Abundance Of Forbs Research Articles

Short‐term effects of experimental goose grazing and warming differ in three low‐Arctic coastal wetland plant communities

AbstractQuestionUnderstanding the sensitivity and magnitude of plant community responses in tundra wetlands to herbivory and warming is pressing as these ecosystems are increasingly threatened by changes in grazing pressure and higher temperatures. Here, we ask to what extent different low‐Arctic coastal wetland plant communities are affected by short‐term goose grazing and warming, and whether these communities differ in their responses.LocationYukon–Kuskokwim Delta, Alaska.MethodsWe conducted an experiment where we simulated goose grazing by clipping the vegetation and summer warming by using open‐top chambers in three plant communities along a 6‐km coastal–inland gradient. We assessed plant community compositional changes following two years of treatments.ResultsGrazing had stronger effects than warming on both plant functional group and species composition. Overall, grazing decreased the abundance of grasses and sedges and increased the abundance of forbs, whereas warming only caused a decrease in forb abundance. However, plant communities and functional groups, both within and across communities, varied widely in their responses to treatments. Grazing decreased grass abundance (−25%) and increased forb abundance (+44%) in the two more coastal communities, and reduced sedge abundance (−22%) only in the most inland community. Warming only decreased forb abundance (−18%) in the most coastal community, which overall was the most responsive to treatments.ConclusionsWe show that short‐term goose grazing predominates over short‐term summer warming in eliciting compositional changes in three different low‐Arctic coastal wetland plant communities. Yet, responses varied among communities and the same functional groups could respond differently across them, highlighting the importance of investigating the effects of biotic and abiotic drivers in different contexts. By showing that tundra wetland plant communities can differ in their immediate sensitivity to goose grazing and, though to a lesser extent, warming, our findings have implications for the functioning of these rapidly changing high‐latitude ecosystems.

Cattle grazing results in greater floral resources and pollinators than sheep grazing in low-diversity grasslands.

Land‐use and land‐cover change associated with agriculture is one of the main drivers of biodiversity loss. In heavily modified agricultural landscapes, grazing lands may be the only areas that can provide essential resources for native grassland species. Management decisions, such as choice of livestock species, affect the extent to which grazing lands provide suitable habitat for native species such as pollinators.Our study compared how sheep versus cattle herbivory affected floral resources and butterfly abundance across low‐diversity, former Conservation Reserve Program (CRP) pastures managed with patch‐burn grazing.Across all years (2017–2019), flowering species richness and abundance were significantly higher in cattle pastures than sheep pastures. On average, we recorded 6.9 flowering species/transect in cattle pastures and 3.8 flowering species/transect in sheep pastures. The average floral abundance per transect was 1278 stems/transect in cattle pastures and 116 stems/transect in pastures grazed by sheep.Similarly, we observed higher butterfly species richness, diversity, and abundance in cattle than in sheep pastures. In cattle pastures, we observed an average of 75 butterflies and 6.75 species per transect, compared with an average of 52 butterflies and 3.37 species per transect in sheep pastures. However, the butterfly community composition did not significantly differ between grazing treatments likely because agricultural‐tolerant, habitat generalists comprised the majority of the butterfly community. Five generalist butterflies comprised 92.3% of observations; Colias philodice was the most abundant (61% of observations). Speyeria idalia and Danaus plexippus, two butterflies of conservation concern, comprised less than 0.5% of butterfly observations.Our results, which are among the first attempt quantifying butterfly use of post‐CRP fields grazed by livestock, show that increased precipitation and cattle grazing promoted higher forb abundance and richness. However, additional interventions may be needed to enhance floral resources to sustain and improve pollinator diversity in these landscapes.

Large herbivores facilitate an insect herbivore by modifying plant community composition in a temperate grassland.

