Geir Hestmark

Disturbance severity and community resilience in a boreal forest

We studied the resilience of southeastern Norwegian old-growth Picea abies forest floor vegetation to experimental disturbance. Five treatments, differing in depth of removal of vegetation and soil layers and making up a gradient in disturbance severity, and three controls, were replicated 10 times. The experiment was analyzed with respect to the full species composition before and for seven years after treatment. The soil-buried propagule bank and local environmental conditions were recorded before treatment. Total cover of vascular plants and bryophytes and lichens increased slowly after treatment and was still below pre-disturbance levels after seven years. The rate of succession, measured as change in floristic dissimilarity between recordings made in successive years, declined with time for all treatments. The magnitude of vegetation change was strongly influenced by disturbance severity. DCA ordination revealed a main gradient in species composition from undisturbed forest floor to severely disturbed vegetation three years after disturbance, while in the fourth year, the direction of vegetation change turned in the direction of pre- disturbance positions. The turning point represented the maximum abundance of pioneer species (e.g., Luzula pilosa and Pohlia nutans) relative to dominant species before the disturbance (e.g., Dicranum majus and Hylocomium splendens). The return to pre-distur- bance positions from the fourth year was, however, slow and will probably take 5-25 more years to be completed if current trends continue. DCA ordination revealed two additional, interpretable, gradients in vegetation; one related to pulses of regeneration from the soil- buried propagule bank; the other represented a gradient in pre-disturbance environmental conditions. We demonstrate that one vegetation gradient related to time after disturbance is insufficient to account for the full complexity of revegetation processes following dis- turbance.

A multigene phylogenetic synthesis for the class Lecanoromycetes (Ascomycota): 1307 fungi representing 1139 infrageneric taxa, 317 genera and 66 families.

The Lecanoromycetes is the largest class of lichenized Fungi, and one of the most species-rich classes in the kingdom. Here we provide a multigene phylogenetic synthesis (using three ribosomal RNA-coding and two protein-coding genes) of the Lecanoromycetes based on 642 newly generated and 3329 publicly available sequences representing 1139 taxa, 317 genera, 66 families, 17 orders and five subclasses (four currently recognized: Acarosporomycetidae, Lecanoromycetidae, Ostropomycetidae, Umbilicariomycetidae; and one provisionarily recognized, Candelariomycetidae). Maximum likelihood phylogenetic analyses on four multigene datasets assembled using a cumulative supermatrix approach with a progressively higher number of species and missing data (5-gene, 5+4-gene, 5+4+3-gene and 5+4+3+2-gene datasets) show that the current classification includes non-monophyletic taxa at various ranks, which need to be recircumscribed and require revisionary treatments based on denser taxon sampling and more loci. Two newly circumscribed orders (Arctomiales and Hymeneliales in the Ostropomycetidae) and three families (Ramboldiaceae and Psilolechiaceae in the Lecanorales, and Strangosporaceae in the Lecanoromycetes inc. sed.) are introduced. The potential resurrection of the families Eigleraceae and Lopadiaceae is considered here to alleviate phylogenetic and classification disparities. An overview of the photobionts associated with the main fungal lineages in the Lecanoromycetes based on available published records is provided. A revised schematic classification at the family level in the phylogenetic context of widely accepted and newly revealed relationships across Lecanoromycetes is included. The cumulative addition of taxa with an increasing amount of missing data (i.e., a cumulative supermatrix approach, starting with taxa for which sequences were available for all five targeted genes and ending with the addition of taxa for which only two genes have been sequenced) revealed relatively stable relationships for many families and orders. However, the increasing number of taxa without the addition of more loci also resulted in an expected substantial loss of phylogenetic resolving power and support (especially for deep phylogenetic relationships), potentially including the misplacements of several taxa. Future phylogenetic analyses should include additional single copy protein-coding markers in order to improve the tree of the Lecanoromycetes. As part of this study, a new module (Hypha) of the freely available Mesquite software was developed to compare and display the internodal support values derived from this cumulative supermatrix approach.

