Shrub Sites Research Articles

Vegetation moisture estimation in the Western United States using radiometer-radar-lidar synergy

Monitoring vegetation moisture conditions is paramount to better understand and assess drought impacts on vegetation, enhance crop yield predictions, and improve ecosystem models. Passive microwave remote sensing allows retrievals of the vegetation optical depth (VOD; [unitless]), which is directly proportional to the vegetation water content (VWC; in units of water mass per unit area [kg/m2]). However, VWC is largely dependent on the dry biomass and structure imprints on the VOD signal. Previously, statistical models have been used to isolate the water component from the biomass and structure components. Physically-based approaches have not yet been proposed for this goal. In this study, we present a multi-sensor semi-physical approach to retrieve the vegetation moisture from the VOD and express it as Live Fuel Moisture Content (LFMC [%]; the percentage of water mass per dry biomass unit). The study is performed in the western United States for the period April 2015 – December 2018. There, in situ LFMC samples are available for assessment. We rely on a VOD model based on vegetation height data from GEDI/Sentinel-2 and radar backscatter from Sentinel-1, which account for the biomass and structure components. Vegetation moisture is retrieved at L-, X- and Ku-bands by minimizing the difference between the modeled VOD and the VOD estimates from SMAP (L-band) and AMSR-2 (X- and Ku-band) satellites. Results show that the LFMC retrievals are independent of canopy height, land cover, and radar backscatter, demonstrating the capability of the proposed algorithm to separate water dynamics from the biomass/structure component in VOD. LFMC estimates at X- and Ku-bands reproduce well the expected spatio-temporal dynamics of in situ LFMC. Results show good agreement with in situ at a regional scale, with Pearson's correlations (r) between in situ LFMC samples and LFMC estimates of 0.64 (Ku-band), 0.60 (X-band) and 0.47 (L-band). Similar results are obtained independently for shrub and forest sites at X- and Ku-bands. In most comparisons between in situ and estimated LFMC, biases are below 10% of the dynamic range of LFMC. Performance at L-band is limited by the fact that this frequency senses the full vertical extent of the canopy, while in situ samples are taken only from top of canopy leaves to which X- and Ku-bands are much more sensitive. More insight will be needed for grasslands (r = 0.44 at X-band) using time-dynamic canopy height data. Furthermore, a pixel-scale assessment is conducted, showing a good agreement in most sites (r > 0.6). The proposed method can be tailored to exploit the synergies of past (e.g., AMSR-E), current (e.g., AMSR-2) and future satellite sensors such as CIMR and ROSE-L for global vegetation moisture mapping at different canopy layers.

Impacts of shrub removal on snow and near-surface thermal conditions in permafrost terrain adjacent to the Dempster Highway, NT, Canada

The Peel Plateau, NT, Canada, is an area underlain by warm continuous permafrost where changes in soil moisture, snow conditions, and shrub density have increased ground temperatures next to the Dempster Highway. In this study, ground temperatures, snow, and thaw depth were monitored before and after tall shrub removal (2014). A snow survey after tall shrub removal indicated that snow depth decreased by a third and lowered winter ground temperatures when compared with control tall shrub sites. The response of ground temperatures to shrub removal depended on soil type. The site with organic soils had cooler winter temperatures and no apparent change in summer temperatures following shrub removal. At sites with mineral soil, moderate winter ground cooling insufficiently counteracted increases in summer ground heat flux caused by canopy removal. Given the predominance of mineral soil along the Dempster, these observations suggest tall shrub removal is not a viable short-term permafrost management strategy. Additionally, the perpendicular orientation of the Highway to prevailing winter winds stimulates snow drift formation and predisposes the site to warmer permafrost temperatures, altered hydrology, and tall shrub proliferation. Subsequent research should explore the effectiveness of tall shrub removal at sites with colder winter conditions or different snow accumulation patterns.

