Grasses and browsers reinforce landscape heterogeneity by excluding trees from ecosystem hotspots

Spatial heterogeneity in woody cover affects biodiversity and ecosystem function, and may be particularly influential in savanna ecosystems. Browsing and interactions with herbaceous plants can create and maintain heterogeneity in woody cover, but the relative importance of these drivers remains unclear, especially when considered across multiple edaphic contexts. In African savannas, abandoned temporary livestock corrals (bomas) develop into long-term, nutrient-rich ecosystem hotspots with unique vegetation. In central Kenya, abandoned corral sites persist for decades as treeless ‘glades’ in a wooded matrix. Though glades are treeless, areas between adjacent glades have higher tree densities than the background savanna or areas near isolated glades. The mechanisms maintaining these distinctive woody cover patterns remain unclear. We asked whether browsing or interactions with herbaceous plants help to maintain landscape heterogeneity by differentially impacting young trees in different locations. We planted the mono-dominant tree species (Acacia drepanolobium) in four locations: inside glades, far from glades, at edges of isolated glades and at edges between adjacent glades. Within each location, we assessed the separate and combined effects of herbivore exclusion (caging) and herbaceous plant removal (clearing) on tree survival and growth. Both caging and clearing improved tree survival and growth inside glades. When herbaceous plants were removed, trees inside glades grew more than trees in other locations, suggesting that glade soils were favorable for tree growth. Different types of glade edges (isolated vs. non-isolated) did not have significantly different impacts on tree performance. This represents one of the first field-based experiments testing the separate and interactive effects of browsing, grass competition and edaphic context on savanna tree performance. Our findings suggest that, by excluding trees from otherwise favorable sites, both herbaceous plants and herbivores help to maintain functionally important landscape heterogeneity in African savannas

Transdisciplinary Research in Practice: Lessons from Participatory, Folklore and Community-Supported Approaches in the Greater American West

Rapid social and ecological changes on global rangelands amplify the challenges to achieving biodiversity conservation, rural economic viability and social well-being, and rangeland sustainability. These dynamics create a need for transdisciplinary science that is inclusive of ecological, sociological, and participatory approaches in order to rebuild meaningful working relationships between scientists, ranchers and managers, and other rangeland stakeholders. In real application, however, transdisciplinary science faces numerous social, ethical, and logistical challenges, including the question of how the work might benefit rangeland stakeholders. Our objective is to advance rangeland researchers’ toolbox for meaningful engaged research by describing three lessons from transdisciplinary projects in the rangeland contexts of the United States. These include the need for 1) ranch-scale, long-term participatory management experiments; 2) folklore and oral history methods and 3) community-supported social-ecological research that creates credible science that can be communicated out to non-ranching decision-makers. These examples illustrate the nuances of transdisciplinary research, reciprocity, and useable knowledge creation in complex rangeland social-ecological contexts

Combining active restoration and targeted grazing to establish native plants and reduce fuel loads in invaded ecosystems

Many drylands have been converted from perennial-dominated ecosystems to invaded, annual-dominated, fire-prone systems. Innovative approaches are needed to disrupt fire-invasion feedbacks. Targeted grazing can reduce invasive plant abundance and associated flammable fuels, and fuelbreaks can limit fire spread. Restored strips of native plants (native greenstrips) can function as fuelbreaks while also providing forage and habitat benefits. However, methods for establishing native greenstrips in invaded drylands are poorly developed. Moreover, if fuels reduction and greenstrip establishment are to proceed simultaneously, it is critical to understand how targeted grazing interacts with plant establishment. We determined how targeted grazing treatments interacted with seed rate, spatial planting arrangement (mixtures vs. monoculture strips), seed coating technology, and species identity (five native grasses) to affect standing biomass and seeded plant density in experimental greenstrips. We monitored for two growing seasons to document effects during the seedling establishment phase. Across planting treatments, ungrazed paddocks had the highest second-year seeded plant densities and the highest standing biomass. Paddocks grazed in fall of the second growing season had fewer seedlings than paddocks grazed in spring, five months later. High seed rates minimized negative effects of grazing on plant establishment. Among seeded species, Elymus trachycaulus and Poa secunda had the highest second-year densities, but achieved this via different pathways. Elymus trachycaulus produced the most first-year seedlings, but declined in response to grazing, whereas P. secunda had moderate first-year establishment but high survival across grazing treatments. We identified clear tradeoffs between reducing fuel loads and establishing native plants in invaded sagebrush steppesimilar tradeoffs may exist in other invaded drylands. In our system, tradeoffs were minimized by boosting seed rates, using grazing-tolerant species, and delaying grazing. In invaded ecosystems, combining targeted grazing with high-input restoration may create opportunities to limit wildfire risk while also shifting vegetation toward more desirable species

