Developing conservation strategies for endemic tree species when faced with time and data constraints: Boswellia spp. on Socotra (Yemen)

Many endemic tree species have important scientific, ecological and economic value but the scarcity of information about their biological and ecological features makes it difficult to develop conservation strategies for them. A four-step approach is presented to address this problem, based on the analysis of data collected in a limited-duration field study: (1) Data collected are used to analyse the ecological niche, population structure and regeneration status of the species in question. (2) Several IUCN Red List (RL) parameters, useful for assessing the species' risk of extinction, are measured, including population counts, number of locations, extent and area of occurrence. (3) The IUCN RL parameters are used together with the other information gathered to set preliminary conservation priorities. (4) The analysis of utilization pattern is used to develop conservation actions specific to the environmental and socio-economic context. To test the applicability of this approach Boswellia spp. of Socotra island were analysed. Ground-rooted species (B. ameero, B. elongata and B. socotrana) were the most abundant and widespread and, according to the spatial analysis, were characterised by a geo-altitudinal zonation. However, the Weibull functions fitted on their stem diameters, and the absence or presence of only a small number of saplings highlighted a poor regeneration status. In the absence of conservation actions, these species will probably be subject to a progressive decline because of uncontrolled grazing. Of the four cliff-rooted species, which grow in sites that are less accessible to livestock, two (B. popoviana and B. dioscorides) were of lower conservation priority and may become the most numerically abundant. Conversely, the other two (B. nana and B. bullata), which may be threatened by stochastic events because of their reduced populations and small number of locations, were considered of very high priority. Different conservation actions were then identified for each species. In particular, for Boswellia species producing gum, the conservation-through-use action was discussed as a potential option.