CliMate Change effeCts

in el Yunque national forest, 

Puerto Rico, and the Caribbean Region

lisa nicole Jennings, Jamison Douglas, emrys treasure, and grizelle gonzález

United States Department of Agriculture

Forest Service

Research & Development

Southern Research Station

General Technical Report SRS-193
The Authors:

Lisa Nicole Jennings, Natural Resource Specialist, USDA Forest 

Service, Grandfather Ranger District, Pisgah National Forest, 109 

East Lawing Drive, Nebo, NC 28761; Jamison Douglas, Research 

Associate, North Carolina State University, College of Natural 

Resources, Department of Forest and Environmental Resources, 

Campus Box 7260, Raleigh, NC 27695; Emrys Treasure, Biological 

Scientist, USDA Forest Service, Southern Research Station, Eastern 

Forest Environmental Threat Assessment Center, Raleigh, NC 27606; 

and Grizelle González, Project Leader, USDA Forest Service, 

International Institute of Tropical Forestry, Jardín Botaníco Sur, 

Río Piedras, PR 00926.

Cover Photos 

top row left to right: Bromeliad blooming in El Yunque National Forest. 

(Photo by M. Solorzano); Common coquí (Eleutherodactylus coqui). 

(Photo by M. Solorzano); View from El Yunque National Forest looking 

south to the Caribbean Sea. (Photo by Maria M. Rivera); Mt. Britton trail 

through Sierra Palm (Prestoea montana) stands in El Yunque National 

Forest. (Photo by Maria M. Rivera); Leaf detail. (Photo by M. Solorzano).

bottom: Looking north from Las Cabezas Observation Point in El Yunque 

National Forest. (Photo by Lisa Jennings).

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.

May 2014

Southern Research Station

200 W.T. Weaver Blvd.

Asheville, NC 28804

www.srs.fs.usda.gov
Climate Change Effects

in El Yunque National Forest, Puerto Rico, 

and the Caribbean Region

Lisa Nicole Jennings, Jamison Douglas, Emrys Treasure, and Grizelle González
View from El Yunque National Forest looking south to the Caribbean Sea. (Photo by Maria M. Rivera)
preface iii

Preface

Forest lands across the world are experiencing increased risk from extreme weather, 

drought, fire, insect and plant invasions, and disease. Scientists project increases in 

air temperature, changes in rainfall patterns, and higher levels of atmospheric carbon 

dioxide (CO2) that may cause these threats to occur more often, with more intensity, or for 

longer durations. Natural resource managers and planners are increasingly tasked with 

considering the effects of climate change in their everyday work. Although many of the 

effects of future changes may be considered negative, natural resource management can 

help mitigate these impacts. Management strategies informed by the best current science 

enable natural resource professionals to better protect the land and resources and sustain 

the benefits of forest lands into the future. However, the ever-increasing volume of useful 

scientific information about climate change makes it difficult for managers and planners 

to effectively consider and apply emerging science. This report provides a knowledge 

base of peer-reviewed climate change science for El Yunque National Forest (EYNF), also 

administratively designated as the Luquillo Experimental Forest (LEF), Puerto Rico, and 

the greater Caribbean region. The extensive literature review reflects the body of sources 

gathered by the U.S. Department of Agriculture (USDA) Forest Service’s Template for 

Assessing Climate Change Impacts and Management Options (TACCIMO; Treasure and 

others 2014) database in collaboration with the International Institute of Tropical Forestry 

(IITF) and local managers from EYNF. 

In the context of increased scrutiny of the effects of climate change on forest resources, the 

Forest Service, U.S. Department of Agriculture released climate change guidance related 

to both project-level management operations and large scale forest planning. The recently 

released National Forest System Land Management Planning Rule (USDA Forest Service 

2012) requires national forests undergoing land and management plan revisions to complete 

a broad assessment of available information, including the best available science identified 

during a thorough review and analysis of relevant peer-reviewed scientific literature. The 

literature review included in this report aims to address climate change needs for land 

and resource management planning in EYNF, but it also expands to encompass effects on 

natural forest lands throughout Puerto Rico and the greater Caribbean region. Content in 

this report resulted from a comprehensive literature review process, driven by collaboration 

between TACCIMO’s content development staff and technical information specialists 

and scientists at the IITF library. Direct TACCIMO output, in the form of quotations, was 

further subject to summarization (see appendix for science summary methodology) and 

extensive input and review by tropical forest resource specialists from IITF, EYNF, and 

partner institutions. First, we present an overview of key findings specific to climate change 

effects on natural resources, focusing on EYNF. Next, we provide a detailed literature 

review of climate change projections and effects on local drivers and stressors, as well as 

ecological, physical, social, and economic resources in the Caribbean region. Sources in 

this report cover over two decades of scientific inquiry, from 1992 to 2013, and reflect the 

evolving understanding of climate change and its impacts on natural resources, with a focus 

on new and emerging best available scientific information. In total, we summarized findings 

from over 240 peer-reviewed literature sources within 16 resource areas. Within each 

resource area, findings specific to EYNF and Puerto Rico (when available) are indicated by 

bullet points shaded by a gradient (as in the example below): 

• Torres and others (2008) found that the climate of EYNF is sensitive to changes in sea 

surface temperatures (SSTs). SSTs have increased 1.5 °C over the ... 

Findings from the broader Caribbean region are indicated by unshaded bullet points.
Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region iv

study Region

The greater Caribbean region comprises an area of approximately 2 754 000 km2 inclusive 

of 35 territories and States that border the Gulf of Mexico and the Caribbean Sea. The entire 

Caribbean region falls within the tropics, geographically delineated by the Tropic of Cancer 

to the north and the Tropic of Capricorn to the south. Islands are grouped into the Greater 

Antilles in the north and the Lesser Antilles in the south and east. Puerto Rico, located in 

the northeastern Caribbean, is the smallest island group in the Greater Antilles with a land 

area of approximately 9100 km2 (fi g. 1). Puerto Rico has a tropical maritime climate typical 

of Caribbean islands (Daly and others 2003). Temperatures are warm year-round, with an 

island-wide average temperature of 25 °C and seasonal differences of only 3 °C between 

December and July (fi g. 2A; Daly and others 2003). Puerto Rico is infl uenced by tropical 

moist systems from June through November and northerly dry systems from December 

through May, leading to distinct wet and dry seasons (Waide and others 2013). While 

rainfall averages 1687 mm/year, differences in monthly average precipitation vary between 

a low of 68 mm in February to a high of 219 mm in October (fi g. 2B; Daly and others 2003). 

When defi ned geographically, Puerto Rico’s vegetation is considered tropical; however, 

when defi ned based on climate variables using Holdridge (1967) life zones, Puerto Rico’s 

vegetation is considered subtropical. Life zone divisions are defi ned by logarithmic 

interactions between biotemperature (calculated from average daily temperatures between 

0 and 30 °C, using “0” for values below 0 °C and above 30 °C), mean annual precipitation, 

potential evapotranspiration, and elevation (Lugo and others 1999). In Puerto Rico, life 

zones include subtropical dry, moist, wet, and rain forests, and lower montane wet and rain 

forests (fi g. 3). Across the island, life zones largely follow precipitation regimes (fi g. 2B; 

Miller and Lugo 2009). Precipitation patterns in Puerto Rico vary widely and are infl uenced 

by topography. Mountain ranges create a rain shadow from east to west and north to south 

as tropical systems move across the island, dropping much of their moisture in the forests 

(A) Temperature (B) Precipitation

Mean temp. (°C)

26

24

22

20

18

Mean precip. (mm)

4598

3623

2649

1675

701

Figure 1—Maps of (A) the greater 

Caribbean region and (B) Puerto Rico, 

showing the location of El Yunque 

National Forest, Pico del Este weather 

station, and El Verde fi eld station.

Figure 2—Spatial patterns of average 

annual temperature (A) and precipitation 

(B) from 1963 to 1995 based on historic 

observations. (From Daly and others 2003)

Puerto Rico

(A) (B)
preface v

of the Luquillo Mountains on the northeast end of the island and creating an arid climate in 

the Guánica dry forest on the southeast end of the island. Elevational gradients also produce 

large local differences in climate, with lower temperatures and greater precipitation, cloud 

cover, and humidity with increasing elevation (González and others 2013b). Areas above 

600 m in the Luquillo Mountains experience frequent cloud cover and relative humidity 

near 100 percent due to passing low clouds and the upward transport of moisture from 

warm Caribbean waters (Weaver 2012). While only six life zones are represented in Puerto 

Rico, they are characterized by a matrix of many locally recognized vegetation associations 

(Miller and Lugo 2009).

The 11 310 ha EYNF is located in the Luquillo Mountains of northeast Puerto Rico 

(fig. 1B) and covers 1.4 percent of the island’s area (Weaver 2012). Elevations range from 

120 m in the lowlands along the northeast boundary to above 1000 m on mountain peaks. 

The Luquillo Mountains have a humid tropical maritime climate (Brokaw and others 

2012). Due to elevational gradients and geographic position, the climate of the national 

forest is cooler and wetter than much of Puerto Rico, with temperatures at high-elevation 

sites averaging 18.5 °C and precipitation averaging greater than 4000 mm annually 

(Weaver 2012). The forest types of EYNF support a large diversity of tropical species. 

Dominant life zone distinctions include subtropical wet forests, subtropical rain forests, and 

subtropical lower montane wet and rain forests (see fig. 3). In EYNF, vegetation types and 

community structure shift as a result of continuous changes in cloud cover, wind exposure, 

soil moisture, temperature, and precipitation across an elevational gradient (Brokaw and 

others 2012, González and others 2013b). Land use histories also vary along the elevational 

gradient, with land use intensity decreasing with elevation from secondary lowland forests 

to protected peaks (González and others 2013b). When extreme weather events occur in 

EYNF, they can have profound effects on vegetation structure and composition (Brokaw 

and others 2012). Hurricanes frequently pass over the island, generally occurring between 

July and November, with direct hits to the Luquillo Mountains occurring every 50–60 years 

(Waide and others 2013). Despite high annual rainfall, severe droughts occur every 15 years 

on average (Waide and others 2013). 

In EYNF, four forest types are locally identified as the dominant vegetation associations, 

appearing across an elevational gradient (fig. 4; Brokaw and others 2012). Tabonuco 

(Dacryodes excelsa) lower montane wet and rain forests, with tall canopies dominated by 

tabonuco and motillo (Sloanea berteriana), cover undisturbed areas at lower elevations 

o

Subtropical dry forest

Subtropical moist forest

Lower montane rain forest

Subtropical rain forest

Lower montane wet forest

Subtropical wet forest

Figure 3—Ecological life zones of Puerto 

Rico. (From Miller and Lugo 2009)
vi Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

between 120 and 600 m. Above the cloud condensation level at 600 m, all vegetation 

associations are considered cloud forests, characterized by hydric soils, an increased 

presence of epiphytes, and a higher density of shorter trees and shrubs (Brokaw and others 

2012, Weaver 2012). Palo colorado (Cyrilla racemiflora) montane wet and rain cloud forests 

are found in areas between 600 and 900 m, composed mainly of fast-growing and longlived palo colorado trees. Elfin woodland montane wet and rain cloud forests (also known 

as dwarf forests) occur on exposed peaks above 900 m, characterized by a single story of 

stunted, low-canopy trees. Sierra palm (Prestoea montana) montane wet and rain cloud 

forests (also known as palm breaks) are found on steep, east-facing slopes and ravines above 

450 m, dominated by disturbance-resistant sierra palms. Beyond the four major vegetation 

types, planted and secondary submontane and montane forests occur on the edges of the 

forest boundary, and riparian submontane and montane forests occur along streams and 

rivers. In addition to diverse ecological communities, the forest supports the headwaters 

for 10 major rivers that provide drinking water to communities in eastern Puerto Rico, 

including the nearby San Juan Metropolitan Area (Weaver 2012). Ecological research 

sites, as part of the Luquillo Experimental Forest designation and the Luquillo Long Term 

Ecological Research (LTER) program, are established across all forest types, with major 

studies from the Bisley experimental watersheds and the El Verde field stations in the lower 

montane forest, and the Pico del Este weather station in the elfin forest. 

How to Use this Report

The purpose of this report is to provide a comprehensive and concise summary of the 

current scientific findings on the effects of climate change on natural resources in Puerto 

Figure 4—Vegetation communities in El 

Yunque National Forest. (From Quiñones 

and others 2013)
preface vii

Rico and the greater Caribbean region to increase understanding and to inform forest 

planning, as well as to direct subsequent research and climate change vulnerability 

assessment efforts. Introductory materials provide context in which to consider the findings 

contained in the report and are not intended to be a comprehensive view of the climatology 

or ecology of the region. The overview of key findings section provides an executive level 

summary of climate change effects specific to EYNF and Puerto Rico that is appropriate 

to use for communication and drawing general conclusions. The body of the report consists 

of detailed literature review summaries, organized by resource area, which provide more indepth information across the projected effects of climate change in the Caribbean region. To 

navigate to a specific issue of interest, the table of contents or keyword searching (Ctrl + F) 

may be used. The concluding section on knowledge gaps and uncertainties provides a brief 

examination of overarching research gaps and the likelihood of major climate trends. 

Although summarized literature focuses on EYNF and Puerto Rico, the scientific 

information in this report represents a wide range of ecological communities throughout 

the greater Caribbean region and the tropics. Comparison among ecological systems 

necessitates an understanding of underlying environmental conditions at various scales 

that may be beyond the scope of information presented here (Brokaw and others 2012). 

Information in this report is summarized from a variety of scientific studies employing 

varying methodologies and may rely on site-specific measurements, modeling, or 

professional scientific opinion. Studies presented use varying models and emission 

scenarios that provide differing and sometimes conflicting projections for the future 

climatology of the Caribbean, especially in the discussion of precipitation patterns. Some of 

the predicted effects of climate change lack precision as to when they may occur, and many 

of the effects may not be seen in local ecosystems until 50–100 years from now. Therefore, 

it is crucial that the specific information presented in this report is considered within the 

larger body of climate change science, studies of recent trends, and best practices for natural 

resource management. In addition, this report does not provide weighting of scientific 

evidence or discussion of management implications. Literature summaries provided in this 

report prepare the decisionmaker for further analysis, including engaging the public and 

local experts through a process that assesses the evidence within the broader context of the 

management decision, often using best professional judgment and other more qualitative 

methods (Linkov and others 2009).

Mt. Britton trail through Sierra palm 

(Prestoea montana) stands in El Yunque 

National Forest. (Photo by Maria M. 

Rivera)
Contents

Overview: Key Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Changes to Drivers and Stressors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Climate Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Extreme Weather . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Air Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

Forest Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Invasive and Introduced Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Effects on Ecological and Physical Resources . . . . . . . . . . . . . . . . . . . . . . . .13

General Biodiversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

Plant Communities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Animal Communities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Freshwater (Aquatic and Riparian) Ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . 22

Water Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Soil and Geologic Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Vegetation Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Effects on Social and Economic Resources . . . . . . . . . . . . . . . . . . . . . . . . . .30

Recreation and Tourism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30

Land Use and Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Coastal Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31

Knowledge Gaps and Uncertainties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35

Appendix: Science Summary Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . 46
OVERVIEW: KEY FINDINGS 1

Climate Change Effects 

in El Yunque National Forest, Puerto Rico, 

and the Caribbean Region

Lisa Nicole Jennings, Jamison Douglas, Emrys Treasure, and Grizelle González

ABSTRACT

Understanding the current and expected future conditions of natural resources under a changing climate is 

essential to making informed management decisions. However, the ever-increasing volume of useful scientific 

information about climate change makes it difficult for managers and planners to effectively sort through and 

apply the emerging science. This report provides a knowledge base of peer-reviewed climate change science for 

El Yunque National Forest (also administratively designated as the Luquillo Experimental Forest), Puerto Rico, 

and the greater Caribbean region. We summarized scientific findings from over 240 peer-reviewed sources, 

covering a wide range of potential effects including changes to drivers and stressors and the effects of climate 

change on ecological, physical, social, and economic systems. Projected and observed changes include increases 

in air temperatures, an extension of the dry season, and changes in cloud cover that may lead to significant 

alterations to the diverse plant and animal communities of the Caribbean region. Species in cloud forests on 

isolated mountain peaks may be most at risk, due to sensitivities to moisture and a limited chance for migration. 

Changes in extreme weather patterns, including an increase in hurricane intensity and more frequent drought 

events, are projected to alter the distribution of tropical forest vegetation. Tourism patterns and recreational 

opportunities may change with an increase in extreme weather and impacts from sea level rise. The information 

presented in this report provides a starting point for natural resource managers, planners, and stakeholders to 

assess the vulnerability of local resources to climate change as part of a broader decision-making framework.

