewpoint of northeastern Puerto Rico

Los Picachos (enclosure on pinnacle) 1938 Pinnacle with panoramic view

Mt. Britton tower (9-m tower) 1937-38 Stone masonry tower, panoramic view; nearby picnic shelter

Río Espíritu Santo NA Panoramic view west from bridge

Yokahú tower (21-m tower) 1962-63 View of Natural Area and mountains

~1991 Post-Hurricane Hugo parking lot and site improvements 

Trailheads

Angelito trail 2008 Trail to freshwater pools in Río Mameyes

Big Tree trail 1934 Site interpretation, trail to La Mina Falls

El Toro-Tradewinds trail 1935-36? Montane and Dwarf forests, El Toro peak

La Coca Trail 1930? Descend to Río Mameyes in Lower montane forest

Mt. Britton trail 1935-36? Trail to Los Picachos, El Yunque Road, and Mt. Britton

Other structures

Camp 8 (CCC work camp) 1930s CCC work center remnants (stone and concrete features) 

Catalina Service Center 1979-82 Forest management offices and parking lot; center enlarged during the mid-1990s

Cubuy House (Cienega Alta house) 1938? One story CCC-constructed ranger station; later, activity center

Eliza Colberg Girl Scout camp 1948-50 Scout field activities

El Verde Field Station 1937-39 Labs (1960-70s), meterological tower (1980s), dorm (2005)

El Yunque Pavilion (or Restaurant) 1936 Mess hall and recreation; nearby cabins built (1940); parking lot improvements (1968); 

closed by Hurricane Hugo (1989) 

El Yunque Radar Postg 1938 Tower, bathroom, diesel storage, dorm

El Yunque Tower (Microfleet Company) 1975-80 50-m tower; new facilities built by 1980

La Condesa school building late 1930s Demolished about 1990 due to recurrent flooding

La Iguaca aviary 2007 Modern facility for parrot rearing

(table continued on following page)
97

Other Resources

Table 17 (continued)—Facilities and structures in the Luquillo Experimental Foresta, b

Major facility or structurec Date(s)d Notes

Interpretation centers

La Mina barracks ~1938 Military housing; used as parrot aviary from 1972-1990s

La Mina house 1940s Ranger station; 1972-1990s, housing for parrot researchers 

La Mina trout hatchery 1934 Hatching trough, circular rearing pools

Molindero Road cottages 1936-1940s Summer vacation cottages; only 3 remain in 2010

Pico del Este radar facilities 1958-62 Two radar domes, sleeping quarters, generator building, communication facilities, 

kitchen

PR telephone communications towerh 1949 50-m tower and facilities consolidated in 1976-81

Quebrada Grande Picnic Area/parking 1978 Picnic shelters along river

Sabana house and office building late 1930s Ranger station; 1986-present, research offices, housing, labs

Stone house ~1934 Overnight ranger facilities; governor’s rest house; oldest CCC building on forest; 

future potential as museum

Summer cottages 1930s + Summer cottages built by permitees on long-term lease; program later terminated 

and most cottages destroyed

Youth Conservation Corps (YCC) Camp 1973-76 Forestry youth activities 16 to 18 years old; plaza, dorms, vocational shops, class 

rooms, mess hall, administration

Trails 

Seven historic trails by 1936 Big tree, El Toro, El Yunque, El Yunque rock, Los Picachos, Mt. Britton, 

and Río de la Mina

aPR route 191, constructed from 1926 to 1942, made other work possible along the route, including Civil Conservation Corps (CCC) activities. 

bSources: Díaz Vega (2004); Gerhart (1936), see endnotes; Huffaker (1989), see endnotes; Rivera (2010), see endnotes; Santiago Cazull (2000), 

see endnotes; Walker and others (1999), see endnotes. Some dates are approximate.

cSeveral wooden structures such as work camps, overnight cottages, shelters, guard houses, and exhibition facilities were originally built. 

Later some were replaced with cement structures. 

dDates refer to plans, construction, or opening of facilities (El Yunque Forest 2009, see endnotes). NA = date is uncertain.

eFirst called La Mina recreation area.

f

Bathing pools were closed during the mid-1950s because of safety hazard.

gA 1938 map shows the tower, which is missing on the 1941 map, most likely for World War II military purposes.

hHeavy density repeater station was formerly the El Yunque communication facilities.
98

Other Resources

Swimming pools. top: The Baño de Oro swimming pool, the first in the La Mina area, was built in the late 1930s in pits previously excavated 

by Spanish gold seekers. bottom: Baño Grande, a larger pool with an arch bridge, was built shortly afterwards in response to public demand. 

(Photos by Iván Vicéns) 
99

Other Resources

• Pico del Este, situated at the radar dome facilities at the end 

of FS-27, has views of dwarf forest, the northeastern tip of 

Puerto Rico with the Fajardo lighthouse, and the area north 

of the old Roosevelt Roads Navy Base.

Other less familiar viewpoints require considerable hiking:

• El Toro Peak along the El Toro-Tradewinds trail provides a 

panorama of the mountains.

• La Mina Peak has a similar albeit lower elevation view of 

the LEF.

• The 1970 major landslide on PR route 191 provides a view of 

the Icacos watershed and secondary vegetation dominated 

by the tree fern Cyathea arborea.

In addition to the above viewpoints, the LEF has 15 hiking 

trails totaling >40 km that offer visitors a closeup view 

of major plant and animal species (U.S. Department of 

Agriculture, Forest Service 1997b) (fig. 5) (table 18). The trails 

range in elevation from about 110 to 1074 m. The Angelito and 

El Portal trails are <200 m in elevation and another two lie 

between 250 and 450 m. Eleven trails lie ≥500 m in elevation. 

Two of these are the El Toro and Tradewinds trails that meet 

at El Toro Peak, passing through montane and dwarf forests 

en route. The hiking time required to traverse all trails would 

take about 2 days. Five trails are classified as easy, three as 

moderate, and seven as challenging. At least one forest type 

is visible from each of the trails. Points of interest include 

fauna and flora, stream crossings, different peaks, old CCC 

structures, and panoramic vistas. One possible concern 

regarding the road and trail network is that it fragments 

wildlife habitat, notably for Amazona vittata.

Other hiking or walking opportunities exist along three forest 

roads currently limited to administrative vehicle use, or at 

three recreation sites (fig. 5):

• The abandoned PR route 191, which extends from the gate 

at the mountain divide (km 13) to the landslide at 600 m 

(km 21), and then traverses the slide, and descends to a new 

picnic area along the Río Sabana near km 23.

• FS-27, which extends from the gate at PR route 930 to the 

Pico del Este radar domes.

• FS-10, which climbs from PR route 191 near km 13 to 

El Yunque Peak.

• The Palo Colorado and the Caimitillo picnic area, both of 

which have hiking trails (table 17).

The LEF also has many stream crossings and small waterfalls 

visible along the hiking trails or from bridges like the one over 

the Río Espíritu Santo on PR route 186 and La Mina Falls on 

the La Mina trail. Finally, trails parallel stretches of the three 

wild and scenic rivers (i.e., Río Icacos, Río de La Mina, and 

Río Mameyes). Much of the scenery along the Río Icacos 

lies near abandoned PR route 191, which descends from the 

mountain divide to the major landslide at 600 m.

Heritage

Heritage resources are archaeological sites, artifacts, or 

buildings that remain after past human activity, and include 

the LEF’s cultural resources from different periods such as the 

pre-Columbian, Spanish colonial, and the early 20th century 

(U.S. Department of Agriculture, Forest Service 1997b). Since 

1983, cultural resource surface inventories have been carried 

out on 3400 ha, revealing > 60 pre-Columbian and historic 

sites. Seven historic sites have been evaluated for inclusion in 

the National Register of Historic Places as a multiple property 

nomination that covers all CCC properties (Walker 1999, 

2009, see endnotes). 

Before colonization, pre-Columbian settlements in 

northeastern Puerto Rico were confined mainly to coastal 

areas. Foraging and fishing camps, agricultural plots, village 

sites, petroglyphs, and burial sites are all potential heritage 

resources in the vicinity of the LEF border. From the time 

of discovery through 1898, the Spanish were active in gold 

mining (e.g., placer and shaft mines) and agricultural activities 

in the LEF (Robinson 1997). Differences in vegetation and the 

presence of refuse dumps provide aboveground evidence of 

past mining activities. At some time in the future, subsurface 

archaeological remains may be excavated. The last major 

historical activity was the CCC work carried out during the 

1930s, which included camp sites, roads, trails, buildings, and 

bridges. The major cultural and historical resources found 

today in the LEF are (Oliver 1973, Robinson 1997):

• Petroglyph groups, including the Coca watershed (two sites), 

near the confluence of the Río Cubuy and Río Icacos, near 

the confluence of the Río Camándulas and Río Sabana, in 

the Quebrada Jiménez watershed, and near La Mina peak.

• A gold mine shaft along Río de La Mina.

• Copper mining remains at La Mina Peak.

• CCC sites and structures dating to the 1930s.

In addition, pieces of iron and pottery were found during 

the construction of the Baño de Oro facilities where the 

Spanish had previously excavated for gold (Gerhart 1936, see 

endnotes).

Several structures in the La Mina and El Yunque areas are 

historic, including the stone house, Baño de Oro and Baño 

Grande pools, Mt. Britton and El Yunque towers, and the 

La Mina barracks (fig. 20) (table 17). The CCC camp at 

La Mina was later converted into parking facilities for the 

Sierra Palm Recreation Area (Gerhart 1936). Picnic shelters 

were constructed from lumber sawn during the construction 
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Table 18—System of trails within the Luquillo Experimental Foresta

Trail name (trail location)

Map 

keyb

Length

km

Timec

h or m Difficultyd

Elevatione

m

Forest 

typesf Points of interest

Northern forest border

Angelito (PR-988, km 4.0) 1 0.7 15 m E 110-150 LM Stream crossing

El Portal (PR-191 at El Portal) 2 0.7 15 m E 160-180 LM-S Tree and bird species

El Toro-Tradewindsg 3-4 11.4 6 h C 650-1075 M, D El Toro peak

El Toro (PR-186, km 10.8) 3 4 2 h C 650-1074 M, D El Toro peak

Tradewinds (PR-191, km 13.4) 4 7.4 4 h C 740-1074 M, D El Toro peak

El Yunque trail system

Baño de Oro (PR-191, km 12.2) 5 0.6 20 m M 650-720 M CCC structuresh, trout nursery

Caimitillo (PR-191, km 12.1)i 6 0.6 20 m M 630-740 M Parrot interpretation 

El Yunque (PR-191 to FS-10) 7 4.4 2 h C 630-1050 M, D El Yunque peak, panoramic view

El Yunque Rock (on FS-10) 8 0.3 7 m E 1030-1040 D Panoramic view

Los Picachos (on El Yunque trail) 9 0.3 8 m E 900-930 D Los Picachos, panoramic view

Mt. Britton (PR-930 to FS 10, tower) 10 1.3 40 m C 760-940 M, D Mt. Britton tower, panoramic view

Mt. Britton link (El Yunque to FS-10) 11 0.5 10 m E 850-900 M, P Gradient in vegetaton

La Mina trail system

Big Tree (PR-191, km 10.4)i 12 1.4 40 m M 500-550 LM La Mina falls, large trees

Carillo (PR-988, km 6.1) 13 3.4 1 h 30 m C 250-300 LM Mameyes river, stream crossings

La Coca (PR-191, km 8.6) 14 2.9 1 h 20 m C 250-450 LM Stream crossings

Río de La Mina (PR-191, km 12.2) 15 1.2 30 m C 500-650 LM, M La Mina falls, La Mina river

Totals (15 trails) 39.9 >14 h E-C-M 110-1074 5 types Several 

aSource: U.S. Department of Agriculture, Forest Service (2008).

bMap key: Numbers are keyed to figure 5.

cTime to walk one way (h = hours, m = minutes).

dDiffculty: C = challenging; M = moderate; E = easy.

eElevation: minimum and maximum.

f

Forests types: LM = Lower montane rain forest; LM-S = secondary Lower montane rain forest; M = Montane rain forest; P = Palm brake; 

D = Dwarf forest. 

gEl Toro-Tradewinds trail was designated a National Recreation trail (U.S. Department of Agriculture, Forest Service 1997b).

hCCC = Civilian Conservation Corps.

i

Interpretative trails (i.e., signs or numbered posts with explanatory handout).

left: Yokahú tower was completed in 1962 and the parking lot was enlarged after a landslide during the 1990s. The tower is a convenient site 

for viewing different forest types and the Baño de Oro Research Natural Area. right: Two hikers enjoy the panoramic view from El Yunque 

rock, one of the best seats in the Luquillo Mountains. On this same site 70 years earlier, entomologist George Wolcott saw a swarm of Polistes 

americanus (Paper wasp). (Photos by Peter L. Weaver)
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top left: The visitors’ center at the Palo Colorado Recreation Area in the early morning hours. top right: The parking lot of the Sierra Palm 

Recreation Area at midday. The plaque commemorating the 1976 designation of the forest as a Biosphere Reserve is mounted on a boulder 

behind the umbrella in background. center left: Recreation areas have picnic shelters and hiking trails in the vicinity. right: A hiker 

walks on recently finished Angelito trail, a name which commemorates Angel Torres, a well-respected forest worker who lived and worked 

in the vicinity. The forest has 15 major trails varying in elevation, length, and scenery. (Photo by Iván Vicéns) Bottom left: A typical trail 

sign within the forest includes a map of trails within the system, trail name, length (km), time to walk (hours), hiking difficulty (easy versus 

challenging), and change in elevation (m). (All photos by Peter L. Weaver except where noted)
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top: The view from the Espíritu Santo bridge on PR route 186 highlights Puerto Rico’s northern shoreline and coastal lowlands in the background. (Photo by Iván Vicéns) bottom: La Coca Falls, located along PR route 191, is one of the best known and favorite stops for visitors. 

(Photo by Peter L. Weaver)
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of PR route 191. Soon damaged by insects, the shelters were 

later replaced with concrete buildings. The picnic and parking 

areas, however, are historic sites; moreover, the construction 

of seven trails also date to CCC days. Historic structures 

also remain at El Verde, La Condesa, and Sabana (figs. 1 and 

20) (table 17). Both the Mt. Britton and Yokahú towers are 

mentioned briefly in a regional guide that highlights historic 

structures (Instituto de Cultura Puertorriqueña 1993). The 

Mt. Britton tower was referenced as neo-medieval and Yokahú 

tower as somewhat less so in appearance.

Finally, most of the structures on Pico del Este (i.e., dormitory 

building, two radar domes, and communication facilities) 

were built around 1960 (fig. 20) (table 17). The site, abandoned 

by U.S. Navy personnel in 2003, is still used by the FAA. 

Past researchers used the dormitory building as a basis for 

field operations. Currently, Pico del Este serves as a field 

site for the collection of atmospheric data. Should the site be 

restored, future uses might include field trips to surrounding 

dwarf forest and excursions to enjoy panoramic views of 

northeastern Puerto Rico.

El Yunque Stories—Myth, Legend, and 

Curious Facts

Myths and legends are a product of time in many regions 

of the world and the LEF is no exception. Myths are false 

whereas legends may be based on observations which become 

enhanced, or possibly misinterpreted with time. There are also 

a few hard-to-believe facts associated with the forest.

First, some names used with regard to the forest have an 

interesting history. Tainos referred to the El Yunque peak and 

surrounding forest as Yuké, or white land, in reference to the 

cloud covered summits. The forest’s current name, El Yunque 

(i.e., meaning anvil in Spanish), is a corrupted derivation 

of the Taino word (Domínguez-Cristóbal 1997a, Moran 

Arce 1971). Although some may believe that the mountains 

resemble an anvil, most will agree that the summits are a 

cloud covered much of the time. Also, some say that the word 

Luquillo is derived either from the name Yukiyú or from 

Loquillo (Barnat 1987). Both refer to a previous indigenous 

chief of the early 1500s noted for his guerrilla warfare against 

the Spanish. Loquillo and his followers hid in the forests at 

the base of the Luquillo Mountains. In commemoration of his 

efforts, the municipality of Luquillo has erected a statue to the 

former chief.

Among the popular myths are those that associate the 

mountains with extraterrestrial beings and flying saucers 

(Domínguez-Cristóbal 1997a). Perhaps these stories are 

nothing more than a 3rd millennium version of pre-Columbian 

lore dealing with benevolent spirits hiding within Puerto 

Rico’s mountains (Morán Árce 1971). Another favorite 

myth is that El Yunque is connected to Roosevelt Roads 

by a complex series of tunnels. The origin of this story is 

uncertain. However, large natural cavities drain surface runoff 

into underground channels along the Tradewinds Trail and 

in the upper reaches of the Río Mameyes watershed. Perhaps 

these cavities combined with an overactive imagination and 

tabloid sensationalism helped generate the myth.

Four other stories have a semblance of truth. The first 

concerns the “Valley of the Giants,” an area which “has 

become myth” (Robinson 1997). The valley is located in a 

remote part of the Río Icacos watershed, a tributary of the 

Río Blanco (fig. 21). The intriguing name originated in 1948 

when foresters exploring the valley found several big Cyrilla 

racemiflora trees, including the LEF’s largest at 2.65 m in 

d.b.h. (Robinson 1997). Because most montane forest trees 

are small, the concentration of a few large ones anywhere 

is noteworthy. Typical d.b.h. growth rates suggested that 

a couple of these large trees may have germinated about 

the time that Columbus discovered the island. The largest 

specimen, however, appeared due to the coalescence of 

proximate stems, a phenomenon seen elsewhere (Weaver 

1986b). Among the other large trees present was a Cordia 

borinquensis measuring 44 cm in d.b.h. Cordia borinquensis, 

abundant within the LEF, rarely exceeds 6 m in height and 13 

cm in d.b.h. (Little and Wadsworth 1964). A sheltered location 

may explain the survival of these large trees, which are hidden 

in a south-facing watershed protected by the forest’s highest 

peaks—Pico del Este and Pico del Oeste to the east, 

El Yunque and Mt. Britton to the north, and El Cacique and 

El Toro to the west (fig. 9). Time and imagination have 

fashioned a legend from a walk in the woods >60 years ago.

The second tale is that the Luquillo Mountains protect Puerto 

Rico from hurricanes. Many hurricanes passing over Puerto 

Rico since 1700 had trajectories to the west of the Luquillo 

Mountains (fig. 12). Moreover, a considerable number had 

trajectories at some distance to the east. Only four hurricanes 

passed directly over the mountains, for an average of one 

storm per 75 years. Regardless, many hurricanes to the east or 

west were large enough to cause considerable damage within 

the mountains. The most recent examples are Hurricanes 

Hugo and Georges with trajectories very close to the LEF. 

Conjecture regarding the effect of the Luquillo Mountains on 

hurricane trajectories, like weather virtually anywhere, will 

likely be the subject of conversation well into the future.

A third story relates to loggers being able to distinguish 

between two types or races of Dacryodes excelsa trees 

before felling them in the field, possibly based on wood color 

or fruits (Francis and Lowe 2000, Wadsworth 2009, see 

endnotes). Similar stories have been told about other timber 

species, notably Cedrela odorata and Swietenia macrophylla
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in Central and South America. One possible explanation is 

that trees grow at different rates according to topography 

(i.e., water availability and soil fertility) and consequently 

vary in wood density and possibly other wood properties as 

well. Experienced loggers may be able to detect some of these 

properties before cutting, or at least associate them with the 

landscape.

Another tale concerns a widespread farming tradition that 

harvesting during certain lunar phases purportedly makes 

tree products more durable (Anon. 1952, Brunet 1929). This 

belief was tested in the LEF with the palm Prestoea montana

and showed that leaves harvested during the full moon had 

higher total carbon, hemicellulose, complex carbon, and lower 

calcium concentrations than leaves harvested at other times 

during the lunar cycle (Vogt and others 2002). The conclusion 

was that leaves cut at full moon display some chemical 

characteristics which should make them less susceptible to 

insect herbivory and more durable in use. In another study, 

fence posts were harvested at different times and placed in the 

ground to determine if the most durable wood was produced 

during the waning moon (Maldonado 1962). No significant 

effect was determined after 4 years. When informed of the 

results, local farmers claimed that “the study was no good, as 

it did not show what everybody knew” (Wadsworth 2009, see 

endnotes). An earlier study based on the production of field 

crops concluded that the “moon is the most variable factor” 

(May 1924). In summary, certain chemical characteristics 

of wood may vary during lunar cycles but their effects on 

product use and longevity after harvest appears to remain a 

matter of opinion.

There are also a few hard-to-believe facts. After construction 

of the weir on the Río Icacos, early measurements indicated 

that the watershed produced more runoff than rainfall (Crook 

and others 2007; Wadsworth 2009, see endnotes). Some 

explanations were suggested to help account for the anomaly, 

including possible nonlinear relationships between the basin 

Figure 21—Major designated areas within the Luquillo Experimental Forest.

" "

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PR-956 PR-966

PR-186

PR-191 PR-983

PR-915

PR-9948

*

Scenic river corredor

" " Wild river corredor

Legend

Trails

Primary roads

Secondary roads

Extension of BaÒo de Oro Natural Area - 1997

El Toro Wilderness

Other: Administration, Communications, Recreation, and Re

search

Valley of the Giants Wild / Scenic River Corredors

*

BaÒo de Oro Natural Area - 1949

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nBaño de Oro Natural Area - 1949

nExtension of Baño de Oro Natural Area - 1997

nEl Toro Wilderness

nOther: Administration, Communications, Recreation, and Research

nWild / Scenic River Corredors

 Scenic river corridor

 Wild river corridor

Legend

 Trails

 Primary roads

 Secondary roads * Valley of the giants

8 4 0 8 km

4 2 0 4 km

0 2 10 0 40 60 80

km

N
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and runoff, the addition of occult rainfall (i.e., the interception 

of cloud moisture by vegetation), or the possible occurrence of 

greater rainfalls slightly to the leeward of the peaks and ridges 

that border the eastern part of the watershed. The anomaly 

in the water balance, however, remains as does conjecture 

about its cause.Also difficult to believe is the discovery of the 

elfin-woods warbler within the dwarf forest nearly one-half a 

century after all Puerto Rican bird species were supposedly 

known (Kepler 2009). Communication with James Bond, an 

authority on West Indian birds at the time (Bond 1971), led 

to the suggestion that specimens be collected. Fritz Scheider, 

who first saw the bird in the late 1960s, didn’t collect them but, 

Cameron and Kay Kepler did in the early 1970s, ultimately 

leading to the confirmation of a new species (Kepler and 

Parkes 1972). Later during a meeting at Cornell, Scheider 

showed his field notes on plumage, behavior, and song to 

Kepler, who asked him how he felt about the discovery. 

Wryly Scheider replied, “Now I know how Leif Erickson felt” 

(Kepler 2009).

