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106 results for “encroachment”
WPE02 Shrub stem data to quantify woody encroachment in Konza watersheds from 2020, 2022, and 2023
Woody plant encroachment (WPE) is one of the most widespread and acute threats affecting grasslands worldwide. Nature-based solutions to reversing WPE in mesic grasslands have proven largely ineffective, with decades of frequent prescribed fire failing to reverse WPE in some instances. One solution is to conduct more extreme fires compared to traditional prescribed fire. However, most tests of this idea have occurred at small scales, a mismatch with the need for landscape-scale land management. We considered two catchments, each with long-term destocking of grazers to increase fuel loads, one which accidentally burned under dry windy conditions that produced an extreme fire, while one burned under prescribed fire conditions. The extreme fire caused a sharp decline in woody cover without corresponding negative externalities such as decreases in grass cover or biodiversity. However, after three years, the woody community completely recoverd with a 23% increase in woody cover from the first to third year post-fire. The prescribed fire catchment saw minor decreases in woody plant dominance that rebounded quickly to pre-fire values. Our results suggest that reversing encroachment will likely require a long-term approach, along with applying a combination of pressures that reduce woody abundance and promote fuel loads to intensify fire.
FWE01 Effects of browsing and fire on woody encroachment at Konza Prairie
Woody encroachment into grasslands, savannas, and steppes have become a management and conservation concern worldwide because of the ability of woody plants to change ecosystems through decreases in biodiversity, alterations in water and nutrient cycles as well as decreases in forage production and quality. In grasslands, woody encroachment can be categorized into two groups: non-resprouting species that can be killed with fire and resprouting species that cannot be killed with fire. Resprouting species require additional active management strategies to remove them from encroached grasslands. In this study we investigate physiological, population and community effects of continuous browsing and fire on Cornus drummondii, a resprouting woody species. Through monitoring the shrub’s physiology, population and the surrounding plant community composition within these treatments we hope to understand how to best prescribe restoration methods for restoring the tallgrass prairie.
WER01 Elevated CO2 counteracts effects of water stress on woody rangeland-encroaching species at Konza Prairie
Woody plants are increasing prevalence and dominance in many rangelands around the world. The reason for their increase is various but two common drivers that have changed are an increase in CO2 concentrations and alteration to precipitation dynamics. We asked what the physiological growth dynamics of four juvenile woody plant species (Cornus drummondii, Rhus glabra, Gleditsia triacanthos and Juniperus osteosperma) when grown in elevated CO2 and chronically water stressed. We found that elevated CO2 counteracts much of the physiological effects of chronic water stress in the four different woody plant species measured. The alleviation of water stress from increased CO2 concentrations will result in juvenile woody plants continuing to expand and establish in North American rangelands. This information will aid land managers in making long-term management objectives for reducing woody plants in rangelands.
WPE01 Assessing the value added of NEON for using machine learning to quantify vegetation mosaics and woody plant encroachment at Konza Prairie
Woody encroachment, or invasion of woody plants, is rapidly shifting tallgrass prairie into shrub and evergreen dominated ecosystems, mainly due to exclusion of fire. Tracking the pace and extent of woody encroachment is difficult because shrubs and small trees are much smaller than the coarse resolution (>10m2) of common remote sensed images. However, the US government has been investing in finer resolution (<2m2) remote sensing through USDA NAIP and the National Ecological Observatory Network (NEON), both of which cost multi-million dollars each year and contain different remote sensed products. We compared two methods of classification (random forests and support vector machines) with these two freely available remotely sensed aerial images to determine if and how much NEON adds to classification accuracy and determine which method of machine learning was more accurate. All models have very high overall classification accuracy (>91%), with the NEON image a few percent more accurate than NAIP. The NEON image significantly relies on canopy height (LiDAR) to make classifications, but the importance of bands is more evenly distributed during NAIP classification. Lastly, accuracy for Eastern Red Cedar specifically is high with NEON (78-84%), compared to the relatively low classification accuracy using NAIP imagery (55-61%).