Large herbivores often co‐occur and share plant resources with herbivorous insects in grassland ecosystems; yet, how they interact with each other remains poorly understood. We conducted a series of field experiments to investigate whether and how large domestic herbivores (sheep; Ovis aries) may affect the abundance of a common herbivorous insect (aphid; Hyalopterus pruni) in a temperate grassland of northeast China. Our exclosure experiment showed that 3 years (2010–2012) of sheep grazing had led to 86% higher aphid abundance compared with ungrazed sites. Mechanistically, this facilitative effect was driven by grazing altering the plant community, rather than by changes in food availability and predator abundance for aphids. Sheep significantly altered plant community by reducing the abundance of unpalatable forbs for the aphids. Our small‐scale forb removal experiment revealed an “associational plant defense” by forbs which protect the grass Phragmites australis from being attacked by the aphids. However, selective grazing on forbs by sheep indirectly disrupted such associational plant defense, making P. australis more susceptible to aphids, consequentially increasing the density of aphids. These findings provide a novel mechanistic explanation for the effects of large herbivores on herbivorous insects by linking selective grazing to plant community composition and the responses of insect populations in grassland ecosystems.

Long‐term litter removal rather than litter addition enhances ecosystem carbon sequestration in a temperate steppe

Abstract Global change can greatly affect plant productivity and subsequently litter input to soil, with potential impacts on soil carbon (C) fluxes. However, the effects of litter layer in mediating C cycling and budget at an ecosystem scale are still not clear. As part of a long‐term litter fall manipulation experiment in a temperate steppe on the Mongolian Plateau, this study was conducted to explore effects of litter removal and addition on ecosystem C budget and the associated mechanisms. Overall, litter removal enhanced photosynthetic active radiation (PAR) at soil surface by 31.0%, but litter addition reduced it by 26.5%. Litter removal decreased soil inorganic nitrogen (SIN) content at the depth of 0–10 cm by 13.6%, but litter addition enhanced it by 14.1%. Litter removal increased legume abundance by 131.1%, whereas litter addition enhanced grass abundance by 30.7% but decreased forb abundance by 33.1%. Litter removal increased gross ecosystem productivity (GEP) through enhancing PAR and legume abundance, whereas litter addition elevated GEP by changing plant community composition mediated by decreasing PAR and increasing SIN. Litter removal did not affect ecosystem respiration (ER), but litter addition stimulated ER by 14.9%. Therefore, while litter addition did not affect net ecosystem productivity (NEP), litter removal surprisingly enhanced NEP by 23.9% over the later 7 years. Our findings highlight that more above‐ground litter input derived from biomass production may not necessarily result in a larger ecosystem C sink in grasslands under global change scenarios in the future. On the contrary, proper litter removal may be an effective way to increase the ecosystem C sink in grassland management. A free Plain Language Summary can be found within the Supporting Information of this article.

Responses of calcareous grassland plant communities to changed seasonal grazing management: Results of a 31 year study

Calcareous grasslands are of high conservation importance and have been maintained by livestock grazing over many centuries. Following the reduction in traditional livestock grazing (cattle and sheep) of semi-natural grassland during the twentieth century, conservation-based grazing management was introduced in order to conserve remaining grasslands. In UK semi-natural grasslands, grazing pressure has fluctuated over time due to changes in conservation funding and stock availability, whilst the time of year at which stock graze has also shifted. There is little quantitative data available to demonstrate the details of changed grazing patterns, or their long-term effects on the vegetation, thus the full impacts of these changes are not well understood. This study examines the response of a diverse calcareous grassland community to changes in grazing management between 1979 and 2010 at Martin Down National Nature Reserve, southern England, using historical vegetation surveys and grazing records collected and recorded by reserve staff. Historical data showed a shift in grazing regime, whereby grazing occurred across all seasons in the early period, but switched to predominately the autumn and winter in the present century. Despite this significant shift in management over time, the vegetation community did not change dramatically over this period, although small increases in species richness and diversity were detected. The richness of calcareous grassland indicator species remained largely consistent, suggesting the conservation value of the grassland persisted, and the community types also stayed fairly constant over the 31 years. Furthermore, weak evidence was found for impacts of grazing in particular seasons on vegetation community measures; species richness, species diversity, indicator richness, indicator abundance, grass abundance and forb abundance. This study suggests that these vegetation communities are robust to changes in grazing seasonality providing that sufficient grazing pressure is provided within the year. The compartmentalised grazing employed at Martin Down may be a useful method for ensuring this outcome. However more research is required, preferably using controlled field experiments before more reliable recommendations can be prescribed.

