Degradation Gradient Research Articles

Soil Water Content Shapes Microbial Community Along Gradients of Wetland Degradation on the Tibetan Plateau.

Soil microbes are important components in element cycling and nutrient supply for the development of alpine ecosystems. However, the development of microbial community compositions and networks in the context of alpine wetland degradation is unclear. We applied high-throughput 16S rRNA gene amplicon sequencing to track changes in microbial communities along degradation gradients from typical alpine wetland (W), to wet meadow (WM), to typical meadow (M), to grassland (G), and to desert (D) in the Zoige alpine wetland region on the Tibetan Plateau. Soil water content (SWC) decreased as wetland degradation progressed (79.4 and 9.3% in W and D soils, respectively). Total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) increased in the soils of WM, and then decreased with alpine wetlands degradation from WM to the soils of M, G, and D, respectively. Wetland degradation did not affect microbial community richness and diversity from W soils to WM, M, and G soils, but did affect richness and diversity in D soils. Microbial community structure was strongly affected by wetland degradation, mainly due to changes in SWC, TOC, TN, and TP. SWC was the primary soil physicochemical property influencing microbial community compositions and networks. In wetland degradation areas, Actinobacteriota, Acidobacteriota, Cholorflexi, and Proteovacteria closely interacted in the microbial network. Compared to soils of W, WM, and M, Actinobacteriota played an important role in the microbial co-occurrence network of the G and D soils. This research contributes to our understanding of how microbial community composition and networks change with varied soil properties during degradation of different alpine wetlands.

Seasonal Changes in Hydrology and Permafrost Degradation Control Mineral Element‐Bound DOC Transport From Permafrost Soils to Streams

AbstractMineral elements bind to dissolved organic carbon (DOC) in permafrost soils, and this may contribute to the stabilization or the degradation of organic carbon along the soil to river continuum. Permafrost thaw enlarges the pool of soil constituents available for soil to river transfer. The unknown is how changes in hydrology upon permafrost degradation affect the connection between soil‐derived mineral element‐bound DOC and headwater streams. Here, we study Al, Fe, Ca, and DOC concentrations in water from a headwater stream at Eight Mile Lake, Alaska, USA (colloidal [0.22 μm–1 kDa] and truly dissolved [<1 kDa] fractions) and in soil pore waters sampled across a gradient of permafrost degradation at the same location. We target the peak flow to base flow transition to show that there is a narrow window of mineral element‐bound DOC colloid transport from soils to streams. We show that during spring thaw and maximum thaw there is an enhanced lateral transfer of mineral element‐bound DOC colloids in extensively degraded sites compared to minimally degraded sites. This is explained by a more rapid response of hydrology at peak flow to base flow transition at degraded sites. Our results suggest that ongoing permafrost degradation and the associated response of soils to changing hydrology can be detected by targeting the composition and size of mineral element‐DOC associations in soil waters and headwater streams during peak flow‐baseflow transitions.

Landscape pattern changes across alpine shrub meadows gradient in warm-season pastures on the Qinghai-Tibet Plateau

Grassland degradation has been one of the major ecological concerns on the Qinghai-Tibet Plateau (QTP) in recent years, but the degradation of alpine shrub meadows, and in particular the changes in its surface landscape pattern, has been less well assessed. This study selected a warm-season pasture on the QTP as a study area, and used an unmanned aerial vehicle (UAV) to collect aerial photographs along the degradation gradient from late June to early July 2018. We then classified the surface landscape as alpine shrub, alpine meadow, bare soil and plateau pika hole and analyzed the landscape pattern changes at different degradation levels. The results showed that the alpine shrub and alpine meadow dominated landscape degraded to a pattern of alpine meadow and bare soil dominance and pika hole pervasiveness, during which vegetation cover declined and the overall landscape pattern tended to fragment. Landscape pattern characteristics related to the area, density, connectivity and boundaries respond more clearly to the shrub degradation, with moderate degradation being the key stage at which the surface landscape pattern changes dramatically. Our study demonstrates a potential application of UAV technology in the study of grassland degradation. Future research should focus on the status, mechanisms and ecological effects of alpine shrub meadows degradation and the quantitative relationships between surface landscape patterns and ecological functions.

