EPA/600/R-05/007

April 2007 

www.epa.gov

A Summary of NHEERL Ecological Research 

on Global Climate Change 

Edited by 

Peter A. Beedlow 

And

David T. Tingey 

Environmental Protection Agency 

Office of Research and Development 

National Health and Environmental Effects Research Laboratory 

Western Ecology Division 

Corvallis, Oregon
ii

Christian P. Andersen 

USEPA National Health and Environmental Effects Research Lab/ORD 

Western Ecology Division, 200 S.W. 35th Street, Corvallis, OR 97333-

4902

9

Peter A. Beedlow 

USEPA National Health and Environmental Effects Research Lab/ORD 

Western Ecology Division, 200 S.W. 35th Street, Corvallis, OR 97333-

4902

1, 2, 13 

Michael Cairns 

USEPA National Health and Environmental Effects Research Lab/ORD 

Western Ecology Division, 200 S.W. 35th Street, Corvallis, OR 97333-

4902

6, 9 

Naomi E. Detenbeck USEPA Environmental Effects Research Laboratory, Mid-Continent 

Ecology, Division/ORD, 6201 Congdon Boulevard, Duluth, MN 55804 3

Robert K. Dixon (formerly US EPA) Deputy Assistant Secretary, US Department of 

Energy, Washington, DC 20585 6

William S. Fisher USEPA Environmental Effects Research Laboratory, Gulf Ecology 

Division/ORD, Sabine Island Drive, Gulf Breeze, FL 32561-5299 12

William Hogsett 

USEPA National Health and Environmental Effects Research Lab/ORD 

Western Ecology Division, 200 S.W. 35th Street, Corvallis, OR 97333-

4902

9

Mark G. Johnson 

USEPA National Health and Environmental Effects Research Lab/ORD 

Western Ecology Division, 200 S.W. 35th Street, Corvallis, OR 97333-

4902

5, 9, 10 

Robert McKane 

USEPA National Health and Environmental Effects Research Lab/ORD 

Western Ecology Division, 200 S.W. 35th Street, Corvallis, OR 97333-

4902

8

Leah M. Oliver USEPA Environmental Effects Research Laboratory, Gulf Ecology 

Division/ORD, Sabine Island Drive, Gulf Breeze, FL 32561-5299 12

David M. Olszyk 

USEPA National Health and Environmental Effects Research Lab/ORD 

Western Ecology Division, 200 S.W. 35th Street, Corvallis, OR 97333-

4902

4, 9 

Donald Phillips 

USEPA National Health and Environmental Effects Research Lab/ORD 

Western Ecology Division, 200 S.W. 35th Street, Corvallis, OR 97333-

4902

2, 5, 9, 11 

John E. Rogers USEPA Environmental Effects Research Laboratory, Gulf Ecology 

Division/ORD, Sabine Island Drive, Gulf Breeze, FL 32561-5299 12

Paul T. Rygiewicz 

USEPA National Health and Environmental Effects Research Lab/ORD 

Western Ecology Division, 200 S.W. 35th Street, Corvallis, OR 97333-

4902

8

Debbie L. Santavy USEPA Environmental Effects Research Laboratory, Gulf Ecology 

Division/ORD, Sabine Island Drive, Gulf Breeze, FL 32561-5299 12

Ray Seidler 

(ret.) USEPA National Health and Environmental Effects Research 

Lab/ORD Western Ecology Division, 200 S.W. 35th Street, Corvallis, OR 

97333-4902

9

Allen M. Solomon 

USEPA National Health and Environmental Effects Research Lab/ORD 

Western Ecology Division, 200 S.W. 35th Street, Corvallis, OR 97333-

4902

1, 6, 7 

David T. Tingey 

USEPA National Health and Environmental Effects Research Lab/ORD 

Western Ecology Division, 200 S.W. 35th Street, Corvallis, OR 97333-

4902

1,9, 10, 13 

Lidia S. Watrud 

USEPA National Health and Environmental Effects Research Lab/ORD 

Western Ecology Division, 200 S.W. 35th Street, Corvallis, OR 97333-

4902

9
iii

Acknowledgements

The editors would like to thank the contributing authors for their timely writings 

and especially for their patience as this document was assembled. A special 

thanks to Karen Gundersen and Nancy Terhaar for locating and organizing the 

publications produced from this research. Over the years many scientists—EPA 

as well as those on cooperative agreements and contracts—have made critical 

contributions to the NHEERL climate change research. We would like to 

recognize the following individuals for their long-term participation and 

contribution to this program: Sandra Brown (Winrock International), Bruce 

McVeety (Battelle), Jack Winjum (NCASI), Paul Schroeder, Ron Neilson (Oregon 

State University), Ted Vinson (Oregon State University), Tanya Kolchugina 

(Oregon State University/Moscow State University), David Turner (Oregon State 

University), Dominique Bachelet (Oregon State University), Richard Meganck 

(OAS), Sandra Henderson, George King (Dynamac), Mark Trexler (Trexler and 

Associates), Richard Houghton (The Woods Hole Research Center), Ed 

Rastetter (MBL), Wendall Cropper and Henry Gholz (University of Florida), 

David Lewis (Oklahoma State University), Dennis Lettenmaier (University of 

Washington), Herman Gucinski (USDA), Danny Marks (USDA), Thomas 

Loveland (USGS), Ken Andrasko (EPA), Steven Winnett (EPA), Dennis Tirpak 

(EPA/UN FCCC Secretariat), Connie Burdick (EPA), and Jeffrey Lee (EPA). 

Notice/Disclaimer

The information in this document has been funded wholly (or in part) by the U.S. 

Environmental Protection Agency. It has been subjected to review by the 

National Health and Environmental Effects Research Laboratory’s Western 

Ecology Division and approved for publication. Approval does not signify that the 

contents reflect the views of the Agency, nor does mention of trade names or 

commercial products constitute endorsement or recommendation for use. 
iv

This page intentionally left blank 
 1. Introduction 

1-1

1. Introduction

The climate change problem is one of truly global proportions with tremendous 

implications to ecological, economic and health conditions of the Earth and its 

human population. “The causes and consequences of the problem are ... 

intertwined at all spatial and temporal scales, providing a single issue of 

unrivaled complexity” (Reichle et al. 1985). As a result, it is critical that the scientific 

basis for mitigation and adaptation policies intended to reduce the risks and take 

advantage of the opportunities presented by climate change be as clear, reliable, 

and up-to-date as possible, without being policy-prescriptive.

The Global Change Research Act of 1990 mandates that the US Global Change 

Research Program (USGCRP) assess the potential consequences of global 

change for the United States. The Environmental Protection Agency’s (EPA) 

Global Change Research Program within the Office of Research and 

Development (ORD) is conducting research and assessment activities that 

contribute to the USGCRP assessment process.

Scientists at the NHEERL, and its predecessor—the Office of Environmental 

Processes and Effects Research—initiated research in 1988 anticipating the 

Global Change Research Act. The purpose of this document is to summarize 

ecological research conducted by NHEERL scientists under the EPA’s 

contribution to the USGCRP from the onset of research through approximately 

2002. The intent is to provide that information as reference material for scientists 

investigating the potential impacts of climate change on ecosystems.

The research was conducted through grants and cooperative agreements, and 

through intramural research, which is research conducted directly by EPA 

scientists. This document focuses on the intramural research in an effort to 

highlight the expertise and contributions of EPA scientists. The research 

summarized is, primarily, the result of activities performed at the NHEERL 

ecology divisions directly involving federal scientists. The objective, here, is to 

show the diversity of research conducted, and to highlight the research results in 

support of EPA’s mission to protect the human health and the environment.

The early research addressed health and ecological effects of exposure to 

ultraviolet radiation resulting from stratospheric ozone depletion as well as the 

effects of global climate change on forests, agriculture, and water resources. This

research supported both the Montreal Protocol and its amendments (UNEP 

2000)—an international agreement curbing the release of ozone depleting 

substances—and the 1989 EPA report to the US Congress on the consequences 

of global climate change.

From 1990 through 1996, a significant portion of the ORD effort focused on 

stabilizing the buildup of atmospheric carbon dioxide and other greenhouse 

gases. The ecological research emphasized terrestrial ecosystem-atmosphere 
 1. Introduction 

1-2

carbon cycling, and strategies for enhancing biospheric carbon sequestration. 

In 1997 as part of a USGCRP effort to better coordinate activities across federal 

agencies and to focus each agency’s work on those topics most consistent with 

its mission, ORD redirected its Global Change Research Program to assessing 

the consequences of global change.

In 1998, EPA’s Global Program began conducting regional assessments in 

support of the USGCRP assessment process. Also, EPA’s Global Program 

shifted resources away from carbon cycle and greenhouse gas mitigation 

research to assessing the potential consequences of global change. While some 

research on cause and effect mechanisms continued, ORD’s primary 

responsibility was leading regional assessments on the consequences of global 

change on air quality, water quality, human health, and ecosystem health within 

the United States.

NHEERL’s research role has changed in concert with EPA’s changing research 

needs regarding global change. Ecological effects research other than that on 

coral ecosystems ended in 2002. During period between 1988 and 2002, 

NHEERL scientists conducted numerous projects on the following topics: 

x The effects on agriculture, specifically rice—the World’s most important 

grain.

x The effects on the global biomes—forest migration and desertification. 

x The effects on aquatic ecosystems—the thermal response of freshwater 

fish.

x The effects on terrestrial ecosystems—forest response to increased 

temperature and carbon dioxide, and the interaction of tropospheric 

ozone.

Currently, NHEERL research is addressing coral ecosystem decline. Coral 

dominated ecosystems are among the most threatened by global climate 

change. Research is examining the impacts of global change stressors including 

UV irradiation, temperature and nutrient loading on coral ecosystems. 

The following chapters summarize the published ecological research conducted 

by NHEERL scientists. The summaries give an overview of the research and 

provide an entrée to the technical literature. A chapter is devoted to describing 

the ongoing coral ecosystem research. The final chapter attempts to synthesize 

the research findings with a perspective on remaining scientific uncertainties. 

Reference Cited 

Reichle, D. E., J. R. Trabalka and A. M. Solomon. 1985. Approaches to studying the global 

carbon cycle. Pp. 15-24 IN Trabalka, J. R., ed., Atmospheric Carbon Dioxide and the Global 

Carbon Cycle. DOE/ER-0239, U.S. Dept. Energy, Washington D.C. 20545 
 2. Water Resources 

2-1

2. Water Resources 

Statement of the Problem 

Climate change is likely to have significant impacts on the availability of fresh water.

Already in short supply throughout many parts of the world, water for human 

consumption, agriculture, and industry will be a major factor in economic growth, 

ecological sustainability, and global conflict. Research was undertaken to make initial 

assessments of potential impacts of climate change on stream flow and water balance 

in the western United States—a region characterized by the shortage of water.

Additionally, research was conducted to address the need for models which account for 

the spatial magnitude and extent of hydrologic processes. The models need to handle 

key parameters such as precipitation, soil moisture, and evaporation, in response to 

changing climatic conditions. The models must account for vegetation interactions with 

soil moisture. This is particularly important for simulating regional vegetation response 

to climate change since vegetation distribution is controlled in large part by the 

availability of soil moisture. 

Approach

Research focused on developing and refining detailed watershed scale hydrology 

models to address stream dynamics and water storage. Regional-scale modeling 

research was directed toward developing physically and mechanically-based water 

balance models which can be spatially distributed at watershed, regional, and 

continental scales. The research effort contributed to developing methods for spatially 

distributing climatic data at scales appropriate for the models, and providing these data 

bases to the climate change research community. This ORD project has been 

completed; extensions of this research are continuing within the US Geological Survey. 

Main Conclusions 

The increasing demand for water by population and industrial growth is creating chronic 

water shortages throughout the world (Revenga 2000). Add to this the potential impacts of 

global climate change on water supplies and chronic shortages could reach crisis levels.

Throughout much of the western United States the supply of water for human 

consumption, agriculture, and industry depends on snowpack and reservoir storage.

Most global climate warming scenarios suggest warmer winters with more rainfall and 

less snowfall for much of the western United States, which would substantially reduce 

snow accumulation and shift the high flow season for many rivers from the spring to the 

winter (Lettenmaier et. al. 1992). A substantial amount of the natural storage of winter 

precipitation that presently occurs in the snowpack would be lost resulting in increased 

spills in the winter and lower reservoir levels in the summer and fall (Lettenmaier and Sheer 

1991).
 2. Water Resources 

2-2

A significant increase in flood hazard in the western US could result from climate 

change, primarily due to an increase in rain-on-snow events (Lettenmaier and Gan 1990).

Such events occur when warm, wet storms move over existing snowpack. Rapid

melting of the snowpack is the result of a combination of warm air temperature, high 

wind and high humidity which cause significant condensation on the snow and is 

particularly severe in forest openings and forest clear-cuts (Marks et al. 1998). This

research suggests that some mitigation of the adverse effects of global climate change 

may be achieved by adapting land and water management practices to changes in 

runoff patterns and maximizing the protective effects of natural vegetation. 

Global climate changes are expected to be regional in nature, and affect land cover and 

land use. Key to understanding such regional effects on water supplies is the response 

of vegetation. Plant communities play a significant role in regional energy and water 

balance. While hydrologic models designed to simulate large river systems are good for 

operating reservoirs systems, they are not adequate for predicting changes to regional 

water balance and, hence, changes in regional vegetation (Marks et al.1993). Dolph et al. 

(1991) developed a spatially distributed regional water balance model to evaluate the 

sensitivity of large river basins to climate change. The model was exercised for the 

Columbia River Basin. This research demonstrated that the existing Historic Climate 

Network of climate monitoring stations underestimate precipitation primarily because 

mountainous areas are underrepresented. With climate warming, the model predicted 

increased evaporative loss, decreased runoff and soil moisture. These conditions could 

have profound effects on vegetation distribution and subsequently regional water 

resources.

The ability to predict changes in regional vegetation is necessary to evaluate the effects 

of climate change on forest resources, agriculture, and water supplies. Changes in soil 

moisture and evapotranspiration resulting from climate will have large impacts on water 

and vegetation. If changes in the regional water balance are significant, major shifts in 

vegetation patterns and condition are a likely (Marks et al. 1993). Neilson and Marks (1994)

incorporated a distributed water balance model with a vegetation model to produce a 

biogeographic model, MAPSS (Mapped Atmosphere-Plant-Soil System). This model 

was used to predict changes in vegetation leaf area index, site water balance and runoff 

as well as changes in biome boundaries. When applied to potential climate change 

scenarios, two areas exhibiting among the greatest sensitivity to drought-induced forest 

decline were determined to be eastern North America and Eastern Europe to western 

Russia.
 2. Water Resources 

2-3

Effects of Global Climate Change (GCC) on streamflow

With climate warming, mountain snow accumulation would be substantially reduced, and 

river’s high flow season would shift from the spring to the winter (Lettenmaier et al. 1992).

Actual evaporation would peak in late spring and early summer due to reduced summer soil 

moisture. The result would be increased spills in the winter, lower reservoir levels in the 

summer and fall, and increased risk of flooding (Lettenmaier and Sheer 1991).

Hydrologic sensitivities across a large part of the western US are driven primarily by runoff 

shifts due to temperature change, not changes in total precipitation (Lettenmaier and Gan 

1990). The exception to the temperature dominance would be in river system with large 

reservoir storage relative to the mean annual flow. In these cases shifts in the seasonality 

of runoff would be less important than the changes in the mean annual flow, which would 

be sensitive to precipitation as well as temperature changes. In populated areas of the 

western US such as California, changes in water demand will almost certainly overshadow 

the possible effects of GCC over the next century.

Projected Streamflow Effects from Climate Change in the Pacific Northwest 

Relative to present flows (dashed), the wetter winters and drier summers simulated by climate models are very 

likely to shift peak streamflow earlier in the year, increasing the risk of late-summer shortages. Source: Hamlet, 

A.F. and D.P. Lettenmaier. 1999. (As shown in the National Assessment Synthesis Team report 2001). 
 2. Water Resources 

2-4

Rain-on-snow

Willamette River, Oregon 1996 flood 

Marks et al. (1998) used an energy 

balance snowmelt model to simulate 

snowmelt processes during a warm, 

very wet Pacific storm that caused 

significant flooding in the Pacific 

Northwest during the Winter of 1996. 

Data from paired open and forested 

sites located just below the Pacific 

Crest were used to drive the model. 

The model accurately simulated snow 

cover mass and depth during the 

development and ablation of the snow 

cover prior to, during, and following 

one of the most extreme rain-on-snow 

events on record. The model 

demonstrated that the melt was 

caused by condensation on the snow 

surface during the event, and by the 

fact that a cold storm had deposited 

significant snow cover down to 

relatively low elevations within the 

snow transition zone. In the snow 

transition zone of the Cascade 

Mountains, clear-cutting is a common 

forest practice. This study showed 

that during this event, snowmelt was 

enhanced in forest openings and 

clear-cuts. If GCC results in a shift to 

warmer winters such rain-on-snow 

events could become more frequent. 
 2. Water Resources 

2-5

Effects on regional water balance 

A spatially distributed regional water balance model was used to look at the sensitivity of the Columbia Basin to climate change

(Dolph et al. 1991). A wet year (1972) and a dry year (1977) were simulated and compared to recorded data. The modeled total 

runoff was significantly less than measured runoff—implying that precipitation data from the Historic Climate Network was 

underestimated by the existing network of measurement stations in mountainous regions. In response to this need, several new 

methods for estimating precipitation at regional scales were developed (Phillips et al. 1992, Daly et al. 1994). Spatial data bases of 

precipitation, temperature, vapor pressure, evapotranspiration, and wind were created for both current conditions and 2xCO2CO2

scenarios for several GCMs and were made publicly available for the global climate change research community (NOAA / EPA 

1992, 1997). 

_________________________________________________________________________________________________

The table below presents annual water balance results for a very wet (1972) and a very dry (1977) water year, and for 

2xCO2 climate conditions predicted by the GFDL general circulation model for the US portion of the Columbia River Basin. 

 All values are in mm H2O per unit area, so they represent an average depth of water over the basin. Measured annual 

runoff at the basin outflow has been corrected to reflect only discharge from the US portion. Annual values refer to water 

years (Oct. to following Sep.). NA: data not available or not applicable. Standard deviation (SD; in parentheses) is used to 

indicate the extent of deviation from the basin average reported in the table; no SD is given for measured runoff from1972 

and 1977 because it is derived from single values measured at the basin outflow; SD is given for the long-term average 

measured runoff because it is based on 40 annual values (Marks et al. 1993). 

Year Measured

annual

precip.

Measured

annual

runoff

Modeled

annual

runoff

Annual

PET

Modeled

annual

ET

Soil

initial

storage

Soil final 

storage

Wet year 

1972

776

(547)

1447a 437

(475)

878

(315)

311

(151)

65

(61)

93

(60)

Dry year 

1977

507

(377)

332 a 259

(295)

898

(325)

254

(150)

65

(57)

59

(63)

Long-term

average 

NA 741 b 

(490)

NA NA NA NA NA

GFDL

2xCO2

scenario

636c

(543)

NA 276

(319)

1627

(470)

396

(215)

63

(57)

27

(37)

aAnnual runoff over the US portion of the Columbia River Basin (Canadian portion of the flow subtracted out) from gage 

measurements at the basin outflow, adjusted for storage effects. 

b40-year average unit runoff for the US portion of the Columbia River Basin (Canadian portion of the flow subtracted out) 

using historical runoff data. 

cAverage precipitation for the US portion of the Columbia River Basin calculated from the 1972 and 1977 precipitation 

data.___________________________________________________________________________________________

The water balance approach incorporating a physically based model of potential evapotranspiration and explicit calculation of soil

water holding capacity, improved our ability to simulate soil moisture under current and future climate conditions. A 2xCO2 scenario 

generated by the GFDL global circulation model provided climate conditions to run the Dolph et al. (1991) water balance model. 

The model predicted increased PET, and ET, and decreased runoff and soil moisture. Marks et al. (1993) predicted that changes in

soil moisture and evapotranspiration resulting from global climate change will have large impacts on water and vegetation 

resources. 

If changes in the regional water balance are significant, major shifts in vegetation patterns and condition are a likely result of global 

climate change. Neilson and Marks (1994) incorporated a distributed water balance model with a biogeographic vegetation model,

MAPSS (Mapped Atmosphere-Plant-Soil System) to predict changes in vegetation leaf area index, site water balance and runoff as 

well as changes in biome boundaries. 2xCO2 scenarios from five different global circulation models (GCMs) were used to predict 

vegetation changes globally. Increased PET due to higher temperatures generally offsets increased precipitation under all 2xCO2

scenarios. Eastern NA and Eastern Europe to western Russia were among the most sensitive regions to drought-induced forest 

decline.
 2. Water Resources 

2-6

References Cited 

Daly, C., R.P. Neilson, and D.L. Phillips. 1994. A statistical-topographic model for mapping climatological 

precipitation over mountainous terrain. J. Appl. Meteorol. 33: 140-158. 

Dolph, J., D. Marks, and G. A. King. 1991. Sensitivity of the regional water balance in the Columbia 

River basin to climate variability: Application of a spatially distributed water balance model. In New

perspectives for watershed management: Balancing Long-Term Sustainability with Cumulative 

Environmental Change, (R. J. Naiman and J.R. Sedell, eds.), pp 233-265. 

Hamlet, A. F., and D. P. Lettenmaier. 1999. Effects of climate change on hydrology and water 

resources objectives in the Columbia River basin, Journal of the American Water Resources 

Association, 35(6),pp.1597-1625. 

Lettenmaier, D. P., K. L. Brettmann, L. W. Vail, S. B. Yabusaki, and M. J. Scott. 1992. Sensitivity of 

Pacific Northwest water resources to global warming. The Northwest Environmental Journal 8:265-283. 

Lettenmaier, D. P. and D. P. Sheer. 1991. Climatic sensitivity of California water resources. J. Water 

Resources Planning and Management 117.1: 108-125. 

Lettenmaier, D. P. and T. Y. Gan. 1990. Hydrologic sensitivities of the Sacramento-San Joaquin river 

basin, California, to global warming. Water Resources Research 26:69-86. 

Marks, D., J. Kimball, D. Tingey, and T. Link. 1998. The sensitivity of snowmelt processes to climate 

conditions and forest cover during rain-on-snow: a case study of the 1996 Pacific Northwest flood.

Hydrol. Process. 12:1569-1587. 

Marks, D., G. A. King, and J. Dolph. 1993. Implications of climate change for the water balance of the 

Columbia River Basin, USA. Clim. Res. 2:203-213. 

Neilson, R. P. and D. Marks. 1994. A global perspective of regional vegetation and hydrologic 

sensitivities from climatic change. J. of Vegetation Science 5:715-730. 

National Assessment Synthesis Team. 2001. Climate Change Impacts on the United States: The 

Potential Consequences of Climate Variability and Change, Report for the US Global Change Research 

Program, Cambridge University Press, Cambridge UK,620pp. 

NOAA / EPA. 1992. Global Ecosystems Database, Disc A. National Oceanic & Atmospheric 

Administration / National Geophysical Data Center – Boulder, CO, and U.S. Environmental Protection 

Agency / Environmental Research Laboratory – Corvallis, OR. 

NOAA / EPA. 1997. Global Ecosystems Database, Disc B. National Oceanic & Atmospheric 

Administration / National Geophysical Data Center – Boulder, CO, and U.S. Environmental Protection 

Agency / Environmental Research Laboratory – Corvallis, OR. 

Phillips, D.L., J. Dolph, and D. Marks. 1992. A comparison of geostatistical procedures for spatial analysis 

of precipitation in mountainous terrain. Agric. & Forest Meterol. 58: 119-141. 

Revenga, C., J. Brunner, N. Henninger, K. Kassem, and R. Payne. 2000. Pilot analysis of global 

ecosystems: Freshwater systems. World Resources Institute 

Washington, DC (This report is also available at http://www.wri.org/wr2000).
 3. Freshwater Fish 

3-1

3. Responses of Freshwater Fish to Temperature Increases 

Statement of the Problem 

Water temperature has long been recognized as one of the most important 

environmental variables influencing the distribution of fish species. Scientists at the MidContinent Ecology Division, Duluth, MN have actively investigated the thermal 

requirements of freshwater organisms especially fish since the 1960's and 1970's,

when a water quality research focused on requirements of aquatic organisms, with a 

special focus on dissolved oxygen and temperature.

Approach

Laboratory studies were conducted on various fish species to establish temperature 

requirements for survival, growth and successful reproduction, data needed for 

development of temperature standards to protect fish against thermal pollution. Since

not all fish species are adaptable to laboratory testing, laboratory tests are expensive, 

and conditions in the environment can alter sensitivity to thermal regimes, we have 

developed a database (FTDMS = Fish Temperature Database Matching System) linking 

fish presence records with thermal records in streams and rivers (Eaton et al. 1995b).

Various alternative methods for estimating an upper extreme habitat temperature 

(UEHT) from fish field distribution data and matched weekly mean stream temperatures 

were compared and their respective advantages and disadvantages examined (Eaton et

al 1995a). As reported in Eaton et al. (1995b), an upper extreme habitat temperature, 

referred to as a maximum tolerance temperature, was derived for species with adequate 

data and a standard error calculated by the bootstrap method. Data above the UEHT 

can be approximated by a three-parameter lognormal distribution; standard error of the 

estimated UEHT varies among species from 0.1 o

 C and 0.6 o C at the 95% cumulative 

probability of occurrence. For 30 common fishes of the U.S., maximum weekly mean 

temperatures derived from the database are less than lethal temperatures derived from 

laboratory tests, and are similar to temperature criteria derived from laboratory data 

interpolated using EPA procedures (Eaton et al. 1995b).