Keywords: Assessment, Caribbean, climate change, El Yunque National Forest, forest planning, Luquillo 

Experimental Forest, technology transfer.

Overview: Key Findings

Climate Trends

Average temperatures in the Caribbean region have increased over the past 40 years 

(Uyarra and others 2005). Around the Luquillo Mountains, a small increase in annual 

maximum and minimum temperatures has been detected in long-term (62-year) records 

(Waide and others 2013). Scientists predict warming will continue at an accelerated pace 

(IPCC 2007); however, climate models vary in the degree of warming (table 1). Projected 

decreases in precipitation in the Caribbean suggest drier wet seasons, and even drier dry 

seasons (table 2; Cashman and others 2010). Increasing sea surface temperatures may lift 

the base altitude of cloud formation (Still and others 1999) and alter atmospheric circulation 

Table 1—Climate model projections for increases in temperature at end of century

Source Spatial extent Projection

Scatena (1998) Puerto Rico +1.5 to +2.5 °C

Girvetz and others (2009), Meehl and others (2007) Puerto Rico +2.2 to +2.7 °C

Campbell and others (2011) Caribbean +2 to +5 °C

Christensen and others (2007)a Central America +1.8 to +5 °C

Magrin and others (2007)b Latin America +1 to +7.5 °C

aFrom the contribution of working group I to the Fourth Assessment Report of the Intergovernmental Panel on 

Climate Change.

bFrom the contribution of working group II to the Fourth Assessment Report of the Intergovernmental Panel on 

Climate Change.

Looking north from Las Cabezas 

Observation Point in El Yunque National 

Forest. (Photo by Lisa Jennings)
2 Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

patterns (Woollings and Blackburn 2012). Any change in the cloud base height will further 

decrease precipitation in El Yunque National Forest (EYNF) (Comarazamy and González 

2011). Climate change may also affect the distribution patterns and concentrations of air 

pollutants through changing wind and precipitation patterns (Bytnerowicz and others 2007) 

as well as increased temperatures (Bedsworth 2012).

Extreme Weather

Heavy rainfall events have become more common in Puerto Rico in recent years, 

particularly since 2009, with changes linked to high sea surface temperatures (Vélez 

Rodríguez and Votaw 2012). The frequency of extreme precipitation events is expected 

to continue to increase, leading to potential increases in inland flooding and landslides 

(Magrin and others 2007, Seneviratne and others 2012). Hurricane events are likely to 

become less frequent but more severe, with increased wind speeds, rainfall intensity, and 

storm surge height (Karl and others 2009, Knutson and others 2010). In the Caribbean, 

the occurrence of very warm days and nights is accelerating, while very cool days and 

nights are becoming less common (Peterson and others 2002), increasing the likelihood of 

extreme heat waves (Anderson 2011). Additionally, as annual rainfall decreases over time in 

the Caribbean region, longer periods of drought are expected in the future (Breshears and 

others 2005, Larsen 2000). In Puerto Rico, where nearly all wildfires are associated with 

human activity, the interactions between climate warming and drying and increased human 

development have the potential to increase the effects of fire (Robbins and others 2008).

Terrestrial Ecosystems

Higher temperatures, changes in precipitation patterns, and any alteration in cloud cover 

will affect plant communities and ecosystem processes in EYNF (Lasso and Ackerman 

2003). Increasing nighttime temperatures may affect tropical tree growth and induce 

tree mortality (Clark and others 2010, Wagner and others 2012). Both intensified extreme 

weather events and progressively drier summer months in the Caribbean are expected to 

alter the distribution of tropical forest life zones (Wunderle and Arendt 2011), potentially 

allowing low-elevation tabonuco forest species to colonize areas currently occupied by palo 

colorado forest (Scatena 1998). Because they occur under narrowly defined environmental 

conditions, EYNF’s cloud forests are among the world’s most sensitive ecosystems to 

climate change (Lasso and Ackerman 2003). Cloud forest epiphytes (e.g., bromeliads) may 

experience moisture stress due to higher temperatures and less cloud cover with a rising 

cloud base, affecting epiphyte growth and flowering (Nadkarni and Solano 2002, Zotz 

and Bader 2009). Plant communities on isolated mountain peaks will be most vulnerable, 

as they will not be able to adapt to the shifting cloud base by moving to higher elevations 

(Laurance and others 2011, Magrin and others 2007).

Table 2—Climate model projections for changes in precipitation at end of century 

Source Spatial extent Projection

Girvetz and others (2009), Meehl and others (2007) Puerto Rico -10 to -30% annually

Campbell and others (2011) Caribbean -25% to -50% annually

Biasutti and others (2012) Caribbean -30% in spring and summer

Magrin and others (2007)a Latin America -40% to +10% annually

aFrom the contribution of working group II to the Fourth Assessment Report of the Intergovernmental Panel on 

Climate Change.
OVERVIEW: KEY FINDINGS 3

Aquatic Ecosystems

Shifts in rainfall patterns due to climate change will lead to periods of flooding and drought 

that can significantly affect aquatic ecosystems and water resources (Seager and others 

2009). Increases in heavy downpours in Puerto Rico and more intense hurricanes in the 

wet season can lead to greater erosion and sedimentation in waterways (Carpenter and 

others 1992, Cashman and others 2010, Karl and others 2009). Riparian areas will see 

changes in structure and composition due to altered temperature, precipitation, and run-off 

regimes as well as changes in the distribution of plant and animal species (Seavy and others 

2009). Extended droughts in the dry season may significantly affect aquatic organisms 

by decreasing dissolved oxygen (DO) content (Mulholland and others 1997). Freshwater 

aquatic communities during drought will experience crowding of species, leading to 

habitat squeezes and a decrease in reproductive output (Covich and others 2003). In EYNF 

streams, extended periods of extreme low water flows may result in increased pollutant 

concentrations and excessive nutrients (Cashman and others 2010, Covich and others 2003).

Wildlife

Climatic warming may push the narrow thermal tolerances of many species in tropical 

environments above their upper limits (Huey and others 2009, Laurance and others 2011), 

prompting population losses and habitat changes that will affect animal communities 

(Blaustein and others 2010). Because of their cool-adapted, range-restricted nature, highelevation amphibians, including Puerto Rican coquí frogs, are especially vulnerable to 

future changes (Barker and others 2011, Brodie and others 2011, Longo and others 2010, 

Stallard 2001). More frequent drought conditions may increase the vulnerability of both 

reptiles and amphibians to water loss, parasites, and diseases including amphibian chytrid 

fungus (Anchukaitis and Evans 2010, Burrowes and others 2004, Rogowitz 1996). Reduced 

rainfall may lead to decreased habitat quality for neotropical migratory birds wintering 

in EYNF (Studs and Marra 2011), while cavity-nesting birds, including the Puerto Rican 

parrot (Amazona vittata), could see an increase in habitat competition and nesting predation 

with an increase in major hurricane disturbances (Arendt 2000, Pounds and others 1999).

Recreation

The Caribbean region, where year-round warm weather is the principal tourism resource, 

may see increasing competition from other regions as warm seasons expand globally (Scott 

and others 2004). Sea level rise will affect coastal resorts, which may affect tourist and 

recreationist preferences throughout Puerto Rico (Lewsey and others 2004, Magrin and 

others 2007). Climate change may affect recreation in EYNF through changes to local 

ecosystems and resources that affect scenic values, as well as changes to weather patterns 

that may disrupt recreational activities and lead to changes in visitor use (Prideaux and 

others 2010). Visitors to EYNF may see effects to the local plant and animal communities 

that make the forest unique (Scatena 1998). An increase in extreme weather events may 

increase damage to facilities and structures, reduce tourist access in some areas, and 

increase the need for road repairs (Joyce and others 2008).

Waterfall in El Yunque National Forest. 

(Photo by F. Scatena)
4 Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

Changes to Drivers and Stressors 

Climate Trends

Large-scale circulation patterns

• Torres and others (2008) found that the climate of EYNF is sensitive to changes in sea 

surface temperatures (SSTs). SSTs have increased 1.5 °C over the last century (PRCCC 

2013), and are projected to increase about 1 °C by 2050, with the largest increases in 

the dry season and the late rainy season (Angeles and others 2007). Increasing SSTs are 

already causing increased air temperatures in coastal regions of Puerto Rico (Torres and 

others 2008).

• Temperature patterns in Puerto Rico are influenced by the El Niño/Southern Oscillation 

(ENSO), while precipitation patterns are largely influenced by the location of the North 

Atlantic Oscillation (NAO) (Malmgren and others 1998), which occurs in a roughly 60-

year cycle (Mazzarella and Scafetta 2012). Climate models project future northward shifts 

in both mid-latitude and tropical jet streams that will affect the NAO, especially in the 

winter season (Woollings and Blackburn 2012).1

• Future projections using the parallel climate model (PCM) show a decrease in average 

easterly winds over the Greater Antilles for the coming century, but an increase elsewhere 

in the Caribbean (Angeles and others 2010).

• A long-term study of climate in the Caribbean (1950–2000) found that trade winds in 

the early rainfall season have increased in magnitude and shifted to a more easterly or 

southeasterly flow, with global climate change playing an important role in the trend 

(Comarazamy and González 2011).

• Observed sensitivities of African dust to changes in climate indicate that future climate 

change could drastically change the amount of African dust reaching the Caribbean 

(Prospero and Lamb 2003).

Temperature trends

Historic trends

• At the National Weather Service station in Fajardo, Puerto Rico near the Luquillo 

Mountains, long-term (62-year) records revealed small but significant increases in annual 

maximum and annual minimum temperatures (Waide and others 2013).

• In the tropical montane cloud forest at Pico del Este in EYNF, mean monthly minimum 

temperatures have increased over the past 30 years (Lasso and Ackerman 2003). Similar 

changes were also found in the Monteverde Cloud Forest Reserve in Costa Rica, where 

temperatures have increased about 2 °C (LaVal 2004, Pounds and others 1999).

• Using an analysis of weather station data across Puerto Rico from 1900 to present, an 

average annual increase in temperatures of 0.012 to 0.014 °C per year was observed 

(PRCCC 2013).

• In the heavily urbanized San Juan Metropolitan Area, air temperatures increased 1.5 °C 

when compared with similar average past conditions (determined by looking at ENSO 

indexes) in 1977–1978 (Torres and others 2008).

• Mean annual temperatures in the Caribbean have increased an average of 0.2 to 0.4 °C 

each decade since 1976 (IPCC 2001, Uyarra and others 2005). Average overnight low 

and daytime high temperatures have also increased in the Caribbean by 1.0 and 1.8 °C, 

respectively, since 1950 (Comarazamy and González 2011).

Future trends

• Scatena (1998) modeled a projected increase in temperatures of 1.5 to 2.5 °C in Puerto Rico 

by the end of the 21st century, while recent studies using regionally downscaled models from 

Campbell and others (2011) predict a larger increase of 2 to 5 °C in the Caribbean.

1 Within each resource area, findings specific to EYNF and Puerto Rico (when available) are indicated with 

bulletpoints shaded by a gradient followed by findings from the broader Caribbean region.

Sunny day looking west from Mt. Britton 

tower in El Yunque National Forest. (Photo 

by Jamison Douglas)
Changes to Drivers and Stressors 5

• Using 3rd Coupled Model Intercomparison Project (CMIP3) models from Meehl and 

others (2007), nonparametric ensembles from Girvetz and others (2009) show average 

annual increases in temperature of 1.5 °C by 2020, 2.7 °C by 2050, and 4.6 °C by 2090 for 

Puerto Rico.

• Projections of future climate for the Caribbean region agree that temperatures will 

increase; yet, the magnitude of increase varies by model and emission scenario as well as 

regional extent (Biasutti and others 2012, Christensen and others 2007, Magrin and others 

2007, Scatena 1998).

• Using the Intergovernmental Panel on Climate Change (IPCC) models, Biasutti and 

others (2012) projected warmer annual temperatures and lower temperature variability for 

the future Caribbean climate.

• By 2020, IPCC models project an increase of 0.4 to 1.8 °C in Latin America (Magrin and 

others 2007).

• The Fourth Assessment Report of the IPCC projects an increase of 1.8 to 5 °C by the end 

of the century in Central America (Christensen and others 2007). In Latin America, an 

increase of 1 to 7.5 °C is expected (Galindo and others 2010, Magrin and others 2007).

Precipitation trends

Historic trends

• Across Puerto Rico, rainfall has declined over the 20th century; however, a specific link to 

climate change has yet to be determined (Waide and others 2013).

• Precipitation in Puerto Rico has varied over the past century, with below-average rainfall 

measured at 87 percent of the normal for 1990–1997, and 24 percent above the normal in 

1998 (Larsen 2000). In Luquillo Experimental Forest (LEF), rainfall decreased an average 

of 0.20 mm/year from 1988 to 2003 with low rainfall periods most frequently occurring in 

March (Heartsill-Scalley and others 2007).

• The incidence of heavy precipitation at Pico del Este in EYNF has increased over the past 

30 years (Lasso and Ackerman 2003).

• Satellite estimates used by Neelin and others (2006) found a significant drying trend in 

the Caribbean and Central America since 1950, and point-based estimates show a drying 

trend of 5–30 percent since 1900. Mid- to long-term data also show drying trends in the 

Bahamas (10–15 percent since 1959) and Jamaica (11 percent since 1995) (Martin and 

Weech 2001, Studds and Marra 2011).

Future trends

• Scatena (1998), applying projected future precipitation patterns to the LEF, found that 

while annual precipitation was projected to remain constant, rainfall variability, including 

the number of heavy rainfall days, was expected to decrease.

• Nonparametric ensembles from Girvetz and others (2009), using CMIP3 models from 

Meehl and others (2007), show average annual decreases in precipitation of 5 percent by 

2020, 13 percent by 2050, and 16 percent by 2090 for Puerto Rico.

• Recent modeling work for the Caribbean region using the latest IPCC model results 

suggests a drying trend (Biasutti and others 2012, Campbell and others 2011, Cashman 

and others 2010).

• Biasutti and others (2012) projected a 30-percent decrease in spring and summer 

precipitation in the Caribbean using the IPCC ensemble model for the end of the century. 

Analysis also suggests that the number of consecutive dry days will increase consistent 

with a lengthening of the dry season, while the number of days with rainfall over 10 mm 

is expected to decrease (Biasutti and others 2012).
6 Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

• Campbell and others (2011) and Cashman and others (2010), using regionally downscaled 

climate models, show a decrease in annual rainfall for the Caribbean, with decreases 

ranging from 25 to 50 percent by the end of the century and the largest decreases in the 

southern Caribbean (Campbell and others 2011).

• Seasonal projections using regionally downscaled models show drying trends in spring, 

summer, and fall, with the strongest decreases of up to 35 percent in the summer months 

(Campbell and others 2011), leading to a drier wet season and even drier dry season, with 

a potential wet spell in the winter (Cashman and others 2010).

• Future changes in precipitation in the tropics vary by model but also by temporal and spatial 

extent. Magrin and others (2007) projected a 20-percent reduction to an 8-percent increase 

in dry season precipitation, and a 30-percent reduction to a 5-percent increase in wet season 

precipitation for Latin America for 2080. Christenson and others (2007) projected a decrease 

in precipitation over Central America using the multi-model data set model for the end of the 

century. Lintner and others (2012) found that the occurrences of both very dry and very wet 

months are projected to increase in the tropics by the end of the century.

• Using the PCM, Angeles and others (2007) projected a warmer and wetter future climate 

for the Caribbean region for 2050, with more intense rainfall in the rainy season due to 

increased SSTs, which increase the amount of available water vapor and a longer and more 

intense hurricane season (Aguilar and others 2005). However, models for the Caribbean 

(Neelin and others 2006) and Puerto Rico (Scatena 1998) also predict increasingly severe 

drought over the next 50 years.

Cloud base trends

• For EYNF, changes to the location of the axis of the convergence zone since 1950 

affected orographic lifting mechanisms, which has led to a higher cloud base and strong 

precipitation reductions during the early rainfall season, ranging from 45 mm at low 

elevations to up to 150 mm at higher elevations (Comarazamy and González 2011).

• Land cover changes were found to affect the height of the cloud base in the LEF, 

evidenced by the temporary lifting of the cloud base following the massive defoliation 

from Hurricane Hugo (Wu and others 2006). However, land use and land cover changes 

in lowland areas upwind from LEF had little influence on precipitation in the cloud forest, 

whereas recent conversion from agriculture to forest was found to lower air temperatures 

(Torres and others 2008).

