Cryptogam Recolonization after Wildfire: Leaders and Laggards in Assemblages?

Abstract

Cryptogams (restricted here to mosses, liverworts, and lichens) have no particular fire-adapted survival strategies and rely on airborne spores or propagules to disperse to new habitats. Following fire, recolonization by cryptogams relies on the propagule sources in regional or local remnant unburned areas and for suitable conditions in the burned area. We used species occurrences on a fire-age (i.e., time since burn) mosaic in jarrah (Eucalyptus marginata Donn ex Sm.) forest near Walpole in southwestern Australia to predict recolonization of cryptogam species in an adjacent forest block. The frequency of a species’ occurrence in a fire mosaic predicted the frequency of occurrence in the adjacent forest block that was subjected to an intense wildfire 7.5 years previously. The residuals from a 1:1 prediction were normally distributed when the total lichen and bryophyte flora were considered. Frequencies of species occurrence in the mosaic of fire ages and after recolonization of the wildfire were similar. We interpreted this to indicate that the composition of regional sources of propagules dominated assembly of cryptogam communities after severe fire, rather than community assembly resulting from filtering of species by dispersal ability or habitat suitability. We inferred that ecological requirements favored or disfavored recolonization by some components of the cryptogam flora. The residuals from the predicted frequency of colonizing species of liverworts positively correlated with the number of types of organic substrate they colonized. Lichens and mosses tended to have different preferences for substrates. The fire mosaic and the wildfire block 7.5 years after fire had similar compositions of substrates, so this could not account for differences in species frequency between the fire mosaic and the wildfire block. Differences at phylum level and substrate preferences affect the ability some species to recolonize after fire.Wildfires have the potential to denude areas of cryptogam species. Regional and landscape-scale mosaics of fire-ages reduce fuel biomass to mitigate intensity and spread of fires while retaining sources of cryptogam propagules and allowing opportunities for recolonization after fires.