Abstract
Profound changes are occurring in forests as native insects, nonnative insects, or pathogens irrupt on foundation tree species; comprehensive models of vegetation responses are needed to predict future forest composition. We experimentally simulated hemlock woolly adelgid ( Adelges tsugae Annand) infestation (by girdling trees) and preemptive logging of eastern hemlock ( Tsuga canadensis (L.) Carrière) and compared vegetation dynamics in replicate 90 m × 90 m treatment plots and intact hemlock stands from 2004 to 2010. Using Chao–Sørensen abundance-based similarity indices, we assessed compositional similarities of trees, shrubs, forbs, and graminoids among the seed bank, seed rain, and standing vegetation over time and among treatments. Post-treatment seed rain, similar among treatments, closely reflected canopy tree composition. Species richness of the seed bank was similar in 2004 and 2010. Standing vegetation in the hemlock controls remained dissimilar from the seed bank, reflecting suppressed germination. Recruits from the seed rain and seed bank dominated standing vegetation in the logged treatment, whereas regeneration of vegetation from the seed bank and seed rain was slowed due to shading by dying hemlocks in the girdled treatment. Our approach uniquely integrates multiple regeneration components through time and provides a method for predicting forest dynamics following loss of foundation tree species.
Highlights
A key aim of forest ecology is to elucidate factors that influence transitions of plants from the seed to the canopy under a range of management conditions
Changes in forest species composition through time are driven by several factors, including recruitment from the seed bank, inputs from seed rain, interactions with standing vegetation, variable edaphic and climatic conditions, and a range of mortality agents including insects and pathogens (Lovett et al 2006; Burton et al 2011)
We present results of a seven-year study that documents species present in the seed bank, seed rain, and tree, sapling, seedling, and herbaceous vegetation before and after hemlock-dominated stands were subjected to three experimental treatments: (1) simulated attack by A. tsugae; (2) preemptive logging; and (3) intact control
Summary
A key aim of forest ecology is to elucidate factors that influence transitions of plants from the seed to the canopy under a range of management conditions. Changes in forest species composition through time are driven by several factors, including recruitment from the seed bank, inputs from seed rain, interactions with standing vegetation, variable edaphic and climatic conditions, and a range of mortality agents including insects and pathogens (Lovett et al 2006; Burton et al 2011). Silvicultural practices and preemptive measures such as logging, undertaken to remove vulnerable and/or economically valuable tree species before an infestation or infection occurs, affect seed-banking, regeneration, and forest dynamics (Graae and Sunde 2000; Decocq et al 2004). Palynological data illustrate that hemlock forests underwent a region-wide decline
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