Increasing frequency of extreme climate events is likely to impose increased stress on ecosystems and to jeopardize the services that ecosystems provide. Therefore, it is of major importance to ...assess the effects of extreme climate events on the temporal stability (i.e., the resistance, the resilience, and the variance) of ecosystem properties. Most time series of ecosystem properties are, however, affected by varying data characteristics, uncertainties, and noise, which complicate the comparison of ecosystem stability metrics (ESMs) between locations. Therefore, there is a strong need for a more comprehensive understanding regarding the reliability of stability metrics and how they can be used to compare ecosystem stability globally. The objective of this study was to evaluate the performance of temporal ESMs based on time series of the Moderate Resolution Imaging Spectroradiometer derived Normalized Difference Vegetation Index of 15 global land‐cover types. We provide a framework (i) to assess the reliability of ESMs in function of data characteristics, uncertainties and noise and (ii) to integrate reliability estimates in future global ecosystem stability studies against climate disturbances. The performance of our framework was tested through (i) a global ecosystem comparison and (ii) an comparison of ecosystem stability in response to the 2003 drought. The results show the influence of data quality on the accuracy of ecosystem stability. White noise, biased noise, and trends have a stronger effect on the accuracy of stability metrics than the length of the time series, temporal resolution, or amount of missing values. Moreover, we demonstrate the importance of integrating reliability estimates to interpret stability metrics within confidence limits. Based on these confidence limits, other studies dealing with specific ecosystem types or locations can be put into context, and a more reliable assessment of ecosystem stability against environmental disturbances can be obtained.
Soil microbial communities in Mediterranean agroecosystems experience long drought periods that are typically combined with heat and frequently interspersed with rapid rewetting events. Agroforestry ...systems are of growing interest and viewed as possible alternative to conventional cropping systems in the context of climate change. Our aim was to evaluate the resistance and resilience of soil microbial communities against drought with or without heat stress at different distances from the tree row in an agroforestry system as compared to a conventional cropping system. Soils were sampled at several distances from the tree row in a 21-year-old walnut agroforestry system and a contiguous conventional crop in Southern France. We simulated two cycles of drying-rewetting under controlled conditions and applied three distinct treatments: control (without stress), drought and drought combined with heat stress. We monitored microbial respiration over the incubation period. The inorganic N and microbial biomass C, N and P contents (MBC, MBN and MBP) were assessed during the drying period (resistance), just after rewetting and at the end of the experiment (resilience), while bacterial and fungal abundances were measured at the end of the resistance period. We demonstrated that an agroforestry system can induce spatial heterogeneity in soil microbial biomass and functions under control conditions. Microbial biomass and activity, soil organic matter (SOM) and mineral N levels increased on the tree row. This spatial heterogeneity pattern was preserved for soil microbial response to drought combined or not with heat. Microorganisms sampled in the middle of the interrow or in the conventional crop exhibited highest biomass resistance and lowest resilience when facing combined drought and heat stress. Soil microbial biomass resistance and resilience were similar whatever the spatial position when microorganisms had to deal with drought stress only. Our findings suggested that despite higher SOM content, microbial biomass and activity at and near the tree row, the legacy effect of the tree row did not lead to higher ecological stability under stressful climatic conditions. We also demonstrated that soil microorganisms can considerably change their stoichiometry depending on the stress treatment. Soil microorganisms showed elevated MBC:MBN, MBC:MBP and variable MBN:MBP during the resistance period. A high stoichiometric flexibility of microorganisms was observed when exposed to drought stress only, while stoichiometric changes were irreversible when exposed to combined drought and heat stress.
•Agroforestry generates spatial heterogeneity in soil microbial response to stress.•Soil microbial biomass is less resistant under the tree rows.•Soil microbial biomass is less resilient in a conventional crop.•Stresses induce important flexibility in soil microbial biomass CNP stoichiometry.
A comprehensive understanding of the relationship between land cover, climate change and disturbance dynamics is needed to inform scenarios of vegetation change on the African continent. Although ...significant advances have been made, large uncertainties exist in projections of future biodiversity and ecosystem change for the world's largest tropical landmass. To better illustrate the effects of climate–disturbance–ecosystem interactions on continental‐scale vegetation change, we apply a novel statistical multivariate envelope approach to subfossil pollen data and climate model outputs (TraCE‐21ka). We target paleoenvironmental records across continental Africa, from the African Humid Period (AHP: ca 14 700–5500 yr BP) – an interval of spatially and temporally variable hydroclimatic conditions – until recent times, to improve our understanding of overarching vegetation trends and to compare changes between forest and grassy biomes (savanna and grassland). Our results suggest that although climate variability was the dominant driver of change, forest and grassy biomes responded asymmetrically: 1) the climatic envelope of grassy biomes expanded, or persisted in increasingly diverse climatic conditions, during the second half of the AHP whilst that of forest did not; 2) forest retreat occurred much more slowly during the mid to late Holocene compared to the early AHP forest expansion; and 3) as forest and grassy biomes diverged during the second half of the AHP, their ecological relationship (envelope overlap) fundamentally changed. Based on these asymmetries and associated changes in human land use, we propose and discuss three hypotheses about the influence of anthropogenic disturbance on continental‐scale vegetation change.
