Fire acting as an increasing spatial autocorrelation force: Implications for pattern formation and ecological facilitation

Fire is an indissoluble component of ecosystems, however quantifying the effects of fire on vegetation is a challenging task as fire lies outside the typical experimental design attributes. A recent simulation study showed that under increased fire regimes positive tree-tree interactions were recorded (Bacelar et al., 2014). Data from experimental burning plots in an African savanna, the Kruger National Park, were collected across unburnt and annual burn plots. Indices of aggregation and spatial autocorrelation of the distribution of trees between different fire regimes were explored. Results show that the distribution of trees under fire were more clumped and exhibited higher spatial autocorrelation than in unburnt plots. In burnt plots spatial autocorrelation values were positive at finer scales and negative at coarser scales potentially indicating co-existence of facilitation and competition within the same ecosystem depending on the scale. The pattern derived here provides inference for (a) fire acting as an increasing aggregation & spatial autocorrelation force, (b) tree survival under fire regimes is potentially facilitated by forming patches of trees and (c) scale-dependent facilitation and competition coexisting within the same ecosystem with finer scale facilitation and coarser scale competition.