Effects of forest plantations on the genetic composition of conspecific native Aleppo pine populations O. STEINITZ,* J. J. ROBLEDO-ARNUNCIO† and R.NATHAN* *Movement Ecology Laboratory, Department of Ecology, Evolution, and Behavior, The Alexander Silberman Institute of Life Sciences, Edmond J. Safra Campus, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel, †Departamento de Ecologı ´a y Gene ´tica Forestal, Centro de Investigacio ´n Forestal (CIFOR) – INIA, Ctra. de la Corun ˜a Km 7.5, 28040 Madrid, Spain Abstract Afforestation is a common and widespread management practice throughout the world, yet its implications for the genetic diversity of native populations are still poorly understood. We examined the effect of Aleppo pine (Pinus halepensis) plantations on the genetic composition of nearby conspecific native populations. We focused on two native populations in Israel with different levels of isolation from the surrounding plantations and compared the genetic diversity of naturally established young trees within the native populations with that of local native adults, using nine nuclear microsatellite markers. We found that the genetic composition of the recruits was significantly different from that of local adults in both populations, with allelic frequency changes between generations that could not be ascribed to random drift, but rather to substantial gene flow from the surrounding planted Aleppo pine populations. The more isolated population experienced a lower gene-flow level (22%) than the less isolated population (49%). The genetic divergence between native populations at the adult-tree stage (F st = 0.32) was more than twice as high as that of the young trees naturally established around native adults (F st = 0.15). Our findings provide evidence for a rapid genetic homogenization process of native populations following the massive planting efforts in the last decades. These findings have important implications for forest management and nature conservation and constitute a warning sign for the risk of translocation of biota for local biodiversity. Keywords: dispersal, gene flow, genetic homogenization, non-indigenous gene pool, Pinus halepensis, planting Received 12 September 2011; revision received 1 November 2011; accepted 2 November 2011 Introduction Biodiversity threats associated with interspecific hybrid- ization between invasive and native species have been widely recognized, and their potential for extinction of native species has been demonstrated (Rhymer & Sim- berloff 1996; Mooney & Cleland 2001). Yet, the potential threats of genetic introgression from non-indigenous conspecifics into native populations have received much less attention (but see Laikre et al. 2006; Robledo- Arnuncio et al. 2009; Byrne et al. 2011). The growing capabilities for artificial massive translocation of plants and animals for agricultural, recreational and environ- mental purposes in the modern era calls for careful con- sideration of the genetic implications of spatial redistribution of biota. Plantations of forest trees are common in large areas of the world and their area is rapidly expanding (Paquette & Messier 2010). Seeds used for plantations are usually collected from a few seed trees that exhibit favourable phenotypes and are grown in nurseries (Larsen 1995; Perevolotsky & Sheffer 2009), bypassing the selection pressure on seed estab- lishment. Moreover, plantations are often established in close proximity to native inter-fertile conspecific popu- lations using seeds from non-local and sometimes dis- tant sources (Perevolotsky & Sheffer 2009; Robledo- Arnuncio et al. 2009; Byrne et al. 2011). Correspondence: Ofer Steinitz, Fax: 972 2 6584655; E-mail: ofer.steinitz@mail.huji.ac.il Ó 2011 Blackwell Publishing Ltd Molecular Ecology (2012) 21, 300–313 doi: 10.1111/j.1365-294X.2011.05394.x