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The bryophyte vegetation of three acidophilous forest communities of four habitats on radiolarian bedrock were investigated in the Bükk Mts. The bryophyte layers of Deschampsio-Fagetum sylvaticae Soó 1962, Genisto pilosae-Quercetum petraeae Zólyomi et al. 1958 and Genisto tinctoriae-Quercetum petraeae Klika 1932 were compared on the basis of the dominance and frequency of 15 bryophyte species in the communities using ordination and cluster analysis methods. The soil pH and the photosynthetically active radiation (PAR) values in the four sampling areas were also compared. The results refer to a strong connection of the bryophyte species composition considering the dominance values and frequency of the species with the community type in different spatial scale. The soil pH values do not differ significantly in the habitats and they refer to a high amount of hidden acidity which is the effect of the radiolarian bedrock type. The PAR values have been statistically analysed and represent the homogeneity or the heterogeneity of the canopy layer and the effect of the exposition. The results show significant difference in the variances of PAR values between Genisto pilosae-Quercetum and the other two community types and the mean PAR value of Deschampsio-Fagetum sylvaticae differ significantly from the mean values of the two Genisto tinctoriae-Quercetum petraeae stands.
We review the population ecology of Allium ursinum according to its life history, phenology, demography, dispersal, and population dynamics. Spatial distribution is reviewed on two spatial scales. First, on a broad scale over Europe, in relation to the habitat requirement of the species. Second, on a fine scale of individual patches, presenting some results about the local processes of density regulation and patch formation. We conclude that A. ursinum has a distinct, hitherto non-described, strategy for monopolizing space and dominating the forest floor. This Clan-of-Clones strategy has the following attributes. 1) Most of the seeds are dispersed close to the parent. 2) Seedling establishment is facilitated by the surrounding adults. 3) Allocation to vegetative reproduction is relatively small; its main role is to prolong local persistence. 4) The genet is not integrated physiologically, except for a transient connection between parent and offspring. An important consequence of the Clan-of-Clones strategy is that occupied patches can be fine-grained mosaics in terms of genetic composition and age groups.
The on-going Biodiversity Monitoring in Switzerland Programme (BDM) has monitored vascular-plant species richness since 2001. This long-term programme focuses on two indicators at different spatial scales. First, the local diversity indicator monitors changes of species richness within habitats or types of land use (within-habitat diversity). Second, the landscape diversity indicator is utilized to describe landscape diversity (i.e., within-habitat mosaic diversity). Here we examine if the reproducibility of the BDM methods is sufficiently precise to detect future changes in species richness. We demonstrate that systematic methodical errors are negligible. Random errors that make changes more difficult to detect are also small. We calculate the Minimum Detectable Difference (MDD) for selected BDM strata using the variance of measured values. Then we deduce the MDD values for paired samples using data from grasslands and forests in the Canton Argovia. With 2.4 and 1.6 species they are promisingly precise. We develop a simple scenario for possible changes in species richness and show that they surpass the deduced MDD values by a factor four to six. We conclude that the BDM methods are appropriate for detecting future changes in species richness.
Ad hoc decisions during fieldwork reduce the accuracy and reliability of vegetation maps. A method is proposed to objectify vegetation (thematic aspects) mapping (spatial aspects) for monitoring (temporal aspects). The most accurate and reliable description of the vegetation is a list of all plant species found within a plot. Therefore, the proposed method is an interpolation of a spatially representative sample of permanent plots combined with aerial photo interpretation. The method is objective because surveyors do not have to make decisions during fieldwork based on their personal judgement. Moreover, it is flexible, because the classification and interpolation methods can be adapted to specific views or needs depending on the aim of a study. The method was applied to an area in the north of the Netherlands in 1998. A sampling design with a density of 1 plot/ha was used, and interpolated with a perpendicular bisector. In 2002, the number of plots/ha was doubled. The influence of sample density on the mapping results was studied because it is an important decision to be made before fieldwork. Two plots/ha seem to be sufficient in order to obtain reliable information on patterns of plant species composition and vegetation types of the area, and their change over time. However, in patches where vegetation varies on a very small spatial scale this plot density was insufficient.
Community ecologists have become increasingly interested in analyzing the phylogenetic diversity of species assemblages. Species that co-occur in the same habitats often share a common phylogenetic history such that at coarse spatial scales a species assemblage with a locally clustered phylogenetic structure is usually associated with the presence of habitat filtering mechanisms. However, more recently it has been hypothesized that environmental filters act primarily on the relative abundance of species rather than on their simple presences and absences, reducing the species’ probabilities to persist in given environmental conditions. This process may produce a non-random distribution of species abundances in the regional phylogeny even in the absence of a locally clustered phylogenetic structure. In this paper, using data from the urban flora of Brussels (Belgium) we tested for the presence of non-randomness in the distribution of abundances among the species phylogenetic structure. We argue that the observed pattern of low species phylogenetic distinctiveness at increasing species abundances is compatible with environmental filtering processes.