Transpiration and evaporative partitioning at a boreal forest and shrub taiga site in a subarctic alpine catchment, Yukon territory, Canada

AbstractDespite widespread observations of climate‐change induced treeline migration and shrubification, there remains few direct measurements of transpiration and dynamics of evaporative partitioning in northern climates. Here, we present eddy covariance and sap flow data at a low elevation boreal white spruce forest and a mid‐elevation shrub taiga comprised of tall willow (Salix spp.) and birch (Betula spp.) in a subarctic, alpine catchment in Yukon Territory, Canada over two hydrologically distinct years. Specific research questions addressed were: (1) How do contributions of T to ET vary between sites and years? and (2) What are the primary meteorological, phenological, and soil moisture controls and limits on ET and T across vegetation covers? In the mid‐growing season, mean T rates were greater at the dense shrub site (2.0 ± 0.75 mm d−1) than the forest (1.47 ± 0.52 mm d−1). During this time, T:ET was lower at the forest (0.48) than at the tall, dense shrub site (0.80). Of the 2 years, 2020 was considerably wetter and cooler than 2019 during the growing season. At the shrub site, during the mid‐growing season (July 1‐Aug 15), T dropped considerably in 2020 (−26%), as T was suppressed during the short, wet growing season. In contrast, T at the forest was only moderately suppressed (−3%) between years in this same period. Evapotranspiration was more strongly controlled by air temperature during the early and late season at the forest, while ET at the shrub site was more sensitive to warmer temperatures in the mid‐growing season. Distinct differences in sap flux densities, sensitivities to environmental drivers, and stomatal resistances existed between shrub species. Results suggest that warming temperatures, increases in growing season length, and increased rainfall will cause differences in evaporative response and partitioning over complex, heterogenous alpine watersheds.

Soil microbial resource limitation along a subarctic ecotone from birch forest to tundra heath

Soil microorganisms regulate the decomposition of organic matter. However, microbial activities can also be rate-limited by the resource in lowest supply. Arctic ecosystems are being exposed to pronounced climate warming, with arctic greening, treeline advance and shrubification resulting in increased plant-derived carbon (C) inputs to soils, and faster rates of decomposition releasing mineral nutrients, potentially shifting the limiting factor for microbial growth. Here we used a “space-for-time” approach across a subarctic ecotone (birch forest, tree line, shrub and tundra sites). N and P fertilization treatments were also applied in the field, to test whether changes in resource limitation could be induced through nutrient loading of soils. In these soils, we measured the responses of bacterial and fungal growth as well as soil respiration to full factorial additions of C, nitrogen (N) and phosphorus (P) (“limiting factor assays”: LFA) to infer how the limiting factor for microbial growth would be affected by future climate change. We found that bacteria were triple-limited by C, N and P, while fungi were co-limited by C and N, with no shift in the limiting factor for bacterial or fungal growth across the ecotone. However, bacterial responses to the LFA were stronger in the tundra, showing 9-fold stronger increases in response to LFA-CNP addition compared to that in the forest. In contrast, fungal responses to the LFA were stronger in the forest, showing a 120% higher growth in response to LFA-CN addition, with no detectable response to LFA-CN addition in the tundra. These contrasting results suggested competitive interactions for resources between the two decomposer groups. Fertilization in the field shifted the bacterial resource limitation, but had no effect on the limiting factor for fungal growth. Together, our findings suggest that resource limitations for soil microorganisms will not change due to future warming, but rather affect degrees of fungal-to-bacterial dominance.

Control of Mosses on Water Flux in an Alpine Shrub Site on the Qilian Mountains, Northwest China.

Mosses are an important component of the alpine shrub, but little is known about their contribution to ecosystem water and energy exchange, especially potential opportunities for alpine shrub expansion under a warming climate. We studied the role of mosses in alpine shrub evapotranspiration by conducting herb and moss removal experiments with different Potentilla fruticosa L. shrub coverage in the Qilian Mountains, Northwest China. The understory evapotranspiration was measured using lysimeters in different shrub coverage (dense shrub cover, medium shrub cover, and thin shrub cover) during the growing season of 2012. The understory evapotranspiration is about 1.61 mm per day in the control treatment (intact moss and herbs) during the growing season, and the evapotranspiration rates differed significantly between canopy covers. We found a 22% increase in evapotranspiration losses after removing the moss layer compared to the control treatment lysimeter with an intact moss layer in the shrub site. This suggests that most of the understory evaporation originated from the organic layer underlying the moss layer. Given this study's large moss evaporation rates, understory contributions cannot be ignored when interpreting eddy covariance data for the whole alpine ecosystem. Our results show that mosses may exert strong controls on understory water fluxes in alpine shrub meadow ecosystems and suggest that changes in moss cover may have significant consequences for season frozen soil thaw.

