Replacement of pine by eucalypt plantations: Effects on the diversity and structure of tree assemblages under land abandonment and implications for landscape management

Abstract

The conversion of natural and semi-natural forests into plantations is an increasing trend across European landscapes under abandonment. In Northwest Iberian Peninsula, current land use changes, namely neglected management (or even abandonment) of maritime pine (Pinus pinaster) and blue gum eucalypt (Eucalyptus globulus) stands by individual landowners, represents a major challenge for landscape planning and management. The consequences of these changes for within-stand tree diversity and structure are still under-investigated. Here, we evaluate how fine-scale diversity and spatial structure of tree assemblages in the core area of stands change with land conversion. Fifty stands were selected in a farming landscape of Northwest Portugal. At the center of each stand, a 100 m2 plot was surveyed for tree species richness and structural diversity, diameter at breast height (DBH) and spatial location of individual trees. Spatial distribution patterns of trees were evaluated using autocorrelation tests and point pattern analyses. Overall, the interior of pine stands showed higher tree diversity, with more heterogeneous DBH structure and complex patterns of tree distribution, compared to eucalypt and even abandoned mixed stands. Such differences seem to result both from the inherent characteristics of the dominant tree species, and from the differential management applied within each type of forest mosaics. Therefore, active landscape management in the study area should be promoted, particularly focusing on pine co-existence with eucalypt stands in the same landscape as a sustainable strategy to achieve both conservation and production goals.