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1.
Joël Broyer 《Bird Study》2013,60(2):141-150
Capsule Mowing postponement in 25% of a meadow system may lead to improved but instable population dynamics in meadow birds.

Aim To monitor the long‐term effects of mowing postponement on the abundance and territory density of meadow passerines in 25% of a 3000‐ha hay‐meadow area in the Saône Valley (eastern France).

Methods From 1993 to 2009, passerine abundance was measured annually in 78 plots using point counts and territory density was assessed in two study areas by Territory Mapping.

Results The programme of mowing postponement led to substantially increased passerine abundance and territory density, with the highest increase detected in Whinchats Saxicola rubetra. No positive trend was observed in Corn Buntings Emberiza calandra. Immediately after the increase in abundance, bird distribution within the study area was not influenced by the timing of mowing. The hatching success, assessed by the systematic observation of food carrying, was negatively influenced by early mowing (<40% recorded when >60% of the meadow area was already harvested on 1 July) or, in late mown areas, by high meadow passerine territory density (<40% when territory density was >10 per 10 ha). Hatching rate was usually higher in Whinchats than in Corn Buntings.

Conclusion By improving meadow passerine breeding outputs and density, mowing postponement led to instable population dynamics with dominance of certain species and density‐dependent breeding success.  相似文献   

2.
After the cessation of regular management and after fertilization a single clonal species tends to dominate in many types of grasslands, whereas in regularly managed meadows these potential dominants usually attain a low cover. It has been hypothesized that plants reaching a high dominance in abandoned and fertilized meadows are selectively suppressed by mowing so that a balanced competition is maintained and competitive exclusion is postponed. We compared regeneration capacity and carbohydrate reserves accumulated by three species of clonal grasses, which markedly increase their dominance in irregularly mown, un-mown or fertilized meadows. Above-ground biomass and the amount of storage carbohydrates of the two largest species, (Molinia arundinacea, Calamagrostis epigejos) were reduced in a mown meadow. This effect was weaker in Bromus erectus, which produces smaller shoots. Shoots of Molinia were most impacted by mowing but their regeneration was efficient due to the large carbohydrate reserves in the shoot bases. Fertilization did not affect Bromus and Calamagrostis. In contrast, fertilized plants of Molinia produced larger storage organs and accumulated more carbohydrates. We conclude that plant size and growth form are important features promoting the ability of potential dominants to tolerate mowing and regenerate after it. Our results confirm that taller plants are selectively suppressed by this type of disturbance, thereby potentially promoting plant coexistence.  相似文献   

3.
Question: How does vegetation and management affect the population stage structure of Serratula tinctoria, a species indicative of highly endangered and species‐rich flood‐plain meadows? Are different management regimes suitable to support viable populations of S. tinctoria? Location: Flood‐plain of the northern Upper Rhine, Germany. Methods: We analysed the population structure of S. tinctoria at 24 meadow sites which differed in vegetation and management. In this comparative study the investigated meadows were either (1) late mown in September; (2) early mown in June or (3) mown in June and then grazed by sheep. Results: The structure of the surrounding vegetation had a clear effect on the population structure of S. tinctoria. The percentage of bare soil, as well as the cover of bryophytes, were positively related, whereas the Ellenberg N‐value of the established vegetation was negatively related to the density and proportion of seedlings. Generally, we found only slight differences between the population structure of S. tinctoria in early and late mown meadows. Both management regimes had high densities of seedlings. In contrast, the meadow pastures supported significantly lower densities of seedlings and generative adults but relatively high densities of juveniles and vegetative adults, indicating a greater importance of clonal propagation under grazing pressure. Conclusions: Our results clearly showed that viable populations of S. tinctoria may occur in all of the studied management regimes. Although S. tinctoria was considered to be highly sensitive to early mowing, our findings suggest a facilitation of the species at more nutrient‐rich sites by mowing in June, which is also a benefit for the integration of management in farming systems.  相似文献   