Measuring peat motion and water table dynamics on tropical peatlands using high-resolution time-lapse camera in four different land cover types across South Sumatra and Central Kalimantan

Peat soils are known to be the most capable soil type to store a huge amount of carbon. However, peatland ecosystems are often disturbed by anthropogenic activities such as excessive water drainage, leading to rapid peat subsidence and carbon loss. Due to its dynamic properties, peatland ecosystem needs to be monitored over time to prevent unwanted socio-economic and environmental impacts. Nonetheless, field measurement of peat motion and subsidence often requires complex and expensive tools. This research aims to measure peat motion and water table dynamics in four sites across South Sumatra and Central Kalimantan Provinces. Peat motion and water table data were observed using a time-lapse camera for approximately a year period. Results of this study showed a good relationship of peat surface motion and water table dynamics with R2 values ranging from 0.74 and 0.95. In Central Kalimantan, peat surface motion indicates a downward motion with the amplitude of 1.66 cm and 0.56 cm, and net subsidence of 1.35 cm and 0.47 cm, over shrub and coconut plantation sites, respectively. In South Sumatra, peat surface showed a high degree of fluctuation, with amplitudes of 4.89 and 4.80 cm, and net subsidence of 1.70 and 0.62, observed on oil palm and forest sites, respectively.

The Right Place at the Right Time: Seasonal Variation of Bacterial Communities in Arid Avicennia marina Soils in the Red Sea Is Specific to Its Position in the Intertidal

Mangrove forests play an important role in facilitating biogeochemical pathways and cycling acting as blue carbon sinks. These services are primarily regulated by the activity of the soil microbiome. However, there is still limited research into spatial and temporal variation patterns of bacterial community assemblages in mangrove soils. This study investigated important ecological scales of microprocesses that govern microbial communities in an arid mangrove ecosystem. Shifts in microbial community composition were influenced by fluctuations in environmental factors within the mangrove forests of the Red Sea influenced by seasonal changes in sea level. Notably, in summer microbial communities in shrub sites differed significantly from the fringe and the winter samples, with lower alpha diversity yet a higher dominance of specialized species capable of surviving in extreme conditions. The onset of dispersal limitation and heterogenous selection and the reduction of drift are likely the main forces shaping community assemblages. Specifically, in summer lower mean tidal levels eliminate tidal inundation creating a harsh high salinity and high temperature environment with no tidal connection thereby influencing the onset of dispersal limitation. An increased understanding of the spatial and temporal variation of bacterial communities is critical when assessing delivery of ecosystem services and their role in soil biogeochemical processes.

Stable Isotope Analysis of Plant Water and Soil Water in a Pair of Grassland and Shrub Sites on the Qinghai-Tibet Plateau

Stable Isotope Analysis of Plant Water and Soil Water in a Pair of Grassland and Shrub Sites on the Qinghai-Tibet Plateau

Environment and plant traits explain shrub biomass allocation and species composition across ecoregions in North China

AbstractQuestionsInterspecific differences in plant biomass allocation reflect plant nutrient use strategy, determining species fitness under different environmental conditions. However, plant biomass allocation may be affected by both habitat and plant traits. We asked how environmental conditions and plant traits jointly affect shrub biomass allocation. Specifically, how they further play roles in understanding community species composition as ecoregion changes.LocationShaanxi province, North China.MethodsPlant biomass, plant traits and community composition were surveyed for 48 shrub sites distributed in five ecoregions. Species‐specific allocation parameters (allometric constants and scaling exponents) and plant traits were weighted with species abundance to calculate the community biomass allocation and community traits. Linear mixed models were used to assess relative contributions of plant traits and environmental factors in explaining biomass allocation pattern. Their roles in explaining species composition were analyzed by canonical correspondence analysis (CCA).ResultsWe reported that shrub biomass allocation parameters of stems vs leaves and roots vs shoots varied significantly among ecoregions. Plant traits explained more variation in stem vs leaf biomass allocation than soil and climate factors, while climate factors played important roles in variation of root vs shoot biomass allocation. Combined with plant traits and environmental conditions, biomass allocation showed a synergistic role in explaining community species composition.ConclusionsEnvironment and plant traits explain different aspects of shrub biomass allocation, and species‐specific biomass allocation strategy have the potential to predict community species composition and distribution across ecoregions. Our study sheds light on the biomass allocations significance in understanding species turnover and community distribution.

