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1.
In Sølendet nature reserve in the upper boreal of central Norway, the effects of controlled trampling from 1977 to 1981 were observed in four rich fen localities. The vegetation recovery was monitored on permanent plots on 3–4 occasions during the period 1981–1995. During trampling the vegetation cover was reduced and bare peat increased, particularly in a wet fen expanse locality. Woody species and herbs disappeared or were considerably reduced in cover, while some graminoids (e.g. Carex spp. and Eriophorum angustifolium ) and bryophytes (e.g. Campylium stellatum and Scorpidium cossonii ), appeared to be quite tolerant. Equisetum palustre and Eriophorum angustifolium increased in cover on two tracks. Several bryophytes survived trampling, but Sphagnum warnstorfii was eradicated. Campylium stellatum and Tomentypnum nitens were able to increase after the decrease in S. warnstorfii . The recovery was dependent on which species were present at the outset and which species arrived early. Further development seemed to depend largely on the species' capacity for rapid increase in cover. Eventually, the more vulnerable dominants of the untrampled vegetation (e.g. Thalictrum alpinum, Trichophorum cespitosum and Sphagnum warnstorfii ) increased in abundance. After 15 years the tracks still contained fewer species and had less vegetation cover than the surroundings.  相似文献   

2.
《Acta Oecologica》2002,23(5):303-312
It is well accepted that intense anthropogenic activities threaten European heathland communities. The negative impact of high intensities of livestock grazing on heath survival has been demonstrated in many studies, however, it does not seem a straightforward consequence in some cases: in the southern Pyrenees, the existence of large heathland patches in intensively grazed areas suggests that other factors interact and affect heath success. In order to gain insight into the factors affecting heath success, this paper analyses the pattern of occurrence of ericaceous shrubs—particularly Erica vagans—and their effects on soils when compared to herbaceous vegetation, under a complex biotic disturbance regime. Survey plots were established in grassland and heathland communities disturbed by both livestock and by burrowing animals on soils with different levels of basic resources. Relative cover of the species on and off molehills was studied. In heathland plots, ericaceous shrubs were more common on old molehills than off them. This pattern was strongest in the poorest soils. Below established heath shrubs, independently of the initial properties of the soils, some basic resources were more available than in intershrub areas. In grazed ecosystems, where continuous trampling and removal of biomass occurs, the heath canopy provides a site for accumulation of litter and insects, which contribute to the build up of a resource-rich layer. We conclude that successful establishment on ubiquitous molehills and suitable, localised changes in the soil under shrubs are some of the factors that explain the success of ericaceous shrubs in complex biotically disturbed areas.  相似文献   

3.
Six 1 ha plots were established in a coastal savanna, called Fathala Forest, in Delta du Saloum National Park, Senegal. Two plots were placed in woodland, two in wooded grassland, and two in transition woodland in order to describe structure and floristic composition of the vegetation. All trees ≥ 5 cm dbh were sampled. The three selected vegetation types showed distinct differences in structure as well as in species composition. Woodland had high density (440–449 individuals per ha), many small trees, and high basal area (13.4 m2per ha). Transition woodland was characterised by low density (54–118 individuals per ha) but many large trees and a relatively large basal area (8.6–12.8 m2 per ha). Wooded grassland was characterised by medium sized trees, it had low density (86–102 individuals per ha) and low basal area (3.8–5.7 m2 per ha). Species richness ranged between 17 and 27 species per ha in the six plots. Only two species were found in all plots, Daniellia oliveri (Caesalpiniaceae) and Prosopis africana (Mimosaceae). Legumes dominated all plots. Wooded grassland and transition woodland had many characteristics of fire-affected vegetation in contrast to woodland. Today wooded grassland encroaches on woodland and transition woodland. Management of the latter two vegetation types should be given priority as they maintain structural and floristic characteristics that are essential to conserve biodiversity and original features of the vegetation, and they are also important for local people who are allowed to make sustainable use of the vegetation.  相似文献   