Another intriguing fact—a sign of the times—is that the 

Forest Service used to arrest cows for trespassing! Although 

it sounds strange today, during the 1930s, forest guards led 

cows that had been found grazing on national forest lands 

to municipal jails where they were held until owners paid a 

fine and related fees to reposses them (Wadsworth 2009, see 

endnotes). Trespass was considered an offense in conflict with 

efforts to protect and manage forest resources.

Finally, a current tourist promotion known as the “New 7 

Wonders of Nature” includes the LEF as one of the candidate 

sites (El Yunque National Forest 2011). Consequently, 

the forest has received ample coverage in the local media 

and numerous first time visits from a curious public. One 

impressive fact, although not a wonder, is that the forest has 

survived, largely intact, a variety of human pressures from 

early gold mining and colonization through the present. 

El Yunque, however, must remain best known for what it was 

before and remains today—a revered place for the island’s 

original occupants, and a tranquil refuge to experience nature 

for current visitors. Recently this feeling was eloquently stated 

as follows: “Para muchos de nosostros, la jornada hacia 

El Yunque es una forma de peregrinaje, casi religioso, en 

la que experimentamos el bosque virgin” (i.e., For many of 

us, the journey to El Yunque is a type of pilgrimage, almost 

religious, in which we experience virgin forest) (Valdés 

Pizzini and others 2011). Puerto Rico has no other place like 

El Yunque.
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Designated Land Uses

The Luquillo Mountains, with their steep elevational gradient, 

highly dissected topography, and wet climate provide a 

variety of habitats and diverse flora. During the past 60 years, 

the entire LEF as well as certain areas within it have been 

recognized or designated for particular uses (figs. 20 and 21) 

(table 2). These include the Baño de Oro Research Natural 

Area in 1949, the entire forest as a Biosphere Reserve in 

1976, both Wild and Scenic Rivers in 2002, and the El Toro 

Wilderness Area in 2005.

The Baño de Oro Research Natural Area

Research Natural Areas (RNAs) are tracts on which natural 

features and processes predominate and which are preserved 

for scientific or educational purposes (Federal Committee of 

Research Natural Areas 1968). The areas need not be pristine; 

however, if they are disturbed, protective measures should be 

undertaken to restore them to their original condition through 

natural processes (Dyrness and others 1975). RNAs serve as 

a baseline to compare with areas that have been influenced by 

human activity (Moir 1972).

The 745 ha Baño de Oro RNA (fig. 21) was established in 1949 

because it contained (Weaver 1994):

• Terrain unmodified by human activity, surrounded and 

buffered by other Forest Service property.

• The four forest types found within the Luquillo Mountains 

(i.e., lower montane forest, 56 percent; montane forest, 

18 percent; palm brake, 19 percent; and dwarf forest, 

7 percent).

• The lower montane forest permanent research plot (i.e., 

tabonuco ridge plot TR-1) established in 1946 at 350 m 

elevation.

• Habitat for at least 40 bird species, including populations 

of the endemic Amazonia vittata confined at that time to 

mid- and upper slopes of the Luquillo Mountains (Wiley and 

Bauer 1985).

Baño de Oro measures 3.55 km from north to south and 

4.15 km east to west. Total relief is 780 m, ranging from 

245 m along the Río Mameyes in the north to 1025 m in 

elevation at Pico del Oeste on the south. The entire area, one 

of the wettest areas in the LEF, receives additional moisture 

through fog interception on the summits. In 1968, the Baño 

de Oro was listed in the national directory of more than 

300 RNAs (as of 2007, > 430 RNAs) set aside on Federal 

lands (Federal Committee of Research Natural Areas 1968; 

Northern Research Station 2006). In 1997, forest planners 

proposed an expansion of the Baño de Oro to encompass 

a total of 2580 ha (U.S. Department of Agriculture, Forest 

Service 1997a). The proposed addition is located to the south 

and east of the original RNA (fig. 21). 

At least 10 major research activities have been implemented 

within or bordering the Baño de Oro during the past 60 years 

(figs. 9 and 21) (table 7):

• From 1946 until the present, the TR-1 permanent plot has 

been monitored, providing a continuous record of forest 

structure, species composition, tree growth, and response to 

hurricane impacts (Weaver 1998, 2002b).

• During the mid-1960s, the staff of the Arnold Arboretum 

undertook a major research effort in dwarf forest on Pico 

del Oeste (Howard 1968; for details see the Pico del Oeste 

research site).

• During the 1970s and 1980s, parrot blinds were set up in the 

upper reaches of the Mameyes watershed to study Amazona 

vittata (Snyder and others 1987).

•In 1984 and 1985, vertebrate and invertebrate faunal 

diversity was tallied in each of the RNA’s forest types 

(Weaver 1994, Wiley and Bauer 1985).

• During the mid-1980s, about 70 tree species were tallied 

during gradient sampling of tree species’ distributions by 

elevation and topography within the RNA (Weaver 1994).

• During the 1980s, studies of Black rat (Stenoderma rufum

and Rattus rattus) were initiated (Layton 1986, Willig and 

Gannon 1991, Zwank and Layton 1989).

• From 1989 to 1993, the growth phenology of Cyrilla 

racemiflora was studied, including flowering, branch 

elongation, leaf litterfall, and xylem cell growth and 

differentiation in the lower stem. These events were related to 

seasonal patterns of rainfall and temperature (Drew 1998).

•In 1991, soil chemistry and the density and biomass of eight 

earthworm species surveyed in each of the four forest types 

showed different distribution patterns according to soil 

types (Borges and Alfaro 1997).

•In 2001-02, plots were established at eight sites along an 

elevational gradient between the coastal lowland and LEF 

summits to determine forest structure and composition. Four 

sites, each representing a different forest type, were situated 

within the RNA (Gould and others 2006) (table 7).

•In 2001-02, woody stems were sampled from 400 to 900 

m in the Baño de Oro. The data were analyzed with new 

metacommunity tools to reveal community changes such 

as: clustered uphill or downhill boundaries of species 

distributions; coherence (i.e., fewer gaps); nestedness in 

species distributions; and species turnover or change in 

composition (Barone and others 2008) (table 7).

Chapter 11. DESIGNATED LAND USES
107

Designated Land Uses

Luquillo Experimental Forest Biosphere 

Reserve

In 1976, the entire LEF was designated as a Biosphere 

Reserve, which is an internationally protected area managed 

to demonstrate the values of conservation (Lugo 1987, Weaver 

1994). Biosphere Reserves are designated by the United 

Nations Educational, Scientific, and Cultural Organization 

(UNESCO) based on nominations submitted by countries 

participating in the Man and the Biosphere Program (MAB) 

launched in 1971. As of 2011, there were 564 biosphere 

reserves in 109 countries (UNESCO 2011). Biosphere 

Reserves represent voluntary cooperation among people to 

conserve resources for human benefit. The reserves provide a 

global network for cooperative research and demonstrate the 

sustainable use of resources. In summary, Biosphere Reserves 

(Man and the Biosphere 1975):

• Conserve characteristic ecosystems in one of the world’s 

natural regions.

• Contain people as an integral component and are managed 

for objectives that vary from complete protection to 

intensive, sustainable production.

• Serve as regional centers for research, monitoring, and 

educational activities for natural and managed ecosystems.

• Serve as places where local people, government officials, 

scientists, and managers cooperate in developing land 

management programs that conserve biological resources 

(i.e., soil, water, flora, and fauna) and natural processes 

while providing for human needs.

Wild and Scenic Rivers

The Wild and Scenic Rivers Act (October 2, 1968) states 

“that certain selected rivers of the Nation which, with their 

immediate environments, possess outstandingly remarkable 

scenic, recreational, geologic, fish and wildlife, historic, 

cultural or other similar values, shall be preserved in 

free-flowing condition, and that they and their immediate 

environments shall be protected for the benefit and enjoyment 

of present and future generations” (U.S. Department of 

Agriculture, Forest Service 1983).

In 2002, more than 15 km of the Río Icacos, Río Mameyes, 

and Río de la Mina Rivers, along with about 2800 ha of their 

above: El Yunque tower provides a view of the upper part of the Baño de Oro Research Natural Area (center left) and Pico del Este radar 

domes in the distance. (Photo by Peter L. Weaver) above right: The Pico del Este radar domes, built in the early 1960s, overlook northeastern 

Puerto Rico. (Photo by Iván Vicéns)
108

Designated Land Uses

watershed areas, were designated as wild or scenic rivers 

(figs. 9 and 21) (table 2). These are the only tropical rivers in 

the National Wild and Scenic River System, which currently 

protects 17 600 km of 166 rivers in 38 states and Puerto Rico 

(National Park Service 2005).

The Río Icacos is in the Río Blanco watershed. Lying within 

an intrusion of tertiary quartz diorite, the river has a sandy 

bed, numerous pools, and large boulders at lower elevation 

(U.S. Department of Agriculture, Forest Service 1997b). 

Riparian palm stands are common. The stream gradient is 

less steep near the headwaters than at the LEF border. The 

Río Mameyes is characterized by numerous large boulders, 

waterfalls, and pools of water; moreover, below its confluence 

with Río de la Mina, it passes through scenic narrows about 

1.5 km in length. The Mameyes contains several species of 

fish and shrimp, and the LEF’s only freshwater crab. Río de 

la Mina, a tributary of the Río Mameyes, has outstanding 

scenery, including large boulders, rapids, waterfalls, and small 

pools of water. Departing from the picnic areas at higher 

elevation, the La Mina trail descends to La Mina Falls, one of 

the most attractive sites within the forest. All three watersheds 

were used in the past by Amazona vittata, and are currently 

inhabited by Epicrates inornatus and other endangered plant 

and animal species.

Wild segments of designated rivers are managed free of 

impoundments and are assessable only by trail. In general, 

wild segments are managed with the following limitations:

• No road construction or development, and primitive 

standards for trails.

• No motorized or mechanized vehicle use.

• No timber harvest, water development, or mining.

• No manipulative research.

• No developed recreation—recreation is managed for 

primitive experiences, anticipating low use.

The El Toro Wilderness Area

The Wilderness Act (September 3, 1964) states that “A 

wilderness, in contrast with those areas where man and his 

own works dominate the landscape, is hereby recognized 

as an area where the earth and its community of life are 

untrammeled by man, where man himself is a visitor who 

does not remain” (U.S. Department of Agriculture, Forest 

Service 1983). The 757 wilderness areas in the United States 

occupy about 443,500 km2 and range in size from Pelican 

Island, FL with 2.4 ha to Wrangell-Saint Elias, AK with 3 675 

577 ha (Wilderness.net 2011). Although difficult to define, 

wilderness appeals to virtually everybody (Watson 2004). 

Wilderness areas provide clean air and water, natural 

habitats for flora and fauna, scenic beauty, solitude, and direct 

economic benefits to nearby communities (Dombeck 1999). 

In 1999, the Forest Service proposed a wilderness agenda 

to increase and diversify areas, and improve monitoring 

programs, recreational opportunities, stewardship, and 

collaboration among managers.

During the mid-1930s, the visiting Forest Service chief 

referred to the area encompassing El Toro as “the ruggedly 

beautiful wilderness of the Luquillo Mountains” (Silcox and 

Kircher 1936). Today, El Toro is the only tropical wilderness 

in the U.S. National Forest System. El Carmen in Mexico, 

set aside 2 months earlier, was the first tropical wilderness 

(Robles Gil 2006). Although occupying only 4050 ha and 

averaging 15 times smaller than U.S. wildernesses, El Toro:

• Covers 36 percent of the LEF, making it proportionally large.

• Extends from 370 m elevation at the Quebrada Grande along 

the northern forest border to 1074 m at El Toro Peak and is 

traversed by one trail but no roads.

• Encompasses the largest block of undisturbed vegetation in 

Puerto Rico and is largely buffered by the LEF,

• Lies within an area of tropical wet forests and contains the 

headwaters of 10 streams that provide pristine water supplies 

to surrounding communities.

• Contains four forest types and an impressive number of tree 

species, ferns, orchids, and rare plants and animals. Among 

the endemics are populations of Amazona vittata and 

Dendroica angelae.

• Lies 40 km east of San Juan and is surrounded by towns 

and suburbs, providing a steep gradient between populated 

landscapes and virtual solitude (fig. 1).

El Toro has a long history of research beginning >60 years before 

the wilderness was officially declared (figs. 13 and 21) (table 7):

• Permanent plots: Between 1946 and 1981, changes in 

stand structure, species composition, and tree growth were 

monitored on seven permanent forest plots totaling 2.8 ha 

within lower montane, montane, and palm brake forests, 

ranging in elevation between 570 and about 900 m (Weaver 

2011) (table 7).

• D.b.h. distributions: D.b.h. distributions on a permanent 

lower montane forest plot were studied over a 30 year period 

with a matrix model (Wadsworth 1977).

• Gradient sampling: Variation in forest structure and species 

composition was studied by elevation and topography on 48 

temporary plots within the wilderness, where 5,105 trees and 

89 species were recorded on only 2.25 ha (Weaver 1991, 2011).

• Riparian palm stand: Forest structure, species composition, 

ecological cycles, and hurricane impacts were described for 

a small, riparian palm plot at 750 m elevation (Frangi and 

Lugo 1985, 1991, 1998).
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Designated Land Uses

Special Use Permits

During the early 1990s, about 80 special use permits had 

been issued in the LEF: electronics and communications, 

7; outfitters and guides, 24; water supply, 15; summer 

cottages, 3; research, 11, including the El Verde field station; 

road easements, 6; organization camps, 3, including the 

Eliza Colberg Girl Scout Camp; and various others, 11 

(U.S. Department of Agriculture, Forest Service 1991, 

see endnotes; 1997b, 2008). In comparison, during fiscal 

year 2006, 97 special use permits were issued. Long-term 

permits included: outfitters and guides, 29; research, 20; 

communication facilities, 7; recreational residences, 4; water 

diversion and pipelines, 2; and 1 a piece for an organization 

camp, a road right-of-way, an electrical transmission line, 

and a food service concession (El Yunque National Forest 

2010). Temporary permits included: research, 3; filming and 

photography, 14; and recreation and group events, 14. In 

addition, renewal of the Puerto Rico Aqueducts and Sewer 

Authority permits for water storage and diversion systems 

were being evaluated. Although not considered a special use, 

permits are also required for camping.

Nearly 13 ha of land, previously covered with dwarf forest, 

have been designated for electronic and communication sites on 

top of El Yunque and Pico del Este. The El Yunque area, first 

occupied by the U.S. Army during World War II, is used by 

government and private entities and the Pico del Este site by the 

Federal government, including the FAA. The summer cottages 

are located along PR routes 9938 and 930. One structure 

previously used as a summer cottage serves as a field station for 

the Biology Department of the University of Puerto Rico.

Earlier special use permits were issued for a variety of 

activities, including the use of former Spanish concessions on 

the Arroyo and Sandoval tracts, fuelwood cutting, subsistence 

agriculture and agroforestry, public roads, screening airborne 

arboricides, and mineral exploitation (Wadsworth 2009, see 

endnotes). In contrast to permits that were granted, several 

formal requests that were considered inconsistent with the 

sustainable management of a public forest were denied. 

Among the major rejected proposals were a hotel complex 

along PR route 191, an aerial tramway from the coast to El 

Yunque, a “parrot jungle” attraction at La Mina recreation 

area, more communication towers near El Yunque, and as 

many as 249 summer cottages above La Mina recreation area 

(Huffaker 1989, see endnotes; Wadsworth 2009, see endnotes).

above: Built in the late 1940s and consolidated in the early 1980s, the island’s major communication towers are situated at nearly 1000 m 

elevation along the spur road to El Yunque peak. (Photo by Iván Vicéns) above right: The Eliza Colberg girls scout camp, dedicated in 1950, has 

provided an outdoor training center for generations of youngsters. (Photo by Peter L. Weaver)
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Major Forest Research Sites

Several sites have been used at one time or another for 

research activities within the LEF. Permanent plots exist in all 

of the forest types (table 7). Ecological studies, however, are 

concentrated at lower montane forest locations like Bisley and 

El Verde, in riparian palm stand in the upper Espíritu Santo 

watershed, and in dwarf forest on Pico del Este. Although 

much is known about certain areas, detailed floral and faunal 

surveys are lacking for the upper watersheds lying to the 

north, east, and south of FS-27 (fig. 5). Unknown wildlife 

species similar to the frog reported 50 years ago could exist 

(Rivero 1963). Rare orchids, for example, are occasionally 

confined to relatively small areas, at times a single mountain 

peak (Kasomenakis 1988).

El Verde Ecological Studies

After purchasing the land in the 1930s, the Forest Service built 

the El Verde field station to provide research personnel with 

their first permanent overnight facilities on the forest (fig. 13) 

(appendix A). Laboratory facilities were added, renovated, and 

expanded in the 1960s and 1970s, and a dormitory was built 

in 2005. A canopy walkway and a permanent walk-up tower 

with monitoring equipment were erected nearby during the 

1980s. Canopy weather data, currently monitored on the 22-m 

tower, are stored in a data logger and later sent to the El Verde 

field station. Two nearby streams are gaged, one by station 

personnel and the other by the U.S. Geological Survey (fig. 9). 

Stream discharge is also monitored and stored in a data logger.

Between 1943 and 1946, plant collecting for the Institute 

herbarium, field surveys for timber species, and the 

establishment of permanent plots were initiated near the 

El Verde field station (table 7). Plot monitoring and limited 

research were carried out in the 1950s. The next major effort 

was between 1961 and 1967 when controlled underground 

nuclear explosions were proposed for the excavation of a 

sea level canal in Panama (Mowbray 2008). Researchers at 

the University of Puerto Rico Nuclear Center in Río Piedras 

established studies to determine how the lower montane 

forest functions before, during, and after gamma irradiation 

(Odum and Pigeon 1970). The LEF was selected because it 

was the only government-owned national forest with tropical 

vegetation. The study was set up at El Verde and concentrated 

Chapter 12. MAJOR FOREST RESEARCH SITES

above: The Institute’s first long-term plot of 0.72 ha was established above the El Verde field house in 1943. Note person next to large 

Dacryodes excelsa at left middle of photo. (Photo by Iván Vicéns) above right: The El Verde field station served as the research center for the 

tropical rain forest project during the 1960s. Today it is a National Science Foundation long-term ecological research (NSF-LTER) site. The 

building in the background dates to 1937 when it was used by the forestry staff during field surveys. (Photo by Peter L. Weaver)
111

Major Forest Research Sites

on plant and animal populations, mineral cycles, metabolism, 

and energy flow within the ecosystem, as follows:

• Chapter A—energy-circuit modules, systems ecology, and 

radiation stress.

• Chapter B—past research; climate; plant species diversity, 

stand structure, and distributions; aerial photography; plant 

geometry and plant assemblages; woody plant identification 

keys and autecological studies; pollen analyses; herbicide 

effects; tropical forest associations; and other Caribbean 

forests.

• Chapter C—radiation experiment and the cesium source; 

and dosimetry, patterns of exposure, and a model of 

radiation response.

• Chapter D—effects of radiation on plant species; tree 

phenology; and hemispherical canopy photographs.

• Chapter E—radiation effects on animals; and studies on 

forest mammals, bird diversity, frogs, and insects.

• Chapters F and G—effects of radiation on microorganisms 

and cytological studies.

• Chapter H—mineral cycling in soils; forest biomass and 

chemical contents; litterfall; hydrogen budget; tritium 

movement; phosphorus cycle; electrical conductivity and 

flow rates of soil water; stomatal variation; foliar metabolite 

leaching; mycorrhiza; myxomycetes; fallout radioactivity 

and epiphytes; and the effects of ionizing radiation on leaffall and soil organisms.

• Chapter I—forest metabolism and energy flows; forestfloor organisms; insect herbivory, termites, and snails; 

photosynthesis; forest metabolism and evapotranspiration; 

and the ecological system at El Verde.

Although irradiation was the major emphasis of the project, 

many of the studies on control plots and elsewhere provided a 

wealth of information on tropical forest structure and function.

During the 1970s, the Terrestrial Ecology Division of 

the Center for Energy and Environmental Research at 

the University of Puerto Rico continued nutrient cycling 

and energy flow studies at El Verde. Between 1980 and 

1987, the Rain Forest Cycling and Transport Project dealt 

with terrestrial and aquatic food webs. After a decade of 

observations, participants summarized their observations 

on the abundance, food habits, and the ecological roles of 

vertebrates and invertebrates (Reagan and Waide 1996). After 

Hurricane Hugo in 1989, research at El Verde focused on 

post-storm recovery (Walker and others 1991, 1996) (table 6). 

Investigations concerning climate, flora, fauna, or mineral 

cycling were summarized as project documents, research 

reports and theses, or as scientific publications in journals.

Since the mid-1950s, the El Verde field station has also 

been used by forestry professionals, scientists, students, and 

teachers for educational programs. In the 1950s, participants 

from all over the world visited the site during tropical 

forestry short courses (Anon. 1954, Barres 1963, Lamb 1959, 

Wadsworth and others 1955). In the early 1960s, the field 

station was used by professors and summer students from U.S. 

universities. Recently, student volunteers have cooperated 

in data collection, as summer interns, or as participants in 

university research programs, workshops, and field trips. 

Workshops for K-12 (i.e., kindergarten through grade 12) 

teachers have also been held at El Verde and at the Eliza 

Colberg Girl Scout Camp (U.S. Department of Agriculture, 

Forest Service 2009).

Luquillo Forest Dynamics Plot (LFDP) 

at El Verde

The LFDP, established in 1990 under the auspices of the 

LTER, occupies 16 ha (500 x 320 m) near El Verde field station 

(Soil Survey Staff 1995) (fig. 13). The plot, located between 

333 and 428 m, has been forest covered since the 1930s 

(Brokaw and others 2004; Thompson and others 2002, 2004). 

About one-third was selectively logged and 7 percent farmed. 

The remainder had been cutover to varying degrees and 

partially planted to shade coffee and fruit trees (Thompson 

and others 2007). In the 1960s, about 320 m2 was clearcut as 

part of experimental work (Odum and Pigeon 1970). Today, 

the plot is part of a network of tropical forest plots managed by 

the Center for Tropical Forest Science. An order 1 soils survey 

carried out on the plot showed that upland soils composed 95 

percent of the total, ranging from gently sloping to very steep 

(Soil Survey Staff 1995). The remaining soils, characteristic 

of stream channels, ranged from gently sloping to moderately 

steep. Past charcoaling activity was evident in certain areas. 

The LFDP and similar large plots elsewhere are needed to:

• Encompass a sufficient number of common and rare species 

to evaluate population changes.

• Determine typical plant spatial relationships.

• Monitor populations of plants to reveal their life history 

characteristics (growth, phenology, and age).

• Determine forest response to disturbances such as 

treefalls, landslides, and hurricanes as well as long-term 

environmental changes associated with global phenomena 

(Zimmerman and others 1994).