Dynamic global vegetation models underestimate net CO2 flux mean and inter-annual variability in dryland ecosystems

Despite their sparse vegetation, dryland regions exert a huge influence over global biogeochemical cycles because they cover more than 40% of the world surface (Schimel 2010 Science 327 418–9). It is thought that drylands dominate the inter-annual variability (IAV) and long-term trend in the global carbon (C) cycle (Poulter et al 2014 Nature 509 600–3, Ahlstrom et al 2015 Science 348 895–9, Zhang et al 2018 Glob. Change Biol. 24 3954–68). Projections of the global land C sink therefore rely on accurate representation of dryland C cycle processes; however, the dynamic global vegetation models (DGVMs) used in future projections have rarely been evaluated against dryland C flux data. Here, we carried out an evaluation of 14 DGVMs (TRENDY v7) against net ecosystem exchange (NEE) data from 12 dryland flux sites in the southwestern US encompassing a range of ecosystem types (forests, shrub- and grasslands). We find that all the models underestimate both mean annual C uptake/release as well as the magnitude of NEE IAV, suggesting that improvements in representing dryland regions may improve global C cycle projections. Across all models, the sensitivity and timing of ecosystem C uptake to plant available moisture was at fault. Spring biases in gross primary production (GPP) dominate the underestimate of mean annual NEE, whereas models’ lack of GPP response to water availability in both spring and summer monsoon are responsible for inability to capture NEE IAV. Errors in GPP moisture sensitivity at high elevation forested sites were more prominent during the spring, while errors at the low elevation shrub and grass-dominated sites were more important during the monsoon. We propose a range of hypotheses for why model GPP does not respond sufficiently to changing water availability that can serve as a guide for future dryland DGVM developments. Our analysis suggests that improvements in modeling C cycle processes across more than a quarter of the Earth’s land surface could be achieved by addressing the moisture sensitivity of dryland C uptake.

Evapotranspiration and energy partitioning across a forest-shrub vegetation gradient in a subarctic, alpine catchment

As a result of altitude and latitude amplified climate change, widespread changes in vegetation composition, density and distribution have been observed across northern regions. Despite wide documentation of shrub proliferation and treeline advance, few field-based studies have evaluated the hydrological implications of these changes. Quantification of total evapotranspiration (ET) across a range of vegetation gradients is essential for predicting water yield, yet challenging in cold alpine catchments due to heterogeneous land cover, including both boreal forest and shrub taiga ecosystems. Here, we present six years of surface energy balance components and ET dynamics at three sites along an elevational gradient in a subarctic, alpine catchment near Whitehorse, Yukon Territory, Canada. These sites span a gradient of thermal and vegetation regimes, providing a space-for-time comparison for future ecosystem shifts: 1) a low-elevation boreal white spruce forest (~12–20 m), 2) a mid-elevation subalpine taiga comprised of tall, dense willow (Salix) and birch (Betula) shrubs (~1–3 m) and 3) a high-elevation subalpine taiga with short, sparse shrub cover (<0.75 m) and moss, lichen, and bare rock. Eddy covariance instrumentation ran year-round at the forest and during the growing season at the two shrub sites. Total ET decreased and interannual variability increased with elevation, with mean May to September ET totals of 349 (±3) mm at the forest, 249 (±10) mm at the tall, dense shrub site, and 240 (±26) mm at the short, sparse shrub site. Comparatively, over the same period, ET:R ratios were the highest and most variable at the forest (2.19 ± 0.37) and similar at the tall, dense shrub (1.22 ± 0.09) and short, sparse shrub (1.14 ± 0.05) sites. Our results suggest that advances in treeline will increase overall ET and lower interannual variability; however, the large growing season water deficit at the forest indicates strong reliance on soil moisture from late fall and snowmelt recharge. In contrast, ET was considerably less at the cooler higher elevation shrub sites, which exhibited similar ET losses over 6 years despite differences in shrub height and abundance. ET rates between the two shrub sites were similar throughout the year, except during the peak growing season. Greater interannual variability in ET at the short, sparse shrub site indicates the reduced influence of vegetation controls on ET. Results suggest that predicted changes in vegetation type and structure in northern regions will have a considerable impact on water partitioning and will vary in a complex way in response to changing precipitation timing, phase and magnitude, growing season length, and vegetation snow and rain interactions.

Landscape analyses using eDNA metabarcoding and Earth observation predict community biodiversity in California.

