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1.
In the Mediterranean region of Europe, land-use changes have allowed for rapid colonisation of open habitats by woody species. As a result, it is critical to gather information on how protected species in open habitats respond to forest spread in such areas. Our objective is to quantify whether spatial heterogeneity of the vegetation associated with recent forest closure influences demographic structure and maternal fertility in a population of the protected Paeonia officinalis L. In closed woodland, adult plants of P. officinalis are almost exclusively vegetative, in open habitats seedlings are rare and on the woodland edge there is a relative over-representation of flowering plants and seedlings. Forest closure dramatically reduces flowering frequency, but has no significant effect on maternal fertility of flowering plants. The spatial aggregation of seedlings close to the maternal plants suggests that dispersal is spatially restricted. Together, these results suggest that the viability of the population requires a transitional habitat between open garrigues or grassland with spaced trees and woodland. A management programme incorporating tree and shrub thinning and cutting of parcels in rotation to maximise the length of the forest edge could maintain a habitat mosaic that favours the persistence of this species in the study site.  相似文献   

2.
In this study we quantified variability in foliage herbivory and pre-dispersal seed predation and its effects on plant performance and demography in populations of a rare and protected perennial herb, Paeonia officinalis. An individual-based survey was performed during four years in four populations, which contained plants in both open habitat and woodland. We detected marked spatial and temporal variation among and within populations in foliage herbivory (by insects) and pre-dispersal seed predation (by insects, rodents and Roe Deer). Foliage herbivory decreased with plant demographic stages in open habitats, from seedlings to reproductive individuals, but no significant trend was detected in woodland habitats. This may be due to different demographic origin of larger vegetative plants in this habitat. Depending on demographic stage, herbivory was higher in open habitats or not significantly different between habitats. This suggests differences in herbivore abundance in different habitats within sites. Pre-dispersal seed predation remained weak and did not depend on habitat. We did not detect any consequence of foliage herbivory on seedling mortality and individual growth in our study. Our results illustrate the need to investigate plant-herbivore interactions over several years in distinct populations in order to more accurately evaluate herbivore impact on plant population dynamics.  相似文献   

3.
Although several factors can limit female fertility in perennial plants, rarely have they been jointly studied in a single species over several years. In this study we experimentally manipulate seed production and simultaneously analyse the potential contribution of pollen limitation, costs of reproduction and plant size to variation in seed output over a 3-year period in the perennial herb Paeonia officinalis, in southern France. Since this rare species is threatened by forest closure in many sites we also examine the causes of female fertility variation in relation to habitat closure (open habitat vs. woodland). P. officinalis has a partial self-incompatibility system and only very low ability for autonomous self pollination in the absence of pollinators. However, supplementary pollination of individual plants in three consecutive years did not significantly increase seed production above natural levels. Forest closure was associated with a decline in ovule and seed production, which again was not due to pollen limitation since supplementary pollination had no significant effect on seed set in the woodland habitat. Comparison of the maternal fertility of plants which were previously excluded from reproduction with those which were hand pollinated to maximise seed set in two previous years produced no evidence that seed production in year three is limited by costs associated with prior reproduction. Likewise, flowering probability was not related to prior seed production but was however positively related to plant size. The absence of any influence of pollen limitation or prior reproduction on seed production suggests that sub-maximal seed production in long-lived perennial herbs may be part of a size-dependent strategy that maximises life-time seed production and fitness without compromising survival.  相似文献   

4.
Abstract. Persistence by longevity has been rarely considered as an alternative to regeneration by seeding for plants showing multiple demographic strategies. We propose a conceptual model of multiple demographic strategies for long‐lived plants in stable habitats, shifting from regeneration by seeding to persistence by longevity and/or vegetative reproduction, along gradients of abiotic stress or interspecific competition. Regeneration by seeding would be promoted under low abiotic stress or under low competition, whereas persistence by longevity and/or vegetative reproduction would predominate at high levels of abiotic stress or competition. We test this model with two threatened species of the Mediterranean region, the shrub Juniperus communis, a widely distributed species which maintains relict populations in the Mediterranean mountains thanks to great adult longevity and Pinguicula vallisneriifolia, a palaeo‐endemic herb relying on a perennial habit and vegetative reproduction under drought imposed stress or high competition at late successional phases. As a main consequence, multiple demographic strategies enhance a plant's ability to exploit environmental heterogeneity at different spatial (patches, localities, regions within the species’ distribution area) and temporal (individual life span, glacial‐interglacial cycles) scales. The potential of multiple demographic dynamics based on persistence and regeneration must be considered as a major ecological trait determining the long‐term viability of peripheral populations of relict species as well as the inertia against extinction of many threatened endemisms, thereby contributing to the maintenance of the high plant diversity characterizing the Mediterranean region.  相似文献   

