Postfire resprouting and recruitment of Quercus humboldtii in the Iguaque Mountains (Colombia)

Abstract

Anthropogenic disturbances, including wildfires, threaten the diversity of tropical Andean ecosystems. However, the response of tropical Andean plant communities to wildfires in human-modified landscapes has to be discovered. Quercus humboldtii is the southernmost species of this genus in the Neotropics and is almost exclusively distributed in Colombia. While the extent of Q. humboldtii forests has decreased recently, to what time these results from the species' inability to thrive under the current climate and disturbance regimes are still being determined. In this study, we describe post-fire resprouting and acorn and seedling density in and around Q. humboldtii forest patches in the Iguaque mountains in Colombia. We discuss the implications for the conservation and restoration of these forests. Resprouting probability was high in burned trees two years after the fire (ca. 80%). Resprouting ability depended on fire severity and tree size. The proportion of trees resprouting from the stump was related to the severity of fire damage and tree size. Acorn density was higher in burned than unburned areas and depended on the slope, distance to the forest edge, and distance to the nearest oak. Conversely, the density of healthy acorns was low across all sites, particularly in burned areas. Seedling density was relatively high in unburned areas, but seedlings could not withstand recurrent fires. The density of acorns and seedlings decreased in the periphery of forest patches. Despite the strong impact of fire on forest structures, Quercus humboldtii adults may withstand the current fire regime thanks to their strong capacity for vegetative and sexual regeneration. However, the ability of this species to establish in areas where oaks are no longer present is scarce. As Q. humboldtii forest cover and spatial continuity have decreased in response to the increasing frequency of wildfires, the current fire regime represents a threat to the recovery of this species. Our results have important implications for the management of Q. humboldtii and Andean forests as they emphasize the need to control the severity and frequency of wildfires and to use assisted regeneration to restore Q. humboldtii forests in degraded areas.