Main Conclusions 

Effects on fish communities in streams and rivers 

In free-flowing streams, the effect of air temperatures and thus global warming on 

stream temperatures can be approximated by an adjustment factor of 0.9 times air 

temperature, based on field studies of air-water temperature relationship (Stefan and 

Preud’homme 1993; Eaton and Scheller 1996). The effects of a doubling of CO2 on shifts in 

suitable fish habitat has been estimated based on predictions of air temperature effects 

from the Canadian Climate Center general circulation model (CCC-GCM) and thermal 
 3. Freshwater Fish 

3-2

tolerances for 57 fish species derived from the FTDMS through extreme-value analysis 

(Eaton et al, 1995b). Loss of cold water or cool water fish species was predicted for 

between 35 and 70% of 1700 USGS temperature monitoring stations, with habitat 

losses distributed throughout species ranges. Habitat losses were greatest for species 

with limited distributions and in areas of the country with greatest warming predicted 

(e.g., the central Midwest). Results for warm water fishes were less certain because of a 

relative paucity of data on summer and winter thermal tolerances for species.

Effects of global warming on habitable stream reaches based on temperature effects 

can be modified either positively or negatively near groundwater or tailwater discharges 

from reservoirs or lakes (Sinokrot et al. 1995). Empirical models to predict groundwater 

inputs to stream reaches based on watershed slope and hydraulic conductivity (based 

on soil texture; Baker et al. 2001), and models in progress to predict modifications to 

stream thermal regimes based on stream shading from topography or riparian 

vegetation and groundwater inputs, will help to fine-tune model predictions of the effects 

of global change on fish species distributions (V. Snarski, personal communication).

Effects of global climate change on warm water fish species in streams are uncertain 

due to a relative paucity of data on winter thermal tolerances. Multivariate discriminate 

function analysis has been used to derive models for warm water fish 

presence/absence based on a combination of up to six thermal variables: cumulative 

temperature as degree-weeks, degree weeks during the feeding period ( weeks > 8 deg 

C), degree-weeks during the non-feeding period (weeks < 8 deg C), length of nonfeeding period in weeks, the ratio of degree-weeks during non-feeding periods to 

feeding periods, and the number of weeks at or below 2 deg C (a level associated with 

mortality due to osmoregulatory dysfunction or other physiological mechanisms).

For the 15 species examined, fish presence models had high specificity (60 - 100%, 

percent absence correctly predicted) and high sensitivity (87 - 100%, percent presence 

correctly predicted). 

Recently, the Fish-Temperature-Database-Matching System (FTDMS; Eaton et al. 1995b)

has been updated with additional data on fish presence from EMAP and STORET and 

matched with corresponding stream temperatures from USGS-monitored streams to 

create additional fish/temperature (F/T) sets. A user-friendly graphical interface was 

developed to facilitate data import, export and query functions to make F/T data 

available to clients requesting access (e.g., states and tribes, regions) without requiring 

extensive programming expertise (Contract #68-W7-0055, Task Order #25, Deliverable 25-15, by 

Lockheed Martin Services, Inc., for U.S. EPA, Office of Information, National Resources Services 

Division, Research Triangle Park, NC 27711, March 29, 2000).
 3. Freshwater Fish 

3-3

Effects on fish communities in lakes 

Our ability to predict climate change effects on fish communities in lakes depends on 

our ability to model the effect of climate-related variables on suitable fish habitat.

Modeling exercises have been conducted to predict fish presence/absence in 

Minnesota lakes as a function of two key driving habitat variables - temperature and 

dissolved oxygen (Stefan et al. 1995, 1996). Model performance varies with lake class, as 

defined by lake morphometry (maximum depth, surface area) and trophic status. For

northern Minnesota, there is full agreement between fish assemblage presence records 

and model habitat suitability prediction. For cool and warm water fishes in southern 

Minnesota, there is full agreement between fish assemblage presence records and 

model simulation results for all 27 lake classes. For cold water fish, model predictions 

agreed with fish assemblage presence data for only 18 of 27 lake classes.

Disagreements between observations and predictions are related to the presence of a 

cold water fish (cisco) in lakes predicted to have unsuitable habitat for coldwater 

assemblages; however, cisco is the most tolerant species in the coldwater fish 

assemblage (Stefan et al. 1995). 

Predicted sensitivity of suitable fish habitat to climate change based on thermal and 

dissolved oxygen requirements varies with fish thermal guild (cold water, cool water, 

warm water), lake morphometry (surface area: maximum depth ratio), and trophic status 

(Secchi depth) (Stefan et al. 1996). Lake morphometry determines the probability of 

thermal stratification and trophic status determines the depth of penetration of solar 

radiation and depth of photic zone and dissolved oxygen generation from 

photosynthesis. Degree of temperature change in lakes following a doubling of CO2

levels and average air temperature increase of 3.8 deg C depends on both lake 

morphometry and lake trophic status. Eutrophic lakes with a geometry ratio ([surface 

area]0.25/maximum depth) between 2 and 4 and oligotrophic lakes with a geometry ratio 

of between 1 and 2 are predicted to show the least change in hypolimnetic temperature 

(0 to 1 deg C as compared to 1-3 deg C). Eutrophic lakes with geometry ratios > 4 and 

oligotrophic lakes with geometry ratios >2 are expected to experience decreases in 

hypolimnetic oxygen minima of up to 3 mg/L, with anoxic conditions resulting in 

eutrophic lakes with geometry ratios of 4 to 20. The length of hypolimnetic anoxia will 

extend up to 60 days, and will be greatest in eutrophic lakes with geometry ratios < 5 

and oligotrophic lakes with geometry ratios of < 2 (Stefan et al. 1996). Overall, cold water 

fish are projected to disappear from southern Minnesota lakes, and experience habitat 

losses of 41% in northern Minnesota lakes. Losses in cold water fish good-growth 

potential (as reflected in suitable habitat volume) and increases in cool water fish goodgrowth potential will be greater in well-mixed lakes. Largest gains in suitable habitat for 

cool and warm water species will occur in oligotrophic lakes (Stefan et al. 1996). 
 3. Freshwater Fish 

3-4

Status of research 

Research on the temperature preferences of fish and predicted effects of climate 

change on fish populations is no longer being pursued as a separate program under 

Global Climate Change in NHEERL. However, under the Aquatic Stressors Framework, 

researchers continue to examine the effects of thermal and flow regimes on fish 

communities as two of many stressors affecting habitat quality. In particular, the effect 

of land-use/land-cover changes on thermal regimes is being examined. 

References Cited 

Baker, M.E., M. J. Wiley, and P.W. Seelbach. 2001. GIS-based hydrologic modeling of riparian areas: 

implications for stream water quality. JAWRA 37 :1615-1628.

Eaton, J.G., J.H. McCormick, H.G. Stefan, and M. Hondzo. 1995a. Extreme value analysis of a 

fish/temperature field database. Ecological Engineering 4:289-305. 

Eaton, J.G., J.H. McCormick, B.E. Goodno, D.G. O’Brien, H.G. Stefany, M. Hondzo, and R.M. Scheller. 

1995b. A field information-based system for estimating fish temperature tolerances. Fisheries 20(4):10-

18.

Eaton, J.G. and R.M. Scheller. 1996. Effects of climate warming on fish thermal habitat in streams of the 

United States. Limnol. Oceanogr. 41:1109-1115.

Sinokrot, B.A., H.G. Stefan, J.H. McCormick, and J.G. Eaton. 1995. Modeling of climate change effects 

on stream temperatures and fish habitats below dams and near groundwater inputs. Climatic Change 

30:181-200. 

Stefan, H.G., M. Hondzo, J.G. Eaton, and J.H. McCormick. 1995. Validation of a fish habitat model for 

lakes. Ecological Modelling 82:211-224. 

Stefan, H.G., M. Hondzo, X. Fang, J.G. Eaton, and J.H. McCormick. 1996. Simulated long-term 

temperature and dissolved oxygen characteristics of lakes in the north-central United States and 

associated fish habitat limits. Limnol. Oceanogr. 41:1124-1135. 

Stefan, H. G., and E. B. Preud’homme. 1993. Stream temperature estimation from air temperature. Water 

Resour. Bull. 29:27-45. 
 4. Rice 

4-1

4. Responses of the Irrigated Rice Ecosystem to Enhanced UV-B 

Radiation and Global Climate Change 

Statement of the Problem 

When this study was conceived there was a critical need for information on the 

ecological effects of UV-B radiation (from stratospheric O3 depletion) and global climate 

change (increased atmospheric CO2 concentration and air temperature) in tropical 

areas to support major international assessments on the environmental effects of ozone 

depletion (by the United Nations Environmental Programme), and climate change (by 

Intergovernmental Panel on Climate Change). Rice is a major food source for many of 

the world's people, especially in Asia, but also in Africa and South America (IRRI 1993).

The irrigated rice agroecosytem, where fields are flooded for much of the growing 

season, is the most widely distributed rice system, with 55% of world's rice field area 

and 75% of the world’s rice production (IRRI 1993). Thus any impacts on rice production 

from UV-B and climate change could have profound impacts on a key component of the 

world’s food supply. In addition to enhancing rice production, flooding of irrigated rice 

fields results in anaerobic soil conditions conducive to the production of the greenhouse 

gas methane (Neue 1993). Therefore, understanding the underlying processes and 

management factors controlling the emission of methane from rice fields was important 

in terms of developing strategies for the potential mitigation of emissions of greenhouse 

gases to the atmosphere (Cole 1996).

Approach

To have the most impact and relevance to real field conditions, research on irrigated 

rice was conducted in tropical countries, in cooperation with local scientists. Thus, the 

rice research was conducted through a unique international partnership between the 

U.S. EPA and the International Rice Research Institute (IRRI) in Los Banos, the 

Philippines; with collaboration by other institutions and researchers in the United States, 

the Netherlands, Germany, Japan, China, Korea, India, Malaysia, and Sri Lanka (Olszyk

and Ingram 1991). The research approach included field experiments, modeling activities 

and assessments which presented possible impacts of UV-B and climate change on a 

regional scale for eastern and southeastern Asia. The research was designed to 

consider responses of irrigated rice production from an ecosystem viewpoint, 

considering not only the direct effects of UV-B, CO2 and temperature on the rice plant, 

but also indirect effects of these stressors on the insects, diseases of rice, and weed 

competition. The roles of CO2 and temperature in methane production were also 

studied. The EPA/IRRI study was coordinated with other international global change 

research through the International Geosphere-Biosphere Programme (IGBP) of 

research on Global Change and Terrestrial Ecosystems (GCTE), Focus 3, Global 

Change Impact on Agriculture, Forestry and Soils. 
 4. Rice 

 4-2 

Main Conclusions 

This research provided critical data for international assessments on the impacts of UVB radiation and climate change on rice and on options to mitigate those impacts not only 

on the rice crop, but on emissions of the greenhouse gas CH4 from rice fields (Peng et al.

1995). The data were included in the extensive literature produced by the project 

including 3 books, 20 book chapters and over 75 peer-reviewed journal papers. 

Key results indicated that rice yields likely will not be affected by increases in UV-B 

predicted from stratospheric ozone depletion under realistic tropical-field conditions 

based on extensive and intensive field experiments (Dai et al. 1997). Under greenhouse 

conditions, enhanced UV-B injury was associated with active oxygen metabolism in rice 

leaves (Dai et al. 1997), and could affect the susceptibility of rice to the important disease, 

rice blast (Finckh et al. 1995).

In contrast to enhanced UV-B, elevated CO2 and temperature likely will have dramatic 

effects on irrigated rice production, not only by directly affecting the plant, but also 

through indirect effects on other aspects of the rice ecosystem (insects, diseases, and 

weed competition). Elevated CO2 enhanced rice plant growth and grain yield provided 

that N fertilization was not limiting growth (Olszyk et al. 1999; Weerakoon et al. 1999; Ziska et al.

1998; Moya et al. 1998). In contrast, while elevated temperature enhanced plant growth, it 

decreased crop yield due to spikelet sterility. Combining elevated CO2 and elevated 

temperature resulted also resulted in enhanced plant growth, but with spikelet sterility.

Climate change also was predicted to affect rice productivity by altering disease 

occurrence (Luo et al. 1995) and insect infestations (Heong et al.1995).

Computer simulations and spatial analysis were used successfully to assess the 

potential impacts of climate change on rice productivity across south and Southeast 

Asia (sidebar). In the EPA/IRRI analysis, potential rice yield either decreased or 

increased depending on the global climate model, crop model, and site within a country.

Overall, the analysis found an average 3.8% decrease in rice production across south 

and Southeast Asia with future increases in CO2 and temperature compared to current 

conditions. Though relatively small, this predicted change would occur at a time when 

rice yields must increase substantially to keep in step with increases in human 

population in the area. 

Unique field experiments indicated that the effects of elevated CO2 and temperature on 

rice plants could increase methane emissions from rice fields, providing an important 

feedback to climate change from rice cultivation (Olszyk et al. 1999; Ziska et al. 1998).

Elevated CO2 or in combination with elevated temperature produced a large increase in 

methane emissions from rice fields compared to current conditions; primarily due to a 

large increase in belowground biomass (see sidebar). In contrast, elevated temperature 

alone tended to decrease methane emissions from rice fields. The magnitude of these 

changes in methane emissions from rice fields were not predicted by current plant 
 4. Rice 

4-3

growth simulation models (Olszyk et al. 1999).

In addition to demonstrating impacts of climate change on the irrigated rice systems, 

research indicated avenues to mitigate those impacts for this intensively managed 

agricultural system. The wide-range in variability among rice cultivars and plant types in 

terms of adverse effects from enhanced UV-B and elevated temperature, as well as 

beneficial effects from elevated CO2, indicates the potential for plant breeding to 

maintain or enhance rice yields in the future (Moya et al. 1998; Dai et al. 1994). Similarly,

methane emissions from rice fields varied considerably with rice cultivar, fertilizer 

amount and form, irrigation timing, and other factors, indicating the potential to reduce 

methane emissions from rice fields through altered management practices (Neue et al.

1995).
 4. Rice 

 4-4 

Elevated UV-B Radiation from Stratospheric O3 Depletion not expected to affect 

Rice Yields 

With depletion of the stratospheric O3 layer, ground-level UV-B levels are expected to increase. The 

effect of potential increases in UV-B under realistic field conditions was determined in rice fields at the 

International Rice Research Institute at Los Baños, the Philippines. Over five growing seasons, both wet 

(cloudy, rainy) and dry (more sunlight, dry) two widely grown (yet potentially UV-B susceptible) rice 

cultivars IR 72 and IR 74 exposed to current and enhanced UV-B radiation. There was no significant 

UV-B effect on rice yield for either cultivar in any season. Across all seasons and both cultivars the 

average yield was the same at 608 g m-2 for both control and enhanced UV-B rice plants. Source: Dai et

al. 1997. 

Increased Atmospheric CO2 and Air Temperature Affects Rice Yields and 

Methane Emissions from Rice Fields 

The effects of increased atmospheric CO2 and consequent predicted increases in air temperature were 

studied for rice -- the world’s most important crop for direct human consumption. Both rice yield and 

methane emissions, a greenhouse gas produced in rice soils, were measured for rice plants grown in 

open-top chambers under realistic tropical field conditions at the International Rice Research Institute in 

the Philippines. Yield and methane emissions were determined for the widely grown rice cultivar, IR 72, 

grown for two wet and two dry seasons under current ambient CO2 and temperature conditions (ACAT) 

and under three future climate scenarios of elevated CO2 and ambient temperature (ECAT), ambient CO2

and, elevated CO2 and elevated temperature (ECET). By itself, elevated CO2 increased rice yields, as 

shown for many other crops grown under conditions of optimum N fertilization and water. However, 

elevated temperature tended to decrease rice yields and thus the increase in rice yield with elevated CO2

alone was negated when temperature also elevated. Emissions of methane were increased when rice 

plants were exposed to elevated CO2 either with or without elevated temperature, which was associated 

with an increase in root biomass; while elevated temperature alone tended to decrease methane 

emissions. Source: Olszyk, et al. 1999; Moya et al. 1998; Ziska et al. 1998. 

Scenarioa Parameter 1994 Wet 1995 Dry 1995 Wetb 1996 Dry 

ACAT Grain Yield (g m-2) 366 683 ---- 874 

ECAT Change Grain Yield (%) +29 +24 ---- +15

ACET Change Grain Yield (%) -26 -16 ---- -13 

ECET Change Grain Yield (%) -14 +9 ---- -6 

ACAT Methane (mg m-2 d-1) ---- ---- 142 260 

ECAT Change in Methane (%) ---- ---- +60 +48

ACET Change in Methane (%) ---- ---- ---- -54 

ECET Change in Methane (%) ---- ---- ---- +45

a

 Experimental values in bold are significantly different from ambient CO2 and ambient temperature at 

p<0.05.

b

 Rice yield severely decreased due to typhoon prior to crop maturity.
 4. Rice 

4-5

Changes in Rice Grain Yield across East and South Asia with Elevated CO2 and 

Elevated Temperature 

Potential effects of climate change (elevated CO2 and elevated temperature) on irrigated rice production 

across south and East Asia were estimated based on computer simulations and spatial analysis. 

Climate change scenarios from the General Fluid Dynamcis Laboratory (GFDL), Goddard Institute of 

Space Studies (GISS), and United Kingdom Meteorological Office (UKMO) General Circulation Models 

(GCMs,) were used, assuming a doubling of current atmospheric CO2. The outputs from those models 

were used with site-specific weather data and two plant process-based rice crop simulation models, 

ORYZA1 and SIMRIW to predict potential rice yield under current and future climate conditions at sits 

across Asia. The changes in rice yield with climate change were assessed using a Geographic 

Information System (GIS). An example of the pattern of these changes in yield from current climate 

conditions based on the UKMO GCM and ORYZA1 model is shown below. In this simulation, global 

climate change produced increases in potential yield (green colors) for much of India and southeast Asia, 

and decreases in yield (yellow to orange colors) in most of China, Japan and Korea; with an average 

5.6% reduction in yield across all of Asia ( Source: Matthews, Horie et al. 1995).
 4. Rice 

 4-6 

References Cited 

Cole, V. (Lead Author), 1996. Agricultural options for mitigation of greenhouse gas emissions. pp. 745-

771. In: Watson, R.T., Zinyowera, M. C., Moss. R.H., (Eds.), Climate Change 1995 Impacts, Adaptations 

and Mitigation of Climate Change: Scientific Technical Analyses. 878 pp. Cambridge University Press, 

New York. 

Dai, Q., S. Peng, A.Q. Chavez, and B.S. Vergara. 1994. Intraspecific responses of 188 rice cultivars to 

enhanced UV-B radiation. Environmental and Experimental Botany Vol. 34,433442. 

Dai, Q. , B.Yan, S. Huang, X. Liu, S. Peng, Ma. L.L. Miranda, A.Q. Chavez, B.S. Vergara and D.M. 

Olszyk. 1997. Response of oxidative stress defense systems in rice (Oryza sativa) leaves with 

supplemental UV-B radiation. Physiologia Plantarum 101,301-308. 

Dai, Q. , S. Peng, A.Q. Chavez, Ma. L.M. Miranda, B.S. Vergara, and D.M. Olszyk. 1997. Supplemental 

Ultraviolet-B radiation does not reduce growth or grain yield in rice. Results From a 7-season field study.

Agronomy Journal 89,793-799. 

Finckh, M.A., A.O. Chavez and P.S. Teng. 1995. Effects of UV-B radiation on the susceptibility of rice to 

rice blast. Agriculture, Ecosystems & Environment 52,223-233. 

Heong, K.L., Y.H. Song, S. Pimsamarn, R. Zhang, and S.D. Bae. 1995. Global warming and rice 

arthropod communities. pp. 326-335, In, Peng S., K. Ingram, H. U. Neue, L. Ziska, Eds. Climate change 

and rice. Springer- Verlag, Berlin. 

International Rice Research Institute (IRRI), 1993. 1993-1995 IRRI Rice Almanac, IRRI, Los Baños, 

Philippines. 

Luo Y., D.O. TeBeest, P.S. Teng, and N.G. Fabellar. 1995. Simulation studies on risk analysis of rice leaf 

blast epidemics associated with global climate change in several Asian countries. Journal of 

Biogeography 22:673-678. 

Matthews, R.B., T. Horie, M.J. Kropff, D. Bachlelet,H.G. Centeno, J.C. Shin, S. Mohandass, S. Singh, Z. 

Defeng, and M.H. Lee. 1995. A regional evaluation of the effect of future climate change on rice 

production in Asia, pp. 95-139, In, Matthews, R.B., M.J. Kropff, D. Bachlelet, and H.H. Van Laar, eds.

Modeling the impact of climate change on rice production in Asia. CAB International, Wallingford, U.K.

Matthews, R.B., M.J. Kropff, D. Bachlelet, and H.H. Van Laar. 1995. Modeling the impact of climate 

change on rice production in Asia. CAB International. 

Moya, T., O.S. Namuco, L.H. Ziska, and D. Olszyk. 1998. Growth dynamics and genotypic variation in 

tropical, field-grown paddy rice (Oryza sativa L.) with increasing carbon dioxide and temperature. Global 

Change Biology 4,645-656. 

Neue, H-U. 1993. Methane emission from rice fields. BioScience 43,466-474. 

Neue. H.-U., Wassmann, R., and R.S. Lantin. 1995. Mitigation options for methane emissions from rice 

fields. pp. 136-144, In, Peng S., K. Ingram, H. U. Neue, L. Ziska, Eds. Climate change and rice. SpringerVerlag, Berlin. 
 4. Rice 

4-7

Olszyk, D.M. and K.T. Ingram. 1991. Effects of UV-B and global change on rice production: The EPA/IRRI 

Cooperative Research Plan. Pp. 234-253. In, M. Ilyas, Ed., Ozone Depletion Implications of the 

Tropics.University Science Malaysia and U.N. Environmental Programme. 

Olszyk, D., Q. Dai, P. Teng, H. Leung, Y. Luo,

 and S. Peng . 1996. UV-B Effects on Crops: Response of 

the Irrigated Rice Ecosystem. Journal of. Plant Physiology, 148,26-34. 

Olszyk, D.M., H.G.S. Centeno, L.H. Ziska, J.S.Kern, and R.B. Matthews. 1999. Global Change, Rice 

Productivity and Methane Emissions: Comparison of Predicted and Experimental Results. Agricultural

and Forest Meteorology 9,87-101. 

Peng S., K. Ingram, H. U. Neue, L. Ziska, Eds. Climate change and rice. 1995. Springer- Verlag, Berlin. 

Weerakoon, W. M., D.M. Olszyk, and D.N. Moss. 1999. Effects of Nitrogen Nutrition on Responses of 

Rice Seedlings to Carbon Dioxide. Agriculture Ecosystems and Environment 72,1-8.

Zhang, R., K.L. Heong, and Q. Dai. 1994. Effect of elevated ultraviolet-B radiation on abscisic acid and 

indoleacetic acid content of rice leaves. IRRN 19,:56-57 September. 

Ziska, L.H., P.A. Manalo, and R. Ordoñez. 1996. Intraspecific variation in the response of rice (Oryza

sativa L.) to increased C02: Evaluation of 17 cultivars. Journal of Experimental Botany 47,1353-1359. 

Ziska, L.H. and P.A. Manalo. 1996. Increasing night temperature reduces seed set in tropical rice.

Australian Journal of Plant Physiology. 23,791-794. 

Ziska, L. H., 0. S. Namuco, T. B. Moya, T. Matsui, and J. Quilang. 1997. Growth and yield 

response of field-grown tropical rice to increasing C02 and air temperature. Agronomy Journal 89,45-53. 

Ziska, L.H., W. Weerakoon, O.S. Namuco, and R. Pamplona. 1996. The influence of nitrogen on the 

elevated C02 response in field-grown rice. Australian Journal of Plant Physiology 23,45-52. 

Ziska, L.H., T. Moya, O.S. Namuco, R. Levine, R. Wassman, and D. Olszyk. 1998. Elevated carbon 

dioxide stimulates methane emission in tropical paddy rice. Global Change Biology 4:657-665.
 5. Ag Soils

5-1

5. Agriculture – Crop yields, soil erosion, and soil carbon 

Statement of the Problem 

Rising atmospheric CO2 concentrations and global climate change could potentially 

have significant effects on American agriculture. While elevated CO2 may have a 

beneficial effect on crop growth, increased temperature and changes in precipitation, 

wind, and other climatic variables may alter crop yields. These climatic changes may 

also affect rates of soil erosion and the carbon content of agricultural soils, which may 

affect carbon sequestration.

Soils are a major reservoir of global carbon, and are equal in magnitude to the 

combined global carbon content of the entire atmosphere plus all aboveground 

biomass. Loss of agricultural soil carbon through erosion, management, and 

decomposition adds to the atmospheric loading of CO2. Agricultural management 

practices which conserve or sequester soil carbon can help mitigate the rate of increase 

of atmospheric CO2. Assessments of the potential for such mitigation through 

widespread adoption of best management practices for major American agricultural 

areas are needed as well.

