How long are thinning-induced resource pulses maintained in plantation forests?

Abstract

Despite the critical role of pulsed resources on the dynamics and conservation of several forest-dwelling species, the transition between the period when the effects of a thinning-induced resource pulse are maximal and the period when only residual effects remain has yet to be documented in forest habitats. In this study, we investigated the occurrence of a transition period after a woody necromass resource pulse produced by commercial thinning operations on flying coleopterans. In a large-scale manipulative study, spruce plantations were subjected to commercial thinning treatments and beetles collected using flight intercept traps during the four years that followed thinning operations. 82,062 beetles from 50 families and 242 species were recovered. For two years after thinning treatments, beetle communities differed in composition between thinned and unthinned plantations, species richness and abundance being higher in thinned areas. By the third and fourth year after thinning treatments, these differences started to fade, indicating that the transition period was occurring. This was associated with a decline in the quality of woody debris found close to or onto thinning trails. These results support our hypothesis that fine woody debris, such as those produced by commercial thinning operations, are attractive to beetles for a short period because they rapidly decay and are rarely colonized by wood-boring species, inhibiting further colonization by fungi and mycophagous beetles. Yet, despite a decline in abundance and species richness in thinned areas during the last two years of the study, thinned plantations still harboured richer and more abundant beetle communities than unthinned plantations, suggesting that thinning trails continue to improve beetle dispersal as the woody necromass resource pulse weakens.