The Institute for Tropical Ecosystem Studies (ITES), a unit 

within the Faculty of Natural Sciences at the University of 

Puerto Rico’s Río Piedras campus, currently carries out research 

at the El Verde field station and elsewhere in the LEF. Research 

is concentrated on long-term ecological studies relevant to the 

management of natural ecosystems. Specific areas of study are 

(Institute for Tropical Ecosystem Studies 2011):
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Major Forest Research Sites

• Population biology, community structure, and the effects of 

disturbance on tropical forests.

• Properties of atmospheric aerosols and their effects on 

clouds and climate on Pico del Este.

• Evolution of floral traits and the effects of invasive plants on 

community structure.

• Properties of inland waters, stream metabolism, 

biogeochemistry, hydrology, and water quality.

• Aquatic insects, their taxonomy, systematics, and role in 

forest ecosystems.

• Satellite image analysis and use of geographic information 

systems for habitat characterization.

• Soil processes and fauna, and the effects of natural and 

human disturbances on soils.

• Vegetation growth and changes on the Luquillo Forest 

Dynamics Plot (LFDP).

• Canopy trimming experiment, involving structural 

modification of trees, variable detritus loads on the forest 

floor, and regeneration.

A recent study was undertaken on the LFDP to determine 

the fate of 12 planted tree species after hurricanes Hugo 

and Georges (Thompson and others 2007). The species 

were: Citrus paradise Macfadyen, Mangifera indica, 

Musa sp., Simarouba glauca DC., Artocarpus altilis, 

Calophyllum calaba, Genipa americana L., Hibiscus 

pernambucensis, Swietenia macrophylla, Syzygium jambos, 

Spathodea campanulata, and Coffea arabica. The first four 

species remained relatively stable over time and the next 

six species first declined and then increased. Spathodea 

campanulata gradually increased and Coffea arabica

declined. Swietenia macrophylla and Syzygium jambos

were the only species that increased under shade. The rates 

of recruitment, mortality, and growth for all introduced 

species indicated that they would likely persist for some 

time, and in the event of greater hurricane frequency, could 

increase in population.

The canopy trimming experiment, with surrounding plot 

buffers, was set up on >1 ha of land. Different treatments 

totaled nearly 0.50 ha of pruned canopy (Richardson and 

others 2010, Shiels and others 2010). Stand manipulation 

increased light levels, throughfall, and total moisture but 

decreased litter moisture. Seedling density, ingrowth, and 

mortality were affected as Cecropia schreberiana and 

Psychotria berteroana quickly increased in abundance. The 

short interval of canopy openness and its influence on the 

regeneration of pioneer trees was the principal factor driving 

short-term recovery. Canopy opening was also the major 

determinant negatively impacting the diversity and biomass 

of the invertebrate communities within forest litter. Debris 

deposition played a secondary role. The effects of disturbance 

on some invertebrate taxa were still evident after 19 months 

when the experiment ended.

Long Term Ecological Research (LTER) 

at Bisley

In 1980, the NSF established the LTER program to provide 

scientists, policy makers, and society with a network of 

sites that would provide knowledge for the conservation and 

management of the nation’s ecosystems, especially with regard 

to maintaining their biodiversity and social benefits. The 26 

selected sites include a variety of ecosystems and researchers 

with a common mission. The Luquillo LTER was authorized 

in 1985 to explore tropical forest structure, dynamics, and the 

role of disturbance (Scatena 1989). Part of the program was set 

up in the Bisley experimental watersheds situated near Sabana 

in the northeastern part of the LEF (fig. 13). Both watersheds 

range in elevation between 265 and 455 m (Scatena 1989, 

Scatena and Lugo 1995). The soils are classified as clayey, 

highly leached, and well-weathered ultisols. Logging and the 

planting of subsistence crops like coffee, bananas, and upland 

rice occurred between 1830 and 1890. In the early 1930s, the 

Since 1985, the Bisley watersheds have been a center for National 

Science Foundation long-term ecological research (NSF-LTER) 

regarding climate, water resources (i.e., water quantity, quality, and 

regimen), nutrient cycling, flora and fauna, and other topics. (Photo 

by Peter L. Weaver)
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Major Forest Research Sites

Forest Service purchased the tracts (Zimmerman and others 

1995). Subsequently, agriculture was abandoned and farmlands 

reverted to secondary forest. Khaya nyascia and Swietenia 

macrophylla were planted in gaps and openings. After 50 years, 

the net result of human activities was an increase in Guarea 

guidonia, Inga laurina, and I. vera, all previously used as coffee 

shade, and the presence of exotic timber species. In summary, 

“although the experimental drainages were never completely 

cleared or drastically altered, they have been selectively logged, 

fished, and probably exploited for placer ores” (Scatena 1989).

Much of the early research concerned introductory work and 

ecosystem responses to Hurricane Hugo, as follows:

• Physiography and history of the watersheds, and the effects 

of human activity on the structure and composition of the 

forest (García Montiel and Scatena 1994, Scatena 1989).

• Climate and water discharge monitoring (Scatena 1990).

• Hurricane impacts on tree species regeneration, biomass, 

litterfall, and nutrient contents (Chinea 1999, Lodge and 

others 1991, Scatena and others 1995).

• Flora, with an annotated plant list with 102 plant families, 

255 genera, and 336 species of tree species, herbaceous 

plants, vines, and lianas (Chinea and others 1993, Rice and 

others 2004).

• Wildlife, including freshwater fish, frogs, and snails (Nieves 

1998).

• Biomass and nutrient cycling, including the spatial 

variability in nutrients, factors controlling their availability 

to vegetation, and their distribution in soil and plants 

(Scatena 1998a, Scatena and others 1993).

Since 1986, LTER researchers have written >800 abstracts, 

research papers, theses, and dissertations (Almanac 2009) 

(LUQ LTER 2011). Today, program cooperators are exploring:

• Climatic effects on litter quality and the regulation of 

decomposition.

• Response of terrestrial and aquatic food webs to detrital 

pulses.

•Impact of disturbances on nutrient cycling, plant 

communities, and organic matter accumulation.

• Carbon export relations in watersheds and their association 

with soil characteristics and detrital dynamics.

• Effects of climatic changes over an elevational gradient on 

detritivore communities and their feedback on litter inputs 

and decomposition.

• Critical zone dynamics, a recently funded project, to address 

how processes, flow, and transformation of materials differ 

in landscapes with different bedrock but similar climates, 

land use, and geologic histories.

Riparian Palm Stand

In 1980, riparian palm research began on a 0.25-ha plot 

located at 750 m in the headwaters of the Río Espíritu Santo 

(Frangi and Lugo 1985, 1991, 1998). The studies revealed:

• About 765 stems >1 cm in d.b.h. of 27 tree species grew on 

the plot.

• Prestoea montana accounted for 40 percent of the tallied 

stems.

Biomass sampling was carried out several times in different parts of the Luquillo Experimental Forest, including Bisley, El Verde, Pico del 

Este, and this area of line planted mahogany near the Río Chiquito. (Photo by Peter L. Weaver) 
114

Major Forest Research Sites

• About 68 percent of the vegetation biomass was in the wood, 

10 percent in leaves, and 22 percent in the roots.

• Details regarding the carbon, phosphorus, and water cycles 

(i.e., rainfall, throughfall, stemflow, interception, runoff, 

transpiration, and evapotranspiration).

Periodic flooding, poor soil aeration, heavy annual rainfall, 

and low atmospheric saturation pressure deficits were 

suggested as the controlling factors in the growth of the palm. 

After Hurricane Hugo, the palm plot, protected by topographic 

position, showed only 1 percent tree mortality. About 30 

percent of the trees had suffered notable impacts, mainly in 

the canopy, with 10 percent of the aboveground biomass being 

transferred to the forest floor. Changes in necromass (i.e., the 

weight of dead organisms) and nutrients on the forest floor 

were also summarized for a 20-year period (Lugo and Frangi 

2003). A point of interest—the riparian palm plot included a 

portion of permanent plot CV-1, which was established along 

with other permanent plots in 1946 (fig. 13) (table 7).

Pico del Oeste Dwarf Forest

Beginning in mid-1960s, research was undertaken in dwarf 

forest on Pico del Oeste to answer questions regarding the 

composition of plant species, their growing conditions, and their 

adaptations for survival in the summit environment (Howard 

1968, 1970a). From 1968 to 1977, the Journal of the Arnold 

Arboretum published 17 articles on the following topics:

• An introduction and review of cloud forest habitats, a list of 

vascular flora found on Pico del Oeste and their geographic 

distribution, and observations on stem growth and form, 

and on leaf structure, damage, and herbivory (Howard 1968, 

1969).

• The microclimate of the summit, including rainfall, 

temperature, relative humidity, solar insolation, and cloud 

moisture interception (Baynton 1968, 1969).

• Transpiration rates (Gates 1969), chromosome numbers 

in flowering plants (Nevling 1970a), chemical studies of 

colored leaves (Wagner and others 1969), and phytochemical 

screening (Persinos and others 1970).

• Aerial roots (Gill 1969), and relations among soils, roots, and 

earthworms (Lyford 1969).

• Numerous plant studies, including two species of 

Marcgravia (Howard 1970b), a new species of Gonocalyx

(Nevling 1970b), epiphytic mossy vegetation (Russell and 

Miller 1977), leafy Hepaticae (Fulford and others 1970, 

1971), and algae (Foerster 1971).

• The dwarf forest flowering and fruiting cycles and an 

interpretation of seasonality (i.e., wet-dry periods) in a high 

rainfall environment (Nevling 1971).

The vascular flora on Pico del Oeste numbered 85 species, 

including 40 Dicotyledoneae (22 endemic to Puerto Rico), 

14 Monocoyledoneae (2 endemic), and 31 ferns (3 endemic) 

(Howard 1969). Pico del Oeste contained 62 of the 156 leafy 

Hepaticae tallied within the LEF. Also encountered were 

18 epiphytic mosses and 129 epiphytic algal species.

Heavy rainfall, the high incidence of fog, cloud moisture 

interception, and attenuation of solar radiation were considered 

as unusual climatic features on Pico del Oeste (Baynton 1968, 

1969), leading one observer to suggest that the dwarf forest was 

a “large natural culture unit” (Foerster 1971, page 107). Soil 

leaching was considered a possible contributor to reduced tree 

stature whereas wind, although persistent, was not.

Pico del Este Dwarf Forest

Research near Pico del Este, about 1.5 km distant from Pico 

del Oeste, started in 1968 and has covered three major topics:

• Cloud moisture interception (i.e., deposition of fog) by 

vegetation on windward, ridge, and leeward sites in 1968-69 

(Weaver 1972).

• Monitoring of dwarf forest recovery after a 1968 airplane 

wreck (Byer and Weaver 1977; Weaver 1990, 2000b, 2008; 

Weaver and others 1973).

• Monitoring post-Hurricane Hugo recovery after 1990 on six 

small plots, two each on ridge, slope, and ravine topography 

(Weaver 2000a, 2008).

The cloud moisture study revealed that intercepted cloud 

water added about 10 percent to the annual moisture budget of 

dwarf forest soils, and highlighted the importance of summit 

vegetation in the water balance of the LEF. Continuous 

monitoring at the airplane wreck and on the small plots near 

Pico del Este showed that that the growth and recovery of dwarf 

forest trees from past disturbance was very slow; moreover, 

monitoring indicated that delayed mortality continued for 

several years after the passage of Hurricane Hugo.

In 1968, much of the 2-m wide trail leading 0.5 km to the 

plane wreck was under dwarf forest canopy. Grass and ferns, 

however, dominated two exposed areas. These patches, still 

evident 40 years later, now contain scattered tree seedlings 

and small saplings. By 2000, after Hurricanes Hugo and 

Georges, most trees shading the trail had perished, leaving 

much of the area in thickets of regenerating stems. Nearly a 

century ago, hurricanes were suggested as a factor in dwarf 

forest occurrence when La Mina Peak was found stripped of 

vegetation (Murphy 1916, Wadsworth 1970).
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Forest Planning and Management

Puerto Rico’s forests declined dramatically from nearly 

complete cover at the time of European discovery to about 

6 percent forested in the early 1940s (Birdsey and Weaver 

1982, Wadsworth 1970). The small forest areas that survived 

reasonably intact were at highest elevations. In the case of 

the LEF, most of the montane, palm brake, and dwarf forests 

survived along with more isolated areas of lower montane forest.

By 2000, the combined population of the greater San Juan 

metropolitan area and larger towns surrounding the Luquillo 

Mountains was approaching 1.6 million, or more than 40 

percent of the island’s inhabitants (CEEPUR 2009) (fig. 1). 

The different forest types, attractive vistas, abundant water 

resources, and cool climate, especially near the summits, 

make the LEF one large, conveniently located refuge where 

visitors can glimpse into the island’s past before human 

settlement and major modifications to the environment.

A survey of the >75 800 ha within eight municipalities 

surrounding the LEF during the 1990s showed 54 percent 

classed as agriculture, 26 as forest, 13 as developed or 

available for development, and 7 percent as protected (Lugo 

and others 2000). Lands in the area were undergoing two 

major trends: an increase in urban and suburban development; 

and a decline in agriculture and pasture accompanied by 

an increase in forest regeneration (Ramos González 2001). 

The Puerto Rican Planning Board suggested a buffer zone 

around the LEF in 1983, amended in 1991, to promote its 

conservation. Development, however, continued in violation of 

the suggested norms (Lugo and others 2000, 2004). Continued 

development near the border along with the uncertain effects 

of global change may make the LEF warmer and drier in 

the future (Crook and others 2007, Scatena 1998b). The 

hydrologic cycle could be altered, affecting water availability 

for ecological processes and human activities. Moreover, 

some global models project that hurricanes may become 

more intense and frequent. Such phenomena could have a 

dramatic impact on the LEF’s forests causing migrations or 

losses of flora and fauna as well as changes in tree species 

abundances and distributions favoring secondary species 

with shorter life spans at the expense of primary species 

(Connell 1978, Scatena 1998b). Several species of frogs have 

already declined or disappeared (Joglar 1998). Increased 

temperatures, particularly during the summer months, could 

also negatively affect lizards that are normally active at low 

body temperatures, such as those that occupy tropical lowland 

forests (Huey and others 2008).

As part of the National Forest System, management of the 

LEF must follow the principal laws relating to Forest Service 

activities such as the Multiple-use Sustained-Yield Act of 1960 

and the National Forest Management Act of 1976 

(U.S. Department of Agriculture, Forest Service 1983). In 

1992, the Forest Service adopted a new operating philosophy 

called ecosystem management aimed at an ecologically 

balanced view of its responsibilities (Wellock 2010). Fashioned 

by the Northern Spotted Owl controversy, the Forest Service 

outlined four key principles to successful land management: 

(1) sustainability; (2) public involvement through comments 

and partnerships; (3) integration with interdisciplinary 

approaches; and (4) collaboration among all interested parties.

Puerto Rico is an island, not a continent, and the LEF is a 

small mountainous landscape located in the northeastern 

corner of that island. Some “multiple uses” that are sustainable 

in larger national forests may be incompatible in the LEF. 

Management modifications have been suggested for the LEF 

based on climate, parrot breeding, migrations of aquatic 

organisms, and seasonal use of recreation sites (Scatena 2002). 

Some suggestions relating to wildlife (i.e., the Puerto Rican 

parrot) are already in use; others dealing with stream fauna, 

water use, and recreation could have future application.

As part of the planning process, the Forest Service solicited 

comments regarding management alternatives for the draft 

version of the forest management plan. Public comments were 

submitted by 23 individuals, 16 Federal and commonwealth 

government agencies, and 14 organizations. The following 

topics, tentatively ranked according to the number of 

responses, were viewed by the public as major forest issues 

(U.S. Department of Agriculture, Forest Service 1997b, pages 

H-1 to H-142):

• Timber extraction—mostly against, with a few suggesting 

restrictions or site changes before implementation.

• Primary forest, wilderness, wild and scenic rivers, and the 

research natural area—all positive, highlighting the public’s 

concern for forest protection.

• Mass transportation (trams or buses)—all in favor of 

alleviating traffic congestion along the highway but most 

against reopening PR route 191 blocked by a landslide 

40 years ago.

• Property—all in favor of regulation of land development 

surrounding the forest and acquisition of property, including 

inholdings.

• Wildlife and habitat—all in favor of rare, endangered, and 

threatened wildlife protection, especially the parrot.

• Water and watersheds—some concerned about soil erosion, 

sedimentation, and water quality, quantity, and regimen 

during the year.

Chapter 13. FOREST PLANNING AND MANAGEMENT
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Forest Planning and Management

• Recreation—some concerned about recreation sites, trails, 

field interpretation, public education, tours, camping, site 

overuse, garbage, and noise.

• Research—most with favorable responses regarding 

research and the use of new information.

• Culture and history—a few concerned about forest history 

and protection of cultural resources.

• Special use permits—a few with comments about access 

roads and forest permits, including electronic sites.

• Law enforcement—some with comments on control at the 

forest border, entrance fees, and field monitoring to help 

maintain the forest.

• Other topics—stated at least once, biodiversity, biosphere 

reserve, use of native plants, species introductions or 

reintroductions, the fish hatchery, vacation cottages, forest 

swimming pools, nontimber products, use of herbicides, 

scenery, flights over the forest, volunteers or scouts in the 

forest, the planning process, and reclassification the LEF 

under the U.S. National Park Service or commonwealth 

environmental agencies.

The LEF’s revised management plan provided direction and 

management guidelines under several topics—primary forest, 

sustainable timber production, wildlife, water, recreation, wild 

and scenic rivers, wilderness, access roads, and research—

for the next 10 to 15 years (U.S. Department of Agriculture, 

Forest Service 1997a, 1997b) (table 19). The plan divided 

the forest into two major uses: protection, including the 

wilderness, the research natural area, and wild and scenic 

rivers, totaling about 65 percent of the LEF; and human 

activities, including administration, communications facilities, 

recreation, and research (fig. 21) (table 19). The planning 

directives are considered below under nine headings.

Primary Forest

Primary forests are undisturbed by humans and contain 

the original structure and composition of species that 

characterized the island before settlement, including many 

rare and endemic plants and animals. Today, Puerto Rico’s 

undisturbed primary forests cover < 1 percent of the entire 

island (Wadsworth 1949, 1950). About 50 percent of the LEF, 

or 5550 ha, contains forested lands that are virtually 

in primary condition.

The LEF’s most valuable resource is its pristine forest land. 

Much of the primary forest has already been set aside as the 

El Toro Wilderness, totaling 4050 ha, or as part of the current 

Baño de Oro Research Natural Area (fig. 21) (table 2). The 

Baño de Oro, with a total of 2580 ha, includes the original 

1949 tract of 745 ha and the proposed 1997 expansion of 1835 

ha (U.S. Department of Agriculture, Forest Service 1997a; 

Weaver 1994). The scarcity of primary forest on the island 

Table 19—Management areas in the Luquillo Experimental Foresta

Management areab

Area

hac Description

Protected areas

Research Natural Area 2580 Existing and proposed expansion of Baño de Oro (i.e., non-manipulative research)

Wild and scenic rivers 524 Designated in 2002

Wilderness 4196 Designated in 2005; boundaries not marked in field

Subtotal 7300 All areas designated primarily for protection (64.6 percent)

Other areas

Administrative sites 83 El Portal, Catalina Work Station, other Forest Service administrative facilities

Communication sites 79 El Yunque and Pico del Este communication facilities, associated roads, electrial transmission lines 

(special use permits total only 13 ha)

Developed recreation 469 Picnic sites, trailhead parking, decentralized interpretative facilities

Integrated activities 2517 Dispersed recreation and research

Research 372 Long-term ecological research (LTER) watersheds, forest dynamics plot, permanent forest plots, 

treatment-control studies

Timber demonstration 472 Sustainable timber production (inactive at moment)

Subtotal 3992 All areas designated primarily for human activity (35.4 percent)

Total 11 292 All areas combined

aData from management plan (U.S. Department of Agriculture, Forest Service 1997a, 1997b).

bAreas shown on maps (figs. 21 and 22).

cBased on total land area during planning activities in the mid-1990s.
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Forest Planning and Management

and its intrinsic value to society are major concerns. During 

the past, virtually every square kilometer of Puerto Rico was 

heavily impacted by human activity. Another issue is the 

unknown future impact of global warming on the island’s 

forests and its possible impact on the LEF’s wildlife.

“Casual observers underestimate the role of continuous use 

of trails and recreation use in modifying the ecology of forest 

stands, behavior of animals, abundance of species, and spread 

of exotic species” (Lugo 1994). It is encouraged that if trail 

development or other increases in human activity are proposed 

for the wilderness that all potential impacts are considered 

with a focus on endangered and endemic species, notably the 

parrot. The main island of Puerto Rico has no other place 

that qualifies for wilderness. Careful monitoring of flora and 

fauna within the wilderness, however, could yield important 

information for improved forest management.

Demonstration of Sustainable Timber 

Production

Sustainable production of wood is needed throughout the tropics 

and the LEF has the potential to demonstrate the productivity of 

managed secondary forests. Previously logged and cultivated, 

the lower slopes of the forest have either recovered naturally 

or have been planted with timber species, mainly Swietenia

hybrid and a few other species. Earlier versions of the forest 

management plan suggested that a small scale sustainable 

commercial timber harvest could be implemented on lands 

reforested since the 1920s. The proposal for commercial timber 

harvest, however, was highly controversial and was suspended 

in the revised plan due to public outcry (U.S. Department of 

Agriculture, Forest Service 1997b).

As urban expansion continues, the LEF’s forest ecosystems 

become increasingly more valuable as an integral unit to 

protect flora, fauna, and water resources benefiting the heavily 

populated northeastern part of the island. Timber harvest 

could negatively impact roads, soils, water quality, wildlife 

habitat, and recreation. Logging could remove future foraging 

and nesting sites, and slow the expansion of the parrot back 

into previous habitat along the LEF border. Sustainable 

timber harvest could be demonstrated on privately owned 

forest lands and at selected sites within the drier forests of the 

commonwealth reserve system.

Wildlife

Puerto Rico’s dense human population either cleared or 

modified most of the island’s forests during settlement 

and development. Today, secondary forests are gradually 

recovering outside of the LEF, but most of those areas differ 

significantly in species composition and are privately owned 

(Birdsey and Weaver 1982, Brandeis and others 2007, Franco 

and others 1997). The upper LEF contains not only the largest 

block of undisturbed forest on the island but also the wettest. 

Moreover, it has a diverse flora and fauna, including several 

island endemics some of which are confined to the LEF. 

Endangered, threatened, and sensitive species living within 

the LEF are primary management concerns (U.S. Department 

of Agriculture, Forest Service 1997a).

