Per-Anders Esseen

Epiphytic Lichen Biomass in Managed and Old-Growth Boreal Forests: Effect of Branch Quality

To maintain biodiversity in managed forests we must understand the patterns and processes that regulate the occurrence and dynamics of species in undisturbed eco- systems. We compared biomass and species composition of canopy lichens on 180 lower branches of Norway spruce (Picea abies) in three pairs of old-growth and managed (se- lectively logged) stands in northern Sweden (30 branches per stand). The purpose was to evaluate the effect of substrate quality (branch characteristics) on patterns of lichen biomass for two different growth forms (foliose and fruticose). Old-growth stands had six times higher lichen mass per spruce branch, and two times higher expressed as percentage of branch mass, compared to mature stands of managed forest. Lichen mass was strongly related to mass, diameter, and age of branches. Fruticose, pendulous species (Alectoria sarmentosa and Bryoria spp.) were highly sensitive to forest practices. In contrast, type of forest had no significant effect on foliose species. Species number per stand was the same (15 species) in both types of forest, but there were marked differences in the relative abundance of different lichen groups. Results suggest that limited amount of substrate (i.e., small branches) available to lichens, and young branches, pro- viding only a short time for lichen colonization and growth, are important factors limiting epiphytic lichen abundance in managed forests. Conversion of old-growth forest into young, managed stands will lead to a significant reduction in epiphytic lichen mass. This in turn may probably affect nutrient cycling in forests and has negative consequences for animals that utilize canopy lichens as food, shelter, or nesting material.

Boreal Forests—The Focal Habitats of Fennoscandia

This chapter deals with the question of maintaining biological diversity in the boreal forests of Fennoscandia, i.e. the Scandinavian Peninsula and Finland. The boreal coniferous forest, or taiga, is the dominant biome, with a latitudinal extension from 56°N to 69°N (Fig. 7.1). The total area of the Fennoscandian forest amounts to more than 50 million ha, of which 13% occurs in Norway, 40% in Finland and 47% in Sweden (Nordic Statistical Secretariat, 1990). Man has utilized the boreal forest, for various purposes, during a very long period of time (Tenow, 1974). However, the most intense utilization has occurred during the last 300 years in connection with the development of the forest industry. At present, Fennoscandian forestry is amongst the most mechanized and efficient in the world. The result is that almost all forest land is now used for production of saw-timber and wood pulp. This has a tremendous impact on the structure and function of the boreal ecosystem. Cutting of old-growth forest and other consequences of forestry have a destructive impact on a large number of boreal organisms, despite the fact that some species are favoured by forest management. The result is decreasing populations for many hundreds of plants and animals, as reflected in recent Red Data lists (Andersson et al., 1987; Ahlen & Tjernberg, 1988; Databanken for hotarer och Naturvardsverket, 1991).

Treefall disturbance maintains high bryophyte diversity in a boreal spruce forest

(1) The effect of disturbance on diversity patterns of cryptogams has received little attention. We compared bryophyte diversity in thirty-seven patches formed by uprooting with that of the undisturbed forest floor in a north Swedish Picea abies forest. (2) Bryophyte diversity and species richness were significantly higher in patches with soil disturbance compared with undisturbed forest floor. Species richness and diversity were highest at intermediate patch ages, but disturbed patches had an altered vegetation composition for at least 100 years. (3) Four causes of high bryophyte diversity in disturbed patches are proposed: (i) uprooting creates space for bryophyte colonization that is free from potential competitors; (ii) disturbed patches have high habitat heterogeneity; (iii) within-patch disturbance continues long after patch formation through erosion from the tip-up mound; and (iv) the small patch size implies a short distance to potential sources of bryophyte diaspores which should increase the chance of establishment. (4) Both early and late successional bryophytes establish shortly after an uprooting has occurred. This suggests that no facilitation by early species is necessary before late successional species invade. (5) Results show that treefall disturbances are important for both the persistence of colonists and the maintenance of high bryophyte diversity in boreal-forest ecosystems. Consequently, the studied system has clear parallels with the gap-phase systems widely recognized in temperate and tropical forests.

