Typology and synecology of aspen woodlands in the central-southern Apennines (Italy): new findings and synthesis

Abstract

In order to review and complete our knowledge of the typology and synecology of the aspen communities from the central-southern Apennines, ten original relevés were performed on the Gargano plateau and a set of 35 relevés assigned to four community types (HP: Holco mollis-Populetum tremulae; MP: Melico uniflorae-Populetum tremulae; FP: Fraxino orni-Populetum tremulae; GP: Geranio versicoloris-Populetum tremulae) were assembled from literature. These relevés along with several environmental variables either measured or estimated were involved in cluster and ordination analyses. The relevés from Gargano formed a distinctive cluster and were assigned to a new community type (SP: Stellario holosteae-Populetum tremulae ass. nova), which can be considered an Adriatic synvicariant of HP that is distributed in similar habitats (doline bottoms) but on the Tyrrhenian escarpment. At low levels of floristic similarity, the grouping of relevés in two clusters induces a sharp separation between the aspen communities distributed in the central Apennines (MP and FP) and those from the southern Apennines (SP, HP and GP), which is mainly due to compositional differences in the regional species pool. The ordination scores of relevés were best related to terrain slope, soil nitrogen, elevation, air temperature, light availability and, to a lesser extent, to soil moisture and reaction. Unlike MP and GP that appear the most mesophilous, the FP stands display a slightly more xerophilous and acidophilous character induced by the steeper slopes on which they occur. The HP habitat is the driest and lightest very likely because of the open overlying canopy, in contrast to MP stands featuring a high shrub cover. The highest occurrence of nitrophilous species was observed in SP and MP. The management of these pioneer woods should be aimed at conservation, as they play an important role in the recovery of forest herb diversity along the ecological succession towards hardwood forests.