Habitat determines plant community responses to climate change in the High Arctic

Plant climate responses may depend on site-specific environmental context. Using fences and open-top chambers, we enhanced snow depth (creating Ambient, Medium, and Deep regimes) over an 11-year period and increased temperatures for two summers in dry heath and mesic meadow habitats on Svalbard, Norway. Comparison of plant growth form abundance and diversity responses in these two habitats showed that the response was more limited in the dry heath than in the mesic meadow. Common to both habitats was a decrease in shrub abundance and vascular plant species richness in the Deep snow regimes. Bryophyte abundance increased with enhanced snow cover in both habitats, but only up to a certain extent of snow depth in the meadow. However, for many growth forms, the effects of snow enhancement were habitat specific. In the mesic meadow, the abundance of forbs and bryophytes increased with snow enhancement, but the effect was stronger when combined with summer warming. The “bryofication” — that is, an increased abundance of bryophytes in response to snow enhancement and summer warming — also influenced overall plant diversity in the mesic meadow. Bryophytes are species-rich taxa and may respond differently than vascular plants to environmental change. We show that the inclusion of even the most common bryophytes in measures of diversity may determine overall plant diversity responses to environmental change in the Arctic.

A matter of time: Recovery of plant species diversity in wild plant communities at declining nitrogen deposition

AbstractAimHigh levels of nitrogen deposition have been responsible for important losses of plant species diversity. It is often assumed that reduction of ammonia and nitrogen oxide emissions will result in the recovery of the former biodiversity. In Western Europe, N deposition peaked between 1980 and 1988 and declined thereafter. In a 60‐year experiment in hay meadows, we tested the hypothesis that increasing and declining nitrogen deposition had negative, respectively, positive effects on plant species diversity.LocationWageningen, the Netherlands.MethodDuplicated plots received different fertilization treatments from 1958 onwards (control, Ca, K, P, PK, N, NPK). Productivity, soil pH and species composition were measured at regular intervals. In the control plots, the correlations between N deposition, diversity, production and soil acidification were analysed. Subsequently, we tested whether the treatment effects (e.g. N addition and liming) confirmed the hypothesized interactions.ResultsIn the control plots, soil pH, species diversity and the abundance of legumes and short forbs declined between 1958 and 1987 when atmospheric N deposition was high but recovered after 1987 when N deposition decreased. However, also in the N addition plots species diversity recovered partly after 1987, although the soil pH of the acidified soils in these plots did not. In addition, also in the limed plots diversity decreased rapidly during the first 30 years while in this treatment soil acidification was more than compensated.Main conclusionsWe conclude that declining N deposition resulted in the recovery of plant species diversity, but not in recovery of the former species composition. Time appears to be an additional, but crucial factor for the recovery of diverse, flowering meadows. Species not adapted to the new management conditions created at the start of the experiment disappeared during the first decades, while species fit for the new environment needed many years to establish.

Shifting community composition determines the biodiversity–productivity relationship under increasing precipitation and N deposition

AbstractQuestionsThe relationships between biodiversity and ecosystem functioning (BEF) vary largely across natural ecosystems, with a unimodal, monotonous linear or no relationship. However, it remains unclear how BEF relationships vary under global change. Given future predicted changes in precipitation and nitrogen (N) deposition, it is crucial to determine how precipitation change and N deposition affect grassland biodiversity and productivity, and regulate their relationships.LocationA Dry Mixed‐Grass Prairie of western Canada.MethodsWe established a manipulative field experiment of increased precipitation (water addition with approximately 15% and 30% more monthly precipitation) and N addition (10 g/m2) using a randomized complete block design, including six treatments, each replicated five times (30 plots). We conducted vegetation sampling with a 1 m × 1 m quadrat in each plot from 2016 to 2017, to examine the individual and interactive effects of water and N addition on plant diversity, functional group composition, above‐ and below‐ground productivity, and the diversity–productivity relationships.ResultsWe found a positive linear diversity–above‐ground biomass (AGB) relationship under increased precipitation, which was attributed to the water‐induced increase in the abundance of forbs in the plant community, further promoting the positive effect of plant diversity on AGB. However, N addition caused a negative linear diversity–AGB relationship by increasing AGB and reducing plant diversity. The effects of N on diversity and productivity can be further strengthened under increased precipitation, which was due to the increase of C3rhizomatous grasses with high above‐ and below‐ground biomass and the decrease of forbs with high richness.ConclusionsOur results suggest that changes in functional group composition determine the plant species’ diversity, productivity, and their relationships under increasing precipitation and N deposition, which has significant implications for understanding and modelling ecosystem productivity in the context of global change.

