Exotic Grasses Research Articles

GROWTH CURVE OF A TROPICAL MIXED-GRASS PASTURE IN A HOT AND HUMID CLIMATE

<p><strong>Background. </strong>Pasture growth rate (PGR, kg/ha/day) depends on climatic and management practices. However, studies on the influence of the environment on pasture production and productivity of dry matter are scarce in tropical, hot, and humid regions of México. <strong>Objective.</strong> To estimate the pasture growth curve using time and climatic variables. <strong>Methodology.</strong> We related, through nonlinear models, the accumulated growth of a pasture composed of native grasses mixed with exotic grasses, using time and the variables temperature and day length as independent variables, the latter integrated into a single variable called thermal photo units (PTU). We estimated the daily growth rates of five divisions; from these, the forage yields for ten days until completing 29 periods. The best-fit models had the largest coefficients of determination and the lowest Akaike’s information criterion. <strong>Results.</strong> The model that best described the relationship between cumulative yield (Y) and cumulative growing days (X) was reciprocal-quadratic: y = x/(0.097535 – 0.0000881x + 0.0000006810x<sup>2</sup>) with R<sup>2</sup><sub>Adj,</sub> of 0.9988 and an AIC<sub>C</sub> of 222.6. The model that best described the relationship between the accumulated performance and the accumulated PTU was rational: y = (- 317.8 + 1.594x + 0.00001307x<sup>2</sup>)/(1 + 0.001059x + 0.00000001964x<sup>2</sup>), with R<sup>2</sup><sub>Adjt</sub>.=0.9985 and AIC<sub>C</sub>=233.4. Likewise, a two-segment model showed a close fit. The logarithmic model described the first segment: y<sub>1</sub> = -2268 + 417.2*(ln(x)), when y<sub>2</sub> =1079.3e<sup>0.00003932X</sup>, if x > 8415; with R<sup>2</sup><sub>Adj.</sub> = 0.9975 and AICc = 245.1. The value 8415 PTU was when the first derivative of both models coincided. <strong>Implications.</strong> The information generated is useful because it allows grazing system adjustment concerning the correct stocking rate application and designing more efficient grazing rotations. <strong>Conclusions. </strong>The conversion of growth rates to accumulated yield for ten-day periods produced a smooth curve that allowed fitting high-precision nonlinear models to predict forage accumulation from time and climatic variables.</p>

Will climate change favor exotic grasses over native ecosystem engineer species in the Amazon Basin?

Several anthropic disturbances, including deforestation, fires, the building of roads and dams, have intensified in Amazon in last decades. These disturbances contribute to an increase in the occurrence and intensity of extreme events, such as more frequent floods and more severe droughts, due to climate change. Along the Amazonian rivers, aquatic herbaceous plants, mainly of the Poaceae family, are very abundant and produce up to three times more biomass than the adjacent flooded forests, and some are considered ecosystem engineers given their structuring role in these environments. Invasive grasses have spread through the Neotropics and are gradually entering the Amazon via the Arc of Deforestation. These invasive species often attain high coverage, suppress other species, and become dominant in both disturbed and pristine habitats. The aim of this study was to establish the current and future distribution patterns of two native ecosystem engineer species (Echinochloa polystachya and Paspalum fasciculatum) and two invasive species (Urochloa brizantha and Urochloa decumbens) in the Amazon Basin. To predict the future climate, we used three scenarios, namely SSP1–2.6, SSP3–7.0 and SSP5–8.5 for the years 2040, 2080 and 2100, to project climatically suitable areas. The current climatically suitable range for the native ecosystem engineer species was estimated at 33–35% of the Amazon Basin, while the invasive ones have a range of 53–84% in potential climatically suitable areas. A decrease in the areas of suitability of the two ecosystem engineer species, E. polystachya and P. fasciculatum, was observed in all scenarios and years, while only the invasive U. brizantha showed an increase in suitable areas in all years. These results raise concerns about the invasion of grasses with high aggressive potential that could result in the exclusion of native ecosystem engineer species and their ecological roles.

