Abstract
Complex early-seral forests support biological legacies and unique understory vegetation (grasses, forbs, shrubs, juvenile trees) important to wildlife and ecosystem functioning. Intensive management in early-seral forest and other stages could reduce understory plant diversity and homogenize community compositions. Furthermore, the relative effects of management regime may vary at different stages of forest development. To what extent do taxonomic, functional and phylogenetic diversity vary by seral stage and/or ownership (a proxy for management regime) after accounting for climatic variation? For 2224 plant species sampled systematically at 16,330 sites in sixteen Plant Association Zones (PAZs) of Washington, Oregon and California, we estimated taxonomic, functional and phylogenetic diversity (both alpha = richness and beta = heterogeneity measures). Seral stage was inferred using forest structural metrics. Permutational multivariate analyses tested the relative effects of seral stage and ownership type. Across PAZs, a common motif emerged: low diversity in sparse, untreed stages indicated an accumulation period after stand-replacing disturbances, followed immediately by peak diversity in early sapling stages, after which gradually declining diversity coincided with the loss of shade-intolerant species during stand development and canopy closure. Departures from this motif tended to be in climatically less-permissive locations. More of the variation in diversity was explained by seral stage than ownership type (and their interactions were seldom significant). Discriminating the nuanced effects of different management regimes will require context-dependent proxies other than ownership. Identifying generalities in vegetation dynamics—and departures from those generalities—can help balance ecological and social objectives in rapidly changing forest landscapes.
Keywords
Complex early-seral forests,
diversity,
ecosystem services,
Forest Inventory and Analysis (FIA),
forest management,
forest structural development,
understory vegetation.
Citation
Smith, Robert J.; Gray, Andrew N.; Swanson, Mark E. 2020. Peak plant diversity during early forest development in the western United States. Forest Ecology and Management. 475: 118410. https://doi.org/10.1016/j.foreco.2020.118410.
