Increasing Disturbance Intensity Research Articles

Stable Soil Biota Network Enhances Soil Multifunctionality in Agroecosystems.

Unraveling how agricultural management practices affect soil biota network complexity and stability and how these changes relate to soil processes and functions is critical for the development of sustainable agriculture. However, our understanding of these knowledge still remains unclear. Here, we explored the effects of soil management intensity on soil biota network complexity, stability, and soil multifunctionality, as well as the relationships among these factors. Four typical land use types representing a gradient of disturbance intensity were selected in calcareous and red soils in southwest China. The four land use types with increasing disturbance intensity included pasture, sugarcane farmland, rice paddy fields, and maize cropland. The network cohesion, the network topological features (e.g., average degree, average clustering coefficient, average path length, network diameter, graph density, and modularity), and the average variation degree were used to evaluate the strength of interactions between species, soil biota network complexity, and the network stability, respectively. The results showed that intensive soil management increased species competition and soil biota network complexity but decreased soil biota network stability. Soil microfauna (e.g., nematode, protozoa, and arthropoda) stabilized the entire soil biota network through top-down control. Soil biota network stability rather than soil biota network complexity or soil biodiversity predicted the dynamics of soil multifunctionality. Specifically, stable soil communities, in both the entire soil biota network and selected soil organism groups (e.g., archaea, bacteria, fungi, arthropoda, nematode, protozoa, viridiplantae, and viruses), support high soil multifunctionality. In particular, soil microfauna stability had more contributions to soil multifunctionality than the stability of soil microbial communities. This result was further supported by network analysis, which showed that modules 1 and 4 had greater numbers of soil microfauna species and explained more variation of soil multifunctionality. Our study highlights that soil biota network stability should be considered a key factor in improving agricultural sustainability and crop productivity in the context of increasing global agricultural intensification.

Functional diversity along disturbance and environmental gradients in Ethiopian moist Afromontane forest

Considering multiple measures to fully capture functional diversity is important. However, the effects of disturbance gradients on diversity have been controversial, as species diversity alone may not fully capture these effects. This study aimed to evaluate trait-based diversity across disturbance gradients in the moist Afromontane forest of Ethiopia, Yayu Coffee Forest Biosphere Reserve (YCFBR). Vegetation data and relevant traits related to plant-life strategies, competition, and responses to disturbances were collected. A multiple regression model was used to test the response of functional diversity to disturbances and environmental gradients. The results revealed functional diversity in plant communities, including dendrogram-based functional diversity for plot-based (FDp), functional richness (FRic), functional evenness (FEve), functional divergence (FDiv), functional dispersions (FDis), and community-weighted mean of maximum tree height (CWM.Hmax), showed decreasing patterns with increasing disturbance intensity in the YCFBR. Additionally, the findings highlighted that FDis and Hmax are the most vulnerable functional traits to anthropogenic factors and are less tolerant in disturbed ecosystem environments. Therefore, reducing disturbances is crucial to maintaining higher levels of these functional diversities. For example, the results showed that the CWM.Hmax declined from 27.25 m to 15 m, indicating a shift towards shorter plant species. In contrast, the community-weighted mean of woody density (CWM.WD), the community-weighted mean of specific leaf area (CWM.SLA), and the community-weighted mean of seed mass (CWM.SM) increased significantly with an increase in disturbance intensity. For instance, CWM.SM and CWM.SLA changed from 5 to 14.25 (g) and 90 to 130 (cm2/g), respectively. These indices may serve as indicators of ecosystem resilience at disturbed forest ecosystem sites. Furthermore, the regression results indicated that FDp, FRic, FEve, FDiv, FDis, CWM.WD, and CWM.Hmax showed increasing patterns with increasing species richness, which suggests that protecting and promoting species diversity can contribute to maintaining high levels of functional diversity. The mixed effects model revealed that anthropogenic disturbance and elevational gradients had significant effects on functional diversity in the YCFBR. Therefore, when managing and conserving biodiversity in heterogeneous environments, both anthropogenic factors and environmental variables need to be considered. Species with low SLA and SM are recommended for the restoration of disturbed ecosystems. Overall, this study demonstrates that trait-based functional diversity is useful for predicting the adaptation potentials of species in heterogeneous environments and disturbance gradients.

