Exotic Grasses Research Articles

Estimating invasive grasses heights with images from a remotely piloted aircraft in Brazilian Cerrado: accuracy of Global Navigation Satellite System from Phantom 4

The purpose of this study was to estimate the height of invasive plants from UAV images using the GNSS integrated into the UAV and to evaluate the accuracy of the GNSS. DSM and DTM elevation models were produced from images collected by remotely piloted aircraft (RPA). The production of CHIS occurred through the subtraction of the DSM and the DTM. In order to assess the accuracy of the CHIS+GNSS model, the CHIS+RTK model was generated as the observed variable. The comparison between the models took place in two sample areas represented by typical vegetation of Cerrado and Brachiaria grass. The statistical tests adopted were: Spearman correlation, RMSE, MAE and Wilcoxon test. The visual interpretation of the selected images showed that the CHIS+GNSS model presented errors in the identification of the ground cover represented by invasive grasses when compared to the CHIS+RTK model, being less accurate in the classification of the canopy heights of the invasive species. Statistical tests indicated that the CHIS+GNSS model showed significant differences in the identification of invasive species, with greater height error (0.24 cm) in the sample area. From these results it can be seen that the CHIS+RTK model is more assertive in detecting ground cover composed by exotic grasses than the CHIS+GNSS model.

Climate change and deforestation increase the vulnerability of Amazonian forests to post‐fire grass invasion

AbstractAimWe aimed to evaluate the vulnerability of the Amazon forest to post‐fire grass invasion under present and future climate scenarios.LocationAmazon Basin.Time period1981–2017 and 2070–2099.Major taxa studiedPlants.MethodsWe combined a fire–ecosystem model with remote sensing data and empirically‐derived equations to evaluate the effects of a high‐intensity fire (i.e., during an extreme drought) and logging in forest edges on tree canopy, and exotic grass cover under present and unmitigated climate change scenarios. We also contrasted simulated vegetation recovery time (as a function of climate variability) and current fire return intervals to identify areas in which fire–grass feedbacks could lock the system in a grass‐dominated state.ResultsUnder current climatic conditions, 14% of the Amazon was found to be vulnerable to post‐fire grass invasion, with the south‐eastern Amazon at the highest risk of invasion. We found that under unmitigated climate change, by the end of the century, 21% of the Amazon would be vulnerable to post‐fire grass invasion. In 3% of the Amazon, fire return intervals are already shorter than the time required for grass exclusion by canopy recovery, implying a high risk of irreversible shifts to a fire‐maintained degraded forest grassy state. The south‐eastern region of the Amazon is currently at highest risk of irreversible degradation.Main conclusionsAlthough resilience is evident in areas with low fire activity, increased fire frequency and intensity could push large Amazon forest areas towards a tipping point, causing transitions to states with low tree and high grass cover.

Water use of selected cover crop species commonly grown in South African fruit orchards and their response to drought stress

Cover crops are widely planted in orchards for a variety of reasons. These include suppressing soil erosion, nutrient cycling, phytosanitary purposes, general orchard aesthetics etc. However, there is need to balance these benefits against use of scarce resources such as water and nutrients. Currently no information exists on how different cover crop species use water in orchards and how they cope with drought stress. The aim of this study was therefore to compare the transpiration dynamics of various cover crop types in order to identify species with conservative water use rates. Studied species included: 1) two exotic legumes i.e. Lupine (Lupinus albus L.), and Common vetch (Vicia sativa), 2) three exotic grasses i.e. Tall fescue (Festuca arundinacea), Rye grass (Loliumperenne), and Kikuyu grass (Pennisetum clandestium) and; 3) grasses that are indigenous to sub-Saharan Africa i.e. African Lovegrass (Eragrostis capensis) and Rhodes grass (Chloris gayana). The crops were planted in pots under controlled greenhouse conditions. Transpiration rates were quantified using miniature stem heat balance sap flow gauges and by manual weighing. Drought stress was imposed by withholding irrigation at selected intervals and the responses were quantified through changes in the water relations of the plants. The study showed that exotic legumes had the highest daily water use which peaked at about 2.4 L per square metre of leaf area per day, followed by exotic grasses at 1.5–2.0 L/m2/d. The indigenous grasses used the least water ranging from 0.8 to 1.2 L/m2/d. The indigenous grasses largely displayed an isohydric response to drought stress by maintaining their leaf water status with increasing soil water deficit. The exotic species, on the other hand, showed risk taking behaviour (anisohydry) wherein both the transpiration and leaf water status decreased sharply as drought stress increased. Consequently, some exotic species failed to recover when stress was relieved. From a water use perspective, this study demonstrates that indigenous grass species are more appropriate as cover crops in South African orchards because of their low transpiration rates and the ability to cope with extended periods of water deficit.

