The epiphytic lichen Usnea longissima is strongly associated with old-growth forests and is declining. Previous studies have documented unimodal relationships between stand density and abundance of U. longissima. The aim of this thesis has been to investigate whether the same relationship is found in Sweden and to determine the optimum level of stand density. The study area (1.4 ha) was divided into a grid with 48 circular plots (10-m radius). Stand density was measured as basal area (m²/ha) using a relascope and abundance of U. longissima was measured as the length of the longest thallus present on the tree nearest the plot center. Usnea longissima was found in 42 plots (mean thallus length of 37 cm). The regression analyses between length of U. longissima and basal area showed that the relationship was not significant (R²=0.082, P=0.066), and tended to be linear rather than unimodal. However, plots with U. longissima had significantly lower basal area (30.4 m²/ha) than plots without the lichen (35.1 m²/ha). The basal area in U. longissima plots was higher than in Norwegian studies, but similar to other Swedish sites. Thus, my results correspond well with earlier studies that have documented higher basal area in U. longissima-locations in Västernorrland than in more oceanic areas in Norway. Thereby a basal area around 27-35 m²/ha seems most favorable for U. longissima in the study area. The lichen cannot develop large populations in dense stands, indicating that management operations to reduce the basal area might be needed in such stands.

In western North America, quaking aspen (Populus tremuloides Michx.) is the most common hardwood in montane landscapes. Fire suppression, grazing, wildlife management practices, and climate patterns of the past century are some of the threats to aspen coverage in this region. Researchers are concerned that aspen-dependent species may be losing habitat, thereby threatening their long-term local and regional viability. Though lichens have a rich history as air pollution indicators, I believe that they may also be useful as a metric of community diversity associated with habitat change. To date, few studies have specifically examined the status of aspen's epiphytic lichen community in the Rocky Mountains. A preliminary study was conducted using 10 transect-based plots to assess lichen species substrate preferences between aspen and various conifer species and to gain basic knowledge of species diversity. Following this work, I established 47 plots in the Bear River Range of northern Utah and southern Idaho to evaluate the effects of forest succession on epiphytic macrolichen communities. Plots were located in a narrow elevational belt (2,134-2,438 m) to minimize the known covariant effects of elevation and moisture on lichen communities. Results show increasing lichen diversity and a decrease in aspen-dependent species as aspen forests succeed to conifer cover types. The interactive roles of stand aspect, basal area and cover of dominant trees, stand age, aspen bark scars, and recent tree damage were examined in relation to these trends. An aspen index score was developed based on lichens showing an affinity for aspen habitat. I present a landscape-level multivariate analysis of short and long-term factors influencing epiphytic lichen communities in aspen forests. Nonrnetric multidimensional scaling (NMS) ordination stressed the importance of succession and local air pollution sources in shaping lichen communities. I also investigated the role of historic human intrusions and climate on aspen forests and aspen dependent epiphytic lichens at the landscape-level. Implications of this work include 1) realization of nitrogen impacts on ecosystems, 2) the potential for using lichens as bioindicators for monitoring aspen stand health, and 3) suggestions for working with natural disturbance regimes to minimize human impacts on aspen and associated species.

Biologisk mångfald har en nyckelroll i välfungerande ekosystem och bevarandet av denna även i stadsmiljö blir väsentligt med tanke på den ökande urbaniseringen. Övervakning av olika slag kan ses som ett steg på vägen till ökad kunskap inom ämnet om hur den biologiska mångfalden skall skötas och stödjas. Då lavar påverkas relativt snabbt av förändringar i miljön kan dessa användas till olika typer av miljöbedömningar. Det är troligt att om lavfloran uppvisar tecken på störning är även andra arter och ekosystem negativt påverkade i mer eller mindre utsträckning. Denna studie har som utgångspunkt att jämföra epifytiska lavar i två tätorter vilka har och har haft olika förutsättningar både ur ett naturligt perspektiv – t.ex. genom olika klimat – samt från mänsklig påverkan från t.ex. andelen luftföroreningar. Orterna som valdes var Uddevalla, en tätort på Sveriges västkust, och Östersund, en stad i södra Norrlands inland. Främst fokus i jämförelsen låg på förekomsten av 13 utvalda lavarter som räknades i artantal, täckningsgrad och frekvens i brösthöjd på nord- respektive sydsida på trädslagen björk, asp och tall. Totalt undersöktes 80 träd, totalt 160 provytor, inom en tre km radie från respektive centrum. Ytterligare antecknades förekomsten av övriga lavarter utöver de utvalda arterna. Även eventuella samband mellan lavförekomst och brösthöjdsdiamer (DBH), lavförekomst