WES01 Woody encroachment impacts on the subsurface at Konza Prairie
Soil sampling pits across three hillslope positions - toeslope, backslope, and summit - were dug in 2020 in watershed N4D (burned every 4 years) and N1D (burned annually) to characterize the impacts of woody encroachment on subsurface soil physical, chemical, and biological properties. Pits were hand-dug to 120 cm in the toeslope position and to 60 cm deep at the backslope and summit positions. Soil pits in N4D were dug directly under dogwood shrubs (Cornus drumondii) while pits in N1B were dug under grasses and forbs. Soil pit faces were photographed to determine root fractions with depth, soil monoliths were take to charaterize soil macroporosity with depth while soil cores were taken in each horizon for water retention analysis. Soil sensors were also installed at four soil depths at the toeslope position and 3 soil depths at the backslope and summit positions to record half hourly soil moisture, soil temperature, soil water potential, soil electrical conductivity, and soil carbon dioxide, and soil oxygen. In addition, geophysical measurements were taken in N4D using time-lapse electrical resistivity in 2023.
WEE01 Impacts of riparian and non-riparian woody encroachment on tallgrass prairie ecohydrology
Plant xylem water samples were collected from Cornus drummondii (rough-leaf dogwood), Andropogon gerardii (big bluestem), Quercus macrocarpa (bur oak), and Quercus muehlenbergii (chinquapin oak) during the summer of 2016. Soil cores were also collected during the summer of 2016 to collect soil water from the surface to 200 cm depth. Isotope values (δ18O and δ2H) were analyzed for each water sample to determine depth of plant water uptake.
LPT01 Leaf physiological and structural traits of encroaching shrub species at Konza Prairie
A variety of leaf-level physiological and structural traits were collected on seven species of encroaching shrubs at Konza Prairie Biological Station during the summer of 2022. Shrub species spanned an order of magnitude in abundance. These data were used to assess if the most abundant encroaching species at Konza Prairie have common growth forms and physiology or unique traits that differentiate their carbon- and water-use strategies. Measurements included A-Ci response curves, light response curves, pressure-volume curves, specific leaf area, leaf dry matter content, leaf carbon and nitrogen content, leaf 13C and wood density. All measurements were collected on the same shrub individuals.
Herbaceous production lost to tree encroachment in United States rangelands
<p>Data products and modeling code supporting the publication:</p> <p><strong>Herbaceous production lost to tree encroachment in United States rangelands</strong> in the <em>Journal of Applied Ecology</em>.</p> <p>Manuscript DOI: 10.1111/1365-2664.14288</p> <p><strong>Abstract</strong></p> <ol> <li>Rangelands of the United States provide ecosystem services that benefit society and rural economies. Native tree encroachment is often overlooked as a primary threat to rangelands due to the slow pace of tree cover expansion and the positive public perception of trees. Still, tree encroachment fragments these landscapes and reduces herbaceous production, thereby threatening habitat quality for grassland wildlife and the economic sustainability of animal agriculture. </li> <li>Recent innovations in satellite remote sensing permit the tracking of tree encroachment and the corresponding impact on herbaceous production. We analyzed tree cover change and herbaceous production across the western United States from 1990 to 2019.</li> <li>We show that tree encroachment is widespread in U.S. rangelands; absolute tree cover has increased by 50% (77,323 km<sup>2</sup>) over 30 years, with more than 25% (684,852 km<sup>2</sup>) of U.S. rangeland area experiencing tree cover expansion. Since 1990, 302 ± 30 Tg of herbaceous biomass have been lost. Accounting for variability in livestock biomass utilization and forage value reveals that this lost production is valued at between $4.1 - $5.6 billion U.S. dollars.</li> <li>Synthesis and applications: The magnitude of impact of tree encroachment on rangeland loss is similar to conversion to cropland, another well-known and primary mechanism of rangeland loss in the U.S. Prioritizing conservation efforts to prevent tree encroachment can bolster ecosystem and economic sustainability, particularly among privately-owned lands threatened by land-use conversion.</li> </ol> <p><strong>Description</strong></p> <p>This archive contains data products and modeling code for production loss and tree cover change estimates provided in the accompanying refereed publication. The easiest way to view and use these data is in Google Earth Engine:</p> <ul> <li><a href="https://smorford.users.earthengine.app/view/yield-gap">https://smorford.users.earthengine.app/view/yield-gap</a></li> <li><a href="https://code.earthengine.google.com/8ad19c7f7a6e04b377953326b274f98d">https://code.earthengine.google.com/8ad19c7f7a6e04b377953326b274f98d</a></li> </ul> <p>Summary data products are included in the <em>data-products</em> folder, and include links and scripts to download all annual data discussed in the manuscript. The full dataset is roughly 660GB and cannot be achieved on Zonodo as of summer 2022.</p> <p>Similarly, the <em>model</em> directory contains the primary codebase for processing raw tree cover data and running XGBoost modeling training and inference for the production loss model. To recreate the production loss data will require downloading approximately 900GB of biomass data and 250GB of tree cover data; total project size will be approximate 1.8 TB after inference.