A resurvey of threatened endemic tree populations in seasonally dry tropical forests of Reunion Island (Indian Ocean) suggests imminent extinctions

Abstract

Seasonally dry tropical forests are among the most threatened forest types in the world. For instance, less than 1 % of original seasonally dry tropical forests remains on Reunion Island (South-West Indian Ocean). There, five endemic woody taxa restricted to seasonally dry tropical forests are included in a dedicated national action plan. This study reports on a resurvey conducted as part of this plan, in which 51 historically described subpopulations were revisited and 46 new subpopulations were discovered. Half of the historical individuals were either found dead or not found. The annual survival rate was therefore relatively low and similar between taxa (0.93–0.95). Because of the lack of regeneration observed in the field, the estimated annual recruitment was even more critical, and varied by a factor of 10 from Abutilon exstipulare (0.09 juveniles produced per reproductive plant) to Tabernaemontana persicariifolia (< 0.01). Based on these data, we performed a series of population viability analyses that led either to extinction within a few decades or to population size at which extinction becomes very likely over the long term. This situation urges local conservation stakeholders to make every possible effort both on site and ex situ to save this unique flora.