5.
Regional persistence of species requires a positive balance between colonizations and local extinctions. In this study, we examined the amount of colonizations and extinctions and their likelihood as a function of patch size, isolation, and habitat characteristics of a riparian perennial plant, Erigeron acer subsp. decoloratus. We also studied the importance of patch dynamics to the regional population growth. Over five successive years, we counted the number of plant patches along 43 km of riverside. Most patches were small in area and population size. The annual finite growth rate in the number of patches varied between years, but the geometric mean was close to 1.0, indicating a viable patch network in spite of local extinctions. Extinction rate was highest on steep slopes and for small patches with few individual plants and a small patch area. When the patches were classified into different stage classes, the most common fate was stasis, i.e., the patch remained at the same stage. Patch survival and local, within-patch dynamics were most important during this five-year period. Between-patch dynamics (including colonization for example) accounted for 5–10% of annual transitions. The overall dynamics were relatively similar to those of other plant species subjected to riparian disturbance regimes. In the long run, the survival of the species depends on how well it is able to escape from competition from forest and meadow species and track the availability of suitable habitats. This kind of habitat tracking differs from classical metapopulation dynamics. In the former, local extinctions occur as a consequence of adverse changes in the habitat and recolonizations are rare, whereas metapopulation models assume a highly persistent habitat structure with frequent recolonizations. In this respect, the regional dynamics of perennial plants in disturbed riparian habitats may differ from classical metapopulations.  相似文献   

6.
Aim To examine biogeographical affiliations, habitat‐associated heterogeneity and endemism of avian assemblages in sand forest patches and the savanna‐like mixed woodland matrix. Location Two reserves in the Maputaland Centre of Endemism (MC) on the southern Mozambique Coastal Plain of northern KwaZulu‐Natal, South Africa. Methods Replicated surveys were undertaken in each of the two habitat types in each reserve, providing species abundance data over a full year. Vegetation structure at each of the survey sites was also quantified. Differences between the bird assemblages and the extent to which vegetation structure explained these differences were assessed using multi‐variate techniques. Biogeographical comparisons were based on species presence/absence data and clustering techniques. Results Bird assemblages differed significantly between habitats both within a given reserve and between reserves, and also between reserves for a given habitat. Differences in vegetation structure contributed substantially to differences between the avian assemblages. Of the four species endemic to the MC, three (Neergaard’s sunbird, Rudd’s apalis, and Woodward’s batis) were consistently present in sand forest. The fourth (pink‐throated twinspot) preferred mixed woodland. None of these endemic species was classed as rare. In the biogeographical analysis, both the sand forest and the mixed woodland bird assemblages were most similar to bird assemblages found in the forest biome or the Afromontane forest biome, depending on the biome classification used. Main conclusions The close affinities of sand forest and mixed woodland assemblages to those of the forest biome are most likely due to similarities in vegetation structure of these forests. Bird assemblages differ between the sand forest and mixed woodland habitats both within a given reserve and between reserves, and also between reserves for a given habitat. These differences extend to species endemic to the MC. Thus, conservation of sand forest habitat in a variety of areas is necessary to ensure the long‐term persistence of the biota.  相似文献   

