Spatial dynamics of late succesional species under Pinus nigra stands in the northern Apennines (Italy).

The present study was carried out in three plots (20 × 50 m) established in even-aged Pinus nigra (Austrian black pine) stands located at approximately the same altitude, characterised by a similar age but showing different growth rate. Spatial distribution of natural regeneration (NR) were examined for each species by calculating Ripley’s K and Moran index and by analysing their age- and size structure. Although the species mixture of NR differed among the plots, Abies alba was always the most frequent. Results showed that the clumped distribution of NR prevails over the random one. The spatial autocorrelation analysis indicated at least two modes of space colonisation in line with clumped distribution of NR. In the first, the seedlings occupy different micro-areas in different times, whereas in the second the colonisation process occurs in the same micro-area for a more extended time. The resulting structure of NR is constituted by several small patches of different age in the first case or by patches with a similar uneven-aged structure in the second. These different colonisation patterns could be ascribed respectively to short-term disturbances such as sudden opening in the canopy and litter removal in the first case and to longterm disturbances or the presence of scarcely modifiable environmental factors such as soil characteristics and micro-morphology in the second. However, the colonisation process was always temporally limited. Age structures of the different species overlapped and were not related to stand basal area. As both colonisation patterns are likely to increase the structural and floristic complexity of the future stands, our data further confirm the important role played by Pinus nigra in recovering degraded lands.