Season of prescribed fire determines grassland restoration outcomes after fire exclusion and overgrazing

AbstractFire exclusion and mismanaged grazing are globally important drivers of environmental change in mesic C4 grasslands and savannas. Although interest is growing in prescribed fire for grassland restoration, we have little long‐term experimental evidence of the influence of burn season on the recovery of herbaceous plant communities, encroachment by trees and shrubs, and invasion by exotic grasses. We conducted a prescribed fire experiment (seven burns between 2001 and 2019) in historically fire‐excluded and overgrazed grasslands of central Texas. Sites were assigned to one of four experimental treatments: summer burns (warm season, lightning season), fall burns (early cool season), winter burns (late cool season), or unburned (fire exclusion). To assess restoration outcomes of the experiment, in 2019, we identified old‐growth grasslands to serve as reference sites. Herbaceous‐layer plant communities in all experimental sites were compositionally and functionally distinct from old‐growth grasslands, with little recovery of perennial C4 grasses and long‐lived forbs. Unburned sites were characterized by several species of tree, shrub, and vine; summer sites were characterized by certain C3 grasses and forbs; and fall and winter sites were intermediate in composition to the unburned and summer sites. Despite compositional differences, all treatments had comparable plot‐level plant species richness (range 89–95 species/1000 m2). At the local‐scale, summer sites (23 species/m2) and old‐growth grasslands (20 species/m2) supported greater richness than unburned sites (15 species/m2), but did not differ significantly from fall or winter sites. Among fire treatments, summer and winter burns most consistently produced the vegetation structure of old‐growth grasslands (e.g., mean woody canopy cover of 9%). But whereas winter burns promoted the invasive grass Bothriochloa ischaemum by maintaining areas with low canopy cover, summer burns simultaneously limited woody encroachment and controlled B. ischaemum invasion. Our results support a growing body of literature that shows that prescribed fire alone, without the introduction of plant propagules, cannot necessarily restore old‐growth grassland community composition. Nonetheless, this long‐term experiment demonstrates that prescribed burns implemented in the summer can benefit restoration by preventing woody encroachment while also controlling an invasive grass. We suggest that fire season deserves greater attention in grassland restoration planning and ecological research.

Climate Impacts on Fire Risk in Desert Shrublands: A Modeling Study

Fire is recognized to be an important disturbance in many ecosystems worldwide, although desert ecosystems are not generally thought of as being prone to fire, primarily because of the lack of a continuous fuel bed. However, the likelihood of catastrophic fires in some desert systems is increasing due to the spread of exotic species, which can grow in the open. A second factor increasing fire risk may be extreme rainfall events caused by climate warming that can lead to an increase in fuel loads. Our work explores the impact of increased rainfall on fire risk in creosote shrublands that have been invaded by exotic grasses. We take experimental results from creosote (Larrea tridentata) shrublands in the Mojave and Sonoran Deserts of the Southwestern United States and develop spatially explicit simulation models to explore the impact of shifting rainfall regimes on biomass production and fire spread. In doing this, we explore two scales that are important in the spread of fire: (1) the macro-scale which considers the likelihood that fire arriving at one edge of a modeled landscape will successfully reach the opposite edge, leading to spread at a broader scale; and (2) the micro-scale, which considers fire spread within the landscape. We use a very simple model to first explore how changes in the distribution of fuel in the landscape impact the ability of fire to spread across and within the landscape. We then add more realism by including a direct consideration of creosote shrub distributions and biomass levels produced in different vegetation zones associated with distance from creosote. Our models show that the spread of fire at both macro- and micro-scales can be predicted from a knowledge of the statistical distribution of biomass in the field. The only additional information that is needed to predict the extent of fire spread is the amount of biomass at a local site (g m–2) required to ignite standing biomass in adjacent sites. This will depend upon species composition as well as amount of biomass, the hydration status of the vegetation and climatic conditions, such as windspeed and relative humidity.