4.
The Azores Archipelago, located in the North Atlantic Ocean, with an extensive hiking trail system is a promising destination for nature tourism. Hiking is becoming an important touristic attraction, but negative impacts may arise on trails. We aim to evaluate plant biodiversity along eight hiking trails located inside Special Areas of Conservation in two islands with different levels of population density and touristic activity (São Miguel and Flores). Along each trail, 3 plots of 5 × 5 m were used to evaluate the vegetation at every 500 m. Effects of distance to the trail border, altitude, trail, and island, were evaluated by: (i) diversity measures; (ii) floristic composition (different life forms; different biogeographic/conservation status); and (iii) identifying indicator species. Bayesian models run in WinBUGS and the R package “Indicspecies” were used. In total, 111 plant taxa were found, with: (i) highest species richness and diversity in the plots closer to the trail; (ii) highest evenness at the lowest altitude class; (iii) a reduction in the proportion of introduced species with increasing altitude; (iv) a variation in life forms’ composition between and within trails (with the altitude); and (v) the presence of indicator species associated to one altitude, one trail, or one island. The results showed a slight impact on vegetation from the presence of the trails, although with no major changes in the community composition. Presently, factors like the type of land use in areas surrounding the trails may have a deeper effect on plant biodiversity than trail use by visitors.  相似文献   

5.
Abstract. In order to restore natural salt marsh in a 460‐ha nature reserve established in man‐made salt marsh in the Dollard estuary, The Netherlands, the artificial drainage system was neglected and cattle grazing reduced. Vegetation changes were traced through two vegetation surveys and monitoring of permanent plots over 15 yr after the management had been changed. Exclosure experiments were started to distinguish grazing effects from effects of increased soil waterlogging caused by the neglect of the drainage system. Both vegetation surveys and permanent plots demonstrated a dichotomy in vegetation succession. The incidence of secondary pioneer vegetation dominated by Salicornia spp. and Suaeda maritima increased from 0 to 20%, whereas the late‐successional (Phragmites australis) vegetation from 10 to 15%. Grazing intensity decreased towards the sea. The grazed area contracted landward, which allowed vegetation dominated by tall species to increase seaward. Grazing and increased waterlogging interacted in several ways. The impact of trampling increased, and in the intensively grazed parts soil salinity increased. This can probably be explained by low vegetation cover in spring. Framework Ordination, an indirect‐gradient‐analysis technique, was used to infer the importance of environmental factors in influencing changes in species composition. Many changes were positively or negatively correlated with soil aeration and soil salinity, whereas elevation was of minor importance. Grazing accounted for only a few changes in species frequency. Changes in permanent plots were greater during the first than during the second half of the study period. In exclosures that were installed halfway through the study period, there was a relatively rapid recovery of previously dominant species that had decreased during the first half of the study period. Species richness per unit area in the reserve increased. At the seaward side of the marsh, the altered management allowed succession to proceed leading to establishment of stands of Phragmites australis, whereas on the landward side, the combination of moderate grazing with neglect of the drainage system appeared an effective measure in maintaining habitats for a wider range of halophytic species.  相似文献   

6.
The impact from tourism, e.g. trampling, may be a real concern in nature reserves. Conradi et al. (2015, this issue) studied disturbance effects on grassland vegetation along paths in a nature reserve and found only small negative effects, in good accordance with the local history. Our understanding of disturbances has changed over history and I advocate an evolutionary perspective.  相似文献   

7.
Aims After abandonment of grasslands, secondary succession leads to the invasion by woody species. This process begins with the accumulation of tree litter in the forest–grassland ecotone. Our objectives were to determine the relationships between litter amounts and vegetation composition and cover along natural forest–grassland ecotones and to experimentally study the initial effects of tree litter accumulation on grassland vegetation and on microsite conditions.Methods We established 11 transects varying from 12 to 15 m in length in different forest–grassland ecotones in the Lahn-Dill highlands, Germany, and measured the mass and cover of tree litter and the cover and composition of vegetation at five sequential positions along each transect by using 1 m 2 plots with five replications. In a field experiment, we established plots subjected to different litter amounts (0, 200 and 600g m ?2) and evaluated changes in grassland vegetation, soil temperature and soil nutrient availability below the litter layer.Important findings Tree litter amounts decrease from 650 to 65g m ?2 across the forest–grassland ecotone. Vegetation changed from shrubs and annual species (adapted to more stressful conditions) in the forests edge to grasses, rosettes and hemirosette species (with higher competitive abilities) in the grassland. These anthropogenic forest–grassland ecotones showed abrupt edges, and the two adjacent ecosystems were characterized by different species pools and functional groups. In the field experiment, the presence of a litter layer reduced vegetation biomass and cover; the species richness was only reduced in the treatment with high litter (600g m ?2). Additionally, adding litter on top of vegetation also reduced thermal amplitude and the number of frost days, while increasing the availability of some nutrients, such as nitrogen and aluminium, the latter being an indicator of soil acidification. Adding a tree litter layer of 600g m ?2 in grassland areas had strong effects on the composition and diversity of grassland vegetation by reducing the cover of several key grassland species. In, or near, forest edges, litter accumulation rapidly changes established vegetation, microsite conditions and soil nutrients.  相似文献   

