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1.
The success of calcareous grassland recreation following abandonment depends to a large extent on the composition of the soil seed bank. We studied the species richness and composition of the seed bank along a chronosequence from well-developed calcareous grassland to scrub and forest vegetation, which had developed on calcareous grassland over the last 225 years. The seed bank density was highest in the calcareous grassland soils (930 seeds/m(2)). However, the seed bank was mainly composed of rather common species of nutrient poor grassland, which were poorly represented in the surface vegetation. There were no significant differences in soil seed bank density and species composition between the calcareous grassland and scrub vegetation that was less than 15 years old, largely because several grassland species had persisted in the scrub vegetation and were therefore able to replenish the soil seed bank. In contrast seed density and species richness declined significantly after 40 years of grassland abandonment. Indeed, forest soils had the lowest seed densities (214 seeds/m(2)) with only a few grassland species represented. This reflects the lack of grassland species in the field layer of the forest, and, therefore, the lack of seed production and seed bank replenishment. It is clear that recreation of calcareous grassland on long abandoned sites cannot rely on germination of target species from the seed bank alone. Even in the calcareous grassland soil, seeds of target species are not abundant as the majority produces transient seeds, which decay rapidly if they do not germinate immediately. Successful grassland recreation on such sites therefore may require seeds of target species to be introduced artificially (e.g. as seed mixtures, green hay, etc.). Alternatively, reinstatement of traditional practices, such as grazing or mowing, will increase the natural dispersal potential of these species, allowing population reestablishment in the long term.  相似文献   

2.
Poor vegetation cover is generally considered to be a major factor causing soil erosion on the Loess Plateau in China. It has been argued that tree planting restoration is ineffective, and natural re-vegetation is an alternative ecological solution for restoring abandoned cropland and controlling soil erosion. The aims of this study were to investigate the characteristics of soil seed banks and to assess the natural restoration potential of abandoned cropland in the hilly-gullied Loess Plateau. The soil seed bank was identified by the germination method with the soil samples, which were collected at four sampling times (April, August, and October 2005 and August 2006) from 12 plots abandoned 3–30 years prior to sampling. The seed bank densities of all of the samples in the 0–10 cm soil layer varied from 1,067 ± 225 to 14,967 ± 1,606 seeds m−2. Fifty-one species (24 annual and 27 perennial species) belonging to 18 families were identified, and 39% of these species belonged to the families Compositae and Gramineae. The pioneer species Artemisia scoparia dominated the seed bank, with an average seed density of 3,722 seeds m−2, and accounted for 74.4% of the seeds in the bank. The local dominant species (such as Lespedeza davurica, Artemisia gmelinii, Bothriochloa ischaemun and Stipa bungeana) of the later succession stages also existed at densities varying from 17 to 1, 383 seeds m−2. The combination of soil seed bank characteristics, reproductive traits of the species, the specific landscape conditions indicates that the potential to restoring the abandoned croplands in the hilly-gullied Loess Plateau via natural re-vegetation could be substantial.  相似文献   

3.
The response of forest understory vegetation to trampling applied at different temporal and spatial scales was determined in a cliff-edge forest in Ontario, Canada. Three frequencies (0, 50, 500 passes per year) of short-term trampling (one year) were applied to plots previously undisturbed. Existing trails that had received three frequencies (approx. 100, 500, 25,000 passes per year) of long-term trampling (18 years) were also studied. Community composition, species richness, and individual species frequency were recorded in plots within 4 m and (or) 1 m of the patch centerline. The quantitative and qualitative form of plant response to increased trampling was compared for short-term and long-term treatments, both within 4 m and within 1 m of the path centerline, to judge the consistency of trampling effects at different temporal and spatial scales. As trampling frequency increased, community composition changed progressively, but consistently, in plots both within 4 m and 1 m of the path centerline. Species richness was less affected by trampling and only decreased within 1 m of the path centerline at the highest level of trampling (25,000 passes per season for 18 years). Effects of trampling on individual species frequency were much less consistent at different temporal and spatial scales of trampling. The scale-dependence results suggest that field workers and resource managers both should try explicitly to include and define multiple scale components when trying to ascertain the response of vegetation to human disturbance factors.  相似文献   