A Meta-Analysis on Degraded Alpine Grassland Mediated by Climate Factors: Enlightenment for Ecological Restoration.

Alpine grassland is the main ecosystem on the Qinghai-Tibet Plateau (QTP). Degradation and restoration of alpine grassland are related to ecosystem function and production, livelihood, and wellbeing of local people. Although a large number of studies research degraded alpine grassland, there are debates about degradation patterns of alpine grassland in different areas and widely applicable ecological restoration schemes due to the huge area of the QTP. In this study, we used the meta-analysis method to synthesize 80 individual published studies which were conducted to examine aboveground and underground characteristics in non-degradation (ND), light degradation (LD), moderate degradation (MD), heavy degradation (HD), and extreme degradation (ED) of alpine grassland on the QTP. Results showed that aboveground biomass (AGB), belowground biomass (BGB), Shannon-Wiener index (H′), soil moisture (SM), soil organic carbon (SOC), soil total nitrogen (TN), and available nitrogen (AN) gradually decreased along the degradation gradient, whereas soil bulk density (BD) and soil pH gradually increased. In spite of a tendency to soil desertification, losses of other soil nutrients and reduction of enzymes, there was no linear relationship between the variations with degradation gradient. Moreover, the decreasing extent of TN was smaller in areas with higher precipitation and temperature, and the decreasing extent of AGB, SOC, and TN was larger in areas with a higher extent of corresponding variables in the stage of ND during alpine grassland degradation. These findings suggest that in areas with higher precipitation and temperature, reseeding and sward cleavage can be used for restoration on degraded alpine grassland. Fencing and fertilization can be used for alpine grassland restoration in areas with lower precipitation and temperature. Microbial enzymes should not be used to restore degraded alpine grassland on a large scale on the QTP without detailed investigation and analysis. Future studies should pay more attention to the effects of climate factors on degradation processes and specific ecological restoration strategies in different regions of the QTP.

Soil quality indicators along a degradation gradient in central Iran: comparison of two regions with contrasting grazing systems

ABSTRACT Soil degradation poses serious environmental problems and requires quantitative assessment. This study aimed to investigate the soil properties in rangelands with different management conditions. Based on the assessment of soil erosion, vegetation cover, vegetation composition, and vegetation vigor, 56 sites were selected in rangelands with moderate, poor, and very poor conditions located in 15 grazing-free areas and one wildlife refuge region. Soil samples (0–10 cm layer) were collected from these sites through a systematic-random method to compare their physical and chemical properties. Results showed that soil organic carbon (OC) and total nitrogen content were significantly different between sites with different range conditions. The mean weight diameter of water-stable aggregates and structural stability index in moderate rangelands were 1.56 mm and 3.98%, respectively, and declined towards more degraded rangeland (i.e. 0.84 mm and 0.83%). Grazing-free rangelands exhibited a relatively larger OC deficit; hence specific management measures and control of grazing are required to enhance the quality of soil in these sites. This study highlighted the role of organic matter in preserving soil structural stability. Increasing protection level of rangelands and decreasing grazing pressure may preserve soil quality and combat desertification in these arid regions.

