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1.
Across large areas of upland Britain Molinia caerulea and Nardus stricta are replacing Calluna vulgaris as the dominant plant species of the vegetation assemblage. Associated changes in the composition of the whole plant assemblage and a phytophagous insect group, the Hemiptera, were investigated. Vegetation and hemipteran assemblages were sampled at six moorland sites in northern England and Scotland. Sampling at each site was carried out in Calluna vulgaris-dominated areas and grass-dominated areas that had previously been dominated by C. vulgaris. Vegetation assemblages of heath and grass sites differed significantly even when species by which sites were selected for sampling (C. vulgaris, M. caerulea and N. stricta) were removed from the analysis with the highest species richness in dry grassland sites. Hemipteran assemblages differed significantly between heath and grass sites with greater species richness also being in grass sites. Plant species composition was the most important explanatory variable of hemipteran assemblages with temperature, latitude, soil loss on ignition and vegetation height also explaining a significant proportion of the variation. Overall a range of vegetation composition and structural variables explained 40.8% of variation in the Hemiptera species data with ranges of soil and biogeographic variables explaining an additional 8.7%.This research demonstrates that the replacement of one dominant plant species by another is associated with a change in other aspects of moorland biodiversity. In particular the loss of C. vulgaris actually leads to an increase in the species richness of Hemiptera and plants although the number of specialist species declines. 相似文献
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Upland heather moors are high priority biotopes for conservation in Britain, but are under threat from a number of sources. One such threat is a change from a vegetation dominated by dwarf shrubs, mainly Calluna vulgaris, to a grassland dominated by Molinia caerulea. Restoration of a dwarf shrub community has proved problematic with studies showing that herbicide use may be necessary to control Molinia. Previously the non-selective herbicide, glyphosate, has been recommended, but this herbicide may damage Calluna and other moorland species severely. Here, we tested a range of selective herbicides (graminicides) for use in an herbicide-based conservation strategy under field conditions. Two selective herbicides, propaquizafop and quizalofop-ethyl, gave a short-term check to Molinia and another, cycloxydim, provided a reduction for at least 1 year, but this effect disappeared after 3 years. Damage to Calluna was less than that caused by glyphosate, and the selective herbicides had little effect on other moorland species present. Our findings suggest that selective herbicides have a potential role in reducing Molinia during moorland restoration, although follow-up applications, and appropriate moorland management, will also be needed. 相似文献
4.
The impact of long-term heavy grazing pressure on montane vegetation and soils was investigated on the Carneddau plateau in North Wales. At this site, historical information suggests that formerly extensive Racomitrium- and Vaccinium-dominated heaths have become degraded and reduced in extent over the last 40-50 years. This coincides with a period when both sheep numbers and atmospheric deposition of nitrogen have greatly increased. Vegetation composition, plant tissue chemistry, soil chemistry and sheep presence were compared between areas of ‘good’ condition Racomitrium and Vaccinium heath and degraded areas. Comparison of species composition data with sheep presence and environmental data showed no significant link between current grazing distribution and species composition in the areas investigated, with all habitats having sheep presence above the recommended maximum for this habitat. Soil chemistry showed several differences between degraded and ‘good’ condition habitats, suggesting that degraded areas had experienced loss of soil organic matter and upper organic horizons. Comparison of soil and vegetation nitrogen content with data from other UK sites suggests a build up of nitrogen has occurred in Carneddau vegetation and soils, possibly related to high levels of nitrogen deposition. It is concluded that restoration of severely degraded areas of montane vegetation may be retarded by deleterious changes in soil properties which could slow recolonisation by montane species. Reductions in stocking density aiming to restore montane communities might have more immediate impact on less degraded areas. 相似文献
5.
Martin Allison 《Biological conservation》2006,127(2):177-182
We investigated ways of optimising the establishment of Calluna vulgaris-dominated heathland vegetation following removal of pines from afforested heathland using a randomised block experiment. Removal of the litter layer, or both the litter and humic layers, resulted in a higher initial establishment rate of C. vulgaris compared to in the control plots. The effect of adding heathland clippings suggested that the rate of establishment of C. vulgaris was limited by seed availability in plots from which both the litter and humic layers had been removed, but not in those from which just the litter layer had been removed. Removal of both the litter and humic layers did, though, result in a long-term reduction in the depth of the humic layer, a lower loss-on-ignition and lower level of nitrate and total nitrogen compared to in the control plots. The optimal method for establishing heathland vegetation at a site will depend on: (1) whether there is a viable seedbank of C. vulgaris and other desirable heathland species present; (2) the importance of quickly establishing a high cover of desirable heathland species; (3) the likely long-term effects of soil nitrogen levels on the maintenance of C. vulgaris dominance; (4) the practicality of removing and disposing of the litter and humus layers. 相似文献
6.