4.
Domestic animals potentially affect the reproductive output of plants by direct removal of aboveground plant parts but also could alter the structure and fertility of the upper soil and the integrity of biological crusts through trampling. We asked whether sheep selectivity of plant patches along grazing paths could lead to negative changes in biological crusts and soil seed banks. We randomly selected ten floristically homogeneous vegetation stands distributed across an area (1250 ha) grazed by free ranging sheep. Vegetation stands were differently selected by sheep as estimated through sheep-collaring techniques combined with remote imagery mapping. At each stand, we extracted 15 paired cylindrical soil cores from biological crusts and from neighboring soil without crusts. We evaluated the crust cover enclosed in each core and incubated the soil samples at field capacity at alternating 10-18 °C during 24 months. We counted the emerged seedlings and identified them by species. Sheep selectivity along grazing paths was largest at mid-distances to the watering point of the paddock. Increasing sheep selectivity was associated with the reduction of the cover of biological crusts and the size and species number of the soil seed bank of preferred perennial grasses under biological crusts. The size of the soil seed bank of annual grasses was reduced with increasing sheep selectivity under both crust and no crust soil conditions. We did not detect changes in the soil seed banks of less- and non- preferred species (shrubs and forbs) related to sheep selectivity. Our findings highlight the negative effects of sheep selectivity on biological crusts and the soil seed bank of preferred plant species and the positive relationship between biological crusts and the size of the soil seed bank of perennial grasses. Accordingly, the state of conservation of biological crusts could be useful to assess the state of the soil seed banks of perennial grasses for monitoring, conservation and planning the sustainable management of grazing lands.  相似文献   

5.
We investigated the effects of human trampling on boreal forest understory vegetation on, and off paths from suburban forest edges towards the interiors and on the likelihood of trampling-aided dispersal into the forests for three years by carrying out a trampling experiment. We showed that the vegetation was highly sensitive to trampling. Even low levels of trampling considerably decreased covers of the most abundant species on the paths. Cover decreased between 10 and 30% on paths which had been trampled 35 times, and at least by 50% on those trampled 70–270 times. On-path vegetation cover decreased similarly at forest edges and in the interiors. However, some open habitat plant species that occurred outside the forest patches and at forest edges dispersed into the forests, possibly through the action of trampling. A higher cover percentage of an open habitat species at the forest edge line increased its probability to disperse into the forest interior. The vegetation community on, next to, and away from lightly trampled paths remained the same throughout the trampling experiment. For heavily trampled paths, the community changed drastically on the paths, but stayed relatively similar next to and away from the paths. As boreal vegetation is highly sensitive to the effects of trampling, overall ease of access throughout the forest floor should be restricted to avoid the excessive creation of spontaneous paths. To minimize the effects of trampling, recreational use could be guided to the maintained path network in heavily used areas.  相似文献   

6.
The Appalachian region in the eastern United Sates is home to the Earth's most extensive temperate deciduous forests, but coal mining has caused forest loss and fragmentation. More than 6000 km in Appalachia have been mined for coal since 1980 under the Surface Mining Control and Reclamation Act (SMCRA). We assessed Appalachian areas mined under SMCRA for forest restoration potentials. Our objectives were to characterize soils and vegetation, to compare soil properties with those of pre-SMCRA mined lands that were reforested successfully, and to determine the effects of site age on measured properties. Soils were sampled and dominant vegetation characterized at up to 10 points on each of 25 post-SMCRA mines. Herbaceous species were dominant on 56%, native trees on 24%, and invasive exotics on 16% of assessed areas. Mean values for soil pH (5.8), electrical conductivity (0.07 dS m(-1)), base saturation (89%), and coarse fragment content (50% by mass) were not significantly different from measured levels on the pre-SMCRA forested sites, but silt+clay soil fraction (61%) was higher, bicarbonate-extractable P (4 mg kg(-1)) was lower, and bulk density (1.20 g cm(-1)) was more variable and often unfavorable. Pedogenic N and bicarbonate-extractable P in surface soils increased with site age and with the presence of weathered rocks among coarse fragments. Our results indicate a potential for many of these soils to support productive forest vegetation if replanted and if cultural practices, including temporary control of existing vegetation, soil density mitigation, and fertilization, are applied to mitigate limitations and aid forest tree reestablishment and growth.  相似文献   