Alpine meadow degradation depresses soil nitrogen fixation by regulating plant functional groups and diazotrophic community composition

Biological nitrogen fixation (BNF), a function performed by diazotrophic microbes, plays an essential role in nitrogen (N) bioavailability in terrestrial ecosystems. However, little is known about the effects of meadow degradation on soil BNF and diazotrophic communities in alpine meadows. We investigated changes in soil BNF and their potential drivers in alpine meadows along a degradation gradient on the Tibetan Plateau (non-degraded, lightly degraded, moderately degraded, and severely degraded meadows) using real-time quantitative PCR and amplicon sequencing. Soil BNF rates decreased significantly along the meadow degradation gradient with a range of 17.34–79.84 nmol C2H4 g−1 dry soil d−1 across all sites. The highest BNF rate in the non-degraded meadow was 1.5–4.6-fold higher than that in the degraded meadows. The abundance and diversity of diazotrophs measured by nifH abundance and Shannon diversity was also decreased in the degraded meadows, accompanied by decreases in plant biomass, soil moisture, and nutrient content (C, N). Soil BNF rate was correlated with plant biomass, soil nutrient content, and diazotrophic abundance (including Nostoc, Scytonema, Rhodopseudomonas, and unidentified genera within the Rhizobiales and Proteobacteria). The community composition of diazotrophs differed markedly among sites with different levels of degradation, with both autotrophic (Cyanobacteria) and heterotrophic (Proteobacteria) diazotrophs contributing significantly to BNF. The plant functional groups, particularly the sedge family, were the primary drivers of soil BNF rates via mediating soil moisture, nutrient content (dissolved organic C and N), nifH gene abundance, and diazotrophic community composition. Our results reveal the main drivers of decreased BNF during alpine meadow degradation and emphasize the importance of plant functional groups in shaping the diazotrophic community and regulating the BNF rate. This information can be applied to the restoration of degraded meadow ecosystems.

滇西北退化高寒草甸植物群落结构对刈割的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 滇西北退化高寒草甸植物群落结构对刈割的响应 DOI: 10.5846/stxb202108112210 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 第二次青藏高原综合科学考察研究项目（2019QZKK0307）；国家自然科学基金项目资助（31901394，31860620） Responses of plant community structure to mowing in the degraded alpine meadows, Northwestern Yunnan Province 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:为探究滇西北不同退化级别高寒草甸植物群落结构对外界干扰的响应敏感性，以香格里拉市的典型高寒草甸为研究对象，于2018-2020年在三个退化梯度上（严重退化，S1；中度退化，S2；轻度退化，S3）开展控制刈割实验，进而分析草甸植物物种丰富度、群落组成相似性、群落复杂度和关键种的变化规律。结果表明：（1）刈割后，S1的物种丰富度显著增加（P<0.05），S2和S3的物种丰富度未发生显著变化（P>0.05）；（2）相较于S2和S3，S1梯度的植物群落组成变化最大；（3） S1、S2和S3的植物群落复杂度在刈割后均呈先下降后增加的趋势，但S1的植物群落复杂度变化幅度高于S2和S3；（4）刈割导致各退化草甸植物群落的关键种发生了变化，2018、2019和2020年S1梯度的关键种在豆科（Leguminsae）和蔷薇科（Rosaceae）之间变化，S2梯度的关键种在禾本科（Gramineae）和菊科（Compositae）之间变化，S3梯度的关键种在蔷薇科（Rosaceae）、菊科（Compositae）和禾本科（Gramineae）之间转变。研究表明，滇西北高寒草甸植物物种丰富度、群落组成和群落复杂度对外界干扰响应的敏感性可能随退化加剧而上升，但群落关键种的响应过程较复杂。 Abstract:To explore the sensibility of the response of plant community structure to external disturbances under different degradation conditions in the Northwestern Yunnan Province (NWYP), we conducted a mowing experiment at three degradation gradients (i.e., S1:severe degradation; S2:moderate degradation; S3:slight degradation) in an alpine meadow in Shangri-La from 2018 to 2020. The effects of mowing on community structure indicators, including species richness, community similarity, community complexity and keystone species were analyzed. The results showed that (1) after mowing, the species richness of S1 increased significantly (P<0.05), while the species richness of S2 and S3 did not change significantly (P>0.05). (2) Mowing caused a greater change in community similarity in S1 than in S2 and S3. (3) The network connectivity of plant community decreased firstly and then increased after mowing in all degradation levels. Moreover, the change range of community complexity in S1 was higher than in S2 and S3. (4) The keystone species of plant communities changed in 2018, 2019 and 2020. In S1, the keystone species varied between Leguminsae and Rosaceae. In S2, the keystone species varied between Gramineae and Compositae. In S3, the keystone species varied among Rosaceae, Compositae and Gramineae. The study suggests that the sensitivity of the response of species richness, community composition and complexity of plant community to external disturbance might increase with meadow degradation levels, while the shifting of the keystone species would be complex in NWYP. 参考文献 相似文献 引证文献

