Effect of grazing on the population of Matteuccia struthiopteris at the southern limit of its distribution in Europe MARCO LANDI,*† ANTONIO ZOCCOLA,‡ VINCENZO GONNELLI,§ LORENZO LASTRUCCI,¶ CARLO SAVERI,* GIOVANNI QUILGHINI,‡ ALESSANDRO BOTTACCI** and CLAUDIA ANGIOLINI† *Ufficio Territoriale per la Biodiversità di Siena, Corpo Forestale dello Stato, Via Cassia Nord 7, 53100 Siena, †Department of Life Sciences, University of Siena, Via P.A. Mattioli 4, 53100 Siena, ‡Ufficio Territoriale per la Biodiversità di Pratovecchio, Corpo Forestale dello Stato, Via Dante Alighieri 41, 52015 Pratovecchio, §Istituto Professionale per l’Agricoltura e l’Ambiente “A.M. Camaiti”, Via S. Lorenzo 18, 52036 Pieve S. Stefano (AR), ¶Department of Biology, Laboratory of Plant Systematics and Phytogeography, University of Florence, Via La Pira 4, 50121 Firenze, and **Ufficio per la Biodiversità, Corpo Forestale dello Stato, Via Carducci 5, 00187 Roma, Italy Abstract We investigated the impact of deer on an isolated marginal population of Matteuccia struthiopteris and on its plant community in the northern Apennines, where in recent decades the species has decreased dramatically. Our experiment was based on a 6-year before and after control impact (BACI) design, comparing plots with deer grazing and plots where deer were excluded. Exclusion of grazing interacted with years, increasing the size of existing plants and favoring production of sporophylls. The yearly sequence of increase and decline of ramets and sterile leaves followed the same pattern in the two treatments. This indicated that their annual variation in growth depended on the sequence of more and less favorable years. Few and short plants were associated with grazing, whereas tall plants, shrubs, and tree regeneration were associated with fenced plots. The few plants to persist and dominate on heavily grazed areas were Oxalis acetosella and Cardamine species, while the genus Rubus and tree saplings were grazing- sensitive species in this forest. Tall herbaceous species increased in size in the fenced areas, however, M. struthiopteris drew more advantage in terms of growth of leaves, showing greater cover than other species. Thus, deer grazing is becoming a threat for the survival of M. struthiopteris in southern Europe where it is already threatened in the long term by climate change. Keywords: BACI design, deer, dynamics, fern, monitoring, plant community. Received 22 May 2014; revision received 26 August 2014; accepted 4 October 2014 Introduction The demographic structure and population dynamics of a plant species can be influenced by abiotic and biotic vari- ables. Plant–animal interactions, such as grazing, are major biotic factors (Bastrenta et al. 1995; Bissels et al. 2004). The influence may depend on the phenology and palatability of an individual plant, as well as on other factors, such as duration, frequency, and timing of grazing (McNaughton 1992; Bullock et al. 1994; Mysterud 2006; Lendvay & Kalapos 2014), and consequently long-term demographics data are important (Ohara et al. 2006). Populations of deer (family Cervidae) have been expand- ing throughout Europe and Italy in recent decades (Gortázar et al. 2000; Mattioli et al. 2001; Milner et al. 2006). Three species of deer are present in the Biogenetic Reserves of the Foreste Casentinesi (northern Apennines, Central Italy): red deer (Cervus elaphus) is the most abun- dant and is spreading (Lucchesi et al. 2011), roe deer (Capreolus capreolus) is found throughout the Casentine Forest and fallow deer (Dama dama) is marginal (Apollonio et al. 2004; Capitani et al. 2006). All three species are protected in the Biogenetic Reserves and Correspondence: Marco Landi Email: marcolandi.siena@gmail.com Plant Species Biology (2016) 31, 3–10 doi: 10.1111/1442-1984.12069 © 2014 The Society for the Study of Species Biology