| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- Hylander, Kristoffer, et al.
(författare)
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In situ survival of forest bryophytes in small-scale refugia after an intense forest fire
- 2010
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 21:6, s. 1099-1109
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Tidskriftsartikel (refereegranskat)abstract
- Question Species can persist in landscapes with recurring disturbances either by migrating to places suitable for the moment or by enduring the threatening conditions. We investigated to what extent boreal forest bryophytes survived an intense forest fire in situ and whether bryophytes had started to recolonize the area 7-8 years later. Location Tyresta National Park, eastern Sweden. Methods We recorded bryophytes in 14 burnt and 12 forest reference plots (50 x 50 m). In each plot we investigated 15 random 1-m2 micro-plots. In plots in the burnt area we also examined micro-plots at locations of all fire refugia, and in case of the forest references, of 10 potential refugia. Results We found on average three small refugia per 50 x 50-m plot; each containing on average 4.8 forest bryophytes, a level similar to that of micro-plots in the references, but significantly higher than in random micro-plots in the burnt plots (1.5 species). Many refugia were located in rocky areas, but few were in wet sites. The burnt area remained dominated by a few fire-favoured species, even if recolonization of forest bryophytes had begun. There was, however, no significant correlation between number of refugia and number of forest species in random micro-plots, leaving open the question of the importance of refugia as regulators of early succession. Conclusion We conclude that small-scale refugia can also occur for sensitive species such as forest bryophytes, and that the refugia in our case were frequently found on rocky or mesic rather than wet sites. The role of such refugia in recolonization, however, warrants further investigation.
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| 5. |
- Johansson, Victor, et al.
(författare)
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Detection probability and abundance estimation of epiphytic lichens based on height-limited surveys
- 2010
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 21, s. 332-341
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Tidskriftsartikel (refereegranskat)abstract
- QuestionsWhat are the detection probabilities of epiphytic crustose lichens on oak (Quercus robur) when only the lowest 2 m of the trunk are surveyed? How does the abundance of lichen species change with height above the ground, and is the change related to tree age? How well can total abundance (0-6 m) be predicted based on data from the lowest 2 m? Which tree characteristics explain the vertical distribution of the study species?LocationSoutheast Sweden.MethodsThe occurrence and abundance of eight crustose lichen species were recorded on 35 oaks, 0-6 m from the ground.ResultsThe detection probability was high (> 96%) for seven out of the eight species. The abundance of six species declined significantly with increasing height. For five species, > 69% of the total abundance (0-6 m) was recorded on the lowest 2 m. The proportion of the total abundance present above 2 m increased significantly with age for three species. Models predicting total abundance based on data from the lowest 2 m and diameter explained > 80% of the deviance for all except one species. The vertical distribution of the study species was explained by bark fissure depth, area and cover of macrolichens.ConclusionsFor crustose lichens associated with old oaks, surveying only the lowest 2 m of the trunk yields reliable occurrence data and fairly good estimates of total abundance. However, before interpreting data from the lowest 2 m, knowledge of species vertical distribution, and how the distribution changes with tree age is essential.
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| 6. |
- Marteinsdottir, Bryndis, et al.
(författare)
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Development of vegetation patterns in early primary succession
- 2010
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 21:3, s. 531-540
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Tidskriftsartikel (refereegranskat)abstract
- Question We investigated colonisation filters in early plant community development on a glacial outwash plain. We asked if these were related to seed limitation or to a lack of safe sites, if topographical heterogeneity affected species patchiness and how species life cycles influence successional trajectories. Location An outwash plain (Skeithararsandur) in southeast Iceland. Methods We identified surface heterogeneity at two different scales, ca. 10-15 cm (larger stones and established plants) and ca. 50 m (shallow depressions representing dry river beds) at two study sites. We quantified species cover, flowering plant density, seed production, seed rain, seed bank density, seedling emergence and seedling survival from June 2005 to June 2007 for the whole plant community, and measured seed production for five species. Results Mean vegetation cover was < 2.5% at the sites. Low emergence rates and high seedling mortality were the two main recruitment filters. Only 1.4% of seedlings emerging in 2005 survived into the 2007 growing season. Topographical heterogeneity had little effect on plant colonisation. High annual variation was recorded, and the two study sites (ca. 2 km apart) differed in their colonisation success. Of the five species, establishment of Cerastium alpinum and Silene uniflora was most limited by lack of seeds, whereas establishment of Luzula spicata, Poa glauca and Rumex acetosella was most limited by safe sites. Conclusions We conclude that colonisation processes and patterns in early primary succession on Skeithararsandur were largely influenced by stochastic factors.