Rangeland Degradation Impacts on Vegetation Cover, Soil Properties and Ecosystem Functioning in an Arid and Semi-Arid Climate, South Africa

The negative effect of soil erosion and soil compaction is well documented for the purpose of optimum rangeland functioning, while the impact of rangeland degradation on effective soil depth is seldom quantified. The aim of this study was to quantify the response of vegetation cover and soil properties, particularly effective soil depth and soil texture to rangeland degradation. Forty-one farms were sampled in the arid and semi-arid climate of South Africa. Within these farms, data was collected over a vegetation degradation gradient. Results showed a significant decline in relative basal cover (94% ± 15% to 39% ± 17%) and soil depth (90% ± 14% to 73% ± 24%) as rangeland degraded. Soil texture changes over the degradation gradients vary for different homogeneous vegetation types. Indications regarding the loss of a functioning rangeland ecosystem were also demonstrated, using objective long-term relations between rangeland conditions and grazing capacity. The study highlights the importance of sustainable rangeland management practices to reduce the loss in effective soil depth and to ensure the sustainable utilization of the rangeland ecosystem. These results can probably extrapolate to other arid and semi-arid rangelands worldwide.

Exchangeable Ca2+ content and soil aggregate stability control the soil organic carbon content in degraded Horqin grassland

Grasslands store 20–30% of global soil organic carbon (SOC) but a majority of grasslands are suffering degradation accompanied by SOC loss. SOC stock is determined by the balance between C input from plants and C output from microbial decomposition, but the relative importance of these factors in controlling SOC and the stabilization mechanisms of SOC are poorly understood. Here, we investigated the main factors influencing SOC loss along a grassland degradation gradient in the Horqin grassland, including non-degraded (ND), lightly degraded (LD), moderately degraded (MD), and severely degraded (SD) grasslands. The contents of SOC, TN and TP at the ND and LD sites were significantly higher than those at the MD and SD sites. Plant aboveground, belowground and litter biomass significantly decreased with the intensification of degradation. Compared to the ND site, the mean weight diameter of soil aggregates decreased by 8.70%, 17.39% and 26.1% at the LD, MD and SD sites, respectively. Exchangeable Ca2+ and Mg2+ contents also decreased along the degradation gradient. Moreover, the results of structural equation modeling indicated that grassland degradation reduced plant biomass, resulting in an increase in soil available phosphorus content, thus causing less energy losses for microbes through their deployment of extracellular enzymes, eventually leading to an increase in microbial carbon use efficiency. Correlation analysis also confirmed that microbial carbon use efficiency was positively correlated with the ratio of G+/G-. The results of boosted regression tree model suggested that exchangeable Ca2+ and mean weight diameter were the two most influential factors on SOC among the 13 studied variables. Stabilization mechanisms linked to chemical stabilization by polyvalent cations and soil aggregation were the most important controlling factors on SOC content during grassland degradation. In summary, although microorganisms mitigated soil carbon loss to some extent by decreasing their total biomass and increasing their carbon use efficiency, the weakened physical protection of SOC resulted in SOC loss during grassland degradation.