Forest restoration in old pasture areas dominated by <i>Urochloa brizantha</i>

In the present study it was evaluated the density of recruits in an area previously occupied by Urochloa brizantha pasture undergoing forest restoration and in a Semideciduous Forest. Was evaluated the effect of the available light on the biomass of the exotic grass, and investigated associations of recruit density with soil variables and understory light availability. The seed rain in both areas was also evaluated. The biomass of U. brizantha was positively associated with available light and, a negative association was found between recruit density and available light when considering the two areas together. A negative associatio between recruit density and soil pH was found. The results suggest that the low soil fertility did not limited recruitment in the semideciduos forest. The results showed that high resource availability favors the competitivity of U. brizantha, impairing the forest restoration in area previously used as pastures. So, pratices that result in decreasing in light availability would favors the forest restoration in areas previously used as pasture.

Mapping the effects of Melinis minutiflora invasion on soil nitrogen dynamics in the Brazilian savanna: A dual-isotope approach

The invasion of exotic grasses in the neotropical savannas is closely linked to the conversion of the native landscape into agriculture and cultivated pastures. Molasses grass (Melinis minutiflora P.Beauv.) is one of the main invasive species in abandoned fields and native vegetation areas with the potential to alter both the structure and functioning of these ecosystems. We used the dual-isotope approach to evaluate the impact of molasses grass invasion on nitrogen dynamics in the soil of a savanna formation located in the Cerrado region of Central Brazil. We divided three plots (70×80 m) in 300 sampling units (7×8 m each) classified by predominant vegetation type: native grasses (NG), native cerrado sensu stricto (CSS), or molasses grass (MG). We interpolated the soil δ15N and δ13C (0–10 cm depth) in the three plots to continuous surfaces using semivariogram fit and ordinary kriging models. We also compared the aboveground biomass, litter decomposition rates, and soil N pools among vegetation types. MG and NG had higher litter decomposition rates than CSS. Soil pH was higher under MG compared to CSS and NG. The local soil δ15N isoscapes show the presence of MG in areas with higher soil δ15N. Soil δ13C under all vegetation types indicates a mixture between the C3 and C4 sources present in the soil organic matter, with the highest soil δ13C under MG. The dual-isotope approach showed the altered processes in the invaded areas with an intensification of the soil N dynamics in the long term compared to the areas dominated by the wood strata and by native grasses. The C and N isoscapes indicated that plant-soil interactions yielded different patterns and showedthe effect of the molasses grass invasion. Therefore, the spatial distribution must be accounted for when assessing the effects and outcome of species interactions and invasion pressure.

Invasion by an exotic grass species homogenizes native freshwater plant communities

Abstract A growing body of evidence has shown that biological invasions cause shifts in species composition of communities in space and time. Although biological invasions are considered a major driver of biotic homogenisation worldwide, most previous studies were conducted at small spatial scales and over short time periods, which may have underestimated the impacts of exotic species on native communities. Using a unique dataset of aquatic plants sampled in 235 sites over 12 years (2007–2010 and 2015–2019) in a large reservoir (Itaipu Reservoir; 1350 km2), we analysed how the invasion of a non‐native grass Urochloa arrecta affects the species richness, ecological uniqueness (i.e. local contribution to beta diversity—LCBD) and temporal β–diversity of native plant communities. From 3934 surveyed plant communities, U. arrecta was recorded in 2888 samples and it was absent from 1046 samples. Overall, species richness and ecological uniqueness of native plant communities were markedly lower in sites invaded than non‐invaded by U. arrecta. From 2007 to 2019, the ecological uniqueness of native plants was 60% lower in the invaded than non‐invaded sites. Whereas in invaded sites species loss was the dominant process driving native communities over time, in non‐invaded sites gain of new native species was the primary process underlying community trajectories. Moreover, comparing native plant communities before and after the invasion of U. arrecta, species richness, ecological uniqueness and species gains of native plant communities decreased, whereas species losses increased after the invasion of U. arrecta. Finally, the positive relationship between native biodiversity and precipitation was stronger in non‐invaded than invaded sites. Synthesis. Our findings provide comprehensive evidence that an invasive plant is decreasing the spatial and temporal β–diversity of native plant communities through declining species richness, rather than simply correlating with them. This suggests that U. arrecta is driving native plants to become less diverse and homogeneous after the invasion, both spatially and temporally. Our findings illustrate that at broad scales, aquatic plant communities may become increasingly homogeneous with the increasing number of biological invasion events taking place worldwide.