Revegetation following experimental disturbance in a boreal old-growth Picea abies forest

. We studied revegetation patterns after experimental fine-scale disturbance (e.g. uprooting) in an old-growth Picea abies forest in southeastern Norway. An experimental severity gradient was established by manipulation of the depth of soil disturbance; two types of disturbed areas were used. Species recovery was recorded in the disturbed patches in three successive years after disturbance. The cover of vascular plants and, even more so the cover of bryophytes and lichens, recovered slowly after disturbance. The least severe treatments (removal of vegetation and removal of vegetation and the litter layer) was followed by the fastest recovery. The mean number of vascular plant species was usually higher three years after disturbance than before disturbance, while the opposite was true for bryophytes. Several vascular plant species that were abundant in intact forest floor vegetation (Vaccinium myrtillus, V. vitis-idaea and Deschampsia flexuosa) recovered during a three-year period primarily by resprouting from intact rhizomes and clonal in-growth. Other important recovery mechanisms included germination from a soil-buried propagule bank (e.g. Luzula pilosa, Plagiothecium laetum agg., Pohlia nutans and Polytrichum spp.) and dispersal of propagules into the disturbed patches (e.g. Betula pubescens and Picea abies). Microsite limitation seemed to occur in several species that were abundant in the soil propagule bank (e.g. the ferns Athyrium filix-femina, Gymnocarpium dryopteris and Phegopteris connectilis) but which did not appear in disturbed patches. n n n nDisturbance severity influenced revegetation patterns, recorded both as trajectories of vegetation composition in a DCA ordination space and as change in floristic dissimilarity. The length of the successional path (compositional change measured in β-diversity units) increased with increasing disturbance severity, and was also influenced by the area of the disturbed patch and the distance to intact vegetation. The rate of succession depended on the method by which it was measured; decreasing year by year in floristic space, while first decreasing and then increasing in ordination space. The reason for this difference is explained.

The effect of breeding systems and pollination vectors on the genetic variation of small plant populations within an agricultural landscape

Within an agricultural landscape (approximately 8 km2) the genetic structures of the herbs Festuca ovina, Lychnis viscaria and Arabis thaliana were examined using isoenzymes. The species have different breeding systems and pollination vectors, and occur in small populations in remnant patches of semi-natural habitats throughout the landscape. There was no or only a weak correlation between population size and genetic diversity. The wind-pollinated, outcrossing species F. ovina had the highest levels of genetic variation, intermediate levels were found in the largely outcrossing and insect pollinated L. viscaria, while lowest levels of variation were found in the inbreeding A. thaliana. Relative to their breeding systems and the small geographical scale of the study all species exhibited remarkably high levels of total genetic variation. In the outbreeding species most of the genetic variation was found within populations (F. ovina: FST = 0.059 and L. viscaria: FST = 0.092). No geographic pattern was found between populations in the outbreeding species, indicating high levels of gene flow. The cereal fields separating the populations may function as conduits rather than barriers to pollen dispersed by wind, and pollinating insects (bumblebees and butterflies) may have no problems moving between patches at this scale, thus alleviating the danger of genetic erosion associated with small population size. In contrast, the fields appear to be efficient barriers to gene flow by seed dispersal. In the inbreeding Arabis thaliana a geographic pattern was evident. Most of the variation in this species was found between populations (FST = 0.722) indicating low levels of gene flow; single populations exhibited large variation in the number of

Cold resistance and metabolic activity of lichens below 0°C

Abstract Laboratory measurements show that lichens are extremely tolerant of freezing stress and of low-temperature exposure. Metabolic activity recovered quickly after severe and extended cold treatment. Experimental results demonstrate also that CO2 exchange is already active at around −20°C. The psychrophilic character of polar lichen species is demonstrated by optimum temperatures for net photosynthesis between 0 and 15°C. In situ measurements show that lichens begin photosynthesizing below 0°C if the dry thalli receive fresh snow. The lowest temperature measured in active lichens was −17°C at a continental Antarctic site. The fine structure and the hydration state of photobiont and mycobiont cells were studied by low-temperature scanning electron microscopy (LTSEM) of frozen hydrated specimens. Water potentials of the frozen system are in the range of or even higher than those allowing dry lichens to start photosynthesis by water vapor uptake at +10°C. The great success of lichens in polar and high alpine regions gives evidence of their physiological adaptation to low temperatures. In general lichens are able to persist through glacial periods, but extended snow cover and glaciation are limiting factors.

Sex, size, competition and escape—strategies of reproduction and dispersal in Lasallia pustulata (Umbilicariaceae, Ascomycetes)

The lichen Lasallia pustulata has a mixed strategy of asexual and sexual reproduction. Close-dispersed, asexual, symbiotic isidia are produced early, when the thalli are small. The asexual propagules are subsequently supplemented by far-dispersed, sexually generated ascospores when the thalli grow larger. This observation is consistent with evolutionary stable strategy (ESS) models of dispersal allocations in heterocarpic plants accordin to which the production of far-dispersed propagules should increase as clutch size and sibcompetition in the local habitat increases. The observation is also consistent with the “tangled bank” or “elbow room” hypothesis for the maintenance of sexuality, according to which sex, by generating genetic variation, represents an escape from competition in biologically saturated environments. Thus the advantage of sex is density dependent. L. pustulata grows in densely packed populations where intraspecific competition results in self-thining and the development of distinct sizehierarchies.