7.
《Acta Oecologica》2004,25(1-2):93-101
Loss and fragmentation of habitat resulting from the clearing of forests for agriculture and urban development threaten the persistence of thousands of species worldwide. The clearing of native forest to plant a monoculture of exotic trees may also reduce and fragment the habitat available for indigenous plants and animals. Metacommunity theory suggests that the species richness of a community in a patch of habitat will increase with patch size but decrease with patch isolation. We investigated whether replacement of native Eucalyptus forest with a plantation of Pinus radiata has reduced and fragmented habitat for frogs, leading to a lower species richness of frog communities in the pine plantation and in small and/or isolated remnant patches of native forest. We surveyed frogs at 60 sites at streams and wetlands in the pine plantation, remnant patches of native forest surrounded by pines, and adjacent areas of contiguous native forest near Tumut in New South Wales, Australia. Only two of eight species of frogs were recorded in the pine plantation, and regression modelling indicated that streams and wetlands in the pines supported fewer frog species than those in remnant patches or the intact native forest. In addition, species richness tended to be higher at wide, shallow swamps and marshes near the headwaters of streams, with herbs, grasses, shrubs, reeds, sedges and rushes in the emergent and fringing vegetation. There was little evidence to suggest that larger eucalypt remnants supported more species of frogs, or that remnants isolated by greater expanses of pines supported fewer species, but we had low power to detect these effects with our data set. Our results support the preservation of all remnants of native forest along drainage lines and around swamps, soaks and bogs, regardless of size. Where new pine plantations are established, for example, on cleared agricultural land, care should be taken to maintain the structural and vegetative characteristics of water bodies to ensure that they continue to provide suitable breeding habitat for frogs.  相似文献   

8.
Pinpointing the factors that alter the population viability of long-lived organisms, such as perennial plants, is especially useful for informing conservation management policies for threatened and endangered species. In this study, I used 4 years of demographic data on rare plant Polemonium vanbruntiae (Eastern Jacob’s ladder, Polemoniaceae) to determine how white-tailed deer herbivory and habitat type (wet meadow and forest seep) affect long-term population viability. I incorporated these factors into matrix population models to estimate the deterministic and stochastic growth rates (λ and λs, respectively), stable stage distribution (SSD), the reproductive value for each stage class, the cumulative probability of extinction, and the elasticity values for all vital rates under each browsing and habitat scenario. Population growth rates of P. vanbruntiae in wet meadow sites are expected to increase at a slightly faster rate than at forest seep sites. Herbivory significantly decreased the predicted population growth rate under stochastic conditions. However, P. vanbruntiae ramets are expected to increase in the future as the population growth rate (λ) > 1 under both “browse” and “no browse” scenarios, but deer herbivory increased the extinction risk to a detectable level. Deer preferentially browsed vegetative and reproductive adult ramets over yearlings and seedlings, and browsing significantly reduced fertility of reproductive ramets and increased the probability of stasis for small and large vegetative ramets. Browsing shifted the elasticity values of vital rates and changed the potential for younger life histories stages, such as seedlings, to change future population growth. Under herbivore pressure, survival and stasis of large vegetative ramets have the largest potential impact on future population growth. This study provides empirical evidence that white-tailed deer are an important ecological factor affecting long-term population dynamics of rare plant populations and offers management suggestions for remaining populations of P. vanbruntiae.  相似文献   

9.
Question: Disturbance effects on dry forest epiphytes are poorly known. How are epiphytic assemblages affected by different degrees of human disturbance, and what are the driving forces? Location: An inter‐Andean dry forest landscape at 2300 m elevation in northern Ecuador. Methods: We sampled epiphytic bryophytes and vascular plants on 100 trees of Acacia macracantha in five habitats: closed‐canopy mixed and pure acacia forest (old secondary), forest edge, young semi‐closed secondary woodland, and isolated trees in grassland. Results: Total species richness in forest edge habitats and on isolated trees was significantly lower than in closed forest types. Species density of vascular epiphytes (species per tree) did not differ significantly between habitat types. Species density of bryophytes, in contrast, was significantly lower in edge habitat and on isolated trees than in closed forest. Forest edge showed greater impoverishment than semi‐closed woodland and similar floristic affinity to isolated trees and to closed forest types. Assemblages were significantly nested; habitat types with major disturbance held only subsets of the closed forest assemblages, indicating a gradual reduction in niche availability. Distance to forest had no effect on species density of epiphytes on isolated trees, but species density was closely correlated with crown closure, a measure of canopy integrity. Main conclusions: Microclimatic changes but not dispersal constraints were key determinants of epiphyte assemblages following disturbance. Epiphytic cryptogams are sensitive indicators of microclimate and human disturbance in montane dry forests. The substantial impoverishment of edge habitat underlines the need for fragmentation studies on epiphytes elsewhere in the Tropics.  相似文献   

