Effects of selection cutting on the abundance and fertility of indicator lichens Lobaria pulmonaria and Lobaria quercizans.
Abstract
Although selection cutting is probably less harmful to forest ecosystems than clear cutting, its effects on biodiversity remain largely unexplored. We investigated the previously unstudied effects of selection cutting on the abundance and fertility of two dominating species of epiphytic lichens, Lobaria pulmonaria and Lobaria quercizans, in a northern hardwood forest of New Brunswick, Canada. Twenty-eight forest stands were selected representing two contrasting silvicultural treatments: fairly recent selection cuts (5-9 years) and 'uncut' stands that had been subjected to low-intensity single-tree cutting at least 35 years ago. Within each stand, we quantified the abundance and fertility of lichens on 36 trees together with selected forest stand variables. Although both species had survived harvesting, the abundance of L. quercizans and L. pulmonaria was four and five times higher, respectively, in uncut stands than in selection cuts. The most important predictive factors for lichen abundance at the stand level were total basal area and canopy closure, which were much lower in selection cuts. Furthermore, the abundance of both species at the tree level was significantly correlated with tree size. Most interestingly, fertile L. quercizans and L. pulmonaria were, respectively, five and 26 times more frequent in uncut stands. In addition, for L. pulmonaria the fertility frequency was only 3% in selection cuts, compared with 37% in uncut stands. The fertility of both lichen species was strongly correlated with their abundance at the tree level. Synthesis and applications. Our results indicate that selection cutting has a strong impact on the abundance and fertility of these two Lobaria species, and that studies ignoring fertility may underestimate the negative effects of forestry on lichens. To reduce the negative effects we have three recommendations. (i) Large trees from old seral stages should be retained during selection cuts. (ii) The cutting cycle should be extended and the basal area removed should be reduced. These actions would improve the microclimate, increase the amount of suitable habitat and prolong the time window for lichen colonization in selection cuts. (iii) Some mature deciduous forest stands should be protected at the regional scale. This would promote the long-term persistence of large, sexually reproductive lichen populations and concurrently benefit all species tightly linked with mature hardwood forests.