Vegetation ecology: theory, methods and applications with reference to Fennoscandia

Nest building in titmice Paridae: Selectivity in bryophyte use

In many bird species, reproductive success is dependent on nest quality. However, detailed data on nest composition are scarce, and quantitative analyses have generally used only rough categories, without species identification. Bryophytes dominate the nests of many passerine bird species, but little is known about whether birds have preferences for certain species. In this study, we determined the bryophyte species composition in nests of blue tits Cyanistes caeruleus and great tits Parus major in a forest near Oslo, Norway. We also sampled the abundance of the bryophyte species in plots on the forest floor surrounding a subset of the great tit nests. Blue tits and great tits both used 15 bryophyte species as nest materials, mainly the same pleurocarpous species but in different proportions. The tits preferred highly branched bryophyte species, i.e., Pleurozium schreberi, Rhytidiadelphus squarrosus, and Sanionia uncinata but avoided common forest floor bryophyte species that are sparsely branched. Great tits clearly collected bryophyte species selectively. We also found that bryophyte species content in great tit nests in the same nest box in different years was very similar. Our results also indicated that the great tits collected bryophyte nest materials close to their nests, mostly within 5 m, supporting the view that collecting nest materials is costly. We review several hypotheses to explain why the tits prefer certain species of bryophytes as nest materials. These include handling costs and their suitability as structural materials. We recommend field experiments to test specific hypotheses and to study whether preferences are heritable.

Reef fishes weaken dietary preferences after coral mortality, altering resource overlap

The direct and indirect effects of climate change can affect, and are mediated by, changes in animal behaviour. However, we often lack sufficient empirical data to assess how large-scale disturbances affect the behaviour of individuals, which scales up to influence communities. Here, we investigate these patterns by focusing on the foraging behaviour of butterflyfishes, prominent coral-feeding fishes on coral reefs, before and after a mass coral bleaching event in Iriomote, Japan. In response to 65% coral mortality, coral-feeding fishes broadened their diets, showing a significant weakening of dietary preferences across species. Multiple species reduced their consumption of bleaching-sensitive Acropora corals, while expanding their diets to consume a variety of other coral genera. This resulted in decreased dietary overlap among butterflyfishes. Behavioural changes in response to bleaching may increase resilience of coral reef fishes in the short term. However, coral mortality has reduced populations of coral-feeders world-wide, indicating the changes in feeding behaviour we document here may not be sufficient to ensure long-term resilience of butterflyfishes on coral reefs.

Floristic Composition and Diversity of Vascular Plants inRemnant Patches of Arsi-Bale Massif of Oromia RegionalState, Ethiopia

This research was done in Arsi-Bale Massif remnant vegetation of southeast Ethiopia to investigate vascular plant diversity and endemism in forest patch, riverine, and grazing land-use types. A total of 126 quadrats, each with 900 m2 (30 m × 30 m), were selected systematically along the altitudinal gradient. Shannon Weiner Diversity index and R Package 3.2 were applied to analyze species composition and diversity, whereas the similarity ratio among land use and other related vegetation was determined using Sorensen’s index. From the study, 382 vascular plant species under 223 genera and 92 families were identified. The growth forms revealed that there were 118 woody (26 trees, 10 lianas, and 82 shrubs) and 239 herbaceous species of plant. Of these, 216, 165, and 154 species are shared by riverine, forest patch, and grazing land-use types, respectively. Asteraceae with 68 species was the most dominant family in the present study, followed by Poaceae, Lamiaceae, and Cyperaceae with 30, 21, and 13 species, respectively. Forty-four endemic species were documented in this study. According to the IUCN Red List, 22 species were not evaluated; 10 species were least concerned; 1 species was endangered; and 1 species was vulnerable, while 4 species have been categorized as not threatened. The highest similarity was observed between grazing and riverine land-use types; this may be due to the presence of many adjacent plots in both land use, associated mechanisms of adaptation, and requirements for species occurrence. Moreover, the floristic composition similarity of the study area in comparison with other vegetation types of Ethiopia shows variation (Ss = 0.223–0.526), maybe due to climatic variation, ecological distance, and disturbances. Generally, the total diversity and evenness of the studied remnant vegetation were 2.917 and 0.948, respectively. This lower diversity value clearly indicates that there are many human-induced factors deteriorating the plant species of the studied vegetation. Therefore, the concerned body of the government should work with local farmers to conserve the remaining plant species including many endemic species by developing appropriate conservation and management plans.

