OOS 40-1 - Patterns of species loss associated with N deposition: Thresholds and reversibility

Thursday, August 11, 2011: 1:30 PM
17A, Austin Convention Center
Chris Clark, National Center for Environmental Assessment, US EPA, AAAS, Washington, DC

N deposition is a major threat to biodiversity world-wide. Although most terrestrial systems are anticipated to be sensitive to this stressor, impacts across regional landscapes are likely to vary considerably because of heterogeneous sensitivities of ecosystems and species. Here we discuss theoretical and observed properties that predispose sites to greater or fewer species losses, the implications of a nonlinear-dynamic response function to N addition, and the likely pathways for recovery following community perturbation.


Theory predicts that species losses through either eutrophication or acidification pathways should be influenced by several climatic, soil biogeochemical, and community characteristics. Quantifying vulnerability of different systems using these characteristics should facilitate identification of systems most at risk. When multiple vulnerabilities align, effects appear additive and lead to greater responsiveness to N. This may explain why some systems such as sand prairie of Minnesota lose many species, while other systems such as Mediterranean grasslands and alpine meadows do not, and, why some systems appear more sensitive to acidification versus eutrophication pathways.

Several endogenous and exogenous processes change following N enrichment, including nutrient cycling, propagule availability, and competition. It is unknown which single or combination of processes prevent recovery, whether these are the same processes that induced species losses, and therefore which management options would yield the most fruitful results. We review the results from several observational studies and experiments that examined system dynamics following cessation of N addition that suggest propagule availability may be a primary inhibitor. These effects, however, may depend on the spatiotemporal scale considered.

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