Colonization of Pinus halepensis in Mediterranean habitats: consequences of afforestation, grazing and fire

The expansion of P. halepensis from plantations into natural sites of high conservation value is becoming a frequent occurrence across the Mediterranean zone of Israel. We studied how colonization of Pinus halepensis in natural Mediterranean habitats is related to afforestation, cattle grazing and fire. The study was conducted in a Mediterranean garrigue (Shrubland) located in Ramat Hanadiv Nature Park, southern Mt. Carmel region, Israel. The study area (ca. 350 ha) was divided into cells (100 × 100 m) each of which was categorized with respect to distance from planted pines, grazing (grazed since 1990/ungrazed), fire (burned in 1980/unburned), and vegetation structure (garrigue, dense garrigue, dense woodland). The location of colonizing pines, typically three m or more in height, was determined using an aerial photograph. Density of colonizing pines decreased linearly with the distance from planted pines within 300 m from planted pines with a long tail that extended out to ca 1,000 m. Over 90% of the colonizing pines that were found were located within a distance of 300 m (56% of the park area) from planted pines. Colonization was about two times greater under grazing than without grazing. The effects of fire and of the interaction fire × grazing were found insignificant. A separate analysis reveled that colonization was about 2 times larger in patches of sparse woody cover than in those of dense cover. In conclusion, pine colonization was mainly determined by the proximity to seed sources. Additionally, pine colonization was enhanced by cattle grazing probably through reduction of the natural vegetation cover.