Ecosystems globally are under threat from ongoing anthropogenic environmental change. Effective conservation management requires more thorough biodiversity surveys that can reveal system-level patterns and that can be applied rapidly across space and time. Using modern ecological models and community science, we integrate environmental DNA and Earth observations to produce a time snapshot of regional biodiversity patterns and provide multi-scalar community-level characterization. We collected 278 samples in spring 2017 from coastal, shrub, and lowland forest sites in California, a complex ecosystem and biodiversity hotspot. We recovered 16,118 taxonomic entries from eDNA analyses and compiled associated traditional observations and environmental data to assess how well they predicted alpha, beta, and zeta diversity. We found that local habitat classification was diagnostic of community composition and distinct communities and organisms in different kingdoms are predicted by different environmental variables. Nonetheless, gradient forest models of 915 families recovered by eDNA analysis and using BIOCLIM variables, Sentinel-2 satellite data, human impact, and topographical features as predictors, explained 35% of the variance in community turnover. Elevation, sand percentage, and photosynthetic activities (NDVI32) were the top predictors. In addition to this signal of environmental filtering, we found a positive relationship between environmentally predicted families and their numbers of biotic interactions, suggesting environmental change could have a disproportionate effect on community networks. Together, these analyses show that coupling eDNA with environmental predictors including remote sensing data has capacity to test proposed Essential Biodiversity Variables and create new landscape biodiversity baselines that span the tree of life.

Variations in active layer soil hydrothermal dynamics of typical wetlands in permafrost region in the Great Hing’an Mountains, northeast China

The freeze–thaw process of active layer can alter soil hydrothermal dynamics and plays an important role in the stability of permafrost ecosystem, particularly under the background of permafrost degradation resulting from climate warming. Wetlands in permafrost regions are considered to be symbiotic with permafrost. However, despite being the principal region of high-latitude permafrost in China, research on the freeze–thaw process in wetland in the Great Hing’an Mountains is limited. In this study, soil temperature and moisture data (from September 2018 to August 2020) collected from shrub and forest swamp observational sites in the Great Hing’an Mountains were used to analyze the freeze–thaw process and soil hydrothermal dynamics. The effect of wetland types on the freeze–thaw process and the coupling characteristics of soil temperature and moisture were discussed. The results demonstrated that the thawing process of active layer was unidirectional, while the freezing was bidirectional, and the thawing process took much longer than freezing process. The distribution of temperature and moisture of active layer varied in different stage of freeze–thaw process, yet similar trends were exhibited in different wetland types during the same freeze–thaw stage. The annual average temperature of forest swamp was higher than that of shrub swamp for all soil depths, while the annual average water content of forest swamp was lower than that of shrub swamp. A significant non-linear correlation was observed between moisture and temperature of each soil layer.

Soil organic carbon and total nitrogen predict large-scale distribution of soil fungal communities in temperate and alpine shrub ecosystems

Soil fungi play important roles in soil organic matter decomposition, nutrient cycling processes and maintaining close associations with aboveground plant communities. However, the large-scale distribution patterns and drivers of soil fungal communities in shrub ecosystems remain largely unknown. In this study, we examined soil fungal communities among different shrub sites, and the relative importance of plant communities, abiotic factors and spatial distance in shaping the variations of soil fungal communities over large scales. Herb plant richness and diversity, shrub aboveground biomass (AGB), and soil properties showed varying differences among different sites. Soil fungal community diversity was the highest in Huangyuan and Guide, whereas the lowest in Dulan. Soil fungal community structures were significantly different among temperate and alpine grasslands. Random forest analysis showed that soil fungal α diversity was mainly predicted by soil organic carbon (SOC) and total nitrogen (TN), followed by other parameters such as AGB and mean annual precipitation. Variation partition analysis and redundancy analysis showed that shifts in shrub fungal community structures were predominantly determined by SOC and TN, followed by plant and spatial factors such as herb plant diversity, latitude and longitude. Collectively, our results suggested that incorporation of SOC and TN into Earth System Model might improve the prediction of fungal communities in terrestrial shrub ecosystems.

