Climate Change, Nitrogen and Biological Diversity

By Chris Clark, Ph.D.

When I visit our national parks, hike in the woods or backpack in the mountains, one of the things I enjoy most is the natural beauty that surrounds me—especially the plants. I’m a plant person, which is hard for some people to understand. (“They don’t do anything” many of my friends quip.) But, to me, that couldn’t be further from the truth.

Prairie scene

Three of the most prevalent dangers to plant biodiversity are habitat loss, climate change and nitrogen deposition.

Plants form the foundation for all robust ecosystems, supporting healthy biogeochemical cycles (how materials—for example, fallen leaves—move through systems and are chemically altered by both biological and geological forces), clean air and water, and all higher life forms. To me, this gives plants a quiet kind of majesty that is beautiful to witness.

All the different types of plant species in an ecosystem, from the largest trees to the tiniest wildflowers, play a role in the healthy functioning of that system. In the systems that I studied as a graduate student, the grasslands of Minnesota, it blew me away how many different species co-existed in one square meter of space. What once was just “green grass” became a teeming system of life to me.

Three of the most prevalent dangers to plant biodiversity nationwide are habitat loss, climate change and nitrogen deposition. These stressors can lead to changes that may reduce plant biodiversity, which can cascade through systems and affect other processes and services.

The work I do at EPA is important because it can help preserve ecosystems. I look at different stressors, like climate change and nitrogen deposition, and their impacts on ecosystems. I identify the types of changes that occur and the rate at which the changes are happening. If we understand this, we will be better poised to support and inform policy decisions that enhance the sustainability of our natural resources and avoid irrevocable damages.

For a recent project, I looked at how nitrogen deposition impacts plant biodiversity on land nationwide.  My collaborators and I examined “critical loads” (the upper limit of nitrogen an ecosystem can handle) from different regions of the U.S.  We then used computer modeling to estimate when deposition was too high and what the effect might be.

The results showed that many regions had nitrogen deposition amounts that may be too high, with losses of species ranging from one to 30 percent using a “worst-case scenario” approach.  When we used a “best-case scenario” approach, we estimated minimal losses. We had to use both of these scenarios because scientists don’t know exactly where in this range the critical loads are, and for which systems.

Before our study, no one knew what the ramifications could be of such a range. Refining these estimates of critical load thus is a very important area of future research.

Our results were recently published in the journal Ecology. Future work will build on this project to look at different aspects of the climate change-nitrogen relationship.  As a whole, the research will help promote a better understanding of how climate change and nitrogen deposition may impact our natural environment; this, in turn, will help policy makers mitigate these impacts. That’s important to me, and probably to anyone, who enjoys walking in the woods, backpacking or any other outdoor activity.

About the Author: EPA research scientist Chris Clark, Ph.D., works on a diversity of issues related to climate change, including biodiversity, biofuels, and urban resilience.