The interplay of disturbance, vegetation structure, and propagule pressure contributes to Pinus kesiya invasion in Tapia woodland, Madagascar

Pinus are among the highly invasive species that have spread outside their plantation area after their introduction in the Southern Hemisphere. The case of Pinus kesiya invasion is observed in the high plateau of Madagascar, inside the sclerophyll Tapia woodland which is dominated by the endemic Uapaca bojeri tree species. The analysis of this invasion was carried out using 375 plots of 100 m(2) each in Tapia woodland. Data on the vegetation structure, the plot characteristics and the propagule pressure were collected. We recorded a total of 740 pines distributed in 29.8% of the plots. The generalized linear model built on P. kesiya at the three different life stages allowed us to highlight a different explicative variable on the species' presence and abundance separately. The factors explaining pine occurrence varied according to the pine life stage. In the seedling stage, the distance of the plot from the propagule source combined with the longitudinal position of the plot explained 18% of the pine presence. In the sapling and adult stages, the vegetation structure was the main important factor (22% and 11% of variation explained regarding presence and abundance). The frequency of U. bojeri and the degree of disturbance were the most important factors characterizing this vegetation structure. Based on these results, a strategy to control pine invasion in the Tapia woodland may focus on enrichment with U. bojeri and limitation of the plantation of P. kesiya in proximity.