Vegetation-environment relationships of boreal spruce swamp forests in Østmarka Nature Reserve, SE Norway

Swamp forests dominated by Picea abies contribute strongly to the total plant species richness in boreal forests. The variation in species composition and environmental conditions in swamp forests and the relationships of swamp forests to mires and upland forest, have, however, remained insufficiently known. From a preliminary survey of 57 spruce swamp forests, eleven localities were selected to represent the variation in the study area with respect to size and nutrient status, and altitude and position in the landscape. Physiographic and hydrotopographic descriptions were made. A total of 150 1-m2 plots were distributed on the localities by a restricted random procedure. In each plot, the abundance of all vascular plants, bryophytes and macrolichens was recorded as frequency in 16 subplots, 53 variables (topographic and geographic, tree influence, water-table, water chemical and physical, and soil chemical and physical) were measured. The gradient ( coenocline) structure of vegetation was found by parallel DCA and LNMDS ordinations, interpreted ecologically by analysis of correlations and geostatistical patterns. The two main coenoclines were the same for the full species composition and for vascular plant and cryptogams considered separately. The first gradient was related to soil acidity and nutrient concentrations: plots segregated into relatively poor (and intermediate) and richer swamp forests. Nitrogen availability is considered a decisive factor for species’ responses to this gradient. The second gradient was related to depth to the water table and mesotopographic relief of the swamp-forest surface, varying mostly on fine (0.75-1.5 m) scales. Vascular plants segregate along this gradient due to a trade-off between tolerances to waterlogging and drought, bryophyte are influenced by a complex set of factors. Two minor vegetation gradients were also found; one related to microtopography (extending from flat, lawn-like areas dominated by large bryophytes to more strongly sloping sites dominated by small mosses and hepatics; ‘pocket species’) and one weakly related to the annual water-table amplitude. Relatively strong coenoclines were found that separated entire swamp forests but were uncorrelated with measured variables. These occurred because all swamp forests, notably the richer, had a strong element of uniqueness in species composition, probably because species are recruited from a large species pool during thousands of years. Swamp forest is proposed as a broad term for all peatlands with trees, including mire margin, from which it is essentially indistinguishable. Similarities with, and differences from, open mire and forest on mineral soil are discussed. Some unique features of swamp forests are pointed out. A classification of swamp forests into eight site-types by division of the two main gradients is proposed. Descriptions are provided for the six site-types encountered in the study area. All intact richer swamp forests and a representative selection of poor swamp forests should be protected if maintenance of the biological diversity of (coniferous) forests in general, and swamp forests in particular, is aimed at.

Vegetational and ecological monitoring of boreal forests in Norway. I. Rausjømarka in Akershus county, SE Norway

Vegetational and ecological monitoring of boreal forests in Norway was initiated in 1988, as a part of the programme “Countrywide monitoring of forest health” at Norwegian Institute of Land Invetory (NIJOS). Ten reference areas for monitoring will be established and analysed within five years; two new areas each year. Each of the monitoring areas is planned to be reanalysed every fifth year. In each monitoring area 10 macro sample plots, 50 m2 each, are selected. Within each macro sample plot 5 meso sample plots, 1 m2 each, are randomly placed and the vegetation is analysed by using frequency in subplots as measure of species abundance. Within each meso sample plot one micro sample plot (two in the first established monitoring area), 0.0625 m2 each, is analysed by the same method. In connection with each meso sample plot several environmental variables are recorded. In each ma cro sample plot several tree variables and variables describing the terrain are recorded. The variables are used for environmental interpretation as well as for monitoring, since known relations between vegetation and environmental gradients form the basis of vegetational and ecological monitoring. Any future changes in vegetation, soil and the health of trees have to be interpreted in relation to the analysis of vegetation-environment relationships in order to identify changes due to air pollution or climatic changes.

The data from the first established monitoring area, Rausj0marka in Akershus county, are subjected to analysis in this paper. The most important vegetational and environmental gradients in the area are discussed, as well as the field methodology and the methods for data analysis to be used in integrated monitoring. The advantages of integrated monitoring of vegetation, soil and trees on the same sample plots are emphasized, including advantages for surveying and monitoring of species (bioindicators).

