Clear-felling effects on colonization rates of shade-tolerant forest herbs into a post-agricultural forest adjacent to ancient forest

Question Does clear-felling influence forest herb colonization into post-agricultural forest? Location A stand of poplar cultivars with a dense understorey of Acer pseudoplatanus in Muizen forest (northern Belgium), planted in 1952 on farmland adjacent to ancient forest and clear-felled in 1997. Methods Shade-tolerant forest herbs were surveyed in 112 grid-based sample plots: just before clear-felling, and 5 and 10 yr afterwards. Shade-tolerant herbs were subdivided into ancient forest species (AFS) and other shade-tolerant species (OSS). Effects of clear-felling on species number per plot, total cover per plot and colonization rate of species groups were compared using non-parametrical tests. Species number per plot was modelled by means of generalized linear mixed models (GLMMs), with inventory time, distance to the nearest parcel edge, and cover of light-loving species (LS) as explanatory variables. The C-S-R signature (competitive, stress-tolerant and ruderal strategies, respectively) shift of sample plots was calculated on the selected shade-tolerant species. Results Frequency of most species increased during the 10-yr period. Number of OSS increased more and faster than that of AFS. OSS increased to the level of the adjacent forest, but was lower where LS cover remained high. There was a positive correlation between the change of the colonization rate and the competitive plant strategy. Conclusions We assume that clear-felling stimulated generative reproduction of shade-tolerant herbs, whereas quickly emerging woody species controlled competitive exclusion by LS. Succession of dark and light phases, such as provided by an understorey managed as a coppice, could promote colonization of shade-tolerant herbs into post-agricultural forest.