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1.
Susan M. Galatowitsch 《应用植被学》2006,9(2):261-270
Question: Do regional species pools, landscape isolation or on‐site constraints cause plants from different guilds to vary in their ability to colonize restored wetlands? Location: Iowa, Minnesota, and South Dakota, USA. Methods: Floristic surveys of 41 restored wetlands were made three and 12 years after reflooding to determine changes in local species pools for eight plant guilds. The effect of landscape isolation on colonization efficiency was evaluated for each guild by plotting local species pools against distance to nearby natural wetlands, and the relative importance of dispersal vs. on‐site constraints in limiting colonization was explored by comparing the local species pools of restored and natural wetlands within the region. Results: Of the 517 wetland plant taxa occurring in the region, 50% have established within 12 years. The proportion of the regional species pool represented in local species pools differed among guilds, with sedge‐meadow perennials, emergent perennials and floating/submersed aquatics least represented (33‐36%) and annual guilds most represented (74‐94%). Colonization‐to‐extinction ratios suggest that floating/submersed aquatics have already reached a species equilibrium while sedge‐meadow and emergent perennials are still accumulating species. Increasing distance to nearest wetlands decreased the proportion of the regional species pool present in local pools for all guilds except native annuals and woody plants. The maximum proportion predicted, assuming no distance constraint, was comparable to the lowest‐diversity natural wetlands for most perennial guilds, and also lower than what was achieved in a planted, weeded restoration. Conclusions: A biotic constraints seem to limit the colonization of floating/submersed aquatics into natural or restored wetlands, whereas all other guilds are potentially constrained by dispersal or biotic factors (i.e. competition from invasive species). Using species pools to evaluate restoration progress revealed that immigration potential varies considerably among guilds, that local species richness does not necessarily correspond to immigration limitations, and that some guilds (e.g. sedge‐meadow perennials) will likely benefit more than others from being planted at restoration sites. 相似文献
2.
Question: Can the biodiversity of fens in Europe and North America be maintained through the use of grazing (especially cattle grazing), fire, and/or cutting? Location: European and North American fens. Methods: This paper is a review of the literature on the effects of grazing, fire and cutting on fens, to explore the relationship between management and biodiversity in fens. Results: A reduction of cattle grazing, mowing and burning in fens has led to a reduction in biodiversity in fens. The vegetation of abandoned fens shifts to trees and shrubs after 10–15 years, which shade the smaller and rarer species of these wetlands. While careful use of fire is used to manage fens in North America, it is not widely used in European fens, perhaps because the peat of drained fens may catch fire. Cattle grazing cannot be considered a natural disturbance in North America, since cattle did not evolve on that continent. In Europe, cattle do not generally graze in unaltered fens, but they do use slightly drained fen meadows. Conclusions: Three approaches have been used to control the dominance of tall woody and herbaceous species in abandoned fens, including the re‐introduction of cattle, mowing, and burning. Overgrazing results in a permanent reduction in biodiversity, therefore cattle re‐introduction must be approached cautiously. In Europe, but not in North America, mowing has been an important management tool, and mowing has been successful in maintaining species richness, particularly in fens that have been mowed annually for centuries. Fire has been the most common and successful management tool in North America although it is not effective in removing shrubs that have become large. Because the problems and solutions are similar, the literature of both European and North American fen management can be analyzed to better assess the management of fens on both continents. Many management questions require further study and these are listed in the paper. 相似文献
3.
Stefan Linquist 《Biology & philosophy》2008,23(4):529-544
As conservation biology has developed as a distinct discipline from ecology, conservation guidelines based on ecological theory
have been largely cast aside in favor of theory-independent decision procedures for designing conservation reserves. I argue
that this transition has failed to advance the field toward its aim of preserving biodiversity. The abandonment of island
biogeography theory in favor of complementarity-based algorithms is a case in point. In what follows, I consider the four
central objections raised against island biogeographic conservation guidelines, arguing that they fail to undermine the credibility
of this framework as a conservation tool. At best, these objections call for a more careful application of this framework
to conservation problems, not its wholesale abandonment. At the same time, complementarily-based algorithms are biased in
favor of networks of small reserves containing non-overlapping species. These conditions threaten to promote inbreeding depression,
genetic drift and other factors that increase a population’s risk of extinction. Therefore, recent developments in the field
of conservation biology have arguably not contributed to its ultimate aim of preserving the maximum amount of biodiversity
in the long run.