Native and exotic grasses share generalist foliar fungi in a Canterbury high country grassland

Communities of foliar fungal pathogens and endophytes can influence the success and impacts of exotic plants. A key unresolved question concerns how these foliar fungal communities are structured, including whether they systematically differ between native and exotic plants, or are influenced by plant phylogeny and host abundance. To address these questions, we used culturing and Sanger sequencing to characterise the culturable foliar fungal communities of three native and seven exotic grass species that co-occurred in a high-country grassland in Canterbury, Aotearoa New Zealand.

Active Restoration Initiates High Quality Forest Succession in a Deforested Landscape in Amazonia

Amazonia is well known for its high natural regeneration capacity; for this reason, passive restoration is normally recommended for the recovery of its degraded forests. However, highly deforested landscapes in southern Amazonia require active restoration. Since restoration methods can shape the quality and speed of early forest recovery, this study aimed to verify how active restoration pushes sites stably covered with exotic grasses towards forest recovery. We evaluated early forest succession at active restoration sites, i.e., soil plowing, direct seeding of pioneer species, and seedling stock planting at low density. We analyzed forest structure, diversity, and species composition in two age classes, 0.5–3.5 and 4.5–7.5 years old. As reference, we evaluated sites able to naturally regenerate in the same region. We sampled 36 active restoration and 31 natural regeneration sites along the Madeira River, southern Amazonia. Active restoration triggered succession to similar or higher levels of forest structure than sites where natural regeneration was taking place. The most dominant species did not overlap between active restoration and natural regeneration sites. The overall composition of species was different between the two restoration methods. Dominant species and size class distribution show that active restoration is performing successfully. Soil preparation combined with a high availability of seeds of pioneer trees resulted in a high stem density and basal area of facilitative pioneer trees. Planted seedlings added species diversity and increased density of large trees. Interventions to increase the odds of natural regeneration can be effective for non-regenerating sites in resilient landscapes.

How effective is direct seeding to restore the functional composition of neotropical savannas?

Species loss leads to changes in ecosystem function and services, impacting human well‐being. Although biodiversity restoration is pivotal to circumvent this situation, the techniques for restoring old‐growth savannas are still limited and the restoration outcomes remain unpredictable. Here, we use a trait‐based approach to understand the functional outcomes of ecological restoration via direct seeding in a Brazilian savanna (cerrado, hereafter neotropical savanna). We compared the functional composition from woody and non‐woody component, total biomass, and biomass allocation of a restored relative to a degraded savanna (abandoned pasture) dominated by exotic grasses and a well‐preserved old‐growth native savanna. We found that the functional composition of restored communities was very similar to those dominated by exotic grasses, both characterized by a greater dominance of species with acquisitive traits, higher above‐ground biomass, and lower investment in root biomass. In contrast, the native vegetation exhibited a dominance of conservative traits and higher investment in belowground rather than aboveground biomass. Even though the acquisitive traits in the restored savanna allow a fast aboveground biomass accumulation and soil cover, the lower belowground biomass investment in the restored savanna may limit its resistance and resilience to droughts and fires. Our findings suggest that restoration efforts in neotropical savanna should focus on fostering the establishment of slow‐growing species to recover the ecosystem properties provided by the high biodiversity in neotropical savannas.

Soil biotic effects and competition; What are the mechanisms behind being a successful invader?

The global threat of plant invasions to native ecosystems mandates an understanding of the mechanisms that determine invasion success. While some exotic species establish, spread and impact native ecosystems, others establish with little or no measurable impact. Competitive ability has been highlighted as a key mechanism influencing invasion success and impact, but there is growing evidence that interactions between plants and soil biota may also be important. In particular, escape from natural enemies during the early stages of establishment may give exotic species an advantage over native species subject to their own natural enemies in the soil. Here, we evaluated whether the invasion success and impact of exotic grass species could be explained by competitive superiority over resident native species, advantages gained from the positive effects of native soil communities, or both. We assessed the competitive abilities of six grass species that vary in their invasion success relative to three widespread native grasses, quantified the effects of native soil microbial communities on the performance of both native and exotic grass species, and determined whether there was an interaction between competitive and soil effects. Overall, we found that exotic species were stronger competitors than natives and that native soil effects were weak and did not predict invasiveness. Differences in species relative competitive abilities also did not correlate with invasiveness but demonstrate how some exotic species could outcompete natives and suppress their growth during the invasion process.