Recent research suggested that estimates of avian extinctions 

based on species-area relations overestimated actual 

extinction rates caused by habitat conversion whereas the use 

of a species-area relationship based on endemics improved 

those estimates (Kinzig and Harte 2000). Moreover, a critical 

level for extinctions appeared after 40 percent of an original 

habitat has been cleared. In summary, “At low levels of habitat 

destruction, estimates of species loss using the endemics-area 

relationship are significantly lower than existing estimates, 

but a rapid rise in predicted species loss when a threshold 

of habitat loss is exceeded suggests that extrapolation of 

recent rates of species loss may underestimate future species 

extinctions under continuous land clearing” (Kinzig and Harte 

2000). The possible implications of these derived relationships 

for the LEF are uncertain. It is noteworthy, however, that the 

LEF contains many endemics, that about half of the LEF has 

already been disturbed by past human activities, and that 

development continues in areas surrounding the forest.

Some proposed activities within the LEF could involve 

disturbance and habitat change. Among them is an increased 

presence of humans whose impact may extend as far as 

0.5 km beyond the roads and recreation areas that have been 

built for their activities (Snyder and others 1987). An endemic 

parakeet (Aratinga maugei) was last recorded late in the 

19th century and Corvus leucognaphallus in 1963. By 1968, 

Amazona vittata was listed as rare and endangered. Today, 

two of the LEF’s frog species, Eleutherodactylus eneidae and 

E. karlschmidti are threatened, or possibly even extinct. Three 

others, E. gryllus, E. locustus, E. portoricensis, have declined 

in numbers. Moreover, Dendroica angelae is being considered 

for listing as an endangered species (tables 11 and 12). Most 

wildlife has survived to the present because the mountainous 

interior remained largely isolated and intact.

Future management would benefit from the suggestions of 

experts who have studied wildlife, notably the parrot. One 

pointed out the importance of Dacryodes excelsa fruits as 

parrot food from August through November (Rodríguez-Vidal 

1959). Others stated that “attempts to spread recreational 

activities more evenly through the forest could have disastrous 

consequences. Parrots are exceedingly sensitive to human 

disturbance near their nests ...” (Snyder and others 1987). 

They added that “most of the present parrot range in Luquillo 
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Forest Planning and Management

Forest is well protected. Still unresolved is the question of what 

areas of lower elevation forest might be reserved for parrot use 

if the population should recover from its present depressed 

condition” (Snyder and others 1987). They also pointed out that 

the undisturbed Cristal-Camándulas area in the northeastern 

part of the forest appeared to be a good site for the future 

release of parrots. An important point to consider for parrot 

management is that the species may never recover in the LEF if 

better lands are not made available at lower elevations.

The critically small parrot population is largely confined 

to only 1500 ha within the El Toro Wilderness Area. The 

area is bounded east and west by two roads, FS-10 and PR 

route 186, with their associated human presence and noise 

(U.S. Department of Agriculture, Forest Service 1997a, 

1997b). The lands surrounding the LEF—abandoned pasture, 

suburban housing, and secondary vegetation—are currently 

not occupied by the parrot. Extinction is most likely for 

species that require large territories for survival, especially 

in areas like the LEF which experience recurrent hurricanes. 

Isolated landscape remnants can experience an influx or 

“supersaturation” (Saunders and others 1991) of species, 

including predators, from surrounding areas. Red-tailed 

hawks, a major threat to the parrot’s survival, abound in the 

LEF where they find adequate prey like lizards and forest 

birds, including parrots. In addition, they have access to a 

“buffet of domestic prey: chickens, pigeons, sundry pets 

including puppies and kittens, scavenging rats, mongooses, 

and no longer truly wild native doves, grackles, and other 

birds that have come to survive on table scraps and the 

panhandled crumbs of human largess” in the suburbanized 

areas surrounding the forest (Watlington 2008). There would 

be great value in seeking a means to extend the parrot’s range 

throughout the LEF and into lower elevations near the forest. 

One approach could involve an integrated landscape that 

protects the forest intact and incorporates land stewardship 

efforts on the part of surrounding landowners (Saunders 

and others 1991). Critical parrot habitat in mature lower 

montane forest must remain protected. Also, some suggest 

that secondary forest along the LEF’s border “is critical to 

the recovery of the PR parrot (especially advanced secondary 

Tabonuco [i.e., lower montane] forest ...” (U.S. Department of 

Agriculture, Forest Service 1997b).

Other current management concerns for LEF wildlife are:

• Defining, expanding, and demarcating critical wildlife 

habitats as a priority, including lower montane forest for the 

future expansion of parrot populations.

• Monitoring management practices to assure the protection of 

wildlife habitat, especially in the heavily used forest interior 

where refuse can support introduced pests like mongooses 

and rats.

• Enforcing Puerto Rican Parrot restrictions at all times, 

notably during the breeding season (i.e., “plan other 

activities ... at least 500 m from [parrot] nest sites” 

(U.S. Department of Agriculture, Forest Service 1997a).

• Restricting entry into Amazona vittata areas during nesting 

season.

• Cooperating with the FAA to restrict flights over the LEF to 

help protect the parrot during the recovery program.

• Controlling and monitoring access to the wilderness area 

(i.e., the currently occupied parrot habitat) because of 

associated problems of noise, refuse, and introduced exotics.

• Ameliorating downstream barriers to fish and shrimp 

migrations, and control of poaching.

• Establishing and enforcing norms for site use and 

monitoring access to favorite recreation areas to assure that 

resource quality is maintained (e.g., La Mina Falls and the 

issues of congestion, sanitation, water quality, and noise).

Water

Densely populated northeastern Puerto Rico receives water 

supplies from intakes within and just below the LEF boundary 

(Naumann 1994). Moreover, forest streams provide habitat 

for aquatic organisms, including fish and shrimp, throughout 

much of their extent. The maintenance of aquatic linkages 

between coastal lowlands and higher elevations is imperative 

if these organisms are to be protected. Diversion of water for 

domestic and other uses reduces streamflow and impedes 

migrations of aquatic organisms.

Population growth, urban and suburban development, and 

tourism will increase water demands in the future. Moreover, 

leaky pipes cause water losses within the island’s current 

delivery system. Losses between the reservoirs and the 

island’s domestic and commercial users average about 43 

percent (Crook 2005). Better water management requires 

(Crook 2005, Naumann 1994):

• Monitoring of LEF’s water resources and biota to assure 

sufficient flow for aquatic organisms, notably in dry years.

• Recognizing the cumulative effects of water withdrawal and the 

limited capacity of streams to simultaneously provide sufficient 

water for aquatic wildlife and municipal water supplies.

• Developing alternative “ecologically friendly” water control 

devices that facilitate wildlife migrations where feasible 

(e.g., in-channel intakes consisting of stainless steel risers or 

intakes with outlets for minimum flow in lieu of dams).

• Requiring construction of future water intakes at or below 

the LEF border to maintain the ecological integrity of the 

forest.

• Requiring maintenance of all water intakes, informing users 

of findings, and imposing fines in cases of negligence.
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Forest Planning and Management

• Requiring local government agencies to assume 

responsibility for reducing island water demand, including 

repair and maintenance of pipes to reduce water losses 

during delivery.

• Taking appropriate measures against illegal water removals.

• Considering further price increases for water to help reduce 

consumption.

“Puerto Rican public water supply has been poorly maintained 

and managed” in the past (Naumann 1994). The ecological 

integrity of the LEF depends on the appropriate conservation 

and management of its water resources. The local government 

is well aware of water distribution problems and is attempting 

to implement conservation measures.

Wild and Scenic Rivers

Three stretches of rivers within the LEF—the Río Icacos, 

Río de La Mina, and Río Mameyes—have been set aside as 

exceptionally attractive scenic areas; moreover, the upper 

portion of the Río Mameyes has been designated as wild 

(fig. 21). These are the only tropical rivers within the national 

Wild and Scenic Rivers system and should remain protected 

through management guidelines. Future water extraction from 

these streams is prohibited (Crook 2005).

Río de La Mina is not only a scenic river, but its attractive 

waterfalls border an area currently classified in the 

management plan as occupied parrot habitat (U.S. Department 

of Agriculture, Forest Service 1997b). The distance of the 

waterfalls from PR route 191 is about 30 minutes for most 

hikers. Local holidays draw massive influxes of people for 

bathing and picnicking near the waterfalls. Noise from the 

site may be heard for a considerable distance providing 

an experience incongruent with the solitude of the forest. 

Moreover, on crowded days, heavy human use around the 

falls may temporarily alter the stream’s chemical composition 

(e.g., human wastes, body lotions, discarded food, and refuse) 

and affect population of algae and aquatic organisms in the 

vicinity. Large groups can also negatively impact riparian 

vegetation causing streambank and soil erosion, especially 

in instances where crowded conditions force some bathers to 

seek alternative bathing sites downstream. Finally, some more 

daring bathers climb the slippery rocks behind the falls, an 

activity that could result in serious injury.

Past experience with water-based activities at higher elevation 

within the same watershed —the near the La Mina Recreation 

Area—were disastrous. “During the 10 years that the pools 

were open we found it impossible to control safe use (e.g., 

drinking and nighttime use) and there were several fatalities” 

(U.S. Department of Agriculture, Forest Service 1997b). 

Swimming and bathing in the freshwater pools have been 

prohibited since the 1950s. The current heavy use of the 

La Mina waterfall site for bathing and water play involves 

issues of water pollution, safety, and future use of the forest by 

the parrot. More accessible bathing sites are available at lower 

elevations near the forest border. 

Wilderness

Naturalness, wildness, and protection from human influence 

highlight the values of wilderness to society. However, during 

the past 17 years, rapid suburban development has occurred 

in areas adjacent to the El Toro Wilderness (Lugo and others 

2004, Ramos González 2001). Active cooperation with the 

local government will be required to enforce buffer zone 

legislation around the forest (Lugo and others 2000, 2004).

Future management of the wilderness needs to define goals 

and desired conditions, and needs to recognize the issues or 

problems that lie between existing and desired conditions 

(McCool and Cole 1997). Several planning processes, 

including the limits of acceptable change, have been proposed 

as a means of improving recreation management in protected 

areas (i.e., specifically, the issue of recreation carrying 

capacity in wilderness areas).

The El Toro-Tradewinds trail, first constructed during the 

CCC days, traverses the wilderness area (figs. 5 and 21). 

Heavy rainfalls and recurrent storms cause treefalls, trail 

erosion, and landslides, notably in drainages and ravines. 

Future trail maintenance expenses could affect access to the 

wilderness. Limiting and monitoring access could reduce 

encounters among hikers (U.S. Department of Agriculture, 

Forest Service 1997a) and would help assure that the wilderness 

remains what the term implies—an experience with nature. 

Recently, a noninvasive plant management plan was drafted. 

The tentative plan indicated that at least 82 exotic plants were 

already growing in the wilderness area (U.S. Department of 

Agriculture, Forest Service 2009, see endnotes).

Other issues to consider are (U.S. Department of Agriculture, 

Forest Service 1983, 1997b):

• Marking wilderness boundaries according to Congressional 

designation.

• Preparing a wilderness plan, including limits of acceptable 

change.

• Maintaining primitive standards for maintenance work 

(e.g., nest cavities in coordination with the Puerto Rican 

Parrot program).

• Conducting research on the flora, fauna, insects, and 

disease, and the mapping of wildlife habitats and cultural 

sites according to management guidelines.
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Forest Planning and Management

• Requiring permits for plant or animal collections.

• Prohibiting timber harvest, timber salvage, and manipulative 

forest research.

• Prohibiting road construction or other developments 

(e.g., water and electrical transmission lines), mineral 

activity, and motorized or mechanized bicycle use.

• Authorizing recreation management for low use and 

primitive experiences such as special use permits for 

nonoccupancy activities compatible with wilderness 

character. The issue of aircraft flying low over the LEF 

recently came to the attention of forest managers and the 

public. Although such flights are presumably prohibited to 

help recovery of the Puerto Rican Parrot, they apparently 

take place recurrently as witnessed by two recent accidents, 

the last of which occurred in 2008 within the wilderness area 

(Hernández Pérez 2008, Torres 2002). Low-flying aircraft 

must be excluded from the airspace above the entire LEF for 

safety and wildlife reasons. In the case of wilderness, low 

flying aircraft could also be viewed as issues of air quality or 

noise pollution such as an intrusion on the natural soundscape 

(Landres and others 2008).

Recreation and Conservation Education 

Programs

Current recreation activities include driving, scenic viewing, 

picnicking, hiking, stream bathing, and nature study. Use of 

summer cottages near La Mina and camping are minor activities. 

Most current forest visits are confined to daylight hours. 

Most recreation sites are concentrated along the major 

roads resulting in traffic congestion at most sites. Although 

hiking trails are sufficient, trailhead parking is restricted 

and interpretive signs are few and limited in content. More 

interpretation and environmental education would benefit 

many forest visitors. However, increased recreational 

development could adversely affect the natural qualities of the 

forest that many visitors find appealing (U.S. Department of 

Agriculture, Forest Service 1997b). Proposed developments 

should not alter the main experience that the LEF can 

provide—an involvement with nature. Guidelines are needed 

for commercially operated visits to the forest. These could 

involve recurrent meetings to discuss safety, forest protection, 

and accuracy of information provided to the public.

Several potential themes are available for interpretation at 

El Portal Rain Forest Center and elsewhere on the forest, 

including:

• Geology and soils: The formation of the Luquillo Mountains 

spans millions of years and has produced different rock 

formations and soil types evident at different locations 

within the forest.

• Climate and water: Rainfall is heavy and residents depend 

on water resources of the Luquillo Mountains for domestic 

and commercial uses. Management is concerned with 

balancing the water needs for aquatic organisms and the 

island’s growing human population. One major objective is 

to maintain water quantity and quality during the year.

• Hurricanes: Forest conditions vary with time ranging from 

pre-hurricane structure and composition through damage 

on the day of the storm to post-storm recovery (i.e., a few 

days, a few months, and a few years later). Information from 

permanent plots on the forest would allow reconstruction of 

likely forest conditions during different phases of recovery.

• Gradient phenomena: The abundance of flora and fauna 

with changes in elevation, aspect, topography (e.g., ridge, 

slope, and ravine), and exposure within the mountains is 

influenced by climatic factors and soil types.

• Species diversity, classification, and life history: The LEF 

has a rich plant and animal diversity maintained by mild 

temperatures and heavy rainfall. The fauna and flora may be 

abundant, rare, endemic, or endangered. Moreover, species 

vary considerably in size and life span and have different 

strategies for reproduction, survival, and growth. 

• Global warming: Changes that the LEF could experience 

during global warming remain speculative and include an 

increase in temperature, a change in rainfall, more frequent 

and violent hurricanes, changes in cloud cover on the 

summits, alteration in forest species and types, an increase 

in secondary tree species, decline of amphibians, and 

changes in the distributions of bird and reptile species.

• Dwarf forest: Among the most interesting forest types on 

the planet, dwarf forest tells a fascinating tale of wind, rain, 

cloud drip, saturated soils, stunted trees, aerial roots, thick 

leaves, endemic flora, and abundant epiphytes. The forest, 

characterized by generally low productivity, is adapted 

to survive in the inclement environmental conditions that 

characterize the summits.

• History: Pre-Columbian use of and Spanish settlement 

Members of the Natural History Society enjoy a short visit to the 

dwarf forest at Pico del Este on a typical wet, cloudy day. During 

the year, cloud cover intercepted by the summit vegetation (i.e., 

trees and epiphytes) adds 10 percent more water to the soil than is 

provided by rainfall. (Photo by Peter L. Weaver)
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Forest Planning and Management

within the Luquillo Mountains, and the impacts of both 

on forest resources make an interesting story. Structures, 

facilities, and sites built or used during the CCC days could 

also be explained with interpretative signs.

• Research and management issues: The role of the Forest 

Service, with its activities in both research and management, 

is not well known by forest visitors. Research in the LEF has 

included climate, geology, soils, water, flora, fauna, human 

history, ecology, and other topics. This information is 

available to managers to help formulate management plans.

• Puerto Rican handicrafts: The onsite production and sale of 

carved native woods, paintings in natural settings, and other 

handicrafts could benefit local artisans and serve to educate 

the public. 

• Law enforcement: The need for regulations and restrictions 

within the LEF are valid topics for public education. Others 

include habitat needs and regulations to protect wildlife, 

prohibition of hunting, and the need for carrying capacity 

estimates and monitoring to conserve and sustain forest 

ecosystems.

• Natural areas in Puerto Rico: Access to other major 

outdoor areas such as the commonwealth forests, Puerto 

Rico Conservation Trust properties, U.S. Fish and Wildlife 

refuges, and botanical gardens.

Conservation education is distinct from interpretation in that 

it targets particular audiences using different methods in a 

structured, formal setting (U.S. Department of Agriculture, 

Forest Service 2009). These efforts are often age specific 

and provide a series of experiences such as classroom 

presentations, teacher training, and curriculum and media 

development. Some of the most widely used conservation 

education programs include Smokey Bear, Woodsy Owl, 

Project Learning Tree, Nature Watch, Partners in Flight, 

Leave No Trace Inc., Passport in Time, The Natural Inquirer, 

Sustainable Operations/Climate Change, More Kids in the 

Woods (substituted by teacher training programs since 2000), 

and Eastern National-EYNF Interpretative Association. In 

1999, the Caribbean National Forest published a training 

document for teachers (Ruiz Díaz and others 1999). 

Among the objectives were to familiarize participants with 

different forest types, the services that they provide, and 

their importance in political, economic, and social events 

on the island. Students would be made aware of the island’s 

renewable natural resources and possible ways that they 

could be involved in their conservation. Ecosystems, erosion, 

limiting factors, and carrying capacities were among the 

topics reviewed. Finally, students were introduced to ways that 

they could reduce human demands on natural resources.

Puerto Rico has many other sites for outdoor recreation. 

These include (Ventosa-Febles and others 2005, Weaver and 

Schwagerl 2008):

• The commonwealth forest reserve system, totaling about 

25 000 ha, contains 15 forests located in coastal mangroves, 

the limestone hills, and in the central mountains.

• The Puerto Rico Conservation Trust has >9800 ha that 

include 20 properties and four easements scattered through 

the island.

• The U.S. Fish and Wildlife Service have five refuges that 

total about 9500 ha. Two are located in southwestern Puerto 

Rico, and the remainder on the offshore islands of Culebra, 

Desecheo, and Vieques.

Outdoor recreation in Puerto Rico would benefit from 

improved collaboration among the island’s management 

agencies and private entities. A shared vision of resources 

and their potential could improve recreational opportunities. 

Several activities would be best done at locations elsewhere 

in Puerto Rico, such as competitive bicycle racing, outdoor 

camping, and geocaching (i.e., GPS location of sites). More 

accessible and safer sites exist for stream bathing on both 

public and private properties outside of the LEF.

Access (Roads, Trails, Aquisitions)

 The 50-km network of existing roads dissects the forest north 

to south, and then west to east from PR route 191 to Pico del 

Este, about 1 km from the southeastern forest boundary 

(fig. 5). Maintenance of the present road system is imperative, 

particularly PR route 191 from Palmer to the recreation and 

communication sites. The large 1970 landslide closed PR route 

191 between km 13 and km 21 (fig. 13). The current situation 

leaves the southern part of the LEF as an integral, roadless 

block of forest. Motor vehicle access to the forest interior is 

controlled at a single point—the intersection of PR route 191 

and PR route 9966 (fig. 5). The slide fortuitously helps to 

protect habitat for the future expansion of the Puerto Rican 

parrot to lower elevations in drier parts of the forest.

Mother Nature—rugged, isolated terrain and heavy rainfall—

allowed the interior of the LEF to survive during the past 

century. The current recreation plan states that “the forest has 

a greater capacity for people (picnicking, hiking, sightseeing, 

etc.) than it has for transiting and parked vehicles” 

(U.S. Department of Agriculture, Forest Service 2009). On 

the same page, the plan mentions that heavy forest use during 

the month of July currently results in “incident” traffic control 

measures to avert clogging of PR route 191. On July 25, 2009, 

the number of cars parked above Coca Falls was estimated 

at > 500 (see footnote 1). Available parking spaces, including 

specially designated overflow parking areas normally closed 

to vehicles, accommodates less than half that amount.

The plan recognizes transportation needs to help alleviate 

congestion and to provide access, especially on holidays and 
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Forest Planning and Management

busy weekends (Parés Arroyo 2010; U.S. Department of 

Agriculture, Forest Service 1997b). Re-opening PR route 191 

would involve costly construction because of geologically 

unstable substrate and would also complicate the operation 

of a mass transit system. Moreover, the public does not favor 

reopening the road. Highways skirting the border still provide 

access to the northern, western, and southern fringe of the forest 

for those interested in driving along other scenic roads. In the 

interim, current restrictions will remain for vehicular traffic on 

the FS-10 and FS-27 roads leading to communication towers. 

Also, foot traffic on permanent plot monitoring sites in the 

Bisley watersheds should be restricted to designated trails.

At least four properties totaling about 62 ha are included in the 

current land acquisition strategy: (1) the 13 ha Cartagena tract 

along PR route 186; (2) the Río Fajardo tracts, two adjacent 

parcels of 20 ha; (3) the 2 ha Río Sabana tract near the Sabana 

Research Station; and (4) the 27 ha Charco Frío tract adjacent to 

the Río Fajardo (El Yunque National Forest 2010). All of these 

lands border the LEF and would serve several purposes such 

as the consolidation of the LEF, expansion of parrot habitat, 

protection of wildlife, and future recreational opportunities.

Research

Research carried out in the LEF during the past century 

has made a valuable contribution to the conservation and 

management of tropical forests worldwide. Much of the earlier 

work concentrated on identification of the flora and fauna, 

reforestation of abandoned agricultural lands, and silviculture. 

Today, the emphasis is on ecosystem management, landscape 

ecology, wildlife, and issues of global warming (U.S. 

Department of Agriculture, Forest Service 2008). Current 

global concern regarding deforestation and its consequences has 

highlighted the need for a greater understanding of the ecology 

of tropical forests to facilitate their recovery, improve their 

management, and provide educational experience for future 

managers and researchers. Research should help to answer 

critical management concerns such as:

• Maintaining and updating inventories of native vascular 

plants and vertebrate fauna.

•Identifying the habitat needs of native species with special 

attention to endangered species.

• Determining the carrying capacity and monitoring use of 

the forest interior, especially its trails and waterways.

• Monitoring water diversions and use, and effects on aquatic 

wildlife.

• Maintaining and publishing records of tree planting and 

growth.

• Monitoring forest health (i.e., insects and disease) via 

surveys of the flora and fauna, including invasive species.

•Investigating and summarizing forest history, including 

information on settlement, previous resource use, and 

existing structures.

• Fostering research on the flora and fauna within parts the 

LEF that have been overlooked in the past.

• Monitoring the effects of global change on the LEF’s 

climate, flora, and fauna.