Changes in Community Composition Induced by Experimental Warming in an Alpine Meadow: Beyond Plant Functional Type

Climate warming exerts profound effects on plant community composition. However, responses to climate warming are often reported at the community and functional type levels, but not at the species level. To test whether warming-induced changes are consistent among community, functional type, and species levels, we examined the warming-induced changes at different levels in an alpine meadow from 2015 to 2018. The warming was achieved by deploying six (open top) chambers [including three non-warmed chambers and three warmed chambers; 15 × 15 × 2.5 m (height) for each] that resulted in a small increase in mean annual temperature (0.3–0.5°C, varying with years) with a higher increase during the non-growing season (0.4–0.6°C) than in the growing season (0.03–0.47°C). The results show that warming increased plant aboveground biomass but did not change species richness, or Shannon diversity and evenness at the community level. At the functional type level, warming increased the relative abundance of grasses from 3 to 16%, but decreased the relative abundance of forbs from 89 to 79%; relative abundances of sedges and legumes were unchanged. However, for a given functional type, warming could result in contrasting effects on the relative abundance among species, e.g., the abundances of the forb species Geranium pylzowianum, Potentilla anserine, Euphrasia pectinate, and the sedge species Carex atrofusca increased in the warmed (compared to the non-warmed) chambers. More importantly, the difference in species identity between warmed and non-warmed chambers revealed warming-induced species loss. Specifically, four forb species were lost in both types of chambers, one additional forb species (Angelica apaensis) was lost in the non-warmed chambers, and two additional species (one forb species Saussurea stella and one sedge species Blysmus sinocompressus) were lost in the warmed chambers. Consequently, changes at the species level could not be deduced from the results at the community or functional type levels. These data indicate that species-level responses to climate changes must be more intensively studied. This work also highlights the importance of examining species identity (and not only species number) to study changes of community composition in response to climate warming.

Super‐abundant C4 grasses are a mixed blessing in restored prairies

Forbs comprise most of the plant diversity in North American tallgrass prairie and provide vital ecosystem services, but their abundance in prairie restorations is highly variable. Restoration practitioners typically sow C4 grasses in high abundances because they are inexpensive, provide fuel for prescribed fires, can dominate reference sites, and suppress weeds that suppress sown forbs. However, C4 grasses can also suppress sown forbs, calling this practice into question. We evaluated how C4 grasses influence the abundance and diversity of sown forbs in 78 restored prairies across Illinois, Indiana, and Michigan. We found that the direct negative effects of C4 grasses on sown forbs outweighed indirect positive effects that occurred as C4 grasses suppressed nonsown species, which in turn suppressed sown forbs. This pattern was especially strong for the C4 grass big bluestem (Andropogon gerardii). Therefore, strategies to promote big bluestem and other C4 grasses would not promote sown forbs. Although C4 grass cover was not strongly related to two hypothesized drivers (time since fire or site age), seeding density of C4 grasses increased their cover. Sown forb cover also increased with forb seeding density, increased indirectly with fire (through its negative effect on nonsown species), and decreased indirectly with soil water‐holding capacity (through its positive effect on nonsown species). These results highlight the complex interplay of species groups during grassland restoration and show how managers can promote sown forbs in restored prairies: increasing forb seeding density and reducing time since fire and the abundance of C4 grasses and weeds.