Approach

Research focused on model assessments of the sensitivity of soil erosion to 

precipitation change scenarios across the US, and more detailed evaluations of crop 

yield, soil erosion, and soil carbon responses to climate change scenarios including 

temperature, precipitation, wind, and CO2 in the US Corn Belt. The research focused on 

two erosional processes: (1) water erosion which is the loss of soil due to rainfall runoff 

from field crops, and (2) wind erosion which is the loss of soil due to wind blown 

particles. Assessments were also made of the effects of widespread adoption of 

various management practices on soil erosion and soil carbon in the United States to 

mitigate the rate of atmospheric CO2 increase. Management scenarios included the 

current mix of tillage and crop rotation practices, and increased use of crop rotation and 

conservation tillage practices which have become more prevalent in recent years. 

Main Conclusions 

Projected water erosion of soil for U.S. croplands, pasturelands, and rangelands 

increased with increases in precipitation in the 2xCO2 climate change scenarios from 

four atmospheric General Circulation Models (Phillips et al. 1993b). Changes in erosion 

were greater when precipitation changes were assumed to be from changes in storm 

intensity rather than storm frequency, indicating the importance of the manner in which 

climatic changes occur in addition to their mean magnitude. Recent reductions in 

national soil erosion indicate the potential for management changes to mitigate the 

magnitude of erosion increases projected under these climate change scenarios. 
 5. Ag Soils

5-2

In a detailed model assessment using 36 climate/CO2 scenarios for croplands in the 

U.S. Corn Belt, water erosion linearly tracked increasing or decreasing precipitation, but 

wind erosion showed dramatic increases as mean wind speeds increased (Lee et al.

1996). Increasing temperature alone decreased water erosion while increasing wind 

erosion and total erosion (water and wind). But, beneficial effects of elevated CO2 on 

plant growth nullified this effect on total soil erosion.

Typical of agricultural soils under long-term cultivation, soil carbon decreased over the 

100 year simulations, adding to atmospheric CO2 loadings. This carbon loss was 

accelerated by increased temperature and precipitation, but elevated CO2 slowed the 

loss rate. Corn and soybean crop yields were projected to decrease slightly due to 

temperature or wind increases alone, track precipitation increases or decreases, and 

increase markedly in response to an 80% increase in CO2 (Phillips et al. 1996).

Model assessments of alternative management practices in the U.S. Corn Belt showed 

that increasing use of conservation tillage practices such as mulch-till and no-till could 

substantially reduce the loss of soil carbon due to erosion and decomposition (Phillips et

al. 1993a, Lee et al. 1993). Agricultural soils could become a small sink for carbon with 

widespread use of no-till cultivation and use of a winter cover crop (Lee et al. 1993). This

indicates the potential for changing agricultural management practices to mitigate the 

buildup of atmospheric CO2 and associated climatic change. Conservation tillage is 

economically and functionally feasible and is likely to occur because of land and soil 

conservation benefits from conservation tillage and rising fuel costs (Kern and Johnson 

1993).
 5. Ag Soils

5-3

Wind and water erosion 

Sensitivity of Corn Belt soil erosion to climatic changes 

0

10

20

30

40

0.8 0.9 1.0 1.1 1.2

Precipitation or Wind Speed Ratio

Soil Erosion (Mg/ha/yr)

Wind

Erosion

Water

Erosion

This figure shows projected soil loss by water and wind erosion across croplands in 

the U.S. Corn Belt under an elevated atmospheric CO2 concentration of 625 ppm 

and a temperature increase of 2o C above current conditions. Current conditions for 

precipitation and wind speed are represented by a ratio of 1.0. When precipitation in 

the climate scenario is varied from 20% below current levels (ratio of 0.8) to 20% 

above current levels (ratio of 1.2), water erosion increases linearly. In contrast as 

mean wind speeds in the climate scenario are varied from –20% to +20% compared 

to current levels, there is a dramatic non-linear increase in wind erosion.
 5. Ag Soils

5-4

Carbon Sequestration in Soil 

Soil organic matter is the largest global terrestrial carbon (C) pool and is a source of CO2, CH4, and other 

greenhouse gases. Soil management affects the amount of C held in soil and the greenhouse gas emissions 

from soil. In the agricultural sector conventional tillage practices such as the use of a moldboard plow, lead to 

a steady loss of soil C to the atmosphere. In contrast, conservation tillage practices that include minimum 

tillage and no-till conserve soil C and reduce that amount of fossil fuel needed for tillage. 

Kern and Johnson (1993) conducted an analysis of the amount of soil C that would either be lost or 

sequestered and the amount of fossil fuel required for agriculture in the contiguous United States using three 

scenarios of conservation tillage: 27% (Scenario 1), 57% (Scenario 2) and 76% (Scenario 3). The analysis 

covered 30 years beginning in 1990. For Scenario 1, the level of conservation tillage was held constant at the 

actual 1990 level of 27% for 30 years. For Scenarios 2 and 3, both began at 27% in 1990 and linearly ramped 

up to 57% and 76%, respectively, over the first 20 years of the analysis and were held constant for the 

remaining 10 years. 

Maintaining 1990 levels of conventional and conservation tillage resulted in a net loss of 41 Tg of soil C (1 Tg = 

1012g) over the 30-year period while using 157 Tg of fossil fuel. A combined 198 Tg of C was estimated to be 

added to the atmosphere under Scenario 1. For Scenario 2, a net sequestration of C in soil (+80 Tg) was 

achieved while fuel consumption dropped slightly. Fossil fuel consumption did not drop concomitantly because 

reduced tillage systems require more herbicides and pesticides -- derived from fossil fuels -- than conventional 

tillage systems. For Scenario 3, an additional 364 Tg of soil C sequestered and 146 Tg of fossil fuel 

consumed, for a net gain of 218 Tg of C. 

Changes in soil organic C and fossil fuel C emission for three scenarios of 

conservation tillage (CT) for agriculture in the contiguous U.S. projected from 1990 

to 2020. 

 Scenarios of Conservation Tillage (CT) 

 27% CTa

 57% CTb 76% CTc

Tillage System Soil Fuel Soil Fuel Soil Fuel 

Conventional Tillage -41 -121 -24 -87 -13 -67 

Minimum Tillage 0 -30 0 -52 0 -66 

No-Tillage 0 -6 +104 -10 +377 -13 

Sums -41 -157 +80 -149 +364 -146 

Net Loss (-) or Gains (+) -198 -69 +218 

a) 27% CT scenario uses the level of conservation tillage used in 1990 (~27%) held constant for 30 years until 

2020.

b) 57% CT scenario begins in 1990 with 27% conservation tillage and linearly ramps up to 57% conservation 

tillage over 20 years (2010) and remains constant at 57% until 2020. 

c) 76% CT scenario begins in 1990 with 27% conservation tillage and linearly ramps up to 76% conservation 

tillage over 20 years (2010) and remains constant at 76% until 2020. 
 5. Ag Soils

5-5

References Cited 

Kern, J.S. and M.G. Johnson. 1993. Conservation Tillage Impacts on National Soil and Atmospheric 

Carbon Levels. Soil Science Society of America Journal 57:200-210. 

Lee, J.J., D.L. Phillips, and R. Liu. 1993. The effect of trends in tillage practices on erosion and carbon 

content of soils in the U.S. Corn Belt. Water, Air, and Soil Pollution 70: 389-401. 

Lee, J.J., D.L. Phillips, and R.F. Dodson. 1996. Sensitivity of the U.S. Corn Belt to climate change and 

elevated CO2: II. Soil erosion and organic carbon. Agricultural Systems 52: 503-521. 

Phillips, D.L., P.D. Hardin, V.W. Benson, and J.V. Baglio. 1993a. Non-point source pollution impacts of 

alternative agricultural management practices in Illinois: a simulation study. Journal of Soil and Water 

Conservation 48: 449-457. 

Phillips, D.L., D. White, and C.B. Johnson. 1993b. Implications of climate change scenarios for soil 

erosion potential in the United States. Land Degradation and Rehabilitation 4: 61-72. 

Phillips, D.L., J.J. Lee, and R.F. Dodson. 1996. Sensitivity of the U.S. Corn Belt to climate change and 

elevated CO2: I. Corn and soybean yields. Agricultural Systems 52: 481-502. 
 6. Forest Management 

6-1

6. The Global Carbon Cycle: Managing Forest Systems 

Statement of the Problem

The accumulation of CO2 in the atmosphere due to fossil fuel use, deforestation and other 

anthropogenic sources is changing the global climate (Harries et al. 2001; IPCC 2002). Current 

understanding of the global carbon cycle suggests that managing forests and agricultural 

lands to increase the sequestration of greenhouse gases (GHG) provide credible policy 

options (Dixon and Turner 1991, Winjum et al. 1993a, Brown 1996a, Brown et al. 1996). EPA/WED

research efforts during the 1990’s estimated the amount of that carbon which could be 

sequestered by purposeful management actions, and the incidental amount of carbon that 

inadvertent land use is likely to release to the atmosphere in the future. The three specific 

objectives of this research were to: 1) develop or refine global, country-level and regional 

estimates of carbon pools and fluxes in forests, 2) evaluate the potential to conserve and 

manage forests to expand the accumulation of carbon, and, 3) project future forest carbon 

pools and fluxes during expected changes in climate and land-use. The annual exchange of 

carbon between forests and the atmosphere, and the amounts of carbon stored in forests, 

varies widely with the nature of forest cover. With land use and management, and with 

climatic constraints, our research showed that management of forests can significantly 

increase the long-term sequestration of atmospheric CO2. However, management efforts 

aimed at storing carbon in the tropics -- the largest pools on Earth -- are being countered by 

carbon emissions from forest destruction. 

Approach

We developed several methods to quantify the major carbon pools and fluxes in forested 

ecosystems (Winjum et al. 1993b, Turner et al. 1995, 1997, Brown et al. 1999). Forest carbon budgets 

were constructed with recently completed national carbon budgets, and with global, national 

or regional databases of carbon densities in various above and below-ground forest pools 

(Dixon and Turner 1992; Kolchugina and Vinson 1993a; Cairns et al. 1997), in forest products (Winjum et al.

1998), and in differing land uses (Brown 1996b) and forest areas (Gaston et al. 1994,1997).

NHEERL researchers applied available static geographic models (Turner and Leemans, 1992; King 

and Neilson 1992, Lugo et al, 1999) or developed new models (Prentice et al. 1992; Solomon et al. 1993; 

Neilson 1995; Kirilenko and Solomon 1998), each using the distributions of current climate variables 

as proxies for vegetation and carbon stocks. The data sets and information developed in 

these studies were then used as a base against which to contrast the amounts of carbon that 

is sequestered by various management techniques (e.g., Winjum et al 1993b, Dixon 1995, 1997; 

Dixon et al. 1993, 1994b). The distribution of future climatic conditions projected by climate 

models could then be used to assess distributions and amounts of future carbon stocks. The 

future global carbon stock estimates from the static geographic models are discussed under 

“F-Vegetation Redistribution” and will not be reiterated here. 
 6. Forest Management 

6-2

Main Conclusions 

Forests play a prominent role in the global carbon cycle and the accumulation of GHG in the 

atmosphere, but the roles vary regionally (Dixon et al. 1994). In the conterminous United States, 

for example, total forest carbon was calculated to be 36.7 Gt C (Gt = Gigatons, i.e., a billion 

tonnes), with annual uptake of about 331 Mt (million tons) C, and losses to harvests of 266 Mt 

C (Turner et al. 1995). However, a different method suggested that annual carbon uptake for 

eastern U.S. forests during the late 1980s and early 1990s was about 416 Mt C/yr (Brown and 

Schroeder 1999). In the eastern United States, forest carbon stocks were estimated at 20.5 Gt, 

80% of that found in hardwoods (Brown et al.1999). Schroeder et al. (1997) noted that these 

carbon stocks were distributed primarily in small stands or lots with small trees, and in larger 

stands with large trees. This suggests that most carbon in the eastern U.S. is stored in young 

forests growing on abandoned farms and in forest reserves with large mature trees. An error 

analysis of the southeastern carbon stocks (Phillips et al. 2000) showed that sampling error was 

only about 1% (95% confidence intervals) but that annual carbon increments carried errors of 

about +/- 40%. 

These carbon stocks and fluxes from the temperate U.S. forests were compared to estimates 

we developed in boreal and tropical regions, and for the world as a whole. Globally, forest 

vegetation and soils contain about 1146 Gt of C, with approximately 37% of this carbon in lowlatitude forests, 1/7 in mid-latitudes, and 49% at high latitudes. Over two-thirds of the carbon 

in forest ecosystems is contained in soils and associated peat deposits (Dixon et al. 1994a). The 

carbon stocks and fluxes of the former Soviet Union (FSU) were examined in several papers 

which focused on the large portion of the world’s biomass held by the boreal forests and 

peatlands. 

Based on calculations from mapped ecoregions of the FSU, and estimated carbon stocks and 

fluxes in those ecoregions, the FSU forests were estimated to contain 69 and 110 Gt C above 

ground, and 331 and 337 Gt C below ground (Kolchugina and Vinson, 1993b and 1993c, 

respectively). A third paper in the series (Vinson and Kolchugina 1993) indicated similar values of 

118 Gt C above ground for all vegetation, and 423 Gt C below ground. Unique environments 

(permafrost, peatlands) of the FSU were analyzed separately, indicating that permafrost 

carried 17 Gt C above ground and 155 Gt C in soils and litter (Kolchugina and Vinson 1993d, 

1993e), including peatland carbon. Carbon in peatlands evaluated alone (Botch et al. 1995) was 

estimated at 215 Gt C.

Estimates of carbon stocks and fluxes from several tropical regions provided additional depth 

to the analysis. Africa, for example, was determined to contain 50.6 Gt C in all vegetation 

cover, both above and below ground (Gaston et al. 1998). In the western Hemisphere, Brazil 

contains the world’s largest expanse of tropical forests, with 136-162 Gt C in above and 

below-ground vegetation and litter (Schroeder and Winjum 1995a), and net emissions of carbon to 

the atmosphere of 174-233 Mt yearly (Schroeder and Winjum 1995b) projected for the 20-yr period 

of 1990 to 2010 (Schroeder and Winjum 1995c, Schroeder 1996). Delany et al (1997, 1998) determined 

that Venezuelan forests held 300-500 T/ha C, with 20-37% of that on and below ground and 
 6. Forest Management 

6-3

with turnover time of litter into CO2 being very rapid (<2 yrs). Biomass burning in Costa Rica 

(Helmer and Brown 2000) contributed to considerable CO2 emissions as well, primarily from 

lowland forest destruction.

In Mexico, like Costa Rica, most carbon stock changes near the end of the 20th century were 

attributable to destruction of tropical and subtropical forests (Cairns et al. 1995, 1996), from 

southern Mexico (Riley et al. 1997, Schuft et al. 1998, Cairns et al. 2000), to the Mexican central 

highlands (De Jong et al. 1999, 2000). The data from Brazil, Mexico, the U.S. and the former 

Soviet Union, were combined in several papers, both for comparing overall carbon budgets 

(Turner et al. 1997, 1998, without Mexico), and to compare land use effects (Cairns et al. 1997).

The results amplified conclusions reached in earlier analyses, demonstrating the importance 

of reducing land use impacts on forest biomass in tropical areas, and of applying forest 

management techniques to enhance carbon sequestration in tropical, temperate and boreal 

regions.

Slowing deforestation, combined with an increase in forestation and other management 

measures to improve forest ecosystem productivity, could conserve or sequester significant 

quantities of C. Future forest carbon cycling trends attributable to losses and regrowth 

associated with global climate and land-use change are uncertain (Dixon et al. 1999). Model 

projections and field experiments suggest that forests could be carbon sinks or sources in the 

future (Dixon et al. 1994). To the end, forest carbon conservation and sequestration options have 

become major policy instruments of the UN Framework Convention on Climate Change 

Activities (UNFCCC) Implemented Jointly (AIJ) pilot over the past decade (Dixon 1999, Dixon 

1995).
 6. Forest Management 

6-4

Estimates of carbon pools and flux in forest vegetation in world forests 

Forests are important in the global 

carbon cycle because they store more 

than 55% of the global carbon stored in 

vegetation and more than 45% of that 

stored in soils, exchange carbon with 

the atmosphere through photosynthesis 

and respiration, are sources of 

atmospheric carbon when they are 

disturbed by human or natural causes 

and become atmospheric carbon sinks 

during regrowth after disturbance 

Forests can influence climate change 

by affecting the level of CO2 in the 

atmosphere; through the production of 

other greenhouse gases such as 

carbon monoxide, ozone, and nitrous 

oxide; and through changes in albedo of 

land as forests are converted to other 

land cover types.

Globally, forest vegetation and soils 

contain approximately 359 and 787 Pg 

of C, respectively (Pg= 1,000 million 

tonnes). Earlier projections ranged 

from 953 to 1400 Pg of global C. The 

allocation of carbon between vegetation 

and soils differs by latitude, with a large 

part of the vegetation (25%) and soil 

(59%) carbon pools located in the highlatitude forests. Mid-latitude forests 

account for a small portion of the global 

carbon pool (16 and 13% of the 

vegetation and soil, respectively). Lowlatitude tropical forests are relatively 

heterogeneous and contain 59 and 27% 

of global forest vegetation and soil C, 

respectively (Dixon et al. 1994a).

The table shows estimated carbon 

pools and area-weighted carbon 

densities in forest vegetation (aboveand below-ground living and dead 

mass) and soils (O horizon, mineral 

soil to a depth of l m, and co-located 

peatlands) in forests of the world 

(from Dixon et al 1999). 

a Includes Nordic nations. A factor of 

1.75 was used to convert stem to total 

vegetation biomass. For soil C, an 

average of 9 kg m2

 for temperate forests 

and the forest area in Table 1 was used. 

b Estimated as the product of carbon 

densities by ecofloristic zone and areas 

of forest in each zone, corrected for 

roots, non-tree components, and woody 

debris. 

c Estimated as the product of forest area 

and an average of 12 kg m2

 of soil 

organic C. 

Latitudinal Belt C Pools (Pg) 

 Vegetation Soils 

High

Russia 74 249 

Canada 12 211 

Alaska 2 11 

Subtotal 88 471 

 

Mid

Cont’l US 15 26 

Europeana 9 25 

China 17 16 

Australia 18 33 

Subtotal 59 100 

 

Low 

Asia 41b-54 43 

Africa 52 b 63c

Americas 119 b 110 c

Subtotal 212 216 

TOTAL 359 787 

1Pg=1015 g or 1 gigatonne 
 6. Forest Management 

6-5

Carbon Sequestration Potential

Global estimates of potential amount of C that could be sequestered and 

conserved by forest management practices between 1995 and 2050 (from 

Brown et al 1996a) 

Latitudinal 

Belt

Country/ 

Region 

Practice C Sequestered/ 

Conserved (Gt) 

High Canada Forestation 0.68 

Nordic Europe 0.03 

FSU 1.76 

 Subtotal 2.4 

Mid Canada Forestation 0.43 

USA 3.07 

Europe 0.96 

China 1.70 

Asia 2.19 

South Africa 0.44 

South America 1.02 

Australia 0.31 

New Zealand 1.7 

 Subtotal 11.8 

USA Agroforestry 0.29 

Australia 0.36 

 Subtotal 0.7 

Low Tr. America Forestation 8.02 

Tr. Africa 0.90 

Tr. Asia 7.50 

 Subtotal 16.4 

Tr. America Agroforestry 1.66 

Tr. Africa 2.63 

Tr. Asia 2.03 

 Subtotal 6.3 

Tr. America Regeneration2 4.8-14.3 

Tr. Africa 3.0-6.7 

Tr. Asia 3.8-7.7 

 Subtotal 11.5-28.7 

Tr. America Slow 

Deforestation1

5.0-10.7 

Tr. Africa 2.5-4.4 

Tr. Asia 3.3-5.8 

 Subtotal 10.8-20.8 

Total 60-87 

1lncludes an additional 25% of aboveground C to account for belowgmund C in 

roots, litter, and soil (based on data in Brown et al.., 1996); range in values 

is based on the use of low and high estimates of biomass C density resulting 

from the uncertainty in these estimates. 

Humans change the size of carbon 

pools and alter the flow of carbon 

between them through forest 

management. Forests can become 

atmospheric carbon sinks during 

regrowth and can be managed to alter 

their role in the carbon cycle. Local 

forests management for carbon 

conservation and sequestration could 

mitigate emission of carbon CO2 by an 

amount equivalent to 11to 15 percent 

of fossil fuel emissions (Brown et al. 1996).

Estimates of unrealized global forest 

carbon conservation and sequestration 

range from 1 to 3 Pg C annually for as 

much as a century. Forest 

management practices to conserve 

and sequester carbon can be grouped 

into four major categories: 1) maintain 

existing carbon pools (e.g., slow 

deforestation) (Dixon et al. 1993), 2) 

expand existing carbon sinks and pools 

through forest management (Dixon 

1997), 3) create new sinks and pools by 

expanding tree and forest cover (Winjum

et al. 1992), and, 4) substitute renewable 

wood-based fuels and products for 

those derived from fossil fuels (Dixon et

al. 1994b). Management of forests as 

carbon reservoirs often complements 

other environmental goals including 

protection of biologic, water, and soil 

resources.
 6. Forest Management 

6-6

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Cairns, M. A., P. K. Haggerty, R. Alvarez, B. H. J. De Jong and I. Olmsted. 2000. Tropical Mexico’s recent landuse and land-cover change: A region’s contribution to the global carbon cycle. Ecological Applications 10:1426-

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Delany, M., S. Brown, A. Lugo, A. Torres-Lezama and N. B. Quintero. 1998. The quantity and turnover of dead 

wood in permanent forest plots in six life zones of Venezuela. Biotropica 30:2-11. 

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Dixon, R.K., S. Brown, R.A. Houghton, A.M. Solomon, M.C. Trexler and J. Wisniewski. 1994a. Carbon pools and 

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Dixon, R.K., J.K. Winjum, K.J. Andrasko, J.J. Lee and P.E. Schroeder. 1994b. Integrated land-use systems: 

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Dixon,R.K., J.B. Smith, S. Brown, O. Masera, L.J. Mata, I. Buksha. 1999. Simulations of forest system response 

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Gaston, G. G., P. L. Jackson, T. S. Vinson, T. P. Kolchugina, M. Botch and K. Kobak. 1994. Identification of 

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vegetation index images. International Journal of Remote Sensing 15:3199-3221. 

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Russian Far East using vegetation and land-cover regions identified by classification of GVI. Photogrammetric 

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Gaston, G. G., S. Brown, M. Lorenzini and K. D. Singh. 1998. State and change in carbon pools in the forest of 

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Harries, J. E., H. E. Brindley, P. J. Sagoo and R. J. Bantges. 2001. Increases in greenhouse forcing inferred from 

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Union. Global Biogeochemical Cycles 7:291-304. 

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the former Soviet Union. Canadian Journal of Forest Research 23:81-88. 

Kolchugina, T. P. and T. S. Vinson. 1993d. Climate warming and the carbon cycle in the permafrost zone of the 

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Kolchugina, T. P. and T. S. Vinson. 1993e. Carbon balance of the countinous permafrost zone of Russia. 

Climate Research 3:13-21. 

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Phillips, D. L., S. Brown, P. E. Schroeder and R. A. Birdsey. 2000. Toward error analysis of large-scale forest 

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Prentice, I. C., W. Cramer, S. P. Harrison, R. Leemans, R. A. Monserud, and A. M. Solomon. 1992. A global 

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Riley, R. H., D. L. Phillips, M. J. Schuft and M. C. Garcia. 1997. Resolution and error in measuring land-cover 

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balance. Forest Ecology and Management 75:87-99. 

Schroeder, P. E. and J. K. Winjum. 1995c. Brazil’s carbon budget for 1990. Interciencia 20:68-75. 

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Schroeder, P. E., S. Brown, J-M. Mo, R. Birdsey and C. Cieszewski. 1997. Biomass estimation for temperate 

broadleaved forest of the United States using inventory data. Forest Science 43:424-434. 

Schuft, M. J., J. R. Barker and M. A. Cairns. 1998. Spatial distribution of carbon stocks in southeast Mexican 

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Solomon, A. M., I. C. Prentice, R. Leemans and W. P. Cramer. 1993. The interaction of climate and land use in 

future terrestrial carbon storage and release. Water, Air, and Soil Pollution 70:595-614. 

Turner, D. P., G. J. Koerper, M. E. Harmon and J. J. Lee. 1995. A carbon budget for forests of the conterminous 

United States. Ecological Applications 5:421-436. 

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anthropogenic factors in national land-base carbon budgets. Ambio 26:220-226. 

Turner, D. P. J. K. Winjum, T. P. Kolchugina, T. S. Vinson, P. E. Schroeder, D. L. Phillips and M. A. Cairns. 

1998. Estimating the terrestrial C carbon pools of the former Soviet Union, the conterminous United States and 

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Vinson, T. S. and T. P. Kolchugina. 1993. Pools and fluxes of biogenic carbon in the former Soviet Union. Water, 

Air and Soil Pollution 70: 223-237. 

Winjum, J.K., R.K. Dixon and P.E. Schroeder. 1993a. Forest management and carbon storage: analysis of 12 

key forest nations. Water, Air and Soil Pollution 70:239-257. 

Winjum,J.K., R.A. Meganck, and R.K. Dixon. 1993b. Expanding global forest management: an easy-first 

approach. Journal of Forestry 91: 38-42. 

