| 1. |
- Bruun, Hans Henrik, et al.
(författare)
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Effects of altitude and topography on species richness of vascular plants, bryophytes and lichens in alpine communities
- 2006
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Ingår i: Journal of Vegetation Science. - 1100-9233 .- 1654-1103. ; 17:1, s. 37-46
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Tidskriftsartikel (refereegranskat)abstract
- Question: What is the relationship between species richness of vascular plants, bryophytes and macrolichens, and two important gradients in the alpine environment, altitude and local topography? Location: Northernmost Fennoscandia, 250-152 m a.s.l. corresponding to the range between timberline and mountain top. Methods: The vegetation was sampled in six mountain areas. For each 25 vertical metres, the local topographic gradient from wind-blown ridge to snowbed was sampled in quadrats of 0.8 m x 0.8 m. Patterns in species richness were explored using Poisson regression (Generalized Linear Models). Functional groups of species, i.e. evergreen and deciduous dwarf-shrubs, forbs, graminoids, mosses, hepatics and lichens were investigated separately. Results: Functional groups showed markedly different patterns with respect to both altitude and topography. Species richness of all vascular plants showed a unimodal relationship with altitude. The same was true for graminoids, forbs and lichens analysed separately, but forb richness peaked at Much higher altitudes than total richness. The richness of dwarf-shrubs decreased monotonically with altitude, whereas richness of mosses and liverworts showed an increasing trend. Significant interactions between altitude and local topography were present for several groups. The unimodal pattern for total plant species richness was interpreted in terms of local productivity, physical disturbance, trophic interactions, and in terms of species pool effects. Conclusions: Patterns in local species richness result from the action of two opposing forces: declining species pool and decreasing intensity of competition with altitude.
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| 2. |
- Reitalu, Triin, et al.
(författare)
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Responses of grassland species richness to local and landscape factors depend on spatial scale and habitat specialization
- 2012
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1654-1103 .- 1100-9233. ; 23:1, s. 41-51
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Tidskriftsartikel (refereegranskat)abstract
- Questions: To what extent is species richness in semi-natural grasslands related to local environmental factors and (present/past) surrounding landscape structure? Do responses of species richness depend on degree of habitat specialization (specialists vs generalists) and/or scale of the study? Location: Öland, Sweden. Methods: Richness of herbaceous vascular plants (subdivided into richness of grassland specialists and generalists) was recorded within 50 9 50 cm plots and 0.1–4.8 ha grassland polygons. Generalized linearmodels and hierarchical partitioning were used to identify local factors (habitat area and heterogeneity, grazing intensity, habitat continuity) and landscape factors (proportion of surrounding grassland in 2004, 1938 and 1800, and landscape diversity in 2004)associated with the richness estimates. Results: At the polygon scale, both specialist and generalist richness was positively associated with local habitat area and heterogeneity and, independently of area and heterogeneity, with grazing intensity, habitat continuity and amount of surrounding grassland in 1800. At the plot scale, specialist species richness was positively associated with habitat heterogeneity, amount of surrounding grassland in 2004 and landscape diversity. Plot-scale generalist richness was negatively associated with surrounding grassland in 1938 and positively associated with local grazing intensity. Conclusions: Because both habitat specialization and study scale influence conclusions about relationships between species richness and local and landscape factors, the study highlights the need to consider species diversity at multiple spatial scales when making decisions about grassland management. Large-scale(polygon) species richness is influenced by immigration processes, with both specialists and generalists accumulating in old grasslands over centuries of grazing management. Habitat heterogeneity increased specialist species richness at both scales, suggesting that management policies should favour maintenance of a heterogeneous mosaic of open areas, trees and shrubs in temperate grazed grasslands. Although grassland specialists are sensitive to grassland isolation, in extensively managed landscapes with high landscape diversity input of grassland species from the landscape matrix may buffer negative effects of habitat fragmentation on grassland communities.
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| 3. |
- Auffret, Alistair G., et al.