7.
Ecological conditions following removal of exotic plants are a key part of comprehensive environmental management strategies to combat exotic plant invasions. We examined ecological conditions following removal of the management-priority buffelgrass (Pennisetum ciliare) in Saguaro National Park of the North American Sonoran Desert. We assessed soil, vegetation, and soil seed banks on seven buffelgrass site types: five different frequencies of buffelgrass herbicide plus hand removal treatments (ranging from 5 years of annual treatment to a single year of treatment), untreated sites, and non-invaded sites, with three replicates for each of the seven site types. The 22 measured soil properties (e.g., pH) differed little among sites. Regarding vegetation, buffelgrass cover was low (≤1 % median cover), or absent, across all treated sites but was high (10–70 %) in untreated sites. Native vegetation cover, diversity, and composition were indistinguishable across site types. Species composition was dominated by native species (>93 % relative cover) across all sites except untreated buffelgrass sites. Most (38 species, 93 %) of the 41 species detected in soil seed banks were native, and native seed density did not differ significantly across sites. Results suggest that: (1) buffelgrass cover was minimal across treated sites; (2) aside from high buffelgrass cover in untreated sites, ecological conditions were largely indistinguishable across sites; (3) soil seed banks harbored ≥12 species that were frequent in the aboveground vegetation; and (4) native species dominated post-treatment vegetation composition, and removing buffelgrass did not result in replacement by other exotic species.  相似文献   

8.
The composition of the herbaceous cover and the seed bank of old and recent hedge banks in Brittany were studied and compared. Concentration method was used for seed bank samples. Grimes plant strategies were used to explain observed patterns. The analysis of the seed bank of these hedge banks showed that the species richness and diversity differed in relation to the date of construction of the hedge banks. The seed banks of recent hedge banks were richer and more diversified than those of old hedge banks. Differences in the floristic composition of the established plant cover between the recent and old hedge banks were determined by multivariate analyses. The species exclusively found in the seed bank and in the herb cover of recent hedge banks were mainly grassland species, whereas the species that only occurred on old hedge banks tended to be woodland species. The floristic composition of the two compartments (established vegetation and seed bank) was very different. A multivariate analysis revealed that the difference between the composition of the seed banks of recent and old hedge banks was less than that between the composition of the established vegetation and seed bank of hedge banks of the same age. Both seed bank and vegetation of recent hedge banks were dominated by ruderal species, whereas old hedge vegetation was dominated by stress-tolerant woodland species, indicating that mechanically constructed hedge banks may impose limitations on colonization by late woodland species.  相似文献   

9.
Controlled trampling was conducted to investigate the trampling resistance of contrasting high fertility basaltic and low fertility rhyolitic soils and their associated highland tropical rainforest vegetation in north east Australia's Wet Tropics. Although this approach has been taken in numerous studies of trampling in a variety of ecosystem types (temperate and subtropical forest, alpine shrubland, coral reef and seagrass beds), the experimental method does not appear to have been previously applied in a tropical rainforest context. Ground vegetation cover and soil penetration resistance demonstrated variable responses to trampling. Trampling, most noticeably after 200 and 500 passes reduced organic litter cover. Bulk density increased with trampling intensity, particularly on basalt soils as rhyolite soils appeared somewhat resistant to the impacts of trampling. The permeability of the basalt and rhyolite soils decreased markedly with increased trampling intensity, even after only 75 passes. These findings suggest physical and hydrological changes may occur rapidly in tropical rainforest soils following low levels of trampling, particularly on basalt soils.  相似文献   