Vegetation-environment relationships of boreal coniferous forests in the Solhomfjell area, Gjerstad, S Norway

The understory vegetation (vascular plants, bryophytes and lichens) in an area dominated by boreal coniferous forests is subjected to detailed ecological analysis. Two hundred meso sample plots (1 m2) are used as basis for vegetation sampling, and provided with measurements of 33 environmental variables. Species abundance is recorded as frequency in 16 subplots. Parallel DCA and 2-dimensional LNMDS ordinations of meso sample plots were largely identical, both provided two coenocline axes interpretable in ecological terms. The first axis is interpreted as the response to a broad-scale topographical complex-gradient, made up of two independent complex-gradients; (1) a topography-soil depth complex-gradient in the pine forest (running from lichen-rich pine forests to submesic Vaccinium myrtillus-dominated spruce forests), and (2) a complex-gradient in soil nutrient status in the spruce forest. The second axis, mainly affecting the species composition of the bottom layer, is interpreted as a fine-scale paludification gradient. The causes of variation along these gradients are discussed: Desiccation tolerance is considered to act directly on the physiology of vascular plant species, setting their limits towards xeric sites. Similarly, cryptogams with optima in the more mesic sites are considered to be excluded from drier sites by physiological tolerance. Limits of cryptogams towards more mesic sites are, however, considered to be set by competitive ability (growth rates) in accordance with the competitive hierarchy theory. N availability is assumed to be the most important factor for differentiation of vascular plants along the nutrient gradient, while bryophytes are expected to respond to a complex of factors, including structural properties of the humus layer. Increasing N accumulation in the humus towards xeric sites may indicate oversaturation due to deposition of airborne NO3- or NH>4 +. Fine-scale paludification, mainly of a soligenous type, occurred in sloping terrain with shallow soil. The cryptogams apparently make up a competitive hierarchy also along the paludification gradient. No other coenoclines could be identified by analysis of 0.0625 m2 micro sample plots, most probably because the response of vegetation to micro-scale environmental gradients (probably most important: the variation in microtopography) not essentially different from the meso-scale gradients, and because the importance of random processes increase towards finer scales. Structuring processes are discussed with reference to the observed patterns. The lack of a closed bottom layer in almost all sample plots is considered a strong indication of high importance of fine-scale disturbance and density-independent mortality in the investigated system, while interspecific competition is of lower importance. The methodology in vegetation ecological studies is discussed with particular reference to monitoring. The potential of an integrated concept using permanent plots, parallel investigation of vegetation and environmental parameters, and gradient analysis, is stressed. Several suggestions for future studies, based on this integrated approach, are made.

Does warming by open-top chambers induce change in the root-associated fungal community of the arctic dwarf shrub Cassiope tetragona (Ericaceae)?

Climate change may alter mycorrhizal communities, which impact ecosystem characteristics such as carbon sequestration processes. These impacts occur at a greater magnitude in Arctic ecosystems, where the climate is warming faster than in lower latitudes. Cassiope tetragona (L.) D. Don is an Arctic plant species in the Ericaceae family with a circumpolar range. C. tetragona has been reported to form ericoid mycorrhizal (ErM) as well as ectomycorrhizal (ECM) symbioses. In this study, the fungal taxa present within roots of C. tetragona plants collected from Svalbard were investigated using DNA metabarcoding. In light of ongoing climate change in the Arctic, the effects of artificial warming by open-top chambers (OTCs) on the fungal root community of C. tetragona were evaluated. We detected only a weak effect of warming by OTCs on the root-associated fungal communities that was masked by the spatial variation between sampling sites. The root fungal community of C. tetragona was dominated by fungal groups in the Basidiomycota traditionally classified as either saprotrophic or ECM symbionts, including the orders Sebacinales and Agaricales and the genera Clavaria, Cortinarius, and Mycena. Only a minor proportion of the operational taxonomic units (OTUs) could be annotated as ErM-forming fungi. This indicates that C. tetragona may be forming mycorrhizal symbioses with typically ECM-forming fungi, although no characteristic ECM root tips were observed. Previous studies have indicated that some saprophytic fungi may also be involved in biotrophic associations, but whether the saprotrophic fungi in the roots of C. tetragona are involved in biotrophic associations remains unclear. The need for more experimental and microscopy-based studies to reveal the nature of the fungal associations in C. tetragona roots is emphasized.

Long-term persistence of seeded grass species: an unwanted side effect of ecological restoration

Spoil heaps are the visible footprint of hydropower production, particularly in vulnerable alpine environments. Speeding up vegetation development by seeding commercial grass species has been a common restoration practice for the last 50 years, but we lack information on whether seeded species decline and allow native plant cover to develop. We visually estimated cover of native vascular plants and five seeded grass species (Agrostis capillaris, Festuca ovina, Festuca rubra, Schedonorus pratensis and Phleum pratense) on eight spoil heaps at different elevations (boreal-alpine zone) in western Norway. Spoil heap vegetation was censused twice (9-20 and 24-36 years after spoil heap construction); the undisturbed surrounding vegetation was also censused on the second occasion. Total cover on the spoil heaps showed some increase, but remained far below that in surrounding areas. Cover of seeded grass species in the surroundings was low (but not negligible), indicating suboptimal establishment ability. Seeded species usually covered less than 20 % of the spoil heaps, and only F. rubra, F. ovina and A. capillaris contributed substantially. Proportional cover indicated better initial establishment by seeded species, but their cover decreased between the censuses on all but the highest located spoil heap. The persistence of seeded grass species is problematic, and despite the decrease in proportional cover, they are likely to persist for decades on spoil heaps, posing a risk of invasion of surrounding areas. We therefore recommend replacing the practice of seeding with more appropriate restoration measures.

