Recent forest area increase in Europe: expanding and regenerating forests differ in their regional patterns, drivers and productivity trends

Abstract

In Europe, forest area is increasing. These recently established forests can be classified into regenerating after disturbances or expanding into agricultural areas after abandonment. We used European Space Agency land cover maps and MODIS data to investigate which socioenvironmental drivers influenced recent forest expansion and regeneration in Europe from 1992 to 2015 and to compare their productivity by means of the Enhanced Vegetation Index (EVI). Our results showed that forest area increased in Europe by 1.4% from 1992 to 2015. The 66% of this forest area increase corresponded to forest expansion mostly in Mediterranean and temperate regions, while regeneration (34%) dominated in boreal areas. Forest area and land cover diversity in 1992 were the main drivers of local forest area increase from 1992 to 2015. Forest expansion occurred on the warmer zones far from urban areas in the boreal region while it was the opposite in temperate and Mediterranean areas. On the other hand, forest regeneration showed mostly a positive relation with the distance to urban areas and water availability but no relation with temperature. The EVI values in 2015 were higher in expanding than in regenerating forests except in the warmer and drier bioclimates of Europe. These EVI trends suggest a higher productivity of expanding forests, except in areas where they cannot benefit from biological and physicochemical legacies of abandoned agricultural soils for tree growth, owing to water shortage. In sum, our results highlight that recent forest area increase in Europe is mostly caused by forest expansion into former agricultural areas but this is mostly occurring in less productive (warmer and drought-prone) bioclimates where advantages of agricultural legacies may not occur. Ultimately, this casts doubts whether there may be a limit for the role of forest expansion into agricultural areas for carbon sequestration in the long term.