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atmospheric carbon dioxide. Forest Science 44:272-284. 
 7. Vegetation 

7-1

7. Vegetation Redistribution 

Statement of the Problem 

Global CO2 emissions may generate two classes of ecological impacts at the 

global scale. One involves the global carbon cycle and another involves the 

Earth’s biodiversity. Both are affected in large part by the potential redistribution 

of vegetation on the Earth. Currently, the many different kinds of unmanaged 

vegetation are adapted to today’s climate; as climate changes, each kind of 

vegetation must change as well, dying out in places the where climate becomes 

too stressful, and prospering where climate becomes salubrious. As the Earth 

warms from increasing atmospheric greenhouse gases, the redistribution of 

vegetation can induce the terrestrial biosphere to become either a source of 

additional CO2 (quickening the warming) or a sink for CO2 (reducing the 

warming). Which course it will take is not known. For example, a warmer earth 

should support more forests that contain high carbon densities, but the warmest 

places on earth today support only sparsely-vegetated deserts. As vegetation 

changes, so do the ecosystems on which populations of plants and animals 

depend for their existence. Hence, biodiversity will also be impacted by 

vegetation redistribution. The NHEERL research effort of the 1990’s focused on 

the carbon cycle implications of vegetation redistribution. 

Approach

Estimating future vegetation redistribution was based on developing predictive 

models. One group of models was designed to correlate the geography of 

climate with the geography of vegetation types. Then the future distribution of 

climate was used as a basis for redrawing the geography of the vegetation types 

(including agriculture). Once the new distributions of vegetation types were 

defined, the carbon they could store was calculated -- assuming that their current 

carbon densities would be supported in their future distributions.

A second group of models accounted mechanistically for processes which 

determine the growth, shifting density, and carbon uptake of vegetation during 

chronic climate change. These processes include the rapid dieback, 

reproduction, and slow regrowth of forests -- all processes which induce lags in 

vegetation response to rapid climate change. Although these processes could 

not be treated mechanistically in the correlative models described above, we did 

approximate the process effects in the correlative models, using values 

consistent with known biotic change rates. 

Main Conclusions 

The redistribution of global vegetation in response to climate and land use 

change during the next century is likely to generate a several-decade long pulse 

of carbon dioxide from the biosphere into the atmosphere. The result will 

enhance the buildup of greenhouse gases resulting from anthropogenic 

emissions. 
 7. Vegetation 

7-2

Critical to the modeling effort was developing precise data bases for climate and 

vegetation (e.g., EPA/NOAA 1992, 1993). Early work used life form classifications 

(e.g., Sedjo and Solomon 1988; King and Neilson 1992). Later work used known climate 

thresholds to assemble different plant functional types (PFTs) in each 1⁄2 X 1⁄2 

degree of latitude and longitude (Prentice et al. 1992). The presence of different 

combinations of PFTs defined biomes (temperate deciduous forest, cold 

grasslands, etc.). In addition to assessing vegetation redistribution impacts on 

the carbon cycle (e.g., Solomon, et al. 1993, 1996; Solomon 1996, 1997), we also 

assessed land use effects (Cramer and Solomon 1993, Leemans and Solomon 1993, 

Solomon and Leemans 1997), rapid tree dieback, differential availability of seeds, and 

slow regrowth of vegetation (Solomon and Kirilenko 1997, Kirilenko and Solomon 1998).

Primary conclusions were:

1) The capacity of the terrestrial biosphere to remove and store 

atmospheric carbon should be greater under a warmer global climate. 

2) The slow death and growth responses by vegetation would generate a 

pulse of carbon from vegetation 15-20% as great as that from 

anthropogenic emissions. 

3) Increasing intensity of agriculture in higher latitudes would permanently 

reduce the capacity of the earth to store carbon below its’ current storage 

capacity.

A second modeling approach used climate correlations (rather than climate 

thresholds) to define the climate space occupied by U.S. vegetation types (Neilson

et al. 1992), and then applied a physiology model which calculated the uptake of 

CO2 by photosynthesis and emission of CO2 by respiration in each vegetation 

type (Neilson 1993a, 1995). This approach used climate projections calculated by 

global climate models to define new vegetation distributions. Then, based on the 

new distributions of vegetation types, the projected balance of carbon uptake and 

emission from vegetation was determined. Expanded to a global scale (Neilson 

1993b, 1998, Neilson and Marks 1994), this approach could simulate the direct effects 

of increasing CO2 (a plant nutrient) on biomass storage. Applied to future climate 

conditions using several climate scenarios, this research suggested, but did not 

confirm, the potential presence of a multi-decade transient pulse of atmospheric 

carbon (Neilson 1993b, 1998). 

The modeling effort could not estimate the effects on carbon storage of slow 

vegetation responses to rapid climate changes. Instead, carbon storage was 

projected assuming that climate and vegetation distributions are stable. However, 

“there is no indication that a stable climate will appear in the foreseeable future. 

Indeed, the global change problem to be assessed involves rapidly changing 

climate, not stable climate” (Solomon et al. 1996). Forest gap models were used to 

estimate the time-related responses of vegetation to rapid climate change. These

models replicate the death, reproduction, growth, and maturity of trees, and the 

development of forest ecosystems (Solomon and Bartlein 1992, Solomon and West 1993, 
 7. Vegetation 

7-3

Bugmann and Solomon 1995, 2000). Although assessment exercises with these 

models (Solomon and Bartlein 1992, Bugmann et al. 2001) confirmed the potential for the 

long-term carbon pulse that was described by the static correlative models, the 

gap models have not yet been applied on the globally-comprehensive basis 

needed to thoroughly evaluate the carbon pulse phenomenon. 

Measured Global Vegetation Biomes 

Map of measured global vegetation biomes, including land dominated by 

agriculture, from various literature sources compiled and mapped by J. S. Olson, 

et al.., 1983 (from Solomon and Leemans, 1997, p. 141). Notice the effects of low 

temperature limits to plant growth shown by the latitudinal bands of boreal 

vegetation in the polar regions, and the dominance of low moisture limits to plant 

growth (1) in temperate and regions, shown by the longitudinal bands of 

agricultural and natural vegetation, and (2) in tropical regions shown by the 

latitudinal presence of hot deserts along the subtropical convergence zone where 

sinking air blocks frontal passage and thus precipitation. The finer-scale 

complexity of the global biome distribution patterns is derived from the local and 

regional variations in soils, topography, and land use. 
 7. Vegetation 

7-4

Modeled Global Vegetation Biomes 

Map of modeled global vegetation biomes, including land suitable for agriculture. 

This map is defined entirely by known cardinal climate thresholds applied through 

the BIOME model, with no reference to the actual vegetation present. Modeled 

biomes are identified in the legend above (from Solomon and Leemans 1997, p. 141).

Comparing this map with the previous one, notice that the model maintains the 

biome distribution patterns with regard to low temperature and low moisture 

dominance in polar, temperate and tropical regions, as well as many of the finerscale biome distribution patterns derived from the local and regional variations in 

soils, topography, and land use. The ability to use climate data as proxy 

vegetation to reproduce the known patterns of biome distribution is critical to 

subsequent efforts aimed at projecting maps of future vegetation and carbon 

storage under climate warming scenarios. 
 7. Vegetation 

7-5

Future Global Vegetation Biomes 

Map of future global vegetation biomes, including land suitable for agriculture, under a 

future climate at the time atmospheric CO2 concentrations double. The climate changes 

used to drive the BIOME model are among the mildest simulated by general circulation 

models of the atmosphere, that is, the global climate model (ECHAM-1 by the Max Plank 

Institute, Hamburg; see Greco et al. 1994) is only moderately sensitive to greenhouse gas 

concentrations. 

Note the great increase in land suitable for agriculture toward polar areas, a feature 

which follows from expected climate changes: all general circulation models of the 

atmosphere (global climate models) project a greater increase in warming at the poles 

than at the equator, a greater warming in winter than in summer, and a greater warming 

at night than in daytime. As a result, the projected climate in high latitudes is expected to 

increase greatly in days with temperatures constantly above freezing, and in the annual 

growing season length. Indeed, polar growing seasons have already increased 12 to 18 

days since 1980, as measured by satellites. 

Note also that, compared with the previous map, this map shows areas of natural 

vegetation in temperate areas dominated by dryland biomes, especially thorn shrub 

vegetation, and boreal forests severely reduced as potential agriculture covers low 

latitude growing areas, with little space to grow toward the higher latitudes. 
 7. Vegetation 

7-6

The CO2 Pulse

Total carbon stored by the terrestrial biosphere in separate biomes and in total in 

Pg (petagrams, 1015g). Carbon storage is simulated for 500 years into the future, 

with a warming scenario from ECHAM-1, by the Max Plank Institute in Hamburg 

(Greco et al. 1994), from year 0 to that from a doubling of atmospheric CO2

concentrations at year 100. Minus values represent release of carbon from the 

terrestrial biosphere to the atmosphere, positive values represent storage of 

carbon into the terrestrial biosphere from the atmosphere (from an unpublished 

version of the MOVE model (Kirilenko and Solomon 1998) which includes stochastic 

rather than constant rates of tree mortality and growth). 

The total biomass of the terrestrial biosphere declines markedly for the first 100+ 

years of this simulation, defining the multi-decadal pulse of carbon to the 

atmosphere discussed in the text. Note that only grassland vegetation initially 

increases in biomass, as it replaces the woody vegetation types which dieback 

during early warming and which only gradually regrow to out compete the 

herbaceous vegetation. 
 7. Vegetation 

7-7

References Cited 

Bugmann, H.K.M. and A.M. Solomon. 1995. The use of a European forest model in North 

America: A study of ecosystem response to climate gradients. J. Biogeography 22:477-484. 

Bugmann, H.K.M. and A.M. Solomon. 2000. Explaining forest composition and biomass across 

multiple biogeographical regions. Ecological Applications 10:95-114. 

Bugmann, H. K. M., S. D. Wullschleger, D. T. Price, K. Ogle, D. F. Clark, and A. M. Solomon. 

2001. Comparing the performance of forest gap models in North America. Climatic Change 

51:349-388. 

Cramer, W. P. and A. M. Solomon. 1993. Climatic classification and future distribution of global 

agricultural land. Climate Research 3:97-110. 

EPA/NOAA. 1992. Global Change Database: Global Ecosystems Database, CD Disk A., Nat. 

Geophys. Data Center, Boulder CO. 

EPA/NOAA. 1993. Global Change Database: Global Ecosystems Database, CD Disk B., Nat. 

Geophys. Data Center, Boulder CO. 

Greco, S., R. H. Moss, D. Viner, and R. Jenne, 1994. Climate Scenarios and Socioeconomic 

Projections for IPCC WG II Assessment. Material assembled for Lead Authors by IPCC WG II 

TSU. Washington D.C. 

King, G. A. and R. P. Neilson, 1992. The transient response of vegetation to climate change: a 

potential source of CO2 to the atmosphere. Water, Air, and Soil Pollution 64:365-383. 

Kirilenko, A. P. and A. M. Solomon. 1998. Modeling dynamic vegetation response to rapid 

climate change using bioclimatic classification. Climatic Change 38:15-49. 

Leemans, R. and A. M. Solomon. 1993. The potential change in yield and distribution of the 

earth’s crops under a warmed climate. Climate Research 3:79-96. 

Neilson, R. P., 1993a. Transient ecotone response to climatic change: some conceptual and 

modeling approaches. Ecological Applications 3:385-395. 

Neilson, R. P. 1993b. Vegetation redistribution: A possible biosphere source of CO2 during 

climatic change. Air Water and Soil Pollution 70:659-673. 

Neilson, Ronald P. 1995. A model for predicting continental-scale vegetation distribution and 

water balance. Ecological Applications 5:362-385. 

Neilson, R. P., 1998. Simulated changes in vegetation distribution under global warming. Annex 

C, pp. 439-456 IN Watson, R. T., M. C. Zinyowera, R. H. Moss and D. J. Dokken, eds., The 

Regional Impacts of Climate Change. Cambridge Univ. Press, NY. 

Neilson, R. P., G. A. King and G. Koerper, 1992. Toward a rule-based biome model. Landscape 

Ecology 7:27-43. 

Neilson, R. P. and D. Marks. 1994. A global perspective of regional vegetation and hydrological 

sensitivities from climatic change. J. Veg. Sci. 5:715-730. 

Olson, J. S., J. A. Watts, and L. J. Allison. 1983. Carbon in Live Vegetation of Major World 

Ecosystems. ORNL/TM-5862, Oak Ridge National Laboratory, Oak Ridge TN. 

Prentice, I. C., W. Cramer, S. P. Harrison, R. Leemans, R. A. Monserud, and A. M. Solomon. 

1992. A global biome model based on plant physiology and dominance, soil properties and 

climate. Journal of Biogeography 19:117-134. 

Sedjo, R. A. and A. M. Solomon, 1989. Climate and forests. pp. 105-119 IN Rosenberg, N. J., 

W. E. Easterling, P. R. Crosson, and J. Darmstadter, Eds., Greenhouse Warming: Abatement 

and Adaptation. Resources for the Future, Washington, D.C. 
 7. Vegetation 

7-8

Solomon, A.M. 1996. Potential responses of global forest growing stocks to changing climate, 

land use and wood consumption. Commonw. For. Rev. 75:65-75. 

Solomon, A.M. 1997. Natural migration rates of trees: Global terrestrial carbon cycle 

implications. Pp. 455-468 IN Huntley, B., W.P. Cramer, A.V. Morgan, H.C. Prentice and J.R.M. 

Allen. Past and future rapid environmental changes: The spatial and evolutionary responses of 

terrestrial biota. Springer-Verlag, NY 

Solomon, A. M. and P. J. Bartlein. 1992. Past and future climate change: Response by mixed 

deciduous-coniferous forest ecosystems in northern Michigan. Canadian Journal of Forest 

Research 22:1727-1738. 

Solomon, A. M. and A. P. Kirilenko. 1997. Climate change and terrestrial biomass: What if trees 

do not migrate? Global Ecol. and Biogeogr. Let. 6:139-148. 

Solomon, A.M. and R. Leemans. 1997. Boreal forest carbon stocks and wood supply: Past, 

present and future responses to changing climate, agriculture and species availability. Journal of 

Agricultural and Forest Meteorology 84:137-151. 

Solomon, A. M. and D. C. West. 1993. Evaluation of stand growth models for predicting 

afforestation success during climatic warming at the northern limit of forests. p. 167-188 IN R. 

Wheelon, ed. Forest Development in Cold Regions. Proceedings, NATO Advanced Research 

Workshop. Plenum Publ. Corp., NY. 

Solomon, A. M., I. C. Prentice, R. Leemans and W. P. Cramer. 1993. The interaction of climate 

and land use in future terrestrial carbon storage and release. Water, Air, and Soil Pollution 

70:595-614. 

Solomon, A.M., N.H. Ravindranath, R.B. Stewart, S. Nilsson and M. Weber. 1996. Wood 

production under changing climate and land use. Chapter 15, pp. 487-510. IN Climate Change 

1995: Impacts, Adaptations and Mitigation of Climate Change. Working Group II, Second 

Assessment Report, Intergovernmental Panel on Climate Change (IPCC), Cambridge University 

Press, Cambridge UK. 
 8. CO2 & Temperature Effects 

 8-1 

8. Effects of Elevated Atmospheric Carbon Dioxide 

Concentration and Temperature on Forests

Statement of the Problem 

Concentrations of carbon dioxide (CO2) and other trace gases have been 

increasing in the atmosphere due to human activity. By the 1980s, accumulating 

evidence suggested that increasing levels of these gases could produce higher 

global temperatures and changes in precipitation patterns. More information on 

how the biosphere controls atmospheric CO2 was needed to understand the 

Earth’s carbon cycle. Foremost, an understanding of source-sink relations 

between the atmosphere and the various components of the biosphere was 

needed. Consequently, research was undertaken to delineate the relations 

between atmospheric CO2 concentrations, changes in global climate drivers, and 

responses of the soil-plant-atmosphere continuum (EPA 1993). The science 

questions governing the research were: 

 What are the effects of elevated CO2 and climate change on the growth 

and productivity of forest trees?

 Will elevated CO2 and climate change alter the sequestration/exchange of 

carbon in the soil-plant-atmosphere continuum?

 What is the magnitude of these elevated CO2 and climate change impacts 

and will they be widely distributed? 

Approach

Research was conducted to investigate ecosystem responses to elevated 

atmospheric CO2 and associated increases in atmospheric temperature over 

several years. NHEERL scientists built a state-of-the-science, sun-lit, controlledenvironment chamber facility in which climatic and edaphic factors could be 

controlled and/or monitored during the multi-season exposure period (Tingey et al.

1996). A tree forest ecosystem was reconstructed in the chambers using Douglasfir seedlings supported by one of its widely represented soil types (Rygiewicz et al.

2000). Climatic treatments were applied based on the natural, temporal variations 

in ambient climatic conditions found at the facility site, thus subjecting the 

reconstructed ecosystem to a realistic climatic profile (Tingey et al. 1996).

Experimental treatments included increased levels of atmospheric CO2 and

elevated temperature (Olszyk and Tingey 1996).

Main Conclusions 

Generally, the effects of increasing the atmospheric CO2 concentration on the 

reconstructed Douglas-fir-soil ecosystem appear to have been limited by low 

nitrogen availability in the soil – a condition common in forest soils of the Pacific 
 8. CO2 & Temperature Effects 

 8-2 

Northwest. This result was supported by the Maine Biological Laboratory’s 

General Ecosystem Model (GEM), used after completing the climate change 

experiment, to project longer-term and broader-scale consequences of climate 

change in Pacific Northwest Douglas-fir forests. Application of GEM to various 

sites in the western Cascades suggests that soil nitrogen is a primary constraint 

on changes in ecosystem carbon storage (McKane et al. 1997). For the nitrogenpoor montane site where the soil for the chamber experiment was obtained, the 

model predicts that total ecosystem carbon storage will increase by less than 

10% during the next 100 years in response to projected increases in atmospheric 

CO2 and temperature. In contrast, GEM predicts that carbon storage will increase 

by over 25% during the same period for a nitrogen-rich site in the western 

Cascades foothills.

Even though elevated atmospheric CO2 increased photosynthetic rates (Lewis et

al. 1999, Lewis et al. 2001), and while chlorophyll and carotenoid concentrations in 

the needles decreased under elevated CO2 (Ormrod et al. 1999), the additional 

carbon acquired was not allocated to produce seedlings of greater biomass 

(Olszyk et al. 2003). Rather, it appears that the carbon was allocated to soil 

organisms which convert stored, unavailable forms of nutrients into available 

forms (Lin et al. 1999, Lin et al. 2001). These available forms can then be acquired by 

diverse and stable mycorrhizal fungi resident on the ephemeral, nutrientabsorbing fine roots (Rygiewicz et al. 2000, Hobbie et al. 2001).

While total carbon storage in the soil increased during the experiment, due to 

seedling growth and decomposition processes in the soil and litter layer, the 

amount of total stored carbon was not different among the climatic treatments.

However, stable isotopic data suggest that a variable allocation of carbon into 

soil organic matter (SOM) of different qualities may have occurred, thus altering 

the long-term storage potential of the soil for carbon. In a related project on 

ponderosa pine, the effect of nitrogen to alter the seedlings’ responses to 

atmospheric CO2 concentration was clearly evident (Johnson et al. 2000), and 

reinforced the results found in the chamber study done on Douglas-fir. Taken

collectively, these results indicate the overriding influence of the low nitrogen 

found in Pacific Northwest forests.

Projecting to larger scales, the responses of forest ecosystems to elevated CO2

may be highly variable temporally and globally. In particular, the responses 

appear highly dependent on the quantity and availability of nutrient resources, 

and the capacity of nutrient acquisition processes relative to the increased 

amount of carbon available in the atmosphere. As the Douglas-fir study was run 

for only four growing seasons, it is uncertain if the observed responses to 

elevated CO2 were transient, and eventually would change as ecosystem 

compartments continued to adjust to the altered ratios of available carbon to 

available nutrients.

Elevated temperature had a greater, and negative, impact on the seedlings than 
 8. CO2 & Temperature Effects 

 8-3 

did the elevated CO2 treatments. Elevated temperature directly and negatively 

affected the development and morphology of the seedlings. Seedlings grown 

under elevated temperatures had greater numbers of aborted and malformed 

buds, and abnormal needle primordial tissue compared with seedlings in the 

ambient temperature treatments (Apple et al. 1998, Apple et al. 2000). In addition, the 

seedlings grown under the higher temperatures were shorter and more “bushlike” in morphology, thus hindering their ability to gain height (Olszyk et al. 1998a, 

Olszyk et al. 1998b). Elevated temperature delayed needle hardening in the fall, 

slowed dehardening in the spring and reduced the maximum hardiness; 

rendering the trees less resistant to low temperatures (Guak et al. 1998).

Climate change will affect forested ecosystems differentially. While elevated 

temperature will most likely affect the growth of plant species directly, the effects 

on ecosystem structure and functioning may be more subtle to discern, but no 

less significant. Elevated temperature could lead to the replacement of sensitive 

species by more heat tolerant species. In the Pacific Northwest, the predominant 

lumber species, Douglas-fir, could experience abnormal growth patterns. But as 

Douglas-fir is a genetically diverse species, adaptation, either natural or 

managed, is likely. However, the cost to timber production is unknown.

Ecosystem effects of increasing levels of atmospheric CO2 will depend on the 

nutrient status of specific forests. Increased forest production will occur where 

soils contain adequate nitrogen. In areas where nitrogen is limiting, elevated CO2

levels will not increase the growth of trees -- even though photosynthesis may 

increase. Without sufficient nitrogen, the trees cannot use the additional CO2 for 

growth. The additional carbon is used by soil organisms and respired to the 

atmosphere (Rygiewicz and Andersen 1994). In addition to contributing to CO2

buildup in the atmosphere such changes in the soil foodweb, which controls 

nutrient availability for plants, could have long-term effects on ecosystem 

functioning.
 8. CO2 & Temperature Effects 

 8-4 

Experimental Approach to Study Seedling and Ecosystem Processes 

A 2 X 2 factorial treatment design was 

used: [ambient CO2 and ambient + 

200 ppm CO2 (179 ppm achieved), 

ambient temperature, and ambient + 4 

qC (3.8 qC achieved)]. Each of the 

four climatic conditions was replicated 

three times, which resulted in a total of 

12 chambers being used for the 

experiment

SPAR (Soil-Plant Atmosphere Research) chambers (1 

x 2 m footprint) were used to simulate natural 

seasonal and diurnal changes in atmospheric [CO2],

air and soil temperatures, vapor pressure deficit 

(VPD), and soil moisture. Fourteen, two-year-old 

Douglas-fir seedlings were planted in each chamber in 

a natural, widely-represented, Cascade Mountains, 

high-elevation (1220 m) soil. The seedlings originated 

from open-pollinated seeds harvested from 5 lowelevation (300 to 460 m) seed zones in the Cascade 

and Coastal Mountain Ranges near Corvallis. Total N 

in the soil was < 0.1% (w/w), and NO3



 and NH4

+

 in 

soil solution were below detection limits (0.04 and 

0.10 mg l-1, respectively). Six cm of forest floor were 

placed on top of the soil. Climatic treatments were 

imposed for 4.5 growing seasons. 

The project was 

highly-integrated

across the aboveand below-ground 

portions of the 

reconstructed

ecosystem, and 

organized around 

eight tasks focused 

on individual seedling 

and ecosystem state 

variables and 

processes.

Ecosystem budgets 

for carbon, water and 

nutrients, therefore, 

could be calculated.

Collecting samples 

and taking 

measurements were 

closely linked across 

above- and belowground phenological 

events. An analysis 

was conducted as the 

project was 

TASK 3

System Nutrients 

• Plant Nutrients 

• Soil Nutrients

TASK 4

System Water 

• Plant Water 

 • Soil Water

TASK 7 

Soil Biology 

TASK 2

Shoot Growth and 

Phenology

TASK 1

Shoot Carbon and 

Water Fluxes

TASK 6

Root Growth and 

Phenology

TASK 5

Litter Layer

TASK 8

Soil Organic 

Matter

An Integrated Sampling Approach Was Designed to Track Carbon, Water and 

Nutrients through the Reconstructed Ecosystem
 8. CO2 & Temperature Effects 

 8-5 

Elevated CO2 Increased Photosynthesis but not Growth 

Greater instantaneous photosynthetic rates (left panel) were observed under elevated CO2

and temperature in the spring and winter. Some acclimation of photosynthetic rates to 

elevated CO2 was evident as the exposure to climatic treatments progressed (data not 

shown). Even so, by the third and fourth growing seasons, elevated CO2 increased net 

photosynthesis by an average of 21% across the two temperature treatments. The additional 

carbon acquired under elevated CO2 was not released through increased “dark” respiration 

(respiration not associated with the process of photosynthesis).

The increased carbon uptake under elevated CO2 and elevated temperature did not increase 

the final size of the seedlings. Moreover, elevated CO2 had no other significant effects on 

whole seedling or individual seedling component biomass, % biomass allocation, or leaf area 

(not all data are shown) Other sinks for the additional carbon acquired are the continual 

production, death and decomposition of the ephemeral, nutrient-absorbing fine roots; the 

various organisms of the soil food web (both their biomass and respiration); and the soil 

organic matter (SOM). PPFD is Photosynthetic Photon Flux Density, expressed as Pmol

photons m-2 s-1. (Lewis et al. 1999).

