Life after fire: the impact of fire on species composition and diversity in coastal heathlands

Abstract

Fire prone coastal heathlands are widespread, and range from naturally fire prone Mediterranean-type heathlands, to the anthropogenic heathlands of north-west Europe. Regardless of its source, fire is an important disturbance factor in these systems. This thesis investigates the effects of fire on the species diversity and composition of two heathland systems; one in south-eastern Tasmania and one in western Norway. I ask whether two important species groups in heathland, plants and carabids depend upon, and to what extent they exhibit adaptations to, recurrent fire. The results suggest that heathlands and their species clearly respond to fire. In the absence of fire, south-east Tasmanian heathlands have seen a 32% reduction in area and an overall reduction in plant species richness since c. 1970. The species composition has transitioned from a dominance of small shrubs and non-woody species, to taller species, thus altering the vegetation structure. In Norwegian heathland, rotational burning was found to increase species richness and turnover of carabids, and lead to the formation of distinct species assemblages associated with different phases of the Calluna life cycle. Heathland specialists were found more often in recently burnt heath, while generalists occurred across all post-fire successional stages. Plants in both study areas exhibited germination responses that imply sensitivity to fire-cues. Typical Tasmanian heathland species were found more often in heat-treated soil seed bank samples, while more invasive species germinated from unheated samples. The Norwegian germination experiment showed that many heathland plants respond positively to smoke and ash cues, although responses varied among functional groups. There were also indications of a trait-driven response to fire in carabids. Moisture-loving and generalist predator species were identified as more fire-sensitive, while collembolan specialists without moisture preferences were more common in recently burnt patches. These findings have implications for the management of these study sites, but also for coastal heathlands in Tasmania and north-western Europe in general. In these areas, burning is generally necessary to maintain vegetation, promote germination in a range of heathland species, and keep plant and carabid diversity high. Fire needs to increase in frequency relative to present-day fire regimes if Tasmanian coastal heathlands are to persist. Burning should also continue in Norwegian coastal heathlands, to create a fire mosaic with a bias to younger phases, thereby maximizing carabid diversity.