Abstract Understanding of natural and human induced changes to freshwater biodiversity patterns is critical for efficiently conserving and managing these highly impacted ecosystems. In this doctoral thesis, I study the natural spatial and temporal variability of littoral macroinvertebrate communities, as well as aquatic biodiversity responses (of bryophytes, macroinvertebrates and diatoms) to human impact on forested headwater streams. I also study the temporal variability of natural and human-impacted stream communities. I show that littoral macroinvertebrate communities are most variable between individual samples and to some extent between littorals, and that the diversity patterns of rare and common littoral macroinvertebrates vary at different spatial scales. Temporal (interannual) variability is of minor importance, particularly for the core species of the community. For rare species, however, the temporal component was generally more important than spatial turnover. For headwater streams, I show that most taxonomic groups responded negatively to human impact on the adjacent riparian forest. Nevertheless, pristine riparian forest is not a sufficient surrogate for stream biodiversity as also streams with relatively disturbed riparian forests supported diverse benthic communities. A rapid classification method based on the physical structure of the stream channel and its riparian forest is able to identify the reference-state communities, as well as the most severely altered communities, but a reliable identification of the intermediately-disturbed sites would need more precise information about the key stressors of stream communities. I found that fine sediments originating from forest drainage were the main factor causing reduction of stream biodiversity. I also found that forestry impacted streams varied temporally more than pristine streams, emphasizing the importance of interannual sampling of impacted streams for a reliable status assessment. / Tiivistelmä Luonnollisen ja ihmisen aiheuttaman biodiversiteettivaihtelun ymmärtäminen hoito- ja suojelutoimissa on tärkeää pienvesien monimuotoisuuden turvaamiseksi. Tarkastelen väitöskirjassani järvien rantavyöhykkeen pohjaeläinten ajallista ja paikallista vaihtelua sekä latvapurojen eliöyhteisöjen (pohjaeläimet, sammalet, piilevät) vasteita ihmisen aiheuttamaan fysikaaliseen muutokseen rantametsässä ja purouomassa. Tarkastelen myös ajallisen vaihtelun eroja luonnontilaisten ja ihmisvaikutteisten latvapurojen eliöyhteisöjen välillä. Osoitan, että järven rantavyöhykkeen pohjaeläinyhteisöt vaihtelevat eniten yksittäisten näytteiden välillä ja pienessä määrin eri rantojen välillä, mutta ajallinen vaihtelu ei heikennä tulosten luotettavuutta muiden kuin harvinaisten lajien osalta yhteen vuoteen rajoittuvassa näytteenotossa. Purotutkimuksissa osoitan, että useiden vesieliöryhmien lajirunsaus muuttuu ihmisen aiheuttaman rantametsän muutoksen seurauksena, mutta luonnontilaista rantametsää ei silti voida pitää yksiselitteisesti myös puron suojelutason mittarina, koska se ei välttämättä turvaa eliöiden lajistollista eheyttä suhteessa alkuperäiseen alueelliseen lajistoon. Rantametsän ja uoman fysikaalisiin rakennepiirteisiin perustuvaa nopeaa luokittelumenetelmää voidaan käyttää eliöyhteisöltään monimuotoisimpien ja metsätalouden voimakkaimmin rasittamien purojen tunnistamisessa. Eliöyhteisöltään lievemmin muutettujen purojen luotettavaan erotteluun luokittelun pitäisi kuitenkin sisältää tarkempaa tietoa metsäojitusten aiheuttamasta liettymisestä, joka on tulosteni perusteella haitallisin metsätaloudesta johtuva puroyhteisöjä rasittava tekijä. Havaitsin myös metsätalouden rasittamien purojen tilanarvioinnin toistettavuuden olevan luonnontilaisia puroja heikompaa, joten metsätalouden rasittamien purojen pidempiaikainen seuraaminen tuntuu välttämättömältä luotettavien tilanarvioiden tuottamiseksi.