Drought reduces invasive grass performance by disrupting plant-microbe interactions that enhance plant nitrogen supply.

Non-native invasive plants can promote their dominance in novel ecosystems by accelerating soil nutrient cycling via interactions with decomposer microbes. Changes in abiotic conditions associated with frequent or prolonged drought may disrupt these interactions, but the effects of disruption on invasive plant performance and the underpinning mechanisms are poorly understood. Here, we used rainout shelters in an experimental field setting to test the hypothesis that drought reduces invasive plant performance by reducing microbial metabolic activity, resulting in decreased nitrogen flow to plants. We imposed growing season drought on populations of the exotic grass Microstegium vimineum, a widespread invasive plant in eastern deciduous forests, and quantified effects on aboveground and belowground biomass, and carbon (C) and nitrogen (N) cycling among plants, decomposers, and soil. Drought resulted in a 24% decrease in soil respiration, a 16% decrease in phenol oxidase enzyme activity, a 12% decrease in dissolved organic N concentration, and a decrease in the C:N ratio of particulate organic matter, suggesting reduced microbial metabolic activity and nutrient mining of soil organic matter. Drought also reduced aboveground Microstegium biomass 33% and increased Microstegium leaf C:N ratio, consistent with a decline in plant N uptake. We conclude that drought can reduce the performance of existing invasive species populations by suppressing plant-microbe interactions that increase nitrogen supply to plants, which may have consequences for the persistence of invasive plants under hydrologic change.

Factors affecting savanna and forest regeneration in pastures across the cerrado

The Cerrado region comprises the world's most biodiverse savanna and the largest cultivated pastures for cattle in Brazil. Forty percent of these pastures are unproductive or degraded, with bare soil and native vegetation increasingly replacing exotic forage grasses. This study sought to investigate the regeneration of native vegetation in the pastures of the Cerrado and to evaluate the contribution of biophysical, land management, and landscape attributes to this process. Across the Cerrado, we analyzed pasture plant communities and the attributes of pasture management intensification, fire events, landscape native vegetation cover, and climate and soil types of 93 active pastures and 15 abandoned pastures. For the abandoned pastures, time since abandonment was an additional variable. On actively cultivated pastures, savanna regeneration varied from 0 to 70%, with a diversity of herbs and woody species. Pasture management was the main predictor of savanna regeneration on cultivated pastures. On abandoned pastures, time since abandonment was the main predictor. Exotic grass cover had a strong negative relationship with savanna regeneration and they were present even in pastures abandoned for 44 years. Our study reveals the potential of natural regeneration of the Cerrado and its particular predictors. The occurrence of pastures with high natural regeneration indicates that national policies can promote native vegetation restoration and silvopastoral systems with predictable, low cost implementation.

Invasive grass and litter accumulation constrain bee and plant diversity in altered grasslands

Ecologists consider biological invasions one of the primary drivers of global change. Many remaining grasslands in North America have extensive invasions of exotic grass species that have replaced native plant species. In the Northern Great Plains, exotic cool-season grasses Kentucky bluegrass (Poa pratensis) and smooth brome (Bromus inermis), paired with human alterations to the landscape and historical disturbance regimes, have resulted in functionally and structurally altered grassland plant communities. These changes may extend to impact species that rely on these plant communities, such as bees. Bees are ecologically diverse and serve important pollinator roles but are at risk from the loss and change of floral and nesting resources in plant communities. Our objectives were to determine whether Kentucky bluegrass and smooth brome alter the bee and forb species richness in invaded Northern Great Plains grasslands and how litter accumulation, grass cover, the amount of bare ground, and forb species richness interact with bee functional traits. To do this, we surveyed 67 grassland sites from 2017 to 2020 with two bee-sampling methods (268 netting and bee bowl surveys total) and vegetation cover surveys at each site. We collected 20,559 bees from 201 bee species and observed 249 forb and shrub species in vegetation surveys. Bee richness and Shannon diversity were associated with greater forb richness while forb richness was significantly lower with thicker litter depths and higher with a greater coverage of all grasses other than Kentucky bluegrass and smooth brome. Bee trait analyses showed varying relationships with plant community variables. Of these, litter depth and Kentucky bluegrass cover were associated with lower ground-nesting bee abundance while small-bodied bee abundance was positively associated with increasing bare ground. While our results support the close relationship between bee and plant diversity, we also found litter depth, in particular, contributed to the structure of these two communities. Specifically, Kentucky bluegrass and smooth brome are two exotic grass species associated with thatch-forming litter layers, especially under idle management that appear to simplify bee and forb communities. Our results make apparent the importance in maintaining structural and compositional diversity in invaded grasslands to support diverse bee communities.

