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.) sapling performance was quantified in three native forests located in two Mediterranean mountains, the Sierra Nevada and Sierra de Baza (SE Spain). More than 98% of the damage to terminal shoots was caused by goats and Spanish ibex in Sierra Nevada and sheep in Sierra de Baza. Some 72% of the tagged saplings (n = 619) were browsed during at least 1 year of monitoring (1995-1997). There were between-forest differences in herbivory pressure. Moreover, the herbivory pressure was significantly higher during a dry year (1995) than during wet ones (1996 and 1997). Overall, when browsing a sapling, ungulates consumed almost 30% of its apical shoots, and 85% of saplings were browsed more than once after establishment. As a consequence, ungulates severely affected the Scots pine sapling growth rate, and therefore browsed saplings grew slower than saplings unbrowsed by ungulates. Thus, according to exponential growth equations, the time necessary to attain a height threshold to escape from mammalian herbivores (150 cm height in our study forests) and start reproduction was retarded by the herbivory up to 12 years. Ungulates are a major factor hindering the natural regeneration and conservation of the last relict forests of Scots pines in SE Spain. (C) 2001 Elsevier Science B.V. All rights reserved.