Herbivory and seedling establishment in Pyrenean forests: Influence of micro- and meso-habitat factors on browsing pressure

Abstract

Browsing damage is among the most determinant factors that limit the establishment of tree seedlings in forests. In some areas, this process leads to massive mortalities that can reduce or even completely prevent the regeneration of some tree species. Mediterranean mountain forests have undergone during the last decades important changes in land-uses that have significantly altered the type and abundance of herbivore populations. In this study we assessed the impact of current grazing conditions in forest regeneration using a set of experimental plantations established in the Eastern Pyrenees in areas visited by domestic livestock (cattle and horses) and wild ungulates (mainly roe deer and chamois). We analyzed during 4 years the role of seedling species and size, mesohabitat (elevation and type of forest cover) and microhabitat (herbaceous cover, distance to shrub, and light availability) on the browsing-induced mortality of more than 500 seedlings of Pinus sylvestris, Pinus uncinata, Betula pendula and Abies alba, the most common tree species in the study area. Browsing-induced mortality for the three conifer species was much lower (<15%) than the one observed for B. pendula (>40%) and depended on both microhabitat - mainly on the distance to protective elements such as shrubs; and mesohabitat, with an interaction between the elevational belt (site) and the type of forest cover (gaps vs. understory). In the subalpine belt, browsing on A. alba and P. uncinata was higher during summer at plots located in the forest understory whereas, during winter, it was higher at plots located in gaps. The study shows that both mesohabitat and microhabitat can exert an effect on the patterns of plant damage by herbivores, providing useful information to adapt forest management in areas particularly exposed to them

This research was primarily supported by the Spanish Ministry of Science and Innovation via the projects DINAMIX (AGL2009-13270-C02) and RESILFOR (AGL2012-40039-C02-01) and by the European Commission through the Marie Curie IRSES project “NEWFORESTS”. The Spanish Ministry of Science provided LC with support through a Ramon y Cajal contract (RYC-2009-04985), and the Spanish Ministry of Education provided AA with support through a predoctoral grant (FPU Program – AP2007-01663). The authors are particularly grateful to A. Bargués, S. Martín, L. Ivorra and M. Pallarés for their invaluable work during field sampling and laboratory processing. F. Cano helped us to find the most suitable forests for this study, and the Socarrel team kindly offered their facilities during the fieldwork stage. We also thank the ‘Parc Natural del Cadí-Moixeró’ and the ‘Montellà i Martinet’ municipality for kindly giving permission to access the park and sample the data.