Climate change reduces resilience to fire in subalpine rainforests

Climate change is affecting the distribution of species and the functioning of ecosystems. For species that are slow growing and poorly dispersed, climate change can force a lag between the distributions of species and the geographic distributions of their climatic envelopes, exposing species to the risk of extinction. Climate also governs the resilience of species and ecosystems to disturbance, such as wildfire. Here we use species distribution modelling and palaeoecology to assess and test the impact of vegetation–climate disequilibrium on the resilience of an endangered fire‐sensitive rainforest community to fires. First, we modelled the probability of occurrence of Athrotaxis spp. and Nothofagus gunnii rainforest in Tasmania (hereon “montane rainforest”) as a function of climate. We then analysed three pollen and charcoal records spanning the last 7,500 cal year BP from within both high (n = 1) and low (n = 2) probability of occurrence areas. Our study indicates that climatic change between 3,000 and 4,000 cal year bp induced a disequilibrium between montane rainforests and climate that drove a loss of resilience of these communities. Current and future climate change are likely to shift the geographic distribution of the climatic envelopes of this plant community further, suggesting that current high‐resilience locations will face a reduction in resilience. Coupled with the forecast of increasing fire activity in southern temperate regions, this heralds a significant threat to this and other slow growing, poorly dispersed and fire sensitive forest systems that are common in the southern mid to high latitudes.     

Forest resilience to drought varies across biomes

Forecasted increase drought frequency and severity may drive worldwide declines in forest productivity. Species‐level responses to a drier world are likely to be influenced by their functional traits. Here, we analyse forest resilience to drought using an extensive network of tree‐ring width data and satellite imagery. We compiled proxies of forest growth and productivity (TRWi, absolutely dated ring‐width indices; NDVI, Normalized Difference Vegetation Index) for 11 tree species and 502 forests in Spain corresponding to Mediterranean, temperate, and continental biomes. Four different components of forest resilience to drought were calculated based on TRWi and NDVI data before, during, and after four major droughts (1986, 1994–1995, 1999, and 2005), and pointed out that TRWi data were more sensitive metrics of forest resilience to drought than NDVI data. Resilience was related to both drought severity and forest composition. Evergreen gymnosperms dominating semi‐arid Mediterranean forests showed the lowest resistance to drought, but higher recovery than deciduous angiosperms dominating humid temperate forests. Moreover, semi‐arid gymnosperm forests presented a negative temporal trend in the resistance to drought, but this pattern was absent in continental and temperate forests. Although gymnosperms in dry Mediterranean forests showed a faster recovery after drought, their recovery potential could be constrained if droughts become more frequent. Conversely, angiosperms and gymnosperms inhabiting temperate and continental sites might have problems to recover after more intense droughts since they resist drought but are less able to recover afterwards.     

Response of wheat seedlings to short-term drought stress with particular respect to nitrate utilization

Abstract. The effect of short-term changes in the water potential (from 0 to – 2.5 MPa) by addition of PEG 4000 to the nutrient solution was investigated with respect to nitrate uptake and reduction in 3-week-old wheat plants ( Triticum aestivum , cv Fidel). Plants were harvested at the end of 12-h treatments in the dark. The water potential of the mature leaves was similar to that of the medium down to – 0.8 MPa and was maintained at this level even though the external water potential was much lower. The medium water potential of 0.8 was a threshold level below which elongation of the youngest leaf was inhibited. Increase of the PEG concentration in the medium brought about a decrease of evapotranspiration and enhancement of nitrate uptake. No difference in the rate of nitrate reduction was observed, although the in vitro nitrate reductase activity was lowered. Nitrate accumulation in the shoot was ascribed both to the stimulation of net uptake from the medium, and to the mobilization and translocation of nitrate from the root. It is suggested that increase in the storage pool of nitrate in shoots was related to the role of NO₃⁻ as an osmoticum.     

Tree resilience to drought increases in the Tibetan Plateau

Forests in the Tibetan Plateau are thought to be vulnerable to climate extremes, yet they also tend to exhibit resilience contributing to the maintenance of ecosystem services in and beyond the plateau. So far the spatiotemporal pattern in tree resilience in the Tibetan Plateau remains largely unquantified and the influence of specific factors on the resilience is poorly understood. Here, we study ring‐width data from 849 trees at 28 sites in the Tibetan Plateau with the aim to quantify tree resilience and determine their diving forces. Three extreme drought events in years 1969, 1979, and 1995 are detected from metrological records. Regional tree resistance to the three extreme droughts shows a decreasing trend with the proportion of trees having high resistance ranging from 71.9%, 55.2%, to 39.7%. Regional tree recovery is increasing with the proportion of trees having high recovery ranging from 28.3%, 52.2%, to 64.2%. The area with high resistance is contracting and that of high recovery is expanding. The spatiotemporal resistance and recovery are associated with moisture availability and diurnal temperature range, respectively. In addition, they are both associated with forest internal factor represented by growth consistence among trees. We conclude that juniper trees in the Tibetan Plateau have increased resilience to extreme droughts in the study period. We highlight pervasive resilience in juniper trees. The results have implications for predicting tree resilience and identifying areas vulnerable to future climate extremes.     

