Agriculture, Ecosystems and Environment 188 (2014) 72–79 Contents lists available at ScienceDirect Agriculture, Ecosystems and Environment j ourna l h omepage: www.elsevier.com/locate/agee Effect of lime and sewage sludge fertilisation on tree and understory interaction in a silvopastoral system N. Ferreiro-Domínguez a , A. Rigueiro-Rodríguez a , E. Bianchetto b , M.R. Mosquera-Losada a,∗ a Departamento de Producción Vegetal, Escuela Politécnica Superior de Lugo, Universidad de Santiago de Compostela, Campus Universitario s/n, 27002 Lugo, Spain b Consiglio per la Ricerca e la Sperimentazione in Agricoltura, Centro di Ricerca per la Selvicoltura CRA-SEL, Viale S. Margherita, 80 52100 Arezzo (AR), Italy a r t i c l e i n f o Article history: Received 25 April 2013 Received in revised form 1 February 2014 Accepted 9 February 2014 Keywords: Soil changes Trees pasture productivity Understory quality and fire risk a b s t r a c t The productivity of the components of a silvopastoral system could be limited by the low soil fertil- ity and the presence of shrubs in the land before planting. However, the understory vegetation can be modified by improving soil chemical properties when lime and organic fertilizers such as sewage sludge are applied. This study evaluated the effect of liming and the application of two doses of sewage sludge (50 kg total N ha -1 or 100 kg total N ha -1 ) on changes in soil chemical properties, tree growth and under- story production as compared to the no fertilisation treatment in a silvopastoral system established in a reforested area with Pinus radiata D. Don. The results of this experiment show that the improved soil fertility caused by liming and fertilisation with sewage sludge modifies the proportion of the herba- ceous/shrubs component in the understory, and promotes facilitation mechanisms which have a positive impact on the understory forage quality, tree growth as well as reducing fire risk. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Land use change is one of the main modifications that has occurred in Galicia (northern Spain) in recent years due to afforesta- tion promoted by the Common Agricultural Policy (CAP) (EU, 2005) through direct payments. In Spain, a total of 668,206 ha were afforested between 1994 and 2006, with about 10% of this area being located in Galicia (MAPA, 2006). Afforested land promotion mainly aimed at producing timber in Galicia (Pasalodos-Tato et al., 2009). However, factors such as fire risk and the need to obtain non- timber benefits make the search for other production alternatives necessary, such as silvopastoral systems in which trees, animals and pasture are integrated within the same area (Mosquera-Losada et al., 2008). The establishment of this type of agroforestry system not only diversifies products and benefits obtained, but also reduces fuel loads in the understory and thus the fire risk, due to the integra- tion of grazing in a forest (Rigueiro-Rodríguez et al., 2008). Galicia is one of the most fire-prone areas of Europe, accounting for approx- imately 35% of the area of Spain affected by forest fires in 2010 (MARM, 2010). Moreover, silvopastoral systems have been recently ∗ Corresponding author. Tel.: +34 600942437; fax: +34 982823001. E-mail addresses: mrosa.mosquera.losada@usc.es, silvopastoreo@yahoo.es (M.R. Mosquera-Losada). promoted by the EU (Council Regulation 1698/2005 (EU, 2005)), mainly due to many environmental advantages. Besides reducing the fire risk, silvopastoral systems also improve nutrient recy- cling, control soil erosion, promote biodiversity and increase carbon sequestration (Rigueiro-Rodríguez et al., 2008; Howlett et al., 2011; Mosquera-Losada et al., 2011a). Pinus radiata D. Don is the most commonly used exotic conifer for afforestation and reforestation in Spain, especially in the north, due to its fast growth of approximately 18–36 m 3 ha -1 year -1 , depending on the altitude, which occurs during a period from plant- ing to harvesting of about 25–35 years (Crecente-Campo et al., 2009). In Galicia, P. radiata D. Don covers an estimated area of 90,000 ha (11% of the total wooded area) (Xunta de Galicia, 2001). Moreover, this is one of the most widely used tree species in the establishment of silvopastoral systems in areas such as Australia, New Zealand and Chile (Peri et al., 2007; Benavides et al., 2009). In Galicia, soil acidity is a natural phenomenon derived largely from its humid climate, with higher rainfall than evapotranspira- tion during most of the year (Álvarez et al., 2009). In silvopastoral systems, soil acidity reduces plant vigour, rendering plants uncom- petitive with weeds and more susceptible to diseases, as well as limiting pasture production and causing uneven tree growth (Fageria and Baligar, 2008, Mosquera-Losada et al., 2012). There- fore, it is advisable to perform management activities such as liming and fertilisation to increase soil fertility and to neutralise http://dx.doi.org/10.1016/j.agee.2014.02.007 0167-8809/© 2014 Elsevier B.V. All rights reserved.