Persistent effects of fire severity on ponderosa pine regeneration niches and seedling growth

Several recent studies have documented how fire severity affects the density and spatial patterns of tree regeneration in western North American ponderosa pine forests. However, less is known about the effects of fire severity on fine-scale tree regeneration niche attributes such as understory plant composition and cover, surface fuel abundance, and soil properties, or how these attributes in turn affect regenerating ponderosa pine growth. Using 1-m2 plots centered on 360 ponderosa pine seedlings that regenerated naturally after the Pumpkin Fire in 2000 in Arizona, we quantified regeneration niche attributes 13 years post-fire and measured their associations with seedling growth 11–16 years post-fire. Plots were established in a) unburned, b) moderate-severity, and two types of high-severity (100% tree mortality) burns, either c) adjacent to residual live forest edges (high-severity edge plots), or d) >200 m from any residual live trees (high-severity interior plots). We found that all burned plots had greater understory plant species richness, percent cover of forbs, exotic plants and coarse wood, as well as higher soil pH, sand and gravel content, and lower soil clay content compared to unburned plots. High-severity burn plots had the greatest total understory plant and shrub cover, the most herbaceous fine fuel biomass, and tended to have the highest soil nitrogen content compared to other burn severity classes. Ponderosa pine growth (i.e., stem diameter at root collar (DRC) and length of terminal leader) was lowest in the unburned compared to burned plots, and ponderosa pine terminal leader growth was consistently greater in the high-severity edge plots compared to other severities. Finally, niche characteristics such as overstory tree canopy cover (−), soil phosphate (+), and cover of coarse wood (+), forbs (+), and the native grasses, mountain muhly (+) and squirreltail (−), were important explanatory variables of ponderosa pine growth. Exotic plant cover did not have a negative association with ponderosa pine growth. These results suggest that if ponderosa pine seeds can disperse and germinate, and if seedlings can survive the first few critical years after germination, then low overstory canopy cover and abundant forbs or coarse wood may be associated with increased growth rates. Alternatively, forbs may be responding to the same site benefits as the seedling; and abundant forbs, coarse wood, and fine fuels might also put seedlings at increased risk of mortality from subsequent fire, at least until they are taller and more fire resistant.

Optimizing yield and flower resources for pollinators in intensively managed multi-species grasslands

Intensively managed grasslands, typically containing a few high-yielding species, play a key role in providing biomass feedstock for animal feed and bioenergy production. However, these grasslands often contain few resources for flower-visiting insects, which provide pollination services for crops. In this study, we investigate if both high yield and floral resources for pollinators can be achieved in intensively managed grasslands by varying species diversity and composition, and cutting frequency. Four perennial grassland mixtures containing 3, 5, 11 and 13 species of grasses and/or forbs were established at three sites varying in surrounding landscape, and plots were managed with three cutting strategies (four cuts per year, two cuts per year and no cut). Biomass production was measured as annual herbage yield. Every 2–4 weeks throughout the flowering season, flower abundance, richness, temporal stability and flower-visiting insects were monitored. The 11- and 13-species mixtures, designed to enhance pollinators, produced similar or higher herbage yield than the 3-species mixture under a two-cut strategy or the 5-species mixture under a four-cut strategy. The 3- and 5- species mixtures had a high accumulated flower abundance due to excessive flowering of lucerne under the two-cut strategy and white clover under the four-cut strategy. Interestingly, flower abundance was not significantly reduced under the two-cut strategy compared to no cut. As expected, the 11- and 13- species mixtures presented a higher diversity of flowers during the flowering season. Flower temporal stability was generally higher in 11- and 13-species mixtures under the two-cut strategy, while it was highest in the 5-species mixture under the four-cut strategy. Pollinator profiles (visits by different functional groups of insects) were plant-species specific, and varied very little among sites. Legume species mainly attracted large bees (honey bees and bumblebees), while the most abundant forbs attracted other insect groups, in particular syrphids and other flies. Our results suggest that multi-species grasslands can be designed to support a high diversity of pollinators without compromising herbage yield. In particular, adding forbs to the grass-legume seed mixtures and managing grasslands with a two-cut strategy may increase flower resources available for a larger range of wild pollinators.