• A global study of cloud forests using cloud frequency data from 1979–2002 found 

that the number of cloudy days decreased in cloud forests occurring in the 10°–20° 

latitudinal band, whereas cloud forests near the equator showed an increase in cloudy days 

(Bruijnzeel and others 2011).

• Empirical studies indicate that climate change will increase the altitude of the cloud base 

in tropical mountains due to higher SSTs (Benisten and others 1997, Still and others 1999). 

This change occurs because warmer seas generate more water vapor and latent heat in 

the surrounding areas, reducing the changes in temperature with increasing elevation that 

cause cloud formation (Nadkarni and Solano 2002, Pounds and others 1999). The “lifting 

cloud base” will decrease inputs of the mist in cloud forests (Nadkarni and Solano 2002) 

and may alter the forest type’s hydrology (Eugster and others 2006).

• In Monteverde Cloud Forest Reserve, Pounds and others (1999) found that dry season 

mist decreased over the past 30 years, and the mean altitude of the cloud base has risen, 

owing both to global climate change and widespread lowland deforestation (LaVal 2004). 

Modeled responses to future climate change project an additional 200-m rise in the cloud 

base at Monteverde during the dry season (Sill and others 1999).

Cloud cover over El Yunque National 

Forest. (Photo by Lisa Jennings)
Changes to Drivers and Stressors 7

Extreme Weather

Precipitation extremes

• Heavy rainfall events have become more common in Puerto Rico, particularly since 2009, 

with changes linked to high SSTs (Vélez Rodríguez and Votaw 2012).

• Historic periods of drought in Puerto Rico, such as the extreme drought experienced from 

1993 to 1995, provide a glimpse into future dry periods, which may increase as annual 

rainfall decreases over time in the Caribbean region (Larsen 2000).

• In northern Puerto Rico, frequently drenched soils and steep slopes contribute to landslide 

frequency; in the relatively drier south, landslides coincide with intense rainfalls (Lepore 

and others 2012).

• O’Gorman (2012) found a strong correlation between the sensitivity of tropical 

precipitation extremes to changes in inter-annual temperature variability.

• In the Caribbean, long-term data (since 1950) show that the maximum number of 

consecutive dry days is falling while measures of extreme precipitation events are 

increasing (Peterson and others 2002).

• Aguilar and others (2005) found that increases in the percentage of warm days during 

wet season months (June, July, August, September, October, and November) suggest 

more insolation and, therefore, fewer cloudy days in Central America and northern South 

America. Given increased precipitation intensity alone, fewer rainy days and more warm 

days would be expected (Aguilar and others 2005).

• Though more dry extremes are expected in all seasons of Central America, a limited 

number of studies have produced estimates of extreme seasonal temperature and 

precipitation frequencies (Magrin and others 2007).

• Overall, heavy precipitation and dry-spell length in the Caribbean, typified by an 

intensified hydrological cycle, agree with global averages for extreme temperature and 

precipitation indices (Aguilar and others 2005, Peterson and others 2002). However, 

careful interpretation of theoretical arguments for local precipitation time scales is 

needed; this consideration is important because throughout the tropics, more extreme 

rainfall and drought counts are mostly affected by wet and dry anomalies, suggesting that 

there will be increased tropical rainfall spatial gradients (Lintner and others 2012).

• Exacerbating climatic changes, model analyses also indicate a likely increase in drought 

severity associated with increased deforestation and other land use change (Werth and 

Avissar 2002).

• Landslides are caused by strong and persistent precipitation events, and in Latin America 

are linked with deforestation and deficient land planning and disaster contingency 

schemes (Magrin and others 2007). Thus, many already vulnerable cities will likely 

experience intensified extreme weather risks and hazards (Magrin and others 2007).

Temperature extremes

• In recent years, an analysis of weather station data (PRCCC 2013) shows that Puerto Rico 

has experienced an increasing number of hot days > 90 °F, and a decreasing number of 

days < 75 °F. In 2010 and 2011 alone, 100 days were recorded with temperatures > 90 °F.

• Temperature is expected to increase substantially in tropical forested regions over the next 

two decades, with seasonal temperature extremes becoming more common (Anderson 

2011, Diffenbaugh and Scherer 2011). Unprecedented heat events are expected to occur 

with increasing regularity at a greater rate in the tropics relative to temperate regions 

(Anderson 2011).

Hurricane Hugo damage at the Bisley 

experimental watersheds in El Yunque 

National Forest. (Photo by S. Moya)
8 Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

• Projected changes in monthly minimum and maximum temperature extremes are 

significant in the Caribbean, whereas the rest of the world has shown greater warming 

in mean monthly minimum temperature. In the Caribbean, the extreme intra-annual 

temperature range is decreasing, meaning the number of very warm days and nights is 

accelerating while very cool days and nights are lessening in frequency (Peterson and 

others 2002).

• Changing temperature extremes from 1960 to 2003 in Central America and northern 

South America reflect evident warming trends with great spatial coherence (Aguilar 

and others 2005). Annual percentage of warm days and nights above the 90th percentile 

maximum have increased 2.5 percent and 1.7 percent each decade, respectively, while the 

annual percentage of cold days and nights below the 10th percentile minimum decreased 

at 2.2 percent and 2.4 percent per decade; these warming trends translate to a per-decade 

rate increase of 0.2 to 0.3 °C in temperature extremes (Aguilar and others 2005).

• Regional cold spells (> 6 days in a row) are lasting 2.2 days per decade less, with most of 

this trend attributed to pre-1980 climate changes (Aguilar and others 2005).

Tropical storms

Future trends

• O’Brien and others (1992) estimate the expected hurricane frequency in Puerto Rico to be 

one hurricane every 4 years, causing up to 15-percent tree mortality per storm.

• Numerous climate change studies illustrate the escalating frequency and occurrence 

of extreme weather events, such as windstorms, tornadoes, hail, heat waves, heavy 

precipitation, ENSO droughts, or extreme temperature lasting from a few hours to several 

days (Lewis and others 2009a, Magrin and others 2007).

• Recent studies using IPCC data predict an increase in hurricane intensity in the Atlantic, 

with higher wind speeds and greater amounts of precipitation, but a reduction in the 

overall number of storms (Knutson and others 2010, Seneviratne and others 2012). Global 

projections for the end of the 21st century show a decrease in hurricane frequency ranging 

from 6 to 34 percent, an increase in wind speed intensity ranging from 2 to 11 percent, 

and an increase in precipitation intensity ranging from 3 to 30 percent (Knuston and 

others 2010).

• Global warming may alter the maximum speed of hurricanes, but the ultimate effects on 

average speed or hurricane frequency are debated, and no evidence shows that hurricane 

disturbance area will increase (Emmanuel 1987, Lugo 2000).

• Kelman and West (2009) indicate that warmer SSTs and changing storm tracks could 

cause more tropical storms among Small Island Developing States near the equator.

• Using a simple theoretical model of hurricane intensification under warmer surface 

water and colder upper tropospheric conditions, Emmanuel (1987) showed that resulting 

changes in SSTs could increase the damaging potential of hurricanes by a maximum of 60 

percent (Hulme and Viner 1998).

Effects of tropical storms on vegetation

• At the El Verde field station, Angulo-Sandoval and others (2004) found that canopy 

disturbances via hurricanes and droughts increase available light and may—along with 

associated reductions in herbivorous species—assist in understory shrub and juvenile 

canopy growth.

• Hurricanes and strong wind storms alter ecosystem structure and organization as well as 

biogeochemical processes by transferring large quantities of organic matter and nutrients 

to the soil over short time periods; these changes result in faster short-term decomposition 

and higher net primary productivity (NPP) (Lugo 2000, O’Brien and others 1992, Silver 

1998). Long-term disturbance effects of soil nutrient flux have been observed in the LEF 

canopy to lead to larger potassium (K) and nitrogen (N) losses (Schaefer and others 2000).

Hurricane Hugo damage surrounding the 

Catalina Service Center in El Yunque 

National Forest. (Photo by S. Moya)
Changes to Drivers and Stressors 9

• O’Brien and others (1992), modeling the effects of increased hurricane frequency and 

intensity over a period of 500 years, found populations of tabonuco and motillo (Sloanea 

berteriana)— two late successional species in LEF— declined at the expense of early 

successional species. In addition, the risk to vascular epiphytes would be particularly large 

compared to other tropical vegetation species (Zotz and Bader 2009).

• The high frequency of hurricane disturbances in the Luquillo Mountains causes 

the accumulating aboveground biomass to be lower than forest stands with smaller 

frequencies of disturbance. Thus, if disturbances return at intervals shorter than the 

recovery time of vegetation, less biomass and nutrients will accumulate (Lugo 2000).

• In Puerto Rico’s tabonuco forests, hurricane frequency and intensity dramatically affect 

the density of trees (O’Brien and others 1992) and may influence species diversity, with 

forests under frequent disturbance attaining lower diversity (based on dominance index 

values) than those under more periodic disturbance (Doyle 1981). However, topography 

is an important factor in forests surviving hurricanes, with coves and leeward slopes 

typically incurring less damage (O’Brien and others 1992).

• Long-term studies following hurricane disturbance in the Bisley experimental watersheds’ 

tabonuco forest found significant changes in both forest structure (Heartsill-Scalley and 

others 2010) and nonarborescent plant community composition (Royo and others 2011). 

While plant diversity returned to or exceeded prehurricane levels within 10 years, species 

composition continued to be altered as vegetation takes time to recover to its original 

state, particularly when exposed to repeated small-scale disturbance from storms and 

drought (Heartsill-Scalley and others 2010).

• Royo and others (2011) found a significant increase in fern and vine species in the Bisley 

experimental watersheds persisting 20 years after Hurricane Hugo.

• Lugo (2000) describes 12 outcomes and effects regarding hurricanes on Caribbean forests: 

immediate and significant tree mortality, delayed patterns of tree mortality, alternative 

methods of forest regeneration, successional changes, high species turnover and 

opportunities for change, diversity of age classes, faster biomass and nutrient turnover, 

substitution of species, lower aboveground biomass in older vegetation, carbon sinks, 

selective pressure on organisms, and community structure convergence.

• If hurricane intensity and frequency increase in the Caribbean, landscapes will be set 

back to earlier successional stages (less mature and more secondary forests), aboveground 

biomass and height will decrease from interrupted vegetation growth, and disturbancetolerant species will replace those preferring long, disturbance-free maturing conditions. 

Decreasing hurricane occurrence and severity would have opposite effects (Lugo 2000).

Air Quality

Airborne pollutants

• From 1985 to 1998 levels of nitric acid, sulfuric acid, and ammonia deposition increased 

significantly in the Luquillo Mountains, with the majority of pollutants coming from longrange transport from the northern hemisphere (Stallard 2001). Long-range transport has 

contributed to the cloud and rainwater chemistry of the Luquillo Mountains (Gioda and 

others 2013). Subsequent long-term studies (1984–2007) have shown varying trends of 

pollutant deposition within LEF, with increases in concentrations of pollutants at El Verde 

field station and decreases at the Bisley experimental watersheds (Gioda and others 2013).

• Mercury deposition at Río Icacos in EYNF is the highest measured in the United States, 

owing to both dry and cloudwater deposition, but retention of the pollutant is minimal due 

to high disturbance regimes (Shanley and others 2008).

View to the town of Luquillo, Puerto Rico, 

from El Yunque National Forest. (Photo by 

Maria M. Rivera)
10 Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

• In the Caribbean region, reductions in air quality from long-range transport of dust and 

other contaminants (Pringle and Scatena 1999)—leading to acid rain and dry deposition 

(Stallard 2001)—is increasingly becoming an issue.

• Air pollution—particularly from ozone (O3), nitrogen oxides (N2O), and mercury (Hg)—is 

already a major forest stressor in many areas globally. Climate change-induced trends in 

temperature, precipitation, and atmospheric circulation patterns may increase the severity 

and duration of air pollution episodes (Bedsworth 2012) and their effects on forests and 

people (Joyce and others 2008).

• Increases in temperature, in addition to changes in wind patterns and precipitation rates 

caused by climate change, all have the potential to increase pollutants (Bytnerowicz and 

others 2007).

Nitrogen deposition

• Nitrogen deposition increased in the Luquillo Experimental Forest at a rate of 0.08 kg 

nitrogen/ha/year from 1986 to 2004. Assuming current trends continue into the future, OrtízZayas and others (2006) project N2

O emissions to increase in Puerto Rico at an average rate 

of 7.8 percent per year, with fuel combustion as the primary source of these emissions.

• In a study on the effects of increased nitrogen deposition on soil microbial communities, 

Cusack and others (2011) found shifts in community structure with increased fertilization, 

with an increase in fungal abundance at higher elevation sites and an increase in bacterial 

abundance in lower elevation sites in the Luquillo Mountains.

• Recent studies near San Juan, Puerto Rico have shown that urbanization increases 

the effects of nitrogen deposition, finding large gradients in soil properties over short 

distances (Cusack 2013).

• Changes in forest nutrient cycles, especially through increased nitrogen deposition 

(Mohan and others 2009), may favor certain species and lead to a reevaluation of forest 

management practices (Bytnerowicz and others 2007).

• Nitrogen deposition is increasing in tropical regions (Cusack 2013), with significant 

effects on carbon and nutrient cycles in forests (Cusack and others 2011), and is expected 

to further increase with global climate change (Mohan and others 2009).

• Cusack and others (2012) found that increased fertilization slowed soil respiration rates, 

increasing the soil carbon pool. However, increased nitrogen deposition also increased the 

temperature sensitivity of soil respiration, making soil carbon stocks more vulnerable to 

future warming (Cusack and others 2012).

Fire

• Land use changes will interact with climate change to alter fire regimes in tropical forests 

(Cochrane and Laurance 2008). In Puerto Rico, where nearly all wildfires are associated 

with human activity, the feedbacks between climate warming and drying and increased 

human development have the potential to increase the ecological and economic effects of 

fire (Robbins and others 2008).

• In Puerto Rico, historical and paleoecological evidence suggests fire frequency is 

increasing (Burney and others 1994, Robbins and others 2008).

• Studies of fire fuel loading in Puerto Rico and the U.S. Virgin Islands found that the 

amount of woody debris was lower than other tropical and temperate forests despite the 

dramatic increase in the amount of fuels and litter following tropical hurricanes (Brandeis 

and Woodall 2008). Hurricane-induced changes can persist for years and increase future 

fire risk (Gould and others 2008).

Fire in a subtropical landscape. (Photo by 

Dale Wade, Bugwood.org)
Changes to Drivers and Stressors 11

• In moist tropical forests, where fires have been historically rare (Lewis 2006, Silver 

1998), an increase in fire frequency from climate change interacting with human-lit fires 

poses a severe threat to natural ecosystems because very few tree species are adapted to 

fire (Brodie and others 2011). Thin bark and limited ability to resprout following fire are 

characteristics of moist tropical forest tree species that make them especially vulnerable to 

fire (Sherman and others 2008).

• Tropical forest fire frequency has increased over recent decades, with the 1997–1998 

ENSO event leading to widespread fires in the tropics (Lewis 2006). If climate change 

leads to more intense ENSO events as predicted (Yeh and others 2006, 2009), the 

incidence, magnitude, and duration of fires in the tropics will continue to increase (Brodie 

and others 2011, Sherman and others 2008).

• Global fire occurrence is projected to rise over the next century with climate change 

(Flannigan and others 2000), owing to a combination of more frequent cloud-to-ground 

lightning ignitions and an increase in the conditions that influence the flammability of 

forest fuels, including temperature, humidity, and precipitation (Brodie and others 2011, 

Flannigan and others 2000, Sherman and others 2008).

• Fires in cloud forests can be highly destructive, as evidenced by high mortality of canopy 

trees and extensive consumption of thick organic soils following a fire in a cloud forest in 

the Dominican Republic (Sherman and others 2008). Severe fires in moist tropical forests 

have the potential to alter microclimates, allowing noncloud-forest species to invade, 

which increases the chance of recurrent fires (Sherman and others 2008).

Forest Health

• Climate change will affect disease cycles through changes in host–pathogen interactions 

in the tropics (Stork and others 2009) and throughout the northern hemisphere and its 

forests (Joyce and others 2008, Sturrock and others 2011).

• Warmer temperatures are predicted to favor conditions for pathogen development, 

survival, and disease transmission (Joyce and others 2008), while changes in precipitation 

will potentially allow pathogens to expand into new areas (Sturrock and others 2011).

• Current global models project a redistribution of insect species under climate change 

(Logan and others 2003). Warming has been shown to increase insect consumption and 

movement in a temperate forest (Dukes and others 2008).

