Natural reforestation is changing spatial patterns of rural mountain and hill landscapes: A global overview

摘要

The present landscape structure and function is the result of centuries of changes produced both by natural processes and human driving forces. For centuries many mountain and hillside areas have been the subject of deforestation to create space for agriculture and grazing, although the abandonment of traditional mountain agriculture has produced a natural forest recovery in many regions of the world. The physical changes imposed on the landscape by the development of secondary woodland have brought both positive and negative consequences, depending on the geographical and economic context and on the scale of the sites. Among the ecological problems caused by natural reforestation, one of great interest is the reduction of open spaces resulting in a loss of landscape heterogeneity and mosaic features. This review paper focused its attention on landscape metrics or indices that are frequently used to assess the structural characteristics of the landscape and to monitor changes in land use: mean patch size (MPS), connectivity (CONN), boundary length (BL) and the patch number (NP). Through the analysis of 52 selected papers and 53 case studies, we identified the main gaps in current knowledge, providing directions for further research. Most of the reviewed studies focused only on a portion of the spatial attributes that we were interested in and only 32 case studies reported accurate data both on forest expansion rate and time range analyzed in the study area. We conclude that the study of changes in all the spatial attributes considered within the same case study is a key to explain ecological consequences in mosaic cycles or in stochastic dynamic landscapes that emerged from the interplay of several processes, and to predict and explain their spatial and temporal characteristics. The current knowledge of how changing spatial attributes affect biodiversity, habitats, and ecosystem functions is limited by the scarcity of studies that explicitly consider the shifting in time of the four spatial attributes together.