Competitive hierarchies of temperate tree species: Interactions between resource availability and white-tailed deer

Abstract

:Rankings of species-specific juvenile tree growth and survivorship define competitive hierarchies that play a central role in forest dynamics and may also vary in response to herbivory. We conducted an experiment to examine species-specific rankings of sapling growth and survival for six common tree species in temperate forests of the northeastern US as a function of both resource availability and herbivory by white-tailed deer (Odocoileus virginianus). Juveniles of six tree species were planted in the presence and absence of deer, in high and low light neighbourhoods dominated by each of two different tree species known to both reflect and alter soil resource availability. Under closed canopy conditions, survival and radial growth of most species was low. Under high light conditions, red oak and eastern hemlock saplings inside exclosures grew significantly faster when protected from deer, and eastern hemlock saplings grew faster in red oak- than red mapledominated neighbourhoods. Browsing significantly decreased survival under high light for all species except beech. Rank order of species-specific growth and survival within treatment combinations changed dramatically. For example, beech saplings had the second highest survivorship under high light / + deer neighbourhoods, but fell to the lowest rank when deer were excluded. These rank-order changes in growth and survivorship indicate that both light availability and herbivory act in concert with gap-phase dynamics to regulate tree population dynamics in eastern deciduous forests.