Changes over a period of 10–30 years in the vegetation of some Dutch heathlands were studied, using aerial photographs and information derived from observations and permanent plots. The sites studied are situated in (formerly) Calluna vulgaris-dominated heathlands, known to be infested in the past by the heather beetle Lochmaea suturalis, Thoms., followed by a Calluna die-off. No interference by management practices had interrupted the natural changes in the vegetation following the infestation. Evidence for both seral and cyclical changes is presented. It is concluded that abiotic factors, i.e. physiographically controlled minor differences in the soil type, determine whether a cyclical or seral change will occur. 相似文献
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This study has compared the phytolith production and soil phytolith assemblages of two native grass communities typical in Argentina, namely the monospecific Paspalum quadrifarium community or “pajonal”, and the Stipa-Piptochaetium community or “flechillar”. Five sites – three of which had been unmanaged while other two had been submitted to fire and fire-grazing management activities – were selected for study. The results show that in these sites a) phytolith production of the plant communities differed due to their diverse floristic composition, b) it was possible to define the type of management or the type of community based on soil phytolith assemblages, c) there were differences between plant communities and soil phytolith assemblages. These results suggest that modern phytolith assemblages are composed not only of local and present vegetation but also of extralocal/regional and probably past vegetation. Hypotheses about the probable processes involved in phytolith incorporation to soil have emerged during the investigation. 相似文献
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The UK Biodiversity Action Plan has identified the creation of lowland heathland as an important objective. Heathland restoration studies have identified soil pH, elevated soil nutrients and large weed seed banks as major problems in the restoration of heathland vegetation on ex-arable land. Heathland vegetation is usually found on nutrient-poor acidic soils. Creating acidic soil conditions on ex-arable sites thus may produce a suitable environment for the establishment of heath vegetation. Soil acidification by the addition of sulphur has been shown to reduce the soil pH and the availability of nutrients in arable soils. A series of experiments was established to investigate the effects of soil acidification using sulphur on the establishment of Calluna vulgaris and the development of weed vegetation. The application of sulphur at 0.24 kg m−2 to an arable soil was found to increase the survival rate of C. vulgaris cuttings planted in it. The mechanism of increased C. vulgaris survival appeared to be by sulphur application significantly reducing the cover of arable weeds arising from the soil seed bank. Higher rates of sulphur application (0.36 and 0.48 kg m−2) resulted in the death of many C. vulgaris plants. However C. vulgaris seedlings were able to establish successfully on these ex-arable soils within 18-24 months following the addition of these levels of sulphur. The application of sulphur appears to offer a practical solution to heathland creation on ex-arable land. However, it may be necessary to provide an interval of between 18 and 24 months between the application of sulphur and the addition of C. vulgaris plants or seeds for the successful establishment of heathland vegetation. 相似文献
9.
