Improving Sustainable Forest Management of Pinus halepensis Mill. Mid-Aged Stands in a Context of Rural Abandonment, Climate Change, and Wildfires

Abstract

Pinus halepensis Mill. covers most lowland forests on limestone soils and semiarid to sub-humid climates in the Mediterranean basin. It is considered a key species in climate change due to its pioneer nature, versatility, and flexibility. Moreover, its industrial potential is an additional incentive to promote forest management to increase its quality and productivity while contributing to other environmental and social objectives. However, there is a considerable gap in science-based knowledge on the effects of different silvicultural treatments on Pinus halepensis stands. Thus, this research compares the impact of four different treatments (light thinnings, strong thinnings, transformation to uneven-aged, and diameter-driven uneven-aged) on even-aged mid-rotation stands of Pinus halepensis in terms of growth, vulnerability, and resilience to extreme weather events, regeneration, and shrub cover. The effects of four treatments are evaluated in 12 research plots of 0.49 ha each (three per treatment) and contrasted with the other three non-managed control plots. Light and strong thinning treatments show better growth—at least in the short term—and stock results than those reported in the reference yield tables. Transformation to uneven-aged treatment shows advantages in maintaining periodic growth, regeneration, and stability. In addition, it offers an alternative for steep slope stands, smallholders, and extended narrow-aged estates to speed up the desirable balanced age class distribution. Diameter-driven uneven-aged treatment implies greater vulnerability to extreme weather events during the first years and considerable stock reduction while offering faster and taller tree regeneration. A dual regeneration pattern of Ulex parviflorus Pourr is observed in addition to post-fire regeneration in the case of sudden and well-distributed tree cover reduction around 40% of the canopy due to the transformation into the uneven-aged stand. An observation period longer than a decade of the research plots will confirm these first conclusions.