Ecological Impacts of Fire on Insects

Abstract

Fires engender change, but there are many limitations to predicting more specific ecological changes from any given fire. Whilst gross impacts – burned forests, removal of ground vegetation and litter – are abundantly clear, and the consistent consequences of planned management burns in familiar ecotopes (such as spring or autumn burns in North American prairies) create confidence in the outcomes, the more subtle (and largely invisible) impacts on the multitude of less heralded biota are almost always ignored and, so, unknown. A perhaps rather general, and unsurprising, finding from studies of the best-studied focal insect groups – and one likely to be relevant also to many other groups that have not been appraised to the same extent – is that the impacts of disturbances such as fire vary greatly in relation to both habitat characteristics and to features of the fire itself. The trajectories and duration of changes from both direct and indirect impacts reflect both changes in habitat structure and distribution, and in the subsequent outcomes in composition and function of the post-fire assemblages. For ants, changes in balance between the various functional groups can change dominance relationships, for example. The effects of any particular disturbance are intrinsically difficult to predict, and implications may be affected also by selectivity or biases of the sampling method(s) used. Indirect impacts and ‘flow-on effects’ may be the more important consequences of fires, following from initial impacts on habitat structure and local microclimates, food supply and dynamics, and interspecific competition. Ants demonstrate also that the variety of possible responses to fire cautions against seeking any real generality of how assemblages may fare. Different surveys of ants after fires in Australia have thus reported (1) decreased richness and abundance (Springett 1976); (2) increased richness and abundance (O’Dowd and Gill 1984); or (3) increased richness with decreased abundance (Andersen and Yen 1985). In Finland outcomes have included (4) near elimination of all ants (Puntilla and Haila 1996) and (5) initial decrease in abundance followed by increased abundance of some species and declines in others (Puntilla et al. 1994). Clarifying the processes underlying any of these patterns remains difficult, even after they have been adjudged to be realistic rather than chance outcomes. They are small consolation to managers seeking predictable outcomes from planned fires. The ecological consequences of such structural changes in assemblages (discussed further in Chap. 7) are correspondingly difficult to interpret and predict.