Litterfall, vegetation structure and tree composition as indicators of functional recovery in passive and active tropical cloud forest restoration

Litterfall is an indicator of ecosystem function and its temporal dynamics can be used to evaluate self-organizing ecosystems on a recovery trajectory following restoration. Few studies have evaluated the recovery trajectories of forest litterfall by simultaneously monitoring forest restoration strategies and reference ecosystems. The general objective of our study was to determine the functional recovery of an abandoned pasture under passive and active restoration, and in secondary (40-year-old) and mature (120-year-old) forest, by analyzing litterfall and its components (leaves, flowers, fruits, woody parts) over a period of five consecutive years. We determined the vegetation structure and tree species composition of these four conditions and compared 1) production of litterfall, leaves, flowers and fruits, 2) leaf litter nutrient inputs (C and N) and, 3) recovery by tree species in leaf litterfall. In five years, litterfall increased from 2.6 to 7.8 Mg ha−1 and from 3.5 to 9.1 Mg ha−1 in the passive and active restoration treatments, respectively, while it increased from 6.0 to 8.6 Mg ha−1 in the secondary forest. In the mature forest, litterfall varied around 10.0 Mg ha−1. The reproductive component increased significantly in restoration (0.3 to 1.5 Mg ha−1) but remained around 0.6 Mg ha−1 in secondary and 1.3 Mg ha−1 in mature forest. Secondary and mature forests both presented correlations to monthly precipitation and maximum and minimum temperatures, indicating strong seasonality. However, litterfall production in the passive and active treatments was continuous throughout the year. Basal area and tree density were higher under active compared to passive restoration. Although the dominant tree species were similar under passive and active restoration, active restoration presented a higher forest species recovery, while the dominance of exotic grass patches persisted under passive restoration. The results suggest that litterfall production can be a useful and accurate indicator with which to evaluate the recovery of ecosystem function, while flower and fruit component can indicate reproductive recovery. Although litterfall production increased rapidly after five years, it did not present a seasonal dynamic. This is probably due to the fact that the species composition still differs from that of the reference systems. Evaluations of cloud forest restoration success should therefore include temporal assessments of vegetation structure and biodiversity recovery in relation to the reference forests in order to establish additional restoration techniques, particularly in the case of passive restoration strategies.

Accelerating tropical cloud forest recovery: Performance of nine late-successional tree species

Tree planting is a common strategy for forest restoration. The use of mid- and late-successional species is less common, but could accelerate succession, enhance diversity and secure their presence. In this study, we determined the survival and growth of 559 saplings from nine native mid- and late-successional species after three years of growth under a range of habitat conditions to evaluate their potential utility in restoration plantings. Since mid- and late-successional tree species have shade-tolerant attributes and the light environment is a determinant factor for their growth and survival, we expected sapling performance to vary among species depending on the percentage of canopy cover and on factors associated with this variable. For this, we identified habitat conditions that influenced sapling performance in a degraded tropical cloud forest: the conditions ranged from closed-canopy secondary forest to open pastures dominated by exotic grasses. Overall, the studied species presented a high performance: sapling survival (40 to 90%) and relative growth rates in height (0.14 to 0.50 cm cm−1 year−1) and in diameter (0.04 to 0.50 mm mm−1 year−1) were within or above the ranges previously reported for cloud forest species. The final sizes and growth rates in height and diameter were mostly explained by the canopy and grass cover (71.5% of the variation). Integrated Response Index (IRI) values showed wide variation among species (from 6.44 to 41.41 with inclusion of height, and from 2.13 to 44.77 with inclusion of diameter). In general, there was a negative correlation between canopy cover and final sapling size and growth rates in height and diameter, but there were important variations among species. Based on their IRI values, species such as Ulmus mexicana and Oreomunnea mexicana are suggested for restoration plantings. Given their low performance, however, Fraxinu uhdei and Juglans pyriformis are recommended for use only in advanced forest successional stages or in conjunction with other restoration techniques to increase their survival. Our results show that these threatened mid- and late-successional native species can be successfully matched to microsite conditions and established in degraded areas as a strategy by which to secure their presence and accelerate forest recovery.