Silvicultural herbicides and forest succession influence understory vegetation and nutritional ecology of black-tailed deer in managed forests

The increasing intensity of forestry practices, especially using herbicides to promote early survival and growth of planted conifers, has the potential to influence the abundance of nutritious, shade-intolerant forbs and shrubs on which black-tailed deer (Odocoileus hemionus columbianus) and other forest ungulates depend. Therefore, we compared summer forage resources and nutrition of female black-tailed deer in stands that received herbicide treatments paired with stands that did not in Douglas-fir/western hemlock forests of western Washington. We investigated how these responses changed as forests aged from early seral to canopy closure (2–20 years post-harvest) in both treatments, and also in unmanaged mid-seral stands (30–90 years old). We measured the biomass and nutritional quality of understory vegetation and the diet composition, diet quality and nutrient intake of tractable black-tailed deer within each paired stand. We found that herbicides did not affect the rate of closure of the overstory canopy, but influenced plant species composition of the understory vegetation and reduced total and non-conifer understory biomass, primarily in the first 9 years before canopy closure. Herbicides also reduced the biomass of two of the six plant functional groups, evergreen shrubs and deciduous shrubs and trees, but did not reduce forb, graminoid, or fern biomass. Herbicides reduced bite size, harvest rate, daily dry matter intake and daily digestible energy (DE) intake of deer, but increased dietary digestible protein (DP) content, and these effects occurred primarily in the first 3 years post-treatment. Biomass of plants suitable for black-tailed deer, and the deers’ bite rate, daily feeding time, dietary DE, and daily digestible DP intake did not respond to herbicides. Our yearling and sub-adult, non-lactating deer met requirements for yearling growth and adult maintenance for dietary DE in 78%, and DE intake in 27% of plots, but only met the higher requirements for lactating females in 5% of plots. All plots where daily DE requirements of lactation or growth were met were <10 years old. Deer were equally likely to obtain diets that satisfied requirements in treated and untreated plots, indicating that although herbicide application reduced understory biomass and DE intake, it did not explain whether deer were able to meet requirements. We also found that the biomass of deciduous shrubs and trees, forbs, and suitable forage was ~25 times greater in 4–9 year old stands than closed canopy stands (14–90 years old), indicating the importance of maintaining early seral habitat for sustaining populations of black-tailed deer.

Shading enhances plant species richness and diversity on an extensive green roof

Green roofs can promote biodiversity in urban areas. The extent to which green roofs stimulate plant diversity can depend on roof characteristics such as roof age, substrate depth and shading. We exploratively studied the vegetation on a Dutch green roof in 50 permanent plots (1 m2) over eight years (2012–2019) following roof construction. Plots were situated either on low substrate depth (6 cm light-weight extensive substrate) or high substrate depth (6 cm light-weight extensive substrate topped with 14 cm native soil) and differed in the amount of shading received from a higher building floor. Increased substrate depth and shading additively increased plant species richness and plant diversity, with high shaded plots supporting on average 6.4 more plant species than low unshaded plots. Shading likely acts via reducing drought stress, whereas increasing substrate depth with native soil may also enhance plant diversity via addition of nutrients and native seeds. The vegetation composition on the roof was dynamic and changed over the years. Sedum acre was initially dominant but disappeared within the first years, whereas Sedum kamtschaticum increased and became dominant in the last years. Trifolium arvense was the most abundant forb species and was especially dominant three years after roof construction. We conclude that increased substrate depth and shading can promote plant species richness and diversity and recommend that both aspects are considered when green roofs are designed. Shading can be achieved by a stepped building architecture and by placing structures on the roof itself, such as solar panels on standards.

‘Home’ and ‘away’ litter decomposition depends on the size fractions of the soil biotic community

The ‘home-field advantage’ (HFA) hypothesis predicts that litter decomposition is accelerated in its home environment (i.e. in conspecific soil). Soil organisms play a key role in driving such HFA effects. Soil biota have a large range of body sizes, referred to as size fractions, which may influence their roles in the decomposition process and in the generation of HFA effects. However, how HFA effects depend on the different size fractions of the soil biotic community is unknown. We conducted a microcosm decomposition experiment to examine how size fractions of the soil biotic community affected litter decomposition and HFA effects. In a semi-natural grassland in the Netherlands, we collected leaf litter and soil from two abundant forbs: Tanacetum vulgare and Jacobaea vulgaris. Watery extracts of the soils were sieved through differently-meshed sieves (ranging from 850 μm to 6 μm) to obtain soil communities of different size fractions. Microcosms were inoculated with these different size fractions of the soil biotic community and we examined their effects on microbial composition, litter mass loss and HFA effects. Three months after inoculation, the diversity of the fungal community in the inoculated pots decreased with decreasing size fractions of the soil biotic community. Similarly, litter mass loss also decreased with decreasing soil biotic community size. In contrast, the HFA effect increased with decreasing size fractions of the soil biotic community, but these differences disappeared after six months of decomposition. Our results indicate that soil microorganisms, mainly the smallest size fractions, are specialized to decompose specific resources and thus promote HFA effects, but that their effect is only apparent during specific stages of litter decomposition.