• Both insect and disease outbreaks will increase with climate change, as these organisms 

will be able to accelerate their life cycles and expand their ranges (Joyce and others 2008).

Invasive and Introduced Species

• There are already several invasive species in EYNF, including Africanized bees (Apis 

mellifera) and bamboo (Poaceae family). If Africanized bees increase in the future there 

will be further competition between the bees and Puerto Rican parrots who utilize the 

same nesting sites (Blundell and others 2003). Bamboo is already expanding in the forest 

at a slow pace, and increased flooding in the future could accelerate its spread (Blundell 

and others 2003).

• Thompson and others (2007) found that populations of introduced species are currently 

not likely to expand in the LEF; however, this could change with more intense or frequent 

disturbance. In a study of the introduced species rose apple (Syzygium jambos), María 

(Calophyllum calaba), and Arabian coffee (Coffea arabica) in LEF, Thompson and others 

(2007) showed that S. jambos is the most likely of the introduced species to increase.

• Increasing intensities of disturbance provide an opportunity for nonnative species planted for 

farming or ornamental purposes to spread and potentially invade natural forests (Thompson 

and others 2007). Post-disturbance, the lower mortality rates for introduced species, when 

compared to native species, allows them to persist (Thompson and others 2007).

Fungi. (Photo by M. Solorzano)

Bamboo, an invasive species in many 

Caribbean forest areas. (Photo by Forest 

and Kim Starr, Starr Environmental, 

Bugwood.org)
12 Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

• Novel communities of native and introduced species on lands in the Caribbean that have 

experienced deforestation and then land abandonment can provide clues into how biota 

may respond in nondisturbed locations to climate change and species invasions (Lugo and 

others 2012).

• Invasive species movements and expansions may be accelerated by climate change; 

however, their effects could lead to fewer native species extinctions in tropical forests than 

in temperate forests (Stork and others 2009).

• Introduced species not historically considered invasive may become invasive under 

climate change if they experience increased vigor and rate of spread with warmer 

temperatures and changes in water availability (Hellmann and others 2008).

• In coastal ecosystems in the Caribbean, introduced Melaleuca species in swamp forests 

may be vulnerable to increases in salinity with sea level rise; however, the genetic 

diversity of the species may allow it to adapt and overcome these increases (Tran and 

others 2012).
EFFECTS ON ECOLOGICAL AND PHYSICAL RESOURCES 13

Effects on Ecological and Physical Resources

General Biodiversity

Subtropical and tropical forest ecosystems (general)

• Rising temperatures threaten tropical ectotherms and trees whose thermal-tolerance 

ranges and acclimation potential are small when compared to their temperate-zone 

counterparts—i.e., even a lower predicted-temperature increase in the tropics may create 

a strong biological effect (Brodie and others 2011, Zotz and Bader 2009).

• Pau and others (2011) suggest that species occupying less variable, aseasonal tropical 

habitats will be forced to shift their ranges or face population declines in future climate 

regimes. Further, if biotic factors dictate species’ phenologies in these areas, there may be 

high variation in phenology, meaning some species may have a greater ability to adapt to 

new climate regimes, while other species may be slower in adapting to novel conditions 

(Pau and others 2011).

• Though climate change adaptation potential may exist within the overall gene pool of 

a species, the alleles needed for assimilation may be specific to a region or population 

(Guariguata and others 2008).

Lowland forests

• Conserving lowland forest will minimize the regional effects on climate change 

associated with deforestation and simultaneously augment the survival of lowland species 

as they colonize higher elevational gradients (Chen and others 2009).

• In Costa Rican lowlands, increasing temperatures are expected to lead to 30- and 

80-percent declines in epiphyte and ant species, respectively (Brodie and others 2011).

Montane cloud forests

• Because of their cool-adapted, range-restricted nature, montane cloud forest endemic 

species (such as epiphytes and amphibians) are especially vulnerable to increasing 

insolation and warming, acute heat waves, forest fires, a rising orthogonal cloud base, 

and less moisture-stripping potential from clouds (Brodie and others 2011, Koopowitz 

and Hawkins 2012, Lasso and Ackerman 2003, Magrin and others 2007). Thus, these and 

other tropical montane species are excellent candidates for monitoring the local effects of 

global climate change (Lasso and Ackerman 2003).

• Changes in temperature are almost certain to have detrimental effects for many tropical 

montane tree species whose average altitudinal range is 500 m, and animals whose 

ranges are typically much narrower (Bruijnzeel and others 2011). To keep pace with 

these changes, montane species are shifting their ranges upslope and may soon be forced 

beyond their upper elevational limits due to narrow thermal tolerance ranges (Laurance 

and others 2011).

• Montane forest features that may be affected by rising temperatures include cloud base 

height, cloud moisture, and pathogen virulence and diversity (Stork and others 2009). 

Effects include reduced cloud cover, drier conditions, and less water capture potential as 

climate conditions continue to affect higher elevations (Şekercioğlu and others 2012).

• Because of their smaller geographic spread as well as high energy and area requirements, 

highland-specialist bird and mammal species are thought to be more prone to extinction 

than are lower-zone specialist ectotherms and plants (Laurance and others 2011).

• While temperature and humidity changes of cloud forests are expected from climate 

change, observational and experimental evidence suggests that cloud forest ecosystems 

may experience additional warming due to deforestation in contiguous lowland areas 

(Bruijnzeel and others 2011).

The mountains of El Yunque National 

Forest support a mix of unique plant and 

animal communities. (Photo by Maria M. 

Rivera)
14 Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

Plant Communities

Subtropical and tropical forest ecosystems (general)

• Wunderle and Arendt (2011) expect that because of global climate change and 

progressively drier summer months in the Caribbean, new drought-adapted species 

colonizing the LEF may alter the distribution of life zones and forest types. Additionally, 

warming trends will likely affect timing of breeding and phenology of flowering and 

fruiting plants (Wunderle and Arendt 2011).

• Studying plant communities along an elevational gradient in the Sonadora and Mameyes 

watersheds in the LEF, Barone and others (2008) found that abiotic factors may limit the 

upper boundary of species, while competition limits the lower boundary. Fog, which has 

been hypothesized to prompt tropical mountain forest type change, may halt the upward 

expansion of lowland forest species adapted to more aerobic soil conditions (Barone and 

others 2008, McGroddy and Silver 2000, Silver and others 1999).

• In unaltered tropical biomes, Brodie and others (2011) suggest that rainforest biodiversity 

response to rising temperatures has not always been strictly negative. Rapid warming 

of the Paleocene-Eocene Thermal Maximum event 56.3 million years ago increased 

floral diversity particularly among epiphytic orchids and ferns. However, it has also been 

suggested that since tropical plant system response is slow to relatively rapid climate 

warming, species diversity may decline (Magrin and others 2007), particularly among 

those plant species with low thermal tolerance occupying high elevational gradients 

(Laurance and others 2011).

• Increasing atmospheric CO2

 and ambient temperatures are attributed to faster liana (longstemmed, woody vines) growth and long-term abundance in undisturbed neotropical 

forests (Guariguata and others 2008).

• As disturbance-adapted liana infestations rise—perhaps due to increasing CO2

concentrations (Granados and Körner 2002) or elevated stem turnover (Phillips and 

Gentry 1994)—increased tree mortality, lower stand biomass, and reduced tree growth 

may be expected (Lewis and others 2004).

• Hannah and others (2011) argue for cautionary interpretation of bioclimatic modeling 

studies, which suggest high vulnerability of tropical tree species to climate change 

(Ferreira de Siquiera and Peterson 2003, Hughes and others 1996, Miles and others 2004), 

because bioclimatic models do not present the full range of conditions under which 

species can exist. While many tropical species could survive higher temperatures with no 

current analog, pronounced changes in the moisture balance or higher CO2 may be harder 

to withstand (Hannah and others 2011).

Secondary forests

• Land use history influences forest species assemblages in subtropical secondary forests 

within a set of specific environmental conditions (Brandeis and others 2009). Among 

the most prominent factors dictating postdisturbance succession of tree and plant 

communities in Puerto Rico and the U.S. Virgin Islands are spring moisture stress, 

extreme temperatures, and topographic variables such as elevation and distance from 

coast (Brandeis and others 2009).

• Due to the exchange in dominance of light-demanding pioneer tree species to shadetolerant species, Chazdon and others (2005) suggest second-growth forest structure should 

change faster than mature forests in response to global warming. Therefore, successional 

dynamics will be helpful in measuring tropical forest response to climate change and 

land-use and land-cover change (Chazdon and others 2005).

Bromeliad blooming in El Yunque National 

Forest. (Photo by M. Solorzano)
EFFECTS ON ECOLOGICAL AND PHYSICAL RESOURCES 15

Submontane forests

• Changing climatic conditions themselves are likely to affect lowland species more than 

are the synergies between climate change and land use (Brodie and others 2011).

• During drought, competition for water and potentially other soil nutrients poses a limiting 

factor to mature lowland tree growth and survival, increasing susceptibility to mortality 

(Chazdon and others 2005).

• Tall, range-restricted, tree-form plant species inhabiting closed lowland forests are 

relatively more threatened by climate change than are the climbing and herbaceous plant 

species present in multiple tropical regions (Bradshaw and others 2008, Stork and others 

2009).

• Tropical lowland nonvascular epiphytes may be severely affected by increasing 

temperatures because of their precarious carbon balance, which could easily become 

negative at higher temperatures (Zotz and Bader 2009).

• Tropical lowland lichens and bryophytes may not be able to endure even a minor 

increase in temperature as these organisms are, arguably, living near to the edge of their 

physiological capabilities (Zotz and Bader 2009).

• In a cross-species, cross-microhabitat study of moss and liverwort tolerances to altered 

relative humidity (RH) in French Guiana lowland tropical forest, dry conditions (43 

percent RH) resulted in early desiccation of understory bryophytes, whereas the majority 

of canopy species showed superior desiccation tolerance (Pardow and Lakatos 2013). 

Thus, canopy species are expected to be able to tolerate drought events and somewhat 

extended dry seasons of climate change scenarios, while the same conditions are likely to 

be detrimental to the diversity of understory species (Pardow and Lakatos 2013).

Lower montane forests

• Scatena (1998) interprets the presence of 600-year-old colorado trees (Cyrilla racemiflora)

occupying isolated proximities well below the cloud base in LEF as evidence of a gradual 

upward shift in vegetation zonation that has occurred over the past several centuries. 

The study estimates that whereas a 33-percent increase in annual rainfall would shift 

the colorado forest species zone down to the boundary of the LEF, either an 11-percent 

decrease in annual rainfall, a 2.5-°C increase in air temperature, or a 1.1-°C increase in 

surface temperature would allow the drier, low-elevation tabonuco-type forest species to 

grow in areas currently occupied by colorado forest types.

• Submontane species expanding their range upslope could place additional resource and 

habitat pressure on high-elevation species (Brodie and others 2011).

• More seasonal rainfall in lower montane neotropical forests via changing climate regimes 

would cause a decline in the abundance of the water-impounding Bromeliaceae family 

(Benzing 1998).

Montane cloud forests

• At the Pico del Este weather station, higher nighttime temperature, increased daytime 

precipitation, and any alteration in cloud cover can affect plant communities and 

ecosystem processes (Lasso and Ackerman 2003).

• Because they occur under narrowly defined environmental conditions, tropical montane 

cloud forests are among the world’s most sensitive and vulnerable ecosystems to climate 

change (Lasso and Ackerman 2003).

• In the absence of changes in vegetation water budget and use, climate change is projected 

to affect hydrological processes specific to montane cloud forests. Both cloud water 

index and rainfall interception are likely to be directly affected through changes in 

fog and rainfall frequency and intensity and indirectly affected through biomass and 

compositional changes of canopy epiphytes and bryophytes (Bruijnzeel and others 2011).

Sierra palm (Prestoea montana). (Photo by 

Maria M. Rivera)
16 Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

• A 1- to 2-°C increase in temperature over the next 50 years would raise the altitude of the 

cloud base during the dry season by 2 m/year and consequently threaten mountainous 

tropical cloud forest species (Magrin and others 2007). Plants in low, isolated mountains 

will not be able to adapt to this shifting cloud base temperature gradient and may become 

locally extinct (Magrin and others 2007).

• Elevated CO2 levels in nutrient-poor conditions common in cloud forests may decrease 

photosynthetic capacity and may alter flowering plant phenology and gene expression 

(Lasso and Ackerman 2003).

Cloud forest epiphytes

• Though the most important environmental constraint for vascular epiphytes is water 

availability, Olaya-Arenas and others (2011) found the flowering of the orchid Lepanthes 

rupestris in the LEF to be temperature dependent. Given projected warming, they expect 

a dramatic reduction in the quantity of reproductive individuals and population growth 

rates of L. rupestris, which will in turn affect seeding production, future recruitment, and 

reproductive capacity.

• At Pico del Este, over the last 30 years Lasso and Ackerman (2003) found an increasing 

mean minimum temperature to be correlated with bromeliad (Werauhia sintenisii) 

induction and a later flowering season.

• Lasso and Ackerman (2012) found that increasing temperatures that boost nutrient 

deposition from forest litter fall may raise the reproductive output of one major component 

in a vascular epiphyte community in Pico del Este. Thus, higher temperatures resulting in 

faster organic soil decomposition may promote epiphyte growth and reproduction unless 

water becomes the primary limiting factor.

• In cloud forest ecosystems, epiphyte loss due to climate change is almost certain, as 

epiphytes are restricted to the atmospheric-terrestrial interface (Nadkarni and Solano 

2002) and thus are highly sensitive to changes in growing conditions (Benzing 1998).

• Climate change will threaten cloud forest epiphytes through increased dryness, due to 

both higher temperatures and less moisture through cloud water, as the cloud base altitude 

rises (Pounds and others 1999, Still and others 1999, Zotz and Bader 2009). Experimental 

evidence suggests reduced cloud cover can also directly affect epiphyte longevity and 

productivity (Nadkarni and Solano 2002).

• Altitudinal increases in the height of cloud banks and increased evapotranspiration will 

affect epiphytes most in the dry season, when cloud forests rely heavily on the deposition 

of cloud droplets (Zotz and Bader 2009).

• Uncharacteristically warm nights or the lack of adequate cooling after sundown may 

subject plants that fix carbon through Crassulacean Acid Metabolism photosynthesis (e.g., 

epiphytic bromeliads) to net carbon losses under otherwise adequate growth conditions 

(Benzing 1998).

• In an 18-month experiment at Monteverde Cloud Forest Reserve, epiphyte exposure to 

environments with gradually less cloud water—a scenario synonymous with expected 

ecosystem changes in global climate models—led to a generally negative effect on 

epiphytic taxa growth, with severity depending on the season of transplant and plant 

species (Nadkarni and Solano 2002). It is predicted that climate change will not only 

decrease epiphyte growth and leaf production and increase mortality, but will alter the 

composition of canopy communities by releasing terrestrial plant seed banks within 

arboreal soils; this could create conditions suitable for only the most desiccation-resistant 

epiphytes (which now occupy low elevation forests) in the canopy of upper cloud forests 

(Nadkarni and Solano 2002).

Dwarf (elfin) woodland in El Yunque 

National Forest. (Photo by Maria M. 

Rivera)
EFFECTS ON ECOLOGICAL AND PHYSICAL RESOURCES 17

Animal Communities

General effects

• Martín González and others (2009) found that rainfall and temperature are significant 

determinants of pollinator composition and importance in the West Indies islands of 

Puerto Rico, Dominica, and Grenada, with rainfall being the key driver of pollinator 

variation. Comprehending how these determinants and other dynamics of future climate 

change influence pollinator processes is vital (Martín González and others 2009).

• According to Stork and others (2009), species traits that indicate risk from climate change 

include: low population densities, narrow niches, low vagility, small range, maturehabitat specificity, large body size, and those dependent on other species for food. Large 

vertebrates are especially vulnerable.

• Tropical species often have narrow thermal tolerances and may be already living close to 

their upper thermal limits (Gunderson and Leal 2012, Huey and others 2009, Laurance 

and others 2011).

• Deutsch and others (2008) investigated four groups of tropical terrestrial vertebrate 

ectotherms (insects, frogs, lizards, and turtles) and found that tropical species will reach 

their critical maximum temperature proportionally faster than similar high-latitude 

species, despite the tropic’s lower absolute rates of warming (Deutsch and others 2008). 

Deleterious thermal performance changes are likely in tropical members of all four 

taxonomic groups (Deutsch and others 2008, Dillon and others 2010, Tewksbury and 

others 2008).