P.D Hulme B.G MerrellL Torvell J.M FisherJ.L Small R.J Pakeman 《Biological conservation》2002,107(3):351-363
Many upland areas of the British Isles have seen declines in the area and condition of heather (Calluna vulgaris)-dominated heathland vegetation. To reverse this decline, management regimes must be designed to rehabilitate areas that have seen this decline. As most of this heathland vegetation is primarily managed by grazing, such management has to determine what stocking levels can maintain the vegetation in a desired state. This paper describes how to reverse this decline through suitable grazing management.A degraded ‘wet-heath’ system, previously grazed at 2.1 sheep ha−1, was subject to a range of grazing treatments over a 5-year period. Treatments varied in intensity (0-1.4 sheep ha−1) and timing (summer only, winter only, or year round) of grazing. Grazing levels were maintained at 2.1 sheep ha−1 outside the fenced areas. Vegetation composition remained stable outside the fenced treatments. All the fenced treatments showed an increase in the relative frequency of the evergreen Calluna vulgaris, with the greatest increase being in the ungrazed treatment, and the least in the year round 1.4 sheep ha−1 treatment. This increase was in line with a reduction in heather utilisation to relatively low and sustainable levels. Other species that benefited from reduced grazing included Carex nigra, Deschampsia flexuosa and to a lesser extent Galium saxatile and Erica tetralix, whereas a range of moss species including Hypnum jutlandicum and Rhytidiadelphus loreus were more frequent at higher grazing levels. Though the recovery of heather was similar in the two seasonally grazed treatments, the vegetation showed different overall trajectories. Winter only grazed allowed a substantial increase in the cover of the deciduous Molinia caerulea, whereas this species was kept in check by summer only grazing. A stocking level of between 0.7 and 1.4 sheep ha−1 appears to be appropriate to maintain and even enhance the cover of heather on degraded wet heath. Complete removal is not necessary. Grazing restricted to the winter period is inappropriate in areas where M. caerulea occurs. Setting appropriate stocking levels to maintain the condition of the vegetation must take into account site conditions, especially the presence of species that can affect the utilisation of heather. 相似文献
10.
Calluna vulgaris-dominated heaths and moorlands are habitats of international conservation importance. Degradation has occurred throughout their range with Calluna typically being replaced by grass species. The cessation of grazing is often impractical and rarely results in the recovery of Calluna abundance when it is initially present at low cover. Thus the development of restoration methods is required; these should be practical at a large-scale, in remote areas and create suitable conditions for Calluna germination and establishment, whilst still allowing grazing to occur. A replicated field experiment was established on Nardus stricta and Molinia caerulea-dominated moorlands to test the efficacy of different grazing regimes and intervention techniques aimed at establishing Calluna. Disturbance (rotavation and trampling by animals) to create bare ground increased Calluna establishment. On the Nardus site, Calluna establishment was equally successful on rotavated and trampled plots, but rotavation was more successful on the Molinia site. Seeding with Calluna increased Calluna establishment irrespective of whether a seed-bank was present. At the Nardus site, 0.5 cow/ha for two months in summer led to Calluna establishment and growth similar to that of ungrazed plots and was more successful than a mixed grazing regime (1 ewe/ha plus 0.5 cow/ha for 2 months) or a sheep only regime (1.5 ewes/ha). The creation of small patches of bare ground, seed addition and low intensity grazing enabled the rapid establishment of Calluna on grass-dominated moorlands; such techniques may also be applicable in other habitats where restoration requires the addition of a single/few species and minimal intervention. 相似文献
11.
At present, forest cover in southwestern Ontario, Canada, remains at less than 5% due to intensive agricultural and urban land use. Although much of the extant forest is increasingly protected by legislation, remnants continue to be degraded by the spread of non-native plant species, overgrazing, and recreational use. Some parks in the region have adopted management programs aimed at mitigating this degradation. Over the last 35 years, cottages and roads at Point Pelée National Park have been removed and sites either passively restored (i.e. road or cottage eliminated and vegetation allowed to regenerate) or actively restored (i.e. road or cottage eliminated, exotic vegetation removed, and native species planted). In 1994 and 1995, we assessed the effectiveness of restoration by comparing the understorey plant communities in 28 restored sites with those in less disturbed reference sites. There was a significant increase (P<0.0001) in the similarity of understorey plant communities between restored and reference sites as time-since-restoration increased. Soil moisture, canopy cover, distance to continuous forest, and site-shape all significantly affected plant species composition. Former road sites recovered significantly (P<0.05) more rapidly than former cottage sites, and the former lawns of passively restored cottage sites were the slowest to recover. Five years following active restoration, non-native ruderal species continued to dominate restored sites. The observed recovery of understorey plant communities in restored sites is attributed to their proximity to natural vegetation, and its function as a seed source. In some sites, recovery is substantial and, assuming present trajectories of change are maintained, we predict that recovery could occur in many mesic sites within the next 20 years. Restoration activity facilitates forest recovery and would appear to have a valuable function in mitigating ongoing conflicts between conservation and human use in this region. 相似文献
12.