Testing water fluxes and storage from two hydrology configurations within the ORCHIDEE land surface model across US semi-arid sites

Abstract. Plant activity in semi-arid ecosystems is largely controlled by pulses of precipitation, making them particularly vulnerable to increased aridity that is expected with climate change. Simple bucket-model hydrology schemes in land surface models (LSMs) have had limited ability in accurately capturing semi-arid water stores and fluxes. Recent, more complex, LSM hydrology models have not been widely evaluated against semi-arid ecosystem in situ data. We hypothesize that the failure of older LSM versions to represent evapotranspiration, ET, in arid lands is because simple bucket models do not capture realistic fluctuations in upper-layer soil moisture. We therefore predict that including a discretized soil hydrology scheme based on a mechanistic description of moisture diffusion will result in an improvement in model ET when compared to data because the temporal variability of upper-layer soil moisture content better corresponds to that of precipitation inputs. To test this prediction, we compared ORCHIDEE LSM simulations from (1) a simple conceptual 2-layer bucket scheme with fixed hydraulic parameters and (2) an 11-layer discretized mechanistic scheme of moisture diffusion in unsaturated soil based on Richards equations, against daily and monthly soil moisture and ET observations, together with data-derived estimates of transpiration / evapotranspiration, T∕ET, ratios, from six semi-arid grass, shrub, and forest sites in the south-western USA. The 11-layer scheme also has modified calculations of surface runoff, water limitation, and resistance to bare soil evaporation, E, to be compatible with the more complex hydrology configuration. To diagnose remaining discrepancies in the 11-layer model, we tested two further configurations: (i) the addition of a term that captures bare soil evaporation resistance to dry soil; and (ii) reduced bare soil fractional vegetation cover. We found that the more mechanistic 11-layer model results in a better representation of the daily and monthly ET observations. We show that, as predicted, this is because of improved simulation of soil moisture in the upper layers of soil (top ∼ 10 cm). Some discrepancies between observed and modelled soil moisture and ET may allow us to prioritize future model development and the collection of additional data. Biases in winter and spring soil moisture at the forest sites could be explained by inaccurate soil moisture data during periods of soil freezing and/or underestimated snow forcing data. Although ET is generally well captured by the 11-layer model, modelled T∕ET ratios were generally lower than estimated values across all sites, particularly during the monsoon season. Adding a soil resistance term generally decreased simulated bare soil evaporation, E, and increased soil moisture content, thus increasing transpiration, T, and reducing the negative bias between modelled and estimated monsoon T∕ET ratios. This negative bias could also be accounted for at the low-elevation sites by decreasing the model bare soil fraction, thus increasing the amount of transpiring leaf area. However, adding the bare soil resistance term and decreasing the bare soil fraction both degraded the model fit to ET observations. Furthermore, remaining discrepancies in the timing of the transition from minimum T∕ET ratios during the hot, dry May–June period to high values at the start of the monsoon in July–August may also point towards incorrect modelling of leaf phenology and vegetation growth in response to monsoon rains. We conclude that a discretized soil hydrology scheme and associated developments improve estimates of ET by allowing the modelled upper-layer soil moisture to more closely match the pulse precipitation dynamics of these semi-arid ecosystems; however, the partitioning of T from E is not solved by this modification alone.

