A retrospective on the performance and viability of planted Southeastern-Mediterranean conifer forests as determined by abiotic factors controlling water availability

Abstract Water availability limits the growth of Mediterranean forests. Projected warming and drying could pose a risk to maintaining the cover of these forests. Water availability is primarily determined by precipitation, but other climatic, topographic, and edaphic factors also modify soil water content and evaporative demand. Here, we assessed how topographic aspect, elevation, and bedrock type interacted with precipitation to affect mature (>40 years) Pinus halepensis (native to the region, n = 96) and P. brutia (exotic to the region, n = 74) forests in Mediterranean Israel. Individual tree (height, stem diameter, and increment) and stand metrics (stem density, basal area, NDVI, natural regeneration, and understory growth) were analyzed with multiple regression models. The performance of P. halepensis forests was mainly and positively influenced by precipitation (40%–92% of explained variation), with additional positive influence of north- vs. south-facing aspects and negative influence of elevation. For P. brutia forests, precipitation × bedrock interactions and elevation (positive effect) were most significant for stand metrics, while aspect × elevation interactions were most significant for tree characteristics. Natural regeneration in P. brutia forests was generally minor, while regeneration of P. halepensis was substantial and responded mostly and positively to soft bedrock types. In both species, understory growth increased with precipitation. The differences between the two species could reflect their respective sensitivities to water limitations and to other climatic and/or topo-edaphic factors (e.g. temperature). Our study offers new insights on how abiotic factors influence forest performance, and we propose site- and species-specific recommendations for managing these water-limited forest ecosystems.