United States

Department of

Agriculture

m

w“f” Southern Forest

Forest Service Research Note

Experiment Station

so-331

February 1987

Forest Area Trends in Puerto Rico

Richard A. Birdsey and Peter L. Weaver

SUMMARY LONG-TERM FOREST AREA TRENDS

Forest area trends in Puerto Rico from 1980 to 1985

are included in this update of earlier studies. Total forest

area has increased from 279,000 ha in 1980 to 300,000

ha in 1985. Most of the new forest is growing on abandoned pasture. Secondary forest and abandoned coffee

shade account for 78 percent of all forest land. Xeric

scrub and active coffee shade account for 11 percent

and 10 percent of all forest land, respectively.

Additional keywords: forest survey, remote sensing, tropical forests.

Puerto Rico’s 890,000 ha of land were mostly forested

in the 18th century. By 1828, timber cutting and development of nonforest land uses had reduced the island’s

forest cover to about 587,000 ha (Wadsworth 1950).

Coffee cultivation under shade trees was just beginning.

By 1899 forest cover was reduced to 182,000 ha. Pasture accounted for about 490,000 ha, and coffee production occupied 77,000 ha (Wadsworth 1950). For the next

20 years, tree cover declined slowly (Murphy 1916). The

forests could yield few products other than fuelwood or

charcoal.

INTRODUCTION

Puerto Rico’s timberland was inventoried in 1980. Detailed statistics on forest area, species composition, and

timber volume were reported (Birdsey and Weaver

1982). For the 1980 inventory, forest area estimates

were made by a dot-count method using black-and-white

aerial photographs taken in the mid-1970’s and from

field checks in 1980. Forest area estimates for some

areas lacking complete photograph coverage were

made from other sources of information.

Additional forest clearing began after 1916; by 1931,

forests covered only 81,000 ha or 9 percent of the land

(Gill 1931). During the late 1940’s, forest declined to only

6 percent of the land area, and coffee shade covered

about the same area (Koenig 1953). Since then, forests

gradually recovered because cropland and pasture were

abandoned on eroded hillsides in the Island’s mountainous regions (fig. 1). By 1980, forests occupied about

250,000 ha and coffee shade about 30,000 ha (Birdsey

and Weaver 1982).

A photographic mission in 1984 provided aerial photographs that were used to develop more current estimates of forest cover, to make reliable estimates for the

entire island, and to estimate rates of change in timberland area. Field checks were made in 1985. This report

covers area trends between 1980 and 1985.

METHODS

Fieldwork was accomplished through cooperation between U.S. Forest Service, Southern Forest Experiment

Station, and the Puerto Rico Department of Natural Resources. Photography was acquired by the National

Aeronautic and Space Administration’s Earth Resources

Laboratory with support from the Southern Forest Experiment Station.

High-altitude color infrared aerial photography, at a

scale of approximately 1:64,000, was acquired for all of

Puerto Rico’s main island during March, 1984. Cloud

cover averaged less than 10 percent. Higher elevations

had more cloud cover-especially the Luquillo Mountains in the east and the Toro Negro region in the center

of the island.

Prior to fieldwork, an experienced photointerpreter

used a dot-count method to identify 12 forest and 3 nonforest land cover classes on film transparencies. (For

land cover classes, see DEFINITIONS). A grid of 25 dots

Southern Forest Experiment Statlonfl-10210 U.S. Postal Services Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S. Department of Agriculture.

Wing Alabama, Arkansas, Loulslana, Mlsslsslppl, E. Oklahoma, Tennessee, E. Texas, Puerto RICO, U.S. Vlrgln Islands

1
Table 1 .-Land area by survey region, Puerto Rico, 1980

___

500 -

2 400 -

5p ” 300 -

R

8 200 -

z

100 -

)H--

C-c-----2.3d’

---_

0 -- 8 ’ ’ ’ ’ ’ c 1 0 1 1 1 8 1

1820 1840 1660 I660 1900 1920 1940 1960 1960

YEAR

Figure l.-Area with tree cover in Puerto Rico, 1828-1985. Forest

does not include nonstocked forest land.

was centered over each of 978 permanent sample plot

locations. Sample plots are located at the intersections

of a square grid of lines spaced 3 km apart. Land cover

class was estimated for each dot and for each plot location. A total of 22,418 dots was interpreted.