Invertebrate communities in boreal forest canopies as influenced by forestry and lichens with implications for passerine birds

Abstract To investigate the effects of commercial forestry on canopy-living invertebrates in the boreal forest, we sampled branches in northern Sweden for invertebrates and lichens from paired natural spruce Picea abies forests and adjacent managed forests that were selectively logged. The study was conducted during late winter, when invertebrate abundance is lowest, and when small differences may be critical to foraging birds. Natural forests had significantly greater invertebrate diversity than managed forests and nearly five times as many invertebrates per branch. The number of large invertebrates (> 2·5 mm, the minimum prey size for foraging passerine birds) was consistently higher in natural forests, with spiders (Araneae), Lepidoptera and Diptera larvae dominating. The number and biomass of invertebrates were related to the abundance of lichens even after controlling for sampling location and branch size. Other studies have implicated forestry in the decline of non-migratory passerine birds in northern Europe through the destruction and fragmentation of forests, but our study indicates that it may also reduce foraging habitat quality through a reduction in lichen abundance.

Growth and vitality of epiphytic lichens

Abstract We tested the hypothesis that changed microclimate at induced forest edges causes reduced growth of epiphytic lichens. Two foliose, green algal lichens were transplanted to the lower canopy of a mature Picea abies forest at six distances (2, 6.25, 12.5, 25, 50 and 100 m) from a clearcut. The biomass growth in Platismatia glauca (6.2% in 16 months) was 41% higher than in Lobaria pulmonaria (4.4%). We found no growth reduction near the forest edge. In contrast, the highest growth in both species occurred within 12 m from the edge. Further, fluorescence and chlorophyll measurements showed that lichen vitality was unaffected by distance from edge. The light intensity was 4.3 times higher at the edge than in the interior during the growing season, but there were only minor differences in air temperature and relative humidity. Monitoring of thallus water content revealed clear differences in both number and length of wetting and drying cycles. However, the total time with water content sufficient for photosynthetic activity was only slightly higher at the edge. The data thus indicate that our gradient in microclimate was too small to significantly affect lichen growth, and that lichens are largely metabolically inactive when large edge-interior contrasts in microclimate occur. Lichen response to forest edge microclimate results from intricate interactions among several biotic and abiotic factors. Linking data on lichen growth, microclimate and thallus water content with physiological measurements provides a framework for future studies of the mechanisms behind abiotic edge effects.

Tree mortality patterns after experimental fragmentation of an old-growth conifer forest

Abstract Five circular forest fragments of increasing size ( 1 16 , 1 8 , 1 4 , 1 2 and 1 ha ) were isolated in 41-ha clearcut in north-western Sweden. I compared changes in the forest structure of these fragments with those of three control plots in adjacent unfragmented forest, during a five-year period. The site was a high-altitude, old-growth Picea abies forest. In the first autumn after isolation a period with high winds caused severe blowdown and other forest damage in all five fragments. Total tree mortality after 67 months showed a steep increase with decreasing area, from 30% in the 1-ha fragment to 98% in the 1 16 - ha fragment. Uprooting was the most common type of mortality (67%) followed by stem-breakage (24%). The marked increase in wind-induced tree deaths shifted the mortality pattern, from being independent of tree size in controls to showing a strong positive relationship with diameter in fragments. The study shows that completely isolated forest fragments up to at least 1 ha in size became entirely edge habitat shortly after logging. Edge-related changes in forest structure, deposition of woody debris and soil disturbance, triggered by altered climate, are key factors for understanding ecological processes operating in forest fragments. This supports the view that changes in small fragments are mainly driven by external factors.