10.
In many annual plant populations, seeds may be dormant for several seasons before they germinate. Here, we investigate the consequences of both conditional (dispersed seeds cannot enter a dormant stage) and unconditional seed dormancy on the amount and the distribution of neutral genetic diversity within and among populations. We present joint demographic and population genetics models for single and subdivided populations and derive the effective size and population differentiation at both local and metapopulation scales. We suggest that a Wahlund effect is unlikely to result from age structure alone. Furthermore, the differentiation among populations is decreased by the presence of seed banks. We also extend these models to describe monocarpic (semelparous) perennial life cycle, where the nonreproductive stages are vegetative rosettes instead of dormant seeds. The main difference between the models relies in the way the density-dependent regulation is acting. The effective size of monocarpic perennial species may be less than the census number of individuals, and among-population differentiation is always larger than in annual species. We discuss our results in the light of recent population genetics surveys of annual plants with seed banks.  相似文献   

11.
Question : How accurately can a suite of suggested functional traits predict plant species response to succession from semi‐open woodland to closed deciduous canopy forest? Location : Southeastern Sweden. Methods : Abundance of 46 field‐layer plant species in a temperate deciduous forest, measured as frequency of occupied plots, was estimated in 1961, 1970 and 2003. Abundance change over time across species was tested for correlations with functional traits and literature information on habitat preference. Results : Increase in abundance was positively correlated with specific leaf area (SLA), weakly negatively correlated with seed mass and not significantly correlated with plant height or start, peak and length of the flowering period. Change in abundance was correlated with the Ellenberg light indicator value, whereas no correlations were found with Ellenberg values for nitrogen, calcium and moisture, or forest preference according to the literature. Conclusions : SLA was a better predictor of how field layer plants responded to succession from semi‐open woodland to closed canopy forest than empirically‐derived measures of habitat preference. The same holds for SLA in relation to seed size, indicating that interactions in the established life‐cycle phase are more important than the recruitment phase for species response to succession.  相似文献   

12.
Question: How important are habitat configuration, quality, history and anthropic disturbance in determining nemoral plant species richness and distribution of fragmented forest patches in a Mediterranean region? Location: Agricultural landscape north of Rome, Italy. Methods: Sixty‐nine woodland patches, identified through a stratified random sampling, were sampled for nemoral plant species. The homogeneity of woodlands was tested through a hierarchical classification of the floristic data and a Mann‐Whitney test of dependent and independent variables. The importance of habitat configuration (area, isolation, shape), quality (soil properties, forest structure, anthropic disturbance) and history (age of woodland) in determining species richness was estimated through a Poisson regression model. Presence‐absence of each species was analysed by logistic regression. Differences among plant life‐trait types (life span, dispersal mode, habitat preference) were analysed by comparing their median β‐values through ANOVA models. Results: Through hierarchical classification, two woodland types were identified that differed in species composition, habitat quality and spatial configuration. Poisson regression showed that habitat configuration and history influenced species richness. Multiple logistic regression resulted in significant fits for 88 species/variable combinations: 38 are habitat quality variables, 25 are habitat configuration variables, and 13 are anthropic factors. Dispersal strategies varied significantly with respect to area, isolation and age, while generalist and specialist species differed according to age of the woodland. Conclusion: Our results show that habitat history and configuration are the key factors determining species richness of woodland. Together with habitat configuration, habitat quality (mainly soil acidity) appeared to influence species composition.  相似文献   

13.
Opening of the forest canopy may result in higher fitness of understory plants due to increased light intensity on the forest soil and increased nutrient availability. Especially, tuberous orchids may profit from increased light as photosynthetic assimilation products and nutrients are accumulated in their belowground storage organs. We investigated the effects of coppicing on demographic structure and fruit and seed set in 15 populations of the tuberous, perennial orchid Orchis mascula, seven of which were located in undisturbed, shaded woodland and eight in recently coppiced woodland. Coppicing resulted in a massive increase in flowering and in increased fruit set. On average, 42.9% of all individuals consisted of flowering plants in coppiced woodland, whereas in undisturbed woodland only 20.8% of all individuals flowered. The percentage fruit set varied between 20% and 55% in coppiced woodland and was strongly related to population size (measured as the number of flowering individuals). Mean fruit weight and fruit size were also significantly higher in populations located in coppiced woodland than in undisturbed woodland, whereas the proportion of viable seeds was not related to woodland type. Given that O. mascula is dependent on seed set to fill space with new individuals, these results suggest that the long-term survival of this species strongly depends on frequent opening of the canopy.  相似文献   