Soundscapes predict species occurrence in tropical forests

Accurate occurrence data is necessary for the conservation of keystone or endangered species, but acquiring it is usually slow, laborious and costly. Automated acoustic monitoring offers a scalable alternative to manual surveys but identifying species vocalisations requires large manually annotated training datasets, and is not always possible (e.g. for lesser studied or silent species). A new approach is needed that rapidly predicts species occurrence using smaller and more coarsely labelled audio datasets. We investigated whether local soundscapes could be used to infer the presence of 32 avifaunal and seven herpetofaunal species in 20 min recordings across a tropical forest degradation gradient in Sabah, Malaysia. Using acoustic features derived from a convolutional neural network (CNN), we characterised species indicative soundscapes by training our models on a temporally coarse labelled point‐count dataset. Soundscapes successfully predicted the occurrence of 34 out of the 39 species across the two taxonomic groups, with area under the curve (AUC) metrics from 0.53 up to 0.87. The highest accuracies were achieved for species with strong temporal occurrence patterns. Soundscapes were a better predictor of species occurrence than above‐ground carbon density – a metric often used to quantify habitat quality across forest degradation gradients. Our results demonstrate that soundscapes can be used to efficiently predict the occurrence of a wide variety of species and provide a new direction for data driven large‐scale assessments of habitat suitability.

The effect of swidden agriculture on ant communities in Madagascar

Swidden agriculture is a widespread subsistence farming method in the tropics, which is being intensified as human populations grow. This study is the first to investigate the impacts of land degradation from swidden upon ant species (both native and introduced) across the full degradation gradient, from forest, to tree fallows, to shrub fallows, to exhausted land. Ant communities in closed canopy forests had higher species diversity and were taxonomically distinct, but as land became increasingly degraded, a significant reduction in overall and native species richness was detected, as were changes in overall community composition. Whilst native species decreased across the degradation gradient, introduced species increased. There was also a significant correlation in community compositional changes between native and introduced species which was independent from environmental factors. Co-occurrence analysis, however, suggested there was little evidence that introduced species were significantly impacting the communities of native species. This suggests these patterns are both separately driven by habitat degradation. Degraded fallow habitats were found to harbour unique and endemic species, including 22.4% of the species found in closed canopy forest. Together, our results highlight the potentially detrimental effects of further spread and increased intensification of swidden systems in tropical ecosystems. The conservation of existing closed canopy forests is of utmost importance but we also highlight that the fauna of degraded swidden habitats could still be important for biodiversity conservation in agricultural landscapes across the tropics.

Alpine meadow degradation enhances the temperature sensitivity of soil carbon decomposition on the Qinghai–Tibetan plateau

Grassland degradation is widespread globally, yet limited information is available on the effects and mechanisms of grassland degradation regarding the response of soil organic carbon (SOC) to temperature change. This is especially true for alpine regions, which can have high SOC storage and are extreme vulnerability to global warming. Here, we studied the temperature sensitivity of SOC decomposition (Q10, proportional change in decomposition rate for a 10 °C difference in temperature) in both the topsoil (0–10 cm depth) and subsoil (20–30 cm) along an alpine meadow degradation gradient on the Qinghai–Tibetan plateau (QTP). Q10 values were increased in response to alpine meadow degradation (severely degraded (2.42) > moderately degraded (2.20) > non-degraded (2.11)) and were higher in subsoil (2.34) than in topsoil (2.14) as a whole. Soil carbon quantity and quality and extracellular enzyme activities all decreased significantly with increasing degradation levels and soil depths. Among all the factors considered (soil texture; soil pH; carbon quantity, availability, and quality; and enzyme activities), Q10 values were found to be primarily mediated by carbon quality and enzyme activities. This result supported the “carbon-quality temperature” hypothesis in degraded alpine grassland, and that considering soil carbon quality and enzyme activity could improve predictions of the feedbacks between soil carbon and global warming under grassland degradation. Our findings suggest that alpine meadow degradation will further increase the losses of SOC in a warming climate, making the ecosystem more vulnerable to climate change.

