Spatial Conservation Prioritization of Persian Squirrel Based on Habitat Suitability and Climate-Induced Forest Mortality Risk
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1. Introduction
Continued habitat degradation attributable to climate change, human population expansion, and unregulated development represent the pre-eminent threats to biodiversity [1,2]. Consequently, effective habitat management and conservation stand as pivotal considerations in species preservation [3]. Forest ecosystems, acknowledged as critical habitats for a myriad of species, encompass over 80% of terrestrial biodiversity and span approximately one third of the Earth’s land area [4,5]. However, both the quantity and quality of forest habitats are undergoing persistent diminishment in numerous regions [4]. The accelerating transformation and exploitation of these ecosystems on a global scale have outpaced their capacity for sustainable regeneration, as indicated by the 3% reduction in global forest coverage between 1990 and 2015, reported in a comprehensive study conducted by the Food and Agriculture Organization [6].
Concurrently, a discernible escalation in climate-induced forest mortality events has been extensively documented in diverse regions worldwide, including Africa [7], Europe [8,9,10,11,12], America [13,14,15,16,17,18,19], and Asia [20,21,22,23,24,25]. Given the noticeable response of forests to contemporary climatic shifts, climate-induced forest mortality is poised to emerge as a significant global phenomenon in the foreseeable future [26,27,28,29]. Consequently, species reliant on forest ecosystems, particularly those exhibiting a pronounced dependency on these habitats, confront an array of threats arising from habitat loss. This is especially important for rare tree species (squirrels and dormice), which are sensitive to changes in the taxonomic and ecological composition of forest stands [30,31]. This predicament is anticipated to be particularly acute in arid regions, where forest ecosystems are already operating at the threshold of water availability.
The Persian or Caucasian squirrel (Sciurus anomalus) exemplifies a species profoundly reliant on forest habitats [32,33]. Despite being categorized as “Least Concern (LC)” with a decreasing population trend in the IUCN Red List [32,33,34] and being listed under Annex IV of the European Habitats Directive [35], the species confronts formidable challenges. These include illegal hunting, habitat fragmentation, and habitat loss attributed to agricultural expansion, fire, timber harvesting, and drought [33,34,36]. The Persian squirrel’s distribution spans Southeast Europe to Southwest Asia, encompassing three recognized subspecies: Sciurus anomalus anomalus, Sciurus anomalus pallescens, and Sciurus anomalus syriacus [32,33,37]. S. a. pallescens holds special ecological importance as the subspecies exclusive to the Zagros range in Iran and Iraq. It stands as the sole tree squirrel within the Sciuridae family in this region and is recognized as a keystone species [38,39]. This designation is attributed to its substantial influence on ecosystem patterns and processes [32,39]. The Persian squirrel’s pivotal role in the regeneration of the Iranian Zagros forest is particularly evident through its winter activities, including the collection and subterranean storage of oak fruits. This underscores the ecological significance of the species [32].
Iran’s forests are estimated to cover approximately 14 million hectares; a total of 41% of this expanse (approximately 6,000,000 hectares) comprises the Zagros Mountain Chain, spanning 11 provinces from Northwest to Southeast Iran (Figure 1). Dominated by coppiced oak species constituting nearly 70% of the flora, these ecologically and genetically rich Zagros forests provide a habitat for diverse wildlife, including the Persian squirrel. Since the turn of the millennium, a notable incidence of forest mortality has been observed throughout the entire Iranian Zagros mountains. A recent assessment conducted by the Iranian Forests, Range, and Watershed Management Organization (IFRWMO) indicates that approximately 25% of all Zagros plant life-forms, including trees, shrubs, and grasses, have experienced varying degrees of forest mortality.
Given the escalating trend of forest mortality in the Zagros Mountains and the pronounced reliance of the Persian squirrel as a keystone species on these habitats, the imperative of formulating a comprehensive conservation plan is evident. Due to resource constraints, spatial prioritization emerges as the initial step in this endeavor. Thus, the objectives of this study encompass (1) identifying suitable habitats for the Persian squirrel, (2) delineating habitat regions susceptible to forest mortality, and (3) prioritizing the conservation of suitable habitats based on insights gained from the first two objectives. Finally, we define and map the optimal spatial allocation of forest conservation area for the Persian squirrel in the Zagros Mountains.
4. Discussion
We employed 15 distinct species distribution models (SDMs) to forecast both habitat suitability and forest mortality risk, ensuring a comprehensive analysis of predictive accuracy. All models exhibited an AUC exceeding 0.5, indicative of predictive performance surpassing random chance. Notably, 14 of the models demonstrated either an excellent or very excellent prediction, with AUC values falling within the ranges of 0.8 to 0.9 and 0.9 to 1. However, the Bioclim model, while exhibiting AUC values exceeding 0.5, did not reach the benchmark of excellence. Given the nuanced variations in model accuracies and the absence of identical behavior among them, a weighted ensemble approach was judiciously employed to amalgamate the diverse predictions of individual models [67]. The robust accuracy observed across the models not only underscores their reliability but also affirms the trustworthiness of SDMs in predicting forest mortality risk, thereby validating their utility as a predictive tool. This corroborates previous recognitions of SDMs’ efficacy in risk prediction [68,69].
