Silvopastoral systems established with Pinus radiata D. Don and Betula pubescens Ehrh.: tree growth, understorey biomass and vascular plant biodiversity

Abstract

In the European Union, the majority of afforestation is carried out on former agricultural land. This afforestation causesfundamentalchangesinecosystemstructureandfunctioning,withthetreesinterceptinglightandprecipitation, producing litterfall and competing for soil nutrients. All of these effects could potentially have a negative impact on understorey biomass and vascular plant biodiversity in a relatively short time span. This study aims to evaluate the effects of afforestation with Pinus radiata D. Don (Monterey pine: pine) and Betula pubescens Ehrh. (Downybirch:birch),establishedattwodifferentdensities(2500and833 trees ha 21 )andsownwithtwodifferent pasture mixtures (Dactylis glomerata L. + Trifolium repens L. + Trifolium pratense L. and Lolium perenne L. + T. repens L. + T. pratense L.), on understorey biomass, alpha plant biodiversity, life cycle type (annuals vs. perennials) and beta biodiversity over a period of 11 years. Pine showed better development than birch throughout the study, although both species were very sensitive to tree density. While increasing density increased pine height and decreased pine diameter, both aspects of birch development were reduced by higher tree densities. Aboveground biomass increased throughout the study. Alpha plant biodiversity was drastically reduced under pine established at high density, 11 years after afforestation. However, the similarities in species richness, species composition and the low beta growth rates found under pine at low density, and birch at both high and low density suggest that, in these cases, the choice of canopy tree has little consequence for understorey biodiversity at this stage of system development.