In addition to the above, the IITF maintains a continuous 

research program that involves ecology, disturbance, ecosystem 

functioning, biodiversity, watershed dynamics, migratory 

birds, and invasive species (U.S. Department of Agriculture, 

Forest Service 2008). Much of this research is carried out with 

cooperators in Puerto Rico, the United States, and elsewhere

left: For many years, heavy use of the forest roads during holidays and weekends has caused congestion in the upper forest. 

right: Dr. Frank H. Wadsworth, Institute of Tropical Forestry director from 1956 to 1979, explains the results of thinning in secondary lower 

montane rain forest to visitors from the World Wildlife Fund, InterAmerican University, and U.S. Department of Agriculture Forest Service 

offices in Washington and Atlanta. (Photos by Peter L. Weaver)
123

Epilogue

The LEF, with its flora, fauna, water supplies, and 

opportunities for recreation and education, has largely 

survived the disturbances caused by settlement and 

development of the island. Human influence within the LEF, 

however, is ubiquitous and includes administration buildings, 

the El Portal Rain Forest Center, main and tributary roads, 

trails, radar and communication towers, recreation areas, 

picnic areas, summer cottages, small dams for water supplies, 

stream gage stations, experimental and permanent plots, and 

people driving, walking, picnicking, and bathing. Moreover, 

the forest is not pristine—at least one-half was disturbed 

in varying degrees by human activity, which included gold 

mining, logging, farming, tree planting, silviculture, and 

recreational developments. Since the 1980s, many homes 

have been built on the lower slopes surrounding the forest. 

All of these activities serve to isolate or fragment the LEF 

and expose its fauna to increased human influence. One bird 

species has been lost, another is listed as rare and endangered, 

and yet another is being considered for listing. Two frog 

species are presumed extinct and three others have declined 

in numbers. Moreover, since 1975, ecologists have warned 

about the future effects of global warming, including rising 

temperatures, more devastating hurricanes, and possible 

migrations or losses of flora and fauna.

Multiple-use planning has designated uses for the LEF. 

Attempts to accommodate more visitors in the forest, 

however, would place a heavier burden on what most needs 

to be protected—wildlife, water, and a tranquil outdoor 

experience. The LEF is not like the other 171 national forests 

located in the United States. First, those forests average 40 

times larger than the LEF and do not contain its abundance 

of endangered or threatened flora and fauna. Second, the LEF 

is surrounded by towns, cities, and summer homes with a 

population density approaching 1250 km-2 (fig. 1). The LEF’s 

natural and human setting requires that attention be given to 

tradeoffs among management alternatives because its size and 

existing pressures do not allow the forest to accommodate 

all options. The LEF is small, representing about 1 percent 

of the island. Sustainable human carrying capacities need 

to be determined, and forest educational programs should 

strive to make the forest a memorable experience with nature. 

Comprehensive land management planning for the island 

should involve all of Puerto Rico’s natural resource entities 

and their land units (i.e., the LEF, the Commonwealth Forest 

Reserve system, the Conservation Trust, and other public and 

private areas).

In summary, the LEF has two major designations—

experimental forest and national forest—and a variety of 

possible uses. Better alternatives for some recreational 

activities exist outside of the forest. No feasible alternatives, 

however, are available for most of the LEF’s endemic or 

classified flora and fauna. Public input to the management 

plan has shown that protection of primary forest (i.e., the 

wilderness, the research natural area, and wild and scenic 

rivers), wildlife (e.g., the parrot and rare frogs), and water 

resources are major concerns.

EPILOGUE—QUO VADIS?
124

Acknowledgments

Several individuals helped with information regarding 

the LEF: Wayne Arendt and Joseph M. Wunderle, Jr. with 

information on the occurrence of bird species seen during 

field studies and annual Christmas counts; Tom Brandeis 

with the survey information; Carlos Domínguez Cristóbal 

and Jeffrey Walker with historic and cultural information; 

William Gould with comparable datasets; Carolyn Krupp and 

Sidney Salyer with property acquisition records and special 

uses; Edgardo Martínez with property details and access 

to old forest maps; Alan Mowbray with details about past 

military activities; Maya Quiñones with preparation of new 

figures and maps; Luis Rivera with information on forest 

plantings; Iván Vicéns with field assistance and photographs; 

and Frank H. Wadsworth with details regarding species trials, 

past plantation records, and numerous anecdotes regarding the 

forest. Reference information was acquired from the Archivo 

General de Puerto Rico in old San Juan and the Puerto Rican 

collection in the University of Puerto Rico main library. 

Jorge Morales and Gisel Reyes helped locate references in 

the Institute’s library, and Liz M. Pagán in the Agricultural 

Experiment Station library.

Reviewers who offered valuable comments on the draft 

manuscript were: Thomas J. Brandeis, U.S. Department 

of Agriculture, Forest Service, Southern Research Station, 

Knoxville, TN; Nicholas V.L. Brokaw, University of Puerto 

Rico, Río Piedras; Peter G. Murphy, retired professor at 

Michigan State University; Héctor Manuel Torres-Camacho, 

U.S. Department of Agriculture, Forest Service, Camp 

Santiago Training Center; and Sheila E. Ward, Mahogany for 

the Future, Inc., San Juan. Additional reviewers were Wayne 

J. Arendt, Frank H. Wadsworth (retired), Skip Van Bloem, and 

Joseph M. Wunderle Jr., colleagues in the U.S. Department 

of Agriculture, Forest Service in Río Piedras; Felipe Cano, 

Carolyn Krupp, José R. Ortega, Carolyn Pabón, and Blanca 

I. Ruiz in the El Yunque National Forest; and Thomas Schmidt 

at the Northern Research Station. This work was done in 

cooperation with the University of Puerto Rico at Río Piedras.

ACKNOWLEDGMENTS
125

Endnotes

Anon. 1941. Annual report of the Tropical Forest Experiment Station. 21 p. 

Unpublished report. On file at: U.S. Department of Agriculture, Forest 

Service, International Institute of Tropical Forestry Library, Jardín 

Bótanico Sur, 1201 Calle Ceiba, San Juan, PR 00926-1119.

Arendt, W. 2008. Birds—El Yunque National Forest. 8 p. Unpublished list. 

On file at: U.S. Department of Agriculture, Forest Service, International 

Institute of Tropical Forestry Library, Jardín Bótanico Sur, 1201 Calle 

Ceiba, San Juan, PR 00926-1119.

Bruner, E.M. 1918. Report upon the preliminary examination of the timber 

and fuel resources of the Luquillo National Forest. 11 p. Unpublished 

report. On file at: U.S. Department of Agriculture, Forest Service, 

International Institute of Tropical Forestry Library, Jardín Bótanico Sur, 

1201 Calle Ceiba, San Juan, PR 00926-1119.

Caribbean National Forest. 1994. Evaluation of emergency water 

withdrawal for Caribbean National Forest. 5 p. Unpublished report. On 

file at: El Yunque National Forest, Route 191, Intersection 988, km 4.4, 

Barrio Barceloneta, Río Grande, PR 00721.

Chudnoff, M. 1981. Unpublished list of specific gravity estimates for several 

species of Puerto Rican woods. Information available at: U.S. Department 

of Agriculture, Forest Service, Forest Products Laboratory, One Gifford 

Pinchot Drive, Madison, WI 53726.

El Yunque National Forest. 2008. Birds—El Yunque National Forest. 3 

p. Unpublished list. On file at: El Yunque National Forest, Route 191, 

Intersection 988, km 4.4, Barrio Barceloneta, Río Grande, PR 00721.

El Yunque National Forest. 2009. Map record file. El Yunque National 

Forest. Maps on file at: El Yunque National Forest, Route 191, Intersection 

988, km 4.4, Barrio Barceloneta, Río Grande, PR 00721.

Gerhart, G.A. 1936. Caribbean National Forest: La Mina Recreational 

Area, accomplishments and proposed recreational developments. 

Washington. DC: U.S. Department of Agriculture, Forest Service; 

Government Printing Office. 27 p. + maps and photographs. On file at: 

U.S. Department of Agriculture, Forest Service, El Yunque National 

Forest, Route 191, Intersection 988, km 4.4, Barrio Barceloneta, Río 

Grande, PR 00721.

Huffaker, L.E. 1989. “Hollow shells”—an analysis of the summer home 

program on the Caribbean National Forest. 45 p. Unpublished document. 

On file at: U.S. Department of Agriculture, Forest Service, El Yunque 

National Forest, Route 191, Intersection 988, km 4.4, Barrio Barceloneta, 

Río Grande, PR 00721.

Kramer, W.P. 1932. Policy statement—Luquillo National Forest, Porto 

Rico. 57 p. Unpublished document. On file at: U.S. Department of 

Agriculture, Forest Service, International Institute of Tropical Forestry 

Library, Jardín Bótanico Sur, 1201 Calle Ceiba, San Juan, PR 00926-1119.

Muñoz, J.E. 1965. Timber management plan for the Luquillo Experimental 

Forest. San Juan, PR: U.S. Department of Agriculture, Forest Service, 

Caribbean National Forest. 54 p. Unpublished document. On file at: U.S. 

Department of Agriculture, Forest Service, International Institute of 

Tropical Forestry Library, Jardín Bótanico Sur, 1201 Calle Ceiba, San 

Juan, PR 00926-1119.

Rivera, L. 2010. Personal communication. Luis Rivera, Forester, U.S. 

Department of Agriculture, Forest Service, El Yunque National Forest, 

Route 191, Intersection 988, km 4.4, Barrio Barceloneta, Río Grande, PR 

00721.

Santiago Cazull, H. 2000. Architectural conservation assessment for 

repairs to ranger dwelling (Cubuy House), Caribbean National Forester, 

Puerto Rico. 27 p. Unpublished document. On file at: U.S. Department 

of Agriculture, Forest Service, El Yunque National Forest, Route 191, 

Intersection 988, km 4.4, Barrio Barceloneta, Río Grande, PR 00721.

Upson, A. 1949. The Caribbean Forest atlas. Río Piedras, PR: U.S. 

Department of Agriculture, Forest Service, Tropical Region. 43 p. + 

tables and maps. Unpublished document. On file at: U.S. Department 

of Agriculture, Forest Service, El Yunque National Forest, Route 191, 

Intersection 988, km 4.4, Barrio Barceloneta, Río Grande, PR 00721.

U.S. Department of Agriculture, Forest Service. 1991. El Yunque peak 

electronic site plan. Unpublished document. On file at: U.S. Department 

of Agriculture, Forest Service, El Yunque National Forest, Route 191, 

Intersection 988, km 4.4, Barrio Barceloneta, Río Grande, PR 00721.

U.S. Department of Agriculture, Forest Service. 1995. Tabulation 

of National Forest lands—Caribbean National Forest: 5490 Status 

(conveyance file). 4 p. Unpublished table. On file at: U.S. Department 

of Agriculture, Forest Service, El Yunque National Forest, Route 191, 

Intersection 988, km 4.4, Barrio Barceloneta, Río Grande, PR 00721.

U.S. Department of Agriculture, Forest Service. 2009. El Yunque National 

Forest, El Toro Wilderness, nonnative invasive plant management plan. 

38 p. Unpublished document. On file at: U.S. Department of Agriculture, 

Forest Service, El Yunque National Forest, Route 191, Intersection 988, 

km 4.4, Barrio Barceloneta, Río Grande, PR 00721.

Vélez, I.L.; Villaluazo, R.; Walker, J.; Valenzuela, F. 1992. Caribbean 

National Forest interpretative plan. 75 p. Unpublished document. On file 

at: U.S. Department of Agriculture, Forest Service, El Yunque National 

Forest, Route 191, Intersection 988, km 4.4, Barrio Barceloneta, Río 

Grande, PR 00721.

Wadsworth, F.H. 2009. Personal communication. Past director, U.S. 

Department of Agriculture, Forest Service, International Institute of 

Tropical Forestry, Jardín Botánico Sur, 1201 Calle Ceiba, San Juan, PR 

00926-1119.

Walker, J.B.; Leone, J.P.; Ortega, J.R. [and others]. 1999. Strategic plan 

for the New Deal era historic properties on the Caribbean National Forest. 

52 p. Unpublished document. On file at: U.S. Department of Agriculture, 

Forest Service, El Yunque National Forest, Route 191, Intersection 988, 

km 4.4, Barrio Barceloneta, Río Grande, PR 00721.

Walker, J. 2009 Personal communication. Jeffery Walker, Past 

Archaeologist, U.S. Department of Agriculture, Forest Service, El Yunque 

National Forest, Route 191, Intersection 988, km 4.4, Barrio Barceloneta, 

Río Grande, PR 00721. Current address: Heritage Program Lead, Pacific 

Northwest Region, U.S. Department of Agriculture, Forest Service, 333 

SW 1st Ave., Portland, OR 97208.

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138

Appendix A

Date Topic 

~3000–1493 Several cultural groups occupy Puerto Rico at different times, including Archaic, Igneri, Ostiones, Tainos, and Caribs. The

pre-Columbian groups inhabit small villages surrounding the Luquillo Mountains where they subsist on tropical crops and

seafood, and occasionally venture into the forest for constuction materials and other purposes (Domínguez Cristóbal 1997a, 

1997b, 1997c; Robinson 1997; Wadsworth 1970).

1493 Columbus sails along Puerto Rico’s south coast during his second voyage most likely viewing the Luquillo Mountains on 

November 17 (Domínguez Cristóbal 1997a, Moran Arce 1971). On November 19 (discovery day), the Spanish land in 

western Puerto Rico. Some claim that the Spanish discovery of Puerto Rico was during November 1492 by Martín Alonzo 

Pinzón (Huerga 2004).

1508–09 Spanish colonization begins in river valleys flowing out of the Luquillo Mountains (Wadsworth 1949).

1508–1946 Placer gold mining begins in Puerto Rico in the valleys of the Río Blanco and Río Fajardo, and continues at different sites 

and times within the Luquillo Mountains, including the Río de la Mina, Río Espíritu Santo, Río Mameyes, Río Prieto, and 

Río Sabana, through the mid-20th century (Cardona 1984, Wadsworth 1949). Some examples are: the upper Río Mameyes 

valley in 1870 and 1903, and the upper Río Blanco valley in 1903 (Scatena 1989); and a large scale operation just below the 

Puente Roto bridge on the Sabana Road (PR route 988), abandoned in 1946 (Wadsworth 1970).

1511–15 Tainos living in the Luquillo Mountains rebel against Spanish colonists (Domínguez Cristóbal 1997a, Wadsworth 1970).

1513 Spanish Crown grants settlers title to about 70 ha of land if they comply with requirements for residence and cultivation

(Wadsworth 1949).

1529–30 Natives attack miners and burn their houses. Gold mining operations decline as colonists substitute agriculture for mining 

(Cardona 1984). 

1550 Island native population devastated by introduced diseases and forced labor (Anderson-Córdova 2005). 

1582 Spanish settlements on lower slopes of the Espíritu Santo and Sabana watersheds are abandoned due to indigeneous attacks 

from their stronghold located within the mountains (Wadsworth 1949, 1970).

1500s Spanish use resin from Dacryodes excelsa (tabonuco tree) to caulk ship timbers (Domínguez Cristóbal 1997a).

1500s A Spanish explorer discards an olive jar, which is found nearly 400 years later (Jeffrey Walker 2009, see endnotes).

1600s Puerto Rico, with only three populated areas (San Germán, San Juan, and Coamo), remains isolated and residents live by 

contraband. Timber exports are negligible (Alegría and Rivera Quiñones 1999, Wadsworth 1949).

1736–1899 Coffee, introduced from the Dominican Republic, is later grown on the lower slopes of the Luquillo Mountains through the end 

of the 19th century when cultivation is ended by a major hurricane (Nolla 1936, Scatena 1989, Wadsworth 1949).

1772—1880 The island population increases and towns surround the Luquillo Mountains—Fajardo (1772), Las Piedras (1773), 

Naguabo (1794), Luquillo and Juncos (1797), Gurabo (1815), Ceiba (1836), and Río Grande (1880)—placing a demand 

on forest resources (Domínguez Cristóbal 1997a, Wadsworth 1949).

1797—98 French botanist Pierre Ledru explores northeastern Puerto Rico and collects plant specimens (Liogier 1996, Urban 1924). 

1815 The “Cédula de Gracia” cedes Crown lands to the public for agricultural use, mandates that boundaries be planted with trees,

and stimulates the local economy with new farms, equipment, and industry, including sawmills (Rosario Rivera 1995).

1820—90 Spanish Crown makes land concessions at the base of the Luquillo Mountains (Scatena 1989, Wadsworth 1949).

1827 Swiss botanist Heinrich Wydler visits Luquillo Mountains during travels to the West Indies (Urban 1903-11, 1924).

1837—95 Timber is cut and exported from the Luquillo Mountains through the port of Luquillo (Wadsworth 1949, 1970).

APPENDIX A

continued

Appendix A— Chronology of critical activities, events, important documents and laws, and little known facts influencing 

the environment of the Luquillo Mountains and its flora and fauna. Related activities and events with multiple occasions 

(e.g., mining) are entered once or twice at the most appropriate datesa, b
139

Appendix A

Date Topic 

1839 Spanish Crown orders the establishment of a board to protect forests, fish, and wildlife. The board recommends that no

cutting be allowed along streams or headwaters of rivers (Scatena 1989).

1853 By royal decree, two Spanish foresters survey and manage Crown forests, including the Luquillo Forest (Wadsworth 1970).

subsistence crops are planted on farms in the area (Scatena 1989).

1857 A tract in the Bisley area is cut for Dacryodes excelsa, Manilkara bidentata, and firewood. Coffee, bananas, and

subsistence crops are planted on farms in the area (Scatena 1989).

1860 Spanish records indicate that 7850 ha of crown lands remained in the Luquillo Mountains, declining to 6190 ha in 1880, and

to about 5040 ha in 1898 (Snyder and others 1987).

1867 Hurricane San Narciso passes over the Luquillo Mountains. Subsequently, five other major huricanes would impact the 

Luquillo Mountains: San Ciriaco in 1899, San Felipe in 1928, San Cipriano in 1932, Hugo in 1989, and Georges in 1998

(Salivia 1972, Weaver 2002b).

1876 Spanish King Alphonso XII proclaims forest reserves in Puerto Rico, including 10 000 ha in the Luquillo Mountains, making 

it one of the oldest in the Western Hemisphere (Domínguez Cristóbal 1997a).

1877 Herpeste auropunctatus (mongoose) is introduced to Puerto Rico with negative impacts on native wildlife throughout the

island, including the Luquillo Mountains (Raffaele 1983).

1880–81 Illicit timber felling, carried out intermittently during Spanish times in the Jiménez and Mameyes valleys, is discontinued 

(Wadsworth 1949). The “Sierra de Luquillo” (Luquillo Mountains) forest reserve is named (Domínguez Cristóbal 1997a).

1883 Henrik F.A. Baron von Eggers (1844-1903), Danish soldier and botanist, collects plant samples from the northwestern

slopes of the Luquillo Mountains and notes farming within the Mameyes drainage (Eggers 1883).

1885 German botanist Paul Ernst Emil Sintenis (1847-1907) visits the Luquillo Mountains and collects several plant specimens

recorded for the first time (Wadsworth 1970).

1885 A forest guard assigned to patrol the Luquillo Forest presents numerous trespass cases to authorities in the town of

Luquillo. Transportation difficulties remain a major deterrent to timber extraction (Wadsworth 1949). 

1891–97 The U.S. Land Revision Act and the Organic Administrative Act allow the President of the United States to set aside forest 

lands from the public domain (U.S. Department of Agriculture, Forest Service 1983).

1898 Augustín Stahl (1842-1917), botanist and ethnologist in Puerto Rico, collects in the Luquillo Mountains (Liogier 1996, 

Wadsworth 1970).

1898 The Treaty of Paris cedes Spanish Crown lands to the United States at the end of the Spanish-American War, with about 

5040 ha situated in the Luquillo Mountains (Wadsworth 1949).

1898 Puerto Rico is designated as Porto Rico from July 16, 1898 until May 17, 1932 purportedly because it was easier to 

pronounce in English (Martínez-Fernández 1998). 

1899 About 16 000 ha of forest and brushlands remain in the Luquillo Mountains, including 2270 ha of virgin forest (Hill 1899,

Wadsworth 1970).

1902 Percy Wilson (1879-1944), botanist working with the New York Botanical Garden, collects 3,000 plant specimens 

between the foothills and summits of the Luquillo Mountains (Britton and Wilson 1923-30, Wadsworth 1970).

1903 Under authority of a 1902 Act of Congress, President Theodore Roosevelt proclaims the Luquillo Forest Reserve 

(Wadsworth 1949).

1903 Proclamation boundary - all land with an area of 9 by 11 miles (i.e., ~25 650 ha) is classified for reservation as public forest 

as soon as it might be acquired by the government (Wadsworth 1949). Subsequently, the boundary is modified (fig. 4).

1903–11 Ignatz Urban (1848-1930), a German botanist, classifies plants from Puerto Rico, including the national forest, and publishes 

“Flora Portoricensis” (Liogier 1996, Urban 1903-11, Wadsworth 1970).

1905 A narrow, infrequently used trail exists to El Yunque and across the mountains to the south, possibly for hiking or hunting 

parrots and pigeons (Wadsworth 1949). 

Appendix A— (continued) Chronology of critical activities, events, important documents and laws, and little known facts 

influencing the environment of the Luquillo Mountains and its flora and fauna. Related activities and events with multiple 

occasions (e.g., mining) are entered once or twice at the most appropriate datesa, b

continued
140

Appendix A

Date Topic 

1905 A report on the Luquillo Forest Reserve discusses climate, forest resources, forest industry, and related topics, including the

general lack of valuable timber species, and the sale of torches made from tabonuco resin (Gifford 1905).

1907 The Luquillo Forest Reserve (1903-1907) becomes the Luquillo National Forest (1907-1935). Subsequently, other forest 

designations are used: Caribbean National Forest or CNF (1935-2007); Luquillo Experimental Forest or LEF (1956- 

present); and El Yunque National Forest or EYNF (2007-present) (Silcox and Kircher 1936, Wadsworth 1970).

1908 The Preservation of American Antiquities Act protects ruins situated on government lands (U.S. Department of Agriculture,

Forest Service 1983).

1908 The Luquillo National Forest proclamation boundaries are located and marked with concrete markers by the U.S. Coast

and Geodetic Survey (Wadsworth 1970). 

1908–09 Trails into the Espíritu Santo and Jiménez watersheds are used to illicitly cut timber. Trespass by charcoal cutters to high

elevations within the mountains leads the Commisioner of Agriculture to request forest guards (Domínguez Cristóbal 1997c,

Wadsworth 1949). 

1910 Surveys determine that El Toro, and not El Yunque, is the highest peak in the Luquillo Mountains (Wadsworth 1970).

1910–11 Property ownership records for the Luquillo Mountains are in chaos. The Governor of the Insular government persuades 

the U.S. Forest Service to survey the land (Murphy 1916, Wadsworth 1970).

