Threats and opportunities for an endangered tree species living in extreme environmental conditions: the case of Cupressus dupreziana (Camus).

Saharan cypress, Cupressus dupreziana (Camus), represents an extreme example of relict tree species on the verge of extinction. It was discovered in 1924 on the Tassili n'Ajjer Plateau (now Tassili n'Ajjer National Park, a World Heritage Site) in southern Algeria and it is listed by the International Union for the Conservation of Nature as one of the Earth's rarest tree species. According to the last inventory (2001) only 233 individuals still survive in an extremely severe habitat, characterized by prolonged drought periods and sudden flooding episodes. Most surviving trees are estimated to be 2500 years old or more, the youngest ones about 50, natural regeneration being difficult and sporadic. The main cause of Saharan cypress disappearing is primarily climate change; other threats are represented by human exploitation (cuttings, fire, carpentry, tourism, migration) and animal grazing (mostly goats). We performed a genetic study in order to describe the genetic diversity within the only existing natural population. We analysed nuclear genetic markers (microsatellites) on a sample of the Tassili n'Ajjer population (represented by 82 individuals) and on individuals collected in ex situ plantations in Tunisia and Israel. Results revealed a very low genetic diversity, the original populations being represented by almost a unique genotype. This suggests a possible clonal origin of the entire population, thus emphasising the vulnerability of this species. Low genetic diversity, difficulties for natural regeneration and seedling survival, and severe habitat conditions underline the need for particular conservation strategies and program for Saharan cypress. The presence of very old remaining individuals also represents a tool for investigating past climate and tracing past environmental condition.