Biogeochemical cycle of chlorine, particularly the formation of organically bound chlorine is still not well understood. In continental ecosystems chlorides act as source of chlorine, and also as a stress factor. Chlorides originate from precipitation of marine cloud masses. Organically bound chlorine in the environment is formed naturally by biotical and abiotical way. The biotical factors are microorganisms, plants, soil enzymes and animals. Volatile chlorinated hydrocarbons (VOCl) represent one group of organically bound chlorines. Several volatile chlorinated hydrocarbons reacts with atmospheric ozone, consequently causing depletion of the ozone layer. The most important known terrestrial source of volatile chlorinated hydrocarbons is the spruce forest ecosystem. Chlorine in the soil can be transformed by microorganisms into organically bound chlorine or translocated by transpiration stream in plants, where they are also transformed enzymatically into organically bound chlorine, and both of them can be emitted into the atmosphere. Too large amounts of chloride can affect the physiological functions of plants. In this thesis experiments were designed for measuring the natural emissions of volatile halogenated hydrocarbons from plants and fungi, with various periods of incubation, and also to...

Bryophilous Pezizales represent a species-rich group of fungi closely associated with bryophytes. Their ascospore morphology is highly variable and they strongly differ also in the genome size and ecology. They could thus represent an interesting model system for the research of evolution of ascospore morphology and their dispersal. The aims of my thesis were to test whether their genome size, number of nuclei in ascospores and ecology of host bryophyte influence their ascospore morphology and to experimentally test the effect of ascospore morphology on their active dispersal. I studied 52 species of bryophilous Pezizales. I reconstructed their phylogeny based on the sequences of three DNA regions, which I then used for the testing of relationships between individual variables using the phylogenetic generalized least squares. For the majority of species, I obtained measurements from morphometric analysis, genome size measurements using flow cytometry, and determined the number of nuclei in their ascospores using the fluorescent microscopy. I localised the infection apparatus and included also the ecological characteristics of the host bryophytes into the analyses. Using the experiments with horizontal ascospore discharge, I measured the distance of active ascospore ejection and recorded whether...

La présence des bancs d'emprunts, utilisés comme sablières et gravières lors de la construction de routes dans la forêt boréale, est problématique. Les facteurs influençant la colonisation naturelle des plantes dans ces milieux ont d'abord été étudiés. Les résultats indiquent que la physicochimie et l'humidité du sol ont la plus grande influence. De plus, les bryophytes et les lichens sont les principaux colonisateurs primaires des bancs d'emprunt. Nous avons donc émis l'hypothèse que l'introduction de ces plantes invasculaires pourrait accélérer la végétalisation des bancs d'emprunt. Trois expériences de restauration à l'aide de bryophytes et de lichens ont été mises en place. Les résultats de ces expériences montrent que l'établissement des bryophytes et des lichens à partir de fragments est possible en une saison de croissance. L'ajout d'un paillis de paille a eu un effet négatif sur leur établissement.

Rain forest canopies are renowned for their very high biodiversity and the critical role they play in key ecological processes and their influence on global climate. Despite that New Zealand supports one of the most diverse and extensive epiphyte flora of any temperate forest system, few studies have investigated epiphyte communities and their invertebrate fauna along with factors that influence their distribution and composition. This thesis represents the first comprehensive study of entire epiphyte communities and their resident invertebrate fauna in the canopy of New Zealand’s indigenous forests. The aim of this study was to determine spatial patterns of epiphyte and invertebrate species richness, abundance and community composition in relation to abiotic variables, and in particular, the responses of these communities to elevated temperature and rainfall. This study was carried out in coastal lowland podocarp-broadleaved forests at two sites on the West Coast of the South Island of New Zealand. Samples from 120 mat-forming epiphyte assemblages located on inner canopy branches of 40 northern rata (Metrosideros robusta) trees were studied to characterise the component flora and fauna. Additionally, biomass, branch and tree characteristics and community