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1.
Schneider NA  Low M  Arlt D  Pärt T 《PloS one》2012,7(2):e31517
Nest predation risk generally increases nearer forest-field edges in agricultural landscapes. However, few studies test whether differences in edge contrast (i.e. hard versus soft edges based on vegetation structure and height) affect edge-related predation patterns and if such patterns are related to changes in nest conspicuousness between incubation and nestling feeding. Using data on 923 nesting attempts we analyse factors influencing nest predation risk at different edge types in an agricultural landscape of a ground-cavity breeding bird species, the Northern Wheatear (Oenanthe oenanthe). As for many other bird species, nest predation is a major determinant of reproductive success in this migratory passerine. Nest predation risk was higher closer to woodland and crop field edges, but only when these were hard edges in terms of ground vegetation structure (clear contrast between tall vs short ground vegetation). No such edge effect was observed at soft edges where adjacent habitats had tall ground vegetation (crop, ungrazed grassland). This edge effect on nest predation risk was evident during the incubation stage but not the nestling feeding stage. Since wheatear nests are depredated by ground-living animals our results demonstrate: (i) that edge effects depend on edge contrast, (ii) that edge-related nest predation patterns vary across the breeding period probably resulting from changes in parental activity at the nest between the incubation and nestling feeding stage. Edge effects should be put in the context of the nest predator community as illustrated by the elevated nest predation risk at hard but not soft habitat edges when an edge is defined in terms of ground vegetation. These results thus can potentially explain previously observed variations in edge-related nest predation risk.  相似文献   

2.
Decomposition of organic matter is an essential process regulating fluxes of energy and matter within ecosystems. Although soil microbes drive decomposition, this is often facilitated by detritivores through comminution. The contribution of detritivores and microbes to comminution and decomposition processes is likely to be affected by the habitat complexity. In urban ecosystems, human activities and management of vegetation and litter and soil components determine habitat complexities unobserved in natural ecosystems. Therefore, we investigated the effect of habitat complexity of low- and high-complexity urban parks and high-complexity woodland remnants on microbial decomposition and detritivore comminution using litter bags of differing mesh size. Detritivores were sampled using pitfall traps and their assemblage structure related to rates of comminution. Habitats of lower complexity had significantly lower decomposition and comminution rates. In more complex habitats, site history did not affect decomposition and comminution processes. Vegetation complexity and the indirect effect on microclimate explained most of the variation in decomposition and comminution processes. The abundance of macrofauna detritivores and their species richness were both positively related to higher comminution rates. The volume of understory vegetation was the best predictor for both macrofauna detritivore assemblage structure and comminution and decomposition processes. The study demonstrated that relatively modest changes in habitat complexity associated with different management practices can exert significant effects on the decomposition and comminution processes. The structure of detritivores assemblages was also subjected to modifications of the habitat complexity with significant effects on comminution processes. Simple management practices aimed to increase the complexity of habitats, particularly in the understory vegetation and litter layers, could restore and enhance soil biodiversity and functioning in urban ecosystems.  相似文献   

3.
张瀚曰  包维楷  胡斌  胡慧 《生态学报》2023,43(16):6878-6888
植被类型变化强烈影响着土壤碳循环。土壤微生物碳利用效率(CUE)是微生物将从环境中获取的碳分配给自身生长的比例,是土壤碳循环的综合指标。研究植被类型变化对CUE的影响有助于从微生物视角理解该过程中的土壤碳动态,可以为评估植被类型变化对土壤质量及生态系统碳循环的影响提供基础,具有重要的理论及实际价值。通过系统查阅相关文献,综述了植被类型变化导致的CUE变化情况,以及该过程中影响CUE的因子与机制。目前,相关研究主要涉及以林地、草地和农业用地为起点或终点的植被变化类型。天然林(原生林、次生林)变化为人工林、林地变化为草地后CUE普遍下降,随终点植被的发展CUE可能恢复至起点水平。植被成熟度越高,发生转变时CUE变化越剧烈。植被类型变化以农业用地为起点或终点时,CUE变化方向的不确定性及幅度的变异性均增加。植被类型变化导致的CUE变化主要受到植被、土壤、微生物因子及其交互作用的驱动,指示CUE的指标、采样季节和土层也会一定程度上影响CUE的变化。今后相关研究应采用直接的CUE测定方法,拓宽研究气候区及植被变化类型,关注植被变化过程中CUE变化的土层差异及动态监测,深入对植被类型变化导致的生态环境因子变化与CUE的关系及作用机制的研究。  相似文献   

