Evidences of homogenization in species assemblages of restored mixed Shorea robusta forest stands of Nepal

Abstract

Recent forest assessment in Nepal has shown an increase in total forest area as a result of implementation of community-based forest management strategies and effective forest restoration interventions. However, success of ecological restoration in some forest stands are argued based on how restoration success is determined. Does increase in spatial coverage and stem densities of preferable plant species alone represent successful restoration or should benefits to alpha diversity of the assemblages also be required? Empirical studies comparing structural attributes of restored and reference forest stands are very limited in Nepal. In this context, species assemblages and structural metrics of woody plants in restored and natural stands of mixed Shorea robusta forests situated in the central lowland of Nepal were assessed and compared. Woody species were evaluated for 60 sub-plots, each of an area of 0.1 ha, established in two sets of stands of 3 Buffer Zone Community Forests. We observed significant difference (p = 0.002) in plant species composition between restored and natural forest stands. Species wise density showed S. robusta with significantly higher (p < 0.0001) density in restored stands compared to natural stands, but densities of other associated woody plants, such as Mallotus philippensis, Lagerstroemia parviflora, Casearia graveolens and Dillenia pentagyna were significantly higher (p < 0.0001) in natural stands. Restored and natural stands did not differ in means of overall basal area of woody plants, but when basal area of S. robusta was considered, it was greater in restored compared to natural stands. Alpha and beta diversity values for woody plant assemblages were significantly higher in natural compared to restored stands. Our study revealed emblematic density diversity deflections in restored forest stands. Indicator species analysis showed substantial fewer numbers of indicator species in restored compared to natural stands. We observed evidence of homogenization in species assemblages in all examined restored mixed S. robusta forest stands of Nepal, so future restoration interventions should focus on increasing species heterogeneity.