responses to treatments designed to elevate temperature and rainfall to simulate predicted climate change were measured. This investigation revealed astonishing diversity and functional complexity of epiphyte and invertebrate life in this ecosystem. The 30.6 kg (dry weight) of epiphyte material collected contained a total of 567 species, 170 epiphyte and 397 invertebrate (excluding immature specimens and mites) species, including at least 10 species new to science and many undescribed species Epiphyte communities were found to be dominated by non-vascular plants (80 % of the total species richness), particularly liverworts and invertebrate communities were dominated with respect to abundance (~ 80 % of the total individuals) by Acari, Collembola and Hymenoptera (primarily ants) and functionally by scavengers and ants. Epiphyte and invertebrate communities were highly variable with respect to spatial patterning of species richness, abundance and composition across sites, among trees within sites and among branches within trees. Overall, a highly significant proportion, > 75 %, of the variance could be attributed to differences at the branch level, but these differences could not be explained by the environmental factors measured. There were no consistent relationships between the spatial pattern of epiphytes and invertebrates, or between vascular and non-vascular plants. However, there were significant positive correlations between epiphyte biomass and invertebrate species richness (r = 0.472; p < 0.0001) and abundance (r = -0.395; p < 0.0001), as well as non-living epiphyte biomass and scavenger species richness (r = 0.4; p < 0.0001). Microclimatic measurements taken on epiphyte mats were also highly variable with respect to temperature and relative humidity at similar physical locations within the same tree as well as across trees within sites. There was also considerable variation in the intensity and frequency of climatic extremes, although potentially harmful climatic conditions were experienced by all the epiphyte mats for which weather variables were measured. Negative correlations existed between both epiphyte and invertebrate community composition and increased temperatures expressed as cumulative degree days above 5˚C. However, variability was such that there was no direct evidence that increased temperature and rainfall treatments had an effect on invertebrate species richness, abundance or diversity. Northern rata host trees harbour an astonishingly diverse and complex canopy flora and fauna that is characterised by high spatial variability. Such variability highlights that to determine species distribution and community dynamics in canopy habitats in response to disturbance caused either by climate change or invasive species the structure of entire communities at different taxonomic and spatial scales, along with their responses to microclimatic factors, need to be studied. If such complexities are not taken into account, inappropriate interpretation may result in poor decisions concerning the conservation status, vulnerability and subsequent management of such unique ecosystems.

<p>The aims of this thesis are to (1) analyze the predictability (indicators) of plant and fungal species diversity in old-growth forests, and (2) assess the history and biodiversity of woodland key habitats (WKHs) and their potential to maintain species diversity in fragmented boreal forest landscapes. </p><p>Predictability was explored in Granlandet nature reserve, an unexploited landscape composed of discrete old-growth Picea forest patches of varying size isolated by wetland, reflecting conditions of insular biota at stochastic equilibrium. Data from 46 patches (0.2-12 ha) showed that most species were rare. However, species richness and composition patterns exhibited a high degree of predictability, which strengthen the possibility to apply biodiversity indicators in old-growth forest stands. Area was a key factor. The increase in species richness starts to level out at 2-3 ha. Large patches host more Red-list species in their interiors than do small ones, i.e. stand size is an important qualitative aspect of old-growth habitat. Nestedness emerged in relation to area but also in equal-sized plots. Structural complexity and habitat quality were important for species richness and compositional patterns, and small habitats of high quality could harbor many rare species. Monitoring of wood-fungi on downed logs showed that species diversity on downed logs changed over periods of 5-10 years and that the occurrences of annual species were unpredictable. It is suggested that monitoring of species with durable fruit bodies (mainly polypores) is likely to be a feasible approach to obtain comparable data over time.