Transient Dynamics Analysis of a Predator-Prey System with Square Root Functional Responses and Random Perturbation

In this paper, we study the asymptotic and transient dynamics of a predator–prey model with square root functional responses and random perturbation. Firstly, the mean square stability matrix is obtained from the stability theory of stochastic systems, and three stability indexes (root-mean-square resilience, root-mean-square reactivity and root-mean-square amplification envelope) of the ecosystem response to stochastic disturbances are calculated. We find that: (1) no matter which population is disturbed, increasing the intensity of disturbance improves the ability of the system leaves steady state and thus decreases the stability. The root-mean-square amplification envelope rises with increasing disturbance intensity, (2) the system is more sensitive to the disturbance of the predator than disturbance to prey, (3) ρmax and tmax are important indicators, which represent the intensity and time of maximum amplification by disturbance. These findings are helpful for managers to take corresponding management measures to reduce the disturbances, especially for predators, thereby avoiding the possible change of the structure and functions of the ecosystem.

Effect of the presence of plateau pikas on the ecosystem services of alpine meadows

Abstract. The activity of small mammalian herbivores influences grassland ecosystem services in arid and semi-arid regions. Plateau pika (Ochotona curzoniae) was considered to be a focal organism to investigate the effect of small mammalian herbivores on meadow ecosystem services in alpine regions. In this study, a home-range scale was used to measure the forage available to livestock, water conservation, carbon sequestration and soil nutrient maintenance (total nitrogen, phosphorus and potassium) in the topsoil layer, and a quadrat scale was used to assess the biodiversity conservation of alpine meadows. This study showed that the forage available to livestock and water conservation was 19 % and 16 % lower in the presence of plateau pikas than in their absence, and biodiversity conservation, carbon sequestration, soil nitrogen and phosphorus maintenance was 15 %, 29 %, 10 % and 8.9 % higher in the presence of plateau pikas than in their absence. In contrast, it had no impact on soil potassium maintenance of meadow ecosystems in alpine regions. The forage available to livestock, biodiversity conservation and soil nutrient maintenance of meadow ecosystems in alpine regions had maximum values as the disturbance intensity of plateau pikas increased; the water conservation tended to decrease linearly with the increasing disturbance intensity of plateau pikas. These results present a pattern of plateau pikas influencing the ecosystem services of meadow ecosystems in alpine regions, enriching our understanding of the small mammalian herbivores in relation to grassland ecosystem service.

Forest disturbances and climate constrain carbon allocation dynamics in trees.

Forest disturbances such as drought, fire, and logging affect the forest carbon dynamics and the terrestrial carbon sink. Forest mortality after disturbances creates uncertainties that need to be accounted for to understand forest dynamics and their associated C‐sink. We combined data from permanent resampling plots and biomass oriented dendroecological plots to estimate time series of annual woody biomass growth (ABI) in several forests. ABI time series were used to benchmark a vegetation model to analyze dynamics in forest productivity and carbon allocation forced by environmental variability. The model implements source and sink limitations explicitly by dynamically constraining carbon allocation of assimilated photosynthates as a function of temperature and moisture. Bias in tree‐ring reconstructed ABI increased back in time from data collection and with increasing disturbance intensity. ABI bias ranged from zero, in open stands without recorded mortality, to over 100% in stands with major disturbances such as thinning or snowstorms. Stand leaf area was still lower than in control plots decades after heavy thinning. Disturbances, species life‐history strategy and climatic variability affected carbon‐partitioning patterns in trees. Resprouting broadleaves reached maximum biomass growth at earlier ages than nonresprouting conifers. Environmental variability and leaf area explained much variability in woody biomass allocation. Effects of stand competition on C‐allocation were mediated by changes in stand leaf area except after major disturbances. Divergence between tree‐ring estimated and simulated ABI were caused by unaccounted changes in allocation or misrepresentation of some functional process independently of the model calibration approach. Higher disturbance intensity produced greater modifications of the C‐allocation pattern, increasing error in reconstructed biomass dynamics. Legacy effects from disturbances decreased model performance and reduce the potential use of ABI as a proxy to net primary productivity. Trait‐based dynamics of C‐allocation in response to environmental variability need to be refined in vegetation models.