Resistance and resilience of macroinvertebrates to irrigation water withdrawals

1. Water withdrawal for irrigated agriculture is one of the leading uses of freshwater resources in the world; however, effects of low flow disturbances on lotic ecosystems are poorly understood. We studied an intensively managed agricultural catchment to determine: (i) how macroinvertebrate assemblages and environmental variables respond to water withdrawals of varying magnitude and duration; (ii) what environmental variables are associated with macroinvertebrate responses and (iii) the resiliency of macroinvertebrate communities to irrigation water withdrawals. 2. We sampled above and below four irrigation diversions that create a gradient of increasing water withdrawal from upstream to downstream (i.e. 0%, 22%, 87%, 90% and 97% water withdrawn) along a 36 km river section. Three reaches were sampled above and below each point of diversion from June to September 2004 and 2005, which represented average and drought water conditions respectively. 3. Irrigation water withdrawals were associated with both direct and indirect changes to the physicochemical environment. Direct effects (e.g. decreased velocity, depth and wetted habitat) were approximately proportional to the amount of water withdrawn, while indirect effects (e.g. increased conductivity and temperature) occurred when water withdrawals exceeded 85% of ambient levels. 4. Changes in macroinvertebrate communities were more strongly related to indirect than direct effects of irrigation water withdrawals. In an average water year, community changes were associated with interacting thresholds of reduced discharge and increased conductivity. During a drought year, community changes were related to the interacting thresholds of reduced discharge and increased temperature. 5. Between years, macroinvertebrate responses differed with the magnitude and duration of low flow conditions. In 2004, high‐intensity, relatively short‐duration water withdrawals (<2 months) and alterations to the physicochemical environment changed the relative abundance of macroinvertebrate communities, while macroinvertebrate indices and proportional abundances of functional feeding groups remained unchanged. In contrast, discharge reductions exceeding 90% of ambient levels and temperatures above 30 °C from July to September 2005 were associated with shifts in community composition from a dominance of collector‐gatherer and filterer Ephemeroptera, Plecoptera and Trichoptera taxa to predatory insects, non‐insect taxa and scraping elmid beetles. 6. On an annual basis macroinvertebrate communities appeared resilient to the impacts of water withdrawals following winter high flows. In contrast, recovery was not observed after discharge and physicochemical variables returned to predisturbance conditions for only one month. 7. Irrigation water withdrawals appear to impact macroinvertebrates through indirect effects that intensify with the magnitude and duration of water withdrawals and annual water availability. Preserving environmental conditions within natural ranges of variability, especially during low water years, appears critical to mitigating adverse biological responses to water withdrawals.     

Ecophysiology of a wild platyopuntia exposed to prolonged drought

The effects of reduced annual rainfall over a 7-year period on the daily patterns of gas exchange were analyzed for a wild platyopuntia (Opuntia robusta) growing in rocky soil. In spite of the prolonged water stress, stomata opened at night and net carbon gain was observed for eight 1-day sampling periods during 2000. Daily net CO₂ uptake increased more than five-fold from the end of the dry spring season to the middle of the summer wet season. Curtailment in the formation of both new cladodes and new roots is considered to be an avoidance strategy to water scarcity, which in combination with net CO₂ uptake responses to temperature and relative humidity at night, and perhaps association with arbuscular-mycorrhizal fungi, were the most important adaptations for O. robusta to the prolonged drought conditions that prevailed in its rocky environment. Such adaptations of O. robusta are in addition to the classical physiological and structural modifications of CAM plants to tolerate prolonged drought.     

Resilience of fishes and invertebrates to prolonged drought in two California streams

Long-term data are needed to assess spatial and temporal variability of communities and their resilience to natural and anthropogenic disturbances, particularly in climatic regions marked by high interannual variability (e.g. mediterranean-climate). A long-term study at four sites on two streams in mediterranean-climate California (annual sampling over 20  yr) allowed us to quantify the influence of a 5-yr prolonged drought on stream invertebrate and fish communities. Invertebrate community composition did not show recovery following drought. The primary environmental factors influencing community composition, identified through principle components and multiple correspondence analyses were precipitation and flow permanence. Invertebrate taxon richness and abundance exhibited few responses (some site specific) and recovered quickly. Native fish abundance was lowest during the drought period and highest during the wet years that occurred at the end of the study period. Importantly, the prolonged drought facilitated the establishment and success of the invasive green sunfish (Centrarchidae: Lepomis cyanellus ) that was then resilient to subsequent large flow events. There was high spatial synchrony in the temporal changes among all four sites, and three distinct periods were identified: early drought, late drought, and post-drought years. However, we still found differences among sites along the flow permanence gradient from temporary to perennial in the response to drought of both invertebrate and fish assemblages likely as a result of changes in substrate, vegetation, and other habitat characteristics. The observed lack of resilience and negative impacts to biodiversity due to prolonged drought associated with long-term habitat changes is important because hydroclimatic extremes are predicted to increase in frequency and magnitude with global climate change.     