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| Stefan LinquistEmail: |
4.
Questions: 1. What is the scale and extent of spatial variability in factors affecting Betula invasion of heaths? 2. How much effect does each factor have on within‐patch patterns of invasion? 3. How can this understanding aid in managing Betula invasions? Location: Lowland heath of southern England. Methods: Determinants of Betula (both B. pubescens and B. pendula) invasion: biomass density, necromass density, mean vegetation height, P‐availability, soil water content and total Betula seed bank density, were measured at two sites on a 5‐ha sampling grid. Spatial pattern was assessed using geostatistics. Contributions of each determinant to within‐site heterogeneity in predicted Betula seedling densities were estimated by varying variables over their full and interquartile ranges in a statistical model derived from experimental data. Results: Salient spatial trends were revealed: strong autocorrelation over distances of < 50 m for soil factors and more extensive autocorrelation (0 to > 150 m) in vegetation variables and Betula seed bank densities. The latter resulted in single across‐site gradients, the former small, distinct patches. All patterns were overlain with variance that was present at distances of < 17.6 m. Variables displaying spatial pattern also accounted for within‐site heterogeneity in predicted Betula seedling densities but their relative contribution to this varied between sites. Conclusions: Identifiable spatial autocorrelation in factors controlling patch‐scale invasion patterns allows managers to target invasion prone patches, potentially reducing management intensities. Furthermore, management effort may be optimised by spatially de‐coupling Betula seed from safe‐sites. This plan may adaptable to the management of other weeds and open‐land ecosystems. 相似文献
5.
Question: How does Alnus alnobetula colonization affect plant communities in sub‐alpine grasslands undergoing land abandonment on a regional scale? Location: Savoie, French Alps. Methods: Variations within and between communities were monitored in 243 plots within three types of stands representing an A. alnobetula colonization chronosequence from grassland to dense vegetation. They were tested for species richness, species strategies and species distribution through multivariate analysis. Regional variations were assessed at three sites along a rain shadow gradient. Results: We detected a convergence of the understorey communities along an A. alnobetula colonization gradient at all sites, associated with a reduction in species richness and the replacement of stress related strategists by competitor strategists. This convergence was unaffected by the rain shadow gradient although it was a key factor of plant distribution. Conclusions: The dense cover and the soil properties provided by A. alnobetula stands buffered the heterogeneity of sub‐alpine communities induced by a rain shadow gradient throughout the study region. It facilitated the development a homogeneous understorey community dominated by competitor related strategists while excluding grasslands stress adapted species through competition processes. The resulting community, although species‐poor, has an interesting conservation value. Accordingly, as a ‘native invader’, A. alnobetula does not display typical traits of biological invaders. Future experimental research on the interactions between A. alnobetula and components of the understorey would be particularly interesting in a severe environment that promotes facilitation among plants. 相似文献
6.
Donald R. Drake 《植被学杂志》1998,9(1):103-112
Abstract. Hawaiian ecosystems are prone to invasion by alien plant species. I compared the seed rain, seed bank, and vegetation of a native Hawaiian forest to examine the potential role that seed ecology plays in allowing alien species to invade native forest. Absolute cover of seed plants in the forest was 126 %, annual seed rain was 5 713 seeds m-2 yr-1, and the mean density of seedlings emerging from the seed bank averaged across four seasons was 1 020/m2. The endemic tree Metrosideros polymorpha was the most abundant species in the vegetation, seed rain and winter seed bank. Overall, native seed plants comprised 95 % of the relative cover in the vegetation and 99 % of the seeds in the seed rain, but alien species comprised 67 % of the seeds in the seed bank. Alien species tended to form persistent seed banks while native species formed transient or pseudo-persistent seed banks. Dominance of the seed bank by alien species with persistent seed banks suggests that aliens are favorably placed to increase in abundance in the vegetation if the forest is disturbed. 相似文献
7.
