Long-term Grazing Research Articles

Soil quality indices following long-term conservation pasture management practices

Monitoring long-term grazing management practices influence on soil quality (SQ) is essential to ensuring pasture sustainability, which is the largest land use in world agroecosystems. The aim of this study was to quantify SQ based on long-term (15-years) conservation pasture management and landscape position using the Soil Management Assessment Framework (SMAF). Treatments were setup in 15 watersheds (0.14 ha each, 8% slope) in a completely randomized design with five pasture management practices: continuously grazed (CG), hayed (H), rotationally grazed (R), rotationally grazed with an unfertilized buffer strip (RB), and rotationally grazed with an un-grazed, unfertilized, and fenced riparian strip (RBR). Each watershed was divided in three zones (A, B, and C), with the riparian buffer strip (RBS) corresponding to the RBR D zone. Selected soil chemical, physical, and biological properties were determined on soil samples collected in 2017 (0−15 cm depth) per zone. Total P, organic C, and total suspended solids (TSS) were measured in 2017 runoff samples. The SMAF SQ scores were evaluated individually and as an overall SQ index (SQI). Exponential models were used to investigate the relationship between SQI and total P, organic C runoff, and TSS loads. Continuously grazed watersheds had improved soil fertility, with greater nutrient concentration at the shoulder landscape position (zone A). Degradation of soil physical properties were not observed for this practice. After 15 years of continuous management, CG and R watersheds had the greatest SQI (7.07 and7.05, respectively), not differing from RBR (6.93), likely owing to cattle manure deposition for these treatments. Increased SQI in RBS (7.33) improved SQI for RBR watersheds. Differences in SQI were mostly driven by changes in pH, electrical conductivity, soil P and K concentrations. The exponential models indicated that 34 and 28 % of the variation in P and TOC runoff loads, respectively, can be explained by the SMAF SQI (p < 0.05). Overall, SMAF identified the impacts of long-term pasture management practices on SQ and the contributions of individual indicators, thus identifying potential benefits of conservation pasture management.

Monthly variation of production of key range species in central arid rangeland, case study: Saveh-Markazi Province, Iran.

Forage production of rangelands differs during different times of grazing season and in the same month of different years. In range management projects, grazing capacity calculated once during the grazing season, which coincides with the maximum production of rangeland species. This may cause more livestock entry into the rangeland during the grazing season, leading to more degradation. Therefore, it is necessary to measure forage production during the months of grazing season over a few years, based on which the long-term grazing capacity of key range species could be estimated. Production variations of the key species, namely Artemisia sieberi, Salsola laricina, and Stipa hohenackeriana were investigated in Khoshkerood-e-Saveh site in growth and grazing season over the course of three years. For this purpose, the production of each species measured in a one-hectare exclosure with one month intervals until the growth dormancy. After air-drying, forage production was analyzed by SAS software. Based on the results, due to the high variability of monthly and annual precipitation in the region, forage production of key range species had significant differences at P ≤5% level. The maximum and minimum mean production (543 and 388 kg/ha) belonged to 2009 and 2008, respectively. According to the production fluctuation in different years, it is recommended that range management plans account for the long-term average of good production.

Soil organic carbon in drylands: shrub encroachment and vegetation management effects dwarf those of livestock grazing.