• Pounds and others (1999) found in the Monteverde Cloud Forest Reserve that the interplay 

of changes in water availability and varying large-scale climate processes, such as the 

ENSO, may induce population losses among amphibians and reptiles as well as habitat 

and biological changes in the bird community, as drier warming periods are correlated 

with such observed changes (Blaustein and others 2010).

Amphibians

• Predictions of changing environments and increased hurricane intensity and drought 

frequency make high-elevation (> 1000 m) Puerto Rican coquí frogs, upland coquí 

(Eleutherodactylus portoricensis) within the Luquillo and Cayey Mountains (Barker and 

others 2011), and common coquí (Eleutherodactylus coqui) within the Luquillo Mountains 

(Longo and others 2010, Stallard 2001) particularly vulnerable to future climate change.

• Stewart (1995) showed that rather than total monthly or annual rainfall, it is the 

distribution of rainfall or the prolonged periods of drought that significantly impact E. 

coqui population densities in the LEF, especially among juveniles.

• Between 1979 and 1989, E. coqui declined at the El Verde field station (Stallard 2001). In 

the past three decades, three species of endemic anurans (frogs and toads) have become 

extinct (Longo and others 2010), while long-term amphibian monitoring data revealed 

eight populations of six different species declined in EYNF between 1990 and 2000 

(Longo and others 2010).

• Ospina and others (2013) studied calling patterns of four Eleutherodactylus species in a 

wetland near Toa Baja, Puerto Rico and found variations in species response to weather 

variables. Calling activity of E. coqui and E. cochranae (whistling coquí) was positively 

correlated with temperature, while calling activity of E. brittoni (grass couqí) and the 

endangered E. juanariveroi (plains coquí) was negatively correlated with temperature and 

precipitation. Future climate change could threaten all four of these species, with more 

intense pressures on the sensitive E. brittoni and E. juanariveroi (Ospina and others 2013).

Common coquí (Eleutherodactylus coqui). 

(Photo by M. Solorzano)
18 Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

• From 1970 to 2000, Burrowes and others (2004) found a significant increase in 

temperature each month from May to October, the warm/wet season peaks of amphibian 

activity in Puerto Rico. Along with increased temperature and dry season length, 

Donnelly and Crump (1998) suggest decreased soil moisture and increased inter-annual 

rainfall variability will strongly affect neotropical amphibians at individual, population, 

and community levels. They found that if a hotter, drier, less predictable climate decreases 

leaf-litter anurans’ main food supply (invertebrates), juveniles will have stunted growth 

rates and adults may devote less energy to reproduction (Donnelly and Crump 1998).

• Anuran declines and extinction may be associated with synergistic patterns of climate 

change and chytrid fungus (Batrachochytrium dendrobatidis) (Anchukaitis and Evans 

2010, Hannah and Lovejoy 2011) and the extension of the dry season (Barker and others 

2011, Burrowes and others 2004), as well as increasing temperatures at higher elevations 

(Brodie and others 2011) and low precipitation in cloud forests (Magrin and others 2007). 

It is likely these anurans and other restricted-range amphibian species of tropical Central 

America will experience high turnover rates as conditions simultaneously become hotter 

and drier (Blaustein and others 2001).

• Suboptimal temperature and humidity regimes induced by climate change negatively 

affect amphibians’ behavior and energy budget and alter host–parasite relationships 

(Donnelly and Crump 1998, Pounds and others 1999). Shifting conditions in montane 

areas of Central and South America create nighttime temperatures closer to the thermal 

optimum for chytrid fungus proliferation, while increased daytime cloud cover prevents 

frogs from finding pathogen refuges (Blaustein and others 2010).

• Loss of suitable habitat and drought conditions (Longo and others 2010) cause anurans to 

clump around remaining moist areas, making them more vulnerable to disease (Burrowes 

and others 2004) and, in particular, the chytrid fungus (Anchukaitis and Evans 2010).

• Pond-breeding neotropical anurans will likely experience compression of the breeding 

season and more competition for moist sites suitable for oviposition, leading to more 

species using a pond simultaneously and higher mortality in early life stages (Donnelly 

and Crump 1998). Sporadic breeders will be least affected by climate changes altering 

pond hydrology while prolonged breeders, where male reproductive success is tied to 

tenure at the breeding site, will be most affected. Explosive breeders, being better adapted 

to reproduce under high density conditions in a short period of time, will likely be less 

affected than prolonged breeders. In general, narrowly endemic amphibians will see 

additional pressures with pond drying (Donnelly and Crump 1998).

• While drier conditions might reduce the likelihood of fungal attack on arboreal amphibian 

eggs, this could be offset by an increase in parasitic drosophilid fly (family Drosophilidae) 

attacks (Donnelly and Crump 1998).

• Amphibians may become more susceptible to or be killed by warming-induced acid 

rain, fog, and other types of airborne and stream contamination (Carey and others 2001, 

Stallard 2001).

Birds

Habitat alterations

• Smith and others (2010) utilized a satellite-derived index of habitat moisture at the 

Roosevelt Roads Naval Station on the east coast of Puerto Rico to assess the underlying 

gradient of northern waterthrush (Seiurus noveboracensis) habitat quality. They found 

that extreme-wet-habitat specialists, such as S. noveboracensis, are quite vulnerable to 

even slight deviations of annual precipitation, especially during El Niño and La Niña 

cycles (Smith and others 2010).

• Endothermic tropical birds are more likely to be indirectly affected by climate change via 

its effects on community vegetation and food sources, rather than via direct physiological 

effects (Şekercioğlu and others 2012).

Puerto Rican parrot (Amazona vittata). 

(Photo by USDA Forest Service).
EFFECTS ON ECOLOGICAL AND PHYSICAL RESOURCES 19

• Though it is possible for tropical bird species living in coastal or island habitats to cope 

with a 2-°C increase in average temperature, more extreme tropical weather events could 

destroy critical habitat or make foraging impossible (Şekercioğlu and others 2012).

• As habitat availability, food, and shelter resources become constrained by warming, 

tropical highland birds’ elevational ranges narrow and extinction risk increases 

(Şekercioğlu and others 2012). Climate warming in the montane cloud forests of Costa 

Rica has raised the average altitude at the base of the orographic cloud bank (Pounds and 

others 1999), resulting in the colonization of the tropical cloud forest by bird species from 

lower altitudes (Crick 2004).

• Winter habitat quality for neotropical migratory birds is expected to be reduced by the 

projected drying of the Caribbean islands (Rodenhouse and others 2008, Studds and 

Marra 2011).

• Sea level rise, worsened by tropical storms, may convert some dynamic wetland areas into 

salt pans, lessening the likelihood of tropical bird colonization (Şekercioğlu and others 

2012).

• Climate change-induced alterations in soil properties of moist tropical forests will 

decrease net available moisture, changing the forest biochemistry into tropical savannah 

rather than dry forests (Toms and others 2012). For birds in tropical dry forests, climate 

change can increase the rate of habitat loss by introducing stressors such as fire, invasive 

species, parasites, or disease (Toms and others 2012).

Population and survival

• In the short term, hurricane-induced mortality may constrain tropical bird populations of 

the LEF below the recovery threshold, particularly the endangered Puerto Rican parrot 

because of its confined range, small population size, and low growth rate (Wunderle and 

Arendt 2011). However, in the long term, hurricanes may be beneficial to bird populations 

with adequate size because of increased nutrient cycling and nest cavity creation 

(Wunderle and Arendt 2011).

• The abundance of migratory ovenbirds (Seiurus aurocapilla) in the Guánica dry forest in 

southwest Puerto Rico decreased in response to increased summer rainfall in the United 

States. Similarly, wintering black-and-white warblers (Mniotilta varia) and American 

redstarts (Setophaga ruticilla) saw decreases in survival with increasing amounts of the 

previous year’s first six months of rainfall in the United States. (Dugger and others 2004).

• Faaborg and others (2013) also found significant declines in the wintering populations 

of S. aurocapilla, M. varia, and S. ruticilla, as well as declines in the overall diversity of 

neotropical migrant birds in Guánica Forest. Winter survival rates remained steady over 

time, meaning that declining populations are due to a decline in recruitment of birds at the 

site, possibly due to habitat quality changes induced by climate change that has led birds 

to winter elsewhere (Faaborg and others 2013).

• Though they enjoy longer lifespans than temperate birds, tropical birds are comparatively 

more vulnerable to climate change because of their smaller clutch size, less active nature, 

and lower tolerance of climatic variability (Şekercioğlu and others 2012). Moreover, 

tropical bird specialists are considered to be more vulnerable to climate change than are 

generalists (Toms and others 2012).

• Şekercioğlu and others (2008) provides that sedentary tropical birds are five times more 

likely to face climate change-induced extirpation in the 21st century than are long-distance 

migrants.

• Nearly 80 percent of bird species restricted to tropical dry forests are considered to be at 

risk for climate change alterations (Toms and others 2012).
20 Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

Behavioral responses

• As shown by Arendt (2000, 2006), following major hurricane alteration of forest 

vegetation, nest predation by rats, nest usurpation by swarming bees, and the prevalence 

and intensity of philornid ectoparasites increased in nests of A. vittata (Puerto Rican 

parrots) and a surrogate study species, the pearly-eyed thrasher (Margarops fuscatus). 

Thrasher reproduction, survival rates, and predator response differed between Hurricanes 

Hugo (1989) and Georges (1998) (Wunderle and Arendt 2011).

• Merola-Zwartjes and Ligon (2000) found that Puerto Rican todies (Todus mexicanus) from 

the Guánica dry forest had significantly lower basal metabolic rates than did those from 

the cooler rain forest site at LEF. While a lower rate of endogenous heat production is 

typical in species inhabiting warm environments compared to the same species in cooler 

climates (Dawson and O’Connor 1996), Guánica T. mexicanus should benefit from lower 

basal metabolic rates because of reductions in both the potential for heat loading and the 

need for evaporative cooling (Merola-Zwartjes and Ligon 2000).

• Cavity-nesters (owls, woodpeckers, and parrots) should expect more competition for 

remaining tree hollows from both tropical birds and cavity-dwelling mammals. According 

to Pounds and others (1999), in Monteverde Cloud Forest Reserve, keel-billed toucans 

(Ramphastos sulfuratus) are nest predators that have recently expanded their range 

into montane highlands, where they both compete for sites with resplendent quetzals 

(Pharomachrus mocinno) and prey on their nests.

• Many tropical birds, such as the white-throated thrush (Turdus assimilis), prefer to 

breed in the wet season due to the abundance of resources. Since climate change causes 

increasingly longer and variable dry seasons and droughts, migratory and reproductive 

routines of tropical birds may be affected, and populations may decline (Şekercioğlu and 

others 2012).

• Pounds and others (1999) observed that from 1973 to 1998 the distribution of lower and 

pre-montane bird species in Monteverde Cloud Forest Reserve, Costa Rica shifted upslope 

and back downslope an average rate of 19 species per decade, with present lower-montane 

species remaining stable and pre-montane species increasing.

• Isotope research by Fraser and others (2008) in Nicaragua showed that several partialfrugivore species, including pollinators such as hummingbirds, make yearly altitudinal 

migrations, which may be greatly impacted by global warming.

• Studds and Marra (2011) found in southwest Jamaica that S. ruticilla (American redstarts) 

adapted the timing of their spring migratory patterns in relation to an increasingly severe 

and unpredictable winter dry season. Birds migrating between North America and the 

Caribbean must therefore attempt to breed earlier, contending with fewer and more 

variable winter food resources (Studds and Marra 2011).

• In the West Indies islands of Dominica, Grenada, and Puerto Rico, Martín González 

and others (2009) found that although there was no significant relationship between 

tropical bird pollinator richness and importance and climatic factors, birds visited a 

higher proportion of plant species and played a more central role in the pollinator network 

towards the wet end of the rainfall gradient. Thus, for the Caribbean as in Central and 

South America, birds tend to become more important as pollinators as rainfall increases 

(Martín González and others 2009).

Reptiles

• Traits such as core temperature and maximum critical thermal temperature of some 

Puerto Rican Anolis species vary over altitudinal gradients, while other species, such as 

the Puerto Rican yellow-chinned anole (Anolis gundlachi), from El Verde field station 

and El Yunque peak sites, show no trait variation (Rogowitz 1996). The ability of Anolis

to thermally adapt their metabolism to changing ambient temperatures may be weak to 

negligible (Gunderson and others 2011). In 14-day experiments at El Verde and El Yunque 

sites, A. gundlachi experienced no change in metabolism from exposure at 15 °C lower 
EFFECTS ON ECOLOGICAL AND PHYSICAL RESOURCES 21

than usual, but suffered a significant decline in metabolism and a consequent loss of body 

mass from exposure to temperatures 30 °C above normal (Rogowitz 1996).

• Huey and others (2009) utilized observational data and a conservative 100-year increase 

of 3 °C over 1970 temperatures to assess body temperature responses of lowland Anolis

and Sphaerodactylus lizards living in Puerto Rican forests, many of which are already 

experiencing temperatures beyond their thermal safety margins. They found many 

tropical lowland lizards are at risk from even a small increase in operative temperatures 

because convection dominates heat exchange in forests (body temperatures increase at the 

same rate as air temperatures) and the thermal environment is already warm relative to 

lizard’s thermal sensitivity (Gunderson and Leal 2012, Huey and others 2009).

• While increased summer heat stress is likely to reduce daily activity time and sprint 

performance of Puerto Rican lizards, particularly during midday, warmer winters will 

create more favorable reproductive conditions (Huey and others 2009). Moreover, some 

species residing in high-latitude or cool montane forest environments should benefit 

with increased activity times and growth rates (Huey and others 2009). Gunderson and 

Leal (2012) show that in assuming a 3-°C increase in ambient temperature, the mean 

performance capacities of the Puerto Rican crested anole (Anolis cristatellus) in dry, 

sparsely vegetated xeric habitats of Puerto Rico are predicted to decrease by 

26 to 32 percent, while mean performance of lizards in cool, vegetated mesic habitats 

should expect an increase of 3–5 percent.

• Gunderson and others (2011) suggest that acclimation alone does not sufficiently account 

for patterns of water loss rate variation found between populations of the A. cristatellus

in Cambalache and Guánica dry forests. Supporting literature of the few lizard species 

studied thus far show negative correlations between arid habitats and water loss rates 

even if lizards from each species population are exposed to identical climatic conditions 

preceding water loss measurement (Gunderson and others 2011, Hertz and others 1979, 

Hillman and others 1979, Perry and others 2000).

• Climate warming may cause tropical forest lizards to suffer increased predation and 

competition from warm-adapted, open-habitat lizards such as the mid-American ameiva 

(Ameiva festiva) (Huey and others 2009).

• Two highland anoline lizard populations (the cloud forest anole and montane anole) in 

Monteverde Cloud Forest Reserve declined since the increase in the number of mist-free 

days in the late 1980s and disappeared by 1996, whereas the gray lichen anole (Anolis 

intermedius) remained stable being better adapted to warmer, drier conditions (Pounds 

and others 1999).

• Smaller body size makes individual lizards more prone to water loss, thus affecting their 

ecology, especially in water-restricted tropical locations such as Guana Island of the 

British Virgin Islands (Nicholson and others 2005).

• In a study by Patiño-Martínez and others (2012), sex ratios in hatchlings of leatherback 

sea turtles (Dermochelys coriacea) in the southwestern Caribbean Sea were clearly 

female skewed by an average of 92 percent over three nesting periods. Backed by 

previous research that establishes patterns of thermal sensitivity for gender determination 

(Godley and others 2001, Hawkes and others 2009), their model predicts that increased 

temperatures via climate warming could lead to a complete feminization of hatchlings 

within a decade. However, deeper and smaller nesting sites lower on the shore on lighter 

colored beaches, where metabolic heating effects would be less detrimental, could create 

conditions more appropriate for future male hatchling sea turtle succession (PatiñoMartínez and others 2012).

Invertebrates

• Microclimate and soil characteristics are more likely to be significant determinants of 

terrestrial gastropod distributions than are the indirect influences of vegetation, which 

provide gastropods with habitat structure and resources (Presley and others 2011). In 

Crested anole (Anolis cristatellus). (Photo 

by Kevin Enge, Florida Fish and Wildlife 

Conservation Commission, Bugwood.org)
22 Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

the LEF, Hurricanes Hugo (1989, category 3) and Georges (1998, category 3) caused a 

relocation of biomass from canopy to the forest floor, which increased the resource base 

for terrestrial gastropods but unfavorably altered microclimate conditions (Bloch and 

Willig 2006).

