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Herbivores alter plant biodiversity (species richness) in many of the world's ecosystems, but the magnitude and the direction of herbivore effects on biodiversity vary widely within and among ecosystems. One current theory predicts that herbivores enhance plant biodiversity at high productivity but have the opposite effect at low productivity. Yet, empirical support for the importance of site productivity as a mediator of these herbivore impacts is equivocal. Here, we synthesize data from 252 large-herbivore exclusion studies, spanning a 20-fold range in site productivity, to test an alternative hypothesis-that herbivore-induced changes in the competitive environment determine the response of plant biodiversity to herbivory irrespective of productivity. Under this hypothesis, when herbivores reduce the abundance (biomass, cover) of dominant species (for example, because the dominant plant is palatable), additional resources become available to support new species, thereby increasing biodiversity. By contrast, if herbivores promote high dominance by increasing the abundance of herbivory-resistant, unpalatable species, then resource availability for other species decreases reducing biodiversity. We show that herbivore-induced change in dominance, independent of site productivity or precipitation (a proxy for productivity), is the best predictor of herbivore effects on biodiversity in grassland and savannah sites. Given that most herbaceous ecosystems are dominated by one or a few species, altering the competitive environment via herbivores or by other means may be an effective strategy for conserving biodiversity in grasslands and savannahs globally.

The article "Exploring biodiversity of Uruguayan vascular plants through DNA barcoding" published in Frontiers in Genetics on October 15, 2024, discusses the use of DNA barcoding to study the biodiversity of Uruguayan vascular plants. The study aims to address the decline in biodiversity in Uruguay by establishing a DNA barcode national network. By analyzing 171 sequences from four loci for 50 vascular plant species, the researchers identified suitable markers for plant DNA barcoding and contributed to the Uruguayan Barcode of Life Initiative. The study highlights the importance of creating a comprehensive public database for species identification and biodiversity research. [Extracted from the article]

Questions: Herbivores change plant communities and biogeochemical cycles by changing species composition and soil organic matter contents through different mechanisms. Our objective was to evaluate the effects of livestock removal on plant species composition and soil organic matter stocks in savannas of the Río de la Plata grasslands. Locations: A subtropical savanna in Río Negro, Uruguay. Methods: The experiment consisted of a paired grazing exclusion randomized block design with five sites, where livestock was excluded for 29 years. We recorded differences in plant species composition in different strata and extracted soil cores to analyze soil carbon and nitrogen stocks, and δ13 carbon contents in two different soil organic matter fractions. Results: Long‐term livestock removal reduced plant species richness and diversity, altered the floristic composition and facilitated native‐shrub encroachment. Grazing exclusion modified the relative frequency of plant functional types and reduced summer‐growing grasses. We recorded 45 species common to both grazing and exclosure treatments, while 19 were present only in exclosure sites and 39 only in grazed sites. Livestock exclusion had a differential effect on soil organic matter formation, increased soil organic carbon and nitrogen stocks in the mineral‐associated organic matter (MAOM) but tended to slightly reduce them in the particulate organic matter fraction (POM). Grazing removal modified the C3/C4 species cover and these differences were reflected in the δ13C contents of both POM and MAOM fractions. Conclusions: Removal of domestic herbivores increased shrub abundance, decreased plant species richness and diversity but increased total carbon and nitrogen contents in soil organic matter. Our results suggest that grazed and exclosure areas should be combined mosaically in the landscape to maximize plant species diversity and soil organic carbon sequestration. [ABSTRACT FROM AUTHOR]