Functional diversity and redundancy of subalpine meadows subjected to anthropogenic disturbances

Abstract Aims The aims of this study were to assess how functional diversity (FD) and functional redundancy respond to subalpine meadow ecosystem degradation under anthropogenic disturbance and how species contribute to functional redundancy along the disturbance gradient. Methods The study was carried out in the subalpine meadow in Mount Jade Dragon, which is located at the southeastern edge of the Tibetan Plateau. Four disturbance intensities [no disturbance (ND), weak disturbance (WD), moderate disturbance (MD) and severe disturbance (SD)] were identified. Species richness, soil properties and five key plant functional traits were assessed along the disturbance gradient. Simpson’s diversity index, FD based on the Rao algorithm, functional redundancy, community-weighted mean of each functional trait and species-level functional redundancy were determined. Important Findings Unimodal change pattern of FD and functional redundancy along the disturbance gradient were found in the present study, with their maximum in MD and WD, respectively. Species diversity showed a decreasing trend with increasing disturbance intensity. As disturbance intensified, species with traits related to conservative growth strategies, such as low specific leaf area (SLA) and high leaf dry matter content (LDMC), decreased, whereas species with resource acquisitive strategies, such as small plant, high SLA and low LDMC, increased in the community. At the species level, species showed species-specific roles in functional redundancy. Notably, some species were important in the community in terms of their unique function. For instance, Ligularia dictyoneura in ND and Potentilla delavayi in MD and SD.

Size distribution law of earthquake-triggered landslides in different seismic intensity zones

Abstract. The Ms 8.0 Wenchuan earthquake in 2008 and Ms 7.0 Lushan earthquake in 2013 produced thousands of landslides in the southern region of the Longmen Mountains in China. We conducted field investigations and analyzed remote sensing data to determine the distribution law of earthquake-triggered landslides. The results show a strong negative power law relationship between the size and frequency of landslides in VII, VIII, and IX seismic intensity zones, a weak power law in the X seismic intensity zone, and a lognormal distribution in the XI seismic intensity zone. Landslide density increases with increasing seismic intensity. A sandpile cellular automata model was built under the conceptual framework of self-organized criticality theory to simulate earthquake-induced landslides. Data from the simulations demonstrate that, with increasing disturbance intensity, the dynamical mechanism of the sandpile model changes from a strong power law to a weak power law and then to a lognormal distribution. Results from shaking table experiments of a one-sided slope sandpile show that, for peak ground acceleration (PGA) in the range of 0.075–0.125 g, the relation between the amount and frequency of sand follows a negative power law. For PGA between 0.15 and 0.25 g, the relation obeys a lognormal distribution. This verifies that the abovementioned distribution of earthquake-induced landslides should be a universal law from a physical viewpoint and may apply to other areas. This new perspective may be used to guide the development of an inventory of earthquake-triggered landslides and provide a scientific basis for their prediction.

Functional response of benthic macroinvertebrates to fire disturbance in patagonian streams

Disturbances often act as ecological filters through which only certain combinations of biological traits may pass. Here, we aimed to determine if an unprescribed human-started wildfire can act as a filter for stream-dwelling macroinvertebrates. To do this, we sampled three burnt and two reference streams in Los Alerces National Park (Patagonia, Argentine side). Sampling began shortly after the fire was extinguished and comprised four visits during the following seven months. We explored how functional richness, evenness, and dispersion at the community level responded to post-fire environmental changes using generalized linear mixed models. We also used RLQ and fourth-corner analysis to identify which trait modalities were specifically affected, either positively or negatively, by the fire. We found that functional richness and dispersion decreased with increasing disturbance intensity, which in this case, was best represented by increased suspended solids. In addition, all three functional metrics were significantly lower in fire-affected sites. Burnt streams were characterized by bi-multivoltine taxa and collector-gatherers, among others. Overall, our study showed how a wildfire can directly constrain the functional composition of macroinvertebrate communities, and highlighted the importance of incorporating trait-based approaches into the study of large-scale disturbances.