Setting the stage for the restoration of an Annona glabra swamp after exotic grass invasion

The expansion of cattle ranching in the coastal plain of the Gulf of Mexico is transforming freshwater swamps resulting in the reduction of swamps area and the introduction of invasive exotic grasses. This study seeks to determine the structure of the remaining population of Annona glabra in a grassland, evaluate vegetation and environmental conditions of the grassland, and determine the germination capability of A. glabra under different cover conditions of grass growth and two flood levels. The study area is a flooded grassland invaded by Echinochloa pyramidalis in central Veracruz, Gulf of Mexico. In the grassland, we censused and mapped the remaining individuals of A. glabra. We sampled the vegetation and measured the physicochemical characteristics of the soil and water. To evaluate the effect of the invasive grass on the germination of A. glabra seeds, we designed two greenhouse experiments: one (E1) under soil moisture at field capacity and another (E2) under flooded conditions. We found 312 remnant individuals. We recorded 31 plant species, most (72.7%) classified as aquatic/semiaquatic. The relative importance value was highest for E. pyramidalis, Mimosa pigra, and Eleocharis mutata. BEST analysis did not detect significant correlations between vegetation and physicochemical variables, indicating homogeneous environmental conditions. Seed germination was above 80% in E1 and below 20% in E2 in all grass cover levels. Although flooding decreases germination rates, substantial proportion of seeds can germinate, suggesting that natural succession is viable. Based on our results, the flooded grassland has conditions to restore swamp.

Niche partitioning overrides interspecific competition to determine plant species distributions along a nutrient gradient

Changes in some combination of niche availability, niche overlap and the strength of interspecific interactions are thought to drive changes in plant composition along resource gradients. However, because these processes are difficult to measure in the field, their relative importance in driving compositional change in plant communities remains unclear. In an Australian temperate grassland, we added seeds of three native and three exotic grasses to 1875 experimental plots in a way that allowed us to simultaneously estimate niche availability, niche overlap and the strength of pairwise interspecific interactions along a gradient of nutrient availability, obtained by adding 0, 5 or 20 g m−2 each of nitrogen, phosphorous and potassium jointly to plots. Niche availability (the proportion of microsites suitable for establishment and growth) was generally low and did not vary in response to nutrient addition. Most species co‐occurred along the nutrient gradient by partitioning the available niche space. Where species interacted due to niche overlap, the abundance of one species, the native Chloris truncata, was usually facilitated by other species, with each of the five other species increasing the niche availability to C. truncata under at least one nutrient treatment. Chloris truncata also competitively excluded two species from some but not all sites they could otherwise have occupied. These outcomes did not clearly differ across nutrient treatments. Our results show that fine‐scale spatial heterogeneity in establishment microsites can enable species to co‐occur via niche partitioning, and competitive exclusion is rare. This finding contributes to an emerging picture that niche partitioning is common and frequently a stronger influence on recruitment outcomes than interspecific competition. The importance of competition in structuring plant communities may be overestimated if recruitment processes are overlooked.