1911 The U.S. Weeks Act allows the Secretary of Agriculture to acquire forested, cutover, or denuded lands in the watersheds of 

navigable rivers by purchase or exchange (U.S. Department of Agriculture, Forest Service 1983).

1912 Beginning in 1912, water from the Luquillo Mountains is tapped for several towns and cities: from the Río Fajardo for 

Fajardo (1912), from Río Gurabo for Juncos (1914), from Quebrada Grande for Naguabo (1922), again from Quebrada 

Grande for Río Grande (1924), from the Río Canovanas for Canovanas (1925), from Río Cristal for Luquillo (1926), from 

the Río Blanco and nearby streams for hydropower (1928), and from the Río Gurabo (stored in the reservoir on Río Loíza)

for San Juan (1950) (Wadsworth 1970). During the 1970s, water from the Río Blanco was supplied to Roosevelt Roads 

and Vieques (PREPA 1974). Water extraction projects continue today with the Valenciano and Río Blanco reservoirs in the 

Juncos and Fajardo areas, respectively (Marino 2011).

1912–16 The forest boundary survey of the proclaimed Luquillo National Forest is completed and shows about 5040 ha. Persons

farming within the boundaries are allowed to continue by permit (Bruner 1923; Wadsworth 1949, 1970).

1913–17 Nathaniel Britton and co-workers of the the New York Botanical Garden conduct a scientific survey of the physical and

natural history of Puerto Rico and the Virgin Islands, including the Luquillo Mountains, and summarize their work in several 

volumes (Britton and Wilson 1923-30, Cook 1928, Gleason and Cook 1927).

<1914 Logging on 160 ha is carried out between Quebrada Grande and the Río Espíritu Santo (Wadsworth 1949). 

1914 Uncontrolled cutting of timber is reported on the north slopes of the Luquillo Mountains (Wadsworth 1970).

1916 Three types of mountain forest—rain forest, hurricane hardwoods, and palm—are described for the Luquillo Mountains. 

An appendix of 170 tree species is included (Murphy 1916).

1916 The Puerto Rican government turns over 1200 ha adjacent to the Luquillo National Forest to the federal government 

(Bruner 1919).

1916–27 The birds of Puerto Rico, about 40 of which nest in the Luquillo Mountains, are described (Wetmore 1916, 1927).

1917 The first forest supervisor is appointed and the U.S. Forest Service begins management of the Luquillo Forest Reserve. The

supervisor helps draft the first forest law after departure of the Spanish. The law forsees the creation of a Forest Service

(Bruner 1923, Kramer 1928, Wadsworth 1970).

1918 Forest guards are appointed to work in the Luquillo National Forest. Also, agriculture is underway at Bisley and along the

southern forest border up to 550 m in elevation (Bruner 1923, Wadsworth 1949).

Appendix A— (continued) Chronology of critical activities, events, important documents and laws, and little known facts 

influencing the environment of the Luquillo Mountains and its flora and fauna. Related activities and events with multiple 

occasions (e.g., mining) are entered once or twice at the most appropriate datesa, b

continued
141

Appendix A

Date Topic 

1919 The first description of four basic forest types is provided for the Luquillo Mountains—cove, slope or lower slope, upper 

slope or sierra palm, and ridge or dwarf forest (Bruner 1918, see endnotes). 

1919–26 About 50 km of horse trails are built to patrol forest boundaries, including along the Río Sabana in the northeast, from Palmer 

to Río Blanco via the Río Mameyes valley and from Catalina to El Yunque in the north, and along the western boundary 

of the forest. One trail traverses the mountains. Another 10 km of trails are built by 1926 (Kramer 1928, Wadsworth 1949).

1919–50s One family lives within the forest boundary in 1919, increasing to 220 families in 1940, then decreasing to 60 by 1949. By 

1953, all families are relocated outside of forest boundaries (Wadsworth 1949, 2009, see endnotes ).

1920–43 Three sawmills operate at low elevations in the Río Sabana and Río Espíritu Santo river valleys near forest boundary, and

remain operational for up to 15 years (Scatena 1989, Wadsworth 1949).

1924 The U.S. Clarke-McNary Act allows the Forest Service to support local tree production (U.S. Department of Agriculture, 

Forest Service 1983).

1925–26 The mammals of Puerto Rico are described, including native bats in the Luquillo Mountains (Anthony 1925, 1926).

1926–42 Construction begins on the Mameyes-Río Blanco highway (PR Route 191) to traverse the Luquillo Mountains. The first

section from Palmer to Catalina is completed by 1929. The road is finished in 1942 (Bagué 1962, Wadsworth 1970). 

Subsequently, another 15 roads are built entirely or partially within or bordering the forest (table 3).

1927 Ecological descriptions of four distinct forest associations are provided for the Luquillo Mountains (Gleason and Cook 1927). 

1928 The U.S. McSweeney-McNary Act authorizes a Federal forest research station in Puerto Rico (U.S. Department of

Agriculture, Forest Service 1983).

1928 A narrow gauge cable railway is built from the lower Río Blanco valley to 430 m elevation then westward (i.e., below the 

forest boundary) on the south slope to facilitate the construction of water control structures on the Río Icacos and other

streams flowing out of the Luquillo Mountains (Krug 1930). 

1928–32 Three hurricanes cause considerable damage to the Luquillo Forest and flood lands in eastern Puerto Rico. Salvage use of 

timber is authorized under the Free Use Provision Act for rural reconstruction after San Felipe in 1928, the island’s legendary 

storm (Crow 1980, Synder and others 1987).

1930–62 Four systematic forest surveys are carried out: stocking in 1930; sawtimber, saplings, and reproduction in 1937; sawtimber

in 1948; and a resample of the most accessible saw timber areas in 1962 (Wadsworth 1951, 1970). 

1930s Stands of exotic bamboo are planted within the national forest to stabilize soils along PR Route 191 (Blundell and others 2003). 

1931 First Swietenia macrophylla x mahagoni (hybrid mahogany) plantations are established on the Harvey tract and 

and experimental plantings at Del Valle (Marrero 1948, Wadsworth 1970).

1931–39 Leslie R. Holdridge, the author of life zone ecology, begins a herbarium collection. By 1948, it contains 3,000 specimens, 

including many trees in the Luquillo National Forest (Wadsworth 1970). In the early 1980s, the collection is donated to the

herbarium at University of Puerto Rico Agricultural Experiment Station.

1931–49 Reforestation, mainly between 1935 and 1945, results in the planting of nearly 1600 ha (Wadsworth 1949, 1970). 

1931–49 The Forest Service authorizes the sale of timber which begins the following year (Wadsworth 1949). Timber sales, >80 percent

fuelwood (i.e., 3.25 million board feet), take place on the most accessible 2150 ha. Supervision of tree cutting assures the 

release of desireable timber species. The charcoal market collapses in 1949 with the importation of kerosene stoves (Snyder

and others 1987; Wadsworth 2009, see endnotes).

1932 The forest supervisor completes a policy statement for the Luquillo National Forest, which calls for forest protection and wood 

production, and allows post-hurricane salvage (Kramer 1932, see endnotes; Wadsworth 1949).

1932 The Forest Service builds overnight cabins on the north and south slopes of the Luquillo Mountains to facilitate patrol and 

protection of the national forest (Wadsworth 1949).

Appendix A— (continued) Chronology of critical activities, events, important documents and laws, and little known facts 

influencing the environment of the Luquillo Mountains and its flora and fauna. Related activities and events with multiple 

occasions (e.g., mining) are entered once or twice at the most appropriate datesa, b

continued
142

Appendix A

Date Topic 

1933 The geology of Puerto Rico is described, including the Luquillo Mountains (Meyerhoff 1933).

1933–34 The Civilian Conservation Corps (CCC) is created in the United States to carry out emergency conservation work (Lavandero 1998).

The U.S. Congress enacts the Emergency Public Works Program for Puerto Rico. U.S. Army reserve officers temporarily 

take charge of the camps to construct buildings and trails (Mowbray 2008). 

1933–49 The area of the Luquillo National Forest increases by nearly one-half of its current size of 11 310 ha (figs. 1 and 4).

1934–37 Troughs and rearing pools for a trout nursery are built near the La Mina Recreation Area. Trout eggs are introduced from 

United States but national forest waters are too warm for reproduction (Domínguez Cristóbal 1997c; Gerhart 1936, see endnotes).

1934 The La Mina area first opens to the public and attracts 2,200 visitors on a single day (Gerhart 1936, see endnotes). 

1934–51 A sawmill is established at Sabana to cut Dacryodes excelsa and build houses for temporary forest residents (i.e., parceleros)

(Holdridge 1940, Wadsworth 1949).

1935–39 Small scale timber stand improvement on an experimental basis is carried out in 55 ha of Lower Montane rain forest in the

Río Espíritu Santo and Río Mameyes Valleys. Study plots are established in 1938 (Wadsworth 1949). 

1935–43 The CCC builds 100 km of roads and 80 km of trails along with two picnic areas, cabins, a fish hatchery, two swimming pools 

and a restaurant (closed in 1989). Subsequently in 1939, the La Mina Recreation Area is built. The trails extend from the La 

Mina Recreation Area to La Mina Falls and Baño de Oro, and from PR route 191 to Mt. Britton, El Yunque, Los Picachos, 

and the summits of Pico del Este, Pico del Oeste, and El Toro. Also, the CCC carries out extensive reforestation within the

mountains (Domínguez Cristóbal 1997a, 1997c; Gerhart 1936a, 1936b; Wadsworth 1949).

1937 A 6 percent timber cruise of 6900 ha is carried out within the forest (Wadsworth 1970).

1937 The Pittman-Robinson Act expands government involvement in wildlife conservation by providing funds to acquire lands, 

restore habitat, and conduct research (Snyder and others 1987).

1937–39 The Puerto Rico Reconstruction Administration builds the El Verde Field Station at 350 m elevation (Odum and Pigeon 

1970; Wadsworth 1970). The station is renovated in early 1960s and laboratory facilities are added in 1963 and 1977. 

Later, a 22-m walk-up tower and canopy walkway are built in the vicinity. In 2005, a dormitory is added.

1938 The El Yunque and Mt. Britton towers are built (El Yunque National Forest 2009, see endnotes; Walker and others 1999, see

endnotes).

1938–40s Spur roads for summer homes are built near La Mina Recreation Area (e.g., Molindero Road) (Gerhart 1936, see endnotes). 

Lack of use or maintenance results in their loss (U.S. Departmentof Agriculture, Forest Service 1997b).

1939 Silviculture is first practiced in the forest by removing vines and poor trees to favor desireable saplings (Wadsworth 1970).

1939 The Tropical Forest Experiment Station (today the International Institute of Tropical Forestry) begins to operate. Site

adapatability testing for more than 100 native and 350 introduced tree species commences. The staff also starts publication 

of the Caribbean Forester, organizes the Institute’s library, and develops a system of research files. Much of the research 

is carried out in the Luquillo Mountains (Anonymous 1939, Francis 1989, Marrero 1948). 

1940s About 220 families resident on acquired tracts of land within the Caribbean National Forest intercrop trees with their 

subsistence crops (i.e., agroforestry), gradually reforesting the land (Holdridge 1940).

1940s Parts of the Bisley watersheds are logged (Scatena 1989)

1940s–2008 A plane crashes in Lower montane forest near the Bisley watersheds, possibly during World War II. Subsequently, crashes 

occur in 1968 on Pico del Este, in 1969 on Cacique, in 2002 near the restaurants on PR route 191, and in 2008 in the El 

Toro Wilderness Area (Hernández Pérez 2008, Rojas Daporta and Ortiz Otero 1969, Torres 2002, Weaver 2000).

1942 The U.S. Geological Survey completes Luquillo Mountains topographic maps at 1/30,000 scale, with revisions in 1952 and

1958 at 1/20,000 scale (Wadsworth 1970).

Appendix A— (continued) Chronology of critical activities, events, important documents and laws, and little known facts 

influencing the environment of the Luquillo Mountains and its flora and fauna. Related activities and events with multiple 

occasions (e.g., mining) are entered once or twice at the most appropriate datesa, b

continued
143

Appendix A

Date Topic 

1942 The U.S. Army builds access road FS-10 from PR route 191 to El Yunque peak for an early warning radar post to detect

enemy aircraft; also, barracks on FS-10 are constructed for off-duty radar crews (Mombray 2008). 

1942–55 Stream gauging stations are maintained on the Río Icacos and Río Espíritu Santo from 1942 to 1955 (Wadsworth 1970).

1943 Long-term research begins with the 0.72-ha El Verde plot. Today, plots to determine tree growth number about 450 and 

are located in all forest types. Some are still monitored (Crow 1980, Weaver 1983) (table 7).

1945 Puerto Rican forest insects are described, including species from the Luquillo Mountains (Martorrel 1945).

1945 Timber stand improvement on 1620 ha in the Río Grande, Río Icacos, and Río Sabana watersheds is used to alleviate a 

post-war energy crisis and provide employment (Snyder and others 1987).

1945–57 The U.S. military carries out maneuvers under permit within the national forest (Wadsworth 2009, see endnotes). 

1945–74 A tree nursery at Catalina is established and within 2 years has the capacity to produce 6 million trees and ornamentals. The

nursery continues to operate until 1974 (Domínguez Cristóbal 1997c). 

1946 All Puerto Rican public forests, including the Luquillo Mountains, are designated as wildlife refuges (Wadsworth 1970).

1946–48 A 2-percent timber cruise is carried out on 4550 ha in Lower Montane and Montane rain forests to help prepare a multiple

use forest management plan (Wadsworth 1951, 1952a, 1952b).

1948 Climatic data from 1935 to 1948 are reported for the La Mina Station at 720 m elevation in the Luquillo Mountains 

(Wadsworth 1948).

1948 An assessment of 4 million seedlings of 27 tree species planted on nearly 1600 ha of abandoned farm land in the Luquillo 

Mountains shows generally poor survival and growth (Marrero 1948).

1948–63 Multi-species volume tables are derived for the Lower montane and Montane rain forests, and later a combined regression

equation is derived to estimate tree volumes (Wadsworth 1949, 1970).

1949 The Baño de Oro Natural Area is established on 745 ha in the Mameyes watershed. The area contains each of four forest

types (Lower montane, Montane, Palm, and Dwarf forests) in pristine condition (Weaver 1994).

1949 The natural vegetation of the Windward and Leeward Islands is described using a forest classification system still employed 

widely in the Caribbean Islands, including the Luquillo Mountains (Beard 1949).

1950 The 5-ha Elizabeth Colberg Girl Scout Camp is established along PR route 186 near El Verde. The camp sign reads—

Marzo 12, 1950 campamento “Eliza Colberg” ninas escuchas—indicating a March 1950 commemorative date.

1950 A Luquillo Forest multiple use and timber management plan calls for reservation of uplands, parrot habitat, watershed 

conservation, and research. A forest type map is produced and timber species in the forest are classified according to utility. 

About 2270 ha of virgin forest remains. Subsequent timber plans for sustainable harvest are revised in mid-1960s (Muñoz 

1965, see endnotes; Wadsworth 1951, 1952a, 1952b, 1970).

1950 Resistance of Puerto Rican woods to attack by dry wood termites is summarized and indexed by species (Wolcott 1950). 

1953 First of 16 international tropical forestry short courses begins with field activities in the Luquillo Mountains. The courses 

emphasize multiple use planning, tree identification, forest mensuration, timber production, silviculture, and public forest 

administration (Anonymous 1954, Barres 1963, Lamb 1959, Wadsworth and others 1955).

1953–56 With support from the Pittman-Robinson Program, the Puerto Rican parrot population in the mid-1950s is estimated at 200

birds within the forest. Other estimates were: 1864, abundant in the eastern lowlands; 1931, about 2,000 in the Luquillo 

Mountains; 1963, about 120 in the LEF; 1972, only 13 birds (Rodríguez-Vidal 1959, Snyder and others 1987 ). 

1955 Swietenia macrophylla and Khaya nyascia are planted in gaps and openings in the Bisley area (Scatena 1989).

1955 All logging with oxen ceases within the forest due mahogany imports (i.e., demand for local timber is depressed). Harvest

and pit sawing of Magnolia splendens for furniture terminates (Wadsworth 1970). 

Appendix A— (continued) Chronology of critical activities, events, important documents and laws, and little known facts 

influencing the environment of the Luquillo Mountains and its flora and fauna. Related activities and events with multiple 

occasions (e.g., mining) are entered once or twice at the most appropriate datesa, b

continued
144

Appendix A

Date Topic 

1955–61 Information on industrial wood use in Puerto Rico, and on the machining, seasoning, and related characteristics of 60 Puerto

Rican timbers, many found in the Luquillo Mountains, are published (Longwood 1955, 1961).

1956 A pilot management program begins on slightly more than 3200 ha of land designated for timber production. It includes the

liberation of promising crop trees and timber plantations (Anonymous 1957, 1958).

1958 Timber access roads to Bisley, Espíritu Santo, Jiménez, and Sabana working areas are completed (Anonymous 1958).

1958–62 Weather (rainfall, temperature, humidity, wind velocity, solar radiation) are continuously recorded for 4 years at El Yunque

Peak. Eight other sites at lower elevations provide comparative data (Briscoe 1966). 

1958–62 The 5-km FS-27 (Pico del Este) road and radar facilities are built (Mowbray 2008, Scatena 1993) (table 3). 

1959 Pinus caribaea is successfully introduced to Puerto Rico with some plantings in the Luquillo Mountains (Mosquera and 

Feheley 1984)

1960 The U.S. Multiple-Use Sustained Yield Act establishes that national forests be managed for outdoor recreation, range, timber, 

watershed, and wildlife and fish purposes (U.S. Department of Agriculture, Forest Service 1983).

1960 An arboretum is established at 625 m elevation on the lower western slope of the LEF along PR route 186 where more 

than 80 native and exotic species are maintained (Francis 1989).

1961–65 The Atomic Energy Commission experiments with the effects of gamma radiation on tropical vegetation as part of the “Atoms 

for Peace” program and proposed sea-level Panama Canal project (Mowbray 2008). The University of Puerto Rico runs the

Verde field station under Forest Service permit. Studies culminate in “A Tropical Rain Forest” (Odum and Pigeon 1970). 

1962 A cottage on the Molindero Road is made available to the University of Puerto Rico as a biological research station 

(Wadsworth 1970).

1962–63 Summer courses in tropical silviculture are offered for forestry students from the United States (Anonymous 1963).

1962–63 Yokahú Tower is built (Domínguez Cristóbal 1997b). 

1963 A major Swietenia hybrid line planting program establishes 1275 ha of plantings by 1981 (Weaver and Bauer 1986).

1963 A new species, tree frog (Eleutherodactylus hedricki), is discovered in the LEF (Joglar 1998, Rivero 1963).

1963 Corvus leucognaphallus (White-necked crow) is last seen within the LEF (Raffaele 1983).

1963 The U.S. Army carries out herbicide research (i.e., Picloram or Agent White) on 0.4 ha in the LEF (Mowbray 2008).

1963–2003 U.S. Navy operates an electronic site at Pico del Este for tracking missiles on Vieques and joint surveillance activities for 

three agencies, including the Federal Aviation Administration (FAA). Navy use discontinues in 2003 but FAA activities 

remain through a special use permit with the USDA Forest Service (Mowbray 2008).

1964 The Wilderness Act establishes a national wilderness system (U.S. Department of Agriculture, Forest Service 1983). 

1964–74 Foresters and plant taxonomists describe and illustrate in two volumes of all known tree species in Puerto Rico and the U.S. 

Virgin Islands, including those in the Luquillo Mountains (Little and Wadsworth 1964; Little and others 1974). 

1965 The LEF timber management plan is drafted (Muñoz 1965, see endnotes).

1965–77 The Arnold Arboretum initiates research in the Dwarf forest on Pico del Oeste. Ultimately, 17 research papers are published

dealing with the climate, soils, and vegetation on the Luquillo Mountain summits (Howard 1968).

1968 The U.S. Wild and Scenic Rivers Act is passed (U.S. Department of Agriculture, Forest Service 1983).

1968–87 Puerto Rican parrot occupies the LEF as a last refuge and is designated an endangered species. The parrot recovery 

program begins with cooperation from the U.S. Fish and Wildlife Service, the Puerto Rico Department of Natural 

Resources, and the World Wildlife Fund. The parrot program work is summarized in a book and in 2000 the first parrots 

reared in captivity are released into the wild (Snyder and others 1987, White and others 2005).

Appendix A— (continued) Chronology of critical activities, events, important documents and laws, and little known facts 

influencing the environment of the Luquillo Mountains and its flora and fauna. Related activities and events with multiple 

occasions (e.g., mining) are entered once or twice at the most appropriate datesa, b

continued
145

Appendix A

Date Topic 

1969 The National Environmental Policy Act states that systematic, interdisciplinary approaches be employed for environmental

planning and decisionmaking, and that environmental impact statements with alternatives be presented for proposed actions

(U.S. Department of Agriculture, Forest Service 1983).

1970 The Toro Negro forest is transferred to the Commonwealth of Puerto Rico Forest Reserve System in exchange for forest

lands added to the LEF in the Luquillo Mountains (Wadsworth 1970).

1970–92 P.R. route 191 near the LEF’s south border is closed by a landslide and by 1992 efforts to reopen it are abandoned. The

highway remains closed between km 13 and 21 (Domínguez Cristóbal 1997c; U.S. Department of Agriculture, Forest

Service 1997a).

1971 Dendroica angelae (Elfin woods warbler), an endemic, is discovered within the LEF (Kepler and Parkes 1972). 

1972 The first Puerto Rican Parrot aviary is established in the LEF’s old army barracks (Snyder and others 1987).

1973 The U.S. Endangered Species Act authorizes the government to designate a species as endangered or threatened, and to

 indicate its critical habitat (U.S. Department of Agriculture, Forest Service 1983).

1973 Life zones are described for Puerto Rico and the U.S. Virgin Islands (Ewel and Whitmore 1973).

1974–76 The U.S. Forest and Rangeland Renewable Resources Planning Act and the U.S. National Forest Management Act establish 

a periodic review of programs for administration and management of the National Forest System, including research and 

cooperation with State and Private Forest Service programs (U.S. Department of Agriculture, Forest Service 1983).

1974–91 The El Yunque Electronics site consolidation plan is implemented, eliminating 23 buildings and reducing permitees from

> 200 to 9 (U.S. Department of Agriculture, Forest Service 1991). In 1981, the Puerto Rican Telephone Company

Communications Tower on El Yunque is completed, culminating > 30 years of construction and modification of facilities.