Large scale environmental drivers of biocrust distribution and development across a sandy desert in China

Biological soil crusts (biocrusts) are widely distributed in arid and semiarid ecosystems and provide critical ecological functions. Understanding how biocrusts change across broad regional scales allows us to manage them more effectively under changing climates and land-use pressures. Based on field surveys, we used boosted regression trees and correlation analysis to examine the changes in cover, distribution and developmental characteristics of biocrust mosses and cyanobacteria, and environmental factors at 40 sites in the Mu Us Sandland in northwestern China. We found that higher elevation sites (~1342 m) were the most suitable for biocrust distribution, and preferred sites were characterized by greater vegetation cover (>43%), values of the aridity index (>0.34), slope (>6.6°), soil pH (>8.85) and soil organic carbon (>0.50%). Increasing levels of disturbance (>1.15 kg dung ha−1) suppressed biocrusts. Moss crust development (e.g., biomass, thickness, bulk density) was significantly positively related to vegetation cover, aridity index, and soil organic carbon, and moss crusts tended to prefer shady shrub communities at low elevations. Shady and steep (5 – 15°) slopes and higher soil nutrient contents were positively correlated with cyanobacteria development. Reduced rainfall and increasing disturbance intensity would reduce the distribution and development of biocrusts. Our study provides a basis for informed decision making about how to manage moss and cyanobacterial crusts in the Mu Us Sandland as the region becomes hotter and drier.

Trampling Disturbance of Biocrust Enhances Soil Carbon Emission

Biocrusts play an important role in the carbon cycle in arid and semiarid ecosystems. Activities such as livestock grazing can disturb ecosystem functions of biocrusts. However, it is unclear whether disturbance intensity impacts carbon emission from these biocrusts. Few studies have investigated the transformation of carbon within biocrusts after disturbance. Here, we conducted a field experiment on the Loess Plateau, China, in which we artificially simulated different intensities of trampling to examine the response of biocrust carbon emissions to disturbance. Our results demonstrate that disturbance significantly reduced biocrust coverage. The largest decreases were observed in the second through fourth intensity, which declined significantly by 12.6–17.1%. Disturbance decreased soil organic carbon content in the biocrust layer by 2.6 g kg−1–3.7 g kg−1 depending on the disturbance intensity. Disturbance significantly increased the soil easily oxidizable carbon (SEOC) content in the biocrust layer. The soil microbial biomass carbon (SMBC) content of the fifth intensity increased significantly by 70.3%. The soil mineralizable carbon (SMC) content of the fourth intensity increased significantly by 78.8%. Soil carbon emissions increased significantly with increasing disturbance intensity, were higher at night than during the day, and were higher in the summer than in the fall. Together, these findings indicate that the increase of carbon emission was mainly due to increases in SEOC and SMC. Trampling disturbance increases carbon emissions from biocrust soils. These losses of CO2 from biocrust soils after disturbance may substantially reduce the biocrust contribution to the soil carbon budget.

