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We investigated the independent and combined effects of experimental warming and grazing on plant species diversity on the north‐eastern Tibetan Plateau, a region highly vulnerable to ongoing climate and land use changes. Experimental warming caused a 26–36% decrease in species richness, a response that was generally dampened by experimental grazing. Higher species losses occurred at the drier sites where N was less available. Moreover, we observed an indirect effect of climate change on species richness as mediated by plant–plant interactions. Heat stress and warming‐induced litter accumulation are potential explanations for the species’ responses to experimental warming. This is the first reported experimental evidence that climate warming could cause dramatic declines in plant species diversity in high elevation ecosystems over short time frames and supports model predictions of species losses with anthropogenic climate change. 相似文献
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Shrub encroachment caused by overgrazing has led to dramatic changes of savannah landscapes and is considered one of the most threatening forms of rangeland degradation leading to habitat fragmentation. Although changes to plant assemblages are becoming better known, however, our understanding of how shrub encroachment affects rodent communities is low. In this study, we investigated relative abundance of five rodent species in sixteen southern Kalahari rangelands where shrub cover ranged from low (<5%) to high (>25%). Rodent abundance was determined on three trapping grids (40 × 100 m) for each site. Our results show that increasing shrub cover affected rodent species differently. The relative abundance of hairy‐footed gerbil, short‐tailed gerbil and bushveld gerbil declined with increasing shrub cover, whereas highveld gerbil and striped mouse exhibited hump‐shaped relationships with shrub cover. Overall, species richness decreased with increasing shrub cover and a negative impact of high shrub cover above 15% on rodent abundance was congruent for all species. We conclude that our results support the hypothesis that long‐term heavy grazing that results in area wide shrub encroachment, threatens the diversity of arid environments. 相似文献
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Abstract Georeferenced digital aerial photographs were used to assess changes in overstorey vegetation cover since 1948 in the Victoria River District, Northern Territory, Australia, across a range of lowland tropical savanna habitats and with explicit consideration of known and variable site‐specific grazing and fire management histories. Vegetation surveys at corresponding locations on the ground identified five distinct woody vegetation communities defined primarily by water drainage and secondarily by soil characteristics. Air‐photo analyses revealed that, contrary to popular perceptions and in contrast to results from other habitats, there has been no generalized net increase in overstorey woody vegetation cover across the full range of lowland savanna habitats. Rather, different habitats exhibited distinctly different vegetation change mechanisms: low‐lying seasonally inundated ‘wet’ habitats have experienced woody vegetation increase since 1948, whereas well‐drained ‘dry’ habitats have experienced overstorey vegetation stability or loss. In almost every instance woody vegetation increase could be attributed to the invasion or proliferation of a single species, Melaleuca minutifolia F.Muell. The extent of M. minutifolia increase was unrelated to historical grazing/fire regime. Demographic analyses for this species revealed that recruitment was often episodic and that synchronized recruitment events occurred uniformly across the full range of historical management treatments, most likely as a consequence of favourable climatic conditions in years with an extended wet season. Heavy grazing facilitated juvenile survival and/or recruitment, most likely by reducing grassy fuel loads and eliminating landscape fire. We conclude that while there has been no generalized net increase in overstorey woody vegetation cover in lowland environments, savanna dynamics are complex, and multiple change mechanisms have occurred simultaneously in different habitats, some of which have been significantly transformed since 1948. Where net woody vegetation increase has occurred it is primarily a natural consequence of episodic M. minutifolia establishment in climatically favourable years, but the extent and magnitude of this effect is likely mediated by fire/grazing regime. 相似文献