4.
Tropical agroecosystems are subject to degradation processes such as losses in soil carbon, nutrient depletion, and reduced water holding capacity that occur rapidly resulting in a reduction in soil fertility that can be difficult to reverse. In this research, a polyphasic methodology has been used to investigate changes in microbial community structure and function in a series of tropical soils in western Kenya. These soils have different land usage with both wooded and agricultural soils at Kakamega and Ochinga, whereas at Ochinga, Leuro, Teso, and Ugunja a replicated field experiment compared traditional continuous maize cropping against an improved N-fixing fallow system. For all sites, principal component analysis of 16S rRNA gene denaturing gradient gel electrophoresis (DGGE) profiles revealed that soil type was the key determinant of total bacterial community structure, with secondary variation found between wooded and agricultural soils. Similarly, phospholipid fatty acid (PLFA) analysis also separated wooded from agricultural soils, primarily on the basis of higher abundance of monounsaturated fatty acids, anteiso- and iso-branched fatty acids, and methyl-branched fatty acids in the wooded soils. At Kakamega and Ochinga wooded soils had between five 5 and 10-fold higher levels of soil carbon and microbial biomass carbon than agricultural soils from the same location, whereas total enzyme activities were also lower in the agricultural sites. Soils with woody vegetation had a lower percentage of phosphatase activity and higher cellulase and chitinase activities than the agricultural soils. BIOLOG analysis showed woodland soils to have the greatest substrate diversity. Throughout the study the two functional indicators (enzyme activity and BIOLOG), however, showed lower specificity with respect to soil type and land usage than did the compositional indicators (DGGE and PLFA). In the field experiment comparing two types of maize cropping, both the maize yields and total microbial biomass were found to increase with the fallow system. Moreover, 16S rRNA gene and PLFA analyses revealed shifts in the total microbial community in response to the different management regimes, indicating that deliberate management of soils can have considerable impact on microbial community structure and function in tropical soils.  相似文献   

5.
Land-use legacies are recognized determinants of vegetation dynamics and plant community assembly. The duration of these legacies and how they influence the structure of vegetation communities developing naturally in nutrient-poor ecosystems is not well understood. Here, we focus on the effects of increased nutrient availability from previous agricultural practices on multiple vegetation properties in a heathland where agriculture and domestic grazing ceased near 1870 and 1895, respectively. We compared diversity, compositional and functional properties of the vegetation responses to land-use legacies in the soil between areas with different agricultural histories (previously cultivated vs. uncultivated). Diversity measures were found to be higher in the previously cultivated soils. β-diversity was mainly driven by changes in species relative cover and increased with increasing nutrient availability in the cultivated area. Furthermore, functional traits related to nutrient acquisition (SLA and Leaf Nitrogen content) and the changes in vegetation composition were directly linked to soil properties only in the previously cultivated part of the heathland. Together these results revealed a shift to a deterministic control of the plant community, where increased nutrient availability leads to stronger associations between soil and vegetation properties. This suggests that as nutrients become available, niche differentiation and competitive interactions become the predominant underlying mechanisms structuring the community. Our study shows that land-use legacies of moderate intensity can alter the assembly mechanisms and diversity patterns in unmanaged vegetation that can be maintained after more than a century since cessation of agricultural practice. Identifying land-use legacies and understanding how they structure heathland communities can thus lead to management decisions adapted to the specific assembly mechanisms and result in a more effective management.  相似文献   

6.
Mountain forests are at particular risk of climate change impacts due to their temperature limitation and high exposure to warming. At the same time, their complex topography may help to buffer the effects of climate change and create climate refugia. Whether climate change can lead to critical transitions of mountain forest ecosystems and whether such transitions are reversible remain incompletely understood. We investigated the resilience of forest composition and size structure to climate change, focusing on a mountain forest landscape in the Eastern Alps. Using the individual‐based forest landscape model iLand, we simulated ecosystem responses to a wide range of climatic changes (up to a 6°C increase in mean annual temperature and a 30% reduction in mean annual precipitation), testing for tipping points in vegetation size structure and composition under different topography scenarios. We found that at warming levels above +2°C a threshold was crossed, with the system tipping into an alternative state. The system shifted from a conifer‐dominated landscape characterized by large trees to a landscape dominated by smaller, predominantly broadleaved trees. Topographic complexity moderated climate change impacts, smoothing and delaying the transitions between alternative vegetation states. We subsequently reversed the simulated climate forcing to assess the ability of the landscape to recover from climate change impacts. The forest landscape showed hysteresis, particularly in scenarios with lower precipitation. At the same mean annual temperature, equilibrium vegetation size structure and species composition differed between warming and cooling trajectories. Here we show that even moderate warming corresponding to current policy targets could result in critical transitions of forest ecosystems and highlight the importance of topographic complexity as a buffering agent. Furthermore, our results show that overshooting ambitious climate mitigation targets could be dangerous, as ecological impacts can be irreversible at millennial time scales once a tipping point has been crossed.  相似文献   