Resistance and resilience of the forest soil microbiome to logging-associated compaction

Soil compaction is a major disturbance associated with logging, but we lack a fundamental understanding of how this affects the soil microbiome. We assessed the structural resistance and resilience of the microbiome using a high-throughput pyrosequencing approach in differently compacted soils at two forest sites and correlated these findings with changes in soil physical properties and functions. Alterations in soil porosity after compaction strongly limited the air and water conductivity. Compaction significantly reduced abundance, increased diversity, and persistently altered the structure of the microbiota. Fungi were less resistant and resilient than bacteria; clayey soils were less resistant and resilient than sandy soils. The strongest effects were observed in soils with unfavorable moisture conditions, where air and water conductivities dropped well below 10% of their initial value. Maximum impact was observed around 6–12 months after compaction, and microbial communities showed resilience in lightly but not in severely compacted soils 4 years post disturbance. Bacteria capable of anaerobic respiration, including sulfate, sulfur, and metal reducers of the Proteobacteria and Firmicutes, were significantly associated with compacted soils. Compaction detrimentally affected ectomycorrhizal species, whereas saprobic and parasitic fungi proportionally increased in compacted soils. Structural shifts in the microbiota were accompanied by significant changes in soil processes, resulting in reduced carbon dioxide, and increased methane and nitrous oxide emissions from compacted soils. This study demonstrates that physical soil disturbance during logging induces profound and long-lasting changes in the soil microbiome and associated soil functions, raising awareness regarding sustainable management of economically driven logging operations.     

Regional and local determinants of drought resilience in tropical forests

The increase in severity of droughts associated with greater mortality and reduced vegetation growth is one of the main threats to tropical forests. Drought resilience of tropical forests is affected by multiple biotic and abiotic factors varying at different scales. Identifying those factors can help understanding the resilience to ongoing and future climate change. Altitude leads to high climate variation and to different forest formations, principally moist or dry tropical forests with contrasted vegetation structure. Each tropical forest can show distinct responses to droughts. Locally, topography is also a key factor controlling biotic and abiotic factors related to drought resilience in each forest type. Here, we show that topography has key roles controlling biotic and abiotic factors in each forest type. The most important abiotic factors are soil nutrients, water availability, and microclimate. The most important biotic factors are leaf economic and hydraulic plant traits, and vegetation structure. Both dry tropical forests and ridges (steeper and drier habitats) are more sensitive to droughts than moist tropical forest and valleys (flatter and wetter habitats). The higher mortality in ridges suggests that conservative traits are not sufficient to protect plants from drought in drier steeper habitats. Our synthesis highlights that altitude and topography gradients are essential to understand mechanisms of tropical forest''s resilience to future drought events. We described important factors related to drought resilience, however, many important knowledge gaps remain. Filling those gaps will help improve future practices and studies about mitigation capacity, conservation, and restoration of tropical ecosystems.     

Enzymes and biogeochemical cycling in wetlands during a simulated drought

Possible interactions between soil enzymes and thebiogeochemistry of wetlands were investigated duringa field-based drought simulation. Under control(waterlogged) conditions, correlations were foundbetween the activity of the enzyme B-glucosidase andtwo properties associated with carbon cycling, namelyi) CH₄ release r = 0.79,p lt 0.01) and ii) dissolvedorganic carbon concentration (r= -0.81, p lt 0.01). In contrast,the transition to drought conditions resulted in correlations betweenB-glucosidase activity and certain mineralisationprocesses, namely the release of mg and Ca(r = 0.72, p lt 0.05). Sulphataseactivity correlated with changes in sulphate concentration during the droughtsimulation (r = 0.73, p lt 0.05).Further support for the suggested enzymic involvement in biogeochemicalprocesses was found in laboratory studies. Theseexperiments indicated that increasing the abundance ofB-glucosidase could stimulate trace gas emissions(p lt 0.001) and increase the concentration ofmagnesium and calcium (p lt 0.05). Increasedsulphatase abundance caused a suppression of methane emissions(p = 0.053).     