(författare)
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Grazing networks provide useful functional connectivity for plants in fragmented systems
- 2012
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 23:5, s. 970-977
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Tidskriftsartikel (refereegranskat)abstract
- Question To what extent does the movement of animals between fragmented habitat patches provide functional connectivity via endozoochorous seed dispersal? Location The Stockholm archipelago, Sweden. Methods We followed all movements of livestock between islands during one grazing season. After each movement, manure was collected and its seed content assessed through seedling emergence. Seedling data were then compared to vegetation surveys from the grazed islands with regard to functional traits. Results Light- and nitrogen-demanding locally abundant species, and those with relatively small and persistent seeds were more likely to be moved between islands. For quantitative traits, only a subset of the available trait ranges were dispersed, with extreme values left behind. Species apparently specialized to other means of dispersal emerged from the manure samples. Neither dispersed traits nor seed density changed with timing of movement, but seed richness and diversity both increased throughout the season. The subsets of endozoochorously-dispersed species in the established vegetation were more similar than non-dispersed subsets between islands linked by livestock. Conclusions Grazing networks contribute to the connectivity of the core species in the system, and could provide useful tools for grassland management in fragmented landscapes.
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| 4. |
- Cousins, Sara
(författare)
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Extinction debt in fragmented grasslands: paid or not?
- 2009
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 20:1, s. 3-7
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Tidskriftsartikel (refereegranskat)abstract
- Fragmentation of grasslands and forests is considered amajor threat to biodiversity. In the case of plants, theeffect of fragmentation or landscape context is still unclearand published results are divergent. One explanation forthis divergence is the slow response of long-lived plants,creating an extinction debt. However, this has not beenempirically confirmed. In this study, data were compiledfrom broad-scale studies of grasslands from throughoutthe world that relate plant diversity to fragmentationeffects. Only seven studies from northern Europe, out ofa total 61, gave any information on actual habitat fragmentationin time and space. In landscapes with 410%grassland remaining, present-day species richness wasrelated to past landscape or habitat pattern. In landscapeswith o10% grassland remaining, in contrast, plant speciesrichness was more related to contemporary landscapeor habitat pattern. Studies from landscapes with 410%grassland remaining supported the concept of an extinctiondebt, while studies from more fragmented landscapesdid not provide any evidence of an extinction debt. Inorder to make generalisations about historical legacies onspecies diversity in grasslands it is important to consider arange of highly transformed landscapes, and not onlylandscapes with a high amount of grassland remaining.
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| 5. |
- Dengler, Jürgen, et al.
(författare)
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Species constancy depends on plot size - a problem for vegetation classification and how it can be solved
- 2009
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 20:4, s. 754-766
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Tidskriftsartikel (refereegranskat)abstract
- Question While it is well known that species richness depends on plot size, it is not generally recognised that the same must be true for constancy. Accordingly, many authors use varying plot sizes when classifying vegetation based on the comparison of constancies between groups of plots. We ask whether the constancy-area relationship follows a general rule, how strong the effect of plot sizes is on constancies, and if it is possible to correct constancies for area. Location For empirical evaluation, we use data from plant communities in the Czech Republic, Sweden and Russia. Methods To assess the potential influence of differences in plot size on constancies, we develop a mathematical model. Then, we use series of nested plot species richness data from a wide range of community types (herbaceous and forest) to determine the parameters of the derived function and to test how much the shape of the constancy-area relationship depends on taxa or vegetation types. Results Generally, the constancy-area relationship can be described by C (A)=1-(1-C-0)((A/A0)boolean AND d), with C being constancy, A area, C-0 known constancy on a specific area A(0), and d a damping parameter accounting for spatial autocorrelation. As predicted by this function, constancies in plant communities always varied from values near 0% to near 100% if plot sizes were changed sufficiently. For the studied vegetation types, a two- to fourfold increase in plot size resulted in a change of conventional constancy classes, i.e. an increase of constancy by 20% or more. Conclusions Vegetation classification, which largely relies on constancy values, irrespective of whether traditional or modern fidelity definitions are used, is strongly prone to distorting scale effects when releves of different plot sizes are combined in studies. The constancy-area functions presented allow an approximate transformation of constancies to other plot sizes but are flawed by idiosyncrasies in taxa and vegetation types. Thus, we conclude that the best solution for future surveys is to apply uniform plot sizes within a few a priori delimited formations and to determine diagnostic species only within these formations. Finally, we suggest that more detailed analyses of constancy-area relationships can contribute to a better understanding of species-area relationships because the latter are the summation of the first for all species.