1975 A book on the common ferns in the Luquillo Forest is published (Kepler 1975).

1976 The LEF is designated as part of the international network of Biosphere Reserves (Domínguez Cristóbal 1997b).

1976 The Youth Conservation Corps (YCC) program begins in the LEF based on the 1970 U.S. YCC Act. The Act implements 

needed conservation work, provides gainful employment, and educates the island’s youth on nature conservation and heritage 

(U.S. Department of Agriculture, Forest Service 1983).

1982 The Catalina Service Center, formerly the district ranger office, serves as a new office complex for the CNF (Luis Rivera 2010, 

see endnotes).

~1982 A parked crane falls off FS-27 road and damages 0.3 ha of Montane rain forest below Pico del Oeste (Weaver, pers. obs).

1984 Mineral resources, the location of > 20 mining sites, and mining history are described for the forest (Cardona 1984).

1985 U.S. Congress authorizes watershed research in the Bisley watersheds where work begins on the Long Term Ecological

Research (LTER) program in 1987 (Scatena 1989).

1985 Two books describe vines and climbing plants in Puerto Rico, including those in the LEF (Acevedo-Rodríguez 2005;

Acevedo-Rodríguez and Woodbury 1985).

1985–97 The descriptive treatment of the flora of Puerto Rico is completed, including all species in the Luquillo Mountains 

(Liogier 1985-97).

1986–97 The land and resource management plan for the CNF (also LEF) is reviewed by the public, revised through amendments,

and finally adopted (U.S. Department of Agriculture, Forest Service 1997a, 1997b). 

1989 The Institute celebrates 50 years (1939-89) of research, much of it carried out in the LEF (Lugo and Lowe 1995). 

1990 Long-term Ecological Research Grid is established in Lower montane rain forest near El Verde (Soil Survey Staff 1995).

1992 The first visitor interpretative plan is completed for the LEF (Vélez and others 1992, see endnotes).

Appendix A— (continued) Chronology of critical activities, events, important documents and laws, and little known facts 

influencing the environment of the Luquillo Mountains and its flora and fauna. Related activities and events with multiple 

occasions (e.g., mining) are entered once or twice at the most appropriate datesa, b

continued
146

Appendix A

Date Topic 

1994 A drought emergency plan is drafted to supply 3 million liters from forest streams to surrounding communities during major

water shortages (Caribbean National Forest 1994, see endnotes).

1996 El Portal Tropical Forest Center opens with 3000 m2 of exhibition space, offering educational opportunities for the public.

The interpretation program highlights an introduction to tropical forests, benefits of forests to humans, and future forest

conservation and management (U.S. Department of Agriculture, Forest Service 1997a).

1999 An environmental education program for teachers is developed to complement tours in the LEF (Ruiz Díaz and others 1999).

2000 A silvics manual is published and includes many tree species that grow in the LEF (Francis and Lowe 2000).

2000 Forest inventory sampling, first carried out in 1980, is expanded to the Luquillo Mountains (Birdsey and Weaver 1982, 

Brandeis and others 2003).

2002 The Caribbean National Forest Wild and Scenic Rivers Act of 2002 (P.L. 107-365 as amended) designates the Río Icacos,

 Río Mameyes, and Río de la Mina, totaling 15.2 km in length (El Yunque National Forest 2009).

2002 The soil survey of the Luquillo Experimental Forest is published (U.S. Department of Agriculture, Natural Resources

Conservation Service 2002). 

2005 H.R. 539, the Caribbean National Forest Act (P.L. 109-118) designates 10,000 acres (about 4050 ha) of National 

Forest land in Puerto Rico as the El Toro Wilderness (El Yunque National Forest 2009).

2007 A forest transportation study concludes that a mass transit system be implemented for PR 191 (U.S. Department of 

Agriculture, Forest Service 2009).

2007 U.S. Fish and Wildlife Service officially opens the new Iguaca (Puerto Rican Parrot) aviary along PR route 9966 (U.S. 

Department of the Interior, U.S. Fish and Wildlife Service 2007).

2009 An interpretation and conservation education master plan is produced for El Yunque (El Yunque National Forest 2009).

aMain and related topics (e.g., gold mining, hurricanes, and others) are presented on one date for convenience.

bAdditional sources: Mosquera and Feheley (1984); also, information derived from IITF archives and notes compiled by Frank H. Wadsworth, 

Institute of Tropical Forestry director from 1956 to 1979 (Wadsworth 2009, see endnotes); and El Yunque National Forest 2011. 

Appendix A— (continued) Chronology of critical activities, events, important documents and laws, and little known facts 

influencing the environment of the Luquillo Mountains and its flora and fauna. Related activities and events with multiple 

occasions (e.g., mining) are entered once or twice at the most appropriate datesa, b
Appendix B

147

APPENDIX B

Appendix B—Forest supervisors of the National Foresta

Years Names (titles)b

1917 Emory M. Bruner, Forest Supervisor, Superintendent General of the Forests of Puerto Rico (Department of Agriculture and Labor)

1923 William P. Kramer, Forest Supervisor, Superintendent General of the Forests of Puerto Rico (Department of Agriculture and Labor)

1931 Thomas R. Barbour, Forest Supervisor, Superintendent General of the Forests of Puerto Rico (Department of Agriculture and Labor)

1935 Evan Worth Hadley, Forest Supervisor, Superintendent General of the Forests of Puerto Rico (Department of Agriculture and Labor)

1943 Arthur T. Upson, Forest Supervisor/Tropical Forest Experiment Station Directorb

1949 Henry B. Bosworth, Forest Supervisor/Tropical Forest Experiment Station Directorb

1951 Irvin P. Murray, Forest Supervisor 

1956 Frank H. Wadsworth, Forest Supervisor and Tropical Forest Research Center Project Leader (later called Institute of Tropical Forestry)c

1963 Lawrence W. Hill, Forest Supervisor at the Institute of Tropical Forestry

1974 Leonard A. Linquist, Forest Supervisord

1976 Juan E. Muñoz, Forest Supervisor

1986 Bernie Ríos, Forest Supervisor

1989 José Salinas, Forest Supervisor

1993 Pablo Cruz, Forest Supervisor

aThe name of the National Forest changed several times during the period 1903-2007; also, the name of the current International Institute of Tropical 

Forestry changed several times between 1939 and 1992 (see Introduction).

bSource: Bagué 1962.

cThe Caribbean National Forest and the Tropical Forest Experiment Station were combined into a unit called the Tropical Region. 

dThe administration of the Caribbean National Forest was separated from the Institute of Tropical Forestry. 
Appendix C

148

APPENDIX C

Appendix C—Gradient sampling tally—occurrence of 105 tree species, mostly natives, by environmental factors within 

the Luquillo Experimental Forest

Species name Typea Stems Elevationb

Occurrence of species 

Forest typec Topographyd

LM MO PA DW R S V Total R S V

total % m --- stems (no.) --- --- plots (no.) --- --- stems (no.) ---

Alchornea latifolia Sw. 64 0.486 350-915 7 47 10 12 7 6 25 31 14 19

Alchorneopsis portoricensis

 Urban

3 0.023 380-630 1 2 0 1 1 2 0 1 2

Andira inermis (W. Wright) DC. 2 0.015 350-380 2 0 1 1 2 0 1 1

Antirhea obtusifolia Urb. LEF 10 0.076 350-760 5 5 1 6 3 10 1 6 3

Ardisia luquillensis (Britton) Alain LEF 22 0.167 640-990 12 10 6 5 2 13 8 12 2

Brunfelsia lactea Krug & Urban LEF 1 0.007 860 1 1 0 0 1 1 0 0

Buchenavia tetraphylla

 (Aublet) R. Howard

15 0.114 350-780 6 9 5 5 2 12 7 5 3

Byrsonima spicata (Cav.) HBK 2 0.015 560-650 1 1 1 1 0 2 1 1 0

Byrsonima wadsworthii Little PR 74 0.562 350-950 3 69 2 16 9 5 30 46 21 7

Calyptranthes krugii Kiaersk. PR 99 0.752 640-1000 37 1 61 14 8 6 28 60 23 16

Calyptropsidium sintensii Kiaersk. 7 0.053 820 7 0 0 1 1 0 0 7

Casearia arborea

 (L.C. Rich) Urban

7 0.053 560-800 6 1 2 1 0 3 6 1 0

Casearia decandra Jacq. 3 0.023 740-750 3 0 1 2 3 0 1 2

Casearia sylvestris Sw. 2 0.015 460 2 0 0 1 1 0 0 2

Cassipourea guianensis Aubl. 13 0.099 350-700 4 9 6 3 0 9 10 3 0

Cecropia schreberiana Mig. 237 1.801 350-950 48 54 130 5 9 13 25 47 66 73 98

Cestrum macrophyllum Vent. 3 0.023 650 3 1 0 0 1 3 0 0

Chionanthus domingensis Lam. 3 0.023 650-920 1 2 1 1 0 2 1 2 0

Citharexylum caudatum L. 34 0.258 645-960 31 3 3 1 11 15 7 1 26

Cleyera albo-punctata (Griseb.) 

 Krug & Urban

2 0.015 820-850 2 2 0 0 2 2 0 0

Clibadeum erosum (Sw.) DC. 13 0.099 730-880 13 1 1 2 4 5 2 6

Clusia clusioides (Griseb.) D’Arcy 220 1.671 450-1000 7 136 1 76 19 17 6 42 91 109 20

Coccoloba swartzii Meisner 2 0.015 670 2 1 0 0 1 2 0 0

Cordia borinquensis Urban PR 432 3.281 350-960 23 347 37 25 25 28 28 81 153 144 135

Cordia sulcata DC. 4 0.03 380-460 4 0 1 2 3 0 1 3

Croton poecilanthus Urban LEF 393 2.985 360-960 51 313 18 11 8 13 29 50 30 84 279

Cyathea arborea (L.) J.E. Smith 121 0.919 460-970 5 70 3 43 7 7 11 25 40 53 28

Cyathea bryophila

 (R. Tryon) Proctor

PR 435 3.304 850-1000 12 2 421 6 8 9 23 47 176 212

Cyathea portoricensis

 Spreng ex Kuhn 

PR 13 0.099 720-870 13 0 1 3 4 0 8 5

Cybianthus sintenisii Mart. LEF 3 0.023 680-950 2 1 1 2 0 3 1 2 0

Cyrilla racemiflora L. 274 2.081 450-970 36 206 2 30 20 18 7 45 154 107 13

Dacryodes excelsa Vahl 192 1.458 350-850 150 41 1 10 10 4 24 104 81 7

Daphnopsis philippiana

 Krug & Urban

PR 234 1.777 450-970 49 140 2 43 19 23 13 55 83 120 31

Dendropanax arboreus

 (L.) Decne & Planch.

2 0.015 750 2 0 0 1 1 0 0 2

Dendropanax laurifolius

 (E. March.) Decne & Planch. 

PR 3 0.023 860-915 1 2 2 0 0 2 3 0 0

continued
Appendix C

149

Appendix C— (continued) Gradient sampling tally—occurrence of 105 tree species, mostly natives, by environmental 

factors within the Luquillo Experimental Forest

Species name Typea Stems Elevationb

Occurrence of species 

Forest typec Topographyd

LM MO PA DW R S V Total R S V

total % m --- stems (no.) --- --- plots (no.) --- --- stems (no.) ---

Ditta myricoides Griseb. 79 0.601 450-950 2 60 12 5 10 11 12 33 23 27 29

Drypetes glauca Vahl 103 0.782 350-800 55 48 4 8 7 19 20 58 25

Eugenia borinquensis Britton LEF 572 4.345 550-1000 1 115 24 432 20 18 20 58 258 204 110

Eugenia eggersii Kiaersk. PR 8 0.061 660-750 4 4 2 1 1 4 4 1 3

Eugenia stahlii (Kiaersk.) 

 Krug & Urban 

PR 41 0.311 380-850 4 37 6 9 3 18 13 24 4

Ficus citrifolia P. Miller 3 0.023 640-760 3 0 2 1 3 0 2 1

Ficus crassinervia Desf. 3 0.023 760-890 3 1 2 0 3 1 2 0

Ficus sintenisii Warb. 3 0.023 460-750 1 2 2 1 0 3 2 1 0

Guarea glabra Vahl 13 0.099 450-780 1 12 0 3 5 8 0 6 7

Guarea guidonia (L.) Sleumer 13 0.099 350-730 12 1 3 3 4 10 3 3 7

Guatteria caribaea Urban 8 0.061 350-470 8 2 2 0 4 6 2 0

Guettarda valenzuelana A. Rich. 32 0.243 380-750 4 28 4 4 3 11 7 8 17

Haenianthus salicifolius Griseb. 231 1.755 350-1000 3 172 8 48 20 20 12 52 110 88 33

Hedyosmum arborescens Sw. 25 0.189 550-1050 1 17 7 7 2 4 13 11 4 10

Henriettea macfadyenii

 (Triana) Alain

2 0.015 820 2 0 0 1 1 0 0 2

Henriettea squamulosa

 (Cogn.) Judd.

PR 1401 10.642 350-1000 34 925 85 357 32 35 32 99 476 594 331

Hirtella rugusa Pers. PR 134 1.018 360-860 10 124 11 9 2 22 89 43 2

Hirtella triandra Sw. 6 0.045 350 6 1 0 0 1 6 0 0

Homalium racemosum Jacq. 14 0.106 350-700 3 11 3 2 2 7 6 6 2

Ilex nitida (Vahl) Maxim. 16 0.122 650-920 13 3 5 6 0 11 9 7 0

Ilex sideroxyloides (Sw.) Griseb. 3 0.023 470-835 2 1 1 2 0 3 1 2 0

Ilex sintenisii (Urban) Britton LEF 4 0.031 1050 4 1 0 0 1 4 0 0

Inga laurina (Sw.) Willd. 37 0.281 350-680 9 28 2 2 3 7 28 6 3

Inga vera Willd. Ex L. 14 0.106 370-780 4 10 2 2 3 7 2 2 10

Ixora ferrea (Jacq.) Benth. 26 0.197 350-780 8 18 7 3 0 10 18 8 0

Laetia procera (Poeppig) Eichl. 1 0.008 370 1 1 0 0 1 1 0 0

Laplacea portoricensis

 (Krug & Urban) Dyer

LEF 2 0.015 350 2 1 0 0 1 2 0 0

Magnolia splendens Urban LEF 88 0.668 350-990 7 59 22 16 14 12 42 40 34 14

Manilkara bidentata (A.DC.) Chev. 82 0.623 350-650 79 3 5 4 3 12 32 38 12

Margaritaria nobilis L. f. 1 0.008 350 1 1 0 0 1 1 0 0

Marliera sintenisii Kiaersk. LEF 25 0.189 640-990 25 5 5 0 10 13 12 0

Matayba domingensis

 (DC.) Radlk.

122 0.927 370-875 17 105 12 10 3 25 68 48 6

Mecranium latifolium

 (Cogn.) Skean

6 0.046 630-960 5 1 1 1 4 6 1 1 4

Meliosma herbertii Rolfe 30 0.228 350-800 13 17 4 3 0 7 21 9 0

Menendezia urbanii Cogn. 25 0.191 350-750 15 10 3 3 1 7 15 7 3

Miconia laevigata (L.) DC. 42 0.319 640-920 40 2 4 8 2 14 10 30 2

Miconia pachyphylla Cogn. PR 12 0.091 680-1000 4 8 3 2 1 6 5 5 2

Miconia prasina (Sw.) DC. 1 0.007 680 1 0 1 0 1 0 1 0

Miconia sintenisii Cogn. PR 9 0.068 720-950 1 3 5 1 1 4 6 1 1 7

Miconia tetrandra D. Don 147 1.116 450-915 8 138 1 13 9 10 32 74 32 41

Micropholis garciniifolia Pierre LEF 1097 8.333 350-1000 83 642 10 362 38 36 15 89 499 539 59

continued
Appendix C

150

Appendix C— (continued) Gradient sampling tally—occurrence of 105 tree species, mostly natives, by environmental 

factors within the Luquillo Experimental Forest

Species name Typea Stems Elevationb

Occurrence of species 

Forest typec Topographyd

LM MO PA DW R S V Total R S V

total % m --- stems (no.) --- --- plots (no.) --- --- stems (no.) ---

Micropholis guyanensis

 (A. DC.) Pierre

369 2.803 370-900 19 349 1 14 11 8 33 206 130 33

Myrcia deflexa (Poir.) DC. 13 0.099 450-880 1 11 1 2 1 2 5 4 1 8

Myrcia fallax (A. Rich) DC. 104 0.791 470-970 3 97 1 3 22 10 2 34 80 21 3

Myrcia leptoclada DC. 20 0.152 380-560 20 1 3 1 5 7 12 1

Myrcia splendens (Sw.) DC. 1 0.007 660 1 0 0 1 1 0 0 1

Myrcine coriaceae (Sw.) 

 R. Br. Ex Roem. & Schult.

1 0.007 850 1 0 0 1 1 0 0 1

Ocotea leucoxylon (Sw.) Mez 75 0.571 350-970 13 46 6 10 20 11 10 41 49 15 11

Ocotea moschata (Meisn.) Mez PR 8 0.061 450-790 1 7 1 2 2 5 1 5 2

Ocotea portoricensis Mez PR 5 0.038 650-915 3 2 3 0 1 4 4 0 1

Ocotea spathulata Mez 931 7.072 350-1000 19 338 9 565 35 30 19 84 528 326 77

Ormosia krugii Urban 27 0.205 380-780 9 18 5 3 0 8 21 6 0

Palicourea croceoides

 W. Hamilton

38 0.289 450-940 4 1 33 3 1 2 6 25 11 2

Prestoea montana

 (R. Grah.) Nichols

2366 17.972 350-970 285 1296 650 135 26 28 43 97 468 503 1395

Psychotria berteroana DC. 108 0.82 450-970 21 56 19 12 16 14 15 45 48 22 38

Pterocarpus officinalis Jacq. 1 0.007 350 1 0 0 1 1 0 0 1

Rheedia portoricensis

 (Urban) Alain

PR 60 0.456 350-750 5 55 4 3 1 8 48 10 2

Rondeletia portoricensis

 Krug & Urban

PR 10 0.076 450-915 1 9 1 1 3 5 2 1 7

Sapium laurocerasus Desf. PR 50 0.381 450-950 5 30 13 2 5 7 13 25 7 10 33

Schefflera morototoni

 (Aubl.) Mcguire

42 0.319 350-790 23 14 5 8 6 4 18 26 12 4

Sloanea berteroana Choisy 90 0.684 350-890 60 28 2 8 8 13 29 30 25 35

Syzygium jambos (L.) Alston EXO 5 0.038 730-760 4 1 1 1 0 2 1 4 0

Tabebuia heterophylla

 (DC.) Britton

14 0.106 350-740 7 7 2 1 5 8 5 1 8

Tabebuia rigida Urban LEF 1303 9.897 450-1000 32 391 36 844 30 26 13 69 606 578 119

Ternstroemia luquillensis

 Krug & Urban

LEF 2 0.015 1050 2 1 0 0 1 2 0 0

Tetragastris balsamifera

 (Sw.) Kuntze

53 0.402 360-780 52 1 4 3 2 9 33 17 3

Torralbasia cuneifolia

 (C. Wright) Krug & Urban

29 0.221 620-1000 15 14 10 3 0 13 25 4 0

Trichilia pallida Sw. 5 0.038 360-460 5 0 0 2 2 0 0 5

Vitex divaricata Sw. 2 0.015 615-960 2 0 1 1 2 0 1 1

Xylosma schwaneckeanum

 Krug & Urban

LEF 8 0.061 710-970 5 3 3 1 1 5 6 1 1

 Total (105 species) 13165 100 350-1000 1390 7023 1135 3617 44 44 44 132 5075 4623 3467

aType: PR = endemic to Puerto Rico; LEF = endemic to Luquillo Experimental Forest; EXO = exotic; blank = non-endemic native species.

bElevational range for species tallied in the gradient sampling.

cSampling by forest type varied. Total number of plots = 132 in LEF (5.77 ha), including 18 in LM (0.90 ha), 69 in MO (3.45 ha), 12 in PA (0.60 ha), 

and 33 in DW (0.82 ha).

dOccurrence by topography—R = ridge (44 plots), S = slope (44 plots), and V = ravine (44 plots). Stem numbers are absolute values (i.e., not 

converted to a hectare basis).

continued
Appendix D

151

APPENDIX D

Appendix D—Tentative successional classification of some tree species within the Luquillo Experimental Forest 

and notes on where they regeneratea

Forest typec Regeneration categoryd

Speciesb LM MO PM DF Open areas Gaps Shade Landslides

Acnistis arborescens (L.) Schlecht. 3

Alchornea latifolia Sw. 8 P W X 1,2,3

Alchorneopsis floribunda (Benth.) Muell. Arg. 4 X X 2

Antirhea coriaceae (Vahl.) Urban 1

Bambusa vulgaris Schrad.e 3

Buchenavia tetraphylla (Aublet) R. Howard 16 X 1,2

Byrsonima spicata (Cav.) HBK 17 X

Byrsonima wadsworthii Little 14 X X

Calophyllum calaba L. 2

Calyptranthes krugii Kiaersk. D W 1

Casearia arborea (L.C. Rich) Urban 2

Casearia decandra Jacq. 5 X

Casearia sylvestris Sw. 2

Cecropia schreberiana Miq 1 1 P HX XH 1,2,3

Cestrum macrophyllum Vent. 2,3

Chionanthus domingensis Lam. 24 X X 2,3

Citharexylum caudatum L. 3

Citharexylum fruticosum L. 1

Cleyera albo-punctata (Griseb.) Krug & Urban 1

Clibadeum erosum (Sw.) DC. P X X 2,3

Clusia clusioides (Griseb.) D’Arcy 6 D TWX XT

Coccoloba schwartzii Meisner 3

Coffea arabica L.e, f 2

Cordia borinquensis Urban P D 1,2

Cordia sulcata DC. 6 X 3

Croton poecilanthus Urban 11 16 P D X X 1,2

Cyathea arborea (L.) J.E. Smith D WX X 1,3

Cyathea bryophila (R. Tryon) Proctor D WX X

Cyathea portoricensis Spreng ex Kuhn P

Cyrilla racemiflora L. 3 3 D XT 1,2,3

Dacryodes excelsa Vahl 19 X 2

Daphnopsis philippiana Krug & Urban D 1

Ditta myricoides Griseb. P 1

Eugenia borinquensis Britton 20 P D W X X 1

Eugenia stahlii (Kiaersk.) Krug & Urban 28 19 X 2

Eupatorium portoricense Urban 2

Ficus citrifolia P. Miller 1

Ficus sintenisii Warb. 2

Guarea glabra Vahl 1

Guarea guidonia (L.) Sleumerf 25 X X 2,3

Guettarda valenzuelana A. Rich. 2

Haenianthus salicifolius Griseb. 17 D XT XT 1
Appendix D

152

Appendix D— (continued) Tentative successional classification of some tree species within the Luquillo 