Does road salting confound the recovery of the microcrustacean community in an acidified lake?

Numerous boreal lakes across the Northern Hemisphere recovering from acidification are experiencing a simultaneous increase in chloride (Cl) concentrations from road salting. Increasing Cl may have profound effects on the lake ecosystem. We examine if an increase in Cl from road salting has modified the recovery of the microcrustacean community in an acidified boreal lake undergoing chemical recovery (study lake). Results from the study lake were compared with an acidified "reference lake". The community changed during the study period in the study lake mainly driven by the reduction in acidification pressure. Despite the community changes and an increase in species richness, the absence of several acid sensitive species, previously occurring in the lake, indicates a delayed biological recovery relative to the chemical recovery. Moreover, changes in occurrence of acid sensitive and acid tolerant species indicated that the biological recovery was slower in the study lake compared to the "reference". Although recurrent episodes of high aluminum and low pH and decreasing Ca are likely important factors for the delay, these do not explain, for instance, the shift from Cyclops scutifer to Bosmina longispina in the study lake. Although the contribution of Cl was not significant, the correlation between Cl and the variation in microcrustacean community was twice as high in the study lake compared to the "reference". We argue that small, sheltered forest lakes may be especially sensitive to increased Cl levels, through changes in pattern of stratification, thus providing a mechanism for the shift from C. scutifer to B. longispina. The reduction of the acidification pressure seems to override the Cl effects on microcrustaceans at low Cl levels in salt-affected lakes recovering from acidification. However, prognoses for growing traffic and increasing road salting raise concern for many recovering lakes located in proximity to roads and urbanized areas.

Different bacterial communities in ectomycorrhizae and surrounding soil

Several eukaryotic symbioses have shown to host a rich diversity of prokaryotes that interact with their hosts. Here, we study bacterial communities associated with ectomycorrhizal root systems of Bistorta vivipara compared to bacterial communities in bulk soil using pyrosequencing of 16S rRNA amplicons. A high richness of Operational Taxonomic Units (OTUs) was found in plant roots (3,571 OTUs) and surrounding soil (3,476 OTUs). The community composition differed markedly between these two environments. Actinobacteria, Armatimonadetes, Chloroflexi and OTUs unclassified at phylum level were significantly more abundant in plant roots than in soil. A large proportion of the OTUs, especially those in plant roots, presented low similarity to Sanger 16S rRNA reference sequences, suggesting novel bacterial diversity in ectomycorrhizae. Furthermore, the bacterial communities of the plant roots were spatially structured up to a distance of 60 cm, which may be explained by bacteria using fungal hyphae as a transport vector. The analyzed ectomycorrhizae presents a distinct microbiome, which likely influence the functioning of the plant-fungus symbiosis.

Seasonal trends in the biomass and structure of bryophyte-associated fungal communities explored by 454 pyrosequencing

Bryophytes are a dominant vegetation component of the boreal forest, but little is known about their associated fungal communities, including seasonal variation within them. Seasonal variation in the fungal biomass and composition of fungal communities associated with three widespread boreal bryophytes was investigated using HPLC assays of ergosterol and amplicon pyrosequencing of the internal transcribed spacer 2 (ITS2) region of rDNA. The bryophyte phyllosphere community was dominated by Ascomycota. Fungal biomass did not decline appreciably in winter (P=0.272). Significant host-specific patterns in seasonal variation of biomass were detected (P=0.003). Although seasonal effects were not the primary factors structuring community composition, collection date significantly explained (P=0.001) variation not attributed to locality, host, and tissue. Community homogenization and a reduction in turnover occurred with the onset of frost events and subzero air and soil temperatures. Fluctuations in the relative abundance of particular fungal groups seem to reflect the nature of their association with mosses, although conclusions are drawn with caution because of potential methodological bias. The moss-associated fungal community is dynamic, exhibiting seasonal turnover in composition and relative abundance of different fungal groups, and significant fungal biomass is present year-round, suggesting a winter-active fungal community.