The Catastrophic Decline of Tortoises at a Fenced Natural Area

ABSTRACTAgassiz’s desert tortoise (Gopherus agassizii), a threatened species of the southwestern United States, has severely declined to the point where 76% of populations in critical habitat (Tortoise Conservation Areas) are below viability. The potential for rapid recovery of wild populations is low because females require 12–20 years to reach reproductive maturity and produce few eggs annually. We report on a 34‐year mark‐recapture study of tortoises initiated in 1979 at the Desert Tortoise Research Natural Area in the western Mojave Desert, California, USA, and provide substantive data on challenges faced by the species. In 1980, the United States Congress designated the Research Natural Area and protected the land from recreational vehicles, livestock grazing, and mining with a wildlife‐permeable fence. The 7.77‐km2study area, centered on interpretive facilities, included land both within the Natural Area and outside the fence. We expected greater benefits to accrue to the tortoises and habitat inside compared to outside. Our objectives were to conduct a demographic study, analyze and model changes in the tortoise population and habitat, and compare the effectiveness of fencing to protect populations and habitat inside the fence versus outside, where populations and habitat were unprotected. We conducted surveys in spring in each of 7 survey years from 1979, when the fence was under construction, through 2012. We compared populations inside to those outside the fence by survey year for changes in distribution, structure by size and relative age, sex ratios, death rates of adults, and causes of death for all sizes of tortoises. We used a Bayesian implementation of a Jolly Seber model for mark‐recapture data. We modeled detection, density, growth and transition of tortoises to larger size‐age classes, movements from inside the protective fence to outside and vice versa, and survival. After the second and subsequent survey years, we added surveys to monitor vegetation and habitat changes, conduct health assessments, and collect data on counts of predators and predator sign. At the beginning of the study, counts and densities for all sizes of tortoises were high, but densities were approximately 24% higher inside the fence than outside. By 2002, the low point in densities, densities had declined 90% inside the fence and 95% outside. Between 2002 and 2012, the population inside the fence showed signs of improving with a 54% increase in density. Outside the fence, densities remained low. At the end of the study, when we considered the initial differences in location, densities inside the fence were roughly 2.5 times higher than outside. The pattern of densities was similar for male and female adults. When evaluating survival by blocks of years, survivorship was higher in 1979–1989 than in 1989–2002 (the low point) and highest from 2002 to 2012. Recruitment and survival of adult females into the population was important for growing the population, but survival of all sizes, including juveniles, was also critical.Major events and activities driving the decline in populations both inside and outside the fence included illegal collecting, upper respiratory tract disease, and hyperpredation by the common raven (Corvus corax) on juvenile tortoises. Other sources of death were gunshots, vehicles, and predation by mammals. Outside the fence, fragmentation and deterioration of habitat was a critical driver. Between the first and last surveys, 2 different ecosystem processes were underway: recovery of vegetation and soils from grazing and vehicles inside the fence and continued deterioration outside the fence. Habitat outside the fence became increasingly denuded of shrubs and fragmented by roads and trails, and habitat fragments increased 50‐fold. Outside the fence, biomass of non‐native annual plants was higher and the cover of shrubs was lower, a reflection of ongoing deterioration. These changes and losses of habitat resulted in loss of shrub cover and sites for burrows, reduction in preferred food plants, and greater exposure to predators and extremes in temperature. Overall, the tortoise population and habitat inside the fence appeared to benefit from protection and showed signs of recovery at the end of the study. Fencing, control of vehicular access, and removal of livestock grazing were among several recommended management actions for critical habitat in the first recovery plan in 1994. At the end of the study, the Natural Area remained as 1 of 2 fenced, official protected areas for the species in the geographic range. We attribute fencing to continuing higher densities of adults inside the fence compared with outside the fence and promising signs of recovery. Densities of adults at the Natural Area also were 2.3 to 5.5 times higher than in 16 of the 17 Tortoise Conservation Areas (critical habitat units) within the geographic range. © 2020 The Authors.Wildlife Monographspublished by Wiley Periodicals, LLC on behalf of The Wildlife Society.

Traditional knowledge of fire use by the Confederated Tribes of Warm Springs in the eastside Cascades of Oregon

We examined traditional knowledge of fire use by the Ichishikin (Sahaptin), Kitsht Wasco (Wasco), and Numu (Northern Paiute) peoples (now Confederated Tribes of Warm Springs, CTWS) in the eastside Cascades of Oregon to generate insights for restoring conifer forest landscapes and enhancing culturally-valued resources. We examined qualitative and geospatial data derived from oral history interviews, participatory GIS focus groups, archival records, and historical forest surveys to characterize cultural fire regimes (CFRs) –an element of historical fire regimes– of moist mixed conifer (MMC), dry mixed conifer (DMC), and shrub-grassland (SG) zones. Our ethnohistorical evidence indicated a pronounced cultural fire regime in the MMC zone, but not in the two drier zones. The CFR of the MMC zone was characterized by frequent (few-year recurrence), low-severity burns distributed in a shifting pattern. This regime helped to maintain forest openings created by previous ignitions, resulting from lightning or possibly human-set, that had burned large areas. The CFR was influenced by the CTWS traditional knowledge system, which consisted of four elements: fire use and associated resource tending practices, tribal ecological principles, the seasonal round (the migratory pattern to fulfill resource needs), and culture. Thinleaf huckleberry (Vaccinium membranaceum), a cultural keystone species, occurs primarily in the MMC zone and was a principle focus of traditional fire use of the CTWS peoples. Fire was deployed to maintain shrub productivity and site access for harvesting. Cessation of fire use by ∼1940 has caused a decline in huckleberry productivity throughout much of the historical harvest zone. Our findings about CFR scale show how a nested, multi-level framework (patch- and landscape-levels) may be employed to reintroduce fire and thereby promote forest restoration and enhance culturally-valued resources. Our findings also highlight the utility of engaging the communities that hold traditional knowledge in the forest management and planning process.