Dryland ecosystems occur worldwide and play a prominent, but potentially shifting, role in global biogeochemical cycling. Widespread woody plant proliferation, often associated with declines in palatable grasses, has jeopardized livestock production in drylands and prompted attempts to reduce woody cover by chemical or mechanical means. Woody encroachment also has the potential to significantly alter terrestrial carbon storage. However, little is known of the long-term biogeochemical consequences of woody encroachment in the broader context of its interaction with common dryland land uses, including "brush management" (woody plant clearing) and livestock grazing. Present assessments exhibit considerable variation in the consequences of these land use/land cover changes, with evidence that brush management may counteract sizeable impacts of shrub encroachment on soil biogeochemical pools. A challenge to assessing the net effects of brush management in shrub-encroached grasslands on soil organic carbon (SOC) and total nitrogen (N) pools is that land management practices are typically considered in isolation, when they are co-occurring phenomena. Furthermore, few studies have assessed spatial patterns in brush management and how these are affected in decades following treatment on sites with contrasting grazing histories. To address these uncertainties and interactions, we quantified the impacts of shrub encroachment and their subsequent mortality resulting from brush management (herbicide application) on SOC and N pools in a Sonoran Desert grassland where long-term grazing manipulations (>100yr) co-occur with shrub encroachment and brush management. Pools of SOC and N associated with herbicided shrubs declined markedly over ~40yr, offsetting 66% of the increases from shrub encroachment. However, spatial patterns in SOC induced by shrubs persisted over the decades following brush management. Century-long protection from grazing did little to change SOC and N pools. Accordingly, shrub encroachment and shrub mortality from brush management each far outweighed livestock grazing impacts. Consideration of the patterns of SOC and N through space (e.g., bole-to-dripline gradients), time (e.g., shrub age/size), land use (e.g., livestock grazing and brush management), and their interactions will position us to improve predictions of SOC and N responses to land use/land cover change, inform C-based management decisions, and objectively evaluate trade-offs with other ecosystem services.

Long-term influence of season of grazing and rainfall on vegetation in the eastern Karoo, South Africa

In the Nama-Karoo, South Africa, rainfall and grazing by livestock are two important drivers of botanical composition. Summer rains are advantageous particularly to the grass layer, whereas the characteristic dwarf shrubs survive better than grasses during drought, and benefit from rainfall during cool months. Heavy grazing by livestock during summer reduces the abundance of grasses, whereas winter grazing increases it. This study examined the influences of season of grazing (summer vs winter) and rainfall on botanical composition at two long-term grazing trials at Grootfontein in the eastern Karoo from 1949 to 1967. Severe summer grazing strongly reduced grass abundance and slightly increased the abundance of both palatable and unpalatable dwarf shrubs. High previous-season rainfall strongly promoted short-lived grasses. Dwarf shrubs and grasses declined in response to a decline in annual rainfall over the study period, except for the creeping grass Tragus koelerioides that increased in abundance, possibly in response to decreased competition and an increase in available gaps in the vegetation layer. Results indicate that grazing systems that exclude repeated summer-only grazing maintain ecological health, and that rainfall is the main driver of composition unless extreme grazing systems are employed.

Dominant species' dominant role and spatial stability are enhanced with increasing stocking rate

Stipa breviflora Grisb. (S. breviflora) is a dominant species in the desert steppe of northern China. Its function and role at the plant community level increases with increasing stocking rate. However, the response of spatial stability remains unclear. We selected treatment areas representing no grazing (CK), light grazing (LG), moderate grazing (MG) and heavy grazing (HG) in a long-term grazing experiment (2004–2017) in a S. breviflora desert steppe in Inner Mongolia, northern China. Using a mechanical sampling method, 40 m × 40 m representative sample plots were selected to obtain the height, coverage and density of the S. breviflora population and community, and we computed the standing crop of mechanical sampling quadrats based on a random sample of cutting quadrats. Analysis of standing crop, density of S. breviflora population and its ratio in the plant community showed that the dominant role of S. breviflora population in the plant community increased with increasing grazing intensity, while the spatial stability of S. breviflora population not only had many dimensions, but also many states. The dimension or combination of dimensions of its stability performance and its adaptive state varied under different disturbance intensities and frequencies.

Long-Term Grazing Exclusion Reduces Species Diversity but Increases Community Heterogeneity in an Alpine Grassland

Extensive grazing activity is threatening the alpine grassland on the Qinghai-Tibetan Plateau. Evidence showed that grazing exclusion may change the composition, structure and functions of grassland ecosystems. However, such effects depends on the intensity and duration of exclusion. We explored the effects of short-term (2 and 4 years) and long-term (9 and 11 years) grazing exclusion on plant height, coverage and diversity and community heterogeneity in the alpine grassland on the Qinghai-Tibetan Plateau. We found no difference in plant diversity between the short-term grazing exclusion and control. However, long-term grazing exclusion reduced species richness and increased the Simpson dominance index. This decrease in plant species richness mainly contributed to the decrease in common species richness (defined as species with a relative coverage of 1~5%). In addition, community heterogeneity (coefficient of variation, CV) was significantly higher in the long-term grazing exclusion than in the controlled plots. A structural equation modeling (SEM) demonstrated that long-term grazing exclusion increased the community heterogeneity mainly by reducing species diversity. These results suggest that the effects of grazing exclusion on the composition, structure and community spatial heterogeneity of the alpine grassland ecosystem are dependent on the exclusion duration. Grazing activity may maintain high biodiversity and community stability of the alpine grassland in the harsh environment of the Qinghai-Tibetan Plateau.

