Swantje Löbel

SPECIES RICHNESS OF VASCULAR PLANTS, BRYOPHYTES AND LICHENS IN DRY GRASSLANDS: THE EFFECTS OF ENVIRONMENT, LANDSCAPE STRUCTURE AND COMPETITION

We studied the relative importance of local habitat conditions and landscape structure for species richness of vascular plants, bryophytes and lichens in dry grasslands on the Baltic island of Öland (Sweden). In addition, we tested whether relationships between species richness and vegetation cover indicate that competition within and between the studied taxonomic groups is important. We recorded species numbers of vascular plants, bryophytes and lichens in 4 m2 plots (n=452), distributed over dry grassland patches differing in size and degree of isolation. Structural and environmental data were collected for each plot. We tested effects of local environmental conditions, landscape structure and vegetation cover on species richness using generalized linear mixed models. Different environmental variables explained species richness of vascular plants, bryophytes and lichens. Environmental effects, particularly soil pH, were more important than landscape structure. Interaction effects of soil pH with other environmental variables were significant in vascular plants. Plot heterogeneity enhanced species richness. Size and degree of isolation of dry grassland patches significantly affected bryophyte and lichen species richness, but not that of vascular plants. We observed negative relationships between bryophyte and lichen species richness and the cover of vascular plants. To conclude, effects of single environmental variables on species richness depend both on the taxonomic group and on the combination of environmental factors on a whole. Dispersal limitation in bryophytes and lichens confined to dry grasslands may be more common than is often assumed. Our study further suggests that competition between vascular plants and cryptogams is rather asymmetric.

Dispersal and life history strategies in epiphyte metacommunities: alternative solutions to survival in patchy, dynamic landscapes.

Host trees for obligate epiphytes are dynamic patches that emerge, grow and fall, and metacommunity diversity critically depends on efficient dispersal. Even though species that disperse by large asexual diaspores are strongly dispersal limited, asexual dispersal is common. The stronger dispersal limitation of asexually reproducing species compared to species reproducing sexually via small spores may be compensated by higher growth rates, lower sensitivity to habitat conditions, higher competitive ability or younger reproductive age. We compared growth and reproduction of different groups of epiphytic bryophytes with contrasting dispersal (asexual vs. sexual) and life history strategies (colonists, short- and long-lived shuttle species, perennial stayers) in an old-growth forest stand in the boreo-nemoral region in eastern Sweden. No differences were seen in relative growth rates between asexual and sexual species. Long-lived shuttles had lower growth rates than colonists and perennial stayers. Most groups grew best at intermediate bark pH. Interactions with other epiphytes had a small, often positive effect on growth. Neither differences in sensitivity of growth to habitat conditions nor differences in competitive abilities among species groups were found. Habitat conditions, however, influenced the production of sporophytes, but not of asexual diaspores. Presence of sporophytes negatively affected growth, whereas presence of asexual diaspores did not. Sexual species had to reach a certain colony size before starting to reproduce, whereas no such threshold existed for asexual reproduction. The results indicate that the epiphyte metacommunity is structured by two main trade-offs: dispersal distance vs. reproductive age, and dispersal distance vs. sensitivity to habitat quality. There seems to be a trade-off between growth and sexual reproduction, but not asexual. Trade-offs in species traits may be shaped by conflicting selection pressures imposed by habitat turnover and connectivity rather than by species interactions.

The basiphilous dry grasslands of shallow, skeletal soils (Alysso-Sedetalia) on the island of Öland (Sweden), in the context of North and Central Europe

The basiphilous dry grasslands of shallow, skeletal soils (Alysso-Sedetalia) on the island of Oland (Sweden), in the context of North and Central Europe

Dry grassland communities on southern Öland: phytosociology, ecology, and diversity