Aim We examined whether the community compositions of birds, lizards and small mammals were nested in a fragmented landscape in the Thousand Island Lake, China. We also assessed whether the mechanisms influencing nestedness differed among these taxonomic groups. Location Thousand Island Lake, China. Methods Presence/absence matrices were compiled for birds (42 islands) and lizards (42 islands) using line‐transect methods, and for small mammals (14 islands) using live‐trapping methods from 2006 to 2009. Nestedness was analysed using BINMATNEST, and statistical significance was assessed using the conservative null model 3. We used Spearman rank correlations and partial Spearman rank correlations to examine associations of nestedness and habitat variables (area, isolation, habitat diversity and plant richness) as well as life‐history traits (body size, habitat specificity, geographical range size and area requirement) related to species extinction and immigration tendencies. Results The community compositions of birds, lizards and small mammals were all significantly nested, but the causal factors underlying nestedness differed among taxonomic groups. For birds, island area, habitat specificity and area requirement were significantly correlated with nestedness after controlling for other independent variables. For lizards, habitat heterogeneity was the single best correlate of nestedness. For small mammals, island area, habitat heterogeneity and habitat specificity were significantly correlated with nestedness. The nested patterns of birds, lizards and small mammals were not attributable to passive sampling or selective colonization. Main conclusions The processes influencing nested patterns differed among taxonomic groups. Nestedness of bird assemblages was driven by selective extinction, and lizard assemblage was caused by habitat nestedness, while nestedness of small mammals resulted from both selective extinction and habitat nestedness. Therefore, we should take taxonomic differences into account when analysing nestedness to develop conservation guidelines and refrain from using single taxa as surrogates for others. 相似文献
8.
Question: How successful is restoration that is focused on a single dominant plant at enabling the reassembly of the whole vegetation assemblage and what factors affect the relative success of such restoration? Location: Moorlands in England and Scotland, UK. Methods: Vegetation composition was sampled in grassdominated (degraded), restored and long established Calluna vulgaris‐dominated (target) areas within eight moorland restoration sites. Additional soil and biogeographic data were collected. Data were analysed by Canonical Correspondence Analysis, which allowed the impact of moorland management to be examined. Results: All sites showed good restoration success when the dominant managed species (Calluna vulgaris, Molinia caerulea and Nardus stricta) were considered. Restoration success of the remainder of the plant assemblage, disregarding these dominant species, was lower with restored samples at some sites differing little from their respective degraded samples. Moors restored solely by grazing exclusion were more similar to their respective targets than were those restored by more intensive mechanical means. The most important factors in explaining vegetation assemblages were management status (i.e. whether samples represented degraded, restored or target parts of the moor) and latitude. Conclusions: The project demonstrates that, where possible, restoration should be attempted by grazing exclusion alone. Furthermore the importance of applying local restoration targets and of monitoring the whole plant assemblages when assessing the success of moorland restoration is highlighted. 相似文献
9.
Abstract. In this study we tested the hypothesis that diaspore buoyancy is an important factor in determining the distribution range of riparian plants, by measuring the floating capacity of fruits and seeds from 17 alpine vascular plant species during 1 yr. Minimum, median, mean, and maximum (≤ 1 yr) floating times of fruits and seeds were then related to the downstream distribution of plants along the free-flowing Vindel River in northern Sweden. The distances from the alpine headwater region to the most downstream occurrence of plants, and to the cessation of a more continuous distribution, were evaluated. The variation in downstream limits of plants could not be statistically explained by variation in seed buoyancy between species, indicating that floating ability of seeds is not important for plant distribution patterns. There may be several reasons for this, and they may differ between species. 相似文献
10.
Question: What factors limit woody plant recruitment in a mosaic landscape where former agricultural lands are dominated by the invasive tree Ligustrum lucidum (Oleaceae)? Location: Subtropical northwestern Argentina. Methods: In secondary forest patches, we measured (1) tree, shrub and liana abundance in different size classes; (2) seed rain of Ligustrum and two native trees and (3) topographic, soil and light variables. We used spatial autoregressive models to test for effects of Ligustrum dominance and environment on native plant abundance in each size class. We used multiple regression on resemblance matrices to quantify the relative importance of spatial (e.g. dispersal) and environmental effects on native species composition. Results: Native tree abundance in the smallest size class was unrelated to Ligustrum canopy dominance, while native tree abundance in larger size classes and native liana abundance were negatively correlated with Ligustrum dominance. Native species composition was both environmentally and spatially structured, suggesting that some species are dispersal limited. Seed rain was spatially correlated with conspecific basal area for one of two native species, but not for Ligustrum. Conclusions: Native tree recruitment appears to be limited primarily by sapling mortality in patches dominated by the invasive Ligustrum. Ligustrum does not appear to be dispersal limited in our study area and is likely to continue spreading. Invaded patches may persist for hundreds of years. 相似文献
11.