Under elevated temperature, compared with the ambient condition, shifts occurred only in the 

amounts of carbon allocated to needles and buds (Olszyk et al. 2003). Allocation of carbon 

related to the production, death and decomposition of the ephemeral, nutrient-absorbing, fine 

roots can not be determined from the final biomass of the seedlings as these roots were 

produced and decayed during the exposure period. The retrospective analysis of the 

allocation of carbon to produce these roots throughout the exposure is ongoing.

0

100

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500

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300

400

500

A m b. Tem p ., A m b. C O 2

A m b. Tem p., + 20 0 ppm

A m b . C O 2 , + 4°C

+ 4°C , + 20 0 ppm

M a xim um A vera g e C lou d y

P P F D C o n dition s

January

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A p ril

Ju ly
 8. CO2 & Temperature Effects 

 8-6 

Elevated Temperature Affected Needle and Bud Growth 

Douglas-fir buds (left panel) 

showed several signs of 

damage due to elevated 

temperature: (A) Dissected 

normal bud from the ambient 

climatic treatment; (B) 

Dissected abnormal bud from 

elevated temperature 

treatment with bud-scale-like 

needle primordial (arrow), and 

(C) convoluted bud scales 

(arrows); (D) Exterior of normal 

bud from ambient conditions; 

(E) Exterior of rosetted bud 

from elevated temperature 

treatment; (F) Normal buds 

from ambient conditions; (G) to 

(I) all are elevated temperature 

treatment showing - (G) 

rosetted abnormal buds, (H) a 

shoot with two small buds and 

reduced needles, and (I) a bud 

with reduced needles and 

elongated stalk originating from 

tree truck. Scale = 1 mm.

Source: Apple et al. 1998.

Under elevated temperature, a greater percentage of leader and branch buds opened early in the 

growing season (lower left panel). However, by the end of bud burst, a smaller total percentage of 

buds had opened under the higher temperatures. Needles produced under elevated temperature 

conditions were less able to withstand the colder temperature of winter (lower right panel).

Indicated is the freezing temperatures at which 50% of the needles displayed visible signs of 

tissue damage (Lt50 qC). Source: Guak et al. 1998.
 8. CO2 & Temperature Effects 

 8-7 

Seedling Size Was Negatively Affected by Elevated Temperature 

Elevated CO2 and Temperature Altered Fine Root Distribution but not 

Production and Turnover 

Legend: ACAT = ambient CO2, ambient temp; ECAT = elevated CO2, ambient temp.; ACET = ambient CO2; elevated temp.; 

ECET = elevated CO2, elevated temp. 

Elevated temperature resulted in shorter Douglas-fir seedlings, beginning during the second 

growing season. The left graph indicates the increase in height over time for seedlings grown 

under the ambient CO2 and temperature levels (ACAT). The other three treatments are 

shown as changes relative to the ACAT treatment. For example the ACET Change = ACETACAT. Elevated CO2 by itself had no effect on plant height (ECET Change). In contrast, 

neither elevated temperature nor elevated CO2 affected stem diameters. The right graph 

indicates annual increases in stem diameter for the ACAT seedlings and the lack of any 

relative change in stem diameter for seedlings grown under any of the other elevated 

temperature or elevated CO2treatments. Modified from: Olszyk et al. 1998a.

-5

0

5

10

15

20

25

30

Jun 1, 93 Jun 1, 94 Jun 1, 95 Jun 1, 96 Jun 1, 97 STEM DIAMETER (mm)

ACAT

ACET Change

ECAT Change

ECET Change

 Stem Diameter

-400

-200

0

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600

800

1000

1200

1400

Jun 1, 93 Jun 1, 94 Jun 1, 95 Jun 1, 96 Jun 1, 97

HEIGHT (mm)

ACAT

ACET Change

ECAT Change

ECET Change

Height Height Stem Diameter 

Fine roots play a key in the acquisition of 

water and nutrients needed to sustain 

growth. The growth of fine roots is 

coordinated with shoot growth so that the 

plant has sufficient resources.

The effects of elevated CO2 and 

temperature on fine production and 

turnover were determined over a 4-year 

period. Elevated CO2 and temperature 

altered fine root distribution; there were 

more fine roots deeper in the soil. There 

were no CO2 effects on annual fine root 

production or turnover. During the first 2 

years, elevated temperature (at ambient 

CO2) increased fine root production, but 

there were no differences in the latter part 

of the experiment. Limited N availability 

likely minimized CO2 response 

belowground as it did aboveground. 
 8. CO2 & Temperature Effects 

 8-8 

The Rhizosphere Responded to Elevated Atmospheric CO2

Percent increase or decrease in the total flux of CO2 released from the 

soil (A), and from its component sources (B, C, D) relative to respective 

CO2 fluxes in the ambient climatic treatment,.

The amounts of carbon 

forming the total soil CO2

efflux were mathematically 

partitioned into their source 

compartments within the soil.

Since the atmospheric carbon 

delivered to the seedlings was 

depleted in 13C, it served as a 

tracer to analyze soil carbon 

dynamics. The dominant 

source of the soil CO2 efflux in 

the soil-Douglas-fir ecosystem 

was the decomposition of the 

litter, followed by rhizosphere 

respiration (= root respiration 

+ respiration of rootassociated soil biota), and 

then from the oxidation of soil 

organic matter (SOM) (data 

not shown). Elevated CO2

stimulated total soil respiration 

(Graph A).

Rhizosphere respiration was stimulated by elevated CO2 and less so by temperature (Graph B).

In contrast, litter decomposition was stimulated mostly by temperature (Graph C). The SOM 

response was highly variable (Graph D): from a decrease in oxidation under elevated CO2, to an 

increased oxidation under elevated temperature; note that elevated CO2 in the double elevated 

treatment countered the oxidation found in the elevated-temperature-only treatment. Differences 

in responses between 1994 and 1995 are attributed to the physical disruption done to the soil 

when it was transported from the Cascade Mountains to the chambers. The likelihood that the 

increased rhizosphere respiration was due to a transient, increased standing crop of the 

ephemeral, fine roots is still being analyzed. 
 8. CO2 & Temperature Effects 

 8-9 

Carbon Delivered to Soil Foodweb to Explore Ecosystem for Nutrients 

1oM

C C T

NUMBERS OF MYCORRHIZAL ROOT TIPS PER ML SOIL

0

1

2

3

4

5

6

7

8

9

10

S94 F94 S95 F95 S96 F96 S97

ACAT ECAT ACET ECET

1o

M

C C T

NUMBERS OF MYCORRHIZAL ROOT TIPS PER ML SOIL

0

1

2

3

4

5

6

7

8

9

10

S94 F94 S95 F95 S96 F96 S97

ACAT ECAT ACET ECET

1oM, 2oMT, 6oM

T T

NUMBERS OF DIFFERENT MORPHOTYPES

0

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4

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S94 F94 S95 F95 S96 F96 S97

ACAT ECAT ACET ECET

1o

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T T

NUMBERS OF DIFFERENT MORPHOTYPES

0

2

4

6

8

10

12

14

16

S94 F94 S95 F95 S96 F96 S97

ACAT ECAT ACET ECET

Legend: ACAT = ambient CO2, ambient temp; ECAT = elevated CO2, ambient temp.; ACET = ambient CO2; elevated temp.; 

ECET = elevated CO2, elevated temp. 

The increased soil CO2 efflux attributed to rhizosphere respiration (= root respiration + 

respiration of root-associated soil biota) (previous sidebar) likely is due to increased standing 

crop of the ephemeral, fine roots and their decomposition, and/or the standing biomass, activity 

and decomposition of soil fungi. Coniferous forest ecosystems rely on free-living and symbiotic 

fungi (attached to the fine roots) to mobilize nutrients stored in the forest floor and soil, and to 

transport the mobilized nutrients to, and into, the plants to balance the carbon acquired 

aboveground. All low-nutrient terrestrial ecosystems increase their dependence on these fungi 

compared to higher nutrient conditions. The Douglas-fir seedlings formed high concentrations 

of mycorrhizal root tips in the low-nutrient soil (left graph), and exhibited a high degree of root 

colonization (nearly 100% of the root tips that developed were colonized, data not shown).

The fungal community formed on the roots was highly-diverse and its structure was resistant to 

the climatic treatments (right graph). However, the most extensive portion of the symbiotic 

fungal biomass is the portion living at distance from the roots, and which explores the soil for 

nutrients, delivering them to the tree. Through the use of direct counting procedures and 

measuring the amounts of stable isotopes delivered into the soil foodweb, we anticipate 

identifying to which trophic structure(s) in the soil ecosystem the additional carbon acquired 

under elevated CO2 was allocated, and then subsequently deposited as soil organic matter 

(SOM).
 8. CO2 & Temperature Effects 

 8-10 

Soil Organic Matter May Be Depository for the Acquired Carbon 

ACAT ACET ECAT ECET

0

5

10

15

20

25

Mineral S

oil C

(kg C m2)

Treatment

The amount of carbon stored in soil 

as organic matter (SOM) increased 

during the exposure, predictably as 

one might expect because of plant 

growth. However, none of the climatic 

treatments affected the total amount 

of carbon stored as SOM (graph at 

left). Soil 13C data suggest that SOM 

levels actually may have increased 

under elevated CO2. As the total 

amount of SOM may not have been 

altered by the climatic treatments, the 

isotopic data suggest that certain 

quality fractions of SOM may have 

been differentially affected by the 

treatments. Thus the large total 

amount of SOM may be masking the 

more subtle responses in the 

individual quality fractions. Ultimately, 

the quality of SOM that is formed 

determines long-term storage of 

carbon in, and productivity of, forested 

ecosystems. SOM from the 

experiment has been separated into 

its quality fractions, and stable 

isotopic analyses are underway to 

address this aspect of the fate of the 

additionally-acquired carbon. 
 8. CO2 & Temperature Effects 

 8-11 

Soil Nitrogen Availability Constrained Carbon Storage in Response to 

Elevated CO2 and Temperature 

We used the General Ecosystem Model (GEM), a process-based model of terrestrial 

ecosystem biogeochemistry, to project longer-term and broader-scale consequences of 

increases in atmospheric CO2 and temperature in Pacific Northwest Douglas-fir forests. 

GEM was used to predict and analyze the effects of projected changes in CO2, temperature 

& soil moisture on ecosystem carbon storage at the Foothills and Montane mature forest 

sites. The model was run with and without the projected changes in CO2, temperature & 

soil moisture. All simulations started in 1995 with post-harvest conditions (90% of tree 

biomass removed). 

Results illustrate that elevated CO2 increases plant growth and net ecosystem C storage 

only when there are sufficient supplies of soil nitrogen as at the Foothills Site. A sensitivity 

analysis showed that CO2 was much more important than temperature in increasing 

ecosystem C storage, and that elevated CO2 increased storage of C in plants more than in 

soils.
 8. CO2 & Temperature Effects 

 8-12 

References Cited 

Apple, M.E., M.S. Lucash, D.M. Olszyk and D.T. Tingey. 1998. Morphogensis of Douglas-fir buds 

is altered at elevated temperature but not at elevated CO2. Environ. Exp. Bot. 40:159-172. 

Apple, M.E., D.M. Olszyk, D.P. Ormrod, J. Lewis, D. Southworth and D.T. Tingey. 2000. 

Morphology and stomatal function of Douglas fir needles exposed to climate change: Elevated 

CO2 and temperature. Int. J. Plant Sci. 161:127-132. 

EPA. 1993. Research Plan: Effects of elevated CO2 and climate change on forest trees.

Environmental Research Laboratory – Corvallis. 

Guak, S., D.M. Olszyk, L.H. Fuchigami and D.T. Tingey. 1998. Effects of elevated CO2 and 

temperature on cold hardiness and spring bud burst and growth in Douglas-fir (Pseudotsuga

menziesii). Tree Physiol. 18:671-679. 

Hobbie, E.A., D.M. Olszyk, P.T. Rygiewicz, D.T. Tingey and M.G. Johnson. 2001. Foliar nitrogen 

concentrations and natural abundance of 15N suggest nitrogen allocation patterns of Douglas-fir 

and mycorrhizal fungi during development in elevated carbon dioxide concentration and 

temperature. Tree Physiol. 21:1113-1122. 

Johnson, D.W., R.B. Thomas, K.L. Griffin, D.T. Tissue, J.T. Ball, B.R. Strain and R.F. Walker. 

1998. Effects of carbon dioxide and nitrogen on growth and nitrogen uptake in ponderosa and 

loblolly pine. J. Environ. Qual. 27:414-425. 

Johnson, M.G., D.L. Phillips, D.T. Tingey and M.J. Storm. 2000. Effects of elevated CO2, Nfertilization, and season on survival of ponderosa pine fine roots. Can. J. For. Res. 30:220-228. 

Lewis, J.D., D.M. Olszyk and D.T. Tingey. 1999. Seasonal patterns of photosynthetic light 

response in Douglas-fir seedlings subjected to elevated atmospheric CO2 and temperature. Tree 

Physiol. 19:243-252. 

Lewis, J.D., M. Lucash, D. Olszyk and D.T. Tingey. 2001. Seasonal patterns of photosynthesis in 

Douglas fir seedlings during the third and fourth year of exposure to elevated CO2 and 

temperature. Plant, Cell Environ. 24:539-548. 

Lin, G., J.R. Ehleringer, P.T. Rygiewicz, M.G. Johnson and D.T. Tingey. 1999. Elevated CO2 and 

temperature impacts on different components of soil CO2 efflux in Douglas-fir terracosms. Global

Change Biology 5:157-168.

Lin, G., P.T. Rygiewicz, J.R. Ehleringer, M.G. Johnson and D.T. Tingey. 2001. Time-dependent 

responses of soil CO2 efflux to elevated atmospheric [CO2] and temperature treatments in 

experimental forest mesocosms. Plant and Soil. 229:259-270. 

McKane, R.B., D. Tingey, P.A. Beedlow, P.T. Rygiewicz, M.G. Johnson, J.D. Lewis. 1997. Spatial

and temporal scaling of CO2 and temperature effects on Pacific Northwest forest ecosystems.

Amer. Assoc. Adv. Science Pacific Div. Abstracts 16(1):56. 

Olszyk, D.M., M.G. Johnson, D. Tingey, P.T. Rygiewicz, C. Wise, E. VanEss, A. Bensen and M. 

Storm. 2003. Whole seed biomass allocation, leaf area, and tissue chemistry for Douglas-fir 

exposed to elevated CO2 and temperature for 4 years.
 8. CO2 & Temperature Effects 

 8-13 

Olszyk, D.M and D.T. Tingey. 1996. Environmental modification and shoot growth in a closed 

ecosystem to evaluate long-term responses of tree seedlings to stress. Acta. Hort. 440:129-134. 

Olszyk, D., C. Wise, E. VanEss and D. Tingey. 1998a. Elevated temperature but not elevated 

CO2 affects long-term patterns of stem diameter and height of Douglas-fir seedlings. Can. J. For. 

Res. 28:1046-1054. 

Olszyk, D., C. Wise, E. VanEss, M. Apple and D. Tingey. 1998b. Phenology and growth of 

shoots, needles, and buds of Douglas-fir seedlings with elevated CO2 and (or) temperature. Can.

J. Bot. 76:1991-2001. 

Ormrod, D.P., V.M. Lesser, D.M. Olszyk and D.T. Tingey. 1999. Elevated temperature and 

carbon dioxide affect chlorophylls and carotenoids in Douglas-fir seedlings. Int. J. Plant Sci. 

160:529-534.

Rygiewicz, P.T. and C.P. Andersen. 1994. Mycorrhizae alter quality and quantity of carbon 

allocated belowground. Nature 369:58-60. 

Rygiewicz, P.T., K.J. Martin and A.R. Tuininga. 2000. Morphotype community structure of 

ectomycorrhizas on Douglas-fir (Pseudotsuga menziesii Mirb. Franco) seedlings grown under 

elevated atmospheric CO2 and temperature. Oecologia 124:299-308. 

Tingey, D.T., B.D. McVeety, R. Waschmann, M.G. Johnson, D.L. Phillips, P.T. Rygiewicz and 

D.M. Olszyk. 1996. A versatile sun-lit controlled-environment facility for studying plant and soil 

processes. J. Environ. Quality 25:614-625. 
 9. O3 & CO2 

9-1

9. Interactive Effects of O3 and CO2 on the Ponderosa 

Pine Plant/Litter/Soil System

Statement of the Problem 

Carbon dioxide is required by plants to grow and is a major greenhouse gas 

contributing to global climate change. Tropospheric ozone (O3) is the major 

phytotoxic air pollutant in the U.S. which adversely impacts crops and forests. 

While much is known about the effects of O3 or CO2 alone, there has been little 

research on the potential interactive effects of these gases on terrestrial 

ecosystems, even though they co-occur. Most of the research has focused on 

the response of individual species rather than at the ecosystem level. There is a 

growing interest in O3 x CO2 combinations fueled by concerns regarding potential 

effects on vegetation from increases in regional O3 levels. These increases 

occur concurrently with an increased global CO2 concentration.

Approach

Therefore, we carried out an in-depth study to address three general hypotheses 

regarding the effects of O3 and CO2 on C, N, and H2O cycling through 

ecosystems (Olszyk et al. 1997): 

1) Elevated O3 decreases C, N and H2O cycling rates.

2) Elevated CO2 increases C, N, and decreases H2O cycling rates.

3) Elevated CO2 eliminates negative effects of O3 on C and N cycling rates 

and has an additive negative effect on H2O cycling rates. 

Our hypotheses were tested using experimental data and simulation models to 

evaluate C, N, and H2O cycles (Olszyk et al. 2001). A reconstructed ponderosa pine 

soil/tree seedling ecosystem was used, as this is system widespread in the 

western U.S., and is known to be affected by both increasing CO2 and O3. The 

experiment was conducted in sunlit, controlled environment chamber facility (see 

sidebar in previous section) to examine above- and belowground responses.

These chambers allowed for precise monitoring and control of climatic and 

edaphic—soil—conditions and for calculation of whole system CO2 and H2O

balances (Tingey et al. 1996, Olszyk and Tingey 1996). The experimental design was a 

2 x 2 factorial with 2 levels of CO2, 2 levels of O3 and three replicate chambers 

per treatment. Carbon dioxide was an elevated level of +280 ppm above ambient 

reflecting an increase in greenhouse gases vs. the ambient concentration.

Ozone was at a high level representative of regional oxidant pollution vs. a low 

level which is representative of a more pristine area. Research tasks measured: 

i) system CO2, O3 and H2O gas exchange; ii) plant phenology, allometry and 

carbon allocation; iii) litter and soil/rhizosphere microbiological community 

structure and function; iv) litter and soil chemical and physical properties; and v) 

system C, N and H2O budgets, pools and fluxes. The modeling research used 
 9. O3 & CO2 

9-2

the Marine Biological Laboratory’s General Ecosystem Model (GEM) (Rastetter et

al. 1991) to evaluate for system scale C and N cycling, and the process-based 

whole-tree growth model TREGRO (Tingey et al. 2001), to study the potential 

impact of increased O3 and CO2 on photosynthesis, respiration, carbon 

accumulation, and carbon allocation. 

Main Conclusions 

Elevated CO2 increased the photosynthetic C uptake by the seedlings beginning 

early in the study (Olszyk et al. 2001) and persisting to the end (Olszyk et al. 2002)

(sidebar). The increase in photosynthesis was associated with an increase in 

water use efficiency (the ratio of CO2 taken up to H2O loss by transpiration). The

increased C uptake appeared to stimulate plant growth as elevated CO2

increased stem diameters (sidebar). This CO2 induced-increase in stem diameter 

was especially noticeable early during the study. Over time, the stimulation in 

stem diameter leveled off, possibly due to growth-limiting factors such as a low 

soil-N fertility level. Elevated CO2 also affected N cycling in the system as 

indicated by lower leaf N concentrations with elevated CO2 (Olszyk et al. 2001).

In contrast to CO2, O3 alone had little effect on the plants, and those responses 

that did occur were affected by the variable O3 concentrations among the three 

years. There were suggestions of significant CO2 x O3 interactions for some 

parameters where the response to the combined pollutants was different from 

that expected based on the responses to the individual pollutants. For example, 

in late August 2000 photosynthesis decreased with high O3 for seedlings at 

ambient CO2 but increased with high O3 for seedlings at elevated CO2. There 

also was a significant CO2 x O3 interaction on plant growth early in the study, as 

stem diameters were greater with elevated CO2 and low O3 compared with 

elevated CO2 and high O3 (Olszyk et al. 2001).

When the data have been completely evaluated from this study, the results will 

provide unique information on the responses of ecosystem functions due to the 

interactions of CO2 and O3, as well as responses to the individual gases.
 9. O3 & CO2 

9-3

Effects of Elevated CO2 and O3 on Net Photosynthesis in Ponderosa pine 

Elevated CO2 increased photosynthetic rates over much of the experiment as shown by 

the higher values for seedlings grown under elevated CO2 at either low O3 (ECLO) or 

elevated CO2 and high O3 (ECHO) vs. seedlings grown under ambient CO2 and either 

low O3 (ACLO) or high O3 (ACHO. The “*” and “o” symbols in the “C” row at the top of 

the figure indicate those periods during which there was a significant CO2 effect on 

photosynthesis based on analysis of variance at the p<0.05 and p<0.10 levels, 

respectively. High O3 had only a minor effect on photosynthesis, with significant O3

alone effects for only three periods as shown by the symbols in the “O” row at the top, 

and significant CO2 x O3 interactions for only 4 periods in the “CxO” row at the top. The 

symbols are averages "SE (bars) for 3 replicate chambers except for 2 replicate 

chambers for the treatment. The dashed lines at base of figure are approximate dates 

of O3 exposures. Source: Olszyk et al. 2002. 
 9. O3 & CO2 

9-4

Effects of CO2 & O3 on Ponderosa Pine Seedlings 

Stem diameter was measured as a key indicator of the overall growth of Ponderosa pine 

seedlings. Rapid growth periods, as shown by an increase in stem diameter, occurred 

during spring and summer of 1998, 1999, and 2000. Over three years, seedlings growing 

with elevated CO2 and either with low (ECLO) or high (ECHO) O3, had larger stem 

diameters than seedlings grown under ambient CO2 and low (ACLO) or high (ACHO) O3

(top figure). Beginning early in the study, compared to plants growing under control 

conditions (ACLO), there was a greater increase in stem diameter for ECLO compared 

with ECHO seedlings, indicating that high O3 inhibited some of the effect of elevated CO2

(lower figure). Source, Olszyk et al. 2001and unpublished data.

0

5

10

15

20

25

30

35

Apr 1, 98 Oct 1, 98 Apr 1, 99 Oct 1, 99 Apr 1, 2000 Oct 1, 2000 STEM DIAMETER (mm)

DATE

ACLO

ECEO

ACEO 

ECLO

A. STEM DIAMETER

0

1

2

3

4

5

Apr 1, 98 Oct 1, 98 Apr 1, 99 Oct 1, 99 Apr 1, 2000 Oct 1, 2000 STEM DIAMETER (mm)

DATE

ECEO

ACEO 

ECLO B. DIFFERENCE VS. ACLO
 9. O3 & CO2 

9-5

References Cited 

Barnes, J.D. and Wellburn, A.R. 1998. Air Pollutant Combinations. In Responses of Plant 

Metabolism to Air Pollution and Global Change (ed. L.J. De Kok, & I. Stulen). pp. 147-164. 

Backhuys Publishers, Leiden, The Netherlands. 

Olszyk, D.M., Tingey,D.T., Wise, C., and Davis, E. 2002. CO2 and O3 alter photosynthesis and 

water vapor exchange for Pinus ponderosa needles. Submitted to Phyton. 

Olszyk, D.M., Tingey,D.T., Watrud, L., Seidler, R. and Andersen, C. 2000. Interactive Effects of 

O3 and CO2: Implications for Terrestrial Ecosystems. In Trace Gas Emissions and Plants. (ed. 

S.N. Singh). pp. 97-136. Kluwer Academic Publishers, Dordrecht, Germany. 

Olszyk, D.M., Johnson , M. G., Phillips, D.L., Seidler, R.. , Tingey,D.T and Watrud, L.S. 2001. Interactive effects of O3 and CO2 on a ponderosa pine plant/litter/soil mesocosm. Environ. Pollut. 

115, 447-462. 

Olszyk, D.M., Tingey,D.T., Watrud, L.,Seidler, R. and Andersen, C. 2000. Interactive Effects of 

O3 and CO2: Implications for Terrestrial Ecosystems. In Trace Gas Emissions and Plants. (ed. 

S.N. Singh). pp. 97-136. Kluwer Academic Publishers, Dordrecht, Germany. 

Olszyk, D.M., Tingey,D.T., Johnson , M. G.,, Seidler, R., Watrud, L., Weber, J., Phillips, D., & 

Andersen, C., Cairns, M., Hogsett, W., Brown, S.and McKane, R. 1997. Research Plan: 

Interactive Effects of O3 and CO2 on the Ponderosa Pine Plant/Litter/Soil System. US EPA, 

NHEERL-COR-876R. 

Rastetter E.B., Ryan M.G., Shaver G.R., Melillo J.M., Nadelhoffer K.J., Hobbie J.E., Aber J.D. 

1991. A general biogeochemical model describing the responses of the C and N cycles in 

terrestrial ecosystems to changes in CO2, climate and N deposition. Tree Physiology 9:101-126. 

Rudorff, B.F.T., Mulchi, C.L. & Lee, E.H. 2000. Plant Responses to Elevated CO2 and 

Interactions with O3. In Trace Gas Emissions and Plants. (ed. S.N. Singh). pp. 155-179. Kluwer 

Academic Publishers, Dordrecht, Germany. 

