Strategic Plan for the
Climate Change
Science Program
Review draft, November 2002

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Chapter 10:
Ecosystems

Ecosystems sustain life on Earth by providing a wide variety of goods and services, including food, fiber, shelter, energy, clean air and water, and recycling of elements. From a human perspective, ecosystems provide renewable resources, together with cultural, spiritual, and recreational benefits. During the next 10 years, research on ecosystems will focus on two overarching questions:

Global environmental changes are altering the structure and functioning of ecosystems, affecting in turn the flow of ecosystem goods and services. Research during the last decade focused on the vulnerability of ecosystems to global change and contributed to assessments of the potential impacts of global change on ecosystems at multiple scales. We now know that impacts of environmental changes and variability may be manifested in complex, indirect, and conflicting ways. For example, warming may enhance tree growth by extending growing season length, but pathogens able to survive the winter because of higher temperatures may decrease forest productivity and further increase vulnerability to disturbances such as fire. Subtle changes in the salinity or temperature of ocean currents may alter the ranges and population sizes of fish species and increase or decrease fish catches. Whether environmental changes are anthropogenic or natural in origin, human societies face substantial challenges in ensuring that ecosystems sustain the goods and services on which we depend for our quality of life and, in some cases, for survival itself.

Ensuring the provision of ecosystem goods and services needed and valued by a growing human population requires understanding the interactions among basic ecosystem processes and developing approaches to reduce the vulnerabilities or take advantage of opportunities that arise within ecosystems as a result of global change. Scientific research can contribute to this societal goal by addressing three questions that will provide information to determine linkages and feedbacks between ecosystems and drivers of global change, identify important consequences for ecosystems on which societies depend for crucial goods and services, and identify options for how society might respond to sustain and enhance ecosystem goods and services as environmental conditions change.

Biological, chemical, and physical processes occurring in ecosystems affect and are affected by weather and climate in many ways. For example, ecosystems exchange large amounts of greenhouse gases with the atmosphere, including water vapor, carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). Moreover, the reflection (or absorption) of solar radiation by ecosystems is important to the temperature of Earth's surface, and several ecosystem processes affect this reflection. Linkages among the physical, chemical, and biological components of ecosystems are important on short time scales (minutes to days) as well as over the long term (years to millennia). Global change has the potential to alter ecosystem structure (e.g., amount of leaf area, plant height, or species composition) and ecosystem functioning (e.g., rate of evapotranspiration, carbon assimilation, or nitrogen cycling), and those potential ecosystem changes might themselves alter linkages between ecosystems and the global chemical and physical environments and therefore contribute to global change through numerous feedback mechanisms.

The most important feedbacks (either positive or negative) are likely to involve:

Better understanding of ecosystem feedbacks on climate and atmospheric chemistry is needed to predict future climate and to inform policy decisions. Achieving this understanding will require collaboration with the Carbon Cycle (Chapter 9), Water Cycle (Chapter 7), and Land Use/Land Use Change (Chapter 8) research elements.

Ecosystems research needs include ecological experimental facilities, improved ecosystem models, and enhanced ecosystem monitoring capabilities and programs (at different scales) to link point observations with remote sensing data to scale up. New research and monitoring programs may be too expensive, so the major efforts might be directed at enhancing existing capabilities. Specific research needs include:

There is considerable evidence that ecosystems are already responding to global change, including climate change and variability and changes in atmospheric chemistry. For example, responses to changes in a single property (e.g., rising or extreme temperatures) have been linked to longer growing seasons (period of leaf display), grass species decline, changes in lake acidity, and coral bleaching. Climate change variables also interact. For example, increased temperatures in the tropics may increase coral bleaching and expand the range of corals poleward. These and other observations have come from long-term ecological research and monitoring, as well as from shorter-term, individual investigations. The few programs that support long-term observations (e.g., forest productivity, ultraviolet (UV) radiation fluxes, nitrogen deposition, and the spread of invasive species) have unambiguously established that large-scale ecological changes are occurring.