14.
Astragalus nitidiflorus is an endangered perennial, but short-lived legume of SE Spain, which has been re-found after 100 years. To identify possible weak points that might contribute to its rarity and hamper its conservation, this paper presents data concerning location, habitat, demographic features and reproductive biology of the species. Censuses of three cohorts of seedlings show that the seedling stage is the most critical in the life cycle. The adult plants show a long flowering season with a high degree of synchrony. Despite the low reproductive success of the species, the annual seed production is very high due to the high floral production. The data show that A. nitidiflorus is a facultative xenogamous species, but the presence of pollinators can enhance fruit set. The viability of the species is not limited by the flowering and fruiting process, however the maintenance of the habitat in the early successional stages seems to be the critical point for long-term survival of the species.  相似文献   

15.
We compared the bud demography of deciduous, dioecious Salix arctica Pall. plants between vegetation of contrasting muskox grazing pressure, and between female, male and vegetative plants, on central Ellesmere Island, Canada. We developed age- and stage-based transition matrix models in order to investigate the contribution of annual shoot generations, and the significance of different bud types (dormant, vegetative, catkin, eaten) to bud population growth. The bud population growth rates were higher in all shoot generations of the grazed plants compared with the ungrazed plants. This was a consequence of a higher bud production rate in the grazed plants, whereas the bud survival rate was similar among all plants. Vegetative plants had the highest bud population growth rates, but the difference was significant only between vegetative plants and females in the grazed habitat. The damage frequency did not differ among female, male and vegetative plants in the grazed habitat, where 96% of the plants were grazed. According to the age- and stage-based model, the newest bud generation and the vegetative shoots determine the majority of demographic processes of the plant. Longer-term observations are required to investigate annual fluctuation in bud population dynamics and herbivory levels in order to make predictions about the long-term impact of muskox on bud demography of S. arctica.  相似文献   

16.
The fragmentation of natural habitat is considered to be a major threat to biodiversity. Decreasing habitat quality and quantity caused by fragmentation may lead to a disruption of plant–pollinator interactions and to a reduction in sexual reproduction in plant species. We conducted a 6-year field experiment to investigate the effects of small-scale fragmentation on plant–pollinator interactions and genetic diversity in the self-compatible Betonica officinalis. We examined the abundance and composition of pollinators, the foraging behaviour of bumblebees and the performance, outcrossing rate and genetic diversity of B. officinalis after 2 and 6 years in experimentally fragmented nutrient-poor, calcareous grassland in the northern Swiss Jura mountains. Fragments of different size (2.25 and 20.25 m2) were isolated by a 5-m-wide strip of frequently mown vegetation. Control plots of corresponding size were situated in adjacent undisturbed grassland. Experimental grassland fragmentation altered the composition of B. officinalis pollinators and reduced their flower visitation rate. Furthermore, the foraging behaviour of bumblebees was changed in the fragments. After 6 years of fragmentation seed weight was higher in fragments than in control plots. However, the densities of B. officinalis rosettes and inflorescences, plant height and inflorescence length were not affected by fragmentation. The outcrossing frequency of B. officinalis growing in fragments was reduced by 15% after 2 years and by 33% after 6 years of experimental fragmentation. This resulted in a significant reduction of the genetic diversity in seedlings emerging in fragments after 6 years. Our study shows that small-scale habitat fragmentation can disturb the interaction between B. officinalis and pollinators resulting in a reduced outcrossing frequency and genetic diversity in plants growing in fragments. However, the response to fragmentation was considerably delayed. This finding strengthens the claim for long-term field experiments with proper replications and controls to assess delayed effects of habitat fragmentation.  相似文献   

17.
Vegetation surveys were carried out at 24 sampling stations distributed over four land use types, namely near-primary forest, secondary forest, agroforestry systems and annual crop lands in the northeastern part of the Korup region, Cameroon, to assess the impact of forest conversion on trees and understorey plants. Tree species richness decreased significantly with increasing level of habitat modification, being highest and almost equal in secondary and near-primary forests. Understorey plant species richness was significantly higher in annual crop lands than in other land use types. The four land use types differed in tree and understorey plant species composition, the difference being smaller among natural forests. Tree and understorey plant density differed significantly between habitat types. Density was strongly correlated with species richness, both for trees and understorey plants. Five tree and 15 understorey plant species showed significant responses to habitat. A 90% average drop in tree basal area from forest to farmland was registered. Our findings support the view that agroforestry systems with natural shade trees can serve to protect many forest species, but that especially annual crop lands could be redesigned to improve biodiversity conservation in agricultural landscapes of tropical rainforest regions.  相似文献   

