From First Generation of Pine Monocultures to Mixed-Forest Ecosystems: Biotic and Abiotic Determinants of Pine Forests’ Dynamics in Mediterranean Israel

Abstract

Two key processes constitute the dynamics of planted pine forests (Pinus halepensis, P. brutia) in Mediterranean Israel: pine regeneration and reestablishment of native broad-leaved tree species (broad-leafs). These two processes are regulated mainly by aridity, overstory cover and grazing. Pine forests in Israel have been planted throughout the semiarid to dry-subhumid climate zones (Wetness Index = 0.13–0.50) and over variable geology and topography. They exhibit a range of pine overstory cover levels (Leaf Area Index = 1–3.5) and are subjected to variable grazing by cattle, sheep and goats. Pine regeneration is mainly observed in P. halepensis stands with annual rainfall >350–400 mm. Above this threshold, the extent of pine regeneration is highly unpredictable and strongly influenced by bedrock type, being considerably higher on soft than on hard calcareous bedrock. Pine regeneration is negatively affected by overstory cover and grazing, which limit survival and growth of recruits. Pine regeneration in P. brutia stands is currently limited, though overstory thinning appears effective in promoting this process. Broad-leafs reestablishment occurs where annual rainfall exceeds 450 mm; it increases sharply with rainfall and is higher on north- than on south-facing slopes. Broad-leafs recruitment is positively influenced by overstory cover while the effect of grazing is minor. Aridity, overstory cover and grazing all restrict the growth rate of broad-leaf recruits. Based on our understanding of these processes, management guidelines are proposed for converting the manmade pine monocultures into complex, sustainable mixed-forest ecosystems.