Understanding and managing the impacts of human nitrogen deposition in endangered bay area serpentine grasslands
Zavaleta, E. S., P. L. Koch, Z. Tzankova and P. Selmants. 2010. Kearney Foundation of Soil Science Final Report
Abstract
In recent decades, fertilizer use and fossil fuel consumption have vastly increased nitrogen (N)
availability in many ecosystems. Understanding and addressing the effects of increasing N is
critically important to land stewardship, particularly in ecosystems of high conservation value.
The goals of this project were to document and understand the effects of ongoing N
deposition on serpentine grassland ecosystems, and the effectiveness of management and
policy strategies available to mitigate these effects in the San Francisco Bay Area.
We have addressed these goals in five parts with interlinked objectives: (i) to document and
quantify the progressive accumulation of N in historically N-limited serpentine grassland at the
largest serpentine complex in the San Francisco Bay Area, (ii) to understand the links between N
deposition and progressive invasion of serpentine grasslands by exotics, through investigation of
species-specific physiological responses to N deposition by exotic and native species, (iii) to
investigate the importance of N deposition relative to other biotic and abiotic factors varying at
landscape scales in affecting serpentine communities, (iv) to explore the interactive effects of
cattle grazing and increasing N availability on serpentine invasion, plant community and soil
dynamics, and (v) to examine the role of science in the formulation of land management and
policy decisions affecting listed species in serpentine and other ecosystems at regional scales.
Our project addressed the core of the Kearney Foundation's mission of cross-scale research
relevant to land management decisions in California and centered on the role of soils as
mediators of environmental change effects on ecosystems and landscapes. Our research spanned
multiple spatial and temporal scales and explicitly addressed questions about cross-scale
relationships and interactions in the biophysical and policy realms. Broadly, we employed the
Coyote Ridge serpentine ecosystem as an integrator of regional- and decadal-scale patterns in
human activity and technology, and we linked changes in regional human activity to changing
ecosystem dynamics at the soil-plant interface. Specifically, we conducted a series of field and
greenhouse studies drawing from the diverse fields of biogeochemistry, stable isotope ecology,
plant community ecology, dendroecology, and political science. Our research examined the
history of N deposition at Coyote Ridge reserve; current interactions of N availability, soil
chemistry and plant community composition; and future consequences of continued N deposition
and cattle grazing on plant and microbial communities. In addition, we explored how sources and
consequences of N deposition are addressed in the N emissions policy process, how political and
technological changes have influenced rates of N deposition, and how management responds to a
directionally changing environment.