8.
Trampling responses of an Atlantic heathland dominated by furzes were experimentally determined. They concerned two levels of biological systems: the vegetal community level (community scale) and the species level (intracommunity scale). Two trampling experiments were conducted: the first one was carried out in summer and the second one in winter. Heathland was trampled over 4 months, at differents intensities: 10, 30 and 90 persons a day. Whether trampling was conducted in the summer or in the winter, immediate responses of heathland (community scale) were similar: resistance of this vegetal community did not vary with the trampling season. Responses also showed that there is no linear relationship between vegetation degradation and trampling intensity. Deferred vegetation responses were similar, but within the community heathland (intracommunity scale) responses of a taxonomic group can depend on the trampling season. For example, resilience of furzes trampled in winter was greater than resilience of furzes trampled in summer. All these results should be considered in order to establish management orientations of trampled heathlands.  相似文献   

9.
The 'resource balance hypothesis' proposes that the species richness of grassland vegetation is potentially highest when the N:P ratio of plant tissues is 10–15 (co-limitation), so that species richness could be raised by fertilisation with N or P at sites with lower or higher N:P ratios, respectively. Here we use data from field surveys in Swiss, Dutch and American fens or wet grasslands to analyse what changes in N:P ratios might produce noticeable changes in species richness. Plant species numbers, above-ground biomass, tissue N and P concentrations and soil pH were recorded in plots of 0.06–4 m2. In each data set, plots with intermediate tissue N:P ratios (6–20) were on average most species-rich, but N:P ratios explained only 5–37% of the variation in species richness. Moreover, these effects were partially confounded with those of vegetation biomass and/or soil pH. The unique effects of N:P ratios (excluding those shared with biomass and pH) explained 11–17% of variation in species richness. The relationship between species richness and N:P ratios was asymmetric: plots with high N:P ratios were more species-poor than those with low N:P ratios. This was paralleled by a smaller species pool size at high N:P ratios (estimated from species numbers in multiple records), suggesting that fewer species are adapted to P-limited conditions than to N-limited conditions. According to these data, species richness in wetlands may possibly be raised by P-fertilisation when the initial N:P ratio of the vegetation is well above 20, but this option is not recommended for nature conservation as it might promote common species at the expense of rare ones.  相似文献   

10.
Question: How do habitat edges and trampling affect mesic (Myrtillus type) understorey vegetation in fragmented urban forests, and what are the relative strengths and spatial extent of these effects? Location: The city of Helsinki, southern Finland. Methods: Vegetation sample plots were placed at different distances from the forest edge. At each distance we selected plots on, next to and away from paths of different levels of wear, and the covers and frequencies of plant species were sampled. We used generalized linear mixed models and ordination techniques to test our hypotheses. Results: The effect of the edge penetrated up to 50 m into the forest interior. Only light effects of trampling were found in seemingly untrampled areas, in addition to the direct effects of trampling on the paths. Both trampling and edge effects changed the forest understorey species composition. Trampling changed plant species composition locally on paths, and provided opportunities for new species to establish in previously unbroken forest vegetation. Urban forest edges were characterised by species better adapted to sunny, warm and dry conditions. These species, such as grasses, replaced more sensitive forest species, such as dwarf shrubs and mosses. We observed a large number of light demanding deciduous trees at the edges, which may be one of the factors increasing soil fertility and consequently promoting the high abundance of fast growing species, such as grasses and herbs related to more fertile site types. Conclusions: We recommend that urban forest fragments left within urban development should be at least 2–3 ha in size and that the shape of the patch and the number of potential recreational users should be taken into account when preserving true forest understorey vegetation from the effects of edges and trampling.  相似文献   