Responses of plant diversity and soil microorganism diversity to water and nitrogen additions in the Qinghai-Tibetan Plateau

The Qinghai-Tibetan Plateau is experiencing significant nitrogen (N) deposition and increased precipitation. Although changes in N deposition and precipitation may cause changes in the composition and diversity of plants, the relationships between plant diversity and soil microbial diversity still has not been fully researched. Thus, we conducted a field simulation experiment in an alpine meadow that included three N and two water (W) addition levels, as well as their interactions. The abbreviations of all treatments are shown below: CK, control; W, added water; N5, added 5 g N m−2 yr−1; N10, added 10 g N m−2 yr−1; N5W, added N5 and W; N10W, added N10 and W. The dominant plant species belong to the Gramineae family and include Elymus dahuricus, Stipa capillata, Poa pratensis and Agropyron cristatum. One year later after N and water addition, the results indicated that soil pH decreased with N addition, and with a combination of N and W addition together. High rate of N addition significantly lowered plant diversity. For different plant functional groups, the relative abundance of grasses significantly increased, while the relative abundance of forbs significantly decreased under N10, N5W and N10W treatments. Under N10W treatment, the relative abundance of legumes was significantly reduced, while the relative abundance of cyperaceae was significantly increased. W and N interactions significantly decreased soil bacterial and fungal diversity. N addition showed an indirect effect on the fungal diversity by directly affecting plant productivity. Water addition showed an indirect effect on bacterial diversity by directly affecting plant diversity. Soil bacterial diversity showed a positive correlation with plant diversity, while soil fungal diversity had no significant correlation with plant diversity, but had a negative correlation with plant productivity. It also indicates that the strength of feedbacks between aboveground and belowground biodiversity will vary depending on which groups of soil biota are considered.

No Net Loss of Species Diversity After Prescribed Fires in the Brazilian Savanna

Although savannas are fire-adapted ecosystems, prescribing fire for biodiversity conservation remains controversial at least in some regions where savannas occur. Faced with uncertainty, many decision makers and even scientists are still reluctant to prescribe fire for conservation purposes in fire-prone ecosystems, invoking the precautionary principle. Knowledge gaps on the ideal fire regime, such as how and when to burn, and especially the fear of biodiversity losses, are among the main arguments against fire management applied to remnants of native savanna vegetation. To inform this debate, we assessed the impact of prescribed fires on diversity of plants (different growth forms), ants, frogs, lizards, birds, and small mammals, in savannas and grasslands of the Brazilian Cerrado. We assessed the existing species richness, composition, and abundance in areas subjected to long periods of fire suppression and compared to that observed over a short period after prescribed dry-season fires, within each group of plants and animals. Whenever possible, we carried out separate analyses for grassland and savanna. Burning did not significantly reduce species richness of any of the groups analyzed, but had a positive effect on richness of graminoids in grassland. When analyzed at the species level, abundance of most animal groups did not show consistent responses to fire, except for a decrease in some frog populations in grasslands. Forbs, graminoids and subshrubs increased in abundance after fire in grassland areas, though in savanna areas, abundance of forbs and subshrubs tended to decline after fire. Species composition changed little in response to fire as indicated by low levels of dissimilarity between burned and unburned areas. These results confirm the high resilience of Cerrado biota to fire, as expected for savanna ecosystems in general. Besides, we demonstrate here that the risk of biodiversity losses cannot justify the objections to the use of prescribed fire for conservation purposes in the Cerrado.

Halving sunlight reveals no carbon limitation of aboveground biomass production in alpine grassland.

