Abstract
Biodiversity is in decline and therefore alternative forest management approaches have gained interest. One of such approaches is uneven-aged silviculture, which has been suggested to better maintain mature or late-successional forest characteristics and species assemblages than even-aged silviculture. Therefore, it is assumed that uneven-aged silviculture can be a useful tool for landscape planning to benefit biodiversity. Nevertheless, there is a lack of empirical studies regarding bird responses to uneven-aged silviculture in north European boreal ecosystems. Here we test the similarity of bird assemblage structure between mature forests within even-aged silviculture (‘thinning’) and uneven-aged silviculture (‘selective felling’). In spring 2018 we censused breeding birds using territory mapping in 14 thinned stands and 14 selectively felled stands. We found higher abundance and different bird assemblages in thinned stands compared to selectively felled stands. The pied flycatcher, tree pipit and great tit contributed most to the variation of bird assemblages between the two management types. None of the species were more abundant in selectively felled than in thinned stands. According to functional guilds, the abundance of ground breeders, ground feeders and generalists was higher in thinned stands than in selectively felled stands, similar results were found in the species richness of long-distance migrants, ground nesters, secondary cavity nesters and generalists. Independent of management type, time since treatment had an overall effect on assemblage structures, the mistle thrush and wren were negatively correlated with time since treatment, while the chiffchaff showed the opposite trend. Our results suggest that at these locations and given this particular type of uneven-age management, selective felling is less suitable for some abundant generalists than even-aged forest stands reaching the thinning age. However, the results from this study does not provide clear management recommendations aiming to maintain biodiversity, as management guidelines should be based on red-listed species and not on common generalists. Nevertheless, our results stresses the urgent need for more long-term studies comparing the effect of these different silvicultural strategies on bird assemblages.
Highlights
Biodiversity is in decline as a result of human-induced habitat loss, fragmentation and structural homogenization at multiple spatial scales (Vitousek et al 1997, Butchart et al 2010, Isbell et al 2013)
This study suggests that selective felling is less suitable for some abundant generalists than even-aged forest stands reaching the thinning age
These common species are currently not listed as high-priority species from a conservation perspective but the pied flycatcher has declined significantly over the last two decades in Northern Sweden (Ram et al, 2017) and may gain conservation interest in the future
Summary
Biodiversity is in decline as a result of human-induced habitat loss, fragmentation and structural homogenization at multiple spatial scales (Vitousek et al 1997, Butchart et al 2010, Isbell et al 2013). A widely adopted framework for counteracting negative impact of forest management on biodiversity is the natural disturbance emulation hypothesis (Pickett and White 1986, Attiwill 1994). Forest dynamics in boreal forest were naturally driven by a variety of other small scale disturbance agents (e.g. wind, pathogens, and insects) that maintained a more or less continuous forest cover with smaller gaps (Kuuluvainen 2009, Bergeron et al 2014) This has triggered interest in uneven-aged silviculture which maintains a continuous forest cover and is often referred to as irregular forestry or continuous cover forestry. Uneven-aged silviculture can be implemented in various ways e.g. by varying the
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