Effect of browsing by ungulates on sapling growth of Scots pine in a Mediterranean environment: consequences for forest regeneration

The impact of mammalian herbivory on Scots pine (Pinus sylvestris L.) sapli ng performance was quantified in three native forests located in two Medite rranean mountains, the Sierra Nevada and Sierra de Baza (SE Spain). More th an 98% of the damage to terminal shoots was caused by goats and Spanish ibe x in Sierra Nevada and sheep in Sierra de Baza. Some 72% of the tagged sapl ings (n = 619) were browsed during at least 1 year of monitoring (1995-1997 ). There were between-forest differences in herbivory pressure. Moreover, t he herbivory pressure was significantly higher during a dry year (1995) tha n during wet ones (1996 and 1997). Overall, when browsing a sapling, ungula tes consumed almost 30% of its apical shoots, and 85% of saplings were brow sed more than once after establishment. As a consequence, ungulates severel y affected the Scots pine sapling growth rate, and therefore browsed saplin gs grew slower than saplings unbrowsed by ungulates. Thus, according to exp onential growth equations, the time necessary to attain a height threshold to escape from mammalian herbivores (150 cm height in our study forests) an d start reproduction was retarded by the herbivory up to 12 years. Ungulate s are a major factor hindering the natural regeneration and conservation of the last relict forests of Scots pines in SE Spain. (C) 2001 Elsevier Scie nce B.V. All rights reserved.