人为干扰对传粉昆虫群落物种多样性及其优势类群生态位的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 人为干扰对传粉昆虫群落物种多样性及其优势类群生态位的影响 DOI: 10.5846/stxb201807021456 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目（41771202，41371195） Effects of anthropogenic disturbance on species diversity and niche of dominant group in pollinators community Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:物种多样性是群落功能复杂性和稳定性的重要量度指标，不同干扰强度下物种多样性和生态位特征不同，人为干扰对传粉群落的影响可以通过群落结构和物种多样性的变化直接表现出来。在巩义市选取24个采样点，3种景观类型（农田、灌丛、林地）进行取样，共捕获传粉昆虫18576头，分属于14目，147科，双翅目、膜翅目、鞘翅目、鳞翅目、半翅目与缨翅目6个传粉功能群。为了解研究区人为干扰对传粉昆虫类群传粉类群及其生态位的影响，本研究选取双翅目、膜翅目、鞘翅目3类主要传粉昆虫作为研究对象，在景观类型分类与实际情况的基础上，依据人为干扰指数赋值表和干扰强度计算公式，分析不同干扰强度下传粉昆虫优势种群生态位特征情况，结果表明：各传粉类群在不同的干扰条件下物种多样性不同；作为优势类群的蠓科、胡蜂科，生态位宽度和生态位重叠均均值高于其他几个类群，且中度干扰强度下值最大，但其生态宽度值与生态重叠值之间没有明显的相关关系。 Abstract:Species diversity is an index reflecting the complexity and stability of community function. We hypothesize that community structure and species diversity vary with the different densities of human disturbance. The effect of human disturbance on community can be directly reflected by the change of community structure and diversity. To study the status of species diversity and niche of dominant group in pollinators community in different types of anthropogenic disturbance, 24 sampling points were selected in field margin systems in hilly regions of western Henan. Yellow, white and blue traps were deployed, and mixture of approximately 200 mL of water and 1 drops of detergent was poured into the traps to capture pollination. The data were combined with the characteristics of local land use to analyze the effect of different disturbance types on diversity and niche of pollinators. We captured 18576 individuals of 14 order and 147 families, mainly belonged to Diptera, Hymenoptera, Coleoptera, Lepidoptera, Hemiptera and Thysanoptera. Hymenoptera, Coleoptera and Lepidoptera were selected as three kinds of main pollinators to be analyzed. The landscape types and actual observations was used to analyze. The results showed that the species diversity of different families of pollinating insects changed differently with the increasing disturbance intensity. An obvious decrease of the level of species diversity was found in Coleoptera. The niche breadth of Ceratopogonidae and Vespidae as dominant groups were higher than those of other groups, and the niche overlap with other species was higher under intermediate disturbance. No obvious correlation between niche breadth and niche overlap was found. 参考文献 相似文献 引证文献

Bacterioplankton community responses and the potential ecological thresholds along disturbance gradients

Increasing intensity and frequency of coastal pollutions are the trajectory to be expected due to anthropogenic pressures. However, it is still unclear how and to what extent bacterioplankton communities respond to the two factors, despite the functional importance of bacterioplankton in biogeochemical cycles. In this study, significant organic pollution index (OPI) and offshore distance gradients, as respective proxies of disturbance intensity and disturbance frequency, were detected in a regional scale across the East China Sea. A multiple regression on matrices (MRM) revealed that the biogeography of bacterioplankton community depended on spatial scale, which was governed by local characters. Bacterioplankton community compositions (BCCs) were primarily governed by the conjointly direct (−0.28) and indirect (−0.48) effects of OPI, while offshore distance contributed a large indirectly effect (0.52). A SEGMENTED analysis depicted non-linear responses of BCCs to increasing disturbance intensity and disturbance frequency, as evidenced by significant tipping points. This was also true for the dominant bacterial phyla. Notably, we screened 30 OPI-discriminatory taxa that could quantitatively diagnose coastal OPI levels, with an overall 79.3% accuracy. Collectively, the buffer capacity of bacterioplankton communities to increasing disturbance intensity and disturbance frequency is limited, of which the significant tipping points afford a warning line for coastal management. In addition, coastal pollution level can be accurately diagnosed by a few OPI-discriminatory taxa.

Effect of fire and thinning on fine-scale genetic structure and gene flow in fire-suppressed populations of sugar pine (Pinus lambertiana Dougl.)