</p><p>Assessments of biodiversity of WKHs were performed in two areas with contrasting histories of forest exploitation, namely in south boreal and north boreal Sweden. Analyses of the history of 15 south boreal WKHs showed that fire-suppression, selective logging until mid-20th century and abandonment by modern forestry has shaped their forest structure. These WKHs are not untouched forests, they lack key structural components and harbor few Red-list species. Artificial interventions to restore natural processes and patterns are needed to further increase their suitability for threatned species. Modeling analyses of species richness in 32 WKHs in north boreal Sweden, some of which have not been isolated by modern forestry until recently, indicated an excess of crustose lichen species, i.e. WKHs may face delayed species extinctions. By contrast, the results indicate that wood-fungi have tracked the environmental changes. Differences in substrate dynamics between epiphytes on living trees and species growing on decaying logs may explain the diffeence between species groups. The results indicate that population densities of Red-list species were low, which may result in further depletion of species diversity.</p><p>Continuing species declines and extinctions are likely if not conservation of WKHs are combined with other considerations in th managed forest landscape. Both WKHs and their surroundings must be managed and designed to maintain biodiversity over time. For a successful future conservation of boreal forest biodiversity monitoring of WKHs must be combined with monitoring of refeence areas. </p>

The aims of this thesis are to (1) analyze the predictability (indicators) of plant and fungal species diversity in old-growth forests, and (2) assess the history and biodiversity of woodland key habitats (WKHs) and their potential to maintain species diversity in fragmented boreal forest landscapes. Predictability was explored in Granlandet nature reserve, an unexploited landscape composed of discrete old-growth Picea forest patches of varying size isolated by wetland, reflecting conditions of insular biota at stochastic equilibrium. Data from 46 patches (0.2-12 ha) showed that most species were rare. However, species richness and composition patterns exhibited a high degree of predictability, which strengthen the possibility to apply biodiversity indicators in old-growth forest stands. Area was a key factor. The increase in species richness starts to level out at 2-3 ha. Large patches host more Red-list species in their interiors than do small ones, i.e. stand size is an important qualitative aspect of old-growth habitat. Nestedness emerged in relation to area but also in equal-sized plots. Structural complexity and habitat quality were important for species richness and compositional patterns, and small habitats of high quality could harbor many rare species. Monitoring of wood-fungi on downed logs showed that species diversity on downed logs changed over periods of 5-10 years and that the occurrences of annual species were unpredictable. It is suggested that monitoring of species with durable fruit bodies (mainly polypores) is likely to be a feasible approach to obtain comparable data over time. Assessments of biodiversity of WKHs were performed in two areas with contrasting histories of forest exploitation, namely in south boreal and north boreal Sweden. Analyses of the history of 15 south boreal WKHs showed that fire-suppression, selective logging until mid-20th century and abandonment by modern forestry has shaped their forest structure. These WKHs are not untouched forests, they lack key structural components and harbor few Red-list species. Artificial interventions to restore natural processes and patterns are needed to further increase their suitability for threatned species. Modeling analyses of species richness in 32 WKHs in north boreal Sweden, some of which have not been isolated by modern forestry until recently, indicated an excess of crustose lichen species, i.e. WKHs may face delayed species extinctions. By contrast, the results indicate that wood-fungi have tracked the environmental changes. Differences in substrate dynamics between epiphytes on living trees and species growing on decaying logs may explain the diffeence between species groups. The results indicate that population densities of Red-list species were low, which may result in further depletion of species diversity. Continuing species declines and extinctions are likely if not conservation of WKHs are combined with other considerations in th managed forest landscape. Both WKHs and their surroundings must be managed and designed to maintain biodiversity over time. For a successful future conservation of boreal forest biodiversity monitoring of WKHs must be combined with monitoring of refeence areas.

