Importance of internal refuges and the external unburnt area in the recovery of rodent populations after wildfire

Abstract

Rodent populations respond quickly to changes in habitat structure and composition resulting from disturbances such as wildfires. Rodents may recolonise burnt areas from individuals that survived the wildfire in ‘internal refuges’ or from the surrounding unburnt area (i.e. external colonisation). With the aim of assessing the relative role of both hypotheses on rodent abundance and foraging behaviour after fire, four Mediterranean burnt areas were studied using sampling stations at increasing distances from the perimeter of the burnt area. In the first 18 months after fire, the abundance of wood mice (Apodemus sylvaticus) and seed removal activity were highest near the perimeter. This suggests the weight of external sources (i.e. from unburnt areas) in the recolonisation process is higher than that of internal refuges. Algerian mice (Mus spretus) colonised the burnt areas from external sources. Vegetation cover was the most important variable affecting the relative abundance of rodents in recently burnt areas. After some months of vegetation recovery, rodent individuals that had dispersed from the unburnt area were likely to take advantage of sparsely occupied habitat with sufficient resources and, at this time, might use internal refuges. Therefore, understanding recolonisation dynamics is fundamental to anticipate biodiversity patterns and promote adaptive management.