• As observed in mosquito larval habitats of Río Piedras, Puerto Rico, sequences of rainfall 

followed by lack of rainfall have led to sharp population declines of mosquitoes (Aedes 

aegypti) (Chaves and others 2012). Even though the study demonstrates that population 

outbreaks are largely correlated with extreme climatic events, Chaves and others (2012) 

contend that the observed mosquito population dynamics support neither the linear 

predictions of increased mosquito abundance, nor the claim that dynamics can be swayed 

by vector control programs.

• In the West Indies islands of Puerto Rico, Dominica, and Grenada, richness, plant 

interaction, and importance of bee species within the pollinator community decreased 

with increased rainfall, while dipterans’ (true flies) importance increased with rainfall, 

thus partially replacing one another as major insect pollinators (Martín González and 

others 2009). Meanwhile, wasps benefited from increased species richness with higher 

rainfall, and lepidopterans (butterflies and moths) showed no significant trend with 

rainfall or temperature (Martín González and others 2009).

• In species- and assemblage-level analyses, Chen and others (2009) showed a steady 

increase in the average elevation of moths on Mount Kinabalu, Borneo between 1965 and 

2007, with the average elevation of species rising 67 m. The findings of an uphill shift 

in habitat, coupled with previous research of tropical insect thermal sensitivity (AddoBediako and others 2000, Deutsch and others 2008, Jazen 1967), indicate that tropical 

insects, given their diversity, may dominate species threatened with extinction from 

climate change (Chen and others 2009).

Mammals

• Increased tropical extreme weather event frequency has a marked, yet species-specific, 

deleterious effect on bat populations, principally among tree-roosting bats; this effect 

is attributed to tree loss and more native hunting rather than direct hurricane mortality 

(Jones and others 2009). Research (Gannon and Willig 2009) suggests the recovery rate 

of the Puerto Rican cave-roosting Jamaican fruit bat (Artibeus jamaicensis) depends on 

hurricane severity, with recovery occurring more rapidly after Hurricane Hugo (1989, 

category 3) than after Hurricane Georges (1998, category 3), while populations of treeroosting, red fig-eating bats (Stenoderma rufum) declined after Hugo.

• Increased temperatures may also impact bat populations. In Costa Rica, LaVal (2004) 

found no net change in the number of bats captured in Monteverde Cloud Forest Reserve 

over a 27-year period, but revealed a growing number of lowland bat species at higher 

elevations—a phenomenon hypothesized to be due to the climatic effects resulting from a 

2-°C increase in minimum temperatures (Pounds and others 1999).

Freshwater (Aquatic and Riparian) Ecosystems

• For two species of freshwater shrimp (Atya lanipes and Xiphocaris elongate) in the 

LEF, Covich and others (2003) observed a two- to three-fold increase in average shrimp 

densities within upper-altitude pools due to the effects of droughts. This has led to severe 

crowding and hence less reproductive success for shrimps as well as a significant shift in 

the size-class distribution.

• When the migratory “cue” of flowing water is barred from juvenile freshwater shrimps, 

they are impounded in low-elevation bottlenecks, making them prey for fish and birds 

(Crook and others 2009). During the drought year of 1994 in EYNF, poor streamflow and 

low stream connectivity limited the ability of shrimp larvae and juveniles to advance to 

La Coca Falls in El Yunque National 

Forest. (Photo by Lisa Jennings)
EFFECTS ON ECOLOGICAL AND PHYSICAL RESOURCES 23

the next life stage (Crook and others 2009). In the same drought year, the lowest mean 

abundance of palaemonid river shrimp (Macrobrachium spp.) in 28 years was recorded 

in the Espiritu Santo drainage of the Luquillo Mountains, with hurricane and storm flows 

having relatively little effect on population (Covich and others 2006).

• Due to climate change, extended droughts in tropical rainforests may significantly 

affect freshwater aquatic communities through crowding of species, leading to habitat 

contraction and a decrease in reproductive output (Covich and others 2003).

• Warmer temperatures, in combination with altered flows due to increased drought, 

may limit dissolved oxygen (DO) availability in freshwater environments by promoting 

macrophyte growth including algal blooms (Cashman and others 2010, Ficke and others 

2007). High macrophyte growth rates may also lead to sediment trapping and excess 

nutrients (Ficke and others 2007).

• Extended droughts in the dry season may significantly affect aquatic organisms by 

decreasing DO content (Mulholland and others 1997).

• Riparian areas will see changes in structure and composition due to altered precipitation 

and run-off regimes, as well as changes in the distribution of plant and animal species 

(Seavy and others 2009).

• Globally, riparian areas will play an important role under climate change by providing 

thermal refugia for sensitive species; this is based on the riparian area’s ability to buffer 

against extreme temperatures due to high water content and shade provided by dense 

vegetation (Seavy and others 2009).

Water Resources

Water balance

• Scatena (1998) found that projected future changes of increased temperatures and 

precipitation could change vegetation types in LEF and alter forest-wide hydrology. If 

the tabonuco-type forest expands upslope into the area currently inhabited by the palo 

colorado-type forest, forest-wide runoff could decrease as much as 17 percent due to the 

lower runoff rates for the tabonuco-type (Scatena 1998).

• Harmsen and others (2009) modeled the effects of climate change on groundwater in 

Puerto Rico and found that projected large increases in precipitation for the rainy season 

will produce a net increase in annual aquifer recharge, whereas projected decreases in 

precipitation in the dry season will have minimal effect. An increase in aquifer recharge 

suggests that groundwater levels could increase, reducing saltwater intrusion in some 

coastal aquifers (Harmsen and others 2009).

• The effect of climate change on the water balance in cloud forests is largely influenced by 

changes in rainfall (Bruijnzeel and others 2011).

• Changes in evapotranspiration due to increased temperatures could decrease runoff, even 

in dry regions (Galindo and others 2010).

Water quantity and quality

• Climate change is likely to amplify existing pressures on water resources and water 

availability in northeastern Puerto Rico, especially in combination with increased urban 

development and water extraction (Crook and others 2007).

• More intense rainfall events lead to increased runoff in the wet season; these events can 

also lead to decreased water quality through increased turbity and erosion as well as 

flooding (Cashman and others 2010). Watersheds that respond quickly to precipitation, such 

as in the Luquillo Mountains, may be especially affected (Schellekens and others 2004).

• As a small island, freshwater resources in Puerto Rico will be affected not only by 

changes in precipitation, but also by changing hurricane cycles and saltwater intrusion 

from sea level rise (Kelman and West 2009).

Icacos River in El Yunque National Forest. 

(Photo by F. Scatena)
24 Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

• Although overall precipitation levels in the Caribbean may remain similar in the future, 

dry years and water shortages may become more frequent or more severe (Biasutti 

and others 2012) as the rainy season becomes wetter and the dry season becomes drier 

(Harmsen and others 2009).

• Extended periods of extreme low flows in the dry season may result in increased pollutant 

concentrations and excessive nutrients in Caribbean streams (Cashman and others 2010, 

Covich and others 2003).

Soil and Geologic Resources

Soil health

• Soils in the Luquillo Mountains will be affected by climate change through increased 

variability in the decay of organic matter, changes to the patterns of soil oxygen 

concentrations, and changes in the accessibility of soil nutrients to plants (González and 

others 2013a).

• The Luquillo Mountains receive deposits of African dust that can change the composition 

and texture of soils, potentially affecting nutrient storage. Projected increases in African 

dust deposits with climate change may further affect soils on mountain peaks (González 

and others 2013a, Ping and others 2013).

• In the LEF, soil oxygen content decreased significantly with increasing annual rainfall, 

exhibiting soil oxygen levels below half of ambient concentrations in > 30 percent of palo 

colorado-type forests and > 60 percent of elfin cloud forests studied over the 18-month 

period (Silver and others 1999). Soil oxygen concentration was consistently found to be 

responsive to both long-term annual and short-term precipitation events (Silver and others 

1999).

• Silver (1998) found that riparian microsite soil conditions in the LEF shifted between 

predominately aerobic and anaerobic in relation to 14-day rainfall cycles; aerobic soils 

supported relatively more plant biomass but less soil organic carbon (SOC) and nutrient 

availability, whereas anaerobic soils became a net source of CH4 (methane).

• Puerto Rican soils in the oxisols and ultisols classes may experience losses in soil 

organic matter due to temperature- and/or rainfall-induced water stress, implying that a 

lengthening dry season is likely to impact tropical forest soils, the resident vegetation, and 

the associations and interactions between them (Silver 1998).

• In tropical forests, seasonal soil decomposition is closely tied to wetting and drying cycles, 

suggesting that seasonal adjustments in temperature and moisture due to climate change 

are likely to affect decomposer communities, soil resource quantity and distribution, and 

litter quality (Silver 1998).

• The negative correlation found by Silver (1998) between litter fall and elevation is likely 

an indirect response to a changing climate, as less litter fall is associated with a lower 

temperature. Since litter fall and decay rates are tightly coupled with nitogen (N) and 

phosphorus (P) cycles, tropical ecosystem decay may be vulnerable to temperature 

changes (Silver 1998).

• Under conditions of higher temperature and CO2 supplement, soil respiration and net 

primary productivity (NPP) will be affected by water and nutrient availability (Silver 

1998). An expected increase in CO2 levels is likely to have a significant impact on the 

biogeochemical cycles of tropical ecosystems (Silver 1998).

• Prolonged drought could disrupt and decouple the highly synchronized nutrient cycles of 

tropical wet forest ecosystems and exacerbate nutrient stress in water-inhibited areas. On 

the other hand, greater precipitation quantity and frequency in dry tropical forests will 

likely increase decomposition rates as well as nutrient availability and uptake (Silver 1998).

Soil showing anaerobic conditions and 

biological activity in the cloud forest of 

El Yunque National Forest. (Photo by 

Maria M. Rivera)
EFFECTS ON ECOLOGICAL AND PHYSICAL RESOURCES 25

Soil carbon and trace gas dynamics

• Under the climate change scenario of increasing temperature and decreasing rainfall 

(Scatena and Lugo 1998), simulation results from Wang and others (2002) provide that 

higher and lower elevations of the LEF can expect losses in soil organic carbon (up to 

4.5 Mg/ha), while middle elevations will experience smaller increases (up to 2.3 Mg/

ha). These findings suggest the effects of climate change on soil decomposition and SOC 

storage and flux will not be uniform across elevations (Wang and others 2002) because of 

the indirect effects of temperature and precipitation (McGroddy and Silver 2000).

• Over the entire LEF, Wang and others (2002) found significant differences in simulated 

total SOC storage from low elevations of tabonuco-type forests (20 Mg/ha) to high 

elevations of the elfin-type forests (230 Mg/ha), with leaf area and average monthly 

temperature and rainfall being the most significant indicators of SOC.

• Li and others (2006) found continuous N addition in tropical soils of LEF significantly 

enhanced decay-resistant SOC (heavy-fraction organic carbon, HF-OC) sequestration, 

with a negligible effect on total SOC pool. More broadly, the study found N accumulation 

considerably increased aboveground leaf litter production and concentration while 

stimulating litter decay and fungal biomass growth (Li and others 2006).

• Despite the assumption that pasture-to-forest conversion will result in net carbon loss 

from soil, Silver and others (2004) found substantial net carbon sequestration in mature 

secondary lowland forest soils in the Cubuy Annex of the LEF.

• Based on drought responses of three study sites within the Bisley experimental 

watersheds, Wood and Silver (2012) found that decreased rainfall in humid tropical forests 

may cause a negative feedback to climate through lower soil CO2

 emission and higher 

CH4 and N2O soil consumption. They project future precipitation changes are likely to 

significantly affect the production and consumption of trace gases in soils.

• In wet tropical forests, hurricane-induced alterations of soil processes are significant. 

Given a doubling of major hurricane frequency to once every 25 years (Krishnamurti 

and others 1998), hurricane contribution to Puerto Rico’s soil N2O flux could increase 

to 30 percent of the period’s total emissions (Erickson and Ayala 2004). Thus, future 

contributions of soil fluxes in Puerto Rico to the global N2O budget are potentially great 

(Erickson and Ayala 2004).

• Together, N deposition and temperature alterations are likely to affect tropical soil CO2

fluxes and carbon storage (Cusack and others 2012). Even small alterations in SOC storage 

may change the role of tropical forests as a carbon source or sink (Wang and others 2002).

• More intense and frequent droughts may favor species that are better able to allocate and 

store carbon to deep roots and lower soil horizons (Silver 1998).

• Fine root stocks are responsible for 30–70 percent of soil CO2 flux (Schlesinger 1977) and 

are found by McGroddy and Silver (2000) to increase significantly with soil moisture. 

Fine root flux was positively correlated with total soil carbon content but negatively 

correlated with soil respiration rates, suggesting slower root turnover in wet soils.

• Greater precipitation quantity and frequency in dry tropical forests may cause more soil 

carbon to be stored aboveground, and will probably increase surface SOC pools (Silver 1998).

• Surface soil carbon pools in the wet tropical forest of Gulfo Dulce Forest Reserve, Costa 

Rica fluctuate respective to increases and decreases in litter inputs, whereas alterations in 

carbon inputs of temperate forest ecosystems are not as marked on carbon pools (Leff and 

others 2012).

Soil organisms

• Because of their high internal temperature optimum, thermo-tolerant bacterial community 

members dominate the warmer tropical soils (Balser and Wixon 2009). Though microbial 

soil processes will likely adjust to changes in rainfall, additional stressors of climate 

change may lower microorganism diversity or productivity, thus reducing microbial pool 

resiliency (Silver 1998). 

Inceptisols from the cloud forest in El 

Yunque National Forest. (Photo by Maria 

M. Rivera)
26 Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

Vegetation Management

Carbon dynamics

• Silver and others (2004) identify the carbon sequestration potential of a 55-year-old 

reforested area within the Cubuy Annex of LEF to be significant in the later 33 years of 

growth, accumulating carbon (1.4 ± 0.05 Mg C/ha/year) at rates faster than documented 

in more mature, old-growth humid tropical forests. Similarly, Marín-Spiotta and others 

(2007) identify an 80-year-old patch of secondary forest in Sierra de Cayey, Puerto Rico 

with significant carbon sequestration rates in aboveground biomass.

• Climate change’s ultimate effect on undisturbed tropical forest is a contended issue. On 

one side are those who argue that forests will continue to be net carbon sinks because of 

increased productivity via higher ambient CO2 levels. On the other side are those who 

note that forests will be carbon sources because higher temperatures may increase plant 

and soil respiration and slow plant growth (Laurance and others 2011, Wood and others 

2012) or because drought will lead to increased forest dieback (Allen and others 2010, 

McDowell and others 2011, Van Mantgem and others 2009).

• Meta-analyses of the effects of temperature on carbon storage and fluxes across a broad 

range of tropical forest sites have found that total NPP, litter production, tree growth, and 

belowground carbon allocation all increase with increasing mean annual temperature 

(Cleveland and others 2011, Raich and others 2006, Silver 1998) and temperature-toprecipitation ratio (Brown and Lugo 1982). However, soil carbon decomposition and 

turnover time also increase with increasing mean annual temperature, indicating that 

atmospheric carbon uptake via increased forest productivity could be offset by increased 

soil carbon loss with warming (Raich and others 2006).

• Numerous atmosphere-biosphere modeling studies suggest that warmer tropical forests 

will likely become an increasing source of carbon to the atmosphere from increased 

heterotrophic soil respiration (Cramer and others 2001), increased plant respiration (White 

and others 2000), decreased NPP or photosynthesis (Cramer and others 2001, White and 

others 2000), and/or forest dieback (White and others 2000).

• Eddy covariance data from the Brazilian Amazon combined with a simple gas-exchange 

model suggest that net ecosystem exchange is quite sensitive to temperature increases, 

and that the forest may switch from a carbon sink to a source with only a 1.2-°C increase 

in mean annual temperature (Grace and others 1996).

• A 1-year Amazonian eddy covariance dataset showed an overall trend of carbon source 

behavior at temperatures above about 27 °C (Doughty and Goulden 2008), and a 3-year 

dataset from a rain forest in Costa Rica showed reduced carbon sink behavior at air 

temperatures above 20 °C (Loescher and others 2003). A longer-term (4-year) eddy covariance 

study in the Amazon found the strongest controls of the components of net ecosystem 

exchange to be phenology and light rather than temperature (Hutyra and others 2007).

• Tian and others (1998) modeled the presence of a CO2

 “fertilization” effect which 

increased the net ecosystem production of undisturbed tropical ecosystems in the Amazon 

Basin from 1980 to 1994. They found plant growth to be directly stimulated by a net CO2

gain of 3.3 Pg carbon and indirectly enhanced by greater plant water use efficiency. Silver 

(1998) contends that greater water use efficiency may result in increased soil moisture, 

potentially offsetting the drier soil expected from warmer and drier conditions.