Long-Term Effects of Sheep Grazing in Various Densities on Marsh Properties and Vegetation Dynamics in Two Different Salt-Marsh Zones

For conservation management of grassland ecosystems, an important question is under which conditions large grazers induce compositional and structural variation in plant communities, which is a prerequisite for high biodiversity. Here we used two long-term projects on the mainland salt marshes of the Wadden Sea to test the hypothesis that long-term grazing management with different stocking densities results in plant communities with distinctively different plant species composition and vegetation structure. The two projects took place on a low clayey and a high sandy salt marsh with different stocking densities of sheep: 0, 1.5, 3.5, 4.5 and the initially 10 sheep ha−1, where measurements were collected 11, 15, 19 and 23 years after the start of the project. Moreover, grazers affect abiotic conditions by reducing soil-redox potential and surface elevation, thereby driving composition and structure of salt-marsh vegetation. On the low salt marsh, a continued high stocking density (10 sheep ha−1) resulted in succession from the early-successional Puccinellia maritima community to the late-successional Atriplex portulacoides community. On the high salt marsh, the early-successional Festuca rubra community was maintained under all stocking densities. Cessation of grazing resulted in succession to the Elytrigia atherica community in both salt-marsh types. Intermediate stocking densities (1.5, 3 or 4.5 sheep ha−1) resulted in a mosaic of tall vegetation and patches of lawn, i.e. short-grazed vegetation, where Puccinellia maritima lawn occurred interspersed with patches of the Festuca rubra and tall Elytrigia atherica communities in both salt-marsh types. Effects of grazers were influenced by the presence of watering points near the sea wall. To conclude, our results show how joint interactions between grazers and abiotic conditions drive vegetation diversity and heterogeneity, with implications for ecosystem functions and services such as wildlife biodiversity and coastal protection.

Species turnover drives grassland community to phylogenetic clustering over long-term grazing disturbance

Abstract Aims Grazing exerts profound effects on grassland ecosystem service and functions by regulating species composition and diversity, and structuring community assembly worldwide. However, adaptions of phylogenetic diversity and phylogenetic community structure to long-term grazing disturbance remain poorly studied, especially for ecosystems distributed in extreme environments. Methods Here, we conducted an experiment with multigrazing intensities to explore the impacts of grazing disturbance on plant phylogenetic diversity and community structure in an alpine grassland of the Tibetan Plateau. Important Findings Grazing disturbance enriched plant species richness (SR), and stimulated species turnover from regional species pool, consequently changing community species composition. Under low intensities, grazing exerted no obvious effects on phylogenetic diversity and community structure, whereas communities changed from overdispersion to clustering under high grazing intensity. High grazing intensity resulted in stronger environmental filtering, which consequently selected those species with high resilience to grazing disturbance. The observed clustering structure was associated with the colonizing species which were closely related to resident species, and locally extinct species, and distantly related to residents. At the plant functional trait level, high grazing intensity increased species colonization largely by altering the effect of root depth on species colonization compared to light grazing. Our results highlight that solely utilization of SR and diversity cannot fully represent grassland communities responses to grazing. The effects of species turnover on community phylogenetic diversity and structure are entailed to be explored in the future grazing studies.