The presented thesis investigates the role of bryophytes in the deadwood and carbon (C) cycle of boreal black spruce forests in Labrador, Canada. All major forest C pools (live-tree, standing and downed deadwood, organic layer, mineral soil) were quantified for three old-growth, nine clearcut harvested, and three burned forest stands in order to characterize forest C dynamics of a high-latitude humid boreal forest ecosystem. Tree and aboveground deadwood C dynamics of Labrador black spruce forests were similar to those of drier or warmer boreal forests. However, due to bryophyte-driven processes such as woody debris (WD) burial and paludification, the studied forests contained high organic layer, mineral soil, and buried wood C stocks. The comprehensive field-measured data on C stocks was used to evaluate the CBM-CFS3, a Canadian national-scale C budget model, with respect to its applicability to Labrador black spruce and humid boreal forests elsewhere. After selected biomass estimation and deadwood decay parameters had been adjusted, the CBM-CFS3 represented measured live-tree and aboveground deadwood C dynamics well. The CBM-CFS3 was initially designed for well-drained upland forests and does not reflect processes associated with bryophytes and high forest floor moisture content, thus not capturing the large amounts of buried wood and mineral soil C observed in the studied forests. Suggestions are made for structural changes to the CBM-CFS3 and other forest ecosystem C models to more adequately represent the bryophyte-regulated accumulation of buried wood, organic layer, and mineral soil C. Accuracy of forest C models could be further improved by differentiating WD decomposition rates by disturbance history, because WD respiration reflects disturbance-induced changes in temperature and moisture regimes. In Labrador, WD respiration was limited by low WD moisture levels and high temperatures in burned stands, and by high WD moisture contents and low temperatures in old-growth stands. Following harvesting, residual vegetation prevents the desiccation of WD, resulting in significantly higher WD respiration compared to old-growth and burned stands. Moreover, the bryophyte layer recovers faster following harvest than following fire, which reduces WD desiccation due to moisture retention, water transfer, and moisture-induced cooling and results in higher WD decomposition rates. Bryophytes are thus a key driver of the deadwood and C cycle of humid boreal Labrador black spruce forests. The author recommends to classify these and similar boreal forests as a functional ecosystem group called “humid boreal forests”, preliminarily defined as “boreal forest ecosystems featuring a bryophyte-dominated ground vegetation layer associated with low soil temperatures, high moisture levels, low dead organic matter decomposition rates, and subsequently (in the absence of stand-replacing disturbances) an accumulation of buried wood embedded in a thick organic layer”. Bryophytes are also an integral component of many coniferous forests outside the boreal biome. Bryophyte-regulated processes such as WD burial or paludification are thus likely significant to the global C cycle. The potential climate change-induced release of large amounts of CO2 from buried wood and soil C pools necessitates an increased understanding of how bryophyte productivity and decomposition constraints will change with increasing temperature and varying moisture regimes. Ecosystems such as humid boreal forests with potentially high C losses to the atmosphere may thus be identified and counteractive forest management strategies can be developed and implemented. / Cette thèse de doctorat s’intéresse à l’influence qu’exercent les mousses sur les cycles du bois mort et du carbone (C) dans des pessières noires boréales humides du Labrador, Canada. Toutes les réservoirs majeurs de C (arbres vivants, bois mort sur pied et effondré, l’horizon de matière organique, sol minéral) de trois pessières vierges, neuf coupes à blanc et de trois pessières brûlées ont été quantifiés pour caractériser le cycle du C des forêts humides boréales du nord. Les dynamismes de C des arbres vivants et du bois mort supraterrestre ressemblaient à ceux des forêts boréales plus sèches ou aux températures plus chaudes. À cause des processus régulés par les mousses (l’enterrement du bois mort ou la paludification), les forêts étudiées contenaient des stocks élevés de C au sein de l’horizon de matière organique, le sol minéral et le bois enterré. Les données ont aussi été utilisées pour évaluer le MBC-SFC3, un modèle national canadien du bilan du C, concernant son applicabilité aux pessières boréales humides de Labrador et d’ailleurs. Suite à l’ajustement de quelques paramètres, p.ex. des taux de décomposition, le MBC-SFC3 reproduisait bien le dynamisme mesuré des