18.
Habitat fragmentation is one of the major threats to species diversity. In this review, we discuss how the genetic and demographic structure of fragmented populations of herbaceous forest plant species is affected by increased genetic drift and inbreeding, reduced mate availability, altered interactions with pollinators, and changed environmental conditions through edge effects. Reported changes in population genetic and demographic structure of fragmented plant populations have, however, not resulted in large-scale extinction of forest plants. The main reason for this is very likely the long-term persistence of small and isolated forest plant populations due to prolonged clonal growth and long generation times. Consequently, the persistence of small forest plant populations in a changing landscape may have resulted in an extinction debt, that is, in a distribution of forest plant species reflecting the historical landscape configuration rather than the present one. In some cases, fragmentation appears to affect ecosystem integrity rather than short-term population viability due to the opposition of different fragmentation-induced ecological effects. We finally discuss extinction and colonization dynamics of forest plant species at the regional scale and suggest that the use of the metapopulation concept, both because of its heuristic power and conservation applications, may be fruitful.  相似文献   

19.
Chasmogamous (CH) and cleistogamous (CL) flower production was investigated in natural populations of the perennial herb Oxalis montana in southern Quebec, Canada. Every 10–12 days during two flowering seasons, we recorded the reproductive output of approximately 2,000 plants distributed among five forest sites. The percentage of plants flowering, proportion of flowering plants producing CH and CL flowers, CH and CL flower number per flowering plant, and the proportion of flowers that are CL differed significantly among sites and corresponded to site differences in forest type and habitat quality. Unlike patterns in most CL species, however, reproduction by cleistogamy increased in sites with habitat conditions favorable to plant growth and sexual reproduction, and decreased in less productive sites. Chasmogamous and CL flower production increased with increasing plant size but plant size explained a significantly greater proportion of the variation in CL flower numbers. The percentage of flowering plants producing CH flowers decreased between years while the proportion of CL flowers increased at all sites during the second flowering season. The somewhat unusual aspects of reproduction in Oxalis may stem from its perennial habit which allows use of stored resources in adjusting the balance of cleistogamy versus chasmogamy in different environmental regimes.  相似文献   

20.
Background and AimsHedgerows have been shown to improve forest connectivity, leading to an increased probability of species tracking the shifting bioclimatic envelopes. However, it is still unknown how species in hedgerows respond to temperature changes, and whether effects differ compared with those in nearby forests. We aimed to elucidate how ongoing changes in the climate system will affect the efficiency of hedgerows in supporting forest plant persistence and migration in agricultural landscapes.MethodsHere we report results from the first warming experiment in hedgerows. We combined reciprocal transplantation of plants along an 860-km latitudinal transect with experimental warming to assess the effects of temperature on vegetative growth and reproduction of two common forest herbs (Anemone nemorosa and Geum urbanum) in hedgerows versus forests.Key ResultsBoth species grew taller and produced more biomass in forests than in hedgerows, most likely due to higher competition with ruderals and graminoids in hedgerows. Adult plant performance of both species generally benefitted from experimental warming, despite lower survival of A. nemorosa in heated plots. Transplantation affected the species differently: A. nemorosa plants grew taller, produced more biomass and showed higher survival when transplanted at their home site, indicating local adaptation, while individuals of G. urbanum showed greater height, biomass, reproductive output and survival when transplanted northwards, likely owing to the higher light availability associated with increasing photoperiod during the growing season.ConclusionsThese findings demonstrate that some forest herbs can show phenotypic plasticity to warming temperatures, potentially increasing their ability to benefit from hedgerows as ecological corridors. Our study thus provides novel insights into the impacts of climate change on understorey plant community dynamics in hedgerows, and how rising temperature can influence the efficiency of these corridors to assist forest species’ persistence and colonization within and beyond their current distribution range.  相似文献   

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