• Terrestrial Ecosystem Models (TEMs) attribute year-to-year fluctuations in carbon storage 

and NPP potential to ENSO phase shifts and inter-annual temperature variations (Tian and 

others 1998). Thus, while normal wet and cool conditions make the Amazon Basin a net 

carbon sink, El Niño events induce drier and warmer weather, which decrease NPP and 

increase RH and make the Amazon a net carbon source in such years (Tian and others 1998).

• Chave and others (2008) found an overall increase in aboveground biomass among 

numerous old-growth forests throughout the tropics in recent decades.

Lianas growing in a moist forest in Costa 

Rica. (Photo by Paul Bolstad, University of 

Minnesota, Bugwood.org)
EFFECTS ON ECOLOGICAL AND PHYSICAL RESOURCES 27

Nutrient factors limiting productivity

• Higher temperatures could increase tropical soil organic matter decomposition rates, thus 

generally increasing soil nutrient availability and plant growth rates (Wood and others 

2012). Conversely, additional nitrogen inputs may acidify the soil, deplete base cations, 

and activate aluminum ions, which when combined may decrease soil nutrient availability 

and plant growth rates (Lewis and others 2004). Furthermore, increased nutrient 

availability in response to rising temperatures could result in additional loss of nutrients 

to leaching if those nutrients are not rapidly utilized by the vegetation (Hedin and others 

2003, Wood and others 2012).

• Current modeling efforts highlight the large role nutrient cycling could play in the 

response of the carbon cycle to climate change (e.g., Wang and Houlton 2009), and the 

few tropical fertilization studies that exist support this conclusion; however, how climate 

change will influence nutrient cycling in tropical forests remains largely unknown (Wood 

and others 2012).

• Nutrient availability has been shown to affect forest productivity and foliar nutrient 

concentrations, as well as rates of net photosynthesis and dark respiration (Cleveland 

and others 2011, Meir and others 2001, Wood and others 2009). Nutrient availability can 

also increase carbon loss to the atmosphere via positive effects on soil respiration and 

decomposition rates (Cleveland and Townsend 2006, Wood and Silver 2012).

• Wardle and others (2005) and McKane and others (1995) suggested that the availability 

of nutrients strongly limits productivity in highly weathered soils, such as those found 

in many tropical forests, and that forests on such soils have the potential to be more 

productive if their soils were more nutrient rich.

• Cleveland and others (2011) provide some evidence that soil phosphorus content and 

availability in moist and wet lowland tropical forests have both direct and indirect effects 

on the tropical carbon cycle.

Growth and yield

• Brandeis and others (2009), employing a cluster analysis of plot-level vegetation data from 

Puerto Rico and the U.S. Virgin Islands, found that vegetation assemblages in Puerto 

Rico are driven primarily by spring moisture stress but also by maximum and minimum 

temperatures, elevation, and distance from the coast.

• Long-term (five or more years) inventory plots in tropical forests around the globe have 

revealed contrasting trajectories of stand-level growth and biomass turnover. Datasets 

in tropical Africa and the Amazon have shown increasing growth rates (Lewis and 

others 2009b, Phillips and others 2004). Plots in Costa Rica, Panama, and Malaysia 

revealed decelerating growth (Clark and others 2003, Feeley and others 2007). A recent 

meta-analysis of large (16–52 ha), long-term tropical forest inventory plots across three 

continents (America, Africa, and Asia) showed an increase in biomass over 20 years in 

7 of 10 plots analyzed (Chave and others 2008).

• Possible drivers of increasing biomass increment include: CO2

 fertilization (Lewis 

and others 2009a, Lloyd and Farquhar 2008); recovery from past disturbance (Chave 

and others 2008); or a shift in community composition towards faster growing species 

(Laurance and others 2004). Observed growth declines have been attributed to 

temperature-induced increases in plant respiration rates (Clark and others 2003, Feeley 

and others 2007, Wagner and others 2012); decreased net photosynthesis from increasing 

temperature beyond the thermal optimum (Doughty and Goulden 2008); or light 

limitation from increased liana shading of canopy trees or from global dimming (Feeley 

and others 2007).

Sierra palm (Prestoea montana) stand 

in El Yunque National Forest. (Photo 

by Whitney Cranshaw, Colorado State 

University, Bugwood.org)
28 Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

Effects of temperature

• The ultimate physiological responses of tropical trees to climatic warming are still highly 

debated (Doughty and Goulden 2008, Lloyd and Farquhar 2008, Wood and others 2012), 

with some suggesting trees in the tropical lowlands are near a high temperature threshold 

(Doughty and Goulden 2008).

• Recent ex-situ studies suggest that the photosynthetic capacity of tropical plants may 

not be able to thermally acclimate to warming temperatures (Wood and others 2012). 

Leaf-level gas-exchange studies in Australia have shown that tropical species have lower 

photosynthetic thermal acclimation potential than temperate species, suggesting that 

tropical species may be more susceptible to climate change because they develop under 

lower seasonal and day-to-day temperature variation (Cunningham and Read 2002). 

In-situ experiments in the Amazon also showed no evidence of photosynthetic thermal 

acclimation in response to 13 weeks of 2 to 5 °C warming of existing leaves (Doughty 

2011).

• It is unclear whether or not tropical plants will be able to thermally acclimate under 

naturally warming conditions, which occur more slowly than experimental warming 

conditions (Wood and others 2012).

• Cleveland and others (2011) found the mean annual temperature explained the largest 

amount of variance in aboveground NPP across moist and wet tropical forests types. 

However, after isolating the cool, upland forests with low NPP and the warm, lowland 

forests with higher NPP, the relationship became insignificant (Cleveland and others 2011).

• Recent studies suggest that increasing nighttime temperature may affect tropical tree 

growth and induce tree mortality (Clark and others 2010, Wagner and others 2012).

• Rain forest gap-phase regeneration will undergo slow changes in tandem with a warmer, 

more seasonal climate (Whitmore 1998).

• Warming may alter the morphology and biomass allocation patterns of trees in addition 

to affecting diameter growth rate (Wood and others 2012). A global meta-analysis of the 

effects of temperature on tree growth found warming increases foliage biomass, decreases 

root biomass, and produces taller, thinner stems, although tropical tree growth decreased 

overall when compared to either boreal or temperate species (Way and Oren 2010). In 

contrast, a study of tropical tree seedlings in Australia showed increased root-to-shoot 

ratios under warming treatments (Cunningham and Read 2003).

• Research on tropical rainforest species in Australia found that optimum growth occurred 

under temperatures that are much higher than is ideal for photosynthesis, indicating that 

growth can continue to increase with rising temperatures even as photosynthesis declines 

(Cunningham and Read 2003). The apparent disconnect between photosynthesis and 

growth showed that carbon source and sink activity could have more influence over a 

tree’s growth rate than CO2

 exchange (Wood and others 2012).

Effects of rainfall (including temperature–moisture interactions)

• Increases in rainfall alone could raise NPP by increasing nutrient availability to the 

generally aerobic soil of the LEF lowland areas (Chacon and others 2006, Wang and 

others 2003, Wood and Silver 2012).

• In the LEF, Wang and others (2003) found that when holding all else constant, rainfall 

variation creates a small net increase in gross primary productivity (GPP) and NPP. 

Increasing only temperature, on the other hand, entails a much larger reduction in 

both GPP and NPP due to an increase in plant maintenance respiration and a decrease 

in stomatal conductance, with tabonuco-type forests being especially sensitive to 

temperature changes. The greatest negative effect to NPP and GPP was observed in a 

simulation of 11-percent less rainfall and a 2.5-°C higher temperature (Wang and others 

2003).

• Wang and others (2003) utilized TEMs to simulate an increase in temperature and 

precipitation, which they found to greatly lower the NPP potential of the LEF. Melillo and 

others (1993) found similar results applying TEMs to a tropical evergreen forest.

Leaf detail. (Photo by M. Solorzano)
EFFECTS ON ECOLOGICAL AND PHYSICAL RESOURCES 29

• Water stress assessments for a generic crop at Adjuntas, Mayagüez, and Lajas, Puerto 

Rico yielded a 20-year average relative crop yield reduction that projected from 2000 to 

2090 decreased water stress (from 12 to 6 percent) in the wet season and increased stress 

(from 51 to 64 percent) in the dry season (Harmsen and others 2009).

• Tropical rain forest seedlings will be affected by decreased rainfall, greater seasonality 

and variability, and lower soil moisture associated with climate change (Whitmore 1998).

• Where data have been combined globally, the sensitivity of rainforest tree mortality rates 

to soil moisture deficit (e.g., drought) appears to vary strongly by region, with the more 

humid rainforests of Southeast Asia showing substantially larger increases in mortality 

than those of Amazonia (Allen and others 2010, Phillips and others 2004).

• Hydraulic architecture may have a strong effect on how species react to global climate 

change. Trees with shallow roots may be at a competitive disadvantage compared to 

deeper rooted species (Stork and others 2007). In Amazonian forests, deep-rooted trees 

passively transfer water at night from deep moist soil to shallow dry soil, or from moist 

shallow to dry deep soil layers, a phenomenon called hydraulic redistribution (Oliveira 

and others 2005). If other tropical forest trees exhibit similar redistributive behaviors, 

the effects of increased evaporative demand with warming may be buffered for shallowrooted species (Wood and others 2012).

Effects of elevated CO2 concentrations

• Tabonuco forest species in the Luquillo Mountains experienced a much greater decrease 

in respiration and thus higher NPP than colorado, palm, or elfin forests under conditions 

of increased CO2, temperature, and rainfall (Wang and others 2003).

• In their TEM simulation, Melillo and others (1993) found the direct effects of enriched 

CO2 levels to be the most significant contributor to increases in NPP, as elevated CO2 may 

decrease tree respiration rate.

• All else equal, lower stomatal conductance in response to higher CO2 concentrations 

would increase water-use efficiency among tropical trees and could assist tree growth 

when water is a limiting factor (Lewis and others 2004).

• Among tropical plants, CO2 has repeatedly been found to stimulate photosynthesis, 

accumulate more carbohydrates in plant tissue, and often deplete N reserves. However, 

tropical plant growth was found by Körner (2004) to be responsive to CO2 only when 

there were abundant nutrients or deep shade and/or isolation.

• Early successional tropical tree species with high fertilization and relative growth rates 

are found to be more responsive to CO2 (Körner 2004, Lewis and others 2004).

• Though CO2-enhanced growth is expected to improve understory seedling survival and 

juvenile growth rates, young lianas may advance out of the forest shade and take greater 

advantage of the CO2 enrichment. Such a biodiversity effect could shift the forest to 

earlier succession life stages and thus reduce the carbon-storing potential of the forest 

(Körner 2004, Lewis and others 2004).

• Recent or projected temperature increases may not decrease photosynthetic rates of 

tropical trees if the optimum temperature for photosynthesis rises and photorespiration 

declines with corresponding increases in CO2 levels (Lewis and others 2004).
30 Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

Effects on Social and Economic Resources

Recreation and Tourism

• Intensive land development, high coastal population density, and the effects of large 

tourism-based industry intensify the vulnerability of Puerto Rico to climatic variability, 

and there is limited human and capital infrastructure to address such problems (Lewsey 

and others 2004).

• Climate change may affect tourism through changes to local ecosystems and resources 

that impact scenic values; as well, changes to weather patterns may disrupt recreational 

activities, which can lead to changes in visitor use (Prideaux and others 2010).

• In wet tropical forests, the projected changes in forest structure and composition due to 

climate change are unlikely to result in noticeable changes in tourism demand; this is 

because most visitors have little knowledge of rainforest complexity and will not be able 

to observe these changes unless they are so extensive they cannot be ignored (Prideaux 

and others 2010). However, increased average high temperatures may affect demand due 

to visitor discomfort when recreating outdoors and an increased chance of heat-related 

illnesses (Prideaux and others 2010).

• Projected increases in disturbance events may lead to reduced tourist access in natural 

areas in an effort to protect public safety following events such as fire, insect outbreaks, 

blowdowns, and flooding. Extreme weather events may increase damage to facilities and 

structures and increase the need for road repairs (Joyce and others 2008).

• Climate change may lead to the redistribution of climatic aspects in tourist regions, which 

can affect tourism seasonality (e.g., changes in the length of the warm-weather tourism 

season), demand (e.g., increased destination choice in the winter), and travel patterns (e.g., 

changes in travel timing and destination). The Caribbean region, where year-round warm 

weather is the principle tourism resource, may see increasing competition from other 

regions as warm seasons expand globally (Scott and others 2004).

• In tropical coastal areas, negative effects of climate change through coral reef bleaching 

and sea level rise effects on beaches could affect economies that are dependent on tourism 

(Uyarra and others 2005). In a survey of tourists in Bonaire and Barbados, Uyarra and 

others (2005) found that 80 percent of tourists were unwilling to revisit the islands if coral 

reef bleaching and beach loss occur, unless they were able to pay a lower price.

• A study of beach-front resorts in the Caribbean found that with as little as 1-m sea level 

rise, 29 percent of properties would be partially or fully flooded, while 50–60 percent of 

properties would experience erosion damage (Scott and others 2012).

Land Use and Planning

Urban interactions

• According to data retrieved from the San Juan ATLAS Mission, the San Juan 

Metropolitan Area has greater sensible heat receptivity and therefore produces higher air 

temperatures (2.5 to 3 °C) (Comarazamy and others 2010).

• Additional urban and natural simulations showed bands of clouds and minimal 

precipitation in southwest San Juan Metropolitan Area, which may be due to less intense 

northeasterly trade winds transporting less available moisture horizontally (Comarazamy 

and others 2010).

• Results from eight urban and suburban forests in the Urban Long Term Research Area 

of Rio Piedras, Puerto Rico suggest that urbanization can alter ecosystem processes, 

microbial activity, and soil organic matter cycling, with a potential for a positive urban 

effect on soil mineral N pools in N-rich tropical forests (Cusack 2013).

PR 191 provides access to El Yunque 

National Forest. (Photo by Lisa Jennings)
EFFECTS ON SOCIAL AND ECONOMIC RESOURCES 31

• Comparing an old growth forested site to a nearby deforested grassland site near Sebana 

Seca, Puerto Rico, Van der Molen and others (2010) found that anthropogenic creation 

of pasture increased albedo and significantly lowered cloud condensate levels when 

compared to forest land, leading to a lower cloud base and reduced precipitation.

• Improved road conditions due to longer dry seasons are likely to influence land use 

decisions; for example, colonization and logging of the remaining “remote” forest may 

become more economically feasible, thus reducing tropical forest biodiversity in exchange 

for economic exploitation (Brodie and others 2011).

• Tropical land-cover change, resulting from direct human activities, interacts with 

anthropogenic ecosystem drivers such as climate change and affects watershed supply 

(Uriarte and others 2011).

• Urbanized landscapes can further exacerbate climate warming at the local scale, while 

highly vegetated tropical forests can have a moderate cooling effect (Lim and others 2005).

Energy production

• The climatological minimum wind blow—both current and future—is 4.84 m/s for the 

entire Caribbean region; therefore, this region can use advanced wind turbine technology 

to harness energy, perhaps enough to become self-sufficient. Wind energy, with small 

seasonal future variation, is particularly viable in both the dry season and early rainfall 

season, where wind power potential reaches at least Class 4 in Puerto Rico and the Lesser 

Antilles (Angeles 2010).

• The Caribbean region is expected to continue to have high solar energy availability in 

the future (currently, values are > 5.5 kWh/m2 per day), making it an excellent candidate 

for sourcing renewable energy (Angeles and others 2007). Particularly, the southwest 

Caribbean is the highest net surface solar energy source, with dry season values ranging 

from 4 to 7 kWh/m2 per day (Angeles and others 2007).

Coastal Resources

Sea level rise trends

• Based on monthly averages from 1962 to 2006 (NOAA 2013), mean sea levels in San 

Juan, Puerto Rico have risen at a pace of 1.65 mm/year (± 0.52 mm/year).

• Average global sea level rise over the 20th century occurred at an average rate of 

1.7 mm/year, with recent accelerations to 3.1 mm/year since the mid-1990s (Biasutti and 

others 2012, Church and White 2006). In the Caribbean specifically, sea levels have risen 

at a rate of about 1 mm/year over the 20th century (Cashman and others 2010).

• The IPCC Fourth Assessment Report projected with very high confidence (> 90 percent 

chance) a global rise in sea levels of at least 0.2 m by 2100, with high end projections of a 

2-m rise in sea levels by 2100 (Parris and others 2012).