Carbon estimation in an integrated crop-livestock system with imaging sensors aboard unmanned aerial platforms

Biomass and carbon estimates in integrated crop–livestock (iLP) systems remain scarce. Recently, sensors aboard an unmanned aerial vehicle (UAV) have been used for such estimation and can represent an efficient and low-cost method for acquiring accurate remote-sensing data. This study aimed to estimate the relationship between vegetation indices (VIs) and carbon stock in an upland rice field intercropped with Brachiaria, an exotic grass species in the savanna ecosystem of Brazil (Cerrado biome), using multispectral aerial imaging with a high cartographic scale. The research was conducted in an experimental iLP system located at the Brazilian Agricultural Research Corporation (Embrapa Arroz e Feijão), Goiás State. During the data collection stage, flights were conducted with a fixed-wing UAV (eBee Plus RTK) on the same day or close to collecting biomass samples in the field. In the processing step, a correlation was performed between the normalized difference vegetation index (NDVI), simple ratio (SR), soil-adjusted vegetation index (SAVI), and modified photochemical reflectance index (MPRI) VIs and the biomass measured in the field. The results indicated that the vegetation index (VI) that used the near-infrared (NIR) band showed a stronger correlation with biomass than the VI that used only the visible band information. All VIs were significantly correlated with the estimated field biomass (P < 0.05) using Pearson's correlation. The regression models were able to predict the biomass and carbon stock in Phase 1 (3.93 Mg ha−1, 1.66 Mg ha−1, R2 = 0.748) and Phase 2 (7.53 Mg ha−1, 3.19 Mg ha−1, R2 = 0.816). From the best model selected for each phase, maps with the spatial and temporal distribution of the biomass of the iLP system were plotted, demonstrating one of the advantages of employing remote sensing techniques based on drones and multispectral imaging sensors.

Subcellular distribution and physiological responses of native and exotic grasses from the Pampa biome subjected to excess manganese

Fungicides containing manganese (Mn) applied to control plant diseases increase the concentration of Mn in soils, which may potentiate Mn toxicity in acid soils. Some species of wild grasses, such as those from the Pampa biome located in South America, or even those introduced into this biome, may possess different mechanisms of tolerance to excess Mn. The present study aimed to evaluate the subcellular distribution and physiological and biochemical responses of exotic and native grasses from the Pampa biome, cultivated in Mn excess. The experiment was conducted in nutrient solution in a greenhouse, in an entirely randomized design, bifactorial 4 × 4, consisting of four Mn concentrations (2 [control], 300, 600 and 900 μM) and four species (two exotic: Avena strigosa and Lolium multiflorum; and two native: Paspalum notatum and Paspalum plicatulum). At 27 days of exposure to the treatments, biomass and growth rates, leaf gas exchange with the environment, photosynthetic pigment concentrations of malondialdehyde and H2O2, antioxidant enzyme activities (SOD and POD), and subcellular distribution of Mn were evaluated. Most of the grasses showed high concentration of Mn in tissues, mainly, in the shoot. In the presence of 900 μM Mn, more than 80% of the absorbed Mn was compartmentalized in the cell walls and vacuoles of the cells. Compartmentalization of Mn excess into metabolically less active organelles is the main tolerance factor in grasses. Physiological and biochemical responses were stimulated in the presence of 300 μM Mn, while 900 μM Mn negatively affected biochemical-physiological responses of grasses. The species L. multiflorum was most sensitive to excess Mn, while P. notatum was the most tolerant.

Exotic Grasses Reduce Infiltration and Moisture Availability in a Temperate Oak Savanna.

Biological invasions represent one of the most urgent conservation challenges. Oregon white oak (Quercus garryana) savannas, a complex of grassland and transitional forest, are especially sensitive to these invasions. These ecosystems have been severely degraded and fragmented over the past century and are being encroached by conifers, and oak seedlings are failing to emerge from the understory at many locations. Understanding competitive interactions between Oregon white oak and associated native and exotic vegetation would provide insight into forest-grassland dynamics and the role of exotic grasses in the decline of native species, the processes that maintain temperate savanna ecosystems, and the role of soil water uptake by individual savanna species in contributing to overall species assemblages. In this study, we quantified the soil moisture budget for invaded and uninvaded oak-associated ecosystems. From February to October 2007 we used a split paired plot experiment in Duncan, British Columbia, Canada to measure soil moisture on treatment sites where exotic grasses were removed with herbicide and control plots where they were not, using three depths (5, 20, and 35 or 50 cm) in the soil profile. Our results show that the plots that contained exotic vegetation had a faster rate of soil drying following precipitation events at the 5 cm depth than plots with the predominantly native species. We attribute this difference to the capacity of exotic vegetation to exploit soil moisture more rapidly than native vegetation at times of the year when native vegetation cannot. These results provide insight into one mechanism by which exotic grasses affect associated native plants and could help guide restoration efforts.

