Alexandro Caruso

Influence of substrate age and quality on species diversity of lichens and bryophytes on stumps

Abstract Stumps from the last felling constitute a large proportion of dead wood in young managed forests. Yet, the knowledge of the diversity of stump-inhabiting organisms is poor. We studied the importance of substrate age and quality to lichen and bryophyte diversity on the cut surface of stumps in south-central Sweden. In total, we found 53 lichens and 35 bryophytes on 449 Norway spruce stumps in a forest stand chronosequence of four age classes: 4–5, 8–9, 12–13 and 16–18 years old stands. The influence of substrate age and substrate quality on species diversity differed between lichens and bryophytes. Lichen species richness was higher for age classes 2–4 compared to age class 1, whereas bryophyte richness was higher in age classes 3–4 than in 1. Further, lichen richness increased with increasing stump height and the presence of surface structural components (chairs and levels), which together with decay also influenced lichen species composition. Conversely, increasing stump height and the presence of levels decreased bryophyte richness, which in turn increased with increasing decay, surface area and number of surrounding trees and shrubs. Only decay explained differences in bryophyte species composition. Stumps in this region seem more important to overall lichen diversity, because there were on average more lichen species per stump and we only found common bryophytes but several uncommon lichens. The different responses of lichens and bryophytes to age and substrate variables indicates, however, the importance of including several organism groups in species diversity studies of dead wood.

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.

Importance of different tree fractions for epiphytic lichen diversity on Picea abies and Populus tremula in mature managed boreonemoral Swedish forests.

Abstract Knowledge of the canopy lichen flora of managed forests is poor, but needs more focus since, for example, slash (tops, branches and twigs) harvest for biofuel may pose a threat to epiphytic lichen diversity. This study compared lichen species richness, density and composition between stems, tops, branches and twigs of mature Norway spruce (Picea abies) and aspen (Populus tremula) in managed boreonemoral forests in south–central Sweden. The stems were also compared with the slash fractions pooled together. All comparisons were made separately for each tree species. In total, 30 lichen species were found on Norway spruce and 46 on aspen. No significant differences in species richness or species density between fractions were found for Norway spruce, whereas aspen tops were significantly less species rich and species dense than the other fractions. Moreover, aspen slash was significantly more species dense than the stem. The lichen species composition of the stems clearly differed from that of the tops, branches and twigs in both tree species. Thus, lichen communities other than those removed with stems by conventional forestry are removed from the stands owing to slash harvest. However, these species are rather common and widespread in Sweden. The impact of slash harvest on the epiphytic lichen flora may therefore be of minor importance in forests established after clear-cutting or on former arable land.

Different patterns in species richness and community composition between trees, plants and epiphytic lichens in semi-natural pastures under agri-environment schemes

Agri-environment schemes (AES) have been established to counteract negative effects of agricultural intensification on e.g. semi-natural pastures and meadows. The efficiency of most AESs have, however, been poorly evaluated. We evaluated the success of a Swedish AES for the management of semi-natural pastures by comparing species richness and composition of vascular plants (except trees), epiphytic lichens and trees among pastures receiving higher (high value pastures) and lower levels of AES paymens (general value pastures). There was no difference in the number of tree species among high and general value pastures, even though AES regulations allow a maximum of 60 and 100 trees/ha in general and high value pastures, respectively. High value pastures had, however, a higher number of plant and epiphytic lichen species than common value pastures. Moreover, a higher number of pasture specialist plant species were indicative of high value pastures than of general value pastures. No lichen species indicating high value pastures are associated with habitats with low canopy cover (such as e.g. pastures). Finally, tree identity was an important factor for explaining the number and composition of epiphytic lichen species. Our study highlights that species groups can respond differently to agri-environment schemes and other conservation measures. Even though the effects are the desired on the diversity of one assessed taxon, this is not always the case for non-target organism groups.

Transient trade-off between climate benefit and biodiversity loss of harvesting stumps for bioenergy

To replace fossil fuel and thereby mitigate climate change, harvesting of wood such as stumps for bioenergy will likely increase. Coarse deadwood is an important resource for biodiversity and stumps comprise the main part of the coarse deadwood in managed forests. We provide the first integrated analysis of the long‐term climate and biodiversity impacts of a whole landscape. We simultaneously project climate and biodiversity impacts of harvesting stumps to substitute for fossil coal, assuming scenarios with different proportions of the landscape with stump harvest (10, 50, 80%) the coming 50 years. A life cycle approach was used to calculate future global temperature changes and future metapopulation changes in six epixylic lichens. Metapopulation dynamics were projected using colonization and extinction models based on times series data. Harvesting stumps from ≥50% of the clear‐cut forest land benefits climate with a net global temperature reduction >0.5·10−9 K ha−1 after 50 years if assuming substitution of fossil coal. For all scenarios, using stump bioenergy leads to immediate (within 1 year) reductions in temperature of 50% compared to using fossil coal, increasing to 70% reduction after 50 years. However, large‐scale stump harvest inflicted substantial metapopulation declines for five of six lichens. High stump harvest levels (≥50%) put common lichens at risk of becoming red‐listed following the IUCN criteria. The net temperature reduction (cooling effect) from substituting fossil coal with stumps harvested for bioenergy increased over time, while lichen metapopulations stabilized at lower equilibria after two to three decades. This indicates that trade‐offs between climate and metapopulations of commons species are transient, where climate benefits become more prevalent in the long term. As both objectives are important for meeting (inter‐)national climate and biodiversity targets, integrated analyses such as this should be encouraged and urged to guide policymaking about large‐scale implementation of stump harvest.