Short-term yak-grazing alters plant-soil stoichiometric relations in an alpine meadow on the eastern Tibetan Plateau

Over-grazing have significantly altered above- and belowground functions in terrestrial ecosystem. However, the influence of grazing intensity on plant-soil stoichiometric relations in alpine ecosystems remains unclear. We investigated the responses of plant-soil nutrient stoichiometric relationships to four grazing intensities (un-grazing (UG), light grazing (LG), moderate grazing (MG) and heavy grazing (HG)) in an alpine meadow on the eastern Tibetan Plateau. We measured carbon (C), nitrogen (N), phosphorus (P) and potassium (K) concentrations and their ratios in plants and soils in the peak growing season after three years of yak-grazing. Compared to UG and LG plots, heavier grazing intensity at community levels and taxonomic groups decreased plant C and K concentrations by 7.6–10.5% and 17.6–21.3%, respectively, while grazing did not significantly influence plant N and P concentrations. Grazing intensity altered plant C:N and C:P ratios but not C:K and N:P ratios. By contrast, grazing intensity had no significant effects on soil nutrients and stoichiometry. Thus, the differential responses of plant and soil nutrients to grazing intensity caused that plants were more sensitive to grazing than soils. Our results confirm that grazing intensity has differential effects on plant and soil nutrients, implying that plant nutrients do not covary with soil nutrients under changing grazing intensity and challenging the past positive relations between plant and soil nutrients. Further long-term grazing experiments are required to understand the drivers of grazing effect on plant-soil nutrient interactions.

Herbage biomass and its relationship to soil carbon under long-term grazing in northern temperate grasslands

While northern temperate grasslands are important for supporting beef production, it remains unclear how grassland above- and belowground biomass responds to long-term cattle grazing. Here, we use a comprehensive dataset from 73 grasslands distributed across a broad agro-climatic gradient to quantify grassland shoot, litter, and shallow (top 30 cm) root biomass in areas with and without grazing. Additionally, we relate biomass to soil carbon (C) concentrations. Forb biomass was greater (p &lt; 0.05) in grazed areas, particularly those receiving more rainfall. In contrast, grass and total aboveground herbage biomass did not differ with grazing (total: 2320 kg ha−1 for grazed vs. 2210 kg ha−1 for non-grazed; p &gt; 0.05). Forb crude protein concentrations were lower (p &lt; 0.05) in grazed communities compared with those that were non-grazed. Grasslands subjected to grazing had 56% less litter mass. Root biomass down to 30 cm remained similar between areas with (9090 kg ha−1) and without (7130 kg ha−1) grazing (p &gt; 0.05). Surface mineral soil C concentrations were positively related to peak grassland biomass, particularly total (above + belowground) biomass, and with increasing forb biomass in grazed areas. Finally, total aboveground shoot biomass and soil C concentrations in the top 15 cm of soil were both positively related to the proportion of introduced plant diversity in grazed and non-grazed grasslands. Overall, cattle grazing at moderate stocking rates had minimal impact on peak grassland biomass, including above- and belowground, and a positive contribution exists from introduced plant species to maintaining herbage productivity and soil C.

The response of grassland mycorrhizal fungal abundance to a range of long-term grazing intensities

Keystone root symbiotic arbuscular mycorrhizal fungi play a major role in maintaining plant biodiversity, increasing plant productivity and enhancing storage of carbon in soil. AM fungi are ubiquitous and found in most ecosystems including grasslands currently experiencing increasing pressures form human activity. Grazing is known to impact AM fungi but very little is known about how AM fungi are affected by different levels of grazing intensity. Here we report on results from a long-term experimental site in a typical steppe in the north of China, containing seven levels of field-manipulated grazing intensities maintained for over 13 years. We assessed arbuscular mycorrhizal fungal abundance, represented by soil hyphal length density and mycorrhizal root colonization (mycorrhizal root frequency, intensity and arbuscule intensity) within the farm-scale field experiment. We also measured environmental variables to explain the responses of mycorrhizal fungi to grazing intensity. Our results showed that with an increase in grazing intensity, soil hyphal length density linearly decreased. There was, however, no significant trend for mycorrhizal root colonization variables in relation to grazing intensity. Mycorrhizal root frequency was negatively correlated with topographic-induced changes in soil nitrogen and phosphorus, while arbuscule intensity was marginally negatively correlated with soil available phosphorus. Further, we found a possible hump-shaped relationship between the ratio of external to internal AM fungal structures and grazing intensity. Our finding showed that external AM fungal structure was clearly impacted by grazing intensity but that this was not the case for internal mycorrhizal structures. This indicated that mycorrhizal functioning was impacted by the intensity of grazing as the mycorrhizal structures responded differently. Indeed the ratio of the foraging extra-radical mycorrhizal hyphae to intra-radical mycorrhizal structures was highest at moderate grazing intensity but strongly decreased by high grazing intensity. Our study suggests that the impacts of grazing intensity on the plant-AMF association could lead to further knock-on effects on the plant-soil system via the feedbacks that exist between plant and AMF communities.