Tingey, D. T., J. A. Laurence, J. A. Weber, J. Greene, W. E. Hogsett, S. Brown, and E. H. Lee. 

2001. Elevated CO2 and temperature alter the response of Pinus ponderosa to ozone: a 

simulation analysis. Ecological Applications 11:1412-1424. 
 10. Fine Roots 

10-1

10. Effects of Elevated CO2 and Nitrogen Fertilization on Fine 

Root Growth in seedling Pinus ponderosa

Statement of the Problem 

In forest trees, less than 20% of the total biomass is belowground while more 

than 50% of the carbon acquired annually by plants may be allocated 

belowground (George & Marschner 1996). With rising atmospheric carbon dioxide 

(CO2) the potential for effects of elevated CO2 on forest trees is large. A number 

of studies have evaluated the effects of elevated CO2 on plants (e.g., Ceulemans & 

Mousseau 1994; Curtis & Wang 1998, Norby 1994, Rogers et al. 1999, Taylor et al. 1994). Their 

general conclusion is that elevated CO2 leads to increased photosynthesis and 

increased plant biomass, including increased root biomass. Will this increase in 

biomass lead to a greater proportion of the carbon being allocated belowground 

and potentially sequestered there? 

Three science questions guided the study on ponderosa pine (Pinus ponderosa 

Dougl.):

x Will the size of the root systems of ponderosa pine seedlings increase to 

facilitate resource (water or nutrients) acquisition in response to elevated 

CO2?

x Will ponderosa pine root systems be affected by the availability of nitrogen? 

x Will the dynamics of ponderosa pine fine root production and mortality be 

affected by elevated CO2 and/or nitrogen treatments? 

Approach

Plants were exposed to CO2 and nitrogen (N) fertilization in open-top fieldexposure chambers located at the US Forest Service Institute of Forest Genetics 

near Placerville, CA. The experimental design was a replicated 3x3 factorial with 

3 CO2 levels (ambient air [~350 μmol mol-1]; ambient air + 175 μmol mol-1 and 

ambient air + 350 μmol mol-1) and 3 levels of nitrogen (N) addition (0, 100 and 

200 kg ha-1); however, the 100 kg ha-1 N treatment at ambient + 175 μmol mol-1

CO2 was omitted from the experimental design because of financial limitations. 

There were 3 replicates of each CO2 and N treatment. The nitrogen was 

broadcast applied each March as ammonium sulfate. Soils were kept moist and 

relatively constant over the course of the study. Root images were collected from 

three minirhizotron tubes in each chamber every 2 months on S-VHS tape using 

a minirhizotron camera. The root images were analyzed using software that 

allows the user to measure the length and diameter of all roots and annotate 

mycorrhizae and fungal hyphae occurrence.
 10. Fine Roots 

10-2

Main Conclusions 

Fine roots explore soil for water and nutrients to support plant growth. Plants

produce more or fewer fine roots as their resource needs change. A given 

species may produce more fine roots in nutrient poor soils than in nutrient rich 

soils. In arid environments plants typically produce more fine roots than in wetter 

environments. In this experiment the ponderosa pine trees – normally a dry forest 

species -- were well watered in order to examine the effects of elevated 

atmospheric carbon dioxide (CO2) and nitrogen (N) on fine root dynamics. 

Elevated CO2 and N treatments both increased plant height, stem diameter and 

leaf area (Tingey et al. 1996, 1997). Elevated CO2 resulted in significantly higher root 

biomass in the first 3 years and higher fine root turnover in the last 2 years. No

significant N effects were noted for annual root biomass production, or turnover.

Fine root nutrient cycling rates varied from 74 to 362 g m-2 yr-1 for C and 0.9 to 

4.6 g m-2 yr-1 for N (Phillips et al, unpublished results).

Fine-root production and life span were strongly influenced by season and soil 

temperature (Johnson et al. 2000). Fine roots declined in importance with time and 

were replaced with mycorrhizae which continued to increase with time. This

temporal pattern of root and shoot growth was not altered by providing additional 

CO2 or N fertilization (Tingey et al. 1996). 

Both CO2 and N affected the fine roots, but the effects were independent and 

displayed contrasting effects. In this study, elevated CO2 increased above and 

below ground plant growth because nitrogen was not limiting even in the 

unfertilized plots. Although elevated CO2 increased fine root growth, it did not 

change the relationship between fine roots and needles indicating that elevated 

CO2 did not increase the proportion of carbon allocated belowground (Tingey et al. 

1996). Elevated CO2 increased root lifespan but N decreased it (Johnson et al. 2000, 

Tingey et al. 1997). Initially, elevated N reduced the fine root area relative to the 

needle area, but this ratio was not altered by elevated CO2 treatments. 

Soil exploration by the roots increased with elevated CO2, but was unaffected 

when nitrogen was abundant as in the fertilized plots. Fine root production was 

increased by elevated CO2 whereas N fertilization had no effect on fine root 

production (Tingey et al. 1996, 1997). This suggests that as the limiting resource, 

nitrogen in this case, increases the plants do not need to produce as many fine 

roots to explore more soil to acquire enough of the resource. In contrast, 

increased CO2 resulted in more images containing roots suggesting more soil 

exploration by roots. 

Elevated CO2 increased mycorrhizal and fungal occurrence earlier than N 

fertilization, and elevated CO2 increased C flux into mycorrhizae (Rygiewicz et al. 

1997, Tingey et al. 1997). Higher levels of N resulted in increased mycorrhizal activity 

relative to fine root production. The amount of mycorrhizae relative to the amount 

of fine roots did not change with increased CO2 – they both increased in the 

same proportion. However, N fertilization resulted in more mycorrhizae relative to 
 10. Fine Roots 

10-3

roots. Under elevated CO2 fine roots increased providing additional infection 

sites, and, consequently, mycorrhizal occurrence increased proportionally. In

contrast, nitrogen fertilization increased root branching without increasing the 

amount of fine roots, thereby providing more site for mycorrhizal infection. 

In summary, limiting resources determined the response of ponderosa pine root 

systems to changes in atmospheric CO2 and soil nitrogen. As plants needed 

more nitrogen their roots explored more soil area to acquire this resource.

Elevated CO2 allowed the trees to take up more carbon for growth both above 

and below ground, but the amount allocated to the root system decreased as soil 

nitrogen become more available. Again, in this study water was not limiting and 

consequently did not affect the root system. With time mycorrhizae became more 

important to the root systems and effectively replaced the fine roots. Their

abundance increased proportionally with fine roots under increased levels of 

CO2, but increased in greater proportion than fine roots with higher levels of soil 

nitrogen.
 10. Fine Roots 

10-4

Effects of Elevated CO2 on Root Production & Turnover 

A 4-year study was conducted to determine the effects of atmospheric 

CO2 and N-fertilization on Pinus ponderosa fine root (<2 mm) responses. 

Seedlings were grown in open-top chambers at 3 CO2 levels (ambient, 

ambient+175 ppm, ambient+350 ppm) and 3 N-fertilization levels (0, 10, 

20 gm-2yr-1). Length and width of individual roots were measured from 

minirhizotron video images collected bimonthly over 4 years. Biomass 

estimates were made by cross-calibrating with soil core root biomass. 

Neither CO2 nor N-fertilization treatments affected root production and 

turnover seasonal patterns. Elevated CO2 resulted in significantly higher 

biomass (gm-2) in the first 3 years and higher turnover (gm-2yr-1) in the 

last 2 years. No significant N effects were noted for annual root biomass, 

production, or turnover. Fine root nutrient cycling rates varied from 74-

362 gm-2yr-1 for C and 0.9-4.6 gm-2yr-1 for N. Higher turnover in 

elevated CO2 was due to higher biomass rather than shorter life-span.

Fine roots lived longer in elevated CO2, and turnover relative to biomass 

was generally < that in ambient CO2, emphasizing the importance of root 

turnover definitions.
 10. Fine Roots 

10-5

Effects of CO2 and Nitrogen Fertilization of Fine Root Life Span 

Ponderosa pine seedlings were grown at varying atmospheric CO2

concentrations paired with varying concentrations of exogenously-applied 

nitrogen. Increasing CO2 levels increased the lifespan of the ephemeral, 

nutrient-absorbing fine roots. Whereas, increasing the amount of applied 

nitrogen decreased root lifespan. These results illustrate: (1) the enhanced 

role of the ephemeral, nutrient-absorbing fine roots under elevated CO2 to 

acquire nitrogen needed to balance the increased available CO2, and (2) 

how the role of these roots was reduced as the available nitrogen increased. 

Source: Johnson et al. 2000. 
 10. Fine Roots 

10-6

References Cited 

Ceulemans R, Mousseau M. 1994. Effects of elevated atmospheric CO2 on woody plants. 

New Phytologist 127: 425-446. 

Curtis PS, Wang X. 1998. A meta-analysis of elevated CO2 effects on woody plant mass, 

form and physiology. Oecologia 113: 299-313. 

George E, Marschner H. 1996. Nutrient and water uptake by roots of forest trees. Zeitschrift 

für Pflanzenernährung und Bodenkulture 159: 11-21 

Johnson, M.J., D.L. Phillips, D. T. Tingey and M.J Storm. 2000. Effects of elevated CO2, Nfertilization and season on survival of ponderosa pine fine roots. Canadian Journal of Forest 

Research 30:220-228. 

Norby RJ. 1994. Issues and perspectives for investigating root responses to elevated 

atmospheric carbon dioxide. Plant and Soil 165: 9-20. 

Rygiewicz, P.T., M.G. Johnson, M.J. Storm, D.T. Tingey and L. Ganio. 1997. Lifetime and 

temporal occurrence of ectomycorrhizae on ponderosa pine (Pinus ponderosa Laws.) 

seedlings grown under varied atmospheric CO2 and nitrogen levels. Plant and Soil 189:275-

287.

Tingey, D.T., D.L. Phillips, M.G. Johnson, M.J. Storm and J.T. Ball. 1997. Effects of elevated 

CO2 and N-fertilization on fine root dynamics and fungal growth in seedling Pinus ponderosa. 

Environmental Experimental Botany 37:73-83. 

Tingey, D.T., M.G. Johnson, D.L. Phillips, D.W. Johnson and J.T. Ball. 1996 Effects of 

elevated CO2 and nitrogen on the synchrony of shoot and root growth in ponderosa pine. 

Tree Physiology 16:905-914.
 11. FACE Experiment 

11-1

11. Free-Air CO2 Enrichment (FACE) Experiment 

Statement of the Problem 

A number of effects of elevated atmospheric CO2 concentrations on plants have been 

demonstrated in greenhouse and controlled environment chamber studies. However,

such studies have inherent limitations that reduce their value in predicting responses to 

rising CO2: (1) physical facilities constrain the plant size and complexity of system which 

can be used, (2) the experimental conditions in these chambers which may be 

unrealistic, and (3) the experiments are short-term and may be unable to detect either 

delayed or transient effects. Greater understanding of direct effects of elevated CO2

requires experiments on intact natural ecosystems, composed of multiple interacting 

species of a variety of sizes and ages, and continued over an extended period of time 

(multiple years). 

Approach

Technology has been developed for Free-Air CO2 Enrichment (FACE) facilities which 

allow CO2 exposure experiments to be performed on large (~500 m2

) plots in intact 

ecosystems. US EPA scientists are collaborating with scientists in the US Department 

of Energy and the University of Nevada at the Nevada Test Site in the Mojave Desert --

the only desert ecosystem FACE facility. EPA scientists are conducting long-term 

monitoring of belowground responses to elevated CO2.

Main Conclusions 

To date, University of Nevada scientists found that elevated CO2 increases 

photosynthetic rates and aboveground biomass growth -- at least in years where 

sufficient soil moisture is available (Hamerlynck et al. 2000, Smith et al. 2000, Huxman and Smith 

2001). The desert plants generally showed decreases in stomatal conductance (loss of 

water through leaf pores) and higher water use efficiency when grown in elevated CO2

(Nowak et al. 2001, Pataki et al. 2000). However, soil moisture was no higher in elevated CO2

plots. Presumably this was because the increased water use efficiency per unit 

biomass was balanced by higher aboveground biomass.

Belowground, EPA researchers have found no differences in the total length, 

production, or turnover of roots, indicating that the same size root systems were able to 

sustain larger aboveground biomass of plants because of the higher water use 

efficiency (Phillips et al. 2002). These results are important in helping us understand the 

likely responses of large tracts of arid lands under global changes of atmospheric CO2

content.
 11. FACE Experiment 

11-2

Nevada Desert FACE Facility 

FACE system maintains elevated CO2 over 25 m diameter plots 

The Free-Air CO2 Enrichment (FACE) technology developed by the Brookhaven National 

Laboratory enables CO2 exposure experiments to be performed on intact ecosystems. The

Mojave Desert ecosystem, shown here, is one of eight such state-of-the-art facilities that 

have been constructed in various ecosystems across United States. Atmospheric CO2

concentrations and wind speed and direction are continuously monitored. In elevated CO2

plots, computer controlled valves on the vertical pipes open on the upwind side of the plot, 

releasing CO2 to maintain a CO2 concentration 200 ppm higher than the ambient CO2 of 

~360 ppm. Transparent plastic tubes inserted to a depth of 1 m in the soil (shown here with 

white insulating caps on top) are used with specialized video cameras to monitor the 

growth and mortality of roots in the experimental plots, to determine the belowground 

effects of elevated CO2.
 11. FACE Experiment 

11-3

Elevated CO2 did not affect fine root standing crop, production, or turnover 

On a monthly basis, specialized video cameras are inserted in transparent tubes installed 

in the soil to make photographic images of roots. These images are digitized and the 

production, growth, and mortality of each root can be tracked over time. These data provide 

detailed dynamics of root populations and how they are affected by CO2 exposure as well 

as season, soil moisture, and other conditions. Elevated CO2 did not significantly affect the 

standing crop (total length), production, or turnover of roots over a very wet year (1998) and 

a dry year (1999) (Phillips et al. 2002). This indicates that the same size root systems were 

able to sustain the larger aboveground biomass of plants in elevated CO2 treatments 

because of higher water use efficiency. Total root length varied from year to year 

depending on soil moisture availability.
 11. FACE Experiment 

11-4

References Cited 

Hamerlynck, E.P., T.E. Huxman, R.S. Nowak, S. Redar, M.E. Loik, D.N. Jordan, S.F. Zitzer, J.S. 

Coleman, J.R. Seemann, S.D. Smith. 2000. Photosynthetic responses of Larrea tridentata to a stepincrease in atmospheric CO2 at the Nevada Desert FACE Facility. Journal of Arid Environments 44: 425-

436.

Huxman, T.E., and S.D. Smith. 2001. Photosynthesis in an invasive grass and native forb at elevated 

CO2 during an El Nino year in the Mojave Desert. Oecologia 128: 193-201. 

Nowak, R.S., L.A. DeFalco, C.S. Wilcox, D.N. Jordan, J.S. Coleman, J.R. Seemann, and S.D. Smith. 

2001. Leaf conductance decreased under free-air CO2 enrichment (FACE) for three desert perennials in 

the Nevada desert. New Phytologist 150: 449-458. 

Pataki, D.E., T.E. Huxman, D.N. Jordan, S.F. Zitzer, J.S. Coleman, S.D. Smith, R.S. Nowak, and J.R. 

Seemann. 2000. Water use of two Mojave Desert shrubs under elevated CO2. Global Change Biology 6: 

889-897.

Phillips, D.L., D.T. Tingey, M.G. Johnson, C.E. Catricala, and T.L. Hoyman. 2002. Effects of elevated 

CO2 on fine root biomass, production, and turnover in a Mojave Desert ecosystem: a FACE study.

Manuscript in preparation. 

Smith, S.D., T.E Huxman, S.F. Zitzer, T.N. Charlet, D.C. Housman, J.S. Coleman, L.K. Fenstermaker, 

J.R. Seemann, and R.S. Nowak. 2000. Elevated CO2 increases productivity and invasive species 

success in an arid ecosystem. Nature 408: 79-82.
 12. Coral Health 

12-1

12. Effects of Global Change on Coral Reef Ecosystems 

Statement of the Problem

Corals and coral reefs of the Caribbean and throughout the world are deteriorating at an 

accelerated rate. Several stressors are believed to contribute to this decline, including 

global changes in atmospheric gases and land use patterns (Fig. 1). In particular, 

warmer water temperatures and elevated exposure to ultraviolet radiation has been 

linked to coral bleaching, which occurs when corals lose symbiotic algae. Bleached 

corals may recover, contract infectious diseases, or become overgrown with a layer of 

macroalgae. Loss of corals has significant socioeconomic repercussions; in Florida, 

Hawaii and most U.S. territories in the Caribbean and Pacific Ocean, coral reefs provide 

valued services in the form of fisheries, recreation, tourism and coastal protection from 

storm erosion. Furthermore, with hundreds of thousands of interdependent species, 

coral reefs are one of the largest global reservoirs of biodiversity and a potential wealth 

of undiscovered natural products. The abundant and diverse reef species are the 

substance of a flourishing and extensive marine ecosystem. 

Geological records show that coral community structure has been stable over the last 

220,000 years (Chadwick-Furman 1996, Aronson and Precht 1997). Yet, during the last 30 

years, coral bleaching and disease have escalated worldwide (Hughes 1994, Hughes and 

Tanner 2000, Gardner et al. 2003, Hughes et al. 2003, Pandolfi et al. 2003). In 1998, the largest 

bleaching event on record affected about 16% of the world’s coral reefs. It has been 

estimated that 27% of the world’s reefs were lost in the last three decades and that 60% 

will be eliminated by 2030 (Wilkinson 2000). Many believe that ecological extinction for 

coral reefs could occur in this century if current trends persist (Gardner et al. 2003, Hughes 

et al. 2003).

Although the situation is alarming, relatively little is known about the environmental 

factors and interactive stresses that lead to coral bleaching. The term ‘bleaching’ refers 

to the loss of color when corals lose their symbiotic algae (Fig. 2), which are 

photosynthetic dinoflagellates often called zooxanthellae. Usually bleaching signifies 

environmental stress leading to a breakdown of the coral-algae symbiosis. In fact, 

bleaching at the local scale has been associated with several stressful environmental 

conditions (Goreau 1964, Glynn 1984) including high and low temperatures, high and low 

solar radiation, reduced salinity, and coral exposure to air, ultraviolet radiation, 

sediments, toxic chemicals, and high levels of bacteria (Mitchell and Chet 1975, HoeghGuldberg and Smith 1989, Glynn 1996, Brown 1997a).

Large-scale bleaching, however, is most strongly associated with elevated sea water 

temperature (Williams et al. 1987, Glynn and de Weerdt 1991, Milliman 1993, Brown 1997b, HoeghGuldberg 1999, Barber et al. 2001, Fitt et al. 2001). Many coral species may be susceptible to 

thermal bleaching because they live near the upper limit of their temperature tolerance 
 12. Coral Health 

12-2

(Scavia et al. 2002). Prior to 1980, bleaching was infrequent and events were confined to 

local scales (Goreau 1964, Goreau and Hayes 1994, Aronson et al. 2000). Since then, however, 

the extent, severity and frequency of bleaching events have increased dramatically.

The link between coral bleaching and global climate change is compelling. Massive 

episodes of coral bleaching have accompanied the last several El Niño phases of the 

Southern Oscillation (ENSO). These events have occurred world-wide and irrespective 

of other local anthropogenic stressors (Hoegh-Guldberg 1999, Wilkinson et al. 1999). Greater 

frequency, intensity, and spatial extent of bleaching have been documented since the 

1982-1983 ENSO, including an exceptionally strong 1997-1998 ENSO that exhibited 

record sea-surface temperatures and coincided with the most geographically 

widespread and severe bleaching in history (Glynn 1984, Wilkinson 1998). Up to 95% of the 

living coral reefs from the central Indian Ocean and its margins were bleached, and 

bleaching occurred along the margins of the Caribbean Sea, the Indian Ocean and the 

Pacific Ocean. Although ENSO phases are measured in the Pacific Ocean, climate and 

weather patterns are altered worldwide. In the Caribbean, ENSO phases generate 

higher sea water temperatures and calm, stratified water conditions (doldrums) that 

allow increased penetration of solar radiation. These conditions are tailor-made for 

bleaching because of the interactive effects of high temperature and the high ultraviolet 

light that reaches coral reefs.

Corals rely on photosynthetic energy derived from algal symbionts found within the 

polyps, or colonial units of the coral. Since photosynthesis requires solar radiation, most 

corals are confined to shallow coastal waters penetrated by sunlight. Coral reefs are 

located in tropical and sub-tropical oceans that are exposed to the most intense solar 

radiation on Earth (Madronich et al. 1998). This distribution, however, places corals at risk 

from exposure to ultraviolet light (UV), particularly the damaging UV-B wavelengths 

(Shick et al. 1996). Increased penetration of UV-B to the earth’s surface has been 

attributed to a decline in UV-absorbing ozone in the stratosphere. Although 

stratospheric ozone depletion in the tropics is not as great as at the poles, there is 

concern that any increase in the high levels already experienced could affect coral 

health. The most variable aspect of coral exposure to UV-B is its penetration through 

the water above reefs. Many local variables, such as water quality and weather, can 

influence attenuation of UV-B with depth. For example, dissolved organic matter 

absorbs UV-B and reduces its penetration, whereas hot, windless conditions create 

thermal stratification of the water column that increases UV-B penetration.

Approach

To fulfill EPA’s assessment role in the US Global Change Research Program, NHEERL 

research is directed toward reducing assessment uncertainties and developing 

assessment tools. Specifically, the NHEERL program uses field and laboratory studies 

to determine which coral species, reefs and geographic regions are most valuable (i.e., 

providing ecosystem services), most at risk, and most responsive to management 
 12. Coral Health 

12-3

alternatives. Research is focused in two principal areas: Development and application of 

methods to assess and compare coral reef condition, and characterization of stressorresponse patterns to determine thresholds for global climate stressors. The research 

approach emphasizes the fact that changes in the environment affect both partners, the 

corals and the algal symbionts, and that effects on either can alter the symbiotic 

relationship. The primary stressors under investigation are elevated temperature and 

UV-B. Other environmental stressors, such as nutrients, contaminants and sediments, 

are expected to exacerbate bleaching at local scales. 

Methods to Assess and Compare Coral Reef Condition

The Florida Keys coral reef tract provides a substantive opportunity to investigate the 

causes and effects of global change on coral reefs. Not only is it a relatively large tract 

(44 km2 ) with reefs in both remote areas and near human population centers, but it has 

experienced major declines in coral health and coral cover during the last thirty years. A 

Coral Reef Monitoring Project has been supported by US EPA Region 4 since 1996 to 

annually determine the total percent of live coral coverage at 160 permanent stations in 

the Florida Keys National Marine Sanctuary (FKNMS). After 5 years (1996-2000), a 

38% decline in live coral coverage has been documented (Fig. 3; Jaap et al. 2000, Wheaton 

et al. 2001, Porter et al. 2002). Much of this loss has been attributed to bleaching events and 

the emergence of new diseases (Antonius 1981, 1985, 1988, Dustan and Halas 1987, Santavy and 

Peters 1997, Richardson et al. 1998, Santavy et al. 1999, 2001, 2004). Of particular concern has 

been the dramatic decline of fast-growing, reef-building acroporid corals (Patterson et al. 

2002), including elkhorn coral (Acropora palmata) and staghorn coral (A. cervicornis).

A complementary survey has been conducted by NHEERL scientists to document 

bleaching and disease across the entire reef tract. Performed in collaboration with 

NOAA (FKNMS), the NHEERL survey includes 60 stations, selected by probability, 

ranging from the Upper Keys to the Dry Tortugas (Fig. 4). Each colony in a radial belt 

transect (113 m2

) is examined, counted and identified (Fig. 5); fifteen coral species and 

eleven disease syndromes are documented. Results show that up to 28% of the coral 

populations near Key West are affected by disease (Santavy et al. 2001). Corals in this 

area do not appear to be recovering and, in the case of elkhorn coral, there has been 

nearly complete destruction (Patterson et al. 2002). NHEERL collaborative research with 

the University of Georgia has shown that elkhorn corals are susceptible to white pox 

disease caused by Serratia marcescens, a common soil and enteric microorganism 

(Patterson et al. 2002). Yet, across the Florida Keys reef tract the prevalence of disease is 

considerably less (Santavy et al. 2004). In August, 2002, the greatest prevalence 

(percentage of diseased corals at any site) was 13%, but this occurred in only 2.2% of 

the sampling area (Fig. 6). Seventy-nine percent of the area had less than 6% disease 

prevalence.

The annual field surveys were initiated and performed in response to the emergence of 

several diseases that were unknown prior to 1970. With continued declines in South 
 12. Coral Health 

12-4

Florida corals, the NHEERL research effort has expanded to characterize coral 

condition. New measurements are being introduced to evaluate the cumulative 

consequences of bleaching and disease, as well as other stressors, on coral individuals 

and populations. Reef-to-reef comparisons of disease prevalence are sometimes 

confounded by different taxonomic composition (e.g., some sites do not have 

susceptible host species); the new condition measures are unrelated to taxonomic 

composition and allow direct comparisons across reefs and geographic areas. 