In temperate alpine environments, the short growing season, low temperature and a slow nutrient cycle may restrict plant growth more than carbon (C) assimilation does. To test whether C is a limiting resource, we applied a shade gradient from ambient light to 44% (maximum shade) of incident photon flux density (PFD) in late successional, Carex curvula-dominated alpine grassland at 2,580m elevation in the Swiss central Alps for 3years (2014-2016). Total aboveground biomass did not significantly decrease under reduced PFD, with a confidence interval ranging from +4% to -15% biomass in maximum shade. Belowground biomass, of which more than 80% were fine roots, was significantly reduced by a mean of 17.9±4.6% (±SE), corresponding to 228g/m2 , in maximum shade in 2015 and 2016. This suggests reduced investments into water and nutrient acquisition according to the functional equilibrium concept. Specific leaf area (SLA) and maximum leaf length of the most abundant species increased with decreasing PFD. Foliar concentration of nonstructural carbohydrates (NSC) was reduced by 12.5±4.3% under maximum shade (mean of eight tested species), while NSC concentration of belowground storage organs were unchanged in the four most abundant forbs. Furthermore, maximum shade lowered foliar δ13 C by 1.56±0.35‰ and increased foliar nitrogen concentrations per unit dry mass by 18.8±4.1% across six species in 2015. However, based on unit leaf area, N concentrations were lower in shade (effect of higher SLA). Thus, while we found typical morphological and physiological plant responses to lower light, shading did not considerably affect seasonal aboveground biomass production of this alpine plant community within a broad range of PFD. This suggests that C is not a growth-limiting resource, matching the unresponsiveness to in situ CO2 enrichment previously reported for this type of grassland.

Effects of fire frequency and microhabitat on the ground layer in a grassy woodland

Grassy woodlands worldwide are vertically structured by trees, a ground layer of grasses and forbs, and a variable mid-storey. In Western Sydney’s Cumberland Plain Woodland this mid-storey is increasingly dominated by the prickly shrub Bursaria spinosa Cav. subsp. spinosa. We investigated whether tree and shrub vegetation affects species richness and composition of ground layer microhabitats in this woodland, and whether fire frequency directly affects the ground layer in addition to any indirect effects via overstorey vegetation. Replicate sites were located in areas that had burnt with a frequency that was high, moderate or low. All sites had a similar time since last fire. Three microhabitats (open, under Bursaria, around tree) within each site were sampled for species richness and composition of native and exotic species. Native species richness was not significantly affected by either microhabitat or fire frequency, for total species, grasses or forbs; however the relative abundance of native grasses decreased significantly as fire frequency declined, while the relative abundance of native forbs increased. Exotic species richness was lowest at high fire frequency and significantly higher at low fire frequency. Species composition was significantly affected by both microhabitat and fire frequency combining independently. Planned burning at relatively short intervals can help managers retain grassy habitat for open patch species, habitat for ground layer species that do best under frequent fire, and a robust Themeda triandra Forssk. sward antagonistic to weeds.

A Three-Dimensional Assessment of Soil δ13C in a Subtropical Savanna: Implications for Vegetation Change and Soil Carbon Dynamics

Tree/shrub encroachment into drylands is a geographically widespread vegetation change that often modifies soil organic carbon (SOC) storage and dynamics, and represents an important yet uncertain aspect of the global carbon (C) cycle. We quantified spatial patterns of soil δ13C to 1.2 m depth in a subtropical savanna to evaluate the magnitude and timing of woody encroachment, and its impacts on SOC dynamics. Woody encroachment dramatically altered soil δ13C spatial patterns throughout the profile; values were lowest in the interiors of woody patches, increased towards the peripheries of those patches, and reached highest values in the surrounding grasslands. Soil δ13C and 14C revealed this landscape was once dominated by C4 grasses. However, a rapid vegetation change occurred during the past 100–200 years, characterized by (1) the formation and expansion of woody patches across this landscape, and (2) increased C3 forb abundance within remnant grasslands. Tree/shrub encroachment has substantially increased SOC and the proportion of new SOC derived from C3 plants in the SOC pool. These findings support the emerging perspective that vegetation in many dryland ecosystems is undergoing dramatic and rapid increases in SOC storage, with implications for the C cycle at regional and global scales.