10.
This study investigated the potential for wildlife feeding to artificially increase population densities of the Australian brush-turkey, Alectura lathami and assessed the indirect adverse effects that this may have on surrounding forest floor vegetation. Census counts and observations of feeding activity conducted in recreation areas of Australia's Gold Coast hinterland confirmed that brush-turkey population densities were significantly elevated by the provision of food by humans. Brush-turkey densities were high at sites where birds are actively fed, moderate at sites where birds feed opportunistically and low at sites where humans have negligible impact on local food availability. Brush-turkeys caused significant environmental impact at sites where their population densities have been substantially elevated by active feeding. Across all sites, increases in brush-turkey density were accompanied by a significant decline in ground cover, leaf litter weight, seed density and seedling density. Natural environmental variables such as gradient, vegetation type and canopy cover did not explain the observed impacts. The impacts were consistent with those described in trampling studies and suggest that at high density, even small animals can have significant trampling impacts on their local environment. This study demonstrates that wildlife feeding can have detrimental impacts on the integrity of local environments and recommends greater consideration of small animals and their potential indirect impacts when regulating wildlife feeding in National Parks and other nature conservation areas.  相似文献   

11.
The composition of the germinable seed bank was studied in four vegetation states of the Festuca pallescens grasslands in semiarid Patagonia during four years. The aim of this study was to test whether above-ground vegetation states resulting from grazing exclusion or different combinations of grazing and topography are reflected in different states of the germinable seed bank. The size of the total and dicot germinable seed bank was positively related to the total cover in each state. Dicots dominated all germinable seed bank states. Carex patagonica increased its cover as well as its germinable seed bank under grazing disturbance. Grazing did not reduce the germinable seed bank of perennial grasses in uplands where the grazing pressure is lower as compared with slopes. In slopes the germinable seed bank of perennial grasses was significantly reduced by grazing. A reduction of the length of the grazing period in late spring increases the germinable seed bank of perennial grasses both in upland and slope. These results are interpreted in the frame of a model of management techniques where grazing exclusion during late spring and late summer increases the seed bank of the perennial grasses and promotes their establishment in uplands. The artificial addition of seeds of perennial grasses and the manipulation of the soil surface in order to increase "safe sites" appear as management alternatives that deserve further evaluation to improve plant reestablishment in slopes.  相似文献   

12.
Repeated cutting of vegetation at or near ground level in power-line corridors is a common practice for inhibiting tree growth and regeneration. However, few data exist on long-term community responses. In this study, we sampled 20 northern Kentucky power-line corridors and compared their seedling and sapling communities to the edges and interiors of adjacent undisturbed forests. Mean seedling and sapling density in corridors was roughly twice that of adjacent undisturbed forest interiors, suggesting that repeated cutting is not a viable method of inhibiting tree regeneration. Corridor communities were dominated byRobinia pseudoacacia (black locust) andFraxinus americana (white ash), but ordinations indicated strong similaritties among communities in corridors and adjacent forests. Many of the tree species found in adjacent forests, with the exception of a few shade-tolerant species, had highest seedling and sapling densities in corridors. Stump or root sprouting by many species appears to regenerate forests quickly after cutting. However, disturbed soil and detritus accumulations caused by management crews and their equipment may also create a large variety of microsites for seedling establishment. Because repeated cutting selects for dominance by species with highest sprout growth rates, it should not be used as the sole management technique. It may instead be used to alter the vigor, stature, and stored reserves of trees so that herbicides or other methods of tree control can be used more efficiently.  相似文献   

13.
A 4-year study was conducted to evaluate the consequences of human trampling on dryas and tussock tundra plant communities. Treatments of 25, 75, 200 and 500 trampling passes were applied in 0.75 m2 vegetation plots at a time of approximately peak seasonal biomass. Immediately after and 1 and 4 years after trampling, plots were evaluated on the basis of plant species cover, percent bare ground, vegetation height, and soil penetration resistance. One year after trampling, soils were collected for nitrogen analysis in highly disturbed and control plots. Immediately after trampling, 500 trampling passes resulted in approximately 50% cover loss in the dryas tundra and 70% cover loss in tussock tundra, but both communities showed a substantial capacity for regrowth. Plots where low and moderate levels of trampling were applied returned to pre-disturbance conditions by 4 years after trampling, but impact was still evident in plots subjected to high levels of disturbance. These results suggest that these tundra communities can tolerate moderate levels of hiking and camping provided that use is maintained below disturbance thresholds and that visitors employ appropriate minimum-impact techniques. By utilizing this information in a visitor education program combined with impact monitoring and management, it is possible to allow dispersed camping and still maintain these vegetation communities with a minimum of observable impact.  相似文献   

