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13 results for “tree encroachment”
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>
Data from: N₂-fixation is linked to the ability to encroach in African savanna trees
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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>
CO2-fertilisation enhances resilience to browsing in the recruitment phase of an encroaching savanna tree
<p>1. CO<sub>2</sub>-fertilisation is implicated in the widespread and significant woody encroachment of savannas due to CO<sub>2</sub>-stimulated increases in belowground reserves that enhance sapling regrowth after fire. However, the effect of CO<sub>2</sub> concentration ([CO<sub>2</sub>]) on tree responses to the other major disturbance in savannas, herbivory, is poorly understood. Herbivory responses cannot be predicted from fire responses, as herbivore effects occur earlier during establishment and are moderated by plant palatability and defence rather than below-ground carbon accumulation.</p> <p>2. The relationship between herbivory and [CO<sub>2</sub>] is explored here using a widespread, strongly-encroaching savanna tree, <em>Vachellia</em> <em>karroo</em>. Using greenhouse-grown seedlings under past- through to predicted future-[CO<sub>2</sub>] (180–1000 ppm) and field-grown seedlings under ambient [CO<sub>2</sub>], we assessed plant survival, growth, defence and palatability.</p> <p>3. Increasing [CO<sub>2</sub>] improves the tolerance of greenhouse-grown seedlings to herbivory by stimulating growth and allowing a critical size-threshold associated with survival to be reached earlier, thereby decreasing the probability of fatal herbivory during the vulnerable recruitment phase. Elevated [CO<sub>2</sub>] also decreases the time taken to reach a second size-threshold linked to accelerated recovery of field-grown seedlings following herbivory. Seedling growth responses to increasing [CO<sub>2</sub>] are non-linear, suggesting that historic growth- and survival enhancements are smaller than those predicted for the future. Increasing [CO<sub>2</sub>] is associated with greater resistance to herbivores (more branched shoot architecture) but not leaf palatability (C:N ratio) or defence (leaf tannins and spine density).</p> <p>4. Increasing <em>V</em>. <em>karroo</em> densities already constitute a major land management problem in southern African savannas. However, encroachment by this species, and likely other savanna tree species, may be greatly exacerbated under future [CO<sub>2</sub>], as tolerance to herbivory at the recruitment stage is further enhanced. </p>
CO2-fertilisation enhances resilience to browsing in the recruitment phase of an encroaching savanna tree
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Not all trees can make a forest: tree species composition and competition control forest encroachment in a tropical savanna
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Data from: Social-ecological landscape patterns predict woody encroachment from native tree plantings in a temperate grassland
Afforestation is often viewed as the purposeful planting of trees in historically non-forested grasslands, but an unintended consequence is woody encroachment, which should be considered part of the afforestation process. In North America's temperate grassland biome, Eastern redcedar (Juniperus virginiana L.) is a native species used in tree plantings that aggressively invades in the absence of controlling processes. Cedar is a well-studied woody encroacher, but little is known about the degree to which cedar windbreaks, which are advocated for in agroforestry programs, are contributing to woody encroachment, what factors are associated with cedar spread from windbreaks, nor where encroachment from windbreaks is occurring in contemporary social–ecological landscapes. We used remotely sensed imagery to identify the presence and pattern of woody encroachment from windbreaks in the Nebraska Sandhills. We used multimodel inference to compare three classes of models representing three hypotheses about factors that could influence cedar spread: (a) windbreak models based on windbreak structure and design elements; (b) abiotic models focused on local environmental conditions; and (c) landscape models characterizing coupled human-natural features within the broader matrix. Woody encroachment was evident for 22% of sampled windbreaks in the Nebraska Sandhills. Of our candidate models, our inclusive landscape model carried 92% of the model weight. This model indicated that encroachment from windbreaks was more likely near roadways and less likely near farmsteads, other cedar plantings, and waterbodies, highlighting strong social ties to the distribution of woody encroachment from tree plantings across contemporary landscapes. Cedar control efforts are insufficient for nearly one-quarter of windbreaks in the Nebraska Sandhills. Our model findings indicate where additional investments into cedar control can be prioritized to prevent cedar spread from windbreaks. This approach can serve as a model in other temperate regions to identify where woody encroachment resulting from temperate agroforestry programs is emerging.