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| 7. |
- Mathisen, Karen Marie, et al.
(författare)
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Moose density and habitat productivity affects reproduction, growth and species composition in field layer vegetation
- 2010
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 21, s. 705-716
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Tidskriftsartikel (refereegranskat)abstract
- QuestionWhat is the effect of a gradient in moose density on reproduction, growth and functional composition of the field layer vegetation in a boreal forest, and how is this effect modified by habitat productivity?LocationNorthwest of Umea, Vasterbotten, northern Sweden.MethodsField layer vegetation was surveyed in an experimental setup with simulation of three different moose densities and a control in eight study sites along a gradient of habitat productivity.ResultsWe found that increased moose density led to decreased cover and reproductive effort of a browsed dwarf shrub (bilberry, Vaccinium myrtillus L.) and increased cover and reproductive effort of a non-browsed graminoid (wavy hair-grass, Avenella flexuosa (L.) Drejer). Increased moose density led to increased light availability and probably reduced competition from V. myrtillus. Total reproductive effort in the field layer vegetation increased, height decreased and cover of light-demanding species and graminoids increased with increasing moose density. The effects of moose density were modified by the productivity gradient, leading to a higher relative increase in light availability and reproductive effort in highly productive areas than in low productive areas.ConclusionsIncreased light availability was an important indirect effect of moose density, leading to less competition for light and a shift towards early successional species. The effect of moose density on light availability was modified by habitat productivity, leading to stronger relative effects in highly productive areas than in low productive areas.
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| 8. |
- Pajunen, A.M., et al.
(författare)
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Compositional differentiation, vegetation-environment relationships and classification of willow-characterised vegetation in the western Eurasian Arctic
- 2010
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 21:1, s. 107-119
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Tidskriftsartikel (refereegranskat)abstract
- Question: How does willow-characterised tundra vegetation of western Eurasia vary, and what are the main vegetation types? What are the ecological gradients and climatic regimes underlying vegetation differentiation?Location: The dataset was collected across a wide spectrum of tundra habitats at 12 sites in subarctic and arctic areas spanning from NW Fennoscandia to West Siberia.Methods: The dataset, including 758 vegetation sample plots (relevés), was analysed using a TWINSPAN classification and NMDS ordination that also included analyses of vegetation-environment correlations.Results: Based on the TWINSPAN classification, eight vegetation types characterised by willow (cover of upright willows >10%) were discerned: (1) Salix glauca-Carex aquatilis type, (2) Aulacomnium-Tomentypnum type, (3) Salix-Betula-Hylocomium type, (4) Salix lanata-Brachythecium mildeanum type, (5) Salix-Pachypleurum type, (6) S. lanata-Myosotis nemorosa type, (7) Salix-Trollius-Geranium type and (8) Salix-Comarum palustre-Filipendula ulmaria type. Willow-characterised vegetation types were compositionally differentiated from other tundra vegetation and were confined to relatively moist valley and sloping tundra sites, from mire to mineral soils. These vegetation types were encountered across a broad latitudinal zone in which July mean temperature ranged from 6 to 10°C.Conclusions: Willow-characterised tundra vegetation forms a broad category of ecologically and geographically differentiated vegetation types that are linked to dwarf shrub tundra, shrub tundra or mire. Because of complex ecological gradients underlying compositional differentiation, predicting the responses of willow-characterised tundra vegetation to a warming climate may be complicated.
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| 9. |
- Plue, Jan, et al.