14.
Urban forests are popular recreation areas in Europe. Several of these temperate broad-leaved forests also have a high conservation value due to sustainable management over many centuries. Recreational activities, particularly the use of fireplaces, can cause extensive damage to soil, ground vegetation, shrubs, and trees. Firewood collection depletes woody debris, leading to a loss of habitat for specialized organisms. We examined the effects of fireplace use on forest vegetation and the amount of woody debris by comparing disturbed and control plots in suburban forests in northwestern Switzerland. At frequently used fireplaces, we found reduced species densities in the ground vegetation and shrub layer and changes in plant species composition due to human trampling within an area of 150–200 m2. Picnicking and grilling also reduced the height and changed the age structure of shrubs and young trees. The amount of woody debris was lower in disturbed plots than in control plots. Pieces of wood with a diameter of 0.6–7.6 cm were preferentially collected by fireplace users. The reduction in woody debris volume extended up to a distance of 16 m from the fire ring, covering an area of 800 m2 at each picnic site. In order to preserve the ecological integrity of urban forests and to maintain their attractiveness as important recreation areas, we suggest depositing logging residues to be used as firewood and to restrict visitor movements near picnic sites.  相似文献   

15.
Anthropogenic disturbances in wetland ecosystems can alter the composition and structure of plant assemblages and affect system functions. Extensive oil and gas extraction has occurred in wetland habitats along the northern Gulf of Mexico coast since the early 1900s. Activities involved with three-dimensional (3D) seismic exploration for these resources cause various disturbances to vegetation and soils. We documented the impact of a 3D seismic survey in coastal marshes in Louisiana, USA, along transects established before exploration began. Two semi-impounded marshes dominated by Spartina patens were in the area surveyed. Vegetation, soil, and water physicochemical data were collected before the survey, about 6 weeks following its completion, and every 3 months thereafter for 2 years. Soil cores for seed bank emergence experiments were also collected. Maximum vegetation height at impact sites was reduced in both marshes 6 weeks following the survey. In one marsh, total vegetation cover was also reduced, and dead vegetation cover increased, at impact sites 6 weeks after the survey. These effects, however, did not persist 3 months later. No effects on soil or water properties were identified. The total number of seeds that germinated during greenhouse studies increased at impact sites 5 months following the survey in both marshes. Although some seed bank effects persisted 1 year, these effects were not reflected in standing vegetation. The marshes studied were therefore resilient to the impacts resulting from 3D seismic exploration because vegetation responses were short term in that they could not be identified a few months following survey completion.  相似文献   

16.
Outdoor recreation and nature-based tourism represent an increasingly intensive form of land use that has considerable impacts on native ecosystems. The aim of this paper is to investigate how revegetation and management of ski runs influence soil nutrients, vegetation characteristics, and the possible invasion of nonnative plant species used in revegetation into native ecosystems. A soil and vegetation survey at ski runs and nearby forests, and a factorial experiment simulating ski run construction and management (factors: soil removal, fertilization, and seed sowing) were conducted at Ruka ski resort, in northern Finland, during 2003–2008. According to the survey, management practices had caused considerable changes in the vegetation structure and increased soil nutrient concentrations, pH, and conductivity on the ski runs relative to nearby forests. Seed mixture species sown during the revegetation of ski runs had not spread to adjacent forests. The experimental study showed that the germination of seed mixture species was favored by treatments simulating the management of ski runs, but none of them could eventually establish in the study forest. As nutrient leaching causes both environmental deterioration and changes in vegetation structure, it may eventually pose a greater environmental risk than the spread of seed mixture species alone. Machine grading and fertilization, which have the most drastic effects on soils and vegetation, should, therefore, be minimized when constructing and managing ski runs.  相似文献   