Adaptive Rotational Grazing and the Story of the Regrazed Grass Plant

Livestock stocking rates and decisions about how to move animals in time and space impact plant responses to livestock grazing. We report on a ranch-scale collaborative experiment comparing adaptive rotational grazing management to season-long continuous grazing during a 4.5-month grazing period during the growing season. As part of this project, stakeholders and scientists worked together to articulate their hypotheses about the mechanisms linking rotational grazing with expected vegetation outcomes. Several stakeholders expected rotational grazing to enhance the production and diversity of grazing-sensitive perennial grass species. The main hypothesized mechanism underlying this expectation was that rotation grazing should reduce regrazing of these grass plants. To test this hypothesis, we monitored patterns of grazing and regrazing on individual tillers (ramets) of a grazing-sensitive grass species, Pascopyrum smithii (western wheatgrass) for three consecutive years. We measured regrazing rates in paddocks managed using moderate stocking and adaptive rotational grazing as well as paddocks grazed continuously, season-long at light, moderate, or heavy stocking rates. Tillers in heavily grazed paddocks were regrazed more than three times as frequently as tillers in moderately grazed pastures, reinforcing the importance of stocking rate as a driver of vegetation impact. At the ranch-scale, tillers were regrazed equally often under adaptive rotational and season-long continuous grazing management, and this result did not vary across years. Adaptive rotational grazing greatly increased heterogeneity among paddocks in patterns of regrazing, with some paddocks experiencing high utilization and others experiencing low utilization. In this semi-arid rangeland, tiller defoliation data do not support the hypothesis that adaptive rotational grazing leads to less regrazing at the ranch-scale. In line with these mechanistic results, the production and diversity of grazing-sensitive perennial grasses also failed to respond to adaptive rotational grazing after five years. However, adaptive rotational grazing may enhance management flexibility and provide opportunities to work towards other objectives, such as wildlife habitat

Adaptive, Multi-Paddock, Rotational Grazing Management: An Experimental, Ranch-Scale Assessment of Effects on Multiple Ecosystem Services

Decisions on how to move livestock in space and time are central to rangeland management. Despite decades of small-scale research, substantial uncertainty exists regarding the relative importance of cattle stocking rates per se, versus the movement of cattle in both space and time, in achieving desired vegetation and livestock outcomes at scales relevant to livestock producers. We report on a ranch-scale experiment comparing effects of collaborative, adaptive, multi-paddock, rotational management (CARM) versus more traditional, season-long, continuous rangeland management (TRM) on perennial grass density and production, cattle performance, and wildlife habitat, while holding the annual stocking rate the same in both systems. We collaborated with stakeholders to develop an adaptive grazing management plan, collected pre-treatment data in 2013, and implemented treatments during 2014 – 2020. Results for 2014 – 2018 were reported by Augustine et al. (2020); here we report on two additional years of results, covering a 7-year period of treatments from 2014 – 2020. With two additional years of measurements, we found no significant difference in total forage production in CARM vs. TRM treatments, averaged across all soil types in the experiment. In one year, we found that CARM increased forage production on loamy soils and decreased forage production on alkaline soils, but these differences were minor and in opposite directions, resulting in no net overall effect. Furthermore, we found that adaptive, rotational grazing management substantially reduced livestock weight gains in each of the first 6 years of the experiment, when cattle were managed as a single, large herd occupying each paddock sequentially. Across the 6 years, cattle weight gain averaged 15% lower in CARM vs. TRM. In the 7th year, stocking density in CARM was reduced 50% by giving cattle access to two paddocks at a time. This year also coincided with a drought. Under these conditions, cattle weight gains were identical in both treatments. Results emphasize the importance of replicated controls in assessing grazing management effects. Even in heterogeneous landscapes where livestock are moved adaptively among paddocks to match seasonal patterns of forage growth, such management may not lead to desired outcomes for vegetation and livestock

Complex Consequences of Herbivory and Interplant Cues in Three Annual Plants

Information exchange (or signaling) between plants following herbivore damage has recently been shown to affect plant responses to herbivory in relatively simple natural systems. In a large, manipulative field study using three annual plant species (Achyrachaena mollis, Lupinus nanus, and Sinapis arvensis), we tested whether experimental damage to a neighboring conspecific affected a plant's lifetime fitness and interactions with herbivores. By manipulating relatedness between plants, we assessed whether genetic relatedness of neighboring individuals influenced the outcome of having a damaged neighbor. Additionally, in laboratory feeding assays, we assessed whether damage to a neighboring plant specifically affected palatability to a generalist herbivore and, for S. arvensis, a specialist herbivore. Our study suggested a high level of contingency in the outcomes of plant signaling. For example, in the field, damaging a neighbor resulted in greater herbivory to A. mollis, but only when the damaged neighbor was a close relative. Similarly, in laboratory trials, the palatability of S. arvensis to a generalist herbivore increased after the plant was exposed to a damaged neighbor, while palatability to a specialist herbivore decreased. Across all species, damage to a neighbor resulted in decreased lifetime fitness, but only if neighbors were closely related. These results suggest that the outcomes of plant signaling within multi-species neighborhoods may be far more context-specific than has been previously shown. In particular, our study shows that herbivore interactions and signaling between plants are contingent on the genetic relationship between neighboring plants. Many factors affect the outcomes of plant signaling, and studies that clarify these factors will be necessary in order to assess the role of plant information exchange about herbivory in natural systems