4.
Semi-natural grasslands resulting from traditional land use practices (mowing and grazing) are severely endangered throughout Europe due to the intensification of agriculture. The ecological impact of mowing and grazing on grassland butterflies was studied in eight mown meadows and eight grazed pastures under traditional animal husbandry in NW Russia and adjacent Finland. Transect count data over 3 years (1997–1999) covered a total of 48 species and 5742 individuals. The butterfly fauna was rather similar under both management forms; species richness, diversity and total abundance did not differ significantly between meadows and pastures, yet meadows were preferred by more species. In both groups, the most abundant species were Aphantopus hyperantus, Pieris napi and Thymelicus lineola. Of 37 species observed as a minimum of five individuals, Polyommatus amandus, Ochlodes sylvanus and A. hyperantus showed a significant preference for mowing management. According to the ordination, butterfly communities were affected more by the origin and age of the grassland than the present management method. Landscape factors (meadow or pasture surrounded by forests or open environments), the abundance of nectar plants and the intensity of tilling were the most important factors differentiating older grasslands from the younger ones evolved from old Finnish hay fields cultivated prior to the 1940s.  相似文献   

5.
6.
Effective conservation of endangered species requires a solid understanding of the demographic causes of population change. Bird populations breeding on agricultural grasslands have declined because their preferred habitat of herb‐rich meadows has been replaced by grassland monocultures. The timing of agricultural activities in these monocultural grasslands is critical, as they often coincide with the nesting phase of breeding birds. Here, we aim to identify the effect of habitat management and targeted nest protection on nest survival of Black‐tailed Godwits Limosa limosa in the Netherlands, a population that has shown a 70% reduction in breeding population size since the 1970s. To protect nests in monocultures from destruction, farmers are paid to either delay mowing or leave a patch of unmown grass around the nest, a patch which in practice varied in size. In herb‐rich meadows, which are typically managed for bird conservation purposes, mowing occurs after hatching. Nest survival declined as the season advanced, more steeply on monocultures than on meadows. Targeted nest protection was only partially successful, as nest predation was considerably higher on mown grassland monocultures with small unmown patches around the nest than in mown monocultures with large unmown patches and in unmown fields. Increased predator densities over the years have been suggested as an important cause of the trend towards lower nest survival, but here we show that nest survival was higher on herb‐rich meadows than on monocultures, and similar to the 1980s. It thus seems that increased predator densities are an increased threat during the egg stage only if habitat quality is low. High‐quality habitat in the form of herb‐rich meadows therefore provides a degree of protection against predators.  相似文献   

7.
We analysed the morphology and phenology of Scabiosa columbaria in relation to grassland management by mowing and grazing. We selected 12 populations from mown and grazed calcareous grassland in six regions of central Europe. At each population site, we collected seed material to produce plants for a morphological and phenological analysis of the species in a simulation experiment, which comprised three treatments (control, simulated mowing and simulated grazing).The simulation experiment revealed a clear morphological and phenological differentiation of S. columbaria. Plants from the two treatment types differed in size, since individuals from mown sites had longer top peduncles than individuals from grazed sites. Individuals from mown populations flowered earlier than individuals from grazed populations. In the control treatment, individuals from both habitat types produced a similar number of fruiting capitulums. When subjected to simulated mowing, the reproductive success of the individuals was clearly reduced. Plants from mown habitats produced, however, a significantly larger number of fruiting capitulums than plants from grazed habitats. Simulated grazing reduced the reproductive success stronger than simulated mowing but differences between individuals from both habitat types were not significant.The results of our simulation experiment clearly indicate morphological and phenological adaptation of S. columbaria to mowing and grazing. The comparatively young selection pressure of mowing obviously selected early flowering individuals, while the original land use by grazing favoured late flowering plants.  相似文献   

8.
Abstract. We studied the effects of abandonment on two common fen plant species. In mown and a chronosequence of abandoned fen meadows spanning 35 yr, we measured fitness traits of the sedge Carex davalliana and the forb Succisa pratensis. Cessation of mowing had little effect on fitness traits and seed production of C. davalliana, but seedling density decreased more than threefold. Population density of S. pratensis decreased with increasing community biomass, but was not affected by the cessation of mowing. However, flowering frequency increased threefold and seed production was 20% higher in fallow meadows. Consequently, seedling density of S. pratensis increased nearly threefold after abandonment. However, these changes were not dependent on the age of the fallow. In a common garden and germination experiment, we found no differences in either species between plants from fallows and mown fen meadows, except for the height of the flowering stalk of S. pratensis. The combined results from the common garden experiment and the field studies indicate that changes in fitness traits observed in fallows were mostly phenotypic and likely to be reversible. If other species react in similar ways, there is a high potential for re‐establishing traditional fen meadow communities from fallows by mowing.  相似文献   

