Species responses to oil palm: Cautionary considerations for multi-site extrapolation

Abstract

Xerophytic thickets (XT) in south-western Madagascar are threatened by deforestation, mainly due to slash-and-burn cultivation. However, few studies have been conducted on how XT ecosystems operate. This study characterizes XT plant biodiversity and analyses the post-cultivation regeneration process of XT on the Belomotse plateau. Sixty 10 m × 10 m plots were sampled according to soil type (calcisol and lixisol) and age of abandonment (1–5, 6–10, 11–20, 21–40 years and >40 years as mature XT). Soil was the main driver of XT floristic composition. Overstory floristic composition did not vary along secondary succession stages. However, structure parameters (height and basal area) increased significantly with age of abandonment, while diversity (species richness and evenness index) did not increase with age of abandonment. Secondary succession in XT vegetation was assimilated to growth of structural parameters. The slowness of the growth of shrub species found in post-cultivation XT plots can explain this lack of change in diversity and floristic composition along secondary succession stages. The reduction of pressure on XT by promoting alternative activities that provide income for local communities (goat breeding and extension of arable areas along rivers delimiting XT) is proposed in order to protect the endangered biodiversity of this region.