11.
Luca Borghesio 《Plant Ecology》2009,201(2):723-731
This study focuses on the effect of fire on lowland heathlands at the extreme southern edge of their European distribution (Vauda Nature Reserve, NW Italy). Forty-nine plots (50 m radius) were surveyed between 1999 and 2006. Each year, fire occurrences were recorded and per cent cover of four vegetation types (grassland, heath, low shrubland, and tall shrubland) was estimated in each plot. Vascular plant species richness was also recorded in 255, 1 m2 quadrats. After a fire, grassland vegetation expanded, but then declined rapidly as heath and shrubland recovered: 7 years after a fire, tall shrubland encroached on to more than 40% of the plots, and grassland declined from 50% to 20% cover. Between 1999 and 2006, Betula pendula shrubland greatly expanded, while grassland decreased over most of the Reserve, even where fire frequency was high. Tall shrubland had low plant diversity and was dominated by widespread species of lower conservation value. By contrast, early successional vegetation (grassland and low shrubland) had higher richness and more narrowly distributed species, indication that the development of tall shrubland causes significant species loss in the heathland. Italian lowland heathlands are characterized by high rates of shrubland encroachment that threatens both habitat and species diversity. Burning frequencies of once in 3–6 years seem appropriate in this habitat, but burning alone might not suffice without actions to increase herbivore grazing.  相似文献   

12.
Abundance and diversity of small mammals are usually affected strongly by grazing either due to decreased food availability or quality, decreased suitability of soil for building burrow systems due to trampling and/or due to increased predation risk in the structurally simpler grazed areas. We estimated the effects of grazing-induced changes in vegetation and soil and of increased predation on small mammals in a Mediterranean grassland landscape. We measured vegetation structure, soil compaction and small mammal abundance and species composition in 22 plots of 8 Sherman live traps each, arranged according to an unbalanced two-way ANOVA design with two grazing levels (grazed areas and cattle exclosures) and two predator abundance levels (increased densities of Eurasian kestrels Falco tinnunculus by means of nest boxes and control). Plots were sampled during 2 consecutive years in early summer and early fall. Exclosure from cattle increased significantly vegetation height and volume and decreased soil compaction. Grazing-induced changes in vegetation height and volume and in soil compaction produced strong effects on small mammal abundance and species richness. Increased kestrel densities did not have significant additive or interactive effects, with the effects of grazing-induced vegetation and soil gradients on abundance or richness of small mammals. Our results suggest that the effects of grazing on small mammal communities in Mediterranean montane grasslands were mainly due to reduced food availability and by negative effects of trampling on the suitability of soils for building burrow systems. Decreased food quality and increased predation in grazed areas seemed to play a minor role, if any. Reductions in stock densities would then favor generalist predator populations in Mediterranean grasslands through the expected positive effects of such reductions on the availability of food and burrows for small mammals.  相似文献   

13.
Question: What is the relationship between plant diversity and species turnover in coastal dune vegetation plots? How is the long‐term change in species composition of vegetation plots related to shifts in functional traits, and what does it tell us about the dominant processes? Location: Coastal dunes, the Netherlands. Methods: Our data set comprised 52 years of vegetation data from 35 permanent plots in grassland/scrub/woodland vegetation. Vegetation dynamics were described in terms of changes in species composition and abundance, and shifts in 13 functional traits related to resources capture and forage quality, regeneration and dispersal. Results: Species turnover in the plots was high, because of local extinction and colonization. Species‐rich plots were more stable in terms of species abundance and composition compared with species‐poor plots. Over time, the plots converged with respect to their abiotic conditions, as reflected by Ellenberg indicator values – indicating that the prevailing process was succession. The high species turnover reflected high invasibility: accordingly, the relative importance of annuals increased. Most newcomer annuals, however, were competitive generalists of little conservation value. The functional trait analysis allowed us to unravel the complexity of effects of disturbances and succession, and yielded information on the processes driving the observed vegetation dynamics. Conclusions: In this study, small‐scale species turnover was negatively related to species diversity, indicating more stability in species‐rich communities. Regarding shifts in trait diversity, unifying filters appeared to be more dominant than diversifying filters. Counteracting this homogenization process poses a challenge for nature management.  相似文献   