Carla P. Catterall Amanda N.D. Freeman John Kanowski Kylie Freebody 《Biological conservation》2012,146(1):53-61
There is vigorous debate about the potential for reforestation to offset losses in biodiversity associated with tropical deforestation, but a scarcity of good data. We quantified developmental trajectories following active restoration (replanting) of deforested pasture land to tropical Australian rainforest, using 20 different bird community indicators within chronosequences of multiple sites. Bird species composition in restored sites (1–24 years old) was intermediate between that of reference sites in pasture and primary rainforest. Total species richness was much less sensitive to land cover change than composition indicators, because of contrasting species-specific response patterns. For example, open-country (grassland/wetland) bird species declined in richness and abundance with increasing site age, while rainforest-dependent species increased. Results from two different landscapes (uplands and lowlands) were remarkably consistent, despite differing bird assemblages. After 10 years, restored sites averaged about half the number of rainforest-dependent bird species typical of rainforest. Mean values at around 20 years overlapped with the “poorest” rainforest reference sites, but projections suggest that >150 years are required to reach mean rainforest levels, and high variability among sites means that many were not on track towards ever achieving a rainforest-like bird community. Regional rainforest endemics were half as likely to occupy older revegetated sites as non-endemic rainforest-dependent species. Between-site variability and slow colonisation by regional endemics strongly constrain the potential of rainforest restoration to offset the biodiversity impacts of tropical deforestation. The results also mean that ongoing monitoring of biodiversity is an essential part of restoration management. 相似文献
13.
In the Mediterranean region, cycles of controlled burning combined with continuous grazing appear to have been an effective tool for maintaining isolated Calluna vulgaris heathlands in the form in which they occur in many places in the Atlantic region. Changes in land use and management of the mosaic of extensively exploited heathland and associated grassland over recent decades, such as bringing land into cultivation followed by its abandonment and the prohibition of fires has resulted in a process of transformation into new shrub communities with lower biodiversity. In the Mediterranean region, these changes are similar to those described in the Atlantic area, but encroachment occurs faster and could lead ultimately to afforestation by Mediterranean woodland.In a study area of 300 ha of heathland in the Spanish Mediterranean basin (specifically, in the Montseny Natural Park and Biosphere Reserve), comparison of present and former vegetation showed that shrub cover increased from 15% in 1967 to 32% in 2000. Broom (Cytisus scoparius) was the main invasive species in abandoned crop fields, whereas Mediterranean holm oak forest (Quercus ilex) increased by 18%. The surface area of fernlands doubled and C. vulgaris heathlands decreased from 35% to just 9% during the same period. Intermixed grasslands also decreased moderately and progressively from 4% to 3%.It seems probable that cycles of fires are more important in terms of shrub control and biodiversity conservation than continuous grazing alone, even at a high rate of stocking (four small ruminants per hectare per year). This encroachment process throws into relief the role that isolated habitats can play as a monitor of land use changes. 相似文献
14.
An important challenge for riparian management is to determine the extent to which landscape context influences the faunal assemblages of riparian habitats. We examined this challenge in the variegated landscapes of southeastern Queensland, Australia where riparian vegetation is surrounded by both extensive grazing and intensive cropping. We investigated whether riparian habitats adjacent to different landuses support similar bird assemblages. Three types of riparian habitat condition were sampled (uncleared ungrazed; uncleared grazed; cleared grazed) in four different land-use contexts (ungrazed woodland; grazed woodland; native pasture; crop) although only six of the 12 possible treatment combinations were available. Eighty percent of bird species responded significantly to changes in both riparian habitat condition and landscape context, while fewer than 50% of species were significantly influenced by landscape context alone. The influence of landscape context on the bird assemblage increased as the surrounding land use became more intensive (e.g., woodland to native pasture to crop). Riparian zones have been shown to have consistently high biodiversity values relative to their extent. These findings suggest it is not enough to conserve riparian habitats alone, conservation and restoration plans must also take into consideration landscape context, particularly when that context is intensively used land. 相似文献
15.
