Modeling Cedrus atlantica potential distribution in North Africa across time: new putative glacial refugia and future range shifts under climate change

Abstract

In recent years, species distribution models have been used to gain a better understanding of past and future range dynamics of species. Here we focuse on a keystone species of the North African forest ecosystem (Cedrus atlantica) by calculating a consensus model of the species current geographic potential distribution in North Africa, based on a weighted average method aiming to decrease uncertainty. The consensus model is obtained using seven species distribution model algorithms taking into account twenty-four environmental variables. The model is then applied to several past and future time slices. Past projections refer to the Middle-Holocene and the Last Glacial Maximum, whereas those of future are related to expect conditions around 2050 and 2070.We found that the current potential distribution of Cedrus atlantica is larger than its actual geographical distribution. For some explanatory variables the analysis revealed their importance for the species current distribution. Among all obtained models, that for the Middle-Holocene showed the maximum expansion of the species potential distribution. The Last Glacial Maximum model provided new putative glacial refugia of Cedrus atlantica, not shown by other mechanistic models and palaeorecord localities. Future projections revealed a significant and fast contraction with shifting in altitude of the species range, showing more fragmented areas and even species disappearance in many North African localities.These findings can help to restore cedar forests and conserve them by ex-situ strategies according to the future defined refugia in North Africa. Attention should be paid to the resolution of related output maps, the current biotic interactions and those that may arise under climate change.

Modeling of the current and future potential distribution of Atlas cedar (Cedrus atlantica) forests revealed shifts in the latitudinal, longitudinal and altitudinal range towards more humid conditions

“…Our findings expect a large decrease in the area occupied by the Atlas Cedar forests for the year 2070 (about 71.6-80.6% of the current range size). This is consistent with changes observed over the past inventories (Bouahmed et al, 2019). According to Boudy (1950), the area covered by Atlas Cedar forests in Algeria was about 300 km², whereas Quézel (1998) mentioned a surface area of 200 km².…”

“…Likewise, the long and intense periods of drought associated with warm stress could greatly alter the structure, composition and geographical distribution of forests resulting in significant mortality, especial in forests located in drought prone areas Linares et al, 2011). Recent studies suggest that these severe environmental changes, if keep worsening with same pace and trend, could lead to the extinction of the Atlas Cedar in the future (Arar et al, 2019;Bouahmed et al, 2019). Already, the situation of Atlas Cedar forests in almost all North African populations is alarming and requires urgent actions (Chenchouni, 2010;Thomas, 2013;Cheddadi et al, 2009Cheddadi et al, , 2017Linares et al, 2011;Abel-Schaad et al, 2018;Navarro-Cerrillo et al, 2019).…”

“…The future dry and warm climatic conditions, marked large decrease of precipitation and an increase of the temperature, drought duration and intensity (Allen et al, 2010), seem to be the main causes of Atlas Cedar dieback at the lower limit of its range. High-altitude migration associated with latitudinal range shift northward the humid climates are more pronounced in species habitats with arid and semiarid conditions (Quézel, 1998;Rhanem, 2010;Bouahmed et al, 2019). Drought triggers species shift towards high altitudes to look for favorable habitats.…”

“…The Atlas Cedar is an endemic species to mountains from Algeria and Morocco, where represents a keystone component of North African forests (Quézel, 1998;Cheddadi et al, 2009Cheddadi et al, , 2017Linares et al, 2011;Bouahmed et al, 2019). In Algeria, the species occurs in mountains of the Tellian and Saharan Atlas, where it has a scattered distribution controlled mainly by climatic and orographic traits (Quézel, 1998;Slimani, 2014).…”

“…As a result, the adaptive capacity of some Atlas Cedar populations has reached a critical limit, which led to their irreversible degradation (Slimani, 2014;Navarro-Cerrillo et al, 2019). Future predictions have shown an altitudinal refuge of Atlas Cedar forests to the mountain peaks, with high risk of stand extinctions at lower altitudes and drier conditions (Cheddadi et al, 2017;Abel-Schaad et al, 2018;Arar et al, 2019;Bouahmed et al, 2019).…”