9.
This study aims at elucidating modern pollen spectra/environmental data relationships from both natural and human-induced vegetation types as an aid for palaeo-ecological reconstructions. A set of 51 surface moss polsters was sampled from different vegetation and land-use types in the Champsaur area (French Alps) and analysed to obtain modern pollen analogues of ancient cultural landscapes in mountain ecosystems. Samples were selected from grazed areas, mown meadows, cultivated fields, fallow land and deciduous and coniferous forests. Vegetation composition around the sampling points and seventeen types of environmental variables (e.g., management type, soil and topography) were collected all for these 51 sites. Patterns of modern local pollen variation in relation to the environmental variables were explored by means of canonical correspondence analysis (CCA) and associated statistical tests. This correlative model allows us to determine the major explanatory variables and to identify taxa indicative of particular anthropogenic activities, and thus may help to calibrate fossil pollen assemblages.The indicator pollen types are evaluated in the light of comparable material from lowland and mid-elevation areas of western Europe. The results of the French data-set confirm some of the conclusions drawn from the North European data-sets, but also show some site specific features. Pollen markers with a broader global significance common to other regions include Rhinanthus type, Apiaceae and Dipsacaceae for mown meadows, Urtica type, Plantago media/major, Trifolium type and Potentilla type for grazed areas, and Cerealia type, Centaurea cyanus, and Polygonum aviculare for cultivated fields. New pollen anthropogenic indicators typical of our study area are Sanguisorba officinalis, Vicia type (mowing), Lotus type, Onobrychis type, Centaurea nigra type, Serratula type (grazing), Sinapis type and Papaver rhoeas (cultivation). This study provides potentially valuable analogues for human-induced vegetation types, and it may then become possible to interpret more objectively local pollen diagrams from Alpine mountain environments in terms of past cultural landscape development.  相似文献   

10.
Background: The rapid decline of semi-natural grasslands in Japan threatens many relic and endemic plant species. There is insufficient knowledge on how the impacts of land-use changes and management of grasslands have been affecting grassland ecosystems and what conservation measures may be taken to conserve as much of the existing plant diversity as possible.

Aim: We assessed the existing management regimes for their suitability for conserving Red Data Book (RDB) species.

Methods: We conducted our study in four districts of Kushima, Kyushu, south-west Japan, with different land-use histories. We compared species richness, plant density and abundance in six grassland types: regularly burnt, regularly mown, paddy levee, roadside, landslip and wetland communities in a total of 289 1 m x 1 m quadrats, recorded in172 grassland patches. Species richness plant density and abundance were analysed with special reference to RDB species under different land use history.

Results: Species richness of grasslands did not differ across different land use histories, yet our analysis showed that the reduced area of grasslands markedly affected the density of RDB species. Grassland types differed in their ability to support RDB species: regularly burnt grasslands were the richest in RDB species and poorest in alien species, followed by regularly mown grasslands, paddy levees, landslip, wetland and roadside communities.

Conclusions: Traditional management regimes, such as regular burning or mowing of grasslands have the best potential for conserving RDB species, and thus should be part of conservation management practices of semi-natural grasslands.  相似文献   

11.
The globally threatened Aquatic Warbler Acrocephalus paludicola is an umbrella species for fen mires and is at risk of extinction in its westernmost breeding population due to severe habitat loss. We used boosted regression trees to model Aquatic Warbler habitat selection in order to make recommendations for effective management of the last remnant habitats. Habitat data were collected in the years 2004–2006 in all remaining breeding sites in Pomerania (eastern Germany and western Poland) as well as in recently abandoned sites. Models were validated using data from similar Aquatic Warbler habitats in Lithuania. The probability of occurrence of Aquatic Warblers in late May/early June was positively associated with low isolation from other occupied sites, less eutrophic conditions, a high proportion of area mown early in the preceding year, high availability of vegetation 60–70 cm high, high prey abundance and high habitat heterogeneity. Early summer land management is needed in the more productive sites to prevent habitat deterioration by succession to higher and denser vegetation. As this also poses a serious threat to broods, management that creates a mosaic of early and late used patches is recommended to preserve and restore productive Aquatic Warbler sites. In less productive sites, winter mowing can maintain suitable habitat conditions. Aquatic Warbler‐friendly land use supports a variety of other threatened plant and animal species typical of fens and sedge meadows and can meet the economic interests of local land users.  相似文献   

