Bryophytes, lichens and dead wood in young managed boreal forests

The decrease in old-growth forests threatens the diversity of a range of organisms. Only a small portion of the forested area in Sweden is formally protected and the majority of unprotected forests are young (<70 years). The objective of this thesis is to provide a deeper understanding of the production forest landscape, with special focus on young forests and to increase the knowledge about man-made substrates. Moreover, this thesis investigates the long-term survival chances of forest bryophytes and lichens, and gives insight into the dispersal biology of bryophytes. After clear-cutting, the remaining dead wood consists of logging residues (slash), logs, snags and man-made high and low stumps. Results from this thesis show that the effect on dead wood supply of harvesting slash for biofuel is most significant for slash and logs. Sixty-five percent of the lying dead wood volume left after clear-cutting was piled for extraction. In addition, 36 % of the remaining dead wood was removed, including a significant volume of coarse dead wood. On stumps in different age classes, bryophytes showed a tendency to increase in richness over time, whereas lichens colonized stands in early succession more rapidly and had an earlier peak in species richness. As a dispersal mechanism for bryophytes living on stumps, ants inhabiting the same substrates were shown to passively carry bryophyte diaspores for a significant period of time. This result sheds light on the complexity of species dispersal. In adjoining young and old forest stands, red-listed bryophytes and lichens were more abundant in the old stands. This difference disappeared when the amount of substrate available was taken into account. When the young stands were positioned north of the old, the bryophytes were equally frequent in both forest stages, indicating that the aspect of a clearcut matters. In conclusion, young forests have the potential to host a high diversity of species. Research on young natural and managed forests is needed to formulate science-based conservation strategies in managed forest landscapes

Forests regenerating after clear-cutting function as habitat for bryophyte and lichen species of conservation concern.

The majority of managed forests in Fennoscandia are younger than 70 years old but yet little is known about their potential to host rare and threatened species. In this study, we examined red-listed bryophytes and lichens in 19 young stands originating from clear-cutting (30–70 years old) in the boreal region, finding 19 red-listed species (six bryophytes and 13 lichens). We used adjoining old stands, which most likely never had been clear-cut, as reference. The old stands contained significantly more species, but when taking the amount of biological legacies (i.e., remaining deciduous trees and dead wood) from the previous forest generation into account, bryophyte species number did not differ between old and young stands, and lichen number was even higher in young stands. No dispersal effect could be detected from the old to the young stands. The amount of wetlands in the surroundings was important for bryophytes, as was the area of old forest for both lichens and bryophytes. A cardinal position of young stands to the north of old stands was beneficial to red-listed bryophytes as well as lichens. We conclude that young forest plantations may function as habitat for red-listed species, but that this depends on presence of structures from the previous forest generation, and also on qualities in the surrounding landscape. Nevertheless, at repeated clear-cuttings, a successive decrease in species populations in young production stands is likely, due to increased fragmentation and reduced substrate amounts. Retention of dead wood and deciduous trees might be efficient conservation measures. Although priority needs to be given to preservation of remnant old-growth forests, we argue that young forests rich in biological legacies and located in landscapes with high amounts of old forests may have a conservation value

Positive edge effects on forest-interior cryptogams in clear-cuts

Biological edge effects are often assessed in high quality focal habitats that are negatively influenced by human-modified low quality matrix habitats. A deeper understanding of the possibilities for positive edge effects in matrix habitats bordering focal habitats (e.g. spillover effects) is, however, essential for enhancing landscape-level resilience to human alterations. We surveyed epixylic (dead wood inhabiting) forest-interior cryptogams (lichens, bryophytes, and fungi) associated with mature old-growth forests in 30 young managed Swedish boreal forest stands bordering a mature forest of high conservation value. In each young stand we registered species occurrences on coarse dead wood in transects 0–50 m from the border between stand types. We quantified the effect of distance from the mature forest on the occurrence of forest-interior species in the young stands, while accounting for local environment and propagule sources. For comparison we also surveyed epixylic open-habitat (associated with open forests) and generalist cryptogams. Species composition of epixylic cryptogams in young stands differed with distance from the mature forest: the frequency of occurrence of forest-interior species decreased with increasing distance whereas it increased for open-habitat species. Generalists were unaffected by distance. Epixylic, boreal forest-interior cryptogams do occur in matrix habitats such as clear-cuts. In addition, they are associated with the matrix edge because of a favourable microclimate closer to the mature forest on southern matrix edges. Retention and creation of dead wood in clear-cuts along the edges to focal habitats is a feasible way to enhance the long-term persistence of epixylic habitat specialists in fragmented landscapes. The proposed management measures should be performed in the whole stand as it matures, since microclimatic edge effects diminish as the matrix habitat matures. We argue that management that aims to increase habitat quality in matrix habitats bordering focal habitats should increase the probability of long-term persistence of habitat specialists

Conflicting demands and shifts between policy and intra-scientific orientation during conservation research programmes

Conservation scientists must meet the sometimes conflicting demands of policy and science, but not necessarily at the same time. We analysed the policy and intra-scientific orientations of research projects on effects of stump extraction on biodiversity, and found shifts over time associated with these demands. Our results indicate that uncertainties related to both factual issues and human decisions are often ignored in policy-oriented reports and syntheses, which could give misleading indications of the reliability or feasibility of any conclusions. The policy versus intra-scientific orientation of the scientific papers generated from the surveyed projects varied substantially, although we argue that in applied research, societal relevance is generally more important than intra-scientific relevance. To make conservation science more socially relevant, there is a need for giving societal relevance higher priority, paying attention to uncertainties and increasing the awareness of the value of cross-disciplinary research considering human decisions and values.Future Forest

Forest indicator species correlate only weakly with richness of red-listed species and perform poorly compared to simple stand variables

In the face of worldwide biodiversity declines, a variety of conservation measures are being implemented to preserve species and their habitats. Due to imperfect ecological knowledge and limited economic resources, these conservation measures often involve the use of shortcuts. Among these, the use of indicator species – organisms whose characteristics are used as an index of other ecosystem attributes – has been proposed as a tool for conservation planning and monitoring in a range of environments. The overarching aim of this study was to evaluate the usefulness of signal species as indicators of high species richness among species of special conservation concern in a managed boreal landscape. To address these questions, we surveyed wood-decay fungi, bryophytes, beetles, and forest structure in a large number of stands characterized by varying management histories within a geographically restricted area, and related the occurrence of signal species and basic forest characteristics to the number of red-listed species. Our study, involving a large number of forest stands covering a wide gradient of forest characteristics, showed that indicator species commonly used in forest conservation planning do indicate red-listed species, at least to some extent: When considering stands of all ages, the presence of signal species was associated with higher richness of red-listed species, and the number of signal species correlated positively with that of red-listed species. However, when restricting the analyses to older forests, we could not detect any correlation between signal species and the richness of red-listed species. When we included information on forest structure in the analyses we found that, for predicting the richness of red-listed species across all of our study stands, the amount of coarse woody debris and stand age were much better predictors than the presence-absence or number of signal species. Moreover, adding information about signal species to models based on these forest variables did not bring any substantial improvements to our capacity to predict the number of red-listed species. This suggests that – in this particular setting – information about signal species does not contribute with information about red-listed species beyond that already derivable from forest stand measurements.peerReviewe