Contrasting effects of native and exotic vegetation on soil infiltrability in the Sonoran Desert

Invasion by exotic grasses is transforming drylands across the planet, but the ecohydrological feedbacks of such invasions are not fully understood. For example, in the Sonoran Desert, previous studies have shown that buffelgrass (Cenchrus ciliaris) alters the spatial patterns of soil moisture, leading researchers to hypothesize that such alterations are related to the plants' effects on soil infiltrability. To evaluate this hypothesis, we compared field-saturated hydraulic conductivity (Kfs) in a native shrubland with that in a neighboring savanna extensively dominated by exotic buffelgrass. We measured Kfs during the dormant and growing seasons in both canopy and intercanopy zones. We found that Kfs was generally lower during the dormant season than during the growing season. There were no significant differences between sites during the dormant season, and at both sites, Kfs was 6–7 times higher under shrubs than in the intercanopies. During the growing season, Kfs for the exotic intercanopy was comparable to that for shrub cluster edges (140 mm h−1) and was more than twice that for the native intercanopy. Both shrubs and buffelgrass improved Kfs by reducing soil bulk density (thus increasing porosity). Additionally, surface roughness in the exotic intercanopy was nearly 3 times higher than in the native intercanopy. The combination of greater surface roughness and higher infiltration rates during the growing season most likely alters hydrological connectivity in savannas invaded by exotic grasses such as buffelgrass. By capturing portions of the runoff generated in the intercanopy, these grasses reduce runon into shrub patches, with potentially substantial impacts on native vegetation dynamics and stability.

How rural actors relate to nature. Perceptions of ecosystem services in the semi-arid Chaco of northern Argentina

In drylands, rapid changes in land use have been interpreted as conflicts over the appropriation of ecosystem services (ES). A better understanding of these conflicts can lead to the formulation of sustainable management policies by capturing the value of nature. We undertake a Q-method study to identify perceptions related to ES and the main drivers of change threatening ES in the semi-arid Chaco region of northern Argentina. Our main results highlight the existence of three significant perspectives, with areas of consensus and disagreement among rural actors, namely: (1) Traditional Creole; (2) Agribusiness; and (3) Territorial Creole. The current viewpoints of rural actors are diverse but include certain unifying themes. All perspectives favor water and exotic grasses as the most important ES. As main drivers of change threatening ES, the legal framework is a very important factor as well as the availability of fodder. Our study is a significant contribution to understanding the reasons for land use decisions and the appropriation strategies that rural actors use in defining their valuation of several ES.

Hacia la restauración con Annona glabra (Annonaceae) de una selva inundable: establecimiento y crecimiento de plántulas, y cambio en la vegetación acompañante

Antecedentes y Objetivos: Actualmente existe deterioro y disminución de selvas inundables debido a la deforestación para ganadería e introducción de pastos exóticos. Los objetivos del presente estudio fueron evaluar el porcentaje de supervivencia de plántulas de Annona glabra, el cambio en la vegetación acompañante, y estimar los costos de los tratamientos experimentales de restauración ecológica de una selva inundable de A. glabra transformada en pastizal e invadida por el pasto exótico Echinochloa pyramidalis. Métodos: El estudio se realizó en un pastizal inundable en la costa central de Veracruz, México. Consistió en sembrar cuatro plántulas de A. glabra en cuadros experimentales expuestos a distintas técnicas de restauración. Se probaron 15 tratamientos experimentales que consistieron en cinco técnicas de restauración (sin modificación, cubierta plástica, plantación de Pontederia sagittata, remoción de suelo, y elevación del suelo) y tres pretratamientos aplicados a las plántulas sembradas (plántulas de vivero con y sin fertilizante, plántulas de selva) en un diseño de bloques al azar.Resultados clave: Se registró baja supervivencia de plántulas (30.7%), siendo mayor en plántulas de selva (41.1%). El mayor porcentaje de supervivencia se registró con la técnica de elevación del suelo, seguido de la de remoción. Se registraron 40 especies en la vegetación; la mayor riqueza específica se observó en las técnicas de elevación del nivel del suelo y remoción. Las especies con mayor Valor de Importancia Relativa fueron Echinochloa pyramidalis, Mimosa pigra y Annona glabra. El pretratamiento en el cual se obtuvieron las plántulas directamente de la selva fue el más económico.Conclusiones: Se requieren acciones para incrementar el éxito de la reforestación. Para futuros proyectos de restauración, recomendamos la elevación del suelo en áreas de transplante y cubierta de plástico previo a la plantación, para incrementar la probabilidad de supervivencia, y reducir la cobertura del pasto; además de la reforestación con plántulas colectadas de un fragmento de selva.