Most ecosystems are subject to multiple changes at any given time. Recent reviews have summarized the range of observed and potential undesirable consequences of combinations of climate and other local and shorter-term drivers (e.g., invasive species, nutrient pollution, and physical habitat modification) on coastal and marine ecosystems. In terrestrial systems, increased primary productivity driven by increased CO₂ depends in part on soil fertility, and warming has the potential to alter the effects of rising CO₂ on primary production processes. Interactions among temperature change, precipitation, and fire regimes can influence ecosystem vulnerability to invasive species. Survival and spread of pathogens and their vectors (carriers) are highly dependent on climate and weather, thus, climate change and increased weather variability can be expected to affect disease-causing organisms that can alter population sizes and genetic diversity of humans, animals, and plant hosts.

Identifying and quantifying the consequences of global change for ecosystems is essential for accurately assessing options for responding to ecosystem changes. Determining the most important and societally relevant ecosystem responses to global change will require collaboration among the physical, biological, and social science communities and an improved understanding of complex interactions between natural and human disturbances and climate variability. Some specific research needs to support this effort include:

As described previously, experiments and observations have demonstrated linkages between climate and ecological processes that indicate that possible future changes in climate could alter ecosystems in ways that might disrupt the flow of ecosystem services. Research has identified and evaluated some specific adaptation measures, including integrated land and water management; selection of plants and livestock for many intensive systems; multiple cropping systems; multiple-use systems for freshwater and land systems; protection programs for key habitats, landscapes, and/or species; intervention programs (e.g., captive breeding and/or introduction programs); efficient use of natural resources; and institution and infrastructure mechanisms (e.g., market responses, crop insurance, and water flow and supply management).

Research has investigated how management practices may affect climate-related ecosystem services. For example, ecosystems emit greenhouse gases such as CH₄, N₂O, CO₂, water vapor, and aerosols; they store carbon, nitrogen, phosphorus, and other elements in soils, plants, wetlands, and oceans; and they reflect solar radiation. Management practices may result in positive or negative feedbacks to the climate system by altering emissions, carbon and nutrient storage, or reflectivity of the Earth's surface. However, while specific management strategies have been investigated, society's knowledge and ability to manage the broad array of ecosystem services in the context of increasing and potentially conflicting demands is extremely limited.

There is a need for evaluations of the influences of societal needs and demands on ecosystems and the values that societies place on ecosystem goods and services. Precise understanding of effective options to maintain and enhance the supply of critical goods and services will require substantial improvements in modeling capabilities to project impacts of interacting environmental changes on ecosystem services and to evaluate the effectiveness of alternative management responses. Specific research needs include:

Given the nature of the drivers of ecosystem change, research must span spatial scales (from small experimental plots to global satellite image mosaics), time scales (taking data from ice cores, tree rings, and fossil pollen to near-real-time forecast models), and the scientific elements of this plan. Monitoring systems at multiple spatial scales are needed to develop a consistent record of environmental change over time. Data from such observation systems would provide inputs to models and also allow evaluation and improvement of model performance. The resulting large collections of environmental data will necessitate large databases. Interagency facilities and mechanisms must be in place to process, archive, and distribute the data collected and generate relevant products.

Future observation systems may rely on networks of terrestrial and aquatic ecosystem observatories within particular biomes or larger ecoregions. They should link together and build on existing networks of field stations, experimental forests and ranges, environmental and resource monitoring programs, and long-term ecological research sites sponsored by many different government and academic organizations, many of which have lengthy records of environmental and ecological data.

For the ecosystems research community to make significant contributions to our understanding and management of global change, explicit scenarios and information to drive ecosystem models must be obtained from other research elements under this plan, including Scenario Development and Applied Climate Modeling (Chapter 4), Atmospheric Composition (Chapter 5), Climate Variability and Change (Chapter 6), Carbon Cycle (Chapter 9), Water Cycle (Chapter 7), Land Use/Land Cover Change (Chapter 8), and Human Contributions and Responses (Chapter 11). In turn, products from studies of the linkages between global change and ecosystems can be expected to improve the scientific products of these other plan elements. Collaboration with appropriate international efforts will involve programs and organizations such as several sponsored wholly or in part by the International Geosphere-Biosphere Programme (IGBP), including the Global Climate and Terrestrial Ecosystems (GCTE) project, the Global Environmental Change and Food Systems (GECaFS) project, or the Biospheric Aspects of the Hydrological Cycle (BAHC) project. Scientists conducting research under the Ecosystems element of this plan will participate in the planning of international collaboration activities.