Ants drive invertebrate community response to cattle grazing

Livestock grazing acts as a disturbance that alters ground-level habitat structure and can shape faunal communities. Invertebrate fauna have complex responses to grazing, driven by grazing-induced changes to vegetation structure, and may also be influenced by changes to predation pressure and prey availability. However, there is a dearth of knowledge about the effects of grazing on invertebrates, and research is rarely conducted across multiple orders, or at multiple trophic levels. We examined the ordinal-level response of a tropical savanna invertebrate assemblage to four replicated grazing treatments in two vegetation types at a long-term grazing trial in northern Australia. We used overall measures of abundance, order richness, and the assemblage composition (using the 17 orders we observed) to compare invertebrate communities among grazing treatments and between vegetation types. Responses of individual orders were modelled in relation to microhabitat variables. At the end of the dry season in October 2014 and 2015, we sampled 25,785 invertebrates from 17 orders. Ants accounted for over 80% of all individuals captured. We found that, overall, invertebrate abundance was higher in the most heavily grazed treatments, driven by the response of ants, but assemblage composition was not significantly different among grazing treatments. Araneae, Orthoptera, Scolopendromorpha and Scorpiones responded to vegetation type and were associated with % cover of Carissa ovata, bare ground, and grass. Ants, while responsive to grazing treatment, was not associated with any of the microhabitat variables, suggesting habitat structure in combination with other factors may be driving this response. Our results confirm the importance of ants as a sensitive biological indicator of disturbance. Considering their role in ecosystem function, invertebrates, and their responses to livestock grazing, need to be considered when making land management decisions on rangelands, and maintaining invertebrate diversity should be a priority for land managers.

Heavy grazing over 64 years reduced soil bacterial diversity in the foothills of the Rocky Mountains, Canada

Grazing is one of the most widespread grassland management strategies. However, the effects of over six decades of different grazing intensities on soil bacterial community composition in the foothills of the Rocky Mountains are uncertain. We analyzed the bacterial community composition in soil samples collected in both summer and fall, 64 years after a long-term grazing intensity study was initiated in 1949. Grazing intensity treatments were (i) 0 animal-unit months (AUM) ha−1, (ii) 2.4 AUM ha−1 and (iii) 4.8 AUM ha−1, which represented the control, moderate and heavy grazing intensities, respectively. The evenness and diversity indices decreased with heavy grazing intensity relative to the other treatments in both summer and fall. In summer and fall, heavy grazing significantly shifted the bacterial community composition compared to the other treatments. Heavy grazing intensity significantly decreased the relative abundances of Bacteroidetes, Chlorobi, Nitrospirae and Proteobacteria, but significantly increased the relative abundance of Actinobacteria. Principal Coordinate Analyses revealed that available nitrogen, moisture content, total nitrogen and organic carbon were the primary environmental factors affecting the soil bacterial community composition. This study suggests that the effects of grazing on soil bacterial community composition are largely dependent on changes in soil physicochemical properties induced by the intensity of grazing over periods of six decades.

Soil phosphorus pools with addition of fertiliser phosphorus in a long-term grazing experiment