Question: Understanding the patterns of alien plant invasions and their underlying drivers is a key step in conserving the remaining native grasslands of Uruguay. We addressed the level of invasion by considering the four invasive alien plants of these ecosystems, Cynodon dactylon, Eragrostis plana, Senecio madagascariensis and Ulex europaeus, throughout the country. Location: Remnant native grasslands of Uruguay, constituting part of the Río de la Plata grasslands. Methods: Extensive fieldwork was carried out over five years of data collection, including hierarchically randomized observations (around 2000) nested in 137 10 × 10‐km2 squares covering different geomorphological regions. For each invasive alien species, we constructed distribution maps to show their patterns; for the two most abundant, we fitted models to identify the main explanatory variables at different spatial scales. Results: We found that 77% of the squares were invaded by at least one target species. The level of invasion varied between regions and target plants. The most abundant invasive alien species were Cynodon dactylon and Senecio madagascariensis; while Eragrostis plana and Ulex europaeus were scarce. Cynodon dactylon cover was related to a set of variables at different spatial scales, including climate, topography and several local community descriptors. Senecio madagascariensis cover was positively associated with grassland fragmentation and anthropic disturbance at the landscape, and a few local descriptors. Conclusions: The large sampling effort at the country level, with a randomized design, allowed for a reliable assessment of the level of invasion of Uruguayan grasslands and its possible drivers. This is an important step in the design of policies to conserve Uruguay's remaining native grasslands. We suggest that the prevention should focus on the Basaltic Cuestas region, while control and containment should prioritize the eastern and south‐central parts of the country, focusing mainly on Cynodon dactylon management. [ABSTRACT FROM AUTHOR]

Current trends in agricultural intensification lead to degraded grasslands, requiring their restoration through native species reintroduction. Various techniques are available for harvesting seeds from donor sites. However, little is known about their performance in South American C3/C4 mixed grasslands, where studies are scarce. Their particular species composition and phenology, with different flowering periods, require specific harvest strategies. We evaluated mechanical seed harvest in a northern Uruguay grassland, part of Río de la Plata grasslands. Performance of two mechanical harvest methods (seed‐stripper and dry hay) was compared in two harvest seasons (late‐spring and mid‐summer). The evaluation considered the quantity and identity of harvested seeds, and their germination in a greenhouse. Hand collections were made to assess standing seed yield. For each seed mixture, efficiency of mechanical harvests (number of seeds and seedlings compared to hand collection), proportion of germinated seeds, species transfer relative to donor site, and composition were calculated. Results revealed trade‐offs between harvests: seed‐stripper in late‐spring presented low seed collection efficiency (2% for seeds, 5% for seedlings) and species richness (43% transfer), but high seed germination (64%), showing selectivity toward winter species; seed‐stripper in mid‐summer and dry hay in both seasons showed high seed collection efficiency (42–154% for seeds, 26–50% for seedlings) and species richness (65–80% transfer), resembling donor site, albeit lower seed germination (9–20%). Seed‐stripper performance varied between seasons, while dry hay remained consistently effective. These results are pioneering for grassland restoration in Uruguay, encouraging future studies to focus on establishment in the field. [ABSTRACT FROM AUTHOR]

Questions: Herbivory and fire are the main disturbance drivers in open ecosystems. The aim of this study was to evaluate the effects of fire, cattle grazing, and their interaction on structural traits and the Normalized Difference Vegetation Index (NDVI) of the tussock grass Saccharum angustifolium, and its temporal dynamics in a subhumid grassland. Location: Grasslands of the Eastern Hills, Uruguay. Methods: We set three blocks (four plots of 300 m2 each) in a homogeneous grazed area dominated by S. angustifolium within a protected area. Each block presented the combinations that emerged from the two levels of cattle grazing (grazed/ungrazed) and burning (burned/unburned) factors. The experimental burning was carried out in the spring. Clump volume, number of flowering culms, NDVI of S. angustifolium, and soil variables were measured for 2 years. Results: Burning efficiency (plant biomass burned of the total available) was 82%, burn intensity ranged from 178–610 kW m−1, and the soil temperature increased 40% compared with pre‐fire measurements. The volume of S. angustifolium clumps decreased with fire, and the difference between burned–unburned plots decreased with time. The burned–ungrazed treatment increased the number of S. angustifolium flowering culms. NDVI of S. angustifolium clumps increased 50% with fire, and then decreased with time. Soil temperature was higher in burned treatments, and moisture was higher in unburned treatments on some dates. Bulk density, for the 0–5‐cm depth, was 9% higher in burned than in unburned plots irrespective of grazing. Conclusions: Our results provide new data in favor of the management practice carried out by ranchers in Uruguayan grasslands dominated by S. angustifolium. Our data complement the evidence that a fire–grazing interaction can maintain grasslands in different phases of a stable state. Our results constitute a useful contribution for the managers/authorities of the protected area, and can be extrapolated to other tussock grass‐dominated grassland areas. [ABSTRACT FROM AUTHOR]