14.
Veer  M.A.C.  Kooijman  A.M. 《Plant and Soil》1997,192(1):119-128
The encroachment of tall grass species in open dune vegetation, as observed in the Dutch dry dune area, is considered unfavourable for nature conservation. The effects of grass-encroachment on the vegetation and the availability of light and its relation to nutrients were investigated through a comparative study of grass-dominated and open dune grassland plots at ten locations along the Dutch coast.Grass-dominated plots have a low species diversity and number of species, especially of mosses and lichens. This is associated with a high biomass and a low availability of light at soil surface. In addition, nutrient availability seems to be important. Root biomass and the amounts of both ectorganic and endorganic matter are significantly higher in grass-dominated plots, which may account for the higher nutrient uptake in the vegetation.It is likely that a grass-dominated system can maintain and consolidate itself because of the better competition for light and nutrients. The relevance of these results for restoration management is briefly discussed.  相似文献   

15.
The effects or vegetation cover on the abundance and species richness of dung beetles (Aphodiidae) were examined in three altitudinal zones: lowland (520–600 m), mid-altitude (950–963 m) and highland (1230–1275 m). Pitfall traps baited with fresh cattle dung were placed in three vegetation types at each altitudinal zone: forest, heathland and pasture. Species richness was lower in forests than in the other vegetation types. The total abundance of beetles also varied with vegetation type, but the effect was dependent on altitude. Number of individuals was higher in pasture at highlands and in heathland and forest at mid-altitude and lowlands. An altitudinal dependence of distribution of individuals between vegetation types was also found for the more abundant species in the study area. These results could be explained if the local distribution of individuals between vegetation types was determined by microcli-matic factors, mainly temperature. Differences in altitude between sites are associated with temperature changes, determining the habitat selection of species at each altitude.  相似文献   

16.
We use national scale data to test the hypothesis that nitrogen (N) deposition is strongly negatively correlated with plant species richness in a wide range of ecosystem types. Vegetation plots from a national ecological surveillance programme were drawn from heathland, acid, calcareous and mesotrophic grassland habitats. Mean species number and mean plant traits were calculated for each plot and related to atmospheric N deposition. There was a significant reduction in species richness with N deposition in acid grassland and heathland even after fitting covarying factors. In acid grassland and heathland, evidence from trait changes suggested that acidification rather than increased fertility was responsible for species loss. In contrast, calcareous grassland showed evidence of eutrophication in response to increasing N deposition. Loss of species richness from chronic N deposition is apparent in infertile grasslands and heathland. Mechanisms associated with loss of species richness differ between habitats so mitigation of N deposition should be targeted to habitat type.  相似文献   

17.
Controlled trampling experiments were undertaken to assess impacts of recreation in a sub-alpine environment in an upper-Mekong mountainous protected area in China. Hiking and recreational horse-riding were applied at different trampling intensity to two typical, widespread vegetation types (Carex grassland and low Rhododendron shrubland) and trampling effects were assessed to study vegetation resistance and soil compaction. The results indicate: (1) low shrub vegetation is highly vulnerable to trampling damage while the graminoids-dominated grassland is more resistant; (2) dry soil with low organic matter, which often is found in the shrubland, is more susceptible to compaction than wet soil and (3) horses cause substantially more damage than hikers at equivalent trampling levels. These data are useful to develop a visitor’s management strategy that allows to minimize the impact from recreation on the vegetation.  相似文献   