Growth and photosynthetic responses of encroaching tree seedlings to CO2 and stress interactions
<p>1. Woody encroachment in southern African savanna has been partly attributed to rising atmospheric CO2 fertilising the growth of C3 trees but less so that of competing C4 grasses. However, growth conditions (resource availability, competition, rooting space, and herbivory) must be suitable for the effects of elevated CO2 (eCO2) to be realised.</p> <p>2. This research investigated the interactions between the positive effect of eCO2 on tree seedling growth and limitations imposed by drought, disturbance, and competition with C4 grasses. Seedlings of the prolific encroacher C3 tree Vachellia karroo were grown at ambient (400 ppm) or eCO2 (800 ppm) in Open-Top Chambers and exposed to a variety of stresses and disturbances typical of savanna systems. Photosynthetic, growth and allocation responses to eCO2 and other treatments were determined.</p> <p>3. Unsurprisingly, we show strong growth and water-saving responses of V. karroo seedlings to eCO2 when in the absence of competition and herbivory. However, the addition of either competition or simulated herbivory in the first season of growth moderated this, while neither drought nor shading diminished the eCO2 effect relative to similarly treated plants grown at ambient [CO2].</p> <p>4. Synthesis. We demonstrate that eCO2-induced C3 stimulation in encroaching savanna species such as V. karroo will be inconsistent across time and space. This research does not detract from the suggestion that increasing atmospheric CO2 is implicated in woody encroachment, but rather that eCO2 benefits to C3 tree seedlings are only realised when growth conditions are suitable. Inconsistencies in eCO2 response will translate into spatial and temporal variation in seedling responses to eCO2 and CO2-driven woody encroachment, explaining some of the variability observed in woody encroachment across geographic regions and disturbance gradients.</p>
Facilitation by isolated trees triggers woody encroachment and a biome shift at the savanna-forest transition
<p>1. Woody encroachment into grassy biomes is a global phenomenon, often resulting in a nearly complete turnover of species, with savanna specialists being replaced by forest-adapted species. Understanding the mechanisms involved in this change is important for devising strategies for managing savannas.</p> <p>2. We examined how isolated trees favor woody encroachment and species turnover by overcoming dispersal limitation and environmental filtering. In a savanna released from fire in southeastern Brazil (Cerrado) we sampled woody plants establishing under 40 tree canopies and in paired treeless plots. These trees comprised eight species selected for habitat preference (savanna or forest) and dispersal syndrome (bird-dispersed or not). We recorded dimensions of each tree, dispersal syndrome and habitat preference of recruits, and quantified the physical environment within each plot, aiming at a mechanistic understanding of woody encroachment.</p> <p>3. We found clear evidence that isolated trees cause nucleation and drive changes in functional composition of savanna. Effectiveness as nucleator differed among species, but was unrelated to their functional guilds (habitat preference or dispersal syndrome). Density of saplings in nuclei was partially explained by soil moisture (+), daily temperature amplitude (-), and sum of bases (-).</p> <p>4. Our results indicate that isolated trees act first as perches, strongly favoring bird-dispersed species. They then act as nurse trees, considerably changing the environment in favor of forest-adapted recruits. In the long term, as the nuclei expand and merge, savanna specialists tend to disappear and the savanna turns into a low-diversity forest.</p> <p>5. Synthesis and applications: Fire suppression has allowed the nucleation process and consequently the woody encroachment and fast replacement of savanna specialists by forest species in the Cerrado. By elucidating the mechanisms behind woody encroachment, we recommend using prescribed fires to burn forest seedlings and to reduce tree canopy size wherever the management goal is to maintain the typical savanna structure and composition.</p>
Facilitation by isolated trees triggers woody encroachment and a biome shift at the savanna-forest transition
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Growth and photosynthetic responses of encroaching tree seedlings to CO2 and stress interactions
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Data from: Positive shrub-tree interactions facilitate woody encroachment in boreal peatlands
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Data from: Social-ecological landscape patterns predict woody encroachment from native tree plantings in a temperate grassland
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