Restoration of wet meadows to enhance Gunnison sage-grouse habitat and drought resilience in arid rangelands

The arid sagebrush landscape of the Gunnison Basin, Colorado is home to the federally threatened Gunnison sage-grouse (GUSG; Centrocercus minimus) and is expected to become hotter and drier with a changing climate. Wet meadows within the sagebrush ecosystem are a critical lifeline for wildlife and livestock, particularly during drought years, yet they occupy less than 2% of the landscape. Our objective was to enhance wet meadow drought resiliency by slowing the water down, reconnecting floodplains, and increasing wetland vegetation. Indirectly we also aimed to enhance GUSG habitat and improve rangeland condition. Between 2012 and 2020, we constructed nearly 900 low-tech restoration structures (Zeedyk structures), across seven drainageways with wet meadows. Six of these years were drought years. We used a before-after-control-impact design to assess vegetation response. Vegetation data were collected on 135 randomly selected treated and 30 control transects. We found that 75% of ephemeral units and all of perennial units achieved or surpassed the wetland plant cover management goal of a 4% yearly increase. This led to an average enhancement of 40% in wetland plant cover in the treated drainageways. There was a significant positive difference between treated and control transects in 50% of the drainageways, regardless of hydroperiod status. The low-tech restoration structures were effective at rewetting perennial and ephemeral wet meadows within the arid landscape, even during a megadrought, and reduced non-native invasive weeds in all but one of the treated units. Forbs and grasses critical to sage-grouse and important to livestock operations increased in 67% of the units.     

神农架大九湖亚高山泥炭湿地水汽通量特征及其与相关环境因子的关系

以神农架大九湖亚高山泥炭湿地为对象,采用涡度相关技术,通过采集湿地水汽通量的年际数据,并进行数据统计和分析,研究水汽通量特征及其与环境因子的关系。结果显示：（1）大九湖泥炭湿地全年蒸散量占降水量的58.59%,能够满足大九湖生态系统水汽循环的需要。（2）大九湖泥炭湿地的水汽通量全年各月份日均变化大多为正值,即释放水汽,表明该地区总体表现为水汽源;在季节尺度上,水汽通量最大值出现在夏季,夏季水汽通量日均变化幅度最大。（3）净辐射月均变化幅度较大,其中夏季净辐射最大,占全年的34.96%。各季节的净辐射与水汽通量均呈正相关,春季、夏季和秋季的拟合效果（R²）均超过0.7,夏季最高（0.8347）,且高于其他同纬度6个地区。（4）除2018年1月外,各月份水汽通量与气温均呈显著正相关,特别是夏季最显著相关,这与夏季植物蒸腾和水分蒸发旺盛有关。（5）气温和净辐射对水汽通量的影响在各季节均显著,但各季节间有所差异。研究表明净辐射在大九湖泥炭湿地水汽循环中的作用大于气温对水汽通量的影响。     

Exploring how viruses enhance plants' resilience to drought and the limits to this form of viral payback

This article comments on: Virulence determines beneficial trade‐offs in the response of virus‐infected plants to drought via induction of salicylic acid     

Effects of snow pack reduction and drought on litter decomposition in subalpine grassland communities

Plant and Soil - In subalpine grasslands, litter decomposition controls soil nutrient availability and is highly sensitive to increasing intensity and frequency of extreme climate events,...     

Hydrologic alterations impact plant litter decay rate and ecosystem resilience in Mojave wetlands

Understanding ecosystem processes is vital for effective restoration of degraded ecosystems, especially wetlands. Restoration has become a necessity for management and conservation of the federally endangered Amargosa vole (Microtus californicus scirpensis) endemic to small, bulrush (Schoenoplectus americanus) dominated wetlands in the Mojave Desert. Recent data indicate catastrophic decrease of the vole population and its habitat from local alterations to hydrology, combined with diminished decomposition rates of bulrush, persistence of plant litter, and minimal plant growth except along narrow margins along stream edges. We conducted a series of three field and one greenhouse experiment(s) testing the effect of (1) moisture level on plant decay rate, (2) litter removal on plant regeneration, (3) the interactive effect of litter removal and moisture level increase on plant regeneration, and (4) potential germination rate of bulrush seeds under multiple hydrologic regimes to understand how hydrologic alteration and litter decay ultimately influences marsh regeneration. Results revealed decrease in water level caused a 20‐fold reduction in decomposition rates of a degraded marsh. Litter removal alone and in combination with water table restoration significantly and positively affected bulrush resprouting (p < 0.0001 for both). Seed bank experiments showed high rates of germination in saturated and flooded soil conditions, emphasizing the potential role of seedlings in ecosystem recovery. This study shows how the interaction of hydrologic change and decreased decomposition can shift an ecosystem toward limits of resilience. These results inform restoration strategies in arid‐region wetlands dominated by plants with slow litter decay where strategic litter removal may beneficially increase plant growth.