Experimental Forest and notes on where they regeneratea

Forest typec Regeneration categoryd

Speciesb LM MO PM DF Open areas Gaps Shade Landslides

Hedyosmum arborescens Sw. 1

Henriettea squamulosa (Cogn.) Judd. 12 15 P D W X X 1

Heterotrichum cymosum (Wendl.) Urban 2,3

Hirtella rugosa Pers. X X 1,2,4

Homalium racemosum Jacq. 9 X 3

Inga laurina (Sw.) Willd.f 22 X X 2,3

Inga vera Willd. ex L.f 13 X 2,3

Lonchocarpus latifolius (Willd.) H.B.K. 3

Magnolia splendens Urban 4 D XT 1

Manilkara bidentata (A.DC.) Chev. 15 XH X 4

Margaritaria nobilis L. f 2,3

Matayba domingensis (DC.) Radlk. 20 7 X X 2

Mecranium latifolium (Cogn.) Skean 1,2

Miconia faveolata Cogn. XHW XH 3

Miconia impetiolaris (Sw.) D. Don. 2

Miconia laevigata (L.) DC. XT

Miconia mirabilis (Aubl.) L.O. Williams 2

Miconia pachyphylla Cogn. W 2

Miconia prasina (Sw.) DC. 2,3

Miconia racemosa (Aubl.) DC. 1,2,3

Miconia serrulata (DC.) Naud. 2,3

Miconia sintenisii Cogn. W 1,3

Miconia tetrandra D. Don 2 W X 1,2,3

Micropholis garciniifolia Pierre 21 12 P D W X 1

Micropholis guyanensis (A. DC.) Pierre 10 X X 1,3

Myrcia citrifolia (Aubl.) Urban 2

Myrcia deflexa (Poir.) DC. X 2,3,4

Myrcia fallax (A. Rich) DC. 13 X X 2

Myrcia leptoclada DC. X 2

Myrcia splendens (Sw.) DC. X 2,4

Myrcine coriaceae (Sw.) R. Br. ex Roem. & Schult. 2

Ocotea leucoxylon (Sw.) Mez D 1,2,3

Ocotea moschata (Meisn.) Mez 26 11 X

Ocotea sintenisii (Mez) Alain 2

Ocotea spathulata Mez 18 D W X X 1,2

Ochroma pyradimale (Cav. ex Lamb) Urbane 2

Ormosia krugii Urban 23 X X

Palicourea croceoides W. Hamilton D X 1,4

Palicourea riparia Benth. X 2,3,4

Pinus caribaea Morelete 3

Piper aduncum L. 1,2,3

Piper amalago L. 2

Prestoea montana (R. Grah.) Nichols 18 9 P D X X 1,2,3

Psidium guajava L.e 3

Psychotria berteroana DC. P D WX X 1,2,3

continued
Appendix D

153

Appendix D— (continued) Tentative successional classification of some tree species within the Luquillo 

Experimental Forest and notes on where they regeneratea

Forest typec Regeneration categoryd

Speciesb LM MO PM DF Open areas Gaps Shade Landslides

Rheedia portoricensis (Urban) Alain 1,2,3

Roystonea borinquena O.F. Cook 3

Sapium laurocerasus Desf. 7 5 P X 1,2,3

Samyda dodecandra Jacq. 2

Schefflera morototoni (Aubl.) Mcguire 14 2 X X 1,2,3

Sloanea berteroana Choisy 27 XH 1,3

Solanum torvum Sw. 2

Swietenia macrophylla G. Kinge X X 2,4

Syzygium jambos (L.) Alstone X 2,4

Tabebuia heterophylla (DC.) Britton 10 X X 1,2,3

Tabebuia rigida Urban 8 P D W XT 1,3

Tetragastris balsamifera (Sw.) Kuntze 29 X 1

Tetrazygia urbanii Cogn. 1,3

Trema lamarckiana (R.&S.) Blume 2

Trema micrantha (L.) Blume 2

Trichilia hirta L. 1

Trichilia pallida Sw. W

Urera baccifera (L.) Gaud.-Bapre 2

aSources: Byer and Weaver (1977); Devoe (1989); Guariguata (1990); Myster and Walker (1997); Shiels (2010); Smith (1970); Wadsworth 

(2009), see endnotes; Weaver (1990, 1992, 2000, 2002).

bSpecies included represent: (a) 34 species that were previously ranked on a successional scale in Lower montane rain forest and/or 

Montane rain forest; (b) species that were tallied in the gradient study; or (c) species that were encountered by authors cited in footnote 

a. Species taxonomy (Liogier 1985, 1997). cForest type: LM = Lower montane; MO = Montane; PM = Palm; DF = Dwarf. Numbers indicate ranking of species from 1 = most 

secondary to 29 = most primary in LM (Smith 1970), and 1 = most secondary to 20 = most primary in MO (Weaver 1999). Species 

lacking numbers were not ranked. Gradient study: P = species with ≥10 individuals recorded in Palm brake; D = species with ≥10 

individuals recorded in Dwarf forest. 

dRegeneration category is based on Lower montane and Montane rankings and other observations. X = regeneration as indicated (i.e., 

open, gap, or shade), H = regeneration after hurricanes, T = regeneration after thinnings, W = regeneration on plane wreck site in dwarf 

forest. Regeneration after landslides according to study: 1 (Guariguata 1990); 2 (Myster and Walker 1997); 3 (landslide on PR route 191 

at km 21, this study); 4 (Wadsworth 2009, see endnotes).

eExotic species.

f

Coffee and tree species used for coffee shade.
Appendix E

154

APPENDIX E

Appendix E—Tree species planted within the Luquillo Experimental Foresta

Species

Purpose of plantingb

AR AG OR PL Originc Percent aread

Acrocarpus franinifolius Arn. AR E

Agathis robusta (C. Moore) F.M. Baileye AR PL ENS

Albizia lebbeck (L.) Benth. PL EN 1.1

Aleurites moluccana (L.) Willd.e AR ENS

Alstonia macrophylla Wall. AR E

Andira inermis (W. Wright) DC. PL NA <0.1

Annona muricata L. AG NI

Annona reticulata L. AG NI

Annona squamosa L. AR NI

Anthocephalis chinensis (Lam.) A. Rich. ex Walp.e AR PL ES

Araucaria angustifolia (Bertol.) O. Kuntze AR E

Araucaria cunninghamii Aiton ex D. Don.e AR ES

Artocarpus altilis (Parkinson) Fosberge AG ENS

Bambusa gigantochloaf SS E

Bambusa longispiculata Gamble ex Brandis SS E

Bambusa textilis McClure SS E

Bambusa tulda Roxb. SS E

Bambusa tuldoides Munro. SS E

Bambusa vulgaris Schrad.e PL ENS

Brunfelsia americana L. OR NA

Byrsonima spicata (Cav.) HBK PL NA 0.5

Callitris glauca R. Br. ex Mirb. AR E

Callitris intratropica R.T. Baker & H.G. Smith AR E

Calophyllum calaba L. OR PL NI

Carapa guianensis Aubl.e AR PL ENS

Castanospermum australe A. Cunn. & C. Fraser ex Hook AR E

Castilla elastica Cervantesg OR EN

Casuarina equisetifolia L. AR PL EN 3.0

Catalpa longissima (Jacq.) Sims OR PL E

Cecropia schreberiana Miq. AR PL NA

Cedrela odorata L. PL NI 13.0

Ceiba pentandra (L.) Gaertn. PL NA 0.1

Chrysophyllum cainito L. AG ?

Chukrasia tabularis A. Juss. AR E

Cibistax donnell-smithii Rose AR PL E

Citrus aurantifolia (L.) Swingle AG E

Citrus aurantium L. AG EN

Citrus limon (L.) Burm. F. AG EN

Citrus sinensis (L.) Osbeck AG EN

Clitoria racemosa G. Don.e AR ES

Coccoloba krugii Lindau. PL NA

Cocos nucifera L. AG OR EN

continued
Appendix E

155

Appendix E— (continued) Tree species planted within the Luquillo Experimental Foresta

Species

Purpose of plantingb

AR AG OR PL Originc Percent aread

Coffea arabica L. AG EN

Cordia alliodora Ruiz & Pav. AR PL NA 8.5

Cryptomera japonica (L. f.) D. Don. AR E

Cunninghamia lanceolata (Lamb.) Hook.e AR ES

Cupressus lusitanica Mill. Cv. Benthamiie AR PL ENS

Dacryodes excelsa Vahl PL NA

Dalbergia sissoo Roxb. PL EN 1.5

Delonix regia (Bojer) Raf.e OR ENS

Dendrocalamus strictus Nees SS E

Entandophragma angolensis C. DC. AR E

Eucalptus maculata Hook AR E

Eucalyptus alba Reinw. ex Blume PL E

Eucalyptus botryoides Sm. PL E

Eucalyptus camaldulensis Dehnh. PL E

Eucalyptus citriodora Hook AR PL E <0.1

Eucalyptus crebra F. Muell. AR E

Eucalyptus grandis Hill ex Maidene AR ES

Eucalyptus kirtoniana F. Muell PL E

Eucalyptus maidenii F. Muell. AR E

Eucalyptus mysore-bangalore (hybrid)f AR E

Eucalyptus paniculata Sm. AR E

Eucalyptus patentinervus R.T. Bak.e AR ES

Eucalyptus resinifera J.E. Smith PL E

Eucalyptus robusta J.E. Smithe AR PL ENS 0.4

Eucalyptus rostrata Schl.e PL ES

Eucalyptus saligna Sm.e AR PL ES

Eucalyptus spp. PL E 0.1

Eucalyptus tereticornis Sm. PL E

Eugenia jambolana Lam. PL E

Eugenia stahlii (Kiaersk.) Krug & Urban PL N

Fraxinus uhdei (Wenzig) Lingelsh.e AR PL ENS

Gliricidia sepium (Jacq.) Kunth ex Griseb. AG EN

Gmelina arborea Roxb.e ES

Goetzia elegans Wydler AR N

Guarea guidonia (L.) Sleumer PL N 1.6

Gyranthera caribensis Pittier AR E

Hernandia sonora L. AR NA

Hibiscus elatus Sw.e AR OR PL ENS

Hibiscus rosa-sinensis L. OR E

Hisbiscus tiliaceus L.e OR ES

Hymenaea courbaril L. PL NA 0.1

Inga vera Willd. AR NA

Jatropha multifida L. OR NA

Khaya grandifoliola C. DC.e AR ES

Khaya nyasica Stapf. ex Bakere AR PL ENS

Khaya senegalensis (Desr.) A. Juss.e AR ENS

continued
Appendix E

156

Appendix E— (continued) Tree species planted within the Luquillo Experimental Foresta

Species

Purpose of plantingb

AR AG OR PL Originc Percent aread

Lagerstroemia speciosa (L.) Pers. OR E

Maesopis eminii Englere AR ENS

Mammea americana L. AG NA

Mangifera indica L.e AG ENS

Manilkara bidentata (A. DC.) Chev. PL NA 0.5

Matayba domingensis (DC.) Radlk. PL NA

Montezuma speciosissima Sessee & Moc. OR PL NI 5.1

Myroxylon balsamum (L.) Harms AR EN

Ochroma pyramidale (Cav.) Urban PL E

Ocotea moschata (Meisn.) Mez AR NA

Olea sp. AR E

Parkia timoriana (DC.) Merr. AR EN

Peltophorum inerme (Roxb.) Naves PL E

Persea americana Mill. AG EN

Petitia dominguensis Jacq. PL NA 4.7

Pinus ayacahuite Ehrenb. ex Schltdl. AR E

Pinus caribaea Morelete, h AR PL ENS

Pinus chiapensis (Martínez) Andresene AR ES

Pinus devoniana Lundi AR E

Pinus douglasiana Martinez AR E

Pinus echinata Mill. AR E

Pinus ellioti var. densa Engelm.e AR ES

Pinus kesiya Royle ex Gordoni AR E

Pinus massoniana Lamb. AR E

Pinus montezumae Lamb. AR E

Pinus occidentalis Sw. AR E

Pinus oocarpa Schiede ex Schltdl.e AR ES

Pinus patula Schiede ex Schltdl. & Cham. AR E

Pinus pseudostrobus Lindl. AR E

Pinus taeda L. AR E

Plumeria rubra L. OR E

Pouteria multiflora (A. DC.) Eyma PL NA

Psidium guajava L. AG E

Pterocarpus indicus Willd. AR PL EN

Pterocarpus macrocarpus Kurz AR EN

Sabinea florida (Vahl.) DC. OR NI

Sambucus simpsonii (Rehd.) OR E

Schizolobium parahybum (Vell.) Blake AR EN

Senna siamea (Lam.) Irwin OR PL EN 1.1

Sequoia sempervirens (D. Don.) Endl. AR E

Sideroxylon foetidissimum Jacq. PL NI

Simarouba amara Aubl. AR EN

Sloanea berteroana Choisey PL NA

Spathodea campanulata Beauv.e OR ENS

Swietenia macrophylla Kinge AR PL ENS 27.3

Swietenia mahagoni Jacq. AR PL EN 23.8

continued
Appendix E

157

Appendix E— (continued) Tree species planted within the Luquillo Experimental Foresta

Species

Purpose of plantingb

AR AG OR PL Originc Percent aread

Swietenia hybrid (macrophylla x mahagoni)e PL ENS

Syzygium jambos (L.) Alstone AG PL ENS <0.1

Tabebuia heterophylla (DC.) Britton AR PL NA 5.7

Taxodium mucronatum Tenore AR E

Tectona grandis L. PL EN 1.6

Terminalia catappa L. AR OR EN

Terminalia ivorensis A. Chev.e AR ENS

Theobroma cacao L. AG EN

Toona ciliata Roem.e AR PL ES

Toona sureni (Blume) Merr. AR E

Vitex divaricata Sw. PL NA 0.2

Widdringtonia whytei Rendle AR E

 Total 75 17 18 61 144 100.0

aSources: Francis (1987, 1989); Francis and Liogier (1991); Little (1976); Marrero (1947, 1948, 1950). Some species 

listed as planted also grow naturally in the mountains.

bAR = arboretum; AG = agriculture; OR = ornamental; PL = forest plantations; SS = soil stabilization along roadsides.

cOrigin: E = exotic; EN = naturalized exotic; ES or ENS = exotic adapted for planting in the LEF; NA = native to Puerto 

Rico, NI = native but introduced to the Luquillo Mountains; ? = uncertain.

dTotal area in forest before 1950 plantations is about 1600 ha, estimated from seedlings planted. Precise areas of other 

species not known (i.e., agricultural, ornamental, or roadside stabilization). Most arboretum species were planted in 

small blocks of 50 trees.

eAdapted to conditions in the LEF (Francis 1987).

f

Nomenclature and authorities from 70 year-old records are uncertain (e.g., Bambusa and Gigantochloa are currently 

both genus names).

gObserved in Mameyes valley near Bisley during the 1990s.

hPinus caribaea has three varieties planted in the LEF: bahamensis, caribaea, and hondurensis. i

Formerly Pinus insularis and P. michoacana, respectively.
158

Appendix F

APPENDIX F

Appendix F—Available wood specific gravities for 87 tree species native to the 

Luquillo Experimental Foresta

Tree species

Density by decimal group Specific gravity

Tree species

Alphabetical Specific gravity

g cm-3 g cm-3

Ochroma pyramiale 0.22 Alchornea latifiolia 0.39

Prestoea montana 0.26 Andira inermis 0.63

Cecropia schreberiana 0.29 Antirhea obtusifolia 0.73

Pterocarpus officinalis 0.32 Ardisia luquillensis 0.70

Hedyosmum arborescens 0.33 Beilschmiedia pendula 0.54

Simarouba amara 0.34 Buchenavia tetraphylla 0.61

Schefflera morototoni 0.36 Byrsonima spicata 0.64

Sapium laurocerasus 0.38 Byrsonima wadsworthii 0.54

Alchornea latifiolia 0.39 Calyptranthes krugii 0.78

Daphnopsis philippiana 0.40 Cassipourea guianensis 0.70

Ficus citrifolia 0.40 Cecropia schreberiana 0.29

Meliosma herbertii 0.42 Chionanthes domingensis 0.81

Ocotea leucoxylon 0.45 Citharexylum caudatum 0.57

Ormosia krugii 0.50 Clusia clusioides 0.90

Nectandra coriacea 0.51 Clusia rosea 0.67

Palicourea riparia 0.51 Cordia borinquensis 0.70

Psychotria berteroana 0.51 Cordia sulcata 0.60

Guarea guidonia 0.52 Croton poecilanthus 0.60

Cyrilla racemiflora 0.53 Cyathea arborea 0.70

Dacryodes excelsa 0.53 Cyrilla racemiflora 0.53

Beilschmiedia pendula 0.54 Dacryodes excelsa 0.53

Byrsonima wadsworthii 0.54 Daphnopsis philippiana 0.40

Guarea glabra 0.54 Ditta myricoides 0.57

Mecranium amydalinum 0.55 Drypetes glauca 0.67

Miconia pachyphylla 0.55 Eugenia borinquensis 0.70

Tetrazygia urbanii 0.55 Eugenia eggersii 0.75

Miconia laevigata 0.56 Eugenia stahlii 0.73

Citharexylum caudatum 0.57 Ficus citrifolia 0.40

Ditta myricoides 0.57 Garcinia portoricensis 0.90

Tabebuia rigida 0.57 Grammadenia sintenisii 0.70

Tabebuia heterophylla 0.58 Guarea glabra 0.54

Tabebuia heterophylla 0.58 Guarea guidonia 0.52

Torralbasia cuneifolia 0.58 Guatteria caribaea 0.80

Inga vera 0.59 Guettarda scabra 0.65

Magnolia splendens 0.59 Haenianthus salicifolius 0.81

Ocotea moschata 0.59 Hedyosmum arborescens 0.33

Cordia sulcata 0.60 Henriettea squamulosa 0.74

Croton poecilanthus 0.60 Hirtella rugosa 0.90

Laplacea portoricensis 0.60 Homalium racemosum 0.77

Rondeletia portoricensis 0.60 Hymenaea courbaril 0.76

Buchenavia tetraphylla 0.61 Ilex sideroxyloides 0.77

Inga laurina 0.62 Inga laurina 0.62

continued
159

Appendix F

Appendix F— (continued) Available wood specific gravities for 87 tree species native 

to the Luquillo Experimental Foresta

Tree species

Density by decimal group Specific gravity

Tree species

Alphabetical Specific gravity

g cm-3 g cm-3

Mammea americana 0.62 Inga vera 0.59

Ocotea spathulata 0.62 Ixora ferrea 0.73

Andira inermis 0.63 Laetia procera 0.68

Tetragastris balsamifera 0.63 Laplacea portoricensis 0.60

Byrsonima spicata 0.64 Magnolia splendens 0.59

Micropholis garciniifolia 0.64 Mammea americana 0.62

Guettarda scabra 0.65 Manilkara bidentata 0.82

Ternstroemia luquillensis 0.65 Margaritaria nobilis 0.90

Clusia rosea 0.67 Marliera sintenisii 0.75

Drypetes glauca 0.67 Matayba domingensis 0.70

Laetia procera 0.68 Mecranium amydalinum 0.55

Micropholis guyanensis 0.68 Meliosma herbertii 0.42

Ardisia luquillensis 0.70 Miconia laevigata 0.56

Cassipourea guianensis 0.70 Miconia pachyphylla 0.55

Cordia borinquensis 0.70 Miconia prasina 0.70

Cyathea arborea 0.70 Miconia sintenisii 0.70

Eugenia borinquensis 0.70 Miconia tetrandra 0.70

Grammadenia sintenisii 0.70 Micropholis garciniifolia 0.64

Matayba domingensis 0.70 Micropholis guyanensis 0.68

Miconia prasina 0.70 Myrcia deflexa 0.80

Miconia sintenisii 0.70 Myrcia fallax 0.75

Miconia tetrandra 0.70 Myrcia splendens 0.80

Antirhea obtusifolia 0.73 Nectandra coriacea 0.51

Eugenia stahlii 0.73 Ochroma pyramiale 0.22

Ixora ferrea 0.73 Ocotea leucoxylon 0.45

Henriettea squamulosa 0.74 Ocotea moschata 0.59

Eugenia eggersii 0.75 Ocotea spathulata 0.62

Marliera sintenisii 0.75 Ormosia krugii 0.50

Myrcia fallax 0.75 Palicourea riparia 0.51

Xylosma schwaneckeanum 0.75 Prestoea montana 0.26

Hymenaea courbaril 0.76 Psychotria berteroana 0.51

Homalium racemosum 0.77 Pterocarpus officinalis 0.32

Ilex sideroxyloides 0.77 Rondeletia portoricensis 0.60

Calyptranthes krugii 0.78 Sapium laurocerasus 0.38

Guatteria caribaea 0.80 Schefflera morototoni 0.36

Myrcia deflexa 0.80 Simarouba amara 0.34

Myrcia splendens 0.80 Sloanea berteroana 0.80

Sloanea berteroana 0.80 Tabebuia heterophylla 0.58

Chionanthes domingensis 0.81 Tabebuia heterophylla 0.58

Haenianthus salicifolius 0.81 Tabebuia rigida 0.57

Manilkara bidentata 0.82 Ternstroemia luquillensis 0.65

Clusia clusioides 0.90 Tetragastris balsamifera 0.63

Garcinia portoricensis 0.90 Tetrazygia urbanii 0.55

Hirtella rugosa 0.90 Torralbasia cuneifolia 0.58

Margaritaria nobilis 0.90 Xylosma schwaneckeanum 0.75

aSources: Reyes and others (1992); Little and Wadsworth (1964); Little and others (1974).

Peter L. Weaver. 2012. The Luquillo Mountains: Forest Resources and Their History. 

Gen. Tech. Rep. IITF-44. San Juan, PR: U.S. Department of Agriculture, Forest Service, 

International Institute of Tropical Forestry. 159 p.

This report presents an overview of the El Yunque National Forest, which is also designated as Luquillo Experimental Forest, in northeastern Puerto Rico. The principal topics 

include the environmental setting (geology, soils, and climate), environmental gradients, 

arborescent flora, vertebrate fauna, and forest management (i.e., plantations, silvicultural 

operations, planning, research, and designated land uses). A chronology from the time 

of European discovery to the present outlines major events in the Luquillo Experimental 

Forest, including an early presence of indigenous peoples, exploration for gold, timber 

extraction, farming, trail and road construction, and recreational developments. 

Keywords: Disturbances, forest resources, gradients, history, Luquillo Mountains of 

Puerto Rico, management, research. 
The Forest Service, United States Department of 

Agriculture (USDA), is dedicated to the principle 

of multiple use management of the Nation’s forest 

resources for sustained yields of wood, water, 

forage, wildlife, and recreation. Through forestry 

research, cooperation with the States and private forest owners, and 

management of the National Forests and National Grasslands, it 

strives—as directed by Congress—to provide increasingly greater 

service to a growing Nation.

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