Grasslands are a globally important use of land for food and fibre production, which often require the addition of phosphorus (P) fertiliser to maximise plant production. However, a large proportion of the added P can accumulate in pools of poorly available inorganic and organic P in the surface soil layer under grasslands. The aim of this study was to identify the chemical nature of the organic P in soils from a long-term fertiliser by grazing permanent pasture experiment that have received varying additions of phosphatic fertiliser (cumulative P input of 27, 169, 311, 513, 745 and 1035 kg P ha−1) over a period of 37 years. The design of the experiment uniquely provides insight into the response of soil organic P to the addition of fertiliser P on the decadal scale. On average, 46% of the added fertiliser P was recovered as total P in the 0–100 mm soil layer after 37 years of phosphate addition. The content of both inorganic and organic forms of soil P increased with the addition of fertiliser P. The accumulation of organic P increased linearly up to a cumulative P input of 745 kg P ha−1 and plateaued thereafter. The majority of organic P in all treatments was detected as a broad signal in the phosphomonoester region of solution 31P nuclear magnetic resonance (NMR) spectra; this also accounted for 79% of the accumulated organic P in fertilised soil. Our results indicate that accumulation of P in the organic portion as complex forms eventually reaches a new equilibrium where no net accumulation would be expected with further addition of phosphate.

Extracellular enzyme activity in grass litter varies with grazing history, environment and plant species in temperate grasslands

Long-term livestock grazing (here after ‘grazing’) affects carbon (C) and nutrient cycling in grassland ecosystems, in part by altering the quantity and quality of litter inputs. Despite their spatial extent and size of carbon and nutrient stocks, the effect of grazing on grassland biogeochemical cycling through the mediation of microbial activity remains poorly understood. To better understand the relationship between grazing and C and nutrient cycling in litter, we conducted an 18-month long study in paired grasslands previously grazed and nongrazed by cattle for 25 years, measuring extracellular enzyme activity (EEA) in various plant litter samples. Litter sources, including seven grass species dominant in one or more subregions and possessing divergent responses to grazing, as well as a community mix of litter sourced from each site, were tested at 15 sites spanning three grassland subregions in Alberta, Canada. We quantified EEAs associated with C cycling (β-glucosidase, β-Cellobiosidase and β-xylosidase), nitrogen (N) cycling (N-acetyl-glucosaminidase) and phosphorus (P) cycling (phosphatase). In general, litter in grasslands exposed to grazing had greater activity of C-liberating and P-liberating enzyme (β-xylosidase and phosphatase) in the mesic grasslands of the Foothills Fescue subregion (P ≤ 0.10). Observed EEAs were strongly mediated by litter type, with greater EEAs in litter of grass species known to increase in abundance under long-term grazing, including Poa pratensis in the Foothills Fescue subregion, and Bouteloua gracilis in arid grasslands of the Mixedgrass Prairie. In contrast, Pascopyrum smithii litter had the lowest enzyme activities in all subregions. We also found that EEAs changed through time (0–18 months) with consistently high levels detected at 1 (June 2014), 6 (October 2014) and 18 months (October 2015) after placement. Overall, these findings indicate grazing enhances EEA, and thus C and N-cycling, in northern temperate grasslands.

Managing Tallgrass Prairies for Productivity and Ecological Function: A Long-Term Grazing Experiment in the Southern Great Plains, USA

The Great Plains of the USA is one of largest expanses of prairie ecosystems in the world. Prairies have been extensively converted to other land uses. The remaining prairie ecosystems are important for livestock grazing and provide benefits including habitat for avian, terrestrial, and aquatic species, carbon regulation, and hydrologic function. While producers, land management agencies, and some researchers have promoted livestock management using rotational stocking for increased production efficiency and enhanced ecosystem function, scientific literature has not provided a consensus on whether rotational stocking results in increased plant biomass or animal productivity. To address this research need, we established long-term grazing research using an adaptive management framework to encompass a wide range of production and ecological interactions on native grassland pastures. This paper describes objectives, design, and implementation of the long-term study to evaluate productivity and ecological effects of beef cow–calf management and production under continuous system (CS) or rotational system (RS) on native tallgrass prairie. Findings from 2009 to 2015 indicate that plant biomass and animal productivity were similar in the two grazing management systems. There were some indicators that forage nutritive value of standing biomass and soil nutrient content were enhanced in the RS system compared with the CS, yet individual calf body weight (BW) at weaning was greater in the CS. This prepares us to engage with producers to help determine the focus for the next phase of the research.

