Partial cutting can enhance epiphyte conservation in temperate oak-rich forests

The strongly increasing demand for biofuel from forests poses new challenges for biodiversity conservation. Methods that may combine biofuel production with conservation goals need to be tested for various forest types. One possible conservation-oriented management alternative is partial cutting of closed canopy oak-rich forests (may also be called conservation thinning). Such cutting may counteract succession and restore a semi-open canopy structure, which may favor epiphytes. We evaluated this possibility by surveying the epiphyte community of lichens and bryophytes on large oaks in 24 oak-rich temperate forests in southern Sweden. Treatment plots, and reference plots with no cutting, were surveyed before, and 6years after cutting. In the treatment plots, about 25% of the basal area was harvested, and mainly small and intermediate sized successional trees were removed. We detected significant positive effects of partial cutting on species density for both lichens and bryophytes. The additional variation in light influx at tree level (after the cutting) could not explain the change in species density. The increase in density of lichen species was highest on oaks with small trunk diameter and on oaks with deep bark crevices. The pooled frequency of species of conservation concern increased after the cutting, but the change in species composition was weak; colonization events occurred over mean minimum distances of 63.5m to the nearest potential source tree (n=22 events and 9 species). Overall, we found significantly higher colonization rates, and significantly lower extinction rates per tree for lichens in the treatment plots. We conclude that partial cutting influenced epiphytes of large oaks positively, as was the case for several other organism groups at the same study sites (previous studies). A mild form of biofuel harvesting may represent sustainable resource-use in these forests, compatible with conservation. However, part of the forest should be kept untouched for species vulnerable to changes in microclimatic conditions, and for evaluation of long-term effects.