Identification of the main environmental determinants and modeling the potential distribution of Aleppo pine, and the impact of climate change in Tunisia

Abstract

The distribution of forest ecosystems in Mediterranean region are largely under the influence of environmental conditions such as climate and orographic parameters. This study aimed to understand the relationship between Aleppo pine (Pinus halepensis Mill.) occurrences and environmental conditions at a regional scale in Tunisia. However, it is important to mention another type of threat that is likely to trouble this forest ecosystem in the future; these are the consequences of climate change. In this study, the Maxent software, based on sample point of the Aleppo pine and the environment variables was used to model the current distribution and to predict the impact of climate change. The model developed showed good predictivity with AUC > 0.90 indicated the prediction model’s high credibility and accuracy. Furthermore, we examined the variable importance and contribution to the prediction results, to distinguish the effect of different variables on the potential distribution area. The results showed that the variables relevant to Aleppo pine distribution area are precipitation, altitude, slope and temperature Annual Range. To investigate the potential effects of climate change on the target species, we used Maxent modeling algorithm for two representative concentration pathways, lower emission scenario (RCP 2.6) and higher emission (RCP 8.5) climate scenarios in 2050 and 2070. A comparison of the current vegetation cover with the current potential distribution highlights a fragmentation of the natural habitat of the Aleppo pine in Tunisia. Indeed, the current species distribution represents only 25% of its suitable area. Human activities had induced severe changes in the natural Aleppo pine forest ecosystems. Future predictions expect an extension of the areas classified as favorable to the Aleppo pine. In response to climate changes, the Aleppo pine may display two contrasted tendencies: a progressive evolution in the north, and a regressive evolution in the southern limit. However, the expansion of suitable areas may be more important than loss of habitat suitability. The future climate could convert areas that are currently not suitable for Aleppo pine (humid sub-humid) into very suitable.

Keywords: Aleppo pine, climate and orographic parameters, climate change, Maxent, Tunisia