arbres vivants et du bois mort supraterrestre. Le MBC-SFC3 a initialement été développé pour les sites bien drainés et ne considère pas les processus associés avec les mousses ou l’humidité élevée du sol. Conséquemment, le MBC-SFC3 ne représentait pas les stocks élevés de C mesurés pour le bois enterré et pour le sol. Les modifications structurelles du MBC-SFC3 et d’autres modèles du C forestier sont nécessaires pour représenter adéquatement l’accumulation du C au sein de ces réservoirs. La précision des modèles du C forestier pourrait encore être améliorée par une différenciation des taux de décomposition selon le régime de perturbations, parce que la respiration du bois mort reflète les changements de la température et d’humidité associés avec une perturbation spécifique. Dans les pessières brûlés du Labrador, la respiration du bois mort était limitée par a faible humidité du bois et des températures élevées; dans les pessières vierges, par l’humidité élevée du bois et des températures basses. Dans les coupes à blanc, la végétation résiduelle empêchait le dessèchement du bois mort. Il s’y ensuivit que la respiration du bois mort y est nettement plus élevée en comparaison avec des pessières brûlés ou vierges. La décomposition du bois mort après coupe à blanc est aussi favorisée par la récupération plus rapide de la couche de mousses, diminuant conséquemment le dessèchement du bois mort par la conservation d’humidité, les transports vertical et horizontale d’eau et le refroidissement induit par l’humidité. Ainsi, les mousses sont les facteurs clés dans les cycles du bois mort et du C des pessières noires boréales au Labrador. L’auteur préconise la classification de ces pessières et des forêts semblables comme un groupe fonctionnel d’écosystèmes nommé : « pessières boréales humides » ; provisoirement définies comme « des écosystèmes forestiers avec une végétation terrestre dominée par les mousses et par conséquent associée avec des températures basses du sol, une humidité élevée, des taux de décomposition faibles et (en l’absence de perturbations) l’accumulation du bois enterré dans des couches organiques epaisses ». En outre, les mousses sont des éléments principaux des nombreuses forêts résineuses n’appartenant pas au biome boréal. Les processus régulés par les mousses tels l’enterrement du bois mort ou la paludification sont probablement importants pour le cycle global de C. La libération potentielle de grandes quantités de CO2 des réservoirs « bois enterré » et « sol » à la suite des changements climatiques exige une meilleure compréhension des transformations de la productivité des mousses et des limitations de la décomposition dues aux températures plus élevées et au taux d’humidités variables. Ainsi, les écosystèmes aux pertes potentielles de C élevées (p.ex. les pessières boréales humides) peuvent être identifiés et des mesures d’aménagement antagonistes peuvent être développées et implémentées. Traduction assistée par : Karl-Heinrich von Bothmer, Géry van der Kelen / Die vorliegende Arbeit untersucht die Einflüsse von Moosen auf den Totholz- und Kohlenstoff-(C)-Kreislauf in borealen Schwarzfichtenwäldern in Labrador, Kanada. Um den C-Kreislauf dieses humiden borealen Waldökosystems zu charakterisieren, wurden alle bedeutenden C-Speicher (lebende Bäume, stehendes und liegendes Totholz, organische Auflage, Mineralboden) von drei Primärwald-, neun Kahlschlags- und drei Brandflächen quantifiziert. Die C-Dynamiken der Bäume und des oberiridischen Totholzes der Untersuchungsflächen ähnelten denen von trockeneren und/oder wärmeren borealen Wäldern, während die organische Auflage, der Mineralboden und das begrabene Totholz bedingt durch von Moosen regulierte Prozesse wie Totholzeinlagerung und Paludifizierung besonders hohe C-Vorräte aufwiesen. Mit dem umfangreichen C-Datensatz wurde das CBM-CFS3, das nationale kanadische C-Modell, am Beispiel Labradors im Hinblick auf seine Anwendbarkeit in humiden borealen Wäldern evaluiert. Nach Anpassung ausgewählter Parameter, z.B. der Totholzabbauraten, wurden die gemessenen C-Dynamiken der Bäume und des oberiridischen Totholzes vom Modell abgebildet. Das CBM-CFS3 wurde ursprünglich für staunässefreie, terrestrische Waldstandorte entwickelt und berücksichtigt keine mit Moosen oder hoher Bodenfeuchte assoziierten Prozesse, so dass es die hohen C-Vorräte des begrabenen Totholzes und des Bodens nicht widerspiegelte. Eine adäquate Abbildung der Akkumulation von C in diesen Speichern erfordert strukturelle Änderungen des CBM-CFS3 und anderer Wald-C-Modelle. Die Genauigkeit von Wald-C-Modellen könnte darüber hinaus durch eine Differenzierung der Totholzabbauraten in Abhängigkeit vom Störungsregime verbessert werden, da störungsspezifische Veränderungen von Temperatur und Feuchte von der Totholzatmung widergespiegelt