12.
Mowing experiments were carried out from1995 to 2001 in Swiss fen meadows toinvestigate whether the abundance of Phragmites australis is reduced by mowingin early summer in addition to mowing inautumn. Experimental plots of 100 m2were established in three fen meadows thatare mown every year in September; treatedplots received an additional cut in lateJune either every year or every two years.Until 1997, the additional cut had noeffect on the above-ground biomass of Phragmites (monitored every year in lateJune). As from 1998, the biomass of Phragmites was 25–30% lower in the plotswith annual June cut than in the controlplots. However, the pooled biomass of allother plant species decreased similarly, sothat the degree of dominance of Phragmites was not reduced. An additionalJune cut every two years had no effect onthe biomass of Phragmites. In June2001, the shoots of Phragmites weresmaller in annually June-cut plots than incontrol plots, but allometric relationshipsbetween shoot length and diameter, shootgrowth from June to August, and nitrogenand phosphorus concentrations of shoots didnot differ between June-cut and controlplots. The additional June cut increasedthe total export of N with the hay by 18%,and that of P by 50% in 2001. Theseadditional nutrient exports were smallerthan those found in the first years of theexperiment and not larger for Phragmites than for the remainder of thevegetation. Together, the results suggestthat a depletion of below-ground storescaused Phragmites to decrease afterseveral years of additional mowing in June.Eighty further permanent quadrats in fenmeadows with normal management (mownannually in September) were surveyed in1995–96 and in 2001. The above-groundbiomass of Phragmites increasedduring this time in 49 out of 80 plots,with a mean relative difference of +35.5%.Thus, even if additional mowing in earlysummer only slightly reduced theperformance of Phragmites compared toplots mown only in September, thistreatment might help to prevent the speciesfrom spreading under the current conditionsin Swiss fen meadows.  相似文献   

13.
《Plant Ecology & Diversity》2013,6(3-4):393-404
Background: The tussock grass Festuca paniculata can become strongly dominant in subalpine grasslands after cessation of mowing. The depletion of water-soluble carbohydrate (WSC) reserves has been suggested as a mechanism by which mowing can contain this species. By affecting plant physiology and especially by favouring WSC accumulation, extreme summer weather (i.e. exceptionally hot and dry) could however counterbalance the effects of mowing on WSC reserves in F. paniculata. The relevance of this hypothesis needs to be tested in the current context of climate and land-use changes.

Aims: We investigated (1) the physiological mechanisms that control the growth of F. paniculata, (2) how they are affected by mowing and (3) whether extreme summer heat and drought could influence physiological mechanisms and thereby the ecological response of F. paniculata to mowing.

Methods: In a field experiment we manipulated weather and mowing during two summers. For current summer weather (W0), ambient temperature was unchanged and precipitation was adjusted on the past 30-year average. Extreme summer weather (W+) corresponded to a seasonal change (+1 °C, –80% in precipitation compared to W0) and a three-week heatwave (+4.3 °C) in the first year. In addition, vegetation was either mown at 5 cm in late summer (M) or left unmown (U). Concentrations and absolute contents of WSC contained in tiller bases, leaf nitrogen concentration (LNC), vegetative multiplication, plant growth and leaf senescence were measured from one to four times, depending on the variable considered, throughout the summer of the second year of the experiment.

Results: As compared to the unmown treatment, late-summer mowing decreased tillering, tussock size and LNC, regardless of the summer weather treatment. However, it depleted WSC pools, including fructans, only under current summer weather (W0).