7.
蓝家程  沈艳 《广西植物》2020,40(6):765-775
为揭示岩溶槽谷区植被恢复对土壤结构、土壤有机碳积累和碳库管理水平的影响,该研究选取了弃耕地、林地和草地三种土地利用方式,测定0~20 cm土层土壤团聚体组成、土壤有机碳(SOC)、团聚体有机碳以及土壤易氧化有机碳(EOC)含量。结果表明:(1)与弃耕地相比,林地和草地土壤团聚体平均重量直径(MWD)、几何平均重量直径(MGD)和2~5 mm团聚体含量显著增加,林地和草地土壤团聚体组成以2~5 mm为主,弃耕地以0.5~1 mm和0.25 mm为主,表明退耕还林还草能够促进土壤团聚体形成和稳定。(2)土壤团聚体有机碳含量呈现出林地草地弃耕地,随团聚体粒级增加而增加的趋势;林地和草地以2~5 mm团聚体有机碳贡献率最大,弃耕地则以0.25 mm团聚体贡献为主,表明弃耕地转变为林地和草地后,土壤SOC积累主要归功于2~5 mm有机碳含量的增加,以及团聚体由小粒径向大粒径转变。(3)与弃耕地比较,林地和草地土壤SOC、EOC含量和碳库管理指数(CPMI)均显著提高,其中土壤EOC含量和CPMI变化较为明显;土壤EOC可作为土壤碳库早期变化的有效指标,CPMI能够良好地表征植被恢复对土壤SOC和EOC的影响。  相似文献   

8.
The two major disturbance types of boreal black spruce forest in north–central Quebec, Canada – natural disturbance by wildfire and anthropogenic disturbance by harvest – may affect processes of recovery differently and leave distinct post‐disturbance soil and vegetation spatial patterns. We tested whether 1) spatial patterns of physico‐chemical soil organic layer properties, black spruce diameter and density, and understory ericaceous shrub cover, differ between these two principal disturbance types; 2) operations associated with forest harvest result in distinct, regular spatial patterns of these same variables related to presence of machine trails; and 3) ericaceous shrub presence is a potential factor contributing to the legacy of spatial patterns after harvest. We explored these patterns on black spruce‐feathermoss forest stands, including fire‐origin stands (18 and 98 years) and stands originating from harvest (16 and 62 years) in central Quebec, Canada. We used two spatial analysis methods, spectral analysis and principal component analysis in the frequency domain, to characterize and relate spatial patterns of these soil and vegetation variables, measured along 50‐m transects on each site. Spatial patterns of distribution of soil and vegetation variables were different on the burned and the harvested forest sites. Wildfire gave rise to spatial patterns in soil and vegetation variables at multiple scales, reflecting the complexity generated by variable burn intensity. Patterns following forest harvest were mainly related to the regular structure defined by trails created by logging operations. In contrast to burned sites, ericaceous shrub patterns on harvested sites were strongly associated with spatial arrangements of spruce diameter and density, promoting absence of canopy closure and persistence of trails. Moreover, different spatial signatures did not converge in the long‐term (62–98 years) between the two disturbance types. The divergence in spatial structure between natural and anthropogenic disturbances has implications for ecosystem structure and function in the longer term.  相似文献   

9.
Animal community dynamics in changing landscapes are primarily driven by changes in vegetation structure and ultimately by how species respond to these changes and at which spatial scale. We consider two major components of local community dynamics, species colonisation and extinction. We hypothesise that (1) the optimal spatial extent needed to accurately predict them will differ between these two processes; (2) it will also likely differ from species to species as a result of life history traits differences related to differences in habitat selection and (3) that a species' primary habitat will determine the spatial extent at which it perceives change in vegetation structure. We used data collected over 25 yr in a changing Mediterranean landscape to study bird species local colonisation and extinction patterns in two groups of species typical from two habitats: open farmland and woodland. Vegetation changes were measured at spatial extents ranging from 0.2 to 79 ha. Local species colonisation and extinction estimates were computed using a method accounting for heterogeneity in detection probability among species. We built linear models between local species colonisation/extinction estimates and vegetation changes and examined variations in model quality with respect to the spatial extent at which vegetation changes had been measured. Models for open habitat species showed that colonisation processes operated at the landscape scale (79 ha), while extinction was more tightly linked to local habitat requirements (0.2 ha). Models for woodland species presented a low and constant model quality whatever the spatial extent considered. Our results suggest that the dynamics of the woodland species considered responded to a combination of vegetation changes at several scales and, in particular, to changes in the vertical structure of the vegetation. We highlight the need to explicitly consider spatial extent in studies of habitat selection and of habitat and population dynamics to improve our understanding of the biological consequences of land use changes and guide more effective conservation efforts.  相似文献   

10.
Patterned vegetation is a characteristic feature of many dryland ecosystems. While plant densities on the ecosystem-wide scale are typically low, a spatial self-organisation principle leads to the occurrence of alternating patches of high biomass and patches of bare soil. Nevertheless, intraspecific competition dynamics other than competition for water over long spatial scales are commonly ignored in mathematical models for vegetation patterns. In this paper, I address the impact of local intraspecific competition on a modelling framework for banded vegetation patterns. Firstly, I show that in the context of a single-species model, neglecting local intraspecific competition leads to an overestimation of a patterned ecosystem’s resilience to increases in aridity. Secondly, in the context of a multispecies model, I argue that local intraspecific competition is a key element in the successful capture of species coexistence in model solutions representing a vegetation pattern. For both models, a detailed bifurcation analysis is presented to analyse the onset, existence and stability of patterns. Besides the strengths of local intraspecific competition, also the difference between two species has a significant impact on the bifurcation structure, providing crucial insights into the complex ecosystem dynamics. Predictions on future ecosystem dynamics presented in this paper, especially on pattern onset and pattern stability, can aid the development of conservation programs.  相似文献   

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