Historically, frequent, low-severity fires in dry western North American forests were a major driver of ecological patterns and processes, creating resilient ecosystems dominated by widely-spaced pine species. However, a century of fire-suppression has caused overcrowding, altering forest composition to shade-tolerant species, while increasing competition and leaving trees stressed and susceptible to pathogens, insects, and high-severity fire. Exacerbating the issue, fire incidence is expected to increase with changing climate, while fire season has been observed to begin earlier and last longer than historic trends. Forest thinning and prescribed fire have been identified as important management tools to mitigate these risks. Yet little is known of how thinning, fire, or their interaction affect contemporary evolutionary processes of constituent pine species that influence fitness and play an important role in the opportunity for selection and population persistence. We assessed the impact of widely used fuel reduction treatments on fine-scale gene flow on an ecologically important and historically dominant shade-intolerant pine species of the Sierra Nevada, Pinus lambertiana Dougl. Treatment prescription (no-thin-no-fire, thin-no-fire, and fire-and-thin) was found to differentially affect both fine-scale spatial and genetic structure as well as effective gene flow in this species. Specifically, the thin-no-fire prescription increases genetic structure (spatial autocorrelation of relatives) between adults and seedlings, while seed and pollen dispersal increase and decrease, respectively, as a function of increasing disturbance intensity. While these results may be specific to the stands at our study site, they indicate how assumptions relating to genetic effects based on spatial structure can be misleading (for instance, in many stands the presence or absence of spatial structure was not indicative the presence or absence of genetic structure). It is likely that these disequilibrated systems will continue to evolve on unknown evolutionary trajectories. The long-term impacts of management practices on reduced fitness from inbreeding depression should be continually monitored to ensure resilience to increasingly frequent and severe fire, drought, and pest stresses.

One-hundred years after shrub encroachment: Policy directions towards sustainable rangeland-use

In many shrub-encroached lands, livestock grazing is the dominant land-use type which shapes stakeholders’ perspective on single ecosystem service provision (i.e., forage production). Although recent ecological studies suggested otherwise, recognition of multiple ecosystem services from shrublands is rarely translated into policy, likely due to the lack of robust scientific evidence on trade-offs between ecosystem services following shrub removal. Based on meta-analysis from global publications, we found that while shrub removal increased forage provision, such effect was generally short-lived (˜5 years). At the same time, shrub removal also increased bare soil, decreased soil nutrients and soil organic carbon, which potentially reduced erosion control and nutrient cycling service. These trade-offs tended to be more prominent with increasing disturbance intensity (i.e., higher shrub removal frequencies or switching from single to multiple shrub removal methods). To encourage adaptation to the provisioning of multiple ecosystem services from shrublands, we provided a framework on how to value such landscapes, including the estimated monetary values that could be generated from maintaining them. Since there will be a time-lag until most monetary values appear, initial incentives may be necessary to encourage the adoption of conservation practices, in addition to efforts to increase society awareness (e.g., eco-labelling, alternative food networks or social media) on multiple ecological benefits from shrublands and investment to provide capacity building for pastoralists.

Effects of selective cutting disturbance on soil phosphorus adsorption and desorption in a Korean pine and broad-leaved mixed forest in the Xiaoxing'an Mountains, China.

This study examined the characteristics of phosphorus (P) adsorption and desorption in surface soil (0-10 cm) of a secondary forest after selective cutting disturbance at three levels of intensity (low, medium, high) in order to reveal the effects of different disturbance intensities on soil P adsorption and desorption. Maximum adsorption amount (Qm), adsorption intensity factor, maximum buffer capacity, maximum desorption amount, average desorption rate and readily desorptable phosphorus were measured. Qm in the focal forests was 1383.93-1833.34 mg·kg-1, and Qmin forests with middle and high disturbance intensities was significantly higher than that in forests with low disturbance intensity and in primary forests. P adsorption intensity was 0.024-0.059 L·mg-1, and forests with high and low disturbance intensities increased the P adsorption intensity significantly. The maximum buffer capacity varied from 35.68 to 97.97 L·kg-1, with the highest value found in the forest with the highest disturbance intensity. Selective cutting significantly reduced the potential for phosphorus supply in the forest soils. The maximum desorption amount, average desorption rate and readily desorptable phosphorus content in the focal forests were 526.32-797.54 mg·kg-1, 14.7%-25.5% and 1.79-5.41 mg·kg-1, respectively, indicating that the ability of soil to release phosphorus significantly decreased with increasing disturbance intensity. Selective cutting changed the phosphorus adsorption and desorption characteristics by reducing the supply and release of soil phosphorus.

