Soil and climate effects on Pinus pinea growth in inland Alentejo

Abstract

Pinus pinea is widely distributed in the Mediterranean basin. In Portugal occurs mainly in southwest coastal areas, but it can also be found in inland southern Portugal. It is known that the site (soil and climate) can influence this forest tree species development. The goal of this study was to analyse the development of stands under different soil and climate conditions in inland Portugal. Four plots located in Evoramonte (1 plot), Évora (2 plots) and Mértola (1 plot) were established in stands of circa 30 years, and dendrometric, soil and climate variables were collected. Plot stand structure was evaluated with absolute density measures, diameter and height distributions and structure indices. Soil map units and physical and chemical soil properties were determined. Air temperature and precipitations were evaluated monthly, quarterly and annually, between 2014 and 2020. Absolute density measures were similar for all plots, diameter and height distributions were representative of even aged stands, and structure indices indicated stable trees with balanced crowns. Soils show several differences between plots in texture, soil organic carbon, carbon and nitrogen ratio, cation exchangeable capacity, and extractable nutrients. There were differences in thermal amplitudes and precipitation levels between the plots, which were reflected in the growth of Pinus pinea. The plots with lower water stress showed a trend towards higher tree growth. The plot with lower annual precipitation and higher temperature had the lowest growth. In all plots, the imbalance between potassium and magnesium, and iron and manganese, might have also affected tree growth.