Grasslands restoration is a key management tool contributing to the long-term maintenance of insect populations, providing functional connectivity and mitigating against extinction debt across landscapes. As knowledge of grassland insect communities is limited, the lag between the initiation of restoration and the ability of these new habitats to contribute to such processes is unclear. Using ten data sets, ranging from 3 to 14 years, we investigate the lag between restoration and the establishment of phytophagous beetle assemblages typical of species rich grasslands. We used traits and ecological characteristics to determine factors limiting beetle colonisation, and also considered how food-web structure changed during restoration. For sites where seed addition of host-plants occurred the success in replicating beetle assemblages increased over time following a negative exponential function. Extrapolation beyond the existing data set tentatively suggested that success would plateau after 20 years, representing a c. 60% increase in assemblage similarity to target grasslands. In the absence of seed addition, similarity to the target grasslands showed no increase over time. Where seed addition was used the connectance of plant–herbivore food webs decreased over time, approaching values typical of species rich grasslands after c. 7 years. This trend was, however, dependent on the inclusion of a single site containing data in excess of 6 years of restoration management. Beetles not capable of flight, those showing high degrees of host-plant specialisation and species feeding on nationally rare host plants take between 1 and 3 years longer to colonise. Successful grassland restoration is underpinned by the establishment of host-plants, although individual species traits compound the effects of poor host-plant establishment to slow colonisation. The use of pro-active grassland restoration to mitigate against future environmental change should account for lag periods in excess of 10 years if the value of these habitats is to be fully realised. 相似文献
16.
In the Yucatan, cenotes or water sinkholes formed by the dissolution of limestone and surrounded with a characteristic dense layer of heterogeneous vegetation, are the main sources of water for plant and animal assemblages. We investigated their importance to bats by comparing the assemblage structure and diversity between tropical forest and pastureland, with and without cenotes. We set ground level mist nets, sub-canopy nets and harp traps for 96 nights and caught 2819 bats of 26 species and six families. Forest had a greater bat species diversity and abundance than pastureland, as well as rare and threatened species. In forest, sites with and without cenotes had a similar bat assemblage structure and diversity, whereas in pastureland there was a greater species diversity and abundance and number of rare and threatened species at cenotes than sites without cenotes. Chrotopterus auritus and Micronycteris schmidtorum, both threatened in Mexico, and Eptesicus furinalis, were exclusively captured at cenotes. We suggest that it may be the vegetation around cenotes rather than the water bodies per se that attracts many bat species in pastureland. Cenotes are threatened by nitrate contamination from untreated domestic and animal waste and fertilizers and the removal of vegetation to allow livestock access to water. In Yucatan’s agricultural landscapes, protection of cenotes and their characteristic vegetation is key not only for bat conservation but also because they represent potential seed sources for the regeneration of the lowland forest, in which bats play key roles as pollinators and seed dispersers. 相似文献
17.
Since 1992 the European Union helps member states to reverse the loss of biodiversity in agricultural landscapes by the financial support of agri-environment schemes. Long-term studies investigating the effects of these schemes are an essential prerequisite for the development of an effective policy to restore biodiversity on farmland. In Dutch meadow landscapes almost all agri-environment schemes focus on the restoration of meadow bird populations by postponement of the mowing date. Between 1990 and 2002 we measured long-term changes in meadow bird densities in areas with and without agri-environment schemes in the Netherlands, both before and after the start of the contract. During these years bird territories were surveyed during five field visits between 15 March and 15 June. Densities of black-tailed godwit (Limosa limosa), and redshank (Tringa totanus) were higher in the areas with management agreements, but these differences were already present before the start of the contracts. After the start of the management contracts densities of black-tailed godwit and oystercatcher (Haematopus ostralegus) did not increase, while those of lapwing (Vanellus vanellus) and redshank even declined relative to the control areas. It is concluded that the current agri-environment schemes are not sufficient to restore meadow bird populations in Dutch agricultural landscapes. In addition to the prescribed postponement of the mowing date, it is probably necessary to raise groundwater levels and to reduce fertilization to allow for the development of an open vegetation structure that will increase chick survival to sufficiently high levels. 相似文献
18.
Patterns of biodiversity are influenced by habitat features at multiple spatial scales, yet few studies have used a multi-scale approach to examine ground-dwelling beetle diversity patterns. We trapped and quantified ground-dwelling beetle assemblages at two spatial scales: (1) microhabitat elements, represented by open ground, ground under trees and ground next to logs and (2) macrohabitat, represented by three vegetation types in a box-gum grassy woodland in south-eastern Australia. Species richness and evenness was highest at samples from under trees and lowest at samples in the open. At the macrohabitat scale, species richness and evenness did not differ among vegetation types. Assemblage composition was significantly different between trees, logs and open elements. Assemblage composition was different only between vegetation types with contrasting high and low shrub cover. Estimation of true species richness indicated assemblages at logs may have a higher number of species compared to trees and open elements, and implied greater spatial heterogeneity in assemblages at logs. Significant spatial autocorrelation in beetle assemblages was detected for logs at up to 400 m, but not for ground under trees or in the open. In agreement with previous studies, a mix of vegetation types at the macrohabitat scale is important for beetle conservation. Assemblage composition, however, appears to be more closely linked with habitat elements at the microhabitat scale, where logs support a high diversity of beetle species. This strongly supports the idea that restoring logs to box-gum grassy woodlands would be useful for increasing beetle species richness and assemblage heterogeneity. 相似文献
19.