Within the context of this study, the Persian squirrel is posited as a surrogate for the broader Zagros forest biodiversity, emphasizing its status as a keystone species in the Iranian Zagros forest with significant impacts on ecosystem patterns and processes [32,39,70]. The pivotal role of the Persian squirrel in the regeneration of Iranian Zagros forest, particularly through the collection and subterranean storage of oak fruits during winter, further underscores its ecological significance [32,70]. The potential diminution in habitat suitability and population of this keystone species could reverberate negatively, impacting other species and fundamental ecosystem processes [70]. Consequently, the conservation of Persian squirrel habitats and populations assumes a crucial role in fostering ecosystem health and biodiversity within the study forests. Monitoring fluctuations in Persian squirrel populations could serve as a valuable indicator of ecosystem dynamics in the ensuing years.
Moreover, a feedback loop linking climate change and forest mortality exists, wherein climate-induced forest mortality may accelerate climate change and global warming. Given that 55% of terrestrial carbon is stored in forests, climate-induced forest mortality could influence wildfire frequency, duration, extent, and intensity, further contributing to fire-induced tree mortality [27,71,72,73,74,75]. Without effective conservation measures, climate-induced forest mortality poses a formidable threat to future forest habitat integrity [26,27,28,29].
In response to these challenges, conservation endeavors should adopt a dual focus, addressing the protection of intact forest habitats and the restoration of degraded ones [76,77]. Our findings reveal that a substantial proportion of habitats classified under the very high conservation priority class (approximately 27%) has already been impacted by forest mortality, necessitating restoration interventions. Conversely, other conservation priority classes remain unaffected by forest mortality and therefore require proactive protection and preventative measures rather than restoration initiatives. This nuanced conservation approach is essential for mitigating the impacts of climate-induced forest mortality and fostering the long-term sustainability of the ecosystem.
Ecological restoration constitutes a multifaceted process aimed at facilitating the recovery of ecosystems that have undergone degradation, damage, or destruction [78]. Globally, diverse restoration initiatives have been increasingly implemented, targeting the restoration of both ecosystem services and biodiversity [4,77,78]. These initiatives span a spectrum of restoration actions, from passive measures that involve the removal and prevention of disturbances to allow for natural recovery—termed “passive restoration”—to more interventionist approaches that actively accelerate and manage the recovery process, referred to as “active restoration” [76,77,78].
Given the apparent irreversibility of forest mortality in the Zagros forests under prevailing climatic conditions and considering the triage concept for judicious resource allocation in conservation and management, the primary focus should be on preserving and safeguarding intact habitats. Acknowledging that Zagros forest mortality, similar to phenomena observed globally [26,27], is predominantly climate-induced, implementing measures to enhance adaptation to climate change [79] emerges as a viable consideration. Climate change adaptation involves making adjustments in ecological, social, and economic systems in response to the impacts of climate change. Strategies for climate change adaptation can be integral components of comprehensive sustainable forest management plans, which serve as risk management mechanisms.
In tandem with climate change adaptation efforts, preventing deforestation, curbing the expansion of cultivated lands, and regulating the harvest of oak fruits by local communities within conservation priority classes are essential measures to protect both the Persian squirrel and the integrity of the forests. The approach employed for spatial conservation prioritization in this study is deemed transferable and applicable to other forested regions grappling with forest mortality, thereby offering a systematic framework for effective conservation strategies in the face of ecological challenges.
The comprehensive analysis presented in this study highlights the critical interplay between climate-induced forest mortality, habitat suitability for the Persian squirrel, and the associated conservation priorities within the Zagros forests of Iran. Our spatial prioritization approach, integrating habitat suitability and mortality risk assessments, provides a nuanced perspective essential for informed conservation and management strategies.
5. Conclusions
In conclusion, our study sheds light on the alarming climate-induced mortality trends within the Zagros forests of Iran and their profound implications for the Persian squirrel, a species intricately tied to these ecosystems. The urgency of our findings cannot be overstated, as approximately 62% of surveyed forests face mortality risks, with a significant portion categorized as high and very high risk. By allocating conservation priority classes to habitats based on their suitability and risk levels, we offer a strategic framework for directing limited resources towards the most critical areas. The allocation of priority classes underscores the need for a nuanced approach, where restoration actions are targeted where feasible, and protective measures are employed to safeguard habitats not yet subjected to irreversible decline.
In line with the principles of conservation triage, our approach acknowledges the practical constraints and directs attention to areas where intervention can yield the most significant benefits. As we navigate the complexities of climate-induced threats to biodiversity, our study underscores the importance of adaptive conservation strategies that evolve with the dynamic nature of ecosystems. By focusing on the preservation of intact habitats, we contribute to the resilience of the Persian squirrel and the broader ecological balance of the Zagros forests. It is our hope that these findings will inform and guide conservation practitioners, policymakers, and stakeholders in developing effective strategies to mitigate the impact of climate-induced mortality and secure a sustainable future for these vital ecosystems and their inhabitants.
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