Structure of old-growth and managed stands and growth of old trees in a Mediterranean Pinus nigra forest in southern Spain

Abstract

The structural attributes of an old-growth forest remnant of Pinus nigra subsp. salzmannii located in southern Spain and those from nearby managed forests were compared. Data on environmental and structural variables were collected in 74 forest inventory plots. Significant differences were tested by means of the Mann-Whitney U-test. A partial redundancy analysis was conducted to assess the relative contribution of both environmental and management variables in explaining differences in the current structure of old-growth and managed stands. Additionally, 25 trees of different size (range 25.4-98 cm) and age (67-803 years) were cored and dendrochronological methods and bootstrap linear regression were used to study the effects of size and age on tree growth. The old-growth stand exhibited a higher density of large trees (diameter at breast height >50 cm) and greater variability in tree size than managed stands, but lower tree density and, consequently, similar values of stand basal area and volume. Environmental variables accounted for 5.7 per cent of the total variance observed in structural attributes, while the contrasting silvicultural condition (old-growth vs managed) accounted for 10.2 per cent. Growth, measured in units of stand basal area, increased continuously with tree size.