Shiro Tsuyuzaki 《Biological conservation》2002,108(2):239-246
The Japanese montane zones are usually covered with well-developed forests, and most ski resorts are constructed there. Therefore, the construction of skislopes requires the destruction of forest ecosystems. To detect vegetation development patterns on skislopes, I assessed vegetation on seven skislopes in the lowland of Hokkaido Island, Japan, using 155 2 m×2 m plots. The surrounding vegetation was mostly consisted of broad-leaved forests with a floor of dwarf bamboo, Sasa senanensis. The skislopes were established 5-28 years before the surveys by scraping off the topsoil and subsequent artificial seeding. The data of vegetation analyzed by TWINSPAN resulted in six different grassland types: (A) Miscanthus sinensis-Hypochaeris radicata, (B) introduced herbs with low richness, (C) introduced herbs, (D) Artemisia montana, (E) M. sinensis-Pueraria lobata-A. montana, and (F) Solidago gigantea var. leiophylla. H. radicata and S. gigantea var. leiophylla were alien species. Vegetation dominated by introduced grasses for erosion control, such as Dactylis glomerata and Poa pratensis, should be initial vegetation on the skislopes. Most tree pioneer species established in the vegetation type A, that was most natural vegetation in the skislopes. Type A seemed to proceed from types B and C, and species richness was the highest. Therefore, this type should be preferable for the management and restoration of skislope vegetation. Type D established on newer skislopes, while types E and F established on older skislopes. Results including detrended correspondence analysis suggested that those vegetation types D-F proceeded to distorted succession, i.e. biological invasion changed native successional sere. Based on these results, I recommended that the restriction of alien invasion and careful monitoring on M. sinensis grasslands are required to restore the natural vegetation. 相似文献
20.
Many areas of heathland in Europe have seen a decline in the area and condition of Calluna vulgaris (heather)-dominated vegetation, with subsequent declines in the associated faunal interest. Grazing, alongside burning, is still the predominant means of managing heathland vegetation, and, therefore, it is by manipulating this management that cost-effective improvements in vegetation condition can be made. This paper investigates the suitability of different grazing treatments for rehabilitating degraded ‘dry heath’. Treatments varied in the intensity (0-1.9 sheep ha−1 year−1) and timing (summer vs. winter) of sheep grazing. These treatments were compared with the behaviour of vegetation outside the fenced area kept under the previous management (open access all year round). As rabbits were common on the site, fences were erected to prevent access to the sheep grazed plots. Vegetation composition remained stable outside the fenced area, whilst all the fenced treatments showed a decrease in heather utilisation and an increase in the relative frequency of heather over the 5 years of the experiment. The increase was in proportion to the reduction in stocking rate, with only slow increases in relative frequency observed in the high grazing treatments (winter and summer). Other species that benefited from reducing grazing included Empetrum nigrum and Vaccinium myrtillus, whilst declines were observed for Agrostis capillaris and total monocotyledonous species. Only small overall differences were observed between the winter low, summer low and no sheep grazing treatments. However, a difference in response was present between the sheep exclosures and the sheep+rabbit exclosures, indicating that rabbits were having a noticeable effect on heather recovery at this site. On this degraded ‘dry heath’ system, imposing a reduction in stocking density improved the condition of the dwarf shrubs present and reduced the grass component of the vegetation. There was little effect of the timing of grazing, such that a reduction in sheep numbers to 0.8/0.9 sheep ha−1 year−1, to give utilisation levels of below 20%, can achieve the desired result of improving vegetation condition whilst still achieving some economic return from grazing. However, the wide range of ‘sustainable’ stocking densities for different heathland systems highlights the need to base effective management on measured utilisation rather than on stock numbers. 相似文献