Three condition endpoints have been added to the disease survey that estimate total 

coral surface area, the percent of living coral, and the living coral surface area of each 

coral encountered in the transect. Total surface area (TSA) serves as a surrogate for 

reef structural complexity and the habitat value associated with high complexity. It also 

supplies a record of the cumulative, or historical, capacity of the habitat to grow and 

sustain corals. Percent living coral (%LC) can be used to examine potential associations 

of adverse effects from diseases or other stressors. Living surface area (LSA) is an 

indicator of the more recent capacity of the environment to support corals; LSA also 

represents the amount of coral with potential to grow and reproduce.

A pilot project was conducted in 2003 to investigate the feasibility of acquiring these 

data in combination with bleaching and disease surveys. Five stations at two study 

areas, Key West and Dry Tortugas, were surveyed. The Key West area has high human 

density relative to the remote Dry Tortugas. Comparison of data demonstrated wide 

differences in species composition, abundance, TSA and %LC (Table 1), but the actual 

living coral (LSA) was nearly identical at both study areas. One promising tool is the 

comparison of %LC among species (Fig. 7), which will indicate whether one species 

has lost more tissue than other species in the same area, and whether the same 

species has lost more tissue in one study area over another. It is anticipated that these 

measures of coral condition will ultimately be integrated into a condition index for 

comparison of reefs and geographic areas over time. Until then, the bleaching, disease 

and condition information provided by the field surveys is directly useful in the 

management of the Florida Keys National Marine Sanctuary and the Dry Tortugas 

National Park. 

Although condition indicators can provide useful insight to status and trend of coral 

populations, it is imperative for future management that declining condition is ultimately 

linked to a cause. Condition indicators can be used to compare reefs with putative coral 

stressors. To this end, NHEERL scientists are investigating chemical contaminants in 

coral reef areas, and collaborate both with Florida International University to measure 

nutrients and chlorophyll and with NERL scientists to measure temperature and UV-B at 

coral reefs. Any associations of these factors with declining coral condition can be 

investigated in the laboratory, as described below. 

Characterization of Stressor-Response Patterns.

Relating coral decline to global change stressors requires knowledge of the thresholds 
 12. Coral Health 

12-5

at which changing environmental conditions create adverse effects. NHEERL has 

developed unique laboratory facilities and expertise to expand this knowledge. Two 

‘solar simulator’ systems have been constructed to expose corals and algal symbionts 

to varying levels of both photosynthetically-active radiation and UV-B. In addition, 

NHEERL scientists retain in culture over 15 reef-building coral species and 28 algal 

symbiont (Symbiodinium spp.) isolates for controlled laboratory experiments (Figs. 8 

and 9). Research using algal symbionts is particularly promising because the interaction 

of temperature and UV-B very likely affect the photosynthetic processes of symbionts. 

Also, results of experiments have potential worldwide application because corals have 

established symbioses with relatively few algal symbiont groups (clades). 

Early studies in the solar simulators validated that different coral species exhibited 

different bleaching responses to elevated UV-B radiation. During these early studies, 

methods for documenting changes in zooxanthellae number, photopigments, 

mycosporine-like amino acids, and photosynthetic efficiency were validated and 

improved. Temperature studies on algal symbionts have documented lethal thresholds 

(35o

 C) and declining growth rates at temperatures above 31oC during short-duration 

exposures. Studies on the interactions of UV-B and temperature have confirmed, for the 

first time in a laboratory system, that elevated UV-B exposure exacerbates the adverse 

effects of high temperature (Fig. 10).

Several physiological mechanisms are being investigated to understand the interactive 

effects elevated temperature and UV-B and to develop biomarkers able to distinguish 

susceptible corals in the field. Corals are experimentally bleached in the solar 

simulators and both corals and algal symbionts are examined for changes that could be 

used as biomarkers of susceptibility. For example, it is expected that changes in 

photopigment concentrations will be an early response to elevated UV-B. To refine 

current methods, an efficient methanol extraction process was developed to quantify 

changes in the symbiotic algae photopigments (Rogers and Marcovich 2004). The technique 

is much improved over previous techniques, yielding greater than 95% recovery of 

pigments in less than half the time. Another technique requires pulse-amplitude 

modulated fluorometry to examine photosynthetic efficiency of the symbiotic algae and 

may help to determine how photosynthesis is affected by temperature and UV-B. An 

immunoassay technique has been adapted in collaboration with the University of 

California to detect thymine dimer formation in coral DNA (Fig. 11; Anderson et al. 2001, 

2004); these specific mutations are characteristically formed only by UV-B exposure. As 

they are generated, biomarkers will be tested in the field to determine their ability to 

predict species at risk to both global change and local stresses. 

Main Conclusions

Coral health in the Florida Keys is deteriorating at unprecedented levels. Tools to 

evaluate coral reef condition are needed to assess potential consequences of this 

decline and to guide management options. Field surveys that estimate prevalence and 

distribution of coral bleaching and disease, using a probability-based sampling design 
 12. Coral Health 

12-6

and a radial belt transect (113 m2

), have been validated and applied at 60 sampling 

stations across the Keys (41 km2

). Bleaching and disease prevalence in the Lower Keys 

was particularly high in 1998 relative to other years (1998-2002), and was higher than 

comparison sites in the Dry Tortugas. A pilot project, comparing only five sites in the 

Lower Keys with five sites in the Dry Tortugas, demonstrated a greater percentage of 

dead coral in the Lower Keys area. 

Various endpoints are being validated to document coral condition. When combined, 

these endpoints must reflect the growth, survival, health and reproduction of corals; 

identify at-risk species; be comparable across stations, reefs and regions; and identify 

associations of condition with disease prevalence and other putative stressors. To 

achieve this goal, bleaching and disease surveys are being supplemented with three 

estimates made for each coral colony in the survey — total surface area, percent living 

coral tissue, and total living coral surface area. Results from a pilot project have 

demonstrated that these measures can be combined to indicate coral population health, 

survival and capacity to reproduce. Continued surveys of coral populations in the 

Florida Keys is expected to lend insight to the species, reefs and regions that are most 

valuable, most at risk, and potentially most responsive to management action. 

Relating coral decline to global change stressors requires knowledge of the thresholds 

at which changing environmental conditions create adverse effects. Controlled 

laboratory exposures, using novel solar simulator systems, have established 

temperature and UV thresholds for various coral species and algal symbionts. Early 

studies demonstrated that different coral species exhibited different bleaching 

responses upon exposure to UV radiation. Temperature studies have confirmed the 

adverse effects above 31o

C for coral symbionts and the interactive effects of high 

temperature with elevated UV-B. Future laboratory studies will document differences in 

sensitivity among the various groups (clades) of algal symbionts to temperature and UV 

radiation, and will evaluate changes in sensitivity from short (acute) to long (chronic) 

exposures. Various biomarkers are being investigated to provide insight to the 

physiological mechanisms of bleaching and for indications of coral susceptibility to 

bleaching. Characterization of stressor-response patterns for different coral species and 

algal clades can be used interactively with field studies to identify which stressors are 

most affecting the various species, reefs and regions of the Florida Keys. 
 12. Coral Health 

12-7

Figure 12-1. Coral reefs are 

affected by environmental 

changes in temperature, UV-B, 

photosynthetically-active

radiation (PAR), carbonate 

(HCO3 -

) availability in sea water, 

nutrients, sediments, 

contaminants and 

microorganisms that fluctuate in 

relation to global atmospheric 

and land use changes. 

Figure 12-2. Bleaching is a term used to 

describe the loss of pigmented symbiotic algae 

from coral tissue. Their loss leaves the coral 

with the stark white appearance of the coral 

skeleton. Coral tissue still covers the surface of 

the skeleton, but is transparent. 

Figure 12-3. Mean percent 

coral cover declined over 160 

stations in the FKNMS during 

1996-2000 (from Wheaton et 

al. 2001). The 2000 coral 

cover represents a 38% 

decline from the 1996 coral 

cover

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 12. Coral Health 

12-8

Figure 12-4.

Coral Reef 

areas and 

NHEERL study 

sites in the 

Florida Keys 

and Dry 

Tortugas.

Figure 12-5. Using SCUBA, surveyors count 

and identify each colony in a 113m2

 radial belt 

transect and examine each for evidence of 

bleaching and disease. 

Figure 12-6.

Cumulative 

distribution function 

depicting overall area 

estimates associated 

with coral disease 

prevalence in South 

Florida (with 95% 

confidence intervals 

(Santavy et al. 2004).

Dry 

Tortugas
 12. Coral Health 

12-9

 Number of TSA LSA 

 Colonies (m2) (m2) %LC

Dry Tortugas

 BK06 178 42.4 32.4 76.4 

 BK07 94 33.1 26.7 80.8 

 LR05 149 33.4 26.2 78.6 

 LR06 165 38.1 32.0 84.1 

 LR07 104 29.0 22.7 78.2

Total 690 175.9 140.0 79.6

Key West

 SK01 240 73.8 44.4 60.1 

 SK02 350 85.1 41.8 49.2 

 SK03 162 26.5 17.7 66.8 

 ED01 155 25.8 15.5 59.8 

 WS03 90 29.6 17.4 58.6

Total 997 240.9 136.9 56.8

Table 12-1. Number of coral colonies, total estimated surface area (TSA), calculated 

surface area of living coral (LSA) and the estimated percent of living coral (%LC) for all 

colonies encountered within the transects at each of five stations in the Dry Tortugas 

and Key West study areas. Totals were determined from combined data of all stations in 

each study area. 

Figure 12-7. Percent living 

coral for several coral 

species that co-occurred at 

Dry Tortugas and Key West 

study areas. Corals, in 

order, are Acropora

cervicornis, Colpophyllia 

natans, Dichocoenia 

stokesii, Diploria clivosa, D. 

strigosa, Montastrea 

annularis, M. cavernosa, M. 

faveolata, Porites porites,

and Siderastrea siderea. 

0

20

40

60

80

100

Percent

Acer

Dstok

Dstrig

Mcav

Past

Ssid

Percent Living Coral (%LC)

DT KW
 12. Coral Health 

12-10

Figure 12-8. Laboratory culture 

of different coral species allows 

comparisons of susceptibility to 

varying levels of temperature 

and UV-B under controlled 

experimental conditions. 

Figure 12-9. Laboratory culture 

of isolated algal symbionts 

(Symbiodinium sp.) allows a 

rapid examination of 

temperature and UV-B effects on 

the photosynthesis, pigment 

production, growth and survival.
 12. Coral Health 

12-11

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12-13

Santavy, D.L., J.K. Summers, V.D. Engle and L.C. Harwell 2004. The condition of coral reefs in south 

Florida using coral disease as an indicator. Environ. Monitoring and Assess. (In press). 

Scavia D., J.C. Field, D.F. Boesch, R.W. Buddemeier, V. Burkett, D.R. Cayan, M. Fogarty, M.A. Harwell 

R.W. Howarth, C. Mason, D.J. Reed, T.C. Royer, A.H. Sallenger and J.G. Titus 2002. Climate change 

impacts on U.S. coastal and marine ecosystems. Estuaries 25:149-164. 

Shick, J.M., M.P. Lesser and P.L. Jokiel 1996. Ultraviolet radiation and coral stress. Global Change 

Biology 2:527-545. 

Wheaton, J.W., C. Jaap, J.W. Porter, V. Kosminyn, K. Hackett, M. Lybolt, M.K. Callahan, J. Kidney, S. 

Kupfner, C. Tsokos and G. Yanev 2001. EPA/FKNMS Coral Reef Monitoring Project, Executive Summary 

2001. In: FKNMS Symposium: An Ecosystem Report Card. Wash., D.C. Available from: 

http://www.floridamarine.org.

Wilkinson, C. 1998. The 1997-1998 mass bleaching event around the world. Pages 15-38 in C. Wilkinson, 

editors. Status of Coral Reefs of the World: 1998. Australian Institute of Marine Science and Global Coral 

Reef Monitoring Network, Townsville, Queensland, Australia. 

Wilkinson, C.R. 2000. World-wide coral reef bleaching and mortality during 1998: a global climate change 

warning for the new millennium? Pages 43-57 in C. Sheppard, editor. Seas at the Millennium: An 

Environmental Evaluation. Elsevier, New York. 

Wilkinson, C., O. Linden, H. Cesar, G. Hodgson, J. Rubens and A.E. Strong 1999. Ecological and 

socioeconomic impacts of 1998 coral bleaching in the Indian Ocean: an ENSO impact and a warning of 

future change? Ambio 28:188-196. 

Williams, E.H., Jr., C. Goenaga and V. Vincente 1987. Mass bleachings on Atlantic coral reefs. Science 

238:877-888. 
 13. Synthesis 

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13. Synthesis 

Introduction

The Global Change Research Program’s mission is to improve the scientific 

basis for evaluating effects of global change in the contexts of other stressors 

and human dimensions, to assess the consequences of global environmental 

change, and to improve society’s ability to effectively respond to the risks and 

opportunities presented by global change as the emerge. NHEERL’s role within 

this program has evolved over the years as the program’s emphasis shifted from 

research on carbon cycling and terrestrial ecosystems to research on and 

assessment of impacts on aquatic ecosystems, including coral reefs. 

As the global climate change debate was heating up in the late 1980’s and early 

1990’s the United States Environmental Protection Agency (EPA) was rethinking 

its approach to environmental protection. After two decades of “end-of-pipe” 

regulation, and faced with non-point sources of pollution like agricultural runoff, 

serious questions were being raised about the cost-effectiveness of 

environmental policy. The EPA’s Science Advisory Board (SAB) was convened 

to develop recommendations for guiding the agency’s policy and research for the 

1990’s and into the 21st century (SAB 1990). The board recommended targeting 

research on problems with the greatest risk while exploring new regulatory 

processes such as market incentives and public education. The high-risk 

ecological problems identified by the SAB were (1) global climate change, (2) 

stratospheric ozone depletion, (3) habitat alteration and destruction, and (4) loss 

of biodiversity. These four issues are not mutually exclusive but interrelated in 

mechanism and mitigation. 

In 1988 at the request of Congress, EPA initiated the first national-scale 

assessment of potential global climate change effects (Smith and Tirpak 1989).

Research within EPA’s Office of Research and Development (ORD) supported 

that Report to Congress and became part of the United States Global Change 

Research Program (USGCRP). Started as a Presidential initiative in 1989, the 

USGCRP was codified by Congress in the Global Change Research Act of 1990 

(P.L. 101-606). The act established a research program "aimed at understanding 

and responding to global change, including the cumulative effects of human 

activities and natural processes on the environment, [and] to promote 

discussions toward international protocols in global change research..." Initially, 

the ORD research addressed stratospheric ozone depletion and global climate 

change to support international treaty negotiations—the Montreal Protocol and 

the United Nations Framework Convention on Climate Change (UNEP 2000, 

UNFCCC 2002).

Today, the USGCRP climate change research is managed within the US Climate 

Change Science Program along with the Climate Change Research Initiative 

(CCSP 2003). The latter is a Presidential initiative which establishes near-term 
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priorities for climate change research focusing on scientific information that can 

be used to address global change risks, including: the role of aerosols in climate 

forcing, inventorying carbon sources and sinks, improved climate modeling, risk 

management, and improved observation and monitoring of the earths climate 

system.

Early research at EPA was geared toward evaluating potential global impacts 

that could most seriously affect humans and the ecosystems on which they 

depend. As part of a larger EPA program addressing potential impacts to 

agriculture, natural resources and human welfare, scientists at ORD’s National 

Health and Environmental Effects Research Laboratory (NHEERL)—and its 

predecessor organizations—addressed potential changes to regional vegetation, 

impacts to rice production in Asia, and the effects on North American freshwater 

fish. The loss of forests, desertification and movement of major biomes with 

global warming were effects that the general public could envision. 

As the world became more aware of the potential seriousness of climate change, 

an interest was stimulated in control technologies to reduce the accumulation of 

greenhouse gases in the atmosphere. The EPA initiated projects on efficient use 

of fossil fuels, accounting for emissions of greenhouse gases country by country, 

and the ecological sources and sinks of carbon compounds. NHEERL scientists 

focused on the terrestrial carbon cycle. A key issue in international negotiations 

was whether or not forests could sequester carbon from the atmosphere in 

amounts that might offset emissions.

These two policy drivers—demonstrating environmental effects of such scale as 

to warrant international attention, and the ability of forests to sequester carbon 

and offset emissions—triggered a long-term research effort at NHEERL to 

understand the interactions between ecosystems and human-caused climate 

change. Throughout the 1990’s this research contributed to the scientific 

underpinnings of mitigation strategies for sequestering atmospheric carbon using 

forests and agriculture. Moreover, this research supported assessments of 

potential ecological effects resulting from climate change both in the US and 

abroad. NHEERL scientists were prominent in assessments of ecological 

vulnerabilities in conjunction with the national assessment process (National 

Assessment Synthesis Team 2000), and contributions to the assessments of the 

International Panel on Climate Change (IPCC 1995, 2001a).

Here, we review the research accomplishments of NHEERL scientists in light of 

changing policy issues, past, present and future. The intent is to show how the 

laboratory’s scientists responded to changing policy needs as the issue of global 

climate change grew from a scientific curiosity to a major worldwide concern. We 

conclude with a discussion that provides a view of emerging scientific issues 

related to effects of global climate change that may impact the EPA’s mission. 
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Humans and ecosystems

Climate change has affected human populations throughout history—indeed, our 

evolution as a species. Dramatic societal changes have resulted from past 

climate change. Climate change could affect the human condition directly as a 

result of extreme temperatures, sea level rise, and catastrophic storms and, 

perhaps more profoundly, indirectly through ecological change (Watson and 

McMichael 2001). The potential impact of global climate change to world food 

production was a major focus of EPA research

Food production is already a critical issue in light of expanding human 

populations worldwide. Potential impacts of climate change on are, therefore, of 

great importance. Whereas carbon conservation and fuel use are the primary 

concerns associated with global climate change in industrialized countries, 

sustainable production of major food crops and drinking water are major issues 

facing non-industrialized countries throughout much of the world (Speidel 2000). An 

early issue raised by the USGCRP was whether or not changing climate could 

compromise food production needed to support the world’s growing human 

population. Assessing the impacts of global climate change on major crop 

species and crop production systems was critical in international negotiations 

(UNFCCC 2002).

Rice is the most important source of calories in the world. It is the principle food 

source for approximately 1.6 billion people, and another 400 million are 

dependent on it for a quarter to half of their caloric intake (Moya et al. 1998). To 

meet the demands of human population growth over the coming decades an 

estimated 70% increase in yield over 1990 levels is needed (IRRI 1993). Of the 

major cultivation practices, irrigated rice makes up 55% of the world's harvested 

rice area and 75% of world rice production (IRRI 2002). 

NHEERL scientists conducted joint research with the International Rice Research 

Institute in The Philippines. In concert with broader EPA-funded research on how 

global climate change may affect the world’s major crops, this research 

examined the effects of climate change and stratospheric ozone (O3) depletion 

on rice production in Asia. Higher UV-B levels do not appear to affect irrigated 

rice production, however, elevated CO2 and temperature can affect production 

both directly and indirectly through disease and pests. Elevated CO2 enhances 

rice plant growth and grain yield if soil nitrogen is not limiting (Olszyk et al. 1999, 

Weerakoon et al. 1999, Ziska et al. 1996), but nitrogen is, generally, limiting and 

fertilizer is a major expense for farmers. In reality, the benefit of increased 

production from elevated atmospheric CO2 may not be realized throughout much 

of the world. Additionally, higher temperatures can result in increased sterility in 

rice leading to reduced grain yield (Moya et al. 1998). Regional analyses for Asia 

predict a nearly 4% decrease in rice yield across south and Southeast Asia with 

projected changes in temperature and precipitation associated with a doubling of 

atmospheric CO2 concentrations over 1990 levels (Matthews et al. 1995).
 13. Synthesis 

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As part of the larger EPA crop assessment program, NHEERL scientists 

determined that for US Corn Belt, soil erosion is likely to increase with increasing 

frequency and intensity of precipitation, and wind erosion will increase with 

increasing temperature (Phillips et al. 1993, Lee et al. 1996). These losses will 

contribute to pollution and affect the sustainable yield of crops. 

Although plant productivity may rise with increases in atmospheric CO2 and, 

consequently, offset some erosion, the overall effect of CO2 increases in 

conjunction with changes in other stresses, including nutrients, temperature, and 

moisture availability, is uncertain and crop specific (Phillips et al. 1996). However, 

increases in plant production could increase soil carbon storage and ameliorate 

erosion losses to some degree so long as nutrients and water do not become 

limiting to crop growth. In fact, agricultural soils could become a small sink for 

atmospheric CO2 if conservation tillage is practiced (Kern and Johnson 1993).

Ecological effects 

EPA research on ecological effects was initiated in 1990 to assess the effects of 

global climate change on aquatic and terrestrial ecosystems as an integral part of 

the USGCRP. Early research at NHEERL assessed the impacts of climate 

change on fresh water fish and changes in the distribution of major vegetation 

types. In the early 1990’s, policy makers became interested in the global carbon 

cycle, particularly in the sources and sinks of atmospheric carbon in the 

terrestrial biosphere. At that time, strategies were being formulated for removing 

carbon compounds from the atmosphere, and for managing the terrestrial 

biosphere to increase carbon sequestration. In particular, the large carbon pools 

in forests and soils were seen as potential sinks for atmospheric carbon. At 

NHEERL, research was initiated to assess forest management practices as a 

means to increase carbon sequestration. At the same time scientists were 

debating whether or not increased levels of atmospheric CO2 would increase the 

productivity of crops and forests. In response, NHEERL scientists initiated longterm experimental research on the effects of increased temperature, elevated 

atmospheric CO2, and air pollution on the carbon balance of forested 

ecosystems. In1998, the USGCRP was refocused; ORD’s primary ecological 

responsibility became watershed and aquatic ecosystem assessments. NHEERL 

research is currently addressing global change effects on coral reefs. 

In the following sections, we summarize the research findings of the NHEERL 

scientists within the context of related research. While the research on thermal 

tolerance in freshwater fish, vegetation redistribution, and carbon sequestration 

has, largely, been completed and published, much of the experimental research 

on carbon cycling is not yet published. With the experiments completed and the 

data collected, scientists are in the process of analyzing and publishing their 

findings on multiple stress effects—publications will continue over the next 

several years. The research on coral reef decline was initiated in the late 1990’s 
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and is continuing, consequently, the research plans and early findings are 

reported here.

Thermal tolerance in fish 

Water temperature has long been recognized as one of the most important 

environmental variables influencing the distribution of fish species. NHEERL 

scientists have investigated the thermal requirements of freshwater organisms; 

especially fish, since the 1960's and 1970’s when water quality research started 

to focus on requirements of aquatic organisms. NHEERL scientists provided 

some of the first assessments of climate change effects on North American fish 

species in support of the USGCRP. They assembled data on fish species, river 

characteristics (Poff and Allen 1995), and air-water temperature relationships (Stefan

and Preud’homme 1993, Eaton and Scheller 1996) to predict the impacts of climate 

change on fish distributions (Eaton et al. 1995).

The effect of air temperatures on stream temperatures was determined based on 

field studies (Stefan and Preud’homme 1993, Eaton and Scheller 1996). The effect of 

climate warming was assessed for 57 North American fish species (Eaton et al.

1995). Results suggest that cold or cool water fish species could be lost from a 

large part of their range. Habitat losses were predicted to be greatest for species 

with limited distributions and in areas of the country anticipated to warm the most 

(e.g., the central Midwest). Results for warm water fish species were less certain 

because of a relative paucity of data on summer and winter thermal tolerances 

for species.

Effects of global warming on habitable stream reaches based on temperature 

changes can be modified near groundwater or tailwater discharges from 

reservoirs or lakes (Sinokrot et al. 1995). Empirical models were developed by 

NHEERL scientists to predict groundwater inputs to stream reaches based on 

watershed slope and hydraulic conductivity (Baker et al. 2001), and to predict 

modifications to stream thermal regimes based on stream shading from 

topography or riparian vegetation and groundwater inputs. These efforts will help 

fine-tune model predictions of the effects of global change on fish species 

distributions.

Global change effects on fish communities will depend not only on stream 

temperature, but also on flow regimes. Altered flow regimes resulting from 

climate change could be particularly pronounced in the western US. Research 

funded by NHEERL (Lettenmaier et al. 1992), and subsequent assessments (Gleick 

2002) predict that the western US will experience a substantial reduction in the 

natural storage of water as snow pack with climate warming despite potential 

increases in precipitation. Loss of snowpack will result in higher stream flows in 

winter and lower water levels in summer (Lettenmaier and Sheer 1991).

Consequently, aquatic ecosystems will experience substantial changes in flow 
 13. Synthesis 

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regimes and sediment loads in streams and rivers, which will impact fish species 

to varying degrees.

Global climate change could profoundly affect freshwater lakes because they are 

sensitive to a wide array of changes in climate. NHEERL research suggested 

that cold water fish are likely to disappear from southern Minnesota lakes, and 

experience habitat losses of 41% in northern Minnesota lakes. Largest gains in 

suitable habitat for cool and warm water species will occur in lakes with low 

production—oligotrophic (Stefan et al. 1996). The recent US National Assessment 

summarized possible climate change effects on water resources (Gleick 2002); the 

effects on lakes include: 

x Small changes in climate can produce large changes in lake levels and salinity. 

x With higher air temperatures, fewer lakes and streams in high-latitude areas will freeze to 

the bottom and the number of ice-free days will increase, leading to increases in nutrient 

cycling and productivity. 

x Increased lake temperatures could result in higher thermal stress for cold-water fish, 

improved habitat for warm-water fish. 

x Higher temperatures will increase lake productivity and lower dissolved oxygen, and 

degrade water quality. 