Fieldwork was accomplished from January to March,

1985. A subsample of 257 locations was checked to

develop a correction factor to account for photointerpretation errors and land use changes between the dates of

photo acquisition and fieldwork. The correction factor

applied to the dot count adjusted the photointerpretation

estimate. Ground check locations were allocated proportional to the 1988 area estimate for each of the land

cover classes.

In 1980 about half the Island was identified as potentially capable of commercial forestry and was inventoried

intensively (table 1). Remaining areas were excluded

from detailed investigation. For this survey, detailed area

Survey region

Commercial

Subtropical Moist Forest Life Zone’

Deep volcanic soils2

Shallow volcanic soils

Granite soils

Limestone soils

Total Subtropical Moist Forest Life Zone

Subtropical Wet Forest Life Zone

Deep volcanic soils

Shallow volcanic soils

Granite soils

Limestone soils

Total Subtropical Wet Forest Life Zone

Total commercial

Noncommercial3

Subtropical Dry Forest Life Zone

Critical watersheds

Unproductive soils

Alluvial and metropolitan

Mangrove and swamp

Noncontinguous Puerto Rico

Total nonnommercial

Total land area

Hectares

69,000

116,700

33,100

61,100

299,900

99,600

20,600

12,000

4,500

136,700

436,600

121,500

109,300

92,200

76,000

7,500

47,200

435,700

690,300

‘Life Zones according to Holdrige (1967) determined by Ewe1 and

Whitmore (1973).

‘Soil groups defined and mapped by Zambrana (1976).

3Areas were defined sequentially in the order presented.

changes were estimated for the commercial forestry region only, and current area estimates were made for the

whole Island. In general, the commercial forestry region

is located in the central highlands, exclusive of the

steepest and wettest areas where forest cover protects

critical watersheds (fig. 2). Land areas were classified

Figure 2.-The 1980 survey region (in black) judged to be capable of growing commercial timber in

Puerto Rico.

Richard A. Birdsey is research forester, U.S. Forest Service, Southern Forest Experiment Station, Starkville, MS. Peter L. Weaver is research

forester, U.S. Forest Service, Southern Forest Experiment Station, Rio Piedras, PR. The authors wish to acknowledge the substantial contributions

to this study by the Puerto Rico Department of Natural Resources. Ralph Schmidt provided administrative support, and Luis Vega and Ruben Padron

assisted in the fieldwork.

2
commercial or noncommercial regardless of ownership.

One of the more challenging tasks was to separate

forested tracts from nonforested tracts of land that were

reverting from actively grazed pasture to forest. Although

the stocking threshold. is defined as lo-percent tree

cover, active grazing or other nonforest use may cause

a tract to be classified as nonforest even if it has more

than 1 O-percent tree cover. In some cases determination

can only be based on the judgment of the timber cruiser.

In 1985, plot records from 1980 for a few sample locations were reviewed and reclassified. This procedural

change does not represent a real change in forest area.

The sampling error for all forest land was estimated to

be plus or minus 2.0 percent by random-sampling formula, based on one standard deviation, or a probability

of two chances out of three. The sampling error was

estimated at 2.6 percent for forests in the commercial

survey region, and 1.9 percent for forests in the noncommercial region. As estimates of totals are divided among

smaller classes, the sampling error increases.

RESULTS

The estimate of total forest area for the entire Island

increased from 279,000 ha in 1980 to 300,000 ha in

1985 (table 2). This increase occurred in the commercial

region as reversions of cropland and pasture to forest

exceeded forest clearing for nonforest uses (table 3). All

new forest land was classified as secondary forest.

About 8,000 ha were cleared for relatively permanent

nonforest uses such as residences and rights-of-way.