Effect of trampling disturbance on soil infiltration of biological soil crusts

The effect of trampling disturbance on soil infiltration of biological soil crusts was investigated by using simulated rainfall. The results showed that the trampling disturbance significantly increased soil surface roughness. The increasing extent depended on the disturbance intensity. Soil surface roughness values at 50% disturbance increased by 91% compared with the undisturbed treatment. The runoff was delayed by trampling disturbance. A linear increase in the time of runoff yield was observed along with the increasing disturbance intensity within 20%-50%. The time of runoff yield at 50% disturbance increased by 169.7% compared with the undisturbed treatment. Trampling disturbance increased soil infiltration and consequently decreased the runoff coefficient. The cumulative infiltration amount at 50% disturbance increased by 12.6% compared with the undisturbed treatment. Soil infiltration significant decreased when biocrusts were removed. The cumulative infiltration of the treatment of biocrusts removal decreased by 30.2% compared with the undisturbed treatment. Trampling disturbance did not significantly increase the soil loss when the distur bance intensity was lower than 50%, while the biocrusts removal resulted in 10 times higher in soil erosion modulus. The trampling disturbance of lower than 50% on biocrusts might improve soil infiltration and reduce the risk of runoff, thus might improve the soil moisture without obviously increa sing the soil loss.

Sediment type rules the response of aquatic plant communities to dewatering in wetlands

AbstractQuestionsThe effect of dewatering on aquatic plant communities may vary with sediment properties, such as particle size and organic matter content, as both control water retention in the sediment during dewatering. No study has tested how sediment type affects the short‐term response of plant communities to dewatering. We hypothesized that for the same dewatering event: (1) organic, silt and coarse sediments rank along a gradient of water deficit, with which community resistance and resilience decrease; (2) species survival during the event depend on their known ecological affinity for water; and (3) a peak in species richness associated with an intermediate water deficit occurs in silty habitats.LocationRiverine wetlands in the floodplain of the Ain River, France.MethodsEighteen sampling units were defined, set over three sediment types: gravel‐dominated coarse sediment, silt and organic matter‐dominated sediment. For each sediment type, three sampling units were permanently aquatic, and three sampling units underwent summer dewatering. A survey of species cover was conducted in each sampling unit at four times: before summer dewatering, at the beginning of the event, at the end of the event and 2 months after rewetting. Community resistance and resilience were assessed, as were changes over time in the proportions of species according their water affinity (hydrophytes, amphiphytes and helophytes, documented from the floras), and the effect of dewatering on species renewal and richness.ResultsThe sediment type affected aquatic plant community resistance and resilience, with increasing disturbance intensity for silty, followed by coarse compared with organic sediment. Organic sediment retained water efficiently during dewatering, supporting high community resistance, with the maintenance of amphiphytes and more tolerant hydrophytes. On silty sediment, disturbance was sufficiently high to cause the disappearance of hydrophyte vegetative parts, but propagules rapidly sprouted after rewetting, suggesting their preservation in the sediment and enabling good community resilience. On coarse sediment, a decrease in resident amphiphyte abundance, together with helophyte colonization and maintenance after rewetting were observed. Coarse sediment is not favourable to propagule survival, explaining the low community resilience. Contrary to our hypothesis, a linear positive relationship between disturbance intensity and species richness was observed after dewatering.ConclusionThe present study demonstrates that a simple description of sediment type allows prediction of dewatering impact on aquatic plant communities: organic, silt and coarse sediments were ranked along a gradient of water deficit, along which resistance and resilience decreased.

Modeling forest carbon cycle response to tree mortality: Effects of plant functional type and disturbance intensity

AbstractNatural and anthropogenic disturbances influence ecological succession and impact the carbon cycle. Understanding disturbance effects and ecosystem recovery is essential to carbon modeling. We hypothesized that (1) species‐specific disturbances impact the carbon cycle differently from nonspecific disturbances. In particular, disturbances that target early‐successional species will lead to higher carbon uptake by the postrecovery, middle‐ and late‐successional community and (2) disturbances that affect the midsuccessional deciduous species have more intense and long‐lasting impacts on carbon uptake than disturbances of similar intensity that only affect the early‐successional species. To test these hypotheses, we employed a series of simulations conducted with the Ecosystem Demography model version 2 to evaluate the sensitivity of a temperate mixed‐deciduous forest to disturbance intensity and type. Our simulation scenarios included a control (undisturbed) case, a uniform disturbance case where we removed 30% of all trees regardless of their successional status, five cases where only early‐successional deciduous trees were removed with increasing disturbance intensity (30%, 70%, 85%, and 100%), and four cases of midsuccessional disturbances with increasing intensity (70%, 85%, and 100%). Our results indicate that disturbances affecting the midsuccessional deciduous trees led to larger decreases in carbon uptake as well as longer recovery times when compared to disturbances that exclusively targeted the early‐successional deciduous trees at comparable intensities. Moreover, disturbances affecting 30% to 100% of early‐successional deciduous trees resulted in an increased carbon uptake, beginning 6 years after the disturbance and sustained through the end of the 100 year simulation.