• Projections using the upcoming fifth edition of the IPCC assessment report estimate a 

global rise in sea levels of 0.57–1.10 m by 2100 (Jevrejeva and others 2012). However, this 

rise in sea level will not be uniform; sea levels in the Caribbean and Atlantic are projected 

to be as much as 5-cm higher than the global average (Galindo and others 2010).

Sea level rise effects

• In Sabana Seca on the northern coast of Puerto Rico, a study by Rivera-Ocasio and others 

(2007) found that small increases in salinity due to sea level rise could have substantial 

effects on coastal bloodwood (Pterocarpus officinalis) forests. Mangrove forests in the 

Caribbean region were also found to be vulnerable to sea level rise, as well as increased 

temperatures and hurricane frequency (Magrin and others 2007).

Visitors to El Portal Rain Forest Center 

in El Yunque National Forest. (Photo by 

Maria M. Rivera)

Urban forests in the San Juan Metropolitan 

Area. (Photo by Lisa Jennings)
32 Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

• In small (e.g., Antigua and Barbuda) and large (e.g., Puerto Rico) island states, sea level 

rise will cause a loss of land area, which could potentially lead to coastal erosion and loss 

of infrastructure as well as inland migrations of populations (Kelman and West 2009, 

Lewsey and others 2004).

• Urbanization throughout the Caribbean, created from the combination of tourism 

growth and deficient land-use planning and development controls, has rendered coastal 

infrastructure vulnerable to extreme weather and rising sea levels characteristic of climate 

change (Lewsey and others 2004).

• Saltwater intrusion into coastal aquifers due to sea level rise is already a threat to 

freshwater supplies in many Caribbean islands, and saltwater intrusion in the Caribbean is 

projected to increase with climate change (Cashman and others 2010, Lewsey and others 

2004).

• Sea level rise, worsened by tropical storms, risks turning dynamic tropical wetland areas 

into salt pans, which may affect the colonization of some tropical birds (Şekercioğlu and 

others 2012).

The beach in Piñones, Puerto Rico. (Photo 

by Lisa Jennings)
KNOWLEDGE GAPS AND UNCERTAINTIES 33

Knowledge Gaps and Uncertainties

Knowledge of observed and projected climate change is continually evolving as scientists 

research the mechanisms and responses of the Earth’s climate system to increased levels of 

CO2 (IPCC 2001, 2007, 2013). In tropical and subtropical forests in particular, significant 

knowledge gaps exist in predicting the response of natural systems to climate change. There 

is a lack of large-scale manipulative experiments exposing species to warming and elevated 

CO2 in the tropics and subtropics, and these studies are critical to understanding whether 

responses to climate change will be positive or negative (Zhou and others 2013). In addition, 

regionally downscaled climate models projecting temperature and precipitation patterns 

at fine scales are not readily available for locations within the Caribbean region, including 

Puerto Rico.2 While existing large-scale global climate models are useful in determining 

potential future trends (Angeles and others 2007), the lack of fine-scale data in Puerto 

Rico’s mountainous regions is especially troublesome as variations in climate with elevation 

over short horizontal distances cannot be captured by existing climate models (Meehl and 

others 2007), especially in predictions of extreme events (ECLAC 2010). Because of the 

lack of high-resolution climate projections, there are also few models representing potential 

implications of climate change for ecosystem functions and characteristics in the Caribbean 

region (see footnote 2). Natural resource managers and planners can look to studies of 

measured historical trends, as well as past periods of extreme climate events and the 

response of species to stress, to help forecast future responses (Walther and others 2002), as 

are presented in this report alongside future projections. However, knowledge gaps remain 

in the research of both historical responses and future trends for local ecosystems in the 

tropics and subtropics, and only a small number of the total plant and animal species in the 

region have been studied. While this section points out several examples of research needs, 

a broader assessment of knowledge gaps related to climate change in EYNF, Puerto Rico, 

and the Caribbean region is needed.

Uncertainties exist with any study forecasting trends in climate. The scientific literature 

assessed here employs various measures of uncertainty related to specific effects of 

climate change. While it is impractical to describe each measure of uncertainty here, it 

is important to understand the inherent uncertainties in the broader discussion of climate 

change. The IPCC provides an overview of key uncertainties in both historic observations 

and projections of climate change in its most recent Fifth Assessment Report (IPCC 2013) 

to help readers understand the uncertainties surrounding drivers and effects of climate 

change. The IPCC relates the probability of changes to terms describing likelihood using 

the following metrics: certain (100 percent probability), virtually certain (99–100 percent), 

very likely (90–100 percent), likely (66–100 percent), about as likely as not (33–66 percent), 

unlikely (0–33 percent), very unlikely (0–10 percent), and exceptionally unlikely (0–1 

percent). Key measures of uncertainty from the IPCC (2013) related to projected future 

conditions described in this report are:

• Globally, climate warming since the 1950s is certain, and it is likely that the 30-year 

period from 1983 to 2012 was the warmest period in the last 1,400 years. It is virtually 

certain that temperatures will continue to increase through the late 21st century.

• It is very likely that climate change has contributed to a global increase in the frequency 

and intensity of temperature extremes. It is virtually certain that these events will become 

more frequent through the late 21st century.

2 Personal communication. 2013. K. Cepero, Research Assistant, North Carolina State University, Campus Box 

7260, Raleigh, NC 27606.
34 Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

• It is likely that climate change has influenced global precipitation patterns since the 1960s, 

including the intensification of both drought and heavy precipitation events. It is very 

likely these events will become more frequent and/or intense through the late 21st century.

• It is virtually certain that there has been an increase in intense hurricanes in the north 

Atlantic Ocean since the 1970s. It is more likely than not that these events will continue to 

increase in intensity through the late 21st century.

• It is virtually certain that sea surface temperatures have warmed since the 1970s. It 

is certain that sea levels are rising, and it is likely that the rate of sea level rise has 

accelerated over the 20th century. It is virtually certain that sea levels will continue to rise 

through the late 21st century.

It is important to note that the uncertainties presented here are not comprehensive. More 

detailed information can be found in the IPCC Fifth Assessment Report (IPCC 2013).

Acknowledgments

Content in this document was produced by the development team for the USDA Forest 

Service TACCIMO tool in conjunction with the IITF and managers at EYNF. This 

work was supported by the USDA Forest Service Eastern Forest Environmental Threat 

Assessment Center (EFETAC) cooperative agreements 11-CR-11330147-016 and 12-CS11330147-113 funded through North Carolina State University, and grant DEB 1239764 

from the National Science Foundation to the Institute for Tropical Ecosystem Studies, 

University of Puerto Rico, and the IITF, as part of the Luquillo Long Term Ecological 

Research Program. Federal staff support was provided by the USDA Forest Service 

Southern Research Station, EFETAC, IITF, and the Southern Region (Region 8) of the 

National Forest System.

Strategic planning—Visioning and key management direction was provided by 

Pedro Rios, Ecosystem Management and Forest Planning Team Leader, EYNF. David 

Meriwether, Ecosystem Management Coordinator, USDA Forest Service Southern Region, 

and Steven McNulty, Landscape Ecologist, EFETAC, are acknowledged for their role in 

strategic planning of the regional response to climate change under the alternative planning 

rule (USDA Forest Service 2012).

Content development—Access to and review of information within the IITF library was 

provided by Gisel Reyes, Technical Information Specialist, and Julie Hernández, Clerk. 

Keren Cepero, Ph.D. candidate, North Carolina State University, is acknowledged for 

her contributions to geospatial products. The EFETAC TACCIMO development team—

including Steven McNulty; Jennifer Moore Myers, Resource Information Specialist; and 

Robert Herring, IT Specialist—is acknowledged for its role in the development of the 

TACCIMO framework.

Review and comments—The interdisciplinary team for the EYNF Land and Resource 

Management Plan revision is acknowledged for contributing reviews and comments on 

TACCIMO products. Ariel Lugo, Frank Wadsworth, Joseph Wunderle, Jennifer Moore 

Myers, Kathleen McGinley, Luis Rivera, Peter Weaver, Steven McNulty, Tamara HeartsillScalley, Tana Wood, Tinelle Bustam, Wayne Arendt, William Gould, and William 

McDowell are acknowledged for their thoughtful reviews of this report.
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46 Climate Change Effects in El Yunque National Forest, Puerto Rico, and the Caribbean Region

Appendix: Science Summary Methodology

Information presented in this appendix provides a summary of methods and an example of 

translating the Template for Assessing Climate Change Impacts and Management Options 

(TACCIMO) direct output—in the form of annotated bibliography-style quotations—to 

scientific summaries in order to aid in the understanding of information sources and to 

provide guidance for science delivery. The use of TACCIMO within the context of the 

2012 Planning Rule (USDA Forest Service 2012) allows forest planners and managers 

to identify best available sources of information quickly and consistently. TACCIMO 

provides users with an interactive framework that efficiently delivers climate change science 

needed to assess, manage, and monitor forest resources under a changing climate. The 

inclusion of information in TACCIMO is performed following documented methods and 

criteria designed to ensure scientific integrity (Treasure and others 2014). This information 

reflects an extensive literature review process concentrating on the effects of climate 

change on key physical, ecological, and social resources within the geographic areas of 

interest. TACCIMO’s public facing website (www.forestthreats.org/taccimotool) provides 

a standardized and scalable resource to help meet the needs of planners and managers 

throughout the United States and greater Caribbean region. Literature-based science is 

organized into a dynamic and interactive information framework that allows for rapid 

addition of new and emerging science and efficient access to a wide variety of subject 

matter. Planning efforts in El Yunque National Forest (EYNF) under the 2012 Planning 

Rule provide an ideal venue to apply extensive content development as reflected in this 

report, which goes beyond the base level of support afforded to all Forest Service regions.

Best available climate change science selected for addition to the TACCIMO database 

undergoes a traditional literature review process in which key sections of the paper 

are highlighted for further analysis. The highlighted information is then subject to an 

organizational framework where quotations are categorized based on key themes. Quotes, 

rather than paraphrases, are preserved to reduce subjectivity and allow for literal linkages 

back to primary sources and supporting literature. Careful consideration is given to 

the context from which quotations are taken, but quotation by its very nature requires 

application of judgment and results in loss of context. To abate the loss of context to the 

greatest extent possible, and to promote the highest level of data quality in TACCIMO, the 

following criteria are strictly applied:

• Literature is peer reviewed, either as stated by the publishing journal’s guidelines, 

explicitly within the paper, or by personal contact with the author.

• The subject and theme of the quotation are consistent with the subject and theme of the 

source as a whole.

• The conclusion of the selected quotation is clearly substantiated by the scientific evidence 

reported in the source article and cited supporting literature.

• If the claim is synthesis-based, supporting literature citations substantiate the synthesized 

conclusion.

• The length of the quotation is kept to the minimum length sufficient for understanding the 

statement independent of accompanying text.

• Qualifying statements and statements addressing uncertainty are included.

Information in TACCIMO can be easily consumed through exploring and reporting tools, 

allowing natural resource professionals to quickly identify credible sources of climate 

change information. Once key sources are identified, quotations within a category can be 

translated into scientific summaries to capture key concepts. To maintain the quality of 

the scientific information, summaries should contain information regarding (1) the area 

or region of study, (2) the time period of observational and empirical data, (3) the affected 

species or experimental unit, and (4) stated uncertainties and limitations, when available. 
APPENDIX: SCIENCE SUMMARY METHODOLOGY 47

All summaries should contain citations back to the original source and any secondary 

sources and should reference only information cited by or hypothesized by the authors (e.g., 

no added statements such as “there will likely be” or “probably”).

The following scientific summaries and TACCIMO outputs for historic temperature trends 

are provided as an example of this process. Scientific summaries are excerpted directly 

from the text of this document. Below the summaries, direct TACCIMO quotations 

are provided, taken directly from the TACCIMO database. For a comprehensive list of 

direct quotations describing the effects of climate change on resources in Puerto Rico 

and the greater Caribbean region, see the TACCIMO Geographic Region Explorer for 

the Caribbean (online at http://www.taccimo.sgcp.ncsu.edu/DirectImpactRegionContent.

aspx?RegionID=19).

Example 1

• In the tropical montane cloud forest at Pico del Este in EYNF, mean monthly minimum 

temperatures have increased over the past 30 years (Lasso and Ackerman 2003). Similar 

changes were also found in the Monteverde Cloud Forest Reserve in Costa Rica, where 

temperatures have increased about 2 °C (LaVal 2004, Pounds and others 1999).

Lasso, E.; Ackerman, J.D. 2003. Flowering phenology of Werauhia sintenisii, a bromeliad from the dwarf 

montane forest in Puerto Rico: an indicator of climate change? Selbyana. 24(1): 95-104.

“At Pico del Este, a TMCF [tropical montane cloud forest] in Puerto Rico, environmental conditions have 

changed during the last 30 years. Monthly mean minimum temperature has increased along with a trend for 

more days with ≥ 12.7 mm precipitation (FIGURE 1).”

LaVal, R.K. 2004. Impact of global warming and locally changing climate on tropical cloud forest bats. 

Journal of Mammalogy. 85(2): 237-244.

“Because climatological data from the early 1970s to the present are available, Pounds and his coauthors were 

able to correlate changes in weather patterns with distribution and abundance of amphibians, reptiles, and 

birds, including species extinctions (Pounds et al. 1999). From these climatic data, Pounds et al. (1999) found 

that the frequency of MCF [Monteverde Cloud Forest Reserve] dry season mist had decreased, average altitude 

at the base of the orographic cloud bank had risen, and mean minimum temperatures have in-creased about 

2 °C during this period.”

Example 2

• Mean annual temperatures in the Caribbean have increased an average of 0.2 to 0.4 °C 

each decade since 1976 (IPCC 2001, Uyarra and others 2005). Average overnight low 

and daytime high temperatures have also increased in the Caribbean by 1.0 and 1.8 °C, 

respectively, since 1950 (Comarazamy and González 2011).

Uyarra, M.C.; Côté, I.M.; Gill, J.A. [and others]. 2005. Island-specific preferences of tourists for 

environmental features: implications of climate change for tourism-dependent states. Environmental 

Conservation. 32(1): 11-19.

“Mean atmospheric temperature in the eastern Caribbean has increased by 0.2– 0.4 °C per decade since 1976, 

and recent models indicate that it might rise by 1.4–5.8 °C in the next century (IPCC [Intergovernmental Panel 

on Climate Change] 2001).”

Comarazamy, D.E.; González, J.E. 2011. Regional long-term climate change (1950–2000) in the 

midtropical Atlantic and its impacts on the hydrological cycle of Puerto Rico. Journal of Geophysical 

Research. 116(D21): D00Q05.

“The large-scale temperature changes at the times of local overnight low and daytime high temperatures over 

the Caribbean region show moderate increases in temperature [in the early rainfall season (April-June) for 

the 1950-2000 time frame] on the order of 1.0 to 1.8°C, respectively; these values increase toward the North 

Atlantic.”

Jennings, L.N.; Douglas, J.; Treasure, E.; and González, G. 2014. Climate change effects 

in El Yunque National Forest, Puerto Rico, and the Caribbean region. Gen. Tech. Rep. 

SRS-193. Asheville, NC: U.S. Department of Agriculture Forest Service, Southern Research 

Station. 47 p.

Understanding the current and expected future conditions of natural resources under a 

changing climate is essential to making informed management decisions. However, the everincreasing volume of useful scientific information about climate change makes it difficult 

for managers and planners to effectively sort through and apply the emerging science. This 

report provides a knowledge base of peer-reviewed climate change science for El Yunque 

National Forest (also administratively designated as the Luquillo Experimental Forest), Puerto 

Rico, and the greater Caribbean region. We summarized scientific findings from over 240 

peer-reviewed sources, covering a wide range of potential effects including changes to drivers 

and stressors and the effects of climate change on ecological, physical, social, and economic 

systems. Projected and observed changes include increases in air temperatures, an extension 

of the dry season, and changes in cloud cover that may lead to significant alterations to the 

diverse plant and animal communities of the Caribbean region. Species in cloud forests on 

isolated mountain peaks may be most at risk, due to sensitivities to moisture and a limited 

chance for migration. Changes in extreme weather patterns, including an increase in hurricane 

intensity and more frequent drought events, are projected to alter the distribution of tropical 

forest vegetation. Tourism patterns and recreational opportunities may change with an 

increase in extreme weather and impacts from sea level rise. The information presented in 

this report provides a starting point for natural resource managers, planners, and stakeholders 

to assess the vulnerability of local resources to climate change as part of a broader decisionmaking framework.

Keywords: Assessment, Caribbean, climate change, El Yunque National Forest, forest 

planning, Luquillo Experimental Forest, technology transfer.

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