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Conversion of Rare Grassy Openings to Forest: Have These Areas Lost Their Conservation Value?

ABSTRACT: Grassy openings have a high conservation value because they provide habitat for a number of rare and endemic species and contribute to landscape level biodiversity. However, these communities are at risk because tree encroachment causes the conversion of grassy openings into closed-canopy forest. Many land managers have taken an active position in maintaining these openings by introducing disturbances such as fire, grazing, or mowing to slow or halt the invasion of tree species. The objective of this study was to trace the closure of grassy openings, in the absence of active management, and identify whether the forest that developed was unique in tree and shrub composition and structure or whether it mirrored the surrounding forest matrix. Our study site was an area with historical grassy openings visible on a 1937 aerial photograph. We sampled the vegetation in these former openings, now closed-canopy forest, and compared them with paired plots on similar aspects and elevations but forested in the 1937 photographs. The tree and shrub composition in the former grassy openings was similar to the composition in the adjacent forested areas and was also similar to regional second-growth forests. Thus, we concluded that in the absence of active restoration, rare grassy openings convert to vegetation communities that are similar to the regional forest conditions.