Epiphytic algae and lichen cover in boreal forests-a long-term study along a N and S deposition gradient in Sweden

The aim was to describe spatiotemporal patterns of colonization of spruce branches by algae and lichens and the relationship with decreasing deposition of N and S. Coverage was estimated annually over 10 years for four Swedish Integrated Monitoring catchments with varying deposition levels. Initial hypotheses were that algal coverage would be positively correlated with deposition and that lichen coverage would be negatively correlated with S and positively with N deposition. Data were analyzed using regression, ANOVA, and partial least square regression. The results showed a temporal decrease in the coverage of algae but an increase in colonization rates, while lichens showed less uniform patterns. Within catchments, algae and lichen coverages were positively correlated with mainly S deposition. Across catchments, coverage of algae increased, while the coverage of lichens decreased with increasing N and S deposition. Colonization rates of both algae and lichens showed weak correlations with both spatial and temporal trends in N and S deposition. Thus, while N and S deposition had an effect on the colonization and coverage of algae and lichens, other factors are also important.

High diversity of root associated fungi in both alpine and arctic Dryas octopetala

BACKGROUND

Dryas octopetala is a widespread dwarf shrub in alpine and arctic regions that forms ectomycorrhizal (ECM) symbiotic relationships with fungi. In this study we investigated the fungal communities associated with roots of D. octopetala in alpine sites in Norway and in the High Arctic on Svalbard, where we aimed to reveal whether the fungal diversity and species composition varied across the Alpine and Arctic regions. The internal transcribed spacer (ITS) region of nuclear ribosomal DNA was used to identify the fungal communities from bulk root samples obtained from 24 plants.

RESULTS

A total of 137 operational taxonomic units (OTUs) were detected (using 97% similarity cut off during sequence clustering) and well-known ECM genera such as Cenococcum, Cortinarius, Hebeloma, Inocybe and Tomentella occurred frequently. There was no decrease in fungal diversity with increasing latitude. The overall spatial heterogeneity was high, but a weak geographical structuring of the composition of OTUs in the root systems was observed. Calculated species accumulation curves did not level off.

CONCLUSIONS

This study indicates that the diversity of fungi associated with D. octopetala does not decrease in high latitude arctic regions, which contrasts observations made in a wide spectrum of other organism groups. A high degree of patchiness was observed across root systems, but the fungal communities were nevertheless weakly spatially structured. Non-asymptotical species accumulation curves and the occurrence of a high number of singletons indicated that only a small fraction of the fungal diversity was detected.

When has an abandoned field become a semi-natural grassland or heathland?

This study presents a meta-analysis of a collective dataset describing the succession from abandoned fields to semi-natural grassland and heathland vegetation over the past century. The study objectives were to develop a method for statistical discrimination between abandoned fields and semi-natural habitats and to analyze the probability that an abandoned field had developed into a semi-natural habitat. A statistical classification model was developed, based on lists of vascular plants from 2059 plots from Danish semi-natural grasslands and heathlands, and abandoned fields of varying age. This model was shown to discriminate effectively between abandoned fields and semi-natural habitats, and it was found to be potentially useful for the detection of abandoned fields approaching semi-natural vegetation. We suggest that the model may help clarify restoration targets and assess biological condition in formerly cultivated areas. Statistical modeling revealed that succession age, period of abandonment and succession trajectory had significant effects on the probability that abandoned fields reached the semi-natural phase. Our study indicates that restoration projects targeting grassland and heathland should take local species pools and soil fertility into account.

The soil propagule bank in a boreal old-growth spruce forest: changes with depth and relationship to aboveground vegetation

The species composition and the depth distribution of the soil propagule banks of bryophytes and vascular plants from three different soil layers in a boreal old-growth spruce forest in SE Norway were studied using the emergence method. A total of 34 taxa germinated with a predominance of ferns and mosses. The frequency of the different species exhibits a common community pattern with a few common and a large number of low frequency species. The tree Betula pubescens, the ferns Athyrium filix-femina, Gymnocarpium dryopteris, and Phegopteris connectilis, and the mosses Plagiothecium laetum agg. and Polytrichum spp. were the most frequent. There is only a moderate correspondence, decreasing with soil depth, between the propagule bank and the aboveground vegetation in the sampled plots. In the soil profile, the litter layer on average had more taxa than the peaty mor and bleached layer (7.7, 6.0, and 5.5 taxa, respectively). Five of the 17 taxa occurring in more than 10% of the soil samples from the different soil layers were significantly more frequent in the upper soil layer, while two taxa were more frequent in either peaty mor and (or) the bleached layer than in the uppermost layer. The propagule bank in the different soil layers represents an in situ potential for regeneration of the vegetation after different degrees of disturbance in the forest floor. Key words: disturbance, soil propagule bank, boreal forest, bryophytes, vascular plants.