A seed–seedling conflict forAtriplex polycarpashrubs competing with exotic grasses and their residual dry matter

AbstractNative saltbush,Atriplex polycarpa, shrub populations are widely diminished and fragmented in the southern San Joaquin Desert of California due to habitat conversion and invasion by exotic annual grasses of mostly Mediterranean origin. The role these grasses play in saltbush population demography is not well understood. We hypothesized that saltbush seedling recruitment and growth is limited by the competitive interactions with exotic grasses, preventing saltbush stands from maintaining their populations and expanding. We predicted that saltbush seedling recruitment would be reduced by (1) light and moisture competition with the grasses; and (2) the physical barrier of grass residual dry matter (RDM) formed during senescence. To test our predictions, we investigated saltbush seedling recruitment under field conditions across six saltbush populations. We examined how variations in edaphic structure and water availability by site may have affected saltbush seedling recruitment and longer‐term population dynamics. In experimental plots where saltbush seeds were sowed, exotic grass RDM reduced saltbush seedling emergence compared to seeds sown in the absence of RDM; competition post‐emergence was not significant. Saltbush seedlings transplanted into the field had lower mortality and less herbivory in invaded grassy habitats compared to seedlings planted in bare zones in between established, mature saltbush shrubs. Edaphic variation and water availability by site were likely key factors affecting the success of both grass invasion and saltbush recruitment. Our results suggest that there is a seed–seedling conflict: Sites favorable for saltbush seedling emergence (minimal grass cover among mature shrubs) are unfavorable for seedling survival due to high herbivory. Conversely, sites favorable for saltbush seedling survival (high grass coverage away from mature shrubs) are unfavorable for seedling emergence. The RDM produced by grasses represents an important stabilizing feedback favoring continued grass dominance.

The effects of tree cover and soil nutrient addition on native herbaceous richness in a neotropical savanna

AbstractExotic grasses and high‐nutrient availability are common factors that may limit recovery of herbaceous diversity in derived savannas, while tree encroachment is a threat to diversity in old‐growth savannas. To understand the impacts of these factors on herbaceous communities, we studied the effect of nutrient addition, and the resulting increase in the exotic grass, Melinis minutiflora, at a savanna‐forest boundary in the Brazilian Cerrado. We inventoried richness of reproductive herbs, tree basal area and cover of the exotic grass, Melinis minutiflora, in each plot. Nutrient addition caused a large increase in Melinis and a large decrease in richness of flowering plants. Unexpectedly, structural equation model analysis suggests that the decline in herbaceous richness was a direct result of nutrient addition, rather than an indirect effect caused by the increase in Melinis. Tree density had a strong negative effect on both Melinis cover and herbaceous richness. Our results reveal that high‐nutrient availability imposes a barrier to the restoration of a diverse, native herbaceous layer in anthropogenic savannas, while tree encroachment is a threat to diversity in old‐growth savannas.Abstract in Portuguese is available with online material.

Using Adaptive Management to Restore Grasslands Invaded by Tall Fescue (Schedonorus arundinaceus)

Invasive grasses reduce habitat quality for multiple taxa and can negatively impact forage quality for livestock. Large-scale experimental studies are needed to inform more effective grassland restoration that is grounded in practice. To this end, we studied the control of a common but highly invasive cool-season grass using a landscape-scale experiment, employing an adaptive management framework. The study design included three patches (average 8.7 ha) at each of seven sites. Treatments included 1) herbicide (glyphosate), 2) herbicide and native seeding, and 3) control. Four sites were grazed by domestic cattle using adaptive stocking. We sampled vegetation composition and structure during one pretreatment year (2014) and four post-treatment years (2015–2018). Our primary objective was to evaluate how these one-time treatments affected the cover of tall fescue (Schedonorus arundinaceus) and native grasses and forbs. Tall fescue cover was reduced after a one-time glyphosate application, and this reduction was maintained over 4 years on grazed and ungrazed sites. We observed increases of warm-season grasses after herbicide and seeding, with the strongest restoration observed on ungrazed sites. Native grasses did not differ strongly between treatments on grazed sites, where there was a resurgence of nonfescue exotic grasses. Percent cover of native forbs was near zero before seeding but ranged from low to moderate levels afterward. Our results indicate a one-time application of herbicide can be used to reduce but not eradicate the invasive grass tall fescue, although other exotic grasses may replace tall fescue, especially on grazed sites. For plant community restoration to be successful, sites should be rested from grazing to give native seedings time to establish. Although eradication of invasive grasses is often infeasible in productive landscapes, restoring at least some native vegetation has the potential to protect ecosystem services provided by grasslands.

