AFFORESTATION OF AGRICULTURAL LAND WITH PINUS RADIATA D. DON AND BETULA ALBA L. IN NW SPAIN: EFFECTS ON SOIL PH, UNDERSTOREY PRODUCTION AND FLORISTIC DIVERSITY ELEVEN YEARS AFTER ESTABLISHMENT

Afforestation of abandoned agricultural lands has been the main change in land use over the past decade in Europe. However, the impact of tree species and understorey management on production and plant diversity over the medium- and long-term has not been thoroughly studied. This paper aims to evaluate the effects of an afforestation of Pinus radiata D. Don and Betula alba L. on soil pH, understorey production and plant diversity and life cycle type (annuals vs. perennials) managed with different soil fertilisation treatments over a period of 11 years. The results show an acidification of the soil 11 years after establishment, better vertical growth and diameter of pine compared with birch as usually happens in the region and important variation in the biomass production and composition of the understorey below both tree species. Understorey species remained similar during the first 5 years below both canopies. However, species richness (S) was drastically reduced under Pinus radiata D. Don plantation compared to Betula alba L. (Spine¼2 vs. Sbirch¼17) after 11 years of tree establishment at a very high density (2500 trees ha 1). Inorganic and organic fertilisation also caused a reduction in floristic diversity. Soil pH, pasture production and floristic understorey plant diversity are better preserved under autochthonous broadleaves, which increased the multiple uses of recently afforested lands in the short- and medium-term. In the European context of high need for sawn wood, the use of autochthonous broadleaved tree species like Betula should be promoted due to their better sustainability