Abstract. We examined the response of tree seedling emergence and survival to the dieback of Sasa and canopy gap formation in an old‐growth forest near Lake Towada, northern Japan. Synchronous death of Sasa occurred in 1995. We established four types of sampling sites differing in forest canopy conditions (Closed or Gap) and Sasa status (Dead or Live). Gap‐Dead sites had the highest light levels and the greatest fluctuation in soil temperatures. The death of Sasa alone facilitated the emergence (Acer japonicum, Fagus crenata, Fraxinus lanuginosa, and Tilia japonica) and survival (Acanthopanax sciadophylloides, F. crenata, F. lanuginosa, Kalopanax pictus, and Sorbus commixta) of species with a seedling bank strategy. Cercidiphyllum japonicum grew at all sites at a higher density than other species, but survived well only in Gap‐Dead sites. This behaviour was associated with a seed rain strategy. The additive effects of Sasa death and canopy gap formation promoted seedling emergence of pioneer tree species (Betula maximowicziana, Lindera umbellata, and Magnolia obovata), probably through break of dormancy by the large temperature fluctuation. In addition, the scarcity of advance regeneration in canopy gaps due to Sasa cover facilitates the regeneration of pioneer species. The dominance and dieback cycle of Sasa contributes to species diversity in this forest. 相似文献
12.
Population structure, fruit production and dispersal, and recruitment of Rhus integrifolia, a gynodioecious sclerophy llous shrub living in coastal chaparral, were studied in two localities in southern California last burned 60 and 90 years ago. Though hermaphroditic plants produce some fruits, only the male-sterile plants bore significant numbers. Among the sample plants, one individual accounted for 50% of the crop measured. Terrestrial animals, through the loss of some seeds taken for consumption, play a decisive role in the seed dispersal, promoting the establishment of seedlings outside the parent's canopy. Birds have not been demonstrated to contribute to long distance dispersal, but they are responsible for dropping 25% of the fruits collected below the R. integrifolia canopies, 36%) of which were completely destroyed. Allelopathic effects were not observed in laboratory assays, and germination is probably not influenced by the species beneath which seeds have been deposited. This pattern can explain the non-aggregated distribution of individuals observed in the studied populations. We conclude that establishment of new individuals has been continuous at both localities and that the populations of R. integrifolia are increasing in these long unburned stands. This may be indicative of a successional trend in unburned chaparral and coastal scrub toward a sclerophy llous woodland. 相似文献
13.
Abstract. This paper focuses on the persistence of seeds in the seed bank of a formerly fertilized flood-meadow into which seeds from an original Alopecurus pratensis-Sanguisorba officinalis community have been introduced. The longevity of seeds in the seed bank of the original community is also estimated. The established vegetation was compared with the seed bank, as divided into two layers (0 - 5 cm and 5–10 cm); this allowed a classification of species into three groups, with (1) transient, (2) short-term persistent and (3) long-term persistent seed bank. The majority of the species of the unfertilized flood-meadow community have a transient or short-term persistent seed bank with seeds showing a large variance in shape i.e. flattened or elongate. Because of this, the characteristic flood-meadow species will disappear soon after the beginning of fertilizer application and will not re-establish from the seed bank, once the fertilizer application is ceased. The formerly fertilized flood-meadow contains many ruderal and arable weed species, the seeds of which tend to be compact or round. Significantly more seeds were found in the seed bank of the formerly fertilized flood-meadow under cattle-grazing than under sheep-grazing and no grazing. 相似文献
14.