Forage offering and seasonal intake comparisons to evaluate European rabbit threat in Nothofagus forests of southern Patagonia

BackgroundThe European rabbit (Oryctolagus cuniculus L. 1758) was introduced into different regions of the world, generating significant trade-offs that critically impacted native vegetation. Here, we evaluate the rabbit's forage intakes in three vegetation types (forests, shrublands, and grasslands) along the four seasons in a temperate forest landscape in Southern Patagonia and discuss the potential threats over native vegetation. We formulated the following questions: (i) what is the forage offer at each vegetation type? (ii) what is the rabbit's forage intake and how it varied across the seasons along the year? and (iii) which vegetation types and plant life forms were more used according to the rabbit's forage intakes?MethodsWe censused understory vegetation to characterize the forage offer at each vegetation type and determined seasonal dietary intakes using microhistological analysis of pellets. The plant species identified in the field were grouped according to life form classes (tree regeneration, shrubs, forbs, graminoids, orchids, ferns, bryophytes, and hemiparasites). Data were analysed through uni- and multi-variate analyses, determining relationships between forage offer and the rabbit's forage intakes.ResultsForage intakes revealed changes in plant life form consumption across vegetation types, where intake pressure was considerably different for tree regeneration (p = 0.001), graminoids (p = 0.001), and hemiparasites (p = 0.001). Besides, significant changes in consumption among seasons were detected for shrubs (p = 0.001), ferns (p = 0.030), and hemiparasites (p = 0.002). Although many species play an important role in the rabbit's forage intake networks (e.g., Chiliotrichum diffusum, Holcus lanatus), the strongest intake linkages were found in exotic grasses (e.g., Poa pratensis and Festuca sp.), native hemiparasites (e.g., Misodendrum sp.), native shrubs (e.g., Empetrum rubrum), and native trees (e.g., Nothofagus sp.). The summer and autumn seasons presented higher intake compared to the winter and spring seasons. Furthermore, hemiparasites intake (e.g., Misodendrum sp.) suggests that rabbits utilize different forage sources depending on the vegetation types.ConclusionsRabbits regularly inhabit the forest, even though it is not their preferred vegetation type to live. Rabbit management entails isolating regions that are more favourable to intake and emphasizing the year's season for rabbit control efforts.

Application of modern coexistence theory to rare plant restoration provides early indication of restoration trajectories.

Restoration ecology commonly seeks to re-establish species of interest in degraded habitats. Despite a rich understanding of how succession influences re-establishment, there are several outstanding questions that remain unaddressed: are short-term abundances sufficient to determine long-term re-establishment success, and what factors contribute to unpredictable restorations outcomes? In other words, when restoration fails, is it because the restored habitat is substandard, because of strong competition with invasive species, or alternatively due to changing environmental conditions that would equally impact established populations? Here, we re-purpose tools developed from modern coexistence theory to address these questions, and apply them to an effort to restore the endangered Contra Costa goldfields (Lasthenia conjugens) in constructed ("restored") California vernal pools. Using 16 years of data, we construct a population model of L. conjugens, a species of conservation concern due primarily to habitat loss and invasion of exotic grasses. We show that initial, short-term appearances of restoration success from population abundances is misleading, as year-to-year fluctuations cause long-term population growth rates to fall below zero. The failure of constructed pools is driven by lower maximum growth rates compared with reference ("natural") pools, coupled with a stronger negative sensitivity to annual fluctuations in abiotic conditions that yield decreased maximum growth rates. Nonetheless, our modeling shows that fluctuations in competition (mainly with exotic grasses) benefit L. conjugens through periods of competitive release, especially in constructed pools of intermediate pool depth. We therefore show how reductions in invasives and seed addition in pools of particular depths could change the outcome of restoration for L. conjugens. By applying a largely theoretical framework to the urgent goal of ecological restoration, our study provides a blueprint for predicting restoration success, and identifies future actions to reverse species loss.