</p> <p>Data can also be downloaded directly from the University of Montana web servers:</p> <ul> <li><a href="http://rangeland.ntsg.umt.edu/data/rap/rap-vegetation-biomass/v2/">http://rangeland.ntsg.umt.edu/data/rap/rap-vegetation-biomass/v2/</a></li> <li><a href="http://rangeland.ntsg.umt.edu/data/rap/rap-derivatives/yield-gap/v1/">http://rangeland.ntsg.umt.edu/data/rap/rap-derivatives/yield-gap/v1/</a></li> </ul> <p><strong>Journal citation:</strong></p> <p>Morford, S.L., Allred, B.W., Twidwell, D., Jones, M.O., Maestas, J.D., Roberts, C.P. and Naugle, D.E., <em>Accepted</em>. Herbaceous production lost to tree encroachment in United States rangelands. <em>Journal of Applied Ecology</em>, August 2022.</p>
Livestock management promotes bush encroachment in savanna systems by altering plant-herbivore feedback
<p>This repository contains all code to reproduce the analysis in Koch et al. 2022 "Livestock management promotes bush encroachment in savanna systems by altering plant-herbivore feedback".</p> <p>We use a set of coupled differential equations to describe competition between shrubs and grasses, as well as plant biomass consumption via grazing and browsing. Grazers were assumed to receive a certain level of care from farmers, so that grazer densities emerge dynamically from the combined effect of vegetation abundance and farmer<br>support. Our main goal was to understand how critical transitions from grass-dominated to shrub-dominated system states were affected by the dynamic role of grazing.</p> <p>Our results show that bistability emerges for intermediate levels of farmer support due to positive feedback that arises from competition between shrubs and grasses and from herbivory. We furthermore demonstrate that disturbances, such as drought events, trigger abrupt transitions from the grass dominated to the shrub dominated state and that the system becomes more susceptible to disturbances with increasing farmer support.</p>
Ungulates mitigate the effects of drought and shrub encroachment on the fire hazard of Mediterranean oak woodlands
<p>Dataset included: Shrub density; Shrub biomass; Fuel load of <em>Cistus ladanifer</em>; Fuel load herbs; Fuel load litter</p>
Data from: Water regime and nitrogen enrichment facilitate the encroachment of woody plants at various developmental stages in freshwater marshes
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Livestock management promotes bush encroachment in savanna systems by altering plant-herbivore feedback
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Data from: N₂-fixation is linked to the ability to encroach in African savanna trees
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Coastal Wetland Basal Consumer and End Member C-13 and N-15 Isotopic Ratios Across a Mangrove Encroachment Gradient, 2019
Foundation species support highly productive and valuable ecosystems, but anthropogenic disturbances and environmental changes are increasingly causing foundation species shifts, where one foundation species replaces another. The consequences of foundation shifts are not well understood, as there is limited research on the equivalency of different foundation species and the functions they support. Here, we provide insight into community-level consequences of foundation shifts in the Gulf of Mexico, where the typical marsh foundation species (Spartina alterniflora) is being replaced with a mangrove foundation species (Avicennia germinans), forcing marsh fauna to rely on Avicennia for foundational support. We evaluated the interactions of two common and ecologically valuable basal consumers, fiddler crabs (Uca spp.) and marsh periwinkle snails (Littoraria irrorata), with both foundation species across sites with different levels of mangrove encroachment. By investigating both physical support, measured as habitat association and co-occurrence, and trophic support, as basal resource diet contributions, we found that Avicennia can physically replace Spartina for some consumers, but is not providing equivalent trophic support. Uca and Littoraria commonly occupy encroached sites and associate with mangroves but incorporate almost no mangrove plant matter into their diets. The ultimate consequences of a foundation shift in the case of mangrove encroachment may include shifting energy flows and resource use and decreased populations of basal consumers. Looking at interactions with foundation species from multiple perspectives is necessary to obtain a complete picture of the effects that foundational shifts are having, especially as such shifts are becoming increasingly common.
Trophic interactions of fiddler crabs (Uca spp.) with black mangrove (Avicennia germinans) detrital matter as a result of mangrove encroachment; 2018 and 2019
Woody plant encroachment is reshaping communities in both terrestrial and coastal environments, but little is known about its effects on basal consumers. We used interactions between fiddler crabs (Uca spp.) and the encroaching mangrove Avicennia germinans in Gulf of Mexico salt marshes to explore trophic interactions between basal consumers and encroaching shrubs. Fiddler crabs were collected from wetlands in Galveston, Texas in summer 2018 and 2019 and used in a series of food preference and food quality trials. Through these trials we collected data on the relative attractiveness and quality of black mangroves and smooth cordgrass (Spartina alterniflora) as food sources for fiddler crabs.
