Atmospheric nitrogen deposition is likely to have globally significant effects on biodiversity, particularly in temperate zone forests. Legumes, and other plants that fix atmospheric nitrogen, may be particularly sensitive to increases in nitrogen deposition but the possible role of this sensitivity in population declines has not been investigated. In the last 30-40 years, New England populations of the perennial legume, Desmodium cuspidatum (large-bracted tick-trefoil), have declined as nitrogen deposition in the northeastern US has increased. These population declines are not associated with habitat loss, conversion or fragmentation. A combination of wide geographical sampling, greenhouse experiments and demographic modeling will be used to determine whether the decline of D. cuspidatum can be explained, at least in part, by the effects of nitrogen deposition on individual growth, reproduction, and survivorship. Range-wide genetic analyses will investigate whether patterns of genetic diversity correspond with those expected from recent population declines.
Because resources available for conservation are limited, efforts that benefit a suite of similar species are preferable to those that focus on only one. Desmodium cuspidatum is among 110 rare plant species in need of research in New England and is a member of the plant family (Fabaceae) that accounts for 10% of the species in the National Collection of Endangered Plants. Furthermore, 36% of the members of this plant family are considered at risk in the US. The results of this study will help determine conservation priorities, will guide management for D. cuspidatum, and will influence conservation strategies for other rare legumes.