Proximate grassland and shrub-encroached sites show dramatic restructuring of soil bacterial communities.

BackgroundChanges in aboveground community composition and diversity following shrub encroachment have been studied extensively. Recently, shrub encroachment was associated with differences in belowground bacterial communities relative to non-encroached grassland sites hundreds of meters away. This spatial distance between grassland and shrub sites left open the question of how soil bacterial communities associated with different vegetation types might differ within the same plot location.MethodsWe examined soil bacterial communities between shrub-encroached and adjacent (one m apart) grassland soils in Chinese Inner Mongolian, using high-throughput sequencing method (Illumina, San Diego, CA, USA).ResultsShrub-encroached sites were associated with dramatic restructuring of soil bacterial community composition and predicted metabolic function, with significant increase in bacterial alpha-diversity. Moreover, bacterial phylogenic structures showed clustering in both shrub-encroached and grassland soils, suggesting that each vegetation type was associated with a unique and defined bacterial community by niche filtering. Finally, soil organic carbon (SOC) was the primary driver varied with shifts in soil bacterial community composition. The encroachment was associated with elevated SOC, suggesting that shrub-mediated shifts in SOC might be responsible for changes in belowground bacterial community.DiscussionThis study demonstrated that shrub-encroached soils were associated with dramatic restructuring of bacterial communities, suggesting that belowground bacterial communities appear to be sensitive indicators of vegetation type. Our study indicates that the increased shrub-encroached intensity in Inner Mongolia will likely trigger large-scale disruptions in both aboveground plant and belowground bacterial communities across the region.

Conversion of cropland into agroforestry land versus naturally-restored grassland alters soil macro-faunal diversity and trophic structure in the semi-arid agro-pasture zone of northern China

Restoration of cropland (termed ‘Farm’) after abandonment including shrubs (termed ‘Shrub’), trees (termed ‘Tree’) and natural grassland (termed ‘Grass’) has become a routine process aimed to improve land productivity and control desertification. During this restoration process, soil macro-faunal diversity, and trophic structure were investigated at four types of sites (Farm, Shrub, Tree, and Grass) during growing season in the semi-arid agro-pasture zone of northern China. Results indicated that the Staphylinidae family was found to dominate at the Grass, Shrub, and Tree sites, whiles larval Pyralidae individuals were found at the Grass site only. The density of the omnivores (i.e., Formicidae family) was significantly (P<0.05) greater at the Grass site than at the Tree and Farm sites. The total density and richness of predator and phytophages were found to be markedly (P<0.05) greater at the Grass site than at the Farm site. Meanwhile, we found the taxon richness of predators was significantly (P<0.05) higher at the Shrub site than at the Farm and Tree sites. Compared with the Farm and afforested Shrub/Tree sites, the Grass site had greater density, taxon richness, and Shannon index (P<0.05). In conclusion, natural restoration of abandoned croplands toward grassland was an effective strategy relative to artificial afforestation for improvement of soil biological diversity. Moreover, planting shrub is a preferable measure in abandoned croplands for land development in the semi-arid agro-pasture zone of northern China.

Evaluation of ten machine learning methods for estimating terrestrial evapotranspiration from remote sensing

Remote sensing retrieval of evapotranspiration (ET), or surface latent heat exchange (LE), is of great utility for many applications. Machine learning (ML) methods have been extensively used in many disciplines, but so far little work has been performed systematically comparing ML methods for ET retrieval. This paper provides an evaluation of ten ML methods for estimating daily ET based on daily Global LAnd Surface Satellite (GLASS) radiation data and high-level Moderate-Resolution Imaging Spectroradiometer (MODIS) data products and ground measured ET data from 184 flux tower sites. Measurements of accuracy (RMSE, R2, and bias) and run time were made for each of ten ML methods with a smaller training data set (n = 7910 data points) and a larger training data set (n= 69,752 data points). Inclusion of more input variables improved algorithm performance but had little effect on run time. The best results were obtained with the larger training data set using the bootstrap aggregation (bagging) regression tree (validation RMSE = 19.91 W/m2) and three hidden layer neural network (validation RMSE = 20.94 W/m2), although the less computationally demanding random kernel (RKS) algorithm also produced good results (validation RMSE = 22.22 W/m2). Comparison of results from sites with different ecosystem types showed the best results for evergreen, shrub, and grassland sites, and the weakest results for wetland sites. Generally, performance was not improved by training with data from only the same ecosystem type.