Changes in plant species richness after cessation of forest disturbance

Questions What will happen to species diversity in a forest when exploitation of the canopy foliage terminates? The foliage of the main canopy tree of a mountain evergreen oak forest was harvested at different intensities prior to a forest survey in 1993 and resampled in 2013 after the harvest of canopy foliage ceased (1995). We predict a decrease in herbaceous species richness with increasing canopy cover, and an opposite trend for vines and woody species. We hypothesise that plant species' alpha and beta diversity will change most in the plots where foliage was most intensively harvested while showing less change in the plots that underwent almost no harvesting. Location Temperate evergreen laurel-oak forest in the Himalaya, Nepal. Methods We resampled all non-epiphytic vascular plants in 64 plots of 10 m x 10 m in 2013, following the same protocol used in 1993. Plant species were categorised into three life forms; woody (except woody vines), herbaceous, and vines. Uni- and multivariate numerical methods were used to assess the significance of the changes in species diversity for different life forms. Results Vines and woody species increased, whereas herbaceous species decreased, but overall gamma diversity remained unchanged. The overall alpha richness for herbaceous species decreased, while the opposite is true for woody and vine richness. Herbaceous richness decreased and woody richness increased in the areas with low and intermediate disturbance (in 1993), whereas vines remained unchanged. Only vine richness increased in the area that was very disturbed in 1993. Total species richness as well as herbaceous and vine richness decreased with increasing tree canopy cover. Conclusions Plots that were intensively harvested in 1993 did not recover their richness because vines dominated the forest floor. Management should prevent overexploitation, and only allow low-intensity canopy disturbance, which may facilitate habitat diversity and thereby enhance species richness.

Automated summary

A study on a mountain evergreen oak forest in the Himalaya, Nepal, revealed that the exploitation of canopy foliage led to a decrease in herbaceous species richness, an increase in woody and vine species, and a dominance of vines in plots that were intensively harvested. The study suggests that management should aim to prevent overexploitation and only allow low-intensity canopy disturbance to enhance species richness and habitat diversity.