We studied dry grassland vegetation on southern Oland, both within and outside the Great Alvar, using the Braun-Blanquet approach. We were able to distinguish 15 associations or equivalent units belonging to three major syntaxa. Dry grasslands on sandy soils (class Koelerio-Corynephoretea; subclass Koelerio-Corynephorenea) occurred along the east and west coasts. Weathered rock and outcrop communities (class Koelerio-Corynephoretea; subclass Sedo-Scleranthenea) inhabited shallow skeletal soils, mainly on the Great Alvar. Semi-dry basiphilous grasslands of the class Festuco-Brometea occurred on moraine soils, which were the least extreme in terms of soil moisture and nutrient availability. Whereas the first category comprises impoverished variants of widely distributed syntaxa, all Sedo-Scleranthenea and Festuco-Brometea communities lack direct counterparts in central Europe. The alvar communities proved to be floristically well separated from the others. Species density on 4 m2 was highest in the Sedo-Scleranthenea (that of the Gypsophilo fastigiatae-Globularietum vulgaris with 80 taxa being one of the highest known), intermediate in the Festuco-Brometea, and lowest in the Koelerio-Corynephorenea. Harsh and variable conditions, small plant sizes, and a large local species pool are considered possible causes.

Evaluating citizen science data for forecasting species responses to national forest management

Abstract The extensive spatial and temporal coverage of many citizen science datasets (CSD) makes them appealing for use in species distribution modeling and forecasting. However, a frequent limitation is the inability to validate results. Here, we aim to assess the reliability of CSD for forecasting species occurrence in response to national forest management projections (representing 160,366 km2) by comparison against forecasts from a model based on systematically collected colonization–extinction data. We fitted species distribution models using citizen science observations of an old‐forest indicator fungus Phellinus ferrugineofuscus. We applied five modeling approaches (generalized linear model, Poisson process model, Bayesian occupancy model, and two MaxEnt models). Models were used to forecast changes in occurrence in response to national forest management for 2020‐2110. Forecasts of species occurrence from models based on CSD were congruent with forecasts made using the colonization–extinction model based on systematically collected data, although different modeling methods indicated different levels of change. All models projected increased occurrence in set‐aside forest from 2020 to 2110: the projected increase varied between 125% and 195% among models based on CSD, in comparison with an increase of 129% according to the colonization–extinction model. All but one model based on CSD projected a decline in production forest, which varied between 11% and 49%, compared to a decline of 41% using the colonization–extinction model. All models thus highlighted the importance of protected old forest for P. ferrugineofuscus persistence. We conclude that models based on CSD can reproduce forecasts from models based on systematically collected colonization–extinction data and so lead to the same forest management conclusions. Our results show that the use of a suite of models allows CSD to be reliably applied to land management and conservation decision making, demonstrating that widely available CSD can be a valuable forecasting resource.

Biological traits explain bryophyte species distributions and responses to forest fragmentation and climatic variation

Forest ecosystems have been subjected to intensive exploitation, and on top of these land use-driven habitat alterations, there is an ongoing and rapid climate change. Understanding why environmental responses differ across species and how differences are mediated by species’ traits is crucial for predicting the complex effects of global change on forest biodiversity. We used (1) single-species distribution models and (2) multispecies predictive fourth-corner models of varying complexity to identify critical response traits of dead wood inhabiting bryophytes and to quantify species’ relationships with climatic and forest landscape variation. We hypothesized that reproductive and life-history traits would be mainly linked with forest connectivity, whereas morphological traits would mostly relate to (micro-)climatic variation. The inferred trait–environment relationships based on the different fourth-corner models were consistent. Unexpectedly, reproduction modes were more closely linked to climatic and habitat factors than to forest connectivity. Sexual reproduction was positively related to high temperatures and broadleaf trees, but negatively to high amounts of precipitation. The opposite was true for species which predominantly, or additionally, reproduce asexually. Bryophyte life-forms were related to both habitat and climatic conditions. The positive relationship of shoot length with both high temperatures and high amounts of precipitation suggested that competitive exclusion is important in determining trailing edges of dead wood inhabiting bryophytes. Synthesis. Differences in physiological tolerances obviously play a much greater role in shaping the distributional pattern of bryophyte species with different reproductive systems than previously thought. Evidence suggests that current geographic ranges were primarily determined by physiological tolerances and competitive abilities. Species’ relationships with forest connectivity were complex and determined by the combination of reproductive traits with other critical species’ properties. Given the different species’ relationships with climatic gradients, and the varying species’ dispersal and competitive capacities, we expect clear changes in metacommunity composition following climate change and an overall decrease in the diversity of dead wood inhabiting bryophytes in Sweden.