Effects of mangrove encroachment on tidal wetland plants and epifauna: 2012-2020
Woody encroachment is occurring in many marsh-mangrove ecotones across the globe, with multiple drivers contributing to an increase in mangrove cover. As a result, marsh plant species are often displaced, resulting in a striking regime shift from grass and forb-dominated habitats to taller, woody vegetation. Our goal was to quantify the bottom-up effects of mangrove woody encroachment into coastal wetlands on associated plant and epifaunal assemblages. In 2012, we established several large (> 20 ha) survey areas at tidal wetland sites with or without black mangroves (Avicennia germinans) on the Texas (USA) coast in the Gulf of Mexico, an area highly susceptible to mangrove encroachment. Starting in 2012, we annually recorded vascular plant cover and diversity and recorded snail (Littoraria irrorata) and fiddler crab (Uca spp.) density along transects perpendicular to the shoreline. Marsh plant species richness was 50% lower at sites with mangroves, and some species, such as Sarcocornia spp. and Distichlis spicata, were relatively rare or absent from sites with mangroves. The wetland plant communities at these sites were relatively unaffected by Hurricane Harvey (August 2017). Epifaunal snails and crabs were common at all sites, with abundances that varied over time. Our results indicate that coastal wetlands dominated by mangroves support different and lower diversity plant assemblages than marsh-dominated areas. These results were largely consistent with the results of a previous manipulative experiment in the same area. Therefore, as woody encroachment continues and mangrove cover gradually increases, this change may lead to complex bottom-up effects on a range of ecosystem processes and services.
Data from: Soil carbon response to woody plant encroachment: Importance of spatial heterogeneity and deep soil storage
1. Recent global trends of increasing woody plant abundance in grass-dominated ecosystems may substantially enhance soil organic carbon (SOC) storage and could represent a strong carbon (C) sink in the terrestrial environment. However, few studies have quantitatively addressed the influence of spatial heterogeneity of vegetation and soil properties on SOC storage at the landscape scale. In addition, most studies assessing SOC response to woody encroachment consider only surface soils, and have not explicitly assessed the extent to which deeper portions of the soil profile may be sequestering C. 2. We quantified the direction, magnitude, and pattern of spatial heterogeneity of SOC in the upper 1.2 m of the profile following woody encroachment via spatially-specific intensive soil sampling across a landscape in a subtropical savanna in the Rio Grande Plains, USA, that has undergone woody proliferation during the past century. 3. Increased SOC accumulation following woody encroachment was observed to considerable depth, albeit at reduced magnitudes in deeper portions of the profile. Overall, woody clusters and groves accumulated 12.87 and 18.67 Mg C ha-1 more SOC compared to grasslands to a depth of 1.2 m. 4. Woody encroachment significantly altered the pattern of spatial heterogeneity of SOC to a depth of 5 cm, with marginal effect at 5-15 cm, and no significant impact on soils below 15 cm. Fine root density explained greater variability of SOC in the upper 15 cm, while a combination of fine root density and soil clay content accounted for more of the variation in SOC in soils below 15 cm across this landscape. 5. Synthesis: Substantial SOC sequestration can occur in deeper portions of the soil profile following woody encroachment. Furthermore, vegetation patterns and soil properties influenced the spatial heterogeneity and uncertainty of SOC in this landscape, highlighting the need for spatially specific sampling that can characterize this variability and enable scaling and modeling. Given the geographic extent of woody encroachment on a global scale, this undocumented deep soil C sequestration suggests this vegetation change may play a more significant role in regional and global C sequestration than previously thought.