(författare)
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Consistent seed bank spatial structure across semi natural habitats determines plot sampling
- 2012
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 23:3, s. 505-516
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Tidskriftsartikel (refereegranskat)abstract
- Question: Seed bank sampling remains a critical bottleneck to the quality of studies investigating community patterns in the seed bank. The main cause is a large knowledge gap in two aspects critical to sampling, i. e. spatial autocorrelation and species-area relations. The central question of this study is howthe seed bank of a single plot should be sampled, in order to obtain more precise estimates on plot seed bank characteristics, without resorting to a disproportionate investment of available resources. Similar seed bank samples may then enable better plot-based statistical inference of ecological patterns in the seed bank in community ecology studies. Location: Semi-natural habitats in Flanders (Belgium) and northern France. Methods: We investigated the fine-scale spatial structure of individual seed banking species across 12 2.1 m 9 2.1 m plots in three widespread habitats: temperate forest, grassland and heathland. Soil core samples (128) were collected in each plot, using a combined systematic (64) and random design (64). This enabled both geostatistical analyses of the fine-scale spatial structure of individual species-plot combinations as well as the calculation of sampled-based species rarefaction curves. Results: Fine-scale (i. e. within plot) spatial seed bank structure was detected in all plots in each habitat, in at least one or usually more plant species. Over half of the species records displayed significant spatial structure -visible as a random distribution of seed clusters -with medium to strong spatial dependence between point observations of a species of ca. 30 cm. Species rarefaction curves did not attain an asymptote at the actual sampling intensity of 128 samples. Seven out of 12 extrapolated species rarefaction curves did reach an asymptote in less than 384 samples. Conclusions: Using these consistent results in spatial structure and species-area relations across habitats, we present a method of how researchers can develop a tailor-made seed bank design to accommodate their individual needs, abiding by simple predefined boundaries. When the tailored design samples ca. 3% of a plot surface area along a systematic grid with a mesh width of at least 30 cm, these studies will potentially significantly increase the comparability among future seed bank community studies in semi-natural habitats.
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| 10. |
- Snäll, Tord
(författare)
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Forest fire history, aspen and goat willow in a Fennoscandian old-growth landscape: are current population structures a legacy of historical fires?
- 2012
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Ingår i: Journal of Vegetation Science. - : Wiley. - 1100-9233 .- 1654-1103. ; 23, s. 1159-1169
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Tidskriftsartikel (refereegranskat)abstract
- Questions Is the current aspen or goat willow populations in boreal old-growth forest a legacy of the historical fires? Location A middle-boreal, old-growth forest landscape with a large proportion of wetlands in eastern Finland. Method Forest fire history of a 2100-ha area was reconstructed using fire scars, forest age estimates and the presence or absence of charred stumps and charcoal particles in the soil in 63 systematically located plots. Age and size structures of aspen and goat willow were studied in a subsample of 12 plots. Results During the past 400yr, forest fires have been seven times more numerous in the study area than could be expected based on modern lightning fire statistics. The ages of mature aspens (average 177 and maximum 213yr) and mature goat willows (average 111 and maximum 173yr) were higher than earlier reported, strikingly so in goat willow. Aspen age structure clearly reflected the past fires. Most aspens originated from the beginning of the 19th century, during a period of frequent forest fires. The regeneration of aspen leading to mature trees has been very low since the cessation of forest fires in the late 19th century. In turn, goat willow has also regenerated in spite of the absence of fires. Conclusions The majority of the mature aspen trees were recruited at the time of the last fires, and there was a notable lack of middle-aged trees. This relationship to fires was not valid for goat willow. The main reason for the lack of young aspen cohorts in aspen populations in Fennoscandian old-growth stands is most likely the lack of forest fires. Small-scale gap dynamics cannot offset the lack of large-scale disturbances, such as forest fires, for the regeneration of aspen, possibly because of the prevailing herbivory and competitive effects. Hence, the population decline of aspen is likely to continue and to threaten a wealth of species specialized on aspen in boreal forests.
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