Abstract. In the mesic grasslands of the central United States, the shrub Cornus drummondii has undergone widespread expansion in the absence of recurrent fire. We quantified alterations in light, water and N caused by C. drummondii expansion in tall‐grass prairie and assessed the hypothesis that these alterations are consistent with models of resource enrichment by woody plants. Responses in graminoid species, particularly the dominant C4 grass Andropogon gerardii, were concurrently evaluated. We also removed established shrub islands to quantify their legacy effect on resource availability and assess the capability of this grassland to recover in sites formerly dominated by woody plants. The primary effect of shrub expansion on resource availability was an 87% reduction in light available to the herbaceous understorey. This reduced C uptake and N use efficiency in A. gerardii and lowered graminoid cover and ANPP at the grass‐shrub ecotone relative to undisturbed grassland. Shrub removal created a pulse in light and N availability, eliciting high C gain in A. gerardii in the first year after removal. By year two, light and N availability within shrub removal areas returned to levels typical of grassland, as had graminoid cover and ANPP were similar to those in open grassland. Recovery within central areas of shrub removal sites lagged behind that at the former grass‐shrub ecotone. These results indicate that the apparent alternative stable state of C. drummondii dominance in tall‐grass prairie is biotically maintained and driven by reductions in light, rather than resource enrichment. Within areas of shrub removal, the legacy effect of C. drummondii dominance is manifest primarily through the loss of rhizomes of the dominant grasses, rather than any long‐term changes in resource availability. C. drummondii removal facilitates grassland recovery, but the effort required to initiate this transition is a significant cost of woody plant expansion in mesic grasslands. Prevention of woody plant expansion in remnant tall‐grass prairies is, therefore, a preferred management option. 相似文献
15.
Abstract. We studied the germinable soil seed bank of tall‐tussock grasslands along an altitudinal gradient in the mountains of central Argentina. We selected 10 sampling plots at three altitudinal levels (1200 m, 1600 m and 2200 m). We assessed the composition of the established vegetation and took ten compound soil samples (0 ‐ 5 cm depth) at each plot in autumn and spring. The soil samples were sieved, chilled, and incubated in a glasshouse to assess the composition of the seed bank. The similarity between the composition of the seed bank flora and that of the established vegetation was low throughout the gradient. Most species did not change their seed bank strategy along the gradient. Seed bank richness and density increased with altitude. Most species had a persistent seed bank at all altitudinal levels, and the proportion of such species increased with altitude. These results suggest that a cold climate directly and/or indirectly favours the formation of seed banks and seed persistence in the soil. 相似文献
16.
PAOLA MENSI ALDO LATTES SEBASTIANO SALVIDIO EMILIO BALLETTO 《Zoological Journal of the Linnean Society》1988,93(3):259-271
Genetic relationships among 15 South West European populations of Polyommatus coridon were evaluated by the electrophoretic study of 16 gene-enzyme systems. Nei's indexes I and D and other statistics demonstrated that two different species are involved, identifiable as Polyommatus coridon (six populations from Southern France and Italy) and Polyommatus caelestissimus (nine populations from Spain), respectively. The Spanish complex is characterized by a different genetic balance, involving much higher degree of interdemic differentiation. It also differs from populations from France and Italy on one alternative locus showing complete fixation. Species-level distinction is independent of haploid chromosome numbers that vary from 87 to 88 in both groups. An evaluation of selective pressures as operated by climatic factors was attempted. The Pleistocene radiation of this group and consequent patterns of the gene flow were reconstructed using spatial autocorrelation analysis. 相似文献
17.
Abstract. Alvars in the Baltic region, particularly on the Swedish islands of Öland and Gotland and in western Estonia, are well‐known for their plant species richness and extensive populations of rare species. Grasslands make up most of alvar vegetation. The extent of these grasslands decreases because of bush enchroachment which takes place in most alvars when traditional land use practice changes, notably when grazing is ceased. The main threat for the alvar grassland is formed by the rapid expansion of Juniperus communis and Potentilla fruticosa in dry and wet sites, respectively. Applied research has been carried out during several years in order to develop plans for the restoration of alvar grassland. Thus it was shown that species richness in areas with a mixture of grassland and shrubland decreases in relation to the increased cover by shrubs. In the case of Juniperus there is a distinct drop in species number as soon as the cover exceeds 75‐80%, while the decrease is more gradual with increased cover of Potentilla. The seed banks under dense stands of these shrubs only contain ca. 20% of the species found in dry and wet alvar meadows. This was confirmed by clearing experiments. Long‐term recordings have shown that establishment of juniper seedlings takes place mainly in half‐open areas between already existing junipers. Intermediate‐sized junipers expanded faster than old and big shrubs. Potentilla shrubs recover fast from cutting or burning. After 2‐4 yr they have almost attained their former size. This recovery can be prevented when cattle grazing is introduced. In the framework of a local alvar restoration project on Öland, covering 7000 ha, grazing regimes are re‐established, fences erected and large‐scale clearings carried out. Recently established juniper shrubs are being cleared, intermediate sized junipers (30‐50 yr old) are selectively removed while creating a mosaic landscape with high biological diversity. Older dense juniper stands are left alone or are only partly cleared. Potentilla stands in moist areas are cut to create moist meadows which are breeding grounds for waders, and to establish corridors between remaining open areas. Three items are discussed (1) the importance of the Stora Alvar area; (2) re‐introduction of grazing and (3) re‐introduction of species. The outstanding importance of the area regarding species richness and endemism should be recognized through a ‘golden list’ to be used along with red and blue lists. 相似文献
18.