18.
Controlled trampling experiments were undertaken to assess impacts of recreation in a sub-alpine environment in an upper-Mekong mountainous protected area in China. Hiking and recreational horse-riding were applied at different trampling intensity to two typical, widespread vegetation types (Carex grassland and low Rhododendron shrubland) and trampling effects were assessed to study vegetation resistance and soil compaction. The results indicate: (1) low shrub vegetation is highly vulnerable to trampling damage while the graminoids-dominated grassland is more resistant; (2) dry soil with low organic matter, which often is found in the shrubland, is more susceptible to compaction than wet soil and (3) horses cause substantially more damage than hikers at equivalent trampling levels. These data are useful to develop a visitor’s management strategy that allows to minimize the impact from recreation on the vegetation.  相似文献   

19.
Succession has a strong influence on species diversity and composition of semi-natural open terrestrial ecosystems. While several studies examined the effects of succession on butterflies in grassland and forest ecosystems, the response of heathland butterflies to succession had not been investigated so far. To address this issue we sampled butterfly abundance and environmental parameters on the Baltic island of Hiddensee (NE Germany) along a gradient of coastal heathland succession from grey dunes to birch forest. Our results provide evidence that succession of coastal heathland has a strong influence on butterfly diversity, abundance, and species composition. Thereby grass and tree encroachment present the main threats for heathland butterflies. Diversity and abundance of butterflies were highest in shrub-encroached heath directly followed by early stages of coastal heathland succession (dwarf-shrub heath, grey dune). Both observed threatened species (Hipparchia semele, Plebeius argus) were negatively affected by succession: abundance decreased with increasing vegetation density (both species) and grass cover (P. argus); consequently, the two later successional stages (shrub, birch forest) were not occupied. Our findings highlight the importance of the preservation of early stages of coastal heathland succession for endangered butterfly species. For coastal heathland management we therefore suggest to maintain early successional stages by sheep grazing, mowing or, in case of high nutrient contents, intensive techniques such as sod-cutting or choppering. To a lower extend shrub-encroached sites should also be present, which might be beneficial for overall species richness.  相似文献   

20.
The spread of competitive grasses, changes in species composition and vegetation structure are direct consequences of grassland and heathland abandonment. As an alternative to more costly management measures such as traditional pastoralism, year-round low-intensity grazing with large herbivores is increasingly used to restore and maintain semi-open habitats. However, the suitability of this grazing regime has not yet been investigated for long-abandoned, highly degraded but nutrient-poor sandy grassland and heathland communities. In particular, it is unclear if year-round grazing is suitable for preventing the further spread of highly competitive grasses such as Calamagrostis epigejos while simultaneously maintaining or improving characteristic species richness and vegetation structure. Hence, we conducted a comprehensive field study on two spatial scales (plot-level: 25 m2, macroplot-level: 1 ha) to analyse the impacts of year-round low-intensity cattle and horse grazing on the development of the highly competitive grass Calamagrostis epigejos, as well as the vegetation structure and plant species richness of long-abandoned but nutrient-poor dry sandy grassland and heathland communities, their mosaics and Calamagrostis stands within an 800 ha heathland between 2008 and 2015. Finally, we assessed the local conservation status of the habitat types after seven years of grazing in comparison to long-abandoned sites.Grazing successfully reduced the coverage of Calamagrostis epigejos, whereby Calamagrostis stands developed towards species-rich sandy grasslands after seven years of grazing. In addition, the quality of the vegetation structure was improved by enhancing the proportion of bare soil, while litter and grass cover, litter thickness and height of the field layer as well as the coverage of ruderal indicators were significantly reduced on grazed sites in comparison to ungrazed sites in 2015. Moreover, we found an overall positive grazing effect on species richness: Total species number, number of target species as well as subordinated target species significantly increased within the vegetation types over time.Thus, year-round low-intensity cattle and horse grazing is a suitable management tool for restoring, maintaining and even improving long-abandoned, nutrient-poor sandy grassland and heathland communities, and thus to enhance the local conservation status of the habitat types. However, if there is a high initial cover of woody species (e.g. shrubs, tree rejuvenation), then an extensive shrub and tree clearance will be necessary, with manual shrub cutting being crucial to reduce the heavy regrowth of the woody species. In addition, a one-time mowing should be implemented in highly degraded heaths to facilitate the vegetative rejuvenation of degenerate stands of Calluna vulgaris, thus improving its attractiveness for the grazing animals.  相似文献   

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