Land use has little influence on the soil seed bank in a central African moist forest

AbstractRegeneration of tropical forest occurs naturally and mainly through early secondary succession by soil seed banks. Here, we analyzed seed bank variation in density and diversity along a degradation gradient. We also explored the relationship (similarity in composition) between the seed and seedling banks and the overstory vegetation. The investigated forests were located at Dja Fauna Reserve and its surroundings, south‐eastern Cameroon. We sampled 33 one‐ha forest plots scattered in a protected area, in a logging concession and in community forests. Within each plot, we inventoried the seed bank in the litter and in four successive soil layers of 5 cm depth interval, and the standing vegetation. Seed density significantly varied with sampling depth but not between land use types. A total of 181 morphospecies were identified. Trees species accounted for 46% of seeds with pioneer species dispersed by animals dominating the seed bank. Species diversity and composition strongly varied with the sampling depth; the litter seed bank was more similar in composition to the soil seed bank than to the seedling bank, sapling, and forest stands. We highlighted the presence of a dense and diverse seed bank in each land use type. We also showed the differentiation of each sampling depth in terms of species composition, thus revealing their complementarity in the dynamics of natural regeneration. The dominance of pioneers in the seed bank and weak relationship with the overstory are universal for tropical forests and logically follow from forest succession after disturbance.Abstract in French is available with online material.

Distribution and functional groups of soil aggregate-associated organic carbon along a marsh degradation gradient on the Zoige Plateau, China

Alpine marsh wetlands in the Qinghai-Tibetan Plateau are ecological hotspots for global carbon (C) cycling in Central Asia; however, the soil C sinks are increasingly limited by marsh degradation. To assess the physical mechanisms by which changes in the soil C sequestration occur, the distribution and functional groups of soil organic C (SOC) in aggregates along a marsh degradation gradient on the Zoige Plateau in China were investigated using soil samples collected from differently degraded marshes. Our results showed that, beyond the state of light degradation, the large aggregate content decreased significantly by 31.1–55.2%, while the micro-aggregate content increased significantly by 23.1–93.1%. The SOC content in the aggregates decreased significantly by 39.1–84.8% and the dominant aggregate size for SOC preservation decreased to small or micro-aggregate. Marsh degradation also decreased the relative ratio of aliphatic-C while increasing that of alcohol and phenolic-C, and polysaccharide-C. Index I (relative decomposition of SOC in aggregates) was 73.5–429.0% higher for degraded marshes than for relatively pristine marsh (RPM), while Index Ⅱ (relative recalcitrance of SOC in aggregates) was 13.8–79.5% lower in comparison. Therefore, we concluded that marsh degradation probably reduces the organic C sequestration capacity of soil by increasing the decomposition of SOC in aggregates after both the dominant aggregate size for SOC preservation and aggregate stability decreased. This result represents the physical mechanism by which the decrease in SOC content occurs in response to marsh degradation in alpine regions.

The conversion of natural riparian forests into agricultural land affects ecological processes in Atlantic forest streams

Agricultural practices affect the integrity of riparian areas of small streams. In this study we tested the hypothesis that the increase of agricultural activities influences negatively the functional conditions of the low order streams in the Atlantic forest of southern Brazil. Litter bags with leaves of Nectandra megapotamica (Spreng.) Mez were located in eight streams with different amounts of woody vegetation and agriculture land uses in their riparian zones. After 7, 15 and 30 days, the litter bags were removed for identification of associated invertebrates and determination of decomposition rate. Decomposition rates were negatively influenced by agriculture in the riparian zone while primary production was positively influenced. On the other hand, the decomposition mediated by microorganisms did not vary along the degradation gradient. The abundance of collectors increased in streams adjacent to agricultural land while the abundance of shredders was decreased. Our results showed that algae biomass and leaf decomposition were sensitive to the replacement of native vegetation by agricultural use. However, the trophic structure of invertebrates was moderately sensitive to agricultural land use.