Abstract. This paper compares the regeneration by seeds of heath and meadow and studies relationships between the floristic composition of phases in the regeneration pathway. Seed densities in the seed rain and seed bank as well as the densities of emerged seedlings in gaps and in closed vegetation were greater in the meadow than in the heath. In the heath, environmental constraints hindered seedling emergence almost completely so seeds accumulated in the seed bank. In the meadow, the decrease in the seed bank was due to high seedling emergence. Within both plant communities, seedling emergence in gaps and in closed vegetation was comparable. In the meadow, the seed rain and seedling emergence in gaps, as well as the seed bank and seedling emergence in gaps were positively correlated. Differences in seed and adult plant sizes were reasons for the low correlation between the standing vegetation and the other phases. In DCA ordination the first axis separated the phase of seedling emergence in closed vegetation and seed bank. The second axis separated the standing vegetation from the other phases. The structure of the seed rain was more heterogeneous than that of other phases. In the heath, the standing vegetation and the seed rain were positively correlated. The ordination of these phases reflected the patchiness of standing vegetation and the ability of the diaspores of Betula nana to disperse over long distances. 相似文献
19.
Abstract. Fen meadows (Cirsio dissecti‐Molinietum) are seriously threatened by desiccation, acidification and eutro‐phication. In The Netherlands several projects were launched to restore damaged fen meadows. This review describes how successes and failures of these restoration projects depend on hydrological systems. Six hydrological systems have been distinguished, which all provide the site conditions required by this community. Nowadays, the best developed fen meadows are found in the higher Pleistocene landscape of The Netherlands, where they depend on base‐rich groundwater discharging from local or large groundwater systems. Fen meadows of the lower Holocene landscape usually occur in man‐made surface water systems. Almost all stands have been severely deteriorated. Restoration of fen meadows in the Pleistocene landscape is promising when the hydrology is only slightly disturbed or when hydrological measures are taken in combination with sod cutting. Restoration prospects of fen meadows in the Holocene landscape are low. Until now a complete regeneration of Cirsio‐Molinietum meadows has not been realized. Restoration measures failed to restore high pH values in the top soil. It is hypothesized that viable seeds of many target species lack in the soil seed bank. In addition, the dispersal capacities of these species seem to be limited. 相似文献
20.
Abstract. A floristic classification of British hedgerows is constructed. Hedges (the woody, structural element) and hedge‐bottoms (the mainly herbaceous ground flora) were analysed separately because different natural and management processes were expected to affect them. The 11 hedge classes varied in size from five to over 500 plots. Over two‐thirds of all hedges were dominated by Crataegus spp. or Primus spinosa. Hedge‐bottoms were more evenly grouped into four classes whose species composition could be related to broad land use/habitat types: intensive arable, rotational/mixed farming, managed grasslands, and woodland. The woodland class was only 12% of the total, and species characteristic of true woodland habitats were uncommon even within that class, so our data do not support the hypothesis of hedgerows acting as‘woodland corridors’for plants. Richness/diversity scores differed markedly between different hedge and hedge‐bottom classes. The richest hedgerows, both in species and inferred habitats, were among the rarer types, while the most common classes (both hedge and hedge‐bottom) were consistently the poorest. Comparison of species composition and diversity in hedges and hedge‐bottoms, and associations between them, all supported the hypothesis that the relative importance of historical, management and ecological effects differed between the two parts of the hedgerow; hedges and hedge‐bottoms should be treated ecologically as largely independent units. The classifications and richness/diversity scores enable easy preliminary assessment of the conservation value of a hedgerow. They also enable individual hedgerows to be placed in a wider (national) context. 相似文献