The effects of disturbance intensity on temporal and spatial patterns of herb colonization in a southern New England mixed-oak forest

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As managing forests for biodiversity becomes more common, it is important to understand how understory species respond to disturbance. We monitored changes in species’ dominance, calculated as importance values, over a 4-year period in order to determine how species’ dominance varied with disturbance intensity and gap position. An experimental linear canopy opening was created in a southern New England mixed-oak forest, and plots were established on the south side, center, and north side of the opening. All vegetation was removed in half of the plots, simulating a lethal disturbance. In the other half of the plots, only the overstory was removed, simulating minimal disturbance (release plot). Before the disturbance, Dennstaedtia punctilobula dominated the plots, but typical forest understory species such as Kalmia latifolia, Trientalis borealis, Maianthemum canadense, and Mitchella repens were very common. After the disturbance, D. punctilobula expanded and continued to remain dominant in all types of plots. Early successional species, such as Carex pensylvanica, Poaceae species, Rubus ideaus, and Rubus allegheniensis dominated the lethal and center plots; late successional forest understory species experienced a reduction in frequency and cover in these plots. However, in release and edge plots, late successional species maintained relatively similar frequencies and covers to pre-disturbance values. The ability of early successional species to seed into lethal plots and grow rapidly in the high light environment of the center plots allowed them to dominate in these plots. Late successional species were able to remain relatively dominant in release plots through clonal expansion and in edge plots through exclusion of early successional species from low light levels. Three years after the disturbance, most of the residual forest understory species had attained similar frequencies and covers to pre-disturbance values in all types of plots. Thus, although there is some initial loss of residual species in highly disturbed areas and in the center of the opening, most of these species are able to recover in a relatively short time period. However, locally uncommon species may be vulnerable to permanent loss. In order to minimize loss of species from the understory, forest managers should attempt to keep groundstory disturbance as minimal as possible where desirable late-successional species exist and create edge-partial shade effects with the remaining canopy for regeneration treatments.









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