Grazing exclusion promotes grasses functional group dominance via increasing of bud banks in steppe community

To understand the bud banks response to grazing exclusion, we conducted a demographic experiment in long-term grazing exclusion (20 year and 30 year) typical steppe. Results showed that grass functional group constituted the vast majority of the aboveground vegetation and belowground bud bank in all treatments. Long-term grazing exclusion significantly increased total aboveground biomass (2.5 and 2.6 times in 20y and 30y grazing exclusion grasslands, respectively), and decreased total stem density (31% and 37% in 20y and 30y grazing exclusion grasslands, respectively). Grazing exclusion for 20 and 30 years increased grass aboveground biomass respectively by 6.0 and 8.0 times, and decreased grass stem density by 38% and 33%. Grazing exclusion had different effects on belowground bud density of grass and forb functional group. Long-term grazing exclusion significantly increased plant buds and bud bank size (25% and 37% in 20y and 30y grazing exclusion grasslands, respectively), especially for grass functional group (49% and 95% in 20y and 30y grazing exclusion grasslands, respectively), but had no significant effects on forb bud density. Changes of aboveground community were significantly related to changes of belowground bud bank under both grazing and grazing exclusion grasslands. The bud bank density of grass functional group was significantly positive with total (R2 = 0.33, P < 0.05) and grass aboveground biomass (R2 = 0.36, P < 0.01), while negative related with total (R2 = −0.27, P < 0.05) and grass stem density (R2 = −0.22, P < 0.05). Grazed grasslands, 20y and 30y grazing exclusion grasslands all were not meristem limited and had large reserve bud banks, which would completely replace the aboveground stem population during the growing season. These findings indicate that grazing exclusion could not only improve a large bud bank for grassland restoration but also improve the dominance of grass functional group by increasing grass belowground bud banks in typical steppe community. We propose that the belowground bud bank might be a good approach to indicating potential succession direction of aboveground community.

Nutrient availability induces community shifts in seagrass meadows grazed by turtles.

In the Caribbean, green turtles graze seagrass meadows dominated by Thalassia testudinum through rotational grazing, resulting in the creation of grazed and recovering (abandoned) patches surrounded by ungrazed seagrasses. We evaluated the seagrass community and its environment along a turtle grazing gradient; with the duration of (simulated) grazing as a proxy for the level of grazing pressure. The grazing levels consisted of Short-term (4 months clipping), Medium-term (8 months clipping), Long-term grazing (8 months of clipping in previously grazed areas), 8-months recovery of previously grazed patches, and ungrazed or unclipped patches as controls. We measured biomass and density of the seagrasses and rhizophytic algae, and changes in sediment parameters. Medium- and Long-term grazing promoted a shift in community species composition. At increasing grazing pressure, the total biomass of T. testudinum declined, whereas that of early-successional increased. Ammonium concentrations were highest in the patches of Medium-term (9.2 + 0.8 μM) and Long-term grazing levels (11.0 + 2.2 μM) and were lowest in the control areas (4.6 + 1.5 μM). T. testudinum is a late-successional species that maintains sediment nutrient concentrations at levels below the requirements of early-successional species when dominant. When the abundance of this species declines due to grazing, these resources become available, likely driving a shift in community composition toward a higher abundance of early-successional species.

Competitive Strategy of Subalpine Tall-Grass Species of the Northwestern Caucasus

The range of ecological CSR strategies for subalpine tall-herb communities of the northwestern Caucasus (Teberda state natural biosphere reserve) has been studied by the measurement of leaves’ functional traits. These communities are developed in swales, river valleys, and runoff depressions of the subalpine belt and represent a typical element of the Caucasian flora. The dominating species are represented by tall forbs, such as Rumex alpinus, Senecio platyphylloides, Cephalaria gigantea, Ligusticum alatum, etc. To evaluate ecological strategies of plants, three functional traits, including leaf area and the weights of wet and dry leaves, have been measured. Based on these measurements, the strategy parameters have been calculated for 42 vascular plant species. The majority of plants of the subalpine tall-grass community manifest traits typical for the competitive (C) and competitive-ruderal (CR) strategies. According to the calculation algorithm, 11 species (Angelica purpurascens, A. tatianae, Cirsium chlorocomos, Heracleum asperum, H. leskovii, H. sosnowskyi, etc.) are referred to the C-strategy. The CR