In this article we make comments on some methodological issues and on the general approach of the paper "Back to the future? Conservative grassland management can preserve soil health in the changing landscapes of Uruguay" by Ina Säumel, Leonardo R. Ramírez, Sarah Tietjen, Marcos Barra, and Erick Zagal, Soil 9, 425–442, https://doi.org/10.5194/soil-9-425-2023. We identified various design and methodological problems that may induce potential misinterpretations. Our concerns are of three different types. First, there are aspects of the study design and methodology that, in our opinion, introduce biases and critical errors. Secondly, the article does not put forth any novel propositions and ignores extensive local literature and aspects that are central to the interpretation of the data Finally, we are concerned about the possible interpretations of a study, generated from institutions based on developed countries with not the participation of local scientists from the Global South in the design of policies and development of non-tariff barriers for South American countries. [ABSTRACT FROM AUTHOR]

Aim: The intensification of livestock systems generates structural and functional changes in native grassland, which alter their capacity to respond to disturbances. Our objective was to evaluate the resilience to an extraordinary consecutive‐droughts event, across an intensification gradient of livestock systems. Our prediction was that sites with more intensive management (less diverse) will have lower resilience (as resistance and/or recovery) to drought. Location: South‐central region of Uruguay. Methods: We evaluated the resilience (as resistance and recovery) to consecutive droughts, across an intensification gradient of livestock systems. We analyzed the effect of diversity on resilience at two scales: (1) regional — an observational experiment with real commercial farms, where we compared three systems with an increasing level of intensification that determine changes in diversity, (2) patch — we carried out a manipulative experiment with different grazing management intensities determined by the level of biomass removal and fertilization. In both experiments, resistance and recovery were calculated from the Normalized Difference Vegetation Index. Results: The most intensified and less diverse management (sown pastures) had significantly lower resistance than native and overseeded grassland. Also, it showed the lowest recovery rate, and its productivity did not reach previous values after the drought's end. The grazing intensification gradient at the plot scale did not show clear differences among treatments both for resistance and recovery. However, resistance of the individual plots showed a positive significant association not only with species richness and diversity, but also with evenness and diversity of functional groups. Conclusion: Our research supports the insurance hypothesis by demonstrating that farms with greater biodiversity (less intensive management) have higher resistance to drought. We found that species richness is not enough to account for the effect of diversity on resilience. Our results emphasize the importance of preserving grassland biodiversity to maintain resilient ecosystems in the face of climate change. [ABSTRACT FROM AUTHOR]

Questions: Disturbances change the fundamental properties of grasslands on different spatio‐temporal scales. Uruguay is part of the Río de la Plata grasslands, and 60% is occupied by native grasslands dominated by perennial species. In plant communities dominated by tall tussock grasses, patchy and asynchronous field burns are a traditional practice among ranchers. We asked: how do the structural characteristics of vegetation vary in patches with different time since the last fire? Location: Grassland of the Eastern Hills, Uruguay. Methods: We selected 18 grazed sites in order to obtain a spatial chronosequence with four age categories since the last fire: 6, 18, 30, and more than 60 months before sampling. Plant composition, species richness, coverage of each species, bare soil, and standing dead biomass were determined in plots of 25 m2. We used non‐metric multidimensional scaling (NMDS) and the multiresponse permutation procedure (MRPP) to determine differences in community composition, and the ANOVA or the Kruskal–Wallis test to compare structural variables between patches of different burning ages. Results: Patches of different burning age had different species compositions. Species richness, Shannon diversity index, evenness, and bare soil decreased, whereas plant coverage, standing dead biomass, and vegetation strata increased as time since the last fire increased. Conclusions: Our study confirmed occasional and localized field‐burns as major driver of vegetation change and structural diversity in a grazed native grassland dominated by a tall tussock grass. On a larger scale, we observed the coexistence of patches in different successional stages and differences in species composition between patches belonging to early stages. These grasslands require asynchronous burning of patches to generate structural changes that maximize both the spatial and temporal heterogeneity. [ABSTRACT FROM AUTHOR]