och avstånd från centrum samt lavförekomst på nord- jämfört med sydsidan undersöktes. Resultatet visade att Östersund hade större förekomst av de utvalda epifytiska lavarterna, högst total av upptäckta arter (utvalda + övriga), högre frekvens samt högre täckningsgrad. Alla 13 utvalda arter förekom i varierande utsträckning i Östersund jämfört med att endast åtta av dessa arter återfanns i Uddevalla. Däremot uppvisade Uddevalla högre andel övriga lavarter (17 jämfört med 12 i Östersund) samt något större individstorlek. Föroreningskänsliga, hängande busklavar såsom tagellav (Bryoria ssp) och luddig skägglav (Usnea hirta) saknades i Uddevalla men förekom i relativt stor utsträckning i Östersund. Mindre känsliga arter såsom flarnlav (Hypocenomyce scalaris) och olika mjöllavar (Lepraria ssp) förekom istället i högre utsträckning i Uddevalla. Inga direkta sambands sågs gällande lavförekomst i förhållande till trädets diameter eller avstånd från centrum. Östersund hade störst andel lavar inom en km från busstationen medan Uddevalla uppvisade lägst värden närmare busstationen.  Provträdens nordsida hade generellt en högre täckningsgrad där skillnaden mellan nord- och sydsida var betydligt större i Östersund, speciellt på tall.   Orsakerna till skillnaderna mellan tätorterna har inte undersökts vidare, men en orsak skulle kunna vara att Sveriges västkust historisk sett varit utsatt för mer luftföroreningar i form av svaveldioxid (SO2) även från andra länder i Europa (Helmersson 2015) – troligtvis i högre grad än norra Sveriges inland – vilket påverkat lavfloran negativt. Orsakerna till skillnaderna mellan tätorterna kan vara objekt för vidare studier. Studien skulle även kunna vara ett första steg för eventuell fortsatt övervakning i tätorterna för att kunna se skillnader i artsammansättning och täckningsgrad över tid. / Biodiversity has a key role in well-functioning ecosystems, hence the conservation of it in urban areas becomes essential with the increasing urbanization. Monitoring biodiversity can be seen as a way to increase knowledge within the area of how biodiversity should be kept and supported. As lichen respond relatively fast to changes in the environment, these can be used for different types of environmental assessments. It’s likely that if the lichen shows signs of disturbance, other species and ecosystems will also be negatively affected to an extent. This study is based on a comparison of epiphytic lichen in two urban areas which have been affected by different conditions both from a natural perspective – e.g. through different climates – and from human influences from e.g. amount of air pollutants. The areas that were chosen were Uddevalla, a town on the Swedish west coast, and Östersund, a town in the middle of Sweden. The main focus in the comparison was the presence of 13 selected lichen, which were counted in number of species, degree of coverage and species frequency. Measurements were done on the north and south side of tree trunks in chest height, on the tree species birch, aspen and pine. A total of 80 trees – a total of 160 sample areas – were examined, within a three km radius from each town center. The presence of other species of lichen besides the selected species was noted. Analyses regarding possible correlations between lichen occurrence and the trees diameter at breast height (DBH), lichen occurrence and distance from the town center and lichen occurrence on the tree’s north side compared to the south was also done. The results showed that Östersund had more of the study’s selected epiphytic lichens, the highest total of observed species (selected + others), higher frequency and higher degree of coverage. All 13 selected species occurred in varying degree in Östersund, compared with only eight of these species being found in Uddevalla. On the other hand, Uddevalla showed a higher proportion of other lichens (17 compared with 12 in Östersund) and a slightly larger size of each individual lichen. More sensitive, hanging lichen such as Bryoria ssp and Usnea hirta were missing in Uddevalla but occurred in larger extent in Östersund. Less sensitive species such as Hypocenomyce scalaris and Lepraria ssp occurred more often in Uddevalla. No obvious connections were seen regarding lichen occurrence in relation to the tree's diameter or distance from the town centers. Östersund had the largest proportion of lichens within one km from the bus station, while Uddevalla showed the lowest values ​​closer to the bus station. The north sides of the sample trees generally had a higher degree of lichen coverage and the difference between the north and south sides was significantly greater in Östersund, especially on pine. The reasons for the differences between the two towns have not been investigated further, though one of the reasons why Östersund had more lichen may be that the Swedish west coast historically has been affected more by air pollutants such as SO2 also from other countries in Europe (Helmersson 2015) – probably to a higher degree than the northern parts of Sweden – which have had a negative effect on lichens. The reasons for the differences between the urban areas may be objects for further studies. The study could also be seen as a first step for continued monitoring in the urban areas over time / <p>2021-06-04</p>