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| 6. |
- Eriksson, Ove, et al.
(författare)
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Land-use history and fragmentation of traditionally managed grasslands in Scandinavia
- 2002
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 13:5, s. 743-748
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Tidskriftsartikel (refereegranskat)abstract
- Plants associated with traditional agricultural landscapes in northern Europe and Scandinavia are subjected to drastic habitat fragmentation. In this paper we discuss species response to fragmentation, against a background of vegetation and land-use history. Recent evidence suggests that grassland-forest mosaics have been prevalent long before the onset of human agriculture. We suggest that the creation of infield meadows and outland grazing (during the Iron Age) increased the amount and spatial predictability of grasslands, resulting in plant communities with exceptionally high species densities. Thus, distribution of plant species in the present-day landscape reflects historical land-use. This holds also when traditional management has ceased, due to a slow response by many species to abandonment and fragmentation. The distribution patterns are thus not in equilibrium with the present habitat distribution. Fragmentation influences remaining semi-natural grasslands such that species density is likely to decline as a result of local extinctions and invasion by habitat generalists. However, species that for a long time have been subjected to changing mosaic landscapes may be more resistant to fragmentation than is usually believed. Conservation should focus not only on 'hot-spots' with high species richness, but also consider species dynamics in a landscape context.
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| 7. |
- Gallegos Torell, Åsa, et al.
(författare)
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Computer-aided calibration for visual estimation of vegetation cover
- 2009
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 20, s. 973-983
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Tidskriftsartikel (refereegranskat)abstract
- QuestionWhat precision and accuracy of visual cover estimations can be achieved after repeated calibration with images of vegetation in which the true cover is known, and what factors influence the results?MethodsDigital images were created, in which the true cover of vegetation was digitally calculated. Fifteen observers made repeated estimates with immediate feedback on the true cover. The effects on precision and accuracy through time were evaluated with repeated proficiency tests. In a field trial, cover estimates, before and after calibration, were compared with point frequency data.ResultsEven a short time of calibration greatly improves precision and accuracy of the estimates, and can also reduce the influence of different backgrounds, aggregation patterns and experience. Experienced observers had a stronger tendency to underestimate the cover of narrow-leaved grasses before calibration. The field trial showed positive effects of computer-based calibration on precision, in that it led to considerably less between-observer variation for one of the two species groups.ConclusionsComputer-aided calibration of vegetation cover estimation is simple, self-explanatory and time-efficient, and might possibly reduce biases and drifts in estimate levels over time. Such calibration can also reduce between-observer variation in field estimates, at least for some species. However, the effects of calibration on estimations in the field must be further evaluated, especially for multilayered vegetation.
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| 8. |
- Hedenås, H, et al.