Decrease in species richness and diversity, and shrub encroachment in Cerrado grasslands: A 20 years study

AbstractQuestionThe Cerrado is a global biodiversity hotspot, highly threatened by changes in land use. Alterations in species composition and the colonization of Cerrado grasslands by woody species can lead to long‐term changes in these communities. In this study, we investigated changes over 20 years in three grassland areas, in terms of species richness and diversity and growth‐form cover, as well as the effects of shrub and grass encroachment on species richness.LocationCerrado Brazilian savanna, moist grassland and dry shrub grassland. Areas under low and high anthropogenic pressure.MethodsPlant species composition and cover were sampled on seven occasions between the years 2000 and 2020, in permanent line‐transects. We compared plant cover, richness, diversity and growth‐form cover between the periods for each area. Next, we developed mixed‐effect linear models to test whether species richness in grasslands at the latest sampling event was altered by species representing 70% of the species cover at this time.ResultsGrasslands located in areas under higher anthropogenic pressure presented reduced richness and diversity, and cover concentrated on a few species of shrubs and large tussock grasses. Moist grassland undergoing encroachment by the native shrub Trembleya parviflora had lost over 50% of its diversity since encroachment. In the same area, a shrub grassland undergoing encroachment by native shrub Raulinoreitzia tremula, three native grass species and one exotic grass presented significantly reduced species richness. The moist grassland in an area under low anthropogenic pressure showed a reordering of the species cover over time, but a decrease in species richness.ConclusionWe observed changes in plant richness, diversity, cover, composition and growth‐form cover over a period of 20 years in grassland communities. We found, however, different trajectories in the three grassland areas sampled, mainly due to the encroachment of a few species, leading to floristic homogenization in grasslands located in areas under high anthropogenic pressure.

Assessing Arthropod Communities during Bermudagrass Pasture Conversion to Diverse Native Grassland on the Southern Great Plains of North America

Plant communities change during the process of converting bermudagrass (Cynodon dactylon [L.] Pers.) pasture monocultures to diverse native grasslands. Our hypothesis was that suppression of bermudagrass and grazing of seeded post-native grassland affected composition of arthropod communities in small plots. Our objectives were to use sweep nets and pitfall traps to collect insects and study their diversity and abundance as affected by four bermudagrass suppression methods and two post-management grazing regimes during 2 years following treatment applications at a Cross Timbers Ecoregion site in northcentral Texas. The first year after suppression of bermudagrass, plant diversity was greatest in plots treated with glyphosate, effectively removing exotic grass and allowing establishment of diverse native vegetation. This resulted in greater insect diversity but less abundance compared to treatments in which bermudagrass was not effectively removed. In plots where residual imazapyr prevented establishment of native seedlings, insect diversity and abundance were less. Short-duration, intensive grazing by cattle increased insect diversity 18% the first year. The second year after suppression of bermudagrass, treatments affected insect abundance only when grazing had not occurred. As in the first year, insects were more abundant in check plots dominated by bermudagrass; however, abundance in imazapyr-treated plots was comparable to glyphosate-treated plots because the residual effects of imazapyr were less after 20 months and weeds volunteered in those plots and attracted canopy-dwelling insects. Results support the use of glyphosate to remove bermudagrass if greater arthropod diversity is desired. Results also indicated that short-term grazing post-seeding promoted greater plant and subsequent insect diversity, but only during establishment of native grassland species.