Humans are fundamentally changing the global environment.

The air we breathe contains significant additions of carbon dioxide, methane, and other industrial gases. The fresh water we drink has been rerouted with dams and reservoirs, and contaminated by agricultural runoff and industrial pollutants. The land we live on has been drastically modified for crops, pastures, and cities.

In SAGE, we are working to understand how human activities affect both the biological and physical systems of our planet. Our current research concentrates on the changing nature of the world's ecosystems and watersheds, and how they interact with the atmosphere and oceans.

Much of our effort focuses on building and testing computer models of the Earth’s ecosystems, watersheds and climate. Using these computer models, we explore how ecological, climatic, and hydrological processes interact to support the rich diversity of life found on this planet.

Understanding Terrestrial Ecosystems – From the Field to the Globe

The Earth's terrestrial (or land-based) ecosystems are critically important to the welfare of humankind. Food, fiber, fresh water, medicines, and forest products are all derived from our terrestrial ecosystems. In addition, terrestrial ecosystems play a central role in regulating the biogeochemical and climate systems of this planet.

To better understand ecological processes, and to evaluate their response to human activity, our research team is developing new comprehensive computer models of the Earth's terrestrial ecosystems. These models are used to simulate a wide variety of ecosystem processes, including: energy, water, and carbon dioxide exchange between plants, the atmosphere, and the soil; physiological processes of plants and soil organisms, including photosynthesis and respiration; seasonal changes of vegetation, including spring budburst, fall senescence, and winter dormancy; plant growth and plant competition; and nutrient cycling and soil processes. These computer models are among the few computer models to incorporate this range of processes in a single framework.

We are currently using the model to study how ecosystems respond to changes in land use and climate. We continue to test our models against detailed field measurements collected from ecosystems around the world.

Environmental Changes in the Amazon Basin

The Amazon basin contains the single largest area of tropical rainforests left on Earth. These forests play an important role in regulating the Earth’s carbon cycle and climate, as well as providing habitats to countless plants and animals.

The Amazon basin is also changing dramatically. Over the last few decades, increasing population and development pressures have led to large areas of deforestation in the Amazon. In the coming years, deforested area will likely increase as more roads are built through the core of the forest, and markets continue to drive a demand for agricultural products.

SAGE scientists are involved in the international LBA (Large-Scale Atmosphere-Biosphere Experiment in Amazônia) project, which studies the climate, ecology, and hydrology of the Amazon basin. Working with other LBA-Ecology investigators in Brazil and the United States, we are developing detailed computer models of the basin, and testing them against field observations and satellite data. Our LBA research focuses on the vegetation structure, carbon cycling and water resources of the Amazon basin, and how these characteristics may be affected by environmental change. Currently, we are examining the potential effects of land use, biomass burning, climatic variations, and increasing carbon dioxide concentrations on the forests of the Amazon.

LANDSAT images showing change in landcover in Rondonia, Brazil

green = forested area
yellow = agricultural area

the amazon river

fieldwork in Brazil – measuring sap flow

Linkages Between Climate and Ecosystems – a Two Way Street

Looking across the globe, we see that patterns of temperature and rainfall limit the range of many plant and animal species. In fact, we see strong geographic associations between climate and ecosystems, ranging from the tropical rainforests, through the subtropical deserts and temperate forests, all the way to the northern boreal forests and Arctic tundra.

But changes in vegetation cover can also affect the physical properties of the land surface and how it interacts with the atmosphere. Removing the forest cover over a large area, for example, reduces the amount of water evaporated back into the atmosphere, leaving less water and energy available to fuel weather systems.

At SAGE, we are building new computer models that fully link the two-way relationships between climate and ecosystems. In particular, we have incorporated our IBIS terrestrial ecosystem model directly within global climate models of the atmosphere and ocean. We have used these “coupled” models to examine how changes in ecosystems could affect the future climate of our planet:

The Effect of Vegetation Feedbacks on Global Warming. Shifting patterns of global vegetation cover, caused by future greenhouse warming, might induce large feedbacks on the climate system. Our initial results suggest that changes in vegetation could magnify the effects of global warming, especially in high northern latitudes.

The Effect of Tropical Deforestation and Global Warming. Over the Amazon basin, the climatic impacts of deforestation may be greater than the impacts of global warming. Deforestation and greenhouse warming both act to increase the average temperature of the basin, while they have opposite effects on precipitation.

The Interactions of Climate and the Carbon Cycle. Future concentrations of atmospheric carbon dioxide will not only be determined by human activity – they will also be determined by the biosphere and the oceans. If, in a warmer world, the biosphere cannot absorb as much carbon dioxide, or the biosphere starts releasing carbon dioxide from dying vegetation communities, global warming could be substantially accelerated.