Bee (Apoidea) community response to perennial grass treatments managed for livestock production and conservation

Most grasslands world-wide have been converted into various row crops for agriculture and pasture for livestock foraging. This conversion has likely disrupted arthropod communities, including pollinating bee communities. Pollinating native bees have been in decline in recent decades and much of this decline has been attributed to intensive agricultural practices. Native warm-season grasses have been promoted as alternatives to non-native grasses [e.g., bermudagrass (Cynodon dactylon)] in beef production systems. Reestablishing native grasses may provide an opportunity for land-sharing where agricultural production can enable conservation practices that potentially enhance bee biodiversity. Therefore, agricultural practices such as growing native perennial grasses for livestock forage that may minimize pollinating bee community disruption should be considered. We used colored pan traps to collect bees in four treatments of perennial grass plantings associated with operational livestock pastures during 2011−2012. The four treatments were: (1) mix of Bermuda and tall fescue (Schedonorus arundinaceus) grass grazed with cattle; (2) monocultures of Indiangrass (Sorghastrum nutans) grazed with cattle; (3) native grass polyculture [(Indiangrass, little bluestem (Schizachyrium scoparium), and big bluestem (Andropogon gerardii)] grazed with cattle; and (4) native grass polyculture without cattle. We generally documented greater abundances and richness of bees in native grass treatments compared to exotic grass treatments; however, treatment-level differences were bee genera- or species-dependent. Lack of grazing in the native grass mixture treatment did result in higher bee abundance and taxa richness compared to the native grass mixture treatment with cattle. Our results support the conception that perennial native grasses have the potential to attract numerous, beneficial bee species and may provide some pollen rewards and suitable nesting substrate for bees. Therefore, using native perennial grasses as livestock forage may be a more ecologically friendly surrogate to non-native forage used for livestock production to promote pollination services and native bee diversity in agricultural lands.

Selective herbicide control: using furrows and carbon seed coatings to establish a native bunchgrass while reducing cheatgrass cover

Invasion by exotic grasses is degrading dryland ecosystems worldwide and efforts to restore native vegetation in invaded areas have been largely unsuccessful. Control of invasive grasses with herbicide also limits restoration efforts using native seed. In this study, we evaluated two approaches that could allow for the restoration of a native species Pseudoroegneria spicata while reducing an invasive annual grass Bromus tectorum with a herbicide mixture in the sagebrush steppe ecosystem (the United States). We used two methods to protect native seeds from herbicide: activated carbon was applied as a seed coating with the intent of absorbing the herbicide around the seed, and furrows were used to side‐sweep soil sprayed with herbicide away from the planted seed. Our results indicate that imazapic + glyphosate herbicide application had a strong negative effect on the invasive annual grass, reducing B. tectorum cover 91% after 1 year, and 39% after 2 years. Herbicide also had strong negative effects on P. spicata without a carbon‐coating or furrow treatment, reducing seedling emergence 38%, 2‐year plant density 65%, and 2‐year total growth 90%. Both activated carbon seed coatings and furrow treatments limited herbicide effects on P. spicata 2‐year growth, but neither treatment alone mitigated herbicide effects on all life stages. Combining carbon coatings and furrow treatments mitigated harmful herbicide effects on several plant stages (seedling emergence, plant densities, and growth). Our results suggest that combining activated carbon coatings and furrow results in similar establishment of a native perennial as a non‐herbicide seeding and lowers B. tectorum abundance.

Maintenance of wetland plant communities: the role of the seed bank in regeneration of native plants

Exotic grasses have been introduced into wetlands and can compete with native plants due to their high tolerance of flood and dry periods. Flooding can facilitate seed dispersal of exotic species and reduce the diversity of native species. We compared two grasslands to assess whether seed banks can maintain the diversity of native plants in wetlands with introduced exotic plants. We recorded a total of 136 species and a predominance of annual plants in the seed bank and vegetation together. The seed bank had high species diversity independently of the dominance of the exotic Urochloa humidicola in the vegetation. The seed banks of the native and cultivated grasslands differed significantly with a positive correlation for aquatic plants in the native grassland and negative correlation in the cultivated grassland. The seed bank revealed potential to maintain the diversity of native species in the cultivated grassland since the flood and dry seasons promoted the presence of distinct species in the seed bank, but lower richness in the vegetation reflects a dependence on the germination stage. The seasonality of flood and dry periods influences distinct growth forms, increasing the diversity of the seed bank and the vegetation.