(författare)
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Spatial distribution of epiphytes on Populus tremula in relation to dispersal mode
- 2003
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 14:2, s. 233-242
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Tidskriftsartikel (refereegranskat)abstract
- We examined if the spatial distribution of epiphytes in a forest stand differs between two sexually and three asexually dispersed species. As study species we have chosen two sexually dispersed species, the lichen Collema curtisporum and the bryophyte Orthotrichum speciosum, and three asexually dispersed species, the lichens C. furfuraceum and Leptogium saturninum and the bryophyte O. obtusifolium. All of these species grow on Populus tremula. In P. tremula stands, individual trees may be regarded as distinct patches for the studied species, while the stand represents a 'landscape" of discrete patches. The study was performed in two relatively homogeneous forest stands. The study revealed that the asexually dispersed species were more common than the sexually dispersed. It was also shown that the sexually dispersed species were more aggregated than P. tremula in both stands. In contrast, the distribution of the asexually dispersed species mirrors, more or less, the distribution of their host, i.e. the spatial pattern shown by P. tremula. It is unlikely that the measured environmental variables strongly influenced the observed spatial distribution. Thus, we suggest that the different dispersal and establishment strategies were important in shaping the local distribution of the species.
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| 9. |
- Hedwall, Per-Ola, et al.
(författare)
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Changes in the abundance of keystone forest floor species in response to changes of forest structure
- 2013
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 24, s. 296-306
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Tidskriftsartikel (refereegranskat)abstract
- Question Does the abundance of keystone forest floor species change in response to changes in the forest structure? Location Sweden Methods We used data from the Swedish National Forest Inventory to investigate changes in the abundance of three common species, as well as the total abundance of all understorey vascular plants (the field layer) in forests in the boreal and temperate parts of Sweden. GLMs and GAMs were used to relate species abundance and temporal changes in abundances to forest structure and forest structural change. Results Productivity, measured as the site index, was the most important determinant of individual species' abundance. The volume of Picea abies, the density of tree stems and forest age were among the most important forest structural variables. We found that the dwarf shrub Vaccinium myrtillus, the narrow-leaved grasses (mainly Avenella flexuosa) and the total field layer cover decreased in boreal Sweden from 1994 through 2010 and that these changes coincided with an increase in forest density and with a reduction in forest age. Conclusions Changes in Swedish forests to higher tree layer density and younger age appear to contribute significantly to current changes in forest floor vegetation. The use of more intensive thinning practices to reduce the total density of the forest and to increase the proportion of broad-leaved tree species and Pinus sylvestris would favour the forest floor species in this study. Moreover, increasing forest age (i.e. the length of rotation periods) might favour V. myrtillus in particular, for which the time since disturbance is important for the recovery of pre-disturbance abundance. However, increased thinning intensity and forest age will reduce the potential for wood production, implying a trade-off between production of wood and maintenance of well-developed forest floor vegetation.
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| 10. |
- Hofgaard, Annika, et al.
(författare)
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Tree recruitment above the treeline and potential for climate-driven treeline change
- 2009
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 20:6, s. 1133-1144
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Tidskriftsartikel (refereegranskat)abstract
- Questions How do population structure and recruitment characteristics of Betula saplings beyond the treeline vary among climatic regions, and what is the potential for development into tree-sized individuals with interacting grazing pressure? Location Scandes Mountains. Methods Sapling characteristics of Betula pubescens subsp. tortuosa, their topographic position above the treeline, growth habitat and evidence of recent grazing was investigated in three areas with a long continuous grazing history, along a latitudinal gradient (62-69 degrees N). Results Saplings were common up to 100 m above the treeline in all areas. The northern areas were characterised by small (< 30 cm) and young (mean 14 years old) saplings in exposed micro-topographic locations unfavourable to long-term survival. In the southern area, broad height (2-183 cm) and age (4-95 years; mean 32 years) distributions were found in sheltered locations. Age declined with altitude in all areas. Sapling growth rate varied within and between areas, and the age x height interaction was significant only in the southern area. Growth rates decreased from south to north and indicated a considerable time required to reach tree size under prevailing conditions. Conclusions Regional differences can be attributed to climatic differences, however, interacting biotic and abiotic factors such as micro-topography, climate and herbivory, mutually affect the characteristics of birch saplings. In view of the long time needed to reach tree size, the generally expected evident and fast treeline advance in response to climate warming may not be a likely short-term scenario. The sapling pool in the southern region possesses strongest potential for treeline advance.
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