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Shrub encroachment can follow grazing or burning release in páramo grasslands. While encroachment decreases herbaceous species richness in some grassland systems, the effects of this process on the herbaceous community in páramo grasslands are currently unknown. We collected data on shrub cover, herbaceous‐species cover and species composition in a páramo grassland 12 years after release from burning and cattle grazing near Zuleta, Ecuador. Topographic and soil measures were also included as predictor variables of differences in community composition. Contrary to studies in other systems, shrub cover did not have a significant effect on herbaceous‐species richness, whereas shrub‐species richness significantly increased with shrub cover. However, shrub cover was associated with significant shifts in herbaceous–community composition. Most notably, there was an increase in some shade‐tolerant forbs and tall‐statured wetland grasses with increasing shrub cover, and a corresponding decrease in some short‐statured grasses and early successional forbs. These results could indicate that the ameliorative effects of shrubs (e.g. frost and wind protection) in harsh alpine environments may partially compensate for the expected competitive effect of shrubs due to shading. 相似文献
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J. O. Caldecott M. D. Jenkins T. H. Johnson B. Groombridge 《Biodiversity and Conservation》1996,5(6):699-727
The Convention on Biological Diversity aims to encourage and enable countries to conserve biological diversity, to use its components sustainably and to share benefits equitably. Species richness and endemism are two key attributes of biodiversity that reflect the complexity and uniqueness of natural ecosystems. National data on vertebrates and higher plants indicate global concentrations of biodiversity and can assist in defining priorities for action. Projections indicate that species and ecosystems will be at maximum risk from human activities during the next few decades. Prompt action by the world community can minimise the eventual loss of species. Highest priorities should be to: (i) strengthen the management of ecosystems containing a large proportion of global biodiversity; (ii) help developing countries complete their biodiversity strategies and action plans, monitor their own biodiversity, and establish and maintain adequate national systems of conservation areas; (iii) support actions at the global level, providing benefit to all countries in managing their own biodiversity. Generally, resources will best be spent in safeguarding ecosystems and habitats that are viable and important for global biodiversity, and which are threatened by factors that can be controlled cost-effectively. Other important criteria are representativeness, complementarity and insurance. 相似文献
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J. Ignacio Ramirez;Maja Sundqvist;Elin Lindén;Robert G. Björk;Bruce C. Forbes;Otso Suominen;Torbjörn Tyler;Risto Virtanen;Johan Olofsson; 《Oikos》2024,2024(11):e10595
Herbivores drive shifts in plant species composition by interacting with vegetation through defoliation, trampling and nutrient addition: urine and faeces. As herbivore effects on vegetation accumulate over time, they might spillover to other trophic levels, but how and when this happens is poorly understood. Since it is methodologically demanding to measure biodiversity across spatial gradients, an alternative approach is to assess it through biodiversity indices of vascular plants. We employed the Index of biodiversity relevance developed for Swedish flora which provides an estimated number of organisms associated with a plant species, allowing the quantification of trophic community size. Values from this index were coupled with vegetation data from a network of 96 fenced and paired grazed plots across Fennoscandia. We analysed the role herbivory has on plant richness and diversity, and on the number of organisms that interact with the vegetation according to the index values. We also explored how herbivores influence the competitive effects of tall shrubs on other plants since the dominance of a vegetation type links directly to biodiversity. Plant diversity had no clear response to grazing. Overall vegetation and the vegetation subgroups herbs and non-fruit shrubs had higher biodiversity index values in fenced plots, indicating a higher number of plant–host interactions. Herb cover was negatively related to shrubs in both treatments but with a faster decline in the absence of herbivores. This study highlights the importance of maintaining herbivore populations in the Arctic to conserve the vegetation structure and biodiversity of the tundra. This method of coupling biodiversity indexes with vegetation data provides complementary information to the plant diversity, especially when methodological or time constraints prevent complete field inventories. 相似文献