About 58 percent of the Island’s forests was classified

Table 2.-Land area by survey region and broad land cover class,

Puerto Rico 1980 and 1985

1980 survey region

and land cover class

Survey date

1980 1985

- Thousand hectares -

Commercial survey region:

Forest 130.5 180.2

Nonforest 308.1 278.4

Total 438.8 438.8

Noncommercial survey region:’

Forest 148.2 139.3

Nonforest 305.5 314.4

Total 453.7 453.7

All regions:

Forest 278.7 299.5

Nonforest 811.8 590.8

Total 890.3 890.3

‘Changes since 1980 may be the result of a more intensive sample

and complete aerial photographic coverage of the noncommercial survey region.

as secondary, with slightly more than half located in the

commercial survey region (table 4). Abandoned coffee

shade comprises the next largest forest class. Abandoned and active coffee shade combined total 82,000

ha. The total area of forest that was once used for coffee

Table 3.-Forest area changes in the commercial survey region,

Puerto Rico 1980 to 1985

Item Area change Total area

Forest area, 1980

Additions from:

Cropland

Pasture

Other’

Total

130.5

+14.7

+32.2

+11.7

+58.8

Diversions to:

Cropland

Pasture

Others

Total

-13.4

-7.4

-8.2

-29.0

Net change +29.8

Forest area, 1985 180.2

------- Thousandhectares ------

‘These additions resulted primarily from a reclassification of some

nonforest plots from the 1980 sample and do not represent an actual

change in land cover.

21ncludes forest clearing for urban and industrial development, rural

residences, rightsof-way, etc.

Table 4.-Land area by detailed land cover class and survey region,

Puerto Rico 1985

Land cover class

1980 Survey region All

Commercial Noncommercial regions

-------- Thousand hectares ____-__

Forest:

Secondary1 89.8 83.9 173.5

Abandonedcoffeeshade 38.5 18.3 52.8

Active coffee shade 22.0 8.8 28.8

Upper mountain . . . . . . . . . . 2.3 2.3

Palm . . . . . . . . . . 1.8 1.8

Dwarf . . . . . . . . . . 1.8 1.8

Xeric scrub 12.12 21.7 33.8

Mangrove . . . . . . . . . . 4.7 4.7

Total forest 180.2 139.3 299.5

Nonforest:

Cropland

Pasture

40.2 80.3 100.5

182.8 148.1 308.9

Others 73.4 108.0 181.4

Total nonforest 278.4 314.4 590.8

All land 438.8 453.7 890.3

‘Also includes nonstocked forest land, plantations, and lower

mountain (tabonuco) types.

2Xeric forest cover on limestone and serpentine soils formerly

classified as secondary forest.

31dle farmland, water, roads and rights-of-way, urban, and industrial

areas.

3
production is more than 82,000 ha, but older abandoned

coffee shade becomes difficult to distinguish from reverted pasture or cropland.

Another common cover class is xeric scrub, accounting for 11 percent of Puerto Rico’s forest. Most of this

vegetation is located along the southern coast, which

receives less than 1,000 mm of rainfall annually. The

remainder is scattered elsewhere on limestone or serpentine soils that are highly permeable or on extreme

slopes that hold very little soil. These conditions produce

scrub vegetation despite adequate rainfall.

Although other forest classes occupy small areas,

they are nevertheless very important as protective

forests for upper watersheds, coastal lowlands, and

wildlife habitat. Some of these small areas are the last

refuge of endangered plant and wildlife species. Plantation and lower mountain forests, not sampled intensively

enough to provide separate area estimates, were included in the secondary forest class.

CONCLUSIONS

Between 1980 and 1985, Puerto Rico’s forest area

increased by about 4,000 ha annually. Puerto Rico’s

forest resource is approaching a stage of recovery that

could support sustained removals of useful timber products from selected areas.

A review of the 1980 survey by Wadsworth and Birdsey (1985) concluded that about half the secondary

forest was adequately stocked with species that have

good timber potential. As the area of adequately stocked

timberland increases, so too will the opportunity to develop silvicultural methods to enhance the value of timber stands. The new forests also are valued for recreation and watershed protection. The increase in forest

area may provide many benefits to the residents of

Puerto Rico.

Land Class

Nonforest Land. -Land not meeting the qualifications

for forest land, land that has never supported forest, and

lands formerly forested where timber management is

precluded by development for other uses. Includes

areas used for crops, improved pasture, residential

areas, improved roads of any width adjoining clearings,

and powerline clearings.

Forest Land.-Land at least 10 percent stocked by

forest trees of any size, or formerly having such tree

cover and not currently developed for nonforest use. The

minimum area for classification of forest land is l/2 ha,

and minimum width for forest strips is 35 m. Includes

unimproved roads and trails, streams, and clearings in

forest areas if less than 35 m in width.