Agricultural Research Service Weed Science Research: Past, Present, and Future

The U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS) has been a leader in weed science research covering topics ranging from the development and use of integrated weed management (IWM) tactics to basic mechanistic studies, including biotic resistance of desirable plant communities and herbicide resistance. ARS weed scientists have worked in agricultural and natural ecosystems, including agronomic and horticultural crops, pastures, forests, wild lands, aquatic habitats, wetlands, and riparian areas. Through strong partnerships with academia, state agencies, private industry, and numerous federal programs, ARS weed scientists have made contributions to discoveries in the newest fields of robotics and genetics, as well as the traditional and fundamental subjects of weed-crop competition and physiology and integration of weed control tactics and practices. Weed science at ARS is often overshadowed by other research topics; thus, few are aware of the long history of ARS weed science and its important contributions. This review is the result of a symposium held at the Weed Science Society of America\u27s 62nd Annual Meeting in 2022 that included 10 separate presentations in a virtual Weed Science Webinar Series. The overarching themes of management tactics (IWM, biological control, and automation), basic mechanisms (competition, invasive plant genetics, and herbicide resistance), and ecosystem impacts (invasive plant spread, climate change, conservation, and restoration) represent core ARS weed science research that is dynamic and efficacious and has been a significant component of the agency\u27s national and international efforts. This review highlights current studies and future directions that exemplify the science and collaborative relationships both within and outside ARS. Given the constraints of weeds and invasive plants on all aspects of food, feed, and fiber systems, there is an acknowledged need to face new challenges, including agriculture and natural resources sustainability, economic resilience and reliability, and societal health and well-being

Pre-mRNA Splicing Modulation by Antisense Oligonucleotides

Pre-mRNA splicing, a dynamic process of intron removal and exon joining, is governed by a combinatorial control exerted by overlapping cis-elements that are unique to each exon and its flanking intronic sequences. Splicing cis-elements are usually 4-to-8-nucleotide-long linear motifs that provide binding sites for specific proteins. Pre-mRNA splicing is also influenced by secondary and higher order RNA structures that affect accessibility of splicing cis-elements. Antisense oligonucleotides (ASOs) that block splicing cis-elements and/or affect RNA structure have been shown to modulate splicing in vivo. Therefore, ASO-based strategies have emerged as a powerful tool for therapeutic manipulation of splicing in pathological conditions. Here we describe an ASO-based approach to increase the production of the full-length SMN2 mRNA in spinal muscular atrophy patient cells

Environmental heterogeneity has a weak effect on diversity during community assembly in tallgrass prairie

Citation: Baer, S. G., Blair, J. M., & Collins, S. L. (2016). Environmental heterogeneity has a weak effect on diversity during community assembly in tallgrass prairie. Ecological Monographs, 86(1), 94-106. doi:10.1890/15-0888.1Understanding what constrains the persistence of species in communities is at the heart of community assembly theory and its application to conserving and enhancing biodiversity. The "environmental heterogeneity hypothesis" predicts greater species coexistence in habitats with greater resource variability. In the context of community assembly, environmental heterogeneity may influence the variety and strength of abiotic conditions and competitive interactions (environmental filters) to affect the relative abundance of species and biodiversity. We manipulated key resources that influence plant diversity in tallgrass prairie (i.e., soil depth and nitrogen availability) to increase environmental heterogeneity prior to sowing native prairie species into a former agricultural field. We compared variability in nutrient availability, aboveground annual net primary productivity (ANPP), and the composition of species between replicate plots containing soil heterogeneity manipulations and plots with no resource manipulations (n = 4 per treatment) during the first 15 yr of community assembly as a test of the "environmental heterogeneity hypothesis." The manipulations increased environmental heterogeneity, measured as the coefficient of variation in NO3-N availability and ANPP. Plant diversity, however, was similar and decayed exponentially and indiscriminately over time between the heterogeneity treatments. Species richness declined linearly over time in both heterogeneity treatments, but richness was higher in the more heterogeneous soil 2 yr following a second propagule addition 8 yr after the initial sowing. As a result, there was a lower rate of species loss over time in the more heterogeneous soil (0.60 species yr(-1)) relative to the control soil (0.96 species yr(-1)). Communities in each treatment exhibited strong convergence over time resulting from a shift in dominant species across all treatments and a gradual increase in the clonal C-4 grass, Andropogon gerardii. We attribute the weak effect of heterogeneity on diversity to increasing dominance of a clonal species, which decreased the scale of soil treatments relative to plant size, dispersal limitation, and absence of a key driver (grazing) known to increase plant diversity under a frequent fire regime. Thus, steering community assembly to attain high biodiversity may depend more on manipulating processes that reduce dominance and facilitate the arrival of new species than promoting environmental heterogeneity