Single origin and subsequent diversification of central Andean endemic Umbilicaria species

We studied an Andean endemic group of species of the lichen-forming fungal genus Umbilicaria from the subalpine and low-alpine zone, with their biogeographic center in Bolivia and Peru. A number of species and varieties have been described from this element, but apparent instability in several morphological traits has made it difficult to precisely delimit taxa. Based on DNA sequences of nuclear ITS, LSU and mitochondrial SSU from extensive collections from Argentina, Bolivia, Chile, Colombia, Ecuador and Peru, we present here a molecular phylogenetic analysis of this Andean endemic element within genus Umbilicaria. All analyses (MP, ML and Bayesian) support a single origin for the element and a division into two major groups characterized by different apothecium types: the Umbilicaria dichroa group and U. calvescens group. Taxa U. krempelhuberi, U. peruviana and U. subcalvescens are nested withinn U. calvescens and are treated as conspecific with the latter species. The endemic element shares a most recent common ancestor with the Umbilicaria vellea group, which has a worldwide distribution and contains several asexually reproducing (sorediate) species. Independent reversals to sexual reproduction might explain the evolution of two types of apothecia in this monophyletic endemic lineage. A number of cosmopolitan, mostly high-alpine, species of Umbilicaria also present in the central Andes are related only remotely to the endemic element and do not exhibit speciation into endemics. Because the An-dean element dominates the Umbilicaria habitats of the low- and subalpine zones we propose that the founder colonized the Andes at a time when the mountains had not yet reached their current elevation while the high-alpine species arrived more recently.

Temptations of the tree

A perennial image of life, history and enlightenment.

Gap-dynamics, recruitment and individual growth in populations of Lasallia pustulata

In the coastal cliff landscape of southern Scandinavia dense populations of the saxicolous, lichen-forming fungus Lasallia pustulata are subject to disturbances creating small or larger gaps; one or several thalli are removed by strong winds, icing, rock slides, log-falls, branch sweeping or trampling. New patches for colonization are also created when mats of bryophytes, fruticose lichens or pine needles are removed by the same forces. The disturbance gaps are major sites of recruitment in the populations and the age structure of a population is spatially structured by the pattern of gap formation. The revegetation of experimentally created gaps were monitored over a four year period, at the end of which the gaps were filled with new, 1–9 mm sized thalli, unevenly scattered, on average 6500 individuals m -2 , covering less than 1% of the substrate. In addition there were clusters of small thalli sprouting from the former attachment site of some of the large thalli that had been removed. The growth of individual thalli in natural gaps and mature populations was also monitored for four years. The largest annual increment in thallus diameter was 15 mm, the average 5.5 mm. Some thalli did not increase in size at all, some became slightly smaller, and some were completely eliminated, apparently by self-thinning. There was no correlation between initial thallus size and annual growth; and age and size are not correlated. The individual variations in growth rate seem to reflect the degree of initial crowding, subsequent competitive success, and local supply of nutrients. The average growth and initial size of individuals plus their density and dispersion are used to model the speed of gap-closure, estimated to be 10–15 years.

Competitive behaviour of umbilicate lichens - an experimental approach

Abstract The lichens Lasallia pustulata and Umbilicaria spodochroa grow in dense monospecific or mixed populations on the coastal cliffs of southern Scandinavia. Attached to the substrate by only a thin central holdfast, their shield-shaped thalli compete for light and space for growth by overlapping each other. Matched pair experiments in the laboratory and field observations of interacting pairs show that different behavioural responses to precipitation tend to result in the margins of U. spodochroa overlapping those of L. pustulata within a few minutes. The behaviour is apparently caused by different capacities for water absorption in the upper and lower cortices of the species. An initial period of repeated encounter caused by thallus expansion and contraction during precipitation will be followed by a period in which U. spodochroa grows to overlap L. pustulata more and more. When the overlapping lichens are wet, flexible and photosynthetically active, the thallus above rests directly on the upper surface of the one below. Very little light is transmitted through thalli of U. spodochroa, and the shaded parts of L. pustulata are retarded in their growth and die off.