Spiders contribute essentially to the arthropod community of forests and are known to be distributed in non-random pattern according to environmental, structural, competitive, and predacious conditions. The aim of the study was to investigate the effects of the distance to trees on the distribution pattern of soil-dwelling spiders. We verified the hypothesis that stem-close and stem-distant microhabitats differ with respect to taxonomical and ecological characteristics of spider assemblages, hence, functional significance on a small spatial scale. Ground-dwelling spiders were collected with pitfall traps in positions close (20–30 cm) and distant (2 m) to the stem bases in mature forests of different stand types (spruce, Douglas fir, beech-spruce, oak-beech). To identify significant drivers of spider assemblage composition, environmental parameters were assessed in relation with the arrangement of pitfall traps. The study documented significant variability in the composition of spider assemblages of stem-close and stem-distant pitfall traps within each of the study sites. The position of traps strongly affected species richness, species composition, activity density, and dominance structure. Thus, sampling at both positions revealed that the species richness of spiders is spatially restricted. Moreover, spider assemblage structure differed in the classification of species to size and ecological preference. Those results implicate potential consequences for their functional role in forests in relation to the distance to the trees.
, J.M. and M.A. Leibold. 2002. Spatial scale dictates the productivity-biodiversity relationship. Nature 416:427-430. Spatial scale dictates the productivity-biodiversity relationship Nature
The effects of stand structure, tree species composition, proportion of habitat types and land use history on breeding bird assemblages in temperate mixed forests in Western Hungary were studied. The species richness, the abundance and the composition of the whole breeding bird assemblage and of some groups formed on the basis of nesting site and rarity were examined. Stand structural variables had the highest impact on the breeding bird assemblage, while tree species composition, the varying proportion of vegetation types and land use history had no significant effect. In the case of the species richness, the abundance and the composition of the whole assemblage, the most important variables were the mean diameter of trees, the vegetation cover of the forest floor and the dead wood volume. The explained variance in the linear models of different groups varied between 20% and 60%, and the relative importance of these three variables also differed considerably. These results indicate that forest management may considerably influence the diversity and the composition of birds, as all the structural elements affecting birds deeply depend on it. Within the shelterwood management system, the elongation of the rotation and regeneration periods, and the relatively high proportion of retention tree groups after harvest could contribute to the conservation of forest birds. Our results also showed that for the forest bird communities, both the prevalence of big trees and the presence of a dense understory layer are important. Management regimes which apply continuous forest cover might be more appropriate for providing these structural elements simultaneously on small spatial scales, and for the maintenance of a more diverse bird community, thus healthier forest ecosystems.
Invasion by alien plant species may be rapid and aggressive, causing erosion of local biodiversity. This is particularly true for islands, where natural and anthropogenic corridors promote the rapid spread of invasive plants. Although evidence shows that corridors may facilitate plant invasions, the question of how their importance in the spread of alien species varies along environmental gradients deserves more attention. Here, we addressed this issue by examining diversity patterns (species richness of endemic, native and alien species) along and across roads, along an elevation gradient from sea-level up to 2050 m a.s.l. in Tenerife (Canary Islands, Spain), at multiple spatial scales. Species richness was assessed using a multi-scale sampling design consisting of 59 T-transects of 150 m × 2 m, along three major roads each placed over the whole elevation gradient. Each transect was composed of three sections of five plots each: Section 1 was located on the road edges, Section 2 at intermediate distance, and Section 3 far from the road edge, the latter representing the “native community” less affected by road-specific disturbance. The effect of elevation and distance from roadsides was evaluated for the three groups of species (endemic, native and alien species), using parametric and non-parametric regression analyses as well as additive diversity partitioning. Differences among roads explained the majority of the variation in alien species richness and composition. Patterns in alien species richness were also affected by elevation, with a decline in richness with increasing elevation and no alien species recorded at high elevations. Elevation was the most important factor determining patterns in endemic and native species. These findings confirm that climate filtering reflected in varying patterns along elevational gradients is an important determinant of the richness of alien species (which are not adapted to high elevations), while anthropogenic pressures may explain the richness of alien species at low elevation.
The vegetation dynamics of semi-arid and arid landscapes are temporally and spatially heterogeneous and subject to various disturbance regimes that act on decadal scales. Traditional field-based monitoring methods have failed to sample adequately in time and space in order to capture this heterogeneity and thus lack the spatial extent and the long-term continuous time series of data necessary to detect anomalous dynamics in landscape behavior. Time series of ecological indicators of land degradation that are collected synoptically from local to global spatial scales can be derived from the 33-year and continuing Landsat satellite archive. Consequently, a retrospective study was conducted on a commercially grazed sagebrush steppe dominated Utah landscape using a time series of standardized Landsat imagery for the period 1972 to 1997. The study had the objectives to (1) characterize and map the historical trends of a remotely-sensed index of vegetation response, a correlate of vegetation cover or phytomass, and (2) to retrospectively infer the cause of this response to historical records of grazing and wet and drought periods. A time series of dry season vegetation index maps were statistically clustered to generate a spatio-temporal map of three coarse trends of vegetation response, i.e., declining, stable, and increasing trends. This study showed that 71% of the landscape's locations had an increasing trend and 29% had a stable trend over the 26-year period. The increasing trend locations were positively correlated with site water balance [the Palmer Drought Severity Index (PDSI)], i.e., vegetation response increased during wet periods and decreased during drought. The increasing trend was positively and negatively (non-linearly) correlated with grazing in individual paddocks from 1980 to 1997.