In an era of global climate change, urban form has significant impacts on resilience and vulnerability to uncertain climate disturbances. However, spatially quantifying urban form resilience across ...different adaptive phases is still in the exploratory stage. This study presented a general framework to build a bridge between the analysis of urban form resilience and climate disturbances. After transforming this general framework into the specific framework for urban form resilience at the mesoscale to climate disturbances in winter city, an evaluation index system comprised of three dimensions of “Absorption-Adaptation-Recovery” was constructed to investigate the evolution of urban form resilience to climate disturbances in Changchun city, which experienced a progression from exploitation (r) phase to conservation (k) phase over the past 100 years. The morphological region was adopted as the basic unit for resilience evaluation. The results showed that, from r to k, almost all urban form regions represented a significant decline in absorption capacity and a dramatic rise in recovery capacity. The adaption capacity also experienced a decreasing trend, but it was not prevalent in every urban form region. The increase in resilience gained by the enhanced recovery capacity could not offset the decrease in resilience caused by the weakened absorption capacity and adaption capacity. In different periods, the emphases of resilience control for urban form regions were different. This study hopes to provide scientific guidance for resilience management in cities.
•Resilient urban form needs excellent balance of absorption-adaptation-recovery.•The decline in absorption capacity caused by ecosystem degradation is irreversible.•An undesirable urban form may lock the city into a vulnerable state permanently.•Trade-offs and synergy of resilience capacities are vital at spatial-temporal scales.
Extreme drought events from climate disturbances are weakening livelihood and limiting agriculture and livestock production in the Sahel region. The lack of relevant information to anticipate coping ...measures has exacerbated impacts leading to climate adaptation failure in most parts. In this regard, the current research paper has collected important datasets with an objective to assess the impact of extreme drought events on household’s livelihoods for better understanding impacts, local people’s perception, and the changes on vegetation cover in order to support a robust adaptation strategy to drought. The study conducted a household survey and collected satellite data for comparative analysis. The first survey was conducted in 2013 to collect data from 465 household heads through a structured questionnaire. Supplementary focus group discussions (FGDs) were also conducted in 2018 to collect qualitative information from targeted respondents such as village leaders and members of other key groups including women and youth. Descriptive statistics and correlation coefficient matrix were used to characterize the impact on households’ main livelihoods and logistic regression to predict people’s perception on pasture depletion over the last 20 years. Satellite data were used to derive spectral vegetation of land covers and unsupervised classification indexes. Both individual survey and focus group discussions identified drought as the main climate constraint which reduced crop production, water and pastures. The logistic analysis revealed that if the respondent’s major occupation is livestock, the probability to perceive a depletion of pasture will increase by 28%. Concurrently, the satellite image observation in perfect agreement with the field survey showed 6.78% and 6.01% losses of water surface and vegetation cover respectively between 1986 and 2016 in the study area. These findings showed that logistic regression coupled with satellite information can inform on past and future impacts which are extremely crucial for sound adaptation planning in the Sahel region.
Question: Predicting the future abundance and distribution of invasive plants requires knowing how they respond to environmental conditions. In arid and semi-arid ecosystems where water is a limiting ...resource, environmental conditions and disturbance patterns influence invasions by altering acquisition and utilization of water over space and time. We ask: 1. How do variations in climatic and soil properties influence temporal soil water dynamics? 2. How does this variation affect the establishment of Bromus tectorum (cheatgrass), a cool-season annual grass that has successfully colonized much of the U.S. Great Basin? Location: Short-grass Steppe in northeastern Colorado, USA; Arid Lands Ecology reserve in southeastern Washington, USA; and the Patagonian steppe of the Chubut province in Argentina. Methods: We utilized a soil water model to simulate seasonal soil water dynamics in multiple combinations of climatic and soil properties. In addition, we utilized a gap dynamics model to simulate the impact of disturbance regime and seed availability on competition between B. tectorum and native plants. Results: Our results suggest that climate is very important, but that soil properties do not significantly influence the probability of observing conditions suitable for B. tectorum establishment. Results of the plant competition model indicate that frequent disturbance causes more Bromus tectorum in invaded areas and higher seed availability causes faster invasion. Conclusions: These results imply a general framework for understanding Bromus tectorum invasion in which climatic conditions dictate which areas are susceptible to invasion, disturbance regime dictates the severity of invasion and seed availability dictates the speed of invasion.
An emerging paradigm regarding vegetation response to climate warming is that the interaction of weather extremes and disturbance will trigger abrupt changes in ecosystem types by overcoming ...resilience of dominant species. Black spruce (
Picea mariana
(Mill.)) ecosystems are widespread across the North American boreal forest, because of ecophysiological adaptations that allowed these communities to thrive in fire-prone areas. We investigated resilience of spruce-moss forests to weather-disturbance interaction after a 3-year period (2005 to 2007) of major fire activity caused by extreme fire weather in eastern Canada. Pre- and post-fire conifer densities and environmental parameters related to seed rain, post-fire seedbeds, microclimate, and post-fire weather were measured in 133 burned stands throughout the closed-crown forest of Quebec. Critically low black spruce (BS) regeneration was observed in almost all of the stands, leading to a decrease in stand density and a shift of species dominance from BS to jack pine (
Pinus banksiana
(Lamb.), JP). The studied sites were characterized by thick residual organic matter, resulting in a predominance of charred duff, a seedbed associated with low water retention and high variation in temperature. While high levels of JP seedling establishment were reported on this seedbed, it was unfavorable to BS germination and survival in the context of warm and dry weather that prevailed in post-fire summers. In these ecosystems, early vegetation establishment patterns are generally reliable predictors of future stand composition and the exclusion of BS will presumably be maintained through succession. During large fire years, high proportions of the landscape are subjected to the interaction of fire regime and weather that creates unsuitable conditions for BS regeneration. Hence, vegetation change is susceptible to happen at a broad scale. Therefore, the frequency of major fire years could have a decisive influence on the rate of vegetation response to climate change in this biome.
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