Conclusions: These results suggest that extreme summer heat and drought could alleviate the sensitivity of F. paniculata to mowing. They raise the question of the consequences of recurrent summer extremes for conservation management in subalpine grasslands.  相似文献   

14.
Mowing a meadow is an example of an equalizing process that reduces differences among species by removing aboveground biomass approximately 5 cm above ground. This regular disturbance that affects all plants prevents competitive exclusion of small species and thus allows coexistence of numerous species differing in shoot size. In this paper we search for the mechanism behind this by comparing the shoot biomass of 41 common species in dry and wet species-rich meadows in mown and recently abandoned plots in June (before mowing) and in October. We asked the following questions: i) Do the plants differ in proportion of biomass lost by mowing? ii) Are the mown plants able to compensate for biomass lost by mowing? iii) Is the compensatory ability of mown plants related to their size? iv) Is the compensatory ability of plants related to severity of disturbance (removed biomass)? v) Does water availability in meadows affect these features? Our results revealed that the earlier explanation of equalization of meadow plants after mowing due to the proportionally larger biomass loss in larger plants than small plants does not represent the entire mechanism. Even when larger plants in the wet meadow lost more biomass, the proportion of lost biomass was not dependent on plant size, and compensation ability (growth of mown in comparison with unmown plants) was not related to the lost biomass in this meadow type. On the contrary, the observed pattern could be explained by different compensation abilities of small versus tall plants. In addition, according to our expectations, the compensation for lost biomass in the wet meadow was higher than in the dry one.  相似文献   

15.
In France, whinchat Saxicola rubetra populations now rarely breed at altitudes below 1,000 m except in flooded alluvial plains. Whinchat reproductive success, the timing of haymaking and meadow bird density were assessed in 2003 in six areas selected in three different flooded plains, in five areas from two massifs at altitudes ranging from 990 to 1,250 m, and in 2004 in six areas of three flooded plains, in seven areas from three massifs at altitudes ranging from 1,200 to 2,000 m. The percentage of whinchat territories in which juveniles were observed was negatively correlated with mown areas at the time when 80% of hatched broods (observation of prey carryings by adults) would theoretically be fledged. Additionally, assessed hatching success was negatively correlated with early haymaking in 2003 and with meadow passerine territory density in 2004. In upland meadows, whinchat populations exhibited either low reproductive success and low density (1,200 m) or high reproductive success and high density (1,200 m). In lowland flooded meadow however, high density could match low reproductive success and whinchat population then acts as a sink population. We conclude that adequate agri-environmental policy should not focus only on lowland meadows, even if the highest meadow bird diversity is often found there.  相似文献   

16.
The changes in agricultural practices during the last century have led to a drastic decrease in the number of traditionally managed hay meadows. Also, traditional management practices are often applied more cursorily in the remaining meadows. In combination with an increase in aerial anthropogenic nitrogen deposition, this has led to a loss of biodiversity. To investigate whether the current management is sufficient for maintaining viable populations of a typical meadow plant, Succisa pratensis, we experimentally reinforced the raking and mowing parts of the traditional management over four years in a two-by-two factorial experiment in three traditionally managed wooded hay meadows on the Baltic island of Gotland, Sweden. We found decreased litter and hay production in two of the three studied meadows as a result of our treatments. Plant sizes and asymptotic population growth rates (??) of S. pratensis increased, particularly in plots receiving the combined raking and mowing treatment. Stochastic long-term population growth rates (?? s ) increased under the reinforced management: projected population sizes 50?years into the future showed a three-fold increase in raked plots and a 17-fold increase in plots that were both raked and mown. Because we found positive responses even in these seemingly well-managed meadows we conclude that it is essential that management is carried out more thoroughly to ensure viable population sizes. Our conclusion applies to most semi-natural grasslands receiving anthropogenic nitrogen, or where traditional management practices are less rigorously applied. We also suggest using biomass estimation instead of vegetation height as a measure of management strength.  相似文献   

17.
Dynamics of common reed (Phragmites australisTrin.) in Central Europe have so far mostly beeninvestigated in connection with studies on reed`die-back' along lake shores. However, there hasrecently been increasing concern about reed expansionat terrestrial sites, such as fens and wet grasslands.In this paper we report on the results of fourseparate studies which monitored reed dynamics inSwiss fens with various mowing regimes over a periodof 4 to 15 years. The first study compared unmownplots with plots mown in winter in a triennialrotation; the second one included unmown plots, plotsmown in summer, and plots mown in winter; the thirdone compared plots mown in June and September withplots only mown in September; the fourth studyinvestigated only plots mown in September. Shootnumber and shoot size were recorded in permanentquadrats. In all studies the performance of P.australisfluctuated without trend or tended todecrease during the period investigated. Thedecreasing tendency concerned shoot size rather thanshoot number, and within a given study it was strongerfor plots with initially taller shoots. The variousmowing regimes did hardly influence these changes.Mowing in winter every three years reduced shoot sizein the year after mowing, but not on the long term.Mowing every year in late summer reduced the shootsize compared with unmown plots on the short term, butthis effect almost disappeared on the long term, aftermowing had become biennial. Mowing in June (inaddition to in September) caused no noticeableeffects. We conclude that other factors (e.g. weatherconditions, competition, or population processes) aremore important than management in determining theabundance of P. australisin the fen communitiesinvestigated here, although long-term effects ofmowing in summer still need more investigation. As apractical consequence it is suggested that at siteswhich are not strongly dominated by P.australis, as most of those investigated here,reducing the performance of this species should notconstitute a major target of nature conservationmanagement, nor can its dynamics be used as anindicator for management success before underlyingcauses are better understood.  相似文献   