Soil seed bank dynamics are regulated by bird diversity and soil moisture during alpine wetland degradation

Increased anthropogenic activities and global warming have accelerated the loss of wetlands worldwide. Given that a seed bank plays an important role in maintaining species diversity, understanding the regulatory mechanism of seed bank dynamics is crucial for using seed banks for restoration of species diversity in degraded wetlands. We collected data on biotic (i.e., aboveground vegetation, birds and rodents) and abiotic (i.e., soil environmental factors) ecosystem components as predictors along a degradation gradient in an alpine wetland and then to identify the relative importance of multiple sets of predictors in the regulating seed bank dynamics (i.e., species richness and composition). Seed bank dynamics were less responsive to environmental change than the aboveground vegetation during wetland degradation. Soil moisture and bird richness were more important than other predictors in regulating species richness and species composition of the seed bank, respectively. Our results suggest that seed banks can be used as potential resources for restoration of degraded wetlands. Birds play an important role in regulating the diversity of wetland ecosystems (seed bank is a potential diversity provider). Therefore, more attention should be paid to the protection of bird diversity in the process of conservation and restoration of degraded wetlands.

Characterization of the spatial distribution of plateau pika burrows along an alpine grassland degradation gradient on the Qinghai-Tibet Plateau.

Plateau pika burrows are common feature of degraded grassland in the Qinghai–Tibet Plateau (QTP) and serve as an important indicator of pika activity and grassland degradation. However, the current understanding of the spatial pattern changes of pika burrows and their critical thresholds across a degradation gradient in alpine grassland is deficient. In this study, we investigated and quantified changes in the spatial pattern of plateau pika burrows under typical degraded alpine shrub meadows in the northeastern QTP using an unmanned aerial vehicle and landscape pattern metrics. The degradation of the alpine shrub meadow leads to a change in landscape pattern from a two‐layered structure of alpine shrub and alpine meadow to a mosaic of alpine meadow and bare soil, with plateau pika burrows scattered throughout. Moderate degradation is the tipping point for changes in surface landscape patterns, followed by the disappearance of alpine shrub, the retreat of alpine meadows and the encroachment of bare soil, and the increasing density and size of pika burrows. The area characteristics of alpine meadows have influenced changes in the spatial pattern of pika burrow, and maintaining its proportional area is a vital measure to control the threat of pika burrows to pastures. The results of this paper provide a methodological reference and guidance for the sustainable utilization of grassland on the QTP.

Sheltering Role of Well-Decayed Conifer Logs for Forest Floor Fungi in Long-Term Polluted Boreal Forests.

Coarse woody debris (CWD) provides food and shelter to a large proportion of forest biota and is considered vital for biodiversity during periods of harsh weather. However, its importance in long-term stressed ecosystems remains largely unknown. In this work, we explored the contribution of CWD to fungal diversity along the gradient of boreal forest degradation caused by 77 years of heavy industrial emissions. We analyzed the diversity and composition of fungi in 270 samples of well-decayed Picea abies and Abies sibirica logs, as well as forest litter both adjacent to and distant from the logs. Compared with forest litter, the wood had higher water content and possessed substantially lower concentrations of heavy metals, which suggests its potential favorability for biota in polluted areas. The pollution-induced loss of fungal diversity in forest litter reached 34% and was stronger in the microhabitats not influenced by CWD. Meanwhile, wood fungal communities lost less than 10% of their total richness and even increased in alpha diversity. These processes led to the diversity and compositional convergence of fungal communities from different microhabitats and substrates in polluted areas. Despite this, the importance of wood and CWD-influenced microhabitats for fungal diversity maintenance was low. Apart from wood-associated fungi, the taxa whose diversity increased in the wood of polluted areas were ectomycorrhizal fungi and eurytopic soil saprotrophs (Mucoromycota, Mortierellomycota, Eurotiomycetes, and Helotiales) that easily tolerate highly toxic litter. Within the majority of pollution-sensitive soil saprotrophic groups, only terricolous Tricholomataceae benefit from CWD as microrefugia. Upon considering the ecological variability within low-rank taxa, the importance of decayed logs as safe sites can be high for certain soil-inhabiting fungal groups in polluted areas.