17.
Practically no information exists on the impact of human trampling on tropical rain forest vegetation. We studied three trails with varying periods of use and recovery in a tropical rain forest in Costa Rica. Human impact on trailside plants was curvilinearly related to use, as found by other workers in temperate zone vegetation. Recovery in a period of two years and eight months had been rapid, and herbs and seedlings were more abundant along the recovering trail than in undisturbed forest. The results imply that a shifting mosaic of trails, analogous to the mosaic created by light gaps, may be the best management technique to minimize the impact of human visitors in tropical rain forests.  相似文献   

18.
The study focuses on understorey-overstorey plant community dynamics in a dry tropical forest to facilitate appropriate management decisions. We compare community composition and species diversity of the understorey vegetation among five dry tropical forest sites in northern India. A total of 1500 quadrats distributed over 15 one-ha permanent plots in five sites differing in the degree of disturbance, were used to enumerate the understorey tree species and the results were compared with overstorey tree layer. The non-metric multidimensional scaling (NMS) ordination revealed that human disturbance intensity, as well as the overall disturbance regimes, and soil water holding capacity controlled the organisation of dry tropical forest understorey composition through effects on soil organic matter. The alpha-diversity and its components decreased with increasing human disturbance intensity, reflecting utilisation pressure and decreased soil fertility, as also revealed by the analysis of overstorey tree layer. There was a significant positive relationship between overstorey and understorey diversity. Results suggest that in the future, the existing understorey tree communities may replace the current dry tropical forest communities under prevailing environmental conditions. The study also asserts that the rate of species accumulation will be greater in more disturbed sites as well as at small spatial scale within each disturbance level.  相似文献   

19.
Fallow vegetation within landscapes dominated by shifting cultivation represents a woody species pool of critical importance with considerable potential for biodiversity conservation. Here, through the analysis of factors that influence the early stages of fallow vegetation regrowth in two contrasting forest margin landscapes in Southern Cameroon, we assessed the impact of current trends of land use intensification and expansion of the cultivated areas, upon the conservation potential of shifting cultivation landscapes. We combined the analysis of plot and landscape scale factors and identified a complex set of variables that influence fallow regrowth processes in particular the characteristics of the agricultural matrix and the distance from forest. Overall we observed a decline in the fallow species pool, with composition becoming increasingly dominated by species adapted to recurrent disturbance. It is clear that without intervention and if present intensification trends continue, the potential of fallow vegetation to contribute to biodiversity conservation declines because of a reduced capacity, (1) to recover forest vegetation with anything like its original species composition, (2) to connect less disturbed forest patches for forest dependent organisms. Strategies to combat biodiversity loss, including promotion of agroforestry practices and the increase of old secondary forest cover, will need not only to operate at a landscape scale but also to be spatially explicit, reflecting the spatial pattern of species reservoirs and dispersal strategies and human usage across landscapes.  相似文献   

20.
Strip-mining operations greatly disturb soil, vegetation and landscape elements, causing many ecological and environmental problems. Establishment of vegetation is a critical step in achieving the goal of ecosystem restoration in mining areas. At the Shouyun Iron Ore Mine in suburban Beijing, China, we investigated selective vegetation and soil traits on a tailings dam 7 years after site treatments with three contrasting approaches: (1) soil covering (designated as SC), (2) application of a straw mat, known as “vegetation carpet”, which contains prescribed plant seed mix and water retaining agent (designated as VC), on top of sand piles, and (3) combination of soil covering and application of vegetation carpet (designated as SC+VC). We found that after 7 years of reclamation, the SC+VC site had twice the number of plant species and greater biomass than the SC and VC sites, and that the VC site had a comparable plant abundance with the SC+VC site but much less biodiversity and plant coverage. The VC site did not differ with the SC site in the vegetation traits, albeit low soil fertility. It is suggested that application of vegetation carpet can be an alternative to introduction of topsoil for treatment of tailings dam with fine-structured substrate of ore sands. However, combination of topsoil treatment and application of vegetation carpet greatly increases vegetation coverage and plant biodiversity, and is therefore a much better approach for assisting vegetation establishment on the tailings dam of strip-mining operations. While application of vegetation carpet helps to stabilize the loose surface of fine-structured mine wastes and to introduce seed bank, introduction of fertile soil is necessary for supplying nutrients to plant growth in the efforts of ecosystem restoration of mining areas.  相似文献   

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