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外来植物物种的入侵和本土植物物种的范围扩张都可能通过化感作用抑制本土植物的生长。然而,国土安全假说表明,某些本土植物可以通过产生抑制入侵植物生长的化感物质来抵抗入侵。以往的研究大多数集中在个体本土和入侵植物之间的化感相互作用,对整个本土植物群落如何通过化感作用抵抗入侵的研究较少。此外,对于扩张范围的本地物种与接收地本地群落之间相互的化感作用及其对入侵成功的影响知之甚少。为此,我们开展了两项温室竞争实验,以测试一种本土的木本扩张物种柴桦(Betula fruticose)与4种本土草本植物种地榆(Sanguisorba officinalis)、东北龙胆(Gentianamanshurica)、泽芹(Sium suave)和小叶章(Deyeuxia angustifolia)组成的群落之间的相互化感作用。我们评估了柴桦和本土群落之间的竞争效应和响应的差异,以及这些差异是否受到活性炭添加的影响(活性炭添加可以中和土壤中的化感物质)。实验结果表明,活性炭的添加降低了本土植物群落对柴桦地上生物量的抑制作用,这表明本土植物群落对柴桦产生了强烈的化感作用。相比之下,活性炭添加仅轻微的增强了柴桦对本土植物群落的抑制作用,表明化感作用不是柴桦抑制本土植物群落生长的主要机制。总之,这些发现支持了国土安全假说,并表明本土草本植物群落的生物抵抗可能限制了木本范围扩张物种柴桦的入侵成功。 相似文献
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Balzs Teleki Judit Sonkoly Lszl Erd&#x;s Bla Tthmrsz Mtys Prommer Pter Trk 《应用植被学》2020,23(2):175-184
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Lars A. Brudvig 《Restoration Ecology》2010,18(1):74-84
Recovering biodiversity is a common goal during restoration; however, for many ecosystems, it is not well understood how restoration influences species diversity across space and time. I examined understory species diversity and composition after woody encroachment removal in a large-scale savanna restoration experiment in central Iowa, United States. Over a 4-year time series, restoration had profound effects across space and time, increasing richness at local and site-level scales. Restoration sites had increased α (within sample) Simpson's diversity and α and γ (site level) species richness relative to control sites, although γ and β (among sample) Simpson's diversity, β richness, and α species evenness were not affected. Changes in richness were driven by graminoids at the α and γ scales and woody species (and some evidence for forbs) at the α scale. Interestingly, indicator species analysis revealed that at least some species from all functional groups were promoted by restoration, although no species were significant indicators of pre-treatment or control sites. Both savanna and nonsavanna species were indicators of restored sites. Restoration promoted exotic species at both scales, although species with spring phenologies were unaffected. Woody encroachment removal may be a means to promote species establishment in savannas; however, in this study, it resulted in establishment and proliferation of native and exotic and savanna and nonsavanna species. Future work might consider reintroduction of key savanna species to supplement those that have established. Work like this demonstrates the utility of restoration experiments for conducting research on large- and multiscale processes, such as species diversity. 相似文献
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Tommaso Chiti Vianet Mihindou Kathryn J. Jeffery Yadvinder Malhi Fabiane L. De Oliveira Lee J. T. White Riccardo Valentini 《Biotropica》2017,49(1):9-12
This study quantifies changes in soil organic carbon (SOC) stock as a result of woody encroachment on savannas. Changes in SOC stocks occur below 30 cm depth, indicating the subsoil as the principal compartment contributing to SOC sequestration, and suggesting the need to consider the entire profile (0–100 cm) to thoroughly assess the effect of woody encroachment on SOC stocks. 相似文献
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There is a need for monitoring the status and trends of freshwater biodiversity in order to quantify the impacts of human
actions on freshwater systems and to improve freshwater biodiversity conservation. Current projects carrying assessment of
freshwater biodiversity focus mainly on leading-better-known groups such as fish, or identify keystone species and/or endemic
freshwater systems for conservation purposes. Our purpose is to complete these existing projects by providing quantitative
estimates of species number for all freshwater groups on each continent and/or major eco-regions. This article present the
results of the first implementation phase carried out from September 2002 to June 2003 and which addressed only freshwater
animal species. The project consisted of: (1) compiling existing data from literature, web sites and museum collections; (2)
contacting scientific experts of each group to provide a ‘to the best of their knowledge, estimates of species numbers. In
this study, we consider as true freshwater species, those that complete part or all of their life cycle in freshwater, and
water-dependant species those that need freshwater for food or that permanently use freshwater habitats. The current order
of magnitude for known freshwater animal species world wide is 100 000, of which half are insects. Among other groups, there
are some 20 000 vertebrate species; 10 000 crustacean species and 5000 mollusc species that are either true freshwater or
water-dependant species. The study highlighted gaps in the basic knowledge of species richness at continental and global scales:
(1) Some groups such as Protozoa, nematodes or annelids have been less studied and data on their diversity and distribution
is scarce. Because current richness estimates for these groups are greatly biased by knowledge availability, we can expect
that real species numbers might be much higher.