Forest Class

Mangrove. -Inundated forest formations along the

shores of protected saline bays, lagoons, and estuaries.

Nonstocked Forest Land.-Forest land less than 10

percent stocked with growing-stock trees or formerly

having such tree cover and not currently developed for

nonforest use. Areas covered by inhibiting vegetation

such as brush, vines, and ferns may be included.

Reversion .-Pasture or cropland with 10 to 50 percent tree and shrub crown closure or stocking.

Secondary Forest Land. -Forest land resulting from

the abandonment of cropland or pasture and forest resulting from the regeneration of previously cutover or

disturbed forest land.

Coffee Shade. -A multistory, multicrop system used

principally for the production of coffee. An upper story of

shade trees is characteristic.

Abandoned Coffee Shade. -Secondary forest land

resulting from the abandonment of coffee production

under shade trees.

Lower Mountain Forest. -The local ‘Yabonuco” forest

type, with Dacryodes excelsa usually, but not necessarily, dominant. Found in the Subtropical Wet Forest Life

Zone. Common associate species are Sloanea berteriana, Prestoea montana, and Manilkara bidentafa.

Upper Mountain Forest. -The local “colorado” forest

type, with Cyril/a racemiflora usually, but not necessarily,

dominant. Found in the Subtropical Lower Montane Wet

Forest Life Zone. Common associate species are

Ocotea spathulata , Micropholis chrysophylloides, and

M. garciniaefolia. Prestoea montana is common in the

central mountains.

Pa/m Brake.-Nearly pure stands of Prestoea montana that form in upper mountain regions.

Dwarf Forest.-Also known as cloud forest or elfin

woodland. Found on the summits of the highest mountains and characterized by densely packed, gnarled

trees less than 7 m tall.

Plantation. -Stands in which artificially regenerated

species comprise more than 25 percent of the total basal

area.

Xeric Scrub. -Small woody vegetation generally less

than 10 m tall at maturity, found under dry conditions

typical of the Subtropical Dry Forest Life Zone and on

certain serpentine and limestone soils.

Survey Region

Commercial. -Land judged capable of growing commercial timber crops. Includes all areas that were not

excluded because of low rainfall, excessive rainfall, excessive slope, unproductive soil, or higher priority use

such as prime farmland or urban development. Also excludes mangrove and swamp areas and all islands not

connected to the mainland.

Noncommercial. -All areas excluded from commercial timber production (see definition of commercial region).

4
Birdsey, FL; Weaver, P. The forest resources of Puerto

Rico. Resour. Bull. SO-85. New Orleans, LA: U.S.

Department of Agriculture, Forest Service, Southern

Forest Experiment Station; 1982. 59 p.

Ewel, J.; Whitmore, J. The ecological life zones of Puerto

Rico and the U.S. Virgin Islands. Res. Pap. ITF-18.

Rio Piedras, PR: US. Department of Agriculture,

Forest Service, Southern Forest Experiment Station;

1973. 72 p.

Gill, T. Tropical forests of the Caribbean. Baltimore, MD:

The Read-Taylor Co.; 1931. 318 p.

Holdridge, L. Life zone ecology. (Revised edition). San

Jose, Costa Rica: Tropical Science Center; 1967.

206 p.

Koenig, N. A comprehensive agricultural program for

Puerto Rico. Washington, DC: U.S. Department of

Agriculture and Commonwealth of Puerto Rico; 1953.

290 p.

Murphy, L. Forests of Puerto Rico, past, present, and

future. Bull. No. 354. Washington, DC: U.S. Department of Agriculture; 1916. 99 p.

Wadsworth, F. Notes on the climax forests of Puerto

Rico and their destruction and conservation prior to

1900. Caribbean Forester 11(l): 38-47; 1950.

Wadsworth, F.; Birdsey, R. A new look at the forests of

Puerto Rico. Turrialba 35(l): 11-17; 1985.

Zambrana, J. Asociaciones de suelos de Puerto Rico y

su potential para la siembra de arboles. Rio Piedras,

PR: U.S. Department of Agriculture, Forest Service,

Southeastern Forest Experiment Station; 1978. 6 p.

aU.S.GOVEFlNMENTPRINllNCORICEd987 -761 086/60020

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