Fragmentation modulates the response of dichotomous landscapes to fire and seed dispersal

Abstract

Contagious processes such as fire and seed dispersal may affect landscape structure, composition and dynamics, and are in turn modulated by structural landscape attributes. Vegetation-fire self-reinforcing processes that lead to the dominance of either pyrophyllic or pyrophobic vegetation are well documented worldwide, but it remains unclear how the interaction between spatial aggregation and contagious processes influences the dynamics of dichotomous landscapes. We subjected landscapes composed by patches of pyrophyllic and pyrophobic cells to increasing frequencies of random ignitions to assess which spatial configuration may promote long-term coexistence (i.e. resilient landscapes), and which ones may lead to dominance by either community (i.e. alternative states). Our results indicate that aggregation favors the persistence and resilience of pyrophyllic communities, whereas the resilience of pyrophobic ones is enhanced by landscape fragmentation. Aggregation promotes larger fires whereas fragmentation favors seed dispersal, these two processes being related to total pyrophyllic core area, and total pyrophobic edge respectively. We propose that highly fragmented landscapes may facilitate the recovery of pyrophobic communities from fire events by affecting both the dynamics of fire and colonization: large numbers of pyrophobic patches function as an immolating network of partial firebreaks that reduce fire size, providing more opportunities for colonization and facing a lower individual risk of patch destruction through fire. Landscape attributes that reduce flammability at the local scale, such as rocky outcrops, creeks, wetlands and roads may fragment pyrophyllic communities thereby enhancing the resilience of pyrophobic ones. The resilience of pyrophyllic communities, on the other hand, will mainly depend on the size of their largest patches, even at low ignition frequencies.