werden. Im Untersuchungsgebiet limitierten geringe Holzfeuchten und hohe Holztemperaturen die Totholzatmung auf Brandflächen. In Primärwäldern wirkten dagegen hohe Holzfeuchten und geringe Holztemperaturen hemmend. Auf Kahlschlägen verhinderte die verbleibende Vegetation die Austrockung des Totholzes, was zu signifikant erhöhten Atmungsraten im Vergleich zu Brand- und Primärwaldflächen führte. Zudem wird der Totholzabbau auf Kahlschlen durch eine schnellere Erholung der Moosdecke als auf Brandflächen gefördert, da Moose durch ihr hohes Wasserspeichervermögen, vertikalen und horizontalen Wassertransport und feuchte-induzierte Kühlung der Austrockung des Totholzes entgegenwirken. Moose sind somit ein Schlüsselfaktor im Totholz- und C-Kreislauf der humiden borealen Schwarzfichtenwälder Labradors. Die Autorin empfiehlt die Klassifikation dieser und ähnlicher borealer Wälder als eine funktionelle Ökosystemgruppe namens “humid boreal forests”; vorläufig definiert als “boreale Waldökosysteme mit durch Moose dominierter Bodenvegetation und damit assoziierten niedrigen Bodentemperaturen, hohen Bodenfeuchten, geringen Abbauraten und (in Abwesenheit großflächiger Störungen) der Akkumulation von begrabenem Totholz in mächtigen organischen Auflagen”. Auch außerhalb des borealen Bioms sind Moose ein wesentlicher Bestandteil vieler Nadelwälder. Durch Moose regulierte Prozesse wie Totholzeinlagerung und Paludifizierung sind daher wahrscheinlich relevant für den globalen C-Kreislauf. Die durch den Klimawandel bedingte potentielle Freisetzung von großen Mengen CO2 aus begrabenem Totholz und dem Boden macht ein besseres Verständnis der zu erwartenden Veränderungen von Mooswachstum und Abbauhemmnissen als Folge erhöhter Temperaturen und variabler Feuchteverhältnisse erforderlich. Somit können Ökosysteme mit potentiell hohen C-Verlusten, wie z.B. humide boreale Wälder, identifiziert und diesen entgegenwirkende Bewirtschaftungsmaßnahmen entwickelt und umgesetzt werden.

The aim of this thesis was to increase knowledge about metapopulation and metacommunity processes in patchy, dynamic landscapes, using epiphytic bryophytes as a model system. Host trees and deciduous forest stands in the coniferous landscape are patchy, temporal and undergo changes in habitat quality during succession. Epiphytes must track this dynamic habitat network for their long-term survival. Community patterns at different spatial scales were explored and linked to regional metapopulation processes and local population dynamics. Spatial structuring in species richness both at a local and regional scale indicated stronger dispersal limitation but lower sensitivity to habitat quality in species with large asexual than in species with small sexual diaspores. In sexually dispersed species, a strong rescue effect was indicated by a bimodal frequency distribution of the species and by increasing local abundance with increasing patch connectivity. Present connectivity to other deciduous forest patches had positive effects on richness of asexually dispersed species, whereas richness of sexually dispersed species was instead related to the landscape connectivity 30 years ago. A study of local growth and reproduction suggested that this is caused by delayed sexual, but not asexual, reproduction. Habitat conditions affected the production of sporophytes, but not of asexual diaspores. No differences in either growth rates or competitive abilities among species with different dispersal and life-history strategies were found. In vitro experiments showed that establishment is higher from large asexual diaspores than from small sexual. Establishment of all diaspore types was limited by pH. There were indications of trade-offs between high germination and protonemal growth rates, desiccation tolerance and a rapid development of shoots from protonema. The results indicated that the epiphyte metacommunity is structured by two main trade-offs: dispersal distance (diaspore size) versus age at first reproduction, and dispersal distance versus sensitivity to habitat quality. Trade-offs in species traits may have evolved as a consequence of conflicting selection pressures imposed by habitat turnover, connectivity and irregular water supply rather than by species interactions. Syndromes of interrelated species traits imply that fairly small changes in habitat conditions can lead to distinct changes in metacommunity diversity: the results indicate that increasing distances among patches cause most harm to asexually dispersed species, whereas cuttings of forests of high age and quality as well as increasing patch dynamics are most harmful to sexually dispersed species. / Senarelagd disputation från: 2009-09-26, Lindahlsalen, EBC, Villavägen 9, 75236 Uppsala, Uppsala, 10:00

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