After the burn: factors affecting land snail survival in post-prescribed-burn woodlands

Abstract

Prescribed burning is commonly used for vegetation management. Whereas effects on vegetation are apparent, effects of these burns on ground-dwelling invertebrates are not. Land snails are especially susceptible to burns. Snail loss occurs directly from burns, but may also occur post-burn because of altered habitat conditions, although post-burn loss has not previously been tested. We used a field experiment to investigate snail survival and factors affecting survival in post-burn habitats. We exposed snails (Discidae: Anguispira alternata) to combinations of intact leaf litter, wood shelters, burned leaf litter, charred wood and ash added to leaf litter, to simulate a variety of post-burn conditions. Half of the replicates were watered every 3 d, which allowed detection of desiccation effects in comparison to ambient water conditions. The on-going drought resulted in high snail mortality. Watering increased survival and, as a consequence, growth. Snail mortality was higher in habitats with burned leaves and/or wood than in unburned habitats. Higher temperatures and rapid initial mortality in burned habitats, and increased survival with watering, indicated that the major cause of post-fire mortality was desiccation, rather than starvation. Contrary to expectations, snails in burned-leaf habitats grew more than snails in unburned habitats, and this greater growth was associated with higher soil pH. Snails surviving fires in burned woodland areas likely have high post-burn mortality. Our experiment highlights the negative impacts of burned woodland habitats on some nontarget organisms and indicates that prescribed burns should be avoided during exceptionally dry conditions.