Land use intensification differentially benefits alien over native predators in agricultural landscape mosaics

AbstractAimBoth anthropogenic habitat disturbance and the breadth of habitat use by alien species have been found to facilitate invasion into novel environments, and these factors have been hypothesized to be important within coccinellid communities specifically. In this study, we address two questions: (1) Do alien species benefit more than native species from human‐disturbed habitats? (2) Are alien species more generalized in their habitat use than natives within the invaded range or can their abundance patterns be explained by specialization on the most common habitats?LocationChile.MethodsWe quantified the use of different habitat types by native and alien coccinellid beetles by sampling individuals in nine habitat types that spanned a gradient in disturbance intensity, and represented the dominant natural, semi‐natural and agricultural habitats in the landscape.ResultsOur results provide strong support for the hypotheses that more‐disturbed habitats are differentially invaded. Both the proportion of alien individuals and the proportion of alien species increased significantly with increasing disturbance intensity. In contrast, we found no evidence that alien species were more generalized in their habitat use than native species; in fact, the trend was in the opposite direction. The abundance of specialized alien coccinellid species was not correlated with the area of the habitat types in the landscape.Main conclusionThe results suggest that successfully established alien coccinellid species may be ‘disturbance specialists’ that thrive within human‐modified habitats. Therefore, less‐disturbed agroecosystems are desirable to promote the regional conservation of native species within increasingly human‐dominated landscapes.

Ecological importance of intermediate windstorms rivals large, infrequent disturbances in the northern Great Lakes

Exogenous disturbances are critical agents of change in temperate forests capable of damaging trees and influencing forest structure, composition, demography, and ecosystem processes. Forest disturbances of intermediate magnitude and intensity receive relatively sparse attention, particularly at landscape scales, despite influencing most forests at least once per generation. Contextualizing the spatial extent and heterogeneity of such damage is of paramount importance to increasing our understanding of forested ecosystems. We investigated patterns of intermediate wind disturbance across a forested landscape in the northern Great Lakes, USA. A vegetation change tracker (VCT) algorithm was utilized for processing near-biennial Landsat data stacks (1984–2009) spanning forests sustaining damage from four recent windstorms. VCT predominantly maps stand-clearing disturbance and regrowth patterns, which were used to identify forest boundaries, young stands, and disturbance patterns across space and time. To map wind damage severity, we compared satellite-derived normalized difference vegetation index (NDVI) values calculated from pre- and post-storm Landsat imagery. A geographic information system (GIS) was used to derive wind damage predictor variables from VCT, digital terrain, soils/landform, land cover, and storm tracking data. Hierarchical and random forests regressions were applied to rank the relative importance of predictor variables in influencing wind damage. A conservative estimate of aggregate damage from the intermediate windstorms (extrapolated to ∼150,000 ha, ∼25,500 severe) rivaled individual large, infrequent disturbances in the region. Damage patterns were relatively congruent among storms and became more spatially heterogeneous with increasing disturbance intensity. Proximity to forest-nonforest edge, stand age, and soils/landform were consistently important damage predictors. The spatial extent and distribution of the first two damage predictors are extremely sensitive to anthropogenic modifications of forested landscapes, the most important disturbance agent in the northern Great Lakes. This provides circumstantial evidence suggesting anthropogenic activities are augmenting and/or diminishing the ecological effects of the natural wind disturbance regime. Natural disturbances of intermediate size and intensity are significant agents of change in this region, and likely in other regions, deserving more attention from ecologists and biogeographers.