Reducing plant community variability and improving resilience for sustainable restoration of temperate grassland

Grassland ecosystem is important for the realization of the global sustainable development goals (e.g. Goal 15) since it provides irreplaceable services for human beings, supporting human health and sustainable development. Most studies have focused on improving grassland restoration techniques, but less attention has been paid to grassland ecosystem stability in succession. Plant community stability of temperate grassland in arid and semi-arid regions is analyzed through 38 sampling sites in Inner Mongolia, China. The degradation succession sequence of grassland is established by principal component analysis, and the species diversity and functional diversity along degradation gradient analyzed by multivariate statistical analysis. The results show that (1) functional diversity has higher explanatory power for community stability than species diversity due to the functional dispersion of plant traits; (2) climate factors rather than grazing or soil control plant community diversity and stability at regional scale; (3) the resistance of plant community does not change in degradation succession, but the trade-off effect of stability components in different plant communities differ, such as the order of trade-off effects (e.g. community resilience (ET)＞community resistance (RT)＞structural variability (St)＞functional variability (Fu) in the community dominated by Stipa grandis, RT＞ET＞St＞Fu in Leymus chinensis community, St＞ET＞Fu＞RT in Stipa capillata community, RT＞St＞Fu＞ET in Artemisia frigida community, St＞Fu＞ET＞RT in Cleistogenes squarrosa community, and Fu＞St＞RT＞ET in Artemisia halodendron community); (4) grassland ecosystem with higher diversity shows greater resilience and lower variability than those with single species, which supports the established diversity hypothesis. Furthermore, sustainable grassland restoration should reduce community variability and improve resilience. These findings highlight the response of diversity to stability in temperate grassland and provide scientific support for grassland ecosystem protection and restoration.

Mapping Boreal Forest Spruce Beetle Health Status at the Individual Crown Scale Using Fused Spectral and Structural Data

The frequency and severity of spruce bark beetle outbreaks are increasing in boreal forests leading to widespread tree mortality and fuel conditions promoting extreme wildfire. Detection of beetle infestation is a forest health monitoring (FHM) priority but is hampered by the challenges of detecting early stage (“green”) attack from the air. There is indication that green stage might be detected from vertical gradients of spectral data or from shortwave infrared information distributed within a single crown. To evaluate the efficacy of discriminating “non-infested”, “green”, and “dead” health statuses at the landscape scale in Alaska, USA, this study conducted spectral and structural fusion of data from: (1) Unoccupied aerial vehicle (UAV) multispectral (6 cm) + structure from motion point clouds (~700 pts m−2); and (2) Goddard Lidar Hyperspectral Thermal (G-LiHT) hyperspectral (400 to 1000 nm, 0.5 m) + SWIR-band lidar (~32 pts m−2). We achieved 78% accuracy for all three health statuses using spectral + structural fusion from either UAV or G-LiHT and 97% accuracy for non-infested/dead using G-LiHT. We confirm that UAV 3D spectral (e.g., greenness above versus below median height in crown) and lidar apparent reflectance metrics (e.g., mean reflectance at 99th percentile height in crown), are of high value, perhaps capturing the vertical gradient of needle degradation. In most classification exercises, UAV accuracy was lower than G-LiHT indicating that collecting ultra-high spatial resolution data might be less important than high spectral resolution information. While the value of passive optical spectral information was largely confined to the discrimination of non-infested versus dead crowns, G-LiHT hyperspectral band selection (~400, 675, 755, and 940 nm) could inform future FHM mission planning regarding optimal wavelengths for this task. Interestingly, the selected regions mostly did not align with the band designations for our UAV multispectral data but do correspond to, e.g., Sentinel-2 red edge bands, suggesting a path forward for moderate scale bark beetle detection when paired with suitable structural data.