Vegetation redistribution 

Of the predicted global warming consequences, widespread changes in the 

distribution of forests, grasslands, and deserts are perhaps the most striking. The 

prospect of the pole-ward migration of temperate forests, the loss of tundra and 

boreal forests, and the desertification of grasslands could impact much of the 

world. The effects of world-wide changes in vegetation zones over a relatively 

short time period would have dramatic effects on fish and wildlife species, on 

forest health, on water quality, and on agriculture. Moreover, such changes in 

vegetation would have significant consequences for carbon storage and loss in 

the terrestrial biosphere. 

The fundamental concept of vegetation redistribution is complex and occurs over 

time scales from years to centuries and at spatial scales from back yards to 

continents. Weeds can appear and spread in a new region within years or 

decades, but the climate-induced appearance of forest tree species new to a 

region requires centuries to millennia in the absence of human intervention. In 

contrast, the death of extant vegetation from climate stresses can occur relatively 

quickly, sometimes in only a few years or a decade.

NHEERL scientists conducted research to address vegetation redistribution 

using models which predict regional vegetation patterns. Precise data bases for 

climate and vegetation were critical to the modeling, and much of the early work 

was dedicated to their development (e.g., EPA/NOAA 1992, 1993). The modeling 

research followed two approaches. One used life form classifications (e.g., Sedjo 

and Solomon 1989, King and Neilson 1992) in conjunction with climate correlations to 
 13. Synthesis 

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define the climate space occupied by vegetation types (Neilson et al. 1992). A 

physiology model was then applied which calculated the uptake of CO2 by 

photosynthesis and emission of CO2 by respiration in each vegetation type 

(Neilson 1993a, 1995). The other approach used known climate thresholds to 

assemble different plant functional types in each 1⁄2 X 1⁄2 degree of latitude and 

longitude (Prentice et al. 1992). Both approaches used climate projections 

calculated by global climate models to define new vegetation distributions. 

The redistribution of global vegetation in response to changing climate and land 

use remains a major uncertainty in predicting carbon sequestering in the 

terrestrial biosphere. Regional changes in temperature, precipitation, and 

consequently, soil moisture, are the driving forces that will alter the distribution of 

natural and managed vegetation as climate changes (Marks et al. 1993). The 

NHEERL modeling results indicated that the capacity of the terrestrial biosphere 

to remove and store atmospheric carbon would increase with a warmer global 

climate (Solomon et al. 1993, 1996; Solomon 1996, 1997). The direct effects of 

increasing atmospheric CO2 on biomass were simulated at a global scale and 

found to increase carbon sequestration (Neilson 1993b, 1998; Neilson and Marks 1994).

Subsequent work has suggested that increases in vegetation density and carbon 

storage will increase with climate warming to a threshold of approximately 4.5oC

above which vegetation density and carbon storage will diminish (Bachelet et al.

2001).

Climate-induced forest dieback and changes in the distribution of land used for 

agriculture could generate a pulse of CO2 from the biosphere into the atmosphere 

lasting several decades (Neilson 1993b, 1998). The size of such a pulse could be 

15-20% of that from anthropogenic emissions over the same time period (Solomon

and Kirilenko 1997, Kirilenko and Solomon 1998). While not considered in recent 

estimates of future carbon releases from the biosphere (Falkowski et al. 2000; Hurtt et 

al. 2002), a carbon release of this magnitude would amplify any warming effect of 

anthropogenic emissions and limit the effectiveness of carbon sequestration 

efforts. 

In an effort to refine estimates of CO2 releases, forest gap models were used to 

estimate the dynamic responses of forests to rapid climate change. These 

models replicate the death, reproduction, growth, and maturity of trees, and the 

development of forest ecosystems (Solomon and Bartlein 1992, Solomon and West 1993,

Bugmann and Solomon 1995, 2000). Although assessment exercises with these 

models (Solomon and Bartlein 1992, Bugmann et al. 2001) confirmed the potential for the 

long-term carbon pulse, the gap models have not yet been applied on the 

globally-comprehensive basis needed to thoroughly evaluate the carbon pulse 

phenomenon.

While the timing and magnitude remains uncertain, CO2 emissions from 

vegetation redistribution will almost certainly occur and will affect greenhouse 

gas concentrations in the atmosphere (Solomon 1996, 1997). Human population 
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growth superimposed on climate related changes in human demographics and 

agricultural land use will have an effect on the size and timing of these releases. 

Analogously, Houghton et al. (1999) estimated that over the period 1700-1990, 25 

petagrams (Pg) of carbon was released into the atmosphere from land use 

change in the US, largely from the conversion of forests to agricultural land and 

cultivation of prairie soils. In comparison, the US emission of CO2 equivalents for 

the ten year period 1990-1999 was approximately 58 Pg (US Dept.of State 2002). In 

a warmer world, the intensity of agriculture is expected to increase at higher 

latitudes, thus reducing the capacity of the earth to store carbon and create 

potential sources of CO2 through soil warming and land conversion (Cramer and 

Solomon 1993, Leemans and Solomon 1993, Solomon and Leemans 1997).

Vegetation zones are likely to shift as climate changes over the next century and 

beyond, but how they shift within regions and watersheds, over what time period, 

and with what ecological effects is still unclear. But that kind of information is 

necessary for developing adaptation strategies. Perhaps most limiting to 

vegetation modeling is the inability to predict regional precipitation and soil 

moisture. Current global and regional climate models cannot predict precipitation, 

soil moisture, and runoff on time scales beyond a few days (Hornberger et al. 2001).

Adding to the uncertainty in predicting vegetation patterns, regional vegetation 

models are unable to simulate processes which control the redistribution of plant 

species—dieback, seed dispersal, and establishment. Global climate change 

involves rapidly changing climate, which may exceed the capacity of many plant 

species to adapt (Solomon et al. 1996, Etterson and Shaw 2001). Rapid loss of 

vegetation assemblages and slow, species-by-species establishment elsewhere 

is much more likely than a gradual process which delivers fully developed plant 

communities instantaneously. It is unlikely that new vegetation communities will 

contain the same species in the same abundances as old ones because 

migration and establishment requirements differ from species to species (Solomon

and Kirilenko 1997, Kirilenko and Solomon 1998). Presently, the models do not account 

for factors controlling seed dispersal and species migration. Such improvements 

are needed before better predictions of species composition and carbon storage 

can be made. 

Wildfires were not included in the NHEERL vegetation modeling, but they will 

affect future redistribution of vegetation and carbon loss from increasing climate 

stress. Large areas of essentially undisturbed forests in the US have been 

protected by fire suppression during the last century, permitting dangerous levels 

of fuels to accumulate and increasing the likelihood of severe, uncontrollable 

fires. Globally, the drought conditions over continental areas projected by most 

climate models (Solomon and Leemans 1997) will increase wildfire occurrences. Only 

recently have dynamic vegetation models included fire factors based on 

vegetation types, climatic conditions, and fuel characteristics (e.g., Bachelet et al.

2001). Currently, methods to include fire intensities and distributions in regional 

vegetation models based on wildfire characteristics, climate conditioning of 

vegetation, land use distributions, soils and topography are being developed by 
 13. Synthesis 

13-9

EPA and USGS scientists. Once tested, these models will provide improved 

predictions of vegetation redistribution and carbon cycling. They will also be 

valuable in predicting health-related effects of wildfire emissions. 

Carbon sequestration in forests 

Sequestration of atmospheric carbon in soils and vegetation could play a key role 

in mitigating anthropogenic CO2 emissions. Forest systems are a globally 

significant terrestrial carbon pool and play a major role in the Earth’s carbon 

cycle through assimilation, storage, and emission of CO2 (Dixon et al. 1994). The 

ability of forests to remove carbon from the atmosphere and store it for long time 

periods—carbon sequestration—is potentially important in mitigating 

anthropogenic emissions of carbon dioxide (Dixon et al. 1999, UNFCCC 2002).

The annual exchange of carbon between forests and the atmosphere, and the 

amount of carbon stored in forests, varies with the nature of forest cover, land 

use, and climatic constraints. Despite this variation NHEERL scientists showed 

that managing forests to maximize growth and biomass retention can significantly 

increase the long-term sequestration of atmospheric CO2 (Dixon et al. 1994).

Maintaining healthy forests was determined to be the most efficient way to store 

carbon, but uncertainties remain.

Most assumptions of how much carbon forests can sequester do not account for 

vegetation redistribution, land use change, or changes in human population 

density resulting from climate change. These factors can significantly affect 

estimates of carbon stored in forests. Changing land use is perhaps the greatest 

threat to sequestering carbon in forests (Dixon et al. 1999). Efforts aimed at storing 

carbon in the tropics—where the world’s largest pools occur—are being 

countered by carbon emissions from forest destruction. Moreover, increasing 

agriculture in response to the growing human population is impacting forested 

regions world-wide. In fact, land use changes may have as large or larger effect 

on terrestrial carbon sequestration than direct climate change effects (Schimel et al.

2000).

Currently, the US is pursuing voluntary limitations on CO2 emissions (EPA 2003),

but should the US decide to pursue and implement strict limits in the future, EPA 

may be asked to regulate sources and sinks (Nature 2003, Samuelsohn 2003, Jeffords 

2003). Moreover, many states within the US have passed or are developing 

legislation to limit CO2 emissions that features sequestration in forests and 

agricultural soils (Murphy 2003). Participating countries under the Kyoto Protocol 

can receive credit for activities that increase carbon absorption such as planting 

forests, although how these credits will be assessed is still vague (Schiermeier 

2002).

Carbon trading is being established under the auspices of the Kyoto Protocol in 

countries that have ratified the treaty. Among participating countries, large scale 
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reforestation projects are underway financed by the sale of carbon emission 

credits (e.g., Evolution Markets 2002). Driven partly by the expectation of some 

future, government-imposed emissions-reduction program, a number of large 

American corporations have banded together to make voluntary reductions in 

greenhouse gas emissions and trade carbon credits (Patrick 2003). 

Despite all the interest and activity, there is no commonly accepted or 

scientifically verifiable way to measure carbon sequestration. Without such 

procedures, deciding how to calculate emissions and credits is problematical. 

Procedural uncertainties exist with the accounting and verification methods (e.g., 

Rypdal and Baritz 2002). Ecological uncertainties surround factors that limit 

ecosystem uptake and storage of carbon, particularly nutrient availability and 

elevated levels of atmospheric CO2 (Pelley 2003, Scholes and Noble 2001).

Multiple stress effects 

In conjunction with rising temperatures, the carbon dioxide concentration in the 

Earth’s atmosphere is expected to double sometime during the second half of the 

21st century (IPCC 2001a). Understanding the response of ecosystems to elevated 

atmospheric CO2 is central to assessing the effects of global climate change on 

ecosystems as well as determining the capability of the biosphere to sequester 

anthropogenic carbon. Ecologists have been studying the effects of temperature 

and precipitation—the primary drivers of productivity—on ecosystems for many 

years. Atmospheric carbon dioxide while essential to ecosystem functioning has 

been viewed as a relative constant. The prospect of increasing levels of 

atmospheric CO2 presents a new paradigm for ecologists trying to predict effects. 

Elevated levels of CO2 may increase primary productivity and water use 

efficiency in plants resulting in increased growth and carbon sequestration—the 

fertilization effect (Ceulemans and Mousseau 1994). Based on such experiments, it is 

commonly assumed that agriculture and forestry will benefit from future climate 

changes. Experimental studies have shown that elevated CO2 increased plant 

height, stem diameter, leaf area index, and fine root biomass of Pinus ponderosa

(Johnson et al. 1998, Tingey et al. 1996b) and increased P. ponderosa growth (Pushnik 

et al. 1995, Surano et al. 1986). Early results from a free air CO2 enrichment (FACE) 

system in a young North Carolina forest show increased NPP during the first two 

years of exposure, however, this may be attributed to the young age of the trees, 

and may decline as the forest ages (DeLucia et al. 1999). Reviewing a number of 

studies, Morison and Lawlor (1999) and Norby et al. (1999) concluded that 

although elevated CO2 increases the carbon assimilation rate, it does not mean 

that growth will be increased because of possible limiting factors in natural 

ecosystems.

In response to the uncertainties surrounding the fertilization effect of elevated 

levels of atmospheric CO2 and the interacting effects of other stresses, NHEERL 

scientists conducted a series of experiments on intact and reconstructed natural 
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ecosystems to study the interactive effects of climate change, elevated CO2,

tropospheric ozone, and soil conditions on important tree species and 

ecosystems. A state-of-the-art, environmental exposure facility that controls and 

manipulates key climatic and edaphic factors was constructed at NHEERL’s 

Western Ecology Division (Tingey et al. 1996a). Located in Corvallis, Oregon, this 

facility was used to study the interacting effects of atmospheric CO2, tropospheric 

ozone, temperature, and soil moisture on forest ecosystem processes. Field 

exposure chambers in the Sierra Nevada Mountains near Placerville, California, 

were used to examine the effects of elevated CO2 and soil nitrogen on the 

Ponderosa pine forests (Johnson et al. 2000). A Department of Energy FACE facility 

in the Mojave Desert on the Nevada Test Site allowed scientists to study the 

direct effects of elevated CO2 on intact natural ecosystems (Phillips et al. 2002).

Finally, a series of field sites were established in the western Cascade Mountains 

of Oregon to compare experimental research with actual field conditions and to 

provide a basis for modeling studies (McKane et al. 1997b).

Ecosystems respond to elevated atmospheric CO2 and temperature in complex 

ways involving interactions between plants, soil processes, and the atmosphere. 

A fertilization response is uncertain, particularly in natural ecosystems. Research 

by NHEERL scientists (Johnson et al. 2000, Olszyk et al. 1998, Tingey et al. 1996b, 1997,

Rygiewicz et al. 1997) suggests that the response to CO2 can be limited by soil 

fertility—primarily nitrogen availability. Experiments in the NHEERL 

environmental exposure facility used a low nitrogen soil, but if the plants that 

were exposed to elevated levels of CO2 were grown in a high nitrogen soil or 

otherwise fertilized, the results may have been different. A sufficient supply of 

nitrogen could increase growth until CO2, water, or another resource became the 

primary limiting factor. This new level of plant productivity would be maintained to 

the extent that nitrogen supplies could be maintained.

Modeling studies support this pattern and further suggest that the commonly 

observed increase, and subsequent re-acclimation, of plant growth to elevated 

CO2 is a consequence of nutrient limitation (e.g., Comins and McMurtrie 1993, McKane 

et al. 1997a). Applying the General Ecosystem Model (Rastetter et al. 1991) to various 

sites in the western Cascade Mountains of the Pacific Northwest led NHEERL 

scientists to suggest that soil nitrogen is a primary constraint on the ability of 

those forests to sequester carbon (McKane et al. 1997a). For a nitrogen-poor site, 

model results indicated that total ecosystem carbon storage will increase by less 

than 10% during the next 100 years in response to projected increases in 

atmospheric CO2 and temperature. In contrast, carbon storage at a nitrogen-rich 

site was calculated to increase by over 25% during the same period. 

Field studies in a variety of ecosystems also support the nutrient limitation 

concept. Orem et al. (2001) reported that mature pines grown on soil with poor 

fertility did not respond to elevated CO2. In grassland ecosystems soil nitrogen 

availability appears to limit the capacity of plants to absorb expected increases in 

atmospheric CO2. Recently published research on grasslands suggests that 
 13. Synthesis 

13-12

there appears to be thresholds of atmospheric CO2 above which ecosystems no 

longer respond (Gill et al. 2002). Moreover, increased concentrations of 

atmospheric CO2 can actually reduce net primary productivity in nutrient-limited

ecosystems (Shaw et al. 2002 ), hence the potential for biosphere sequestration of 

atmospheric CO2 may be limited.

The response of desert ecosystems to elevated CO2 is limited by water. 

NHEERL’s collaborative research with the Desert Research Institute in the 

Mojave Desert showed a measurable CO2 response only when adequate soil 

moisture was available (Smith et al. 2000). With adequate water, elevated CO2

increased photosynthetic rates, water use efficiency, and above ground biomass 

of vegetation. However, root production and turnover were not affected (Phillips et

al. 2002). Because water is the most limiting resource in this desert ecosystem, 

elevated atmospheric CO2 increased production by increasing water use 

efficiency, but only when adequate water was available. 

The fate of carbon in ecosystems that show no biomass increases to elevated 

levels of atmospheric CO2 remains an enigma. In long term chamber 

experiments at NHEERL’s Western Ecology Division, elevated levels of 

atmospheric CO2 increased photosynthetic rates (Lewis et al. 1999, 2001), but tree 

biomass was not affected (Olszyk et al. 2003). The additional carbon assimilated by 

plants exposed to elevated CO2 was allocated to the below ground biota. But the 

movement of carbon into long term storage as soil organic matter could not be 

detected as gross changes in total soil carbon. Similar findings were reported for 

a loblolly pine forest exposed to elevated CO2 (Schlesinger and Lichter 2001). If plants 

are photosynthesizing more with increased concentrations of atmospheric CO2,

then where is this carbon going? Increases, if any, found in above ground or 

below ground carbon pools are too small to explain where the additionally-fixed 

carbon is being allocated—although accelerated rates of carbon cycling by 

increased respiration has been suggested by NHEERL scientists and their 

collaborators (Lin et al. 1999). It appears that biologically-mediated processes 

belowground that transform and acquire nutrients may ultimately determine how 

an ecosystem will respond to CO2 fertilization.

Further analyses using stable isotope techniques detected a small increase in 

soil organic matter over several years (Lin et al. 2001). Although these results are 

preliminary, increased allocation of carbon to soil organic matter under elevated 

levels of atmospheric CO2 could result in a substantial amount of sequestered 

carbon over decades to centuries, but it is uncertain if this will be a long term or 

transient process. The processing of atmospheric carbon through plants and soil 

biota to long term storage as soil organic matter, and how elevated temperature 

and CO2 associated with global climate change affects this process remains a 

major scientific uncertainty. 

How ecosystems respond to elevated temperatures and increased levels of 

atmospheric CO2 is becoming clearer. It is safe to say that the fertilization effect 
 13. Synthesis 

13-13

of CO2 is not universal. In fact, it may be rare among unmanaged ecosystems. 

Forests, grasslands, and deserts can be expected to respond differently to 

climate change. Limiting resources seem to play an important, but uncertain role 

in this response. Perhaps the most challenging aspect of predicting how specific 

ecosystems respond to climate change is deciphering how multiple, interacting 

stress factors— temperature, moisture, elevated CO2, air pollution, and 

nutrients—combine to affect ecosystem structure and functioning. 

In addition to increased temperature and CO2, ecosystems will be exposed to 

increased air pollution resulting from warmer climates and increases in human 

population. The primary cause of air pollution damage to vegetation is 

tropospheric ozone (O3). Damaging O3 concentrations currently occur over 29% 

of the world’s temperate and sub-polar forests but are predicted to affect fully 

60% by 2100 (Fowler et al. 1999). In multiple stress experiments, elevated levels of 

tropospheric ozone tend to cancel the stimulatory effect of CO2 on plant growth 

(U of Wisconsin 2002, Felzer et al. 2002, Percy et al. 2002). Research in NHEERL’s sunlit, 

controlled environment chambers suggests that increased levels of CO2 may 

moderate the detrimental effects of O3 on primary production (Olszyk et al. 2001). In 

conjunction with the NHEERL chamber research, Tingey et al. (2001) used a 

process-based whole-tree growth model to study the interactions of CO2,

temperature, and O3. They found that increasing CO2 can reduce, but not 

eliminate the O3 impact. However, elevated O3 also reduced the stimulant effect 

of CO2 on plant growth and would be expected to limit carbon sequestration.

Moreover, the interacting effects of O3 and CO2 on below-ground processes are 

poorly understood, but those processes are critical in determining the responses 

of ecosystems to those stresses (Andersen 2003).

With global climate change, ecosystems will be subjected to a changing milieu of 

stresses. Elevated CO2, higher temperatures and changes in precipitation 

patterns combined with the effects of increased air pollution—nitrogen deposition 

and increased levels of tropospheric O3—will produce a range of effects on 

natural and managed ecosystems. Ollinger et al. (2002) indicate that O3 may 

counteract the increases in productivity afforded by elevated CO2 and nitrogen 

deposition in the northeastern US resulting in little or no altered growth over the 

long term. Indirect effects and natural ecosystem processes can also limit the 

ability of plants to sequester CO2. Changing climatic patterns can alter net 

ecosystem productivity (Knapp et al. 2002). The ability of forests to sequester 

carbon decreases as they age (Finzi et al. 2002, Schimel et al. 2001). The interacting 

effects of CO2 and air pollution can alter the susceptibility of plants to pest 

damage and diseases (Percy et al. 2002). Ultimately, separating climate change 

effects from land management and invasive species effects on ecosystems is an 

obstacle to developing adaptation and mitigation plans. 

Global change research has led us to appreciate the ramifications of multiple 

stresses acting in concert, and helped us realize that controlling single pollutants 

is not likely to achieve the desired results. While the NHEERL research provided 
 13. Synthesis 

13-14

insights on the interaction between, climate, CO2, and air pollution, the effects of 

multiple stresses simultaneously interacting on ecosystems are still major 

uncertainty. Comprehensive assessments of climate change effects on 

ecosystems need to consider multiple stresses, and projects intended to mitigate 

or adapt to climate change should factor in multiple stress effects. 

Coral reef ecosystems 

Coral reef ecosystems throughout the world are deteriorating at an accelerating 

rate. This decline is attributed to multiple stress factors, which include global 

changes in atmospheric gases and land use patterns. In the Florida Keys, coral 

health is deteriorating at unprecedented levels. The focus of current NHEERL 

research is to evaluate coral reef condition, to assess potential consequences of 

this decline, and to guide management options. 

 Bleaching and disease prevalence in the Lower Keys was particularly high in 

1998 relative to other years (1998-2002), and was higher than comparison sites 

in the Dry Tortugas. A pilot project, comparing only five sites in the Lower Keys 

with five sites in the Dry Tortugas, demonstrated a greater percentage of dead 

coral in the Lower Keys area. Continued surveys of coral populations in the 

Florida Keys will provide information on the species, reefs and regions that are 

most at risk, as well as management recommendations. 

Controlled laboratory experiments have established temperature and UV 

thresholds for important coral species and algal symbionts. Results of early 

research suggest that different coral species exhibit different bleaching 

responses with exposure to UV radiation. Temperature experiments have 

confirmed the adverse effects above 31o

C for coral symbionts. Also, the 

interactive effects of high temperature with elevated UV-B have been quantified. 

Future research will determine differences in sensitivity among the various 

groups (clades) of algal symbionts to temperature and UV radiation, and will 

evaluate changes in sensitivity from short (acute) to long (chronic) exposures. 

Biomarkers are being developed to aid in determining the physiological 

mechanisms underlying the bleaching process, and to determine coral 

susceptibility to bleaching. Once the mechanisms are understood, stressorresponse patterns for different coral species and algal clades can then be used 

interactively with field studies to identify which stressors are most affecting the 

various species, reefs and regions of the Florida Keys. 

Better tools for environmental assessments

NHEERL’s climate change research program has evolved to meet changing 

policy needs. Along with ongoing research, the results of past research, both 

published and forthcoming, will continue to support critical policy decisions, but 

future assessments may need different analytical tools. The dynamic interactions 
 13. Synthesis 

13-15

between humans and ecosystems require study because climate change 

interacts with other forms of human-induced change including land use change, 

air and water pollution, and invasive species. Assessments conducted at the subregional and watershed levels can inform the implementation of adaptation and 

mitigation strategies by state and local governments. 

After more than a decade of assessing the impacts of global climate change in 

one manner or another, the basic conclusions and uncertainties about potential 

ecological effects remain much the same. We continue to refine our predictions, 

but the models and databases needed to make assessments for manageable 

parcels of land are still lacking. To some extent this is a result of the relatively 

coarse resolution of global climate models from which future patterns of 

temperature and precipitation are derived. But from an ecological perspective we 

still lack the ability to resolve ecosystem responses to multiple stresses at an 

ecologically reasonable scale. 

To date, the USGCRP National Assessment has considered effects at national 

and regional levels. Comprehensive assessments of the effects of CO2 and 

temperature changes on ecosystems at a “management” level are needed to 

plan mitigation projects and guide land use decisions. Planners in both the public 

and private sector will need information at the level of forest stands or 

watersheds in order to fully assess effects or to implement adaptation actions. 

Carbon sequestration projects will need to be designed at the scale of local land 

holders, not regions.

Should CO2 controls become mandatory, managing natural ecosystems to 

maximize carbon sequestration will require a detailed knowledge of past, present 

and future land use, and how those practices affect carbon sources and sinks. 

Major questions remain about carbon uptake, translocation, and storage above 

and below ground. Social, political, and economic influences on land use and 

resource management, and how these forces affect the carbon storage must be 

resolved. Ultimately, the data and assessment tools to evaluate actions at the 

scale of projects—watersheds, forest plots, and specific crops—will be required. 

To address these needs, assessment tools to evaluate land management options 

in conjunction with pollution and climate effects at the scale of forest stands, or 

sub-watersheds, will be critical. Ecosystem process models working at the 

watershed scale will be needed to assess climate change effects on both 

terrestrial and aquatic ecosystems. Continued development of spatially 

distributed ecosystem models capable of accounting for the interacting effects of 

elevated CO2, climate change, pollution, and land use along with the supporting 

data bases is clearly warranted. 
 13. Synthesis 

13-16

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