Are epiphytic lichens in young forests limited by local dispersal

Abstract We investigated whether dispersal limitation is an important factor for the low abundance of epiphytic lichens in young boreal forests. The number of lichen thalli on branch sections of Pinus sylvestris was counted in five second-growth stands (35-78 years old) at increasing distances (10 m, 50 m, and 100 m) from adjacent old-growth stands (122-298 years old) presumed to function as propagule sources. The number of thalli displayed a pronounced decrease with increasing distance from the old growth in both foliose and pendulous fruticose lichens. The effect of distance was statistically significant in five out of six groups of lichens. The number of thalli at 100 m constituted 22% (Parmelia sulcata) to 61% (Vulpicida pinastri) of the number found near the forest edge (10 m). In the two most abundant groups, Bryoria (fruticose) and Hypogymnia (foliose), there was close to 50% reduction in thallus numbers. The thallus size distribution of both Bryoria and Hypogymnia was strongly skewed towards small thalli but the shape of the distributions was only marginally affected by distance to the old growth stands. Our data strongly suggest that both foliose and fruticose lichens are apparently limited by local dispersal in young boreal forests and that old-growth stands function as a source of lichen propagules. Consequently, efforts to enhance abundance of epiphytic lichens in managed boreal forests should include retention and creation of old stands throughout the landscape.

National Inventory of Landscapes in Sweden (NILS) - scope, design, and experiences from establishing a multiscale biodiversity monitoring system

The landscape-level and multiscale biodiversity monitoring program National Inventory of Landscapes in Sweden (NILS) was launched in 2003. NILS is conducted as a sample-based stratified inventory that acquires data across several spatial scales, which is accomplished by combining aerial photo interpretation with field inventory. A total of 631 sample units are distributed across the land base of Sweden, of which 20% are surveyed each year. By 2007 NILS completed the first 5-year inventory phase. As the reinventory in the second 5-year phase (2008–2012) proceeds, experiences and insights accumulate and reflections are made on the setup and accomplishment of the monitoring scheme. In this article, the emphasis is placed on background, scope, objectives, design, and experiences of the NILS program. The main objective to collect data for and perform analyses of natural landscape changes, degree of anthropogenic impact, prerequisites for natural biological diversity and ecological processes at landscape scale. Different environmental conditions that can have direct or indirect effects on biological diversity are monitored. The program provides data for national and international policy and offers an infrastructure for other monitoring program and research projects. NILS has attracted significant national and international interest during its relatively short time of existence; the number of stakeholders and cooperation partners steadily increases. This is constructive and strengthens the incentive for the multiscale monitoring approach.

Demographics and disturbance history of a boreal old-growth Picea abies forest

Abstract Question: To what extent do tree growth, mortality, and long-term disturbance patterns affect stand structure and composition of an old-growth Picea abies forest? Location: Boreal Sweden. Methods: We linked data from three 50 m × 50 m permanent plots established in 1986 with dendrochronology data to evaluate tree growth and mortality over an 18-year period and to describe a several-hundred-year disturbance history for this forest type. Results: Averaged over all diameters, P. abies trees had an annual mortality rate of 0.60%; however, diameter had a striking effect on both growth and mortality, with trees of intermediate diameters (ca. 20–30 cm) showing faster growth and lower mortality. Their increased vigor gave rise to a diameter distribution resembling the ‘rotated sigmoid’ (not reverse-J) proposed for such conditions, and it led to a deficit of snags of intermediate diameters. Slow-growing trees had an increased likelihood of dying. Although recruitment occurred in most decades over the past 400 years, two prominent recruitment peaks occurred (mid 1700s and 1800s), neither of which appeared to cause a shift in tree species composition. The lack of fire evidence suggests that fire was not responsible for these recruitment peaks. Conclusions: Taken together, these results depict a rather impassive system, where canopy trees die slowly over decades. Field observations suggest that fungal infections, mediated by wind, account for much of the mortality during these periods of relative quiescence. However, these periods are at times punctuated by moderate-severity disturbances that foster abundant recruitment. Nomenclature: Mossberg & Stenberg (2003).

OCCURRENCE AND ECOLOGY OF USNEA LONGISSIMA IN CENTRAL SWEDEN

The past and present occurrence of Usnea longissima has been investigated at 31 localities in an area of eastern central Sweden. A marked decline was found which is due to different forestry practices, and, to a minor extent, air pollution. The species is confined to old spruce forests, mainly located on north-facing slopes with a slightly oceanic climate. The population size showed a large variation both within and between seven investigated localities. Specific habitat demands and low dispersal ability make U. longissima very sensitive to environmental disturbances.