Corticolous lichens as potential bioindicators of fire history : A study in the cerrado of the Distrito Federal, central Brazil.

The aim of this thesis is to investigate the potential use of epiphytic corticolous lichens as indicators of fire history in the cerrado (savannas) of central Brazil. Work was carried out at the Reserva Ecologica do IBGE and the Jardim Botanico de Brasilia, 33 km outside Brasilia D.F., in plots of cerrado denso within the 'Fire Project' area. Each plot was subjected to a specific prescribed burning regime, with study sites varying from a plot protected from fire for over 20 years to a plot burned every two years. The research was carried out in three stages: 1) a preliminary survey of plots with different fire histories, measuring variables about the lichen habitat and the lichen communities present in the habitats; 2) lichen sampling in plots with different fire histories, where collection and identification of lichen species took place; 3) sampling of the lichen genus, Bulbothrix, in plots with different fire histories, measuring abundance and size of individual lichens. Field techniques used included plotless sampling, and identification of lichens was carried out using taxonomic keys, both in the field and in the laboratory. The results show that fire is a major determinant of epiphytic corticolous lichen communities in cerrado denso vegetation. The abundance, distribution, and recolonisation of lichen communities can clearly be correlated with the frequency and behaviour, in terms of homogeneity and flame heights, of the fires that have occurred in each of the plots surveyed. Particular lichen species show differential sensitivities to fire frequency and behaviour, and as the length of the fire-free period increases, Bulbothrix individuals become greater in size. Using these various responses of lichens, at the community, population and species level, a Lichen Fire History (LFH) Key was constructed for estimating fire frequency, fire behaviour, and the 'time-since-the-last' fire. The LFH Key is then presented as a simple booklet to be used in the field