(2) Continents are not equal in the face of scientific studies: South America and Asia are especially lacking global estimates
of species richness for many groups, even for some usually well-known ones such as molluscs or insects.
The second phase of the project will address freshwater plants and algae. The present status should be considered as a first
sketch of the global picture of freshwater biodiversity. We hope that this project will initiate interactive exchange of data
to complete and update this first assessment. 相似文献
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Evan P. Tanner Samuel D. Fuhlendorf John A. Polo Jacob M. Peterson 《Ecology and evolution》2021,11(19):12886
Temperature has long been understood as a fundamental condition that influences ecological patterns and processes. Heterogeneity in landscapes that is structured by ultimate (climate) and proximate (vegetation, topography, disturbance events, and land use) forces serve to shape thermal patterns across multiple spatio‐temporal scales. Thermal landscapes of grasslands are likely shifting as woody encroachment fragments these ecosystems and studies quantifying thermal fragmentation in grassland systems resulting from woody encroachment are lacking. We utilized the August 21st, 2017, solar eclipse to mimic a rapid sunrise/sunset event across a landscape characterized as a grassland to experimentally manipulate levels of solar radiation in the system. We then quantified changes in near‐surface temperatures resulting from changes in solar radiation levels during the eclipse. Temperatures were monitored across three grassland pastures in central Oklahoma that were characterized by different densities (low, medium, and high) of Juniperus virginiana to understand the impact of woody encroachment on diurnal temperature patterns and thermal heterogeneity in a grassland''s thermal landscape. The largest temperature range across sites that occurred during the eclipse was in the mixed grass vegetation. Similarly, the largest change in thermal heterogeneity occurred in the grassland with the lowest amount of woody encroachment. Thermal heterogeneity was lowest in the highly encroached grassland, which also experienced the lowest overall change in thermal heterogeneity during the eclipse. Time series models suggested that solar radiation was the most influential factor in predicting changes in thermal heterogeneity as opposed to ambient temperature alone. These results suggest that highly encroached grasslands may experience lower diurnal variability of temperatures at the cost of a decrease in the overall thermal heterogeneity of that landscape. It appears that fine‐scale spatio‐temporal thermal variation is largely driven by solar radiation, which can be influenced by vegetation heterogeneity inherent within a landscape. 相似文献
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A six-year experimental restoration of biodiversity by shrub-clearing and grazing in calcareous grasslands of the French Prealps 总被引：5，自引：0，他引：5
The conservation of dry calcareous grasslands in the French Prealps strongly depends on the maintenance of low-intensity farming systems supported by agri-environmental schemes. An experimental assessment of the effect of current agro-pastoral management on the biodiversity of plant communities was conducted during a six-year permanent plot survey in four sites with contrasting habitat conditions (mesic to xeric). Analyses of species changes showed: (i) a strong increase in species richness and open grassland species frequencies four years after shrub-clearing, and (ii) a noticeable recovery of rare annuals and perennial species of conservation interest establishing in gaps created by grazing. At the community level, the restoration effect was evaluated by a between-year Correspondence Analysis, explaining 10.9% of the total floristic variability versus 29.5% for the site effect (between-site CA). Species ordination by between-year CA showed similar trajectories of vegetation changes during restoration despite different habitat conditions and grazing regimes between sites. The successful restoration of prealpine calcareous grasslands was explained by the availability of seed sources during the study in adjacent grazed or mown grasslands. Thus, restoration assessment should focus on dispersal possibilities and functional roles of species rather than species richness only. Finally, the spatial (i.e. the area of patches that need to be restored) and temporal (i.e. the frequency of shrub-clearing) implications for the large-scale conservation of prealpine calcareous grasslands by current agro-pastoral management are discussed. 相似文献