Where Have the Native Grasses Gone?: What a Long-Term, Repeat Study Can Tell Us about California’s Native Prairie Landscapes

Much of the foothill and valley areas of coastal southern California are covered by stands of non-native grasses with occasional scattered patches of native bunch grasses. For decades, the dominant view held that these native bunchgrasses, particularly Stipa pulchra, once covered these lands and that grazing practices were a key cause of their decline. The so-called bunchgrass dominant paradigm (BDP) put forth by Clements influenced thinking on grassland ecology and biogeography for decades until it was discredited. Recent research suggests that grazing and related disturbances might have supported native bunchgrasses, but results are mixed and most studies cover only a short time frame. This research uses a long-term, repeat study design to analyze and compare data from three surveys of 15 permanent quadrats in La Jolla Valley, California, to determine changes in grassland cover over 34 years. A unique aspect of the study is that the site was selected by researchers precisely because it contained excellent ‘relic’ stands of Stipa pulchra (in accordance with the BDP) and the baseline study was conducted shortly after the area was released from grazing and placed under conservation management. We compared data on species frequency and percent cover collected using the same sampling routine for three periods: 1981, 1994, and 2015, to document the shifts in vegetation. We found that native grass cover decreased dramatically (especially on the valley floor), exotic grass cover fluctuated widely over time, while both native and exotic forb cover increased over time. The findings support the notion that prior grazing management practices may have supported the former stands of Stipa pulchra.

Diversity and structural changes in Cerrado Rupestre under effects of disturbances

Vegetation formations are undergoing constant floristic and structural change over time and space. Assessing these changes represents an important step to understand the effects of disturbances and propose ecosystem conservation and management strategies. We still lack, however, information on the dynamics of the woody vegetation in Cerrado Rupestre (rupestrian Cerrado—RC) formations over time, which comprise important refuge of the vegetation of the Brazilian Savanna and occur on rocky outcrops, which are considered restrictive environments. In this context, we describe the changes in floristic composition, richness, species diversity and structure of vegetation in RC over 12-year and link patterns to the disturbances that occur in the area—wildfire and cattle presence. We gathered data from three surveys conducted in RC in the Pireneus State Park (PSP), Goias, Brazil. We also registered hot pixels inside the study area and in the PSP neighboring area indicating presence of bovine and equine cattle in the Park. Disturbances, occurrence of wildfires, and presence of cattle promoted changes in vegetation structure, with a decrease in the number of small individuals, but not in diversity parameters. The increase in richness, evenness and diversity, even under the effect of disturbances, demonstrates the resilience of the RC. However, if these disturbances keep occurring, resilience will be compromised, with clearer changes in floristic composition and vegetation structure, according to what we proposed in a theoretical model describing the synergistic influence of cattle presence, exotic grass and wildfires on the dynamics of the Cerrado Rupestre.

Taxonomic and phylogenetic composition show biotic resistance to exotic invasion in acid seep springs

BackgroundFew studies have incorporated the evolutionary insights provided by analysis of phylogenetic structure along with community composition to assess the effects of exotic invasion on freshwater wetlands. Here, we assess the taxonomic and phylogenetic relationships among acid seep springs to investigate the potential homogenization or resistance of communities due to invasion of an exotic grass.ResultsMultivariate community analyses indicated differences in community and phylogenetic composition and dispersion among acid seep springs, associated with gradients in soil moisture, canopy cover, and phylogenetic diversity. By contrast, univariate analyses showed differences in taxonomic diversity but not phylogenetic diversity among acid seep springs.ConclusionsDespite exotic invasion, individual acid seep springs remained taxonomically and phylogenetically distinct from each other. Taxonomic and phylogenetic diversity metrics revealed different aspects of composition, reinforcing the importance of including both in analyses of plant communities for understanding community assembly following exotic invasion and for management purposes. Within acid seep springs, taxonomic and phylogenetic composition appear to be driven more through environmental filtering by light and moisture than by the competitive effects following invasion of an exotic grass in support of Elton’s biotic resistance hypothesis.