18.
Grasslands recovered by sowing low diversity seed mixtures of local provenance are usually managed by mowing. Besides restoration success only a few studies have focused on the direct effects of post-restoration mowing on recovered grassland vegetation. In this study we followed vegetation changes in 13 successfully recovered grasslands in 5 × 5-m-sized sites with continuous and ceased mowing at Hortobágy National Park, East-Hungary. We asked the following questions: (i) What are the effects of cessation of mowing on the vegetation structure and diversity of recovered grasslands? (ii) What are the effects of cessation of mowing on the abundance of sown grasses, target and undesirable species? (iii) Is yearly mowing an appropriate management tool for the maintenance of recovered grasslands? Our results showed that the cessation of mowing caused litter accumulation, while diversity, total vegetation cover and the cover of sown grasses decreased compared to the mown sites. The cover of undesirable perennial species was significantly higher in unmown sites than in mown ones. The species composition of mown sites remained more similar to near-natural grasslands than the unmown ones. Our results suggest that without regular post-restoration mowing the favourable status of recovered grasslands can rapidly decline due to litter accumulation and by the expansion of undesirable species, even in the short-run. We also stress that while yearly mowing is enough to maintain grasslands recovered by low-diversity seed sowing, it cannot be considered to be enough to recover target vegetation composition.  相似文献   

19.
Question: Which one of the two mainly used mowing regimes along road verges, mowing once or twice a year is a better option regarding flowering and seed‐producing success of grassland species and plant species in general? Location: Southeast Finland. Methods: Plant species composition, flowering and seed production success were studied in road verges (1) mown once in August and (2) mown at the end of June and August. Flowering shoots were counted and phenological phases were estimated four times during a growing season. Results: The numbers of flowering or seed‐producing species and shoots indicated that mowing once a year corresponding to the timing of traditional management was markedly better than mowing twice a year. The difference between the management groups was greatest at the end of July when the number of flowering species was 43% and the number of flowering and seed‐producing shoots 76% less after the first mowing than in the still unmown sites. The species avoided early cutting either through the timing of flowering or due to their growth form. Early season mowing had no effect on the occurrence and seed‐producing success of grassland species and the first flowering species. Seed production of grasses succeeded poorly in the verges mown twice. Conclusion: Mowing once in August resulted in higher seed production in general, but mowing twice a season might be a better way to manage young verges on nutrient‐rich soils. The useful qualities of the management options should be considered locally when planning road verge management.  相似文献   

20.
Capsule: Forb-rich and diverse, annually mown vegetation is the preferred Corncrake Crex crex breeding habitat in floodplains.

Aims: To identify habitat preferences of female Corncrakes and characteristics of breeding sites in floodplain habitats and derive recommendations for management.

Methods: We tracked six female Corncrakes and compared vegetation characteristics at 78 male calling sites with regard to breeding records and diurnal call activity of males, because we expect the latter to indicate female occurrence. Additionally, we analysed how practice and timing of land use in the preceding year affected vegetation structure.

Results: Females preferred areas with high cover of forbs and a distinct relief heterogeneity, which was associated with overall vegetation diversity. All calling sites with breeding records and diurnal call incidence of males showed high forb and low sedge cover, low litter heights and a close location to ditches. Favourable conditions were best provided by mowing in the preceding year.

Conclusion: In eutrophic habitats, female Corncrakes preferred a vegetation structure created by annual mowing. Because nests and unfledged chicks are threatened by mowing operations, we recommend an alternating management regime based on the identification of breeding sites using male diurnal calling activity.  相似文献   


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