Data from: Repeated clearing as a mechanism for savanna recovery following bush encroachment
<p>Many savannas are experiencing increased cover of trees and shrubs, resulting in reduced herbaceous productivity, shifts in savanna functional structure, and potential reductions in ecotourism. Clearing woody plants has been suggested as an effective management strategy to mitigate these effects and restore these systems to an open state with higher rates of grass production and herbivory. This study investigated the effectiveness of repeated shrub clearing as a tool to mitigate bush encroachment in a semi-arid savanna in Southern Africa.</p> <p>We present data from a 7-year experiment in the Mthimkhulu Game Reserve bordering Kruger National Park, South Africa. <em>Colophospermum mopane</em> stems and re-sprouting shoots were basally cut 2-3 times per year (2015-2022) in 3 pairs of treatment and control plots of 60 m x 60 m. We monitored changes in soil moisture, grass biomass, and herbivore activity via dung counts. We assessed <em>C. mopane</em> physiological responses to repeated cutting using non-structural carbohydrates and stable water isotopes to infer changes to energy storage and functional rooting depth, respectively.</p> <p>The cleared treatment had higher soil moisture and grass biomass than the control treatment. Dung counts showed impala and buffalo visited the cleared treatment more frequently than the control treatment.</p> <p>Repeated cutting had limited effects on <em>C. mopane</em> survival in the first 2-3 years after initial clearing, but 80% of individuals were dead after 7 years. Repeatedly cut <em>C. mopane</em> had lower belowground starch concentrations and used water from shallower soil depths than <em>C. mopane</em> in control plots.</p> <p><em>Synthesis and applications</em>: Repeated cutting increased soil moisture availability and grass biomass, and attracted charismatic grazing herbivores. While more costly than once-off clearing methods, this practice created more employment opportunities for a neighbouring rural community. Transforming portions of the ecosystem to a grass-dominated state may increase ecotourism potential through improved game viewing in open systems.</p>
Not all trees can make a forest: tree species composition and competition control forest encroachment in a tropical savanna
<p>Forest encroachment into savannas is a widespread phenomenon, the rate of which may depend on soil conditions, species composition, or changes in stand structure. As savanna specialist trees are replaced by generalist species, rates of stand development may increase. Because generalists can persist in forests, they are likely to grow more quickly and survive longer in dense stands, compared to savanna specialists. Furthermore, the faster growth rates of generalists may allow them to overtop and outcompete savanna specialists, causing rapid species turnover.</p> <p>We measured growth and survival of 6147 individuals of 112 species of savanna and generalist tree species over a period of 10 years in an ecological reserve in Assis, São Paulo State, Brazil. We modeled growth and mortality as a function of soil texture and nutrients, tree size, competitive neighborhood, and membership in savanna or generalist (species which can persist in forests and savannas) functional groups.</p> <p>Tree growth and survival was strongly influenced by competition, as estimated by the basal area of trees taller than a focal tree. At the stand level, savanna species are unable to contribute basal area growth in closed stands, while generalist species continue to increase in basal area even at high stand basal area. This phenomenon is driven by differences in growth and mortality. Generalists grew faster than savanna species, both in height and diameter. This difference in growth rates led to savanna species becoming suppressed more rapidly than generalists. When suppressed, savanna species were more than twice as likely to die than were generalists. Soils had inconsistent and mostly weak effects which were difficult to separate from gradients of stand structure.</p> <p>Synthesis: We demonstrate that the presence of generalist trees accelerates rates of basal area accumulation due to their greater growth rates and tolerance of shading. Generalists outcompete savanna trees by growing faster in the open and overtopping savanna specialists. Due to the slow growth and high mortality of savanna species in the shade, they are unable to form closed-canopy stands. Accounting for differences among functional types and development of vegetation structure is critical for modeling forest encroachment.</p>
Data from: Increased precipitation attenuates shrub encroachment by facilitating herbaceous growth in a Mongolian grassland
<p>Widespread shrub encroachment is profoundly impacting the structures and functions of global drylands, and precipitation change is assumed to be one of the most critical factors affecting this phenomenon. However, there is little evidence to show how precipitation changes will affect the process. In this study, we conducted a 6-year precipitation manipulation experiment (-30%, ambient, +30%, and +50%) to investigate the effects of precipitation changes on the growth of shrubs and herbaceous plants in a shrub-encroached grassland in Inner Mongolia. We found that the increasing precipitation significantly increased the mean height, coverage, and aboveground biomass of herbaceous species, while the growth of shrub species did not exhibit a significant response to precipitation changes. With increasing precipitation, the relative coverage of shrubs decreased, while that of herbs increased. The native dominant herbaceous plant (Leymus chinensis) with more sensitive maximum photosynthetic rate to the precipitation change, showed higher photosynthetic nitrogen use efficiency and water use efficiency than those of the encroached shrub species (Caragana microphylla) at high soil moisture contents, reflecting that the ecophysiological characteristics of L. chinensis might provide it a competitive advantage under increased precipitation. Our findings suggest that increasing precipitation may slow down shrub encroachment by facilitating herbaceous growth in Mongolian grasslands, and consequently affect the forage value and carbon budget in these ecosystems. </p>
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