Decadal effects of forest fire on biodiversity and browsing : a comparison between wildfire and prescribed burning

Abstract: The role of fire as a natural disturbance in northern European boreal ecosystems has largely disappeared due to effective fire suppression with large consequences for fire-associated biodiversity. Recently, prescribed burns have been introduced as a conservation action that aims to promote biodiversity. Not only fire regimes but also wildlife densities have been heavily impacted by human activities. Forest fires can result in pervasive changes with early successional forest stages, large amounts of deciduous trees, and newly formed deadwood, habitats which are largely missing in the managed boreal landscape. In this thesis, I evaluate decadal post-burn effects on community composition of wood-inhabiting polypores, beetles, bird and mammal species, vegetation differences, and moose browsing levels. I compare three unusually large wildfires in northernmost Sweden with nearby unburnt forests and five prescribed burns. I found differences in community composition among all taxa a decade after burning and a distinct turnover of beetles the years immediately postburn. No wildlife species had higher visitation frequency in the wildfire areas, suggesting that burnt areas did not necessarily add much habitat in a landscape already dominated by early successional forest stages. Unburnt forests were also important for red-listed polypores, reindeer, and western capercaillie. However, wildfire, in contrast to prescribed burning, did provide large amounts of deadwood and rich field layer vegetation impacting biodiversity and functional trait composition of beetles and polypores and changing moose forage availability and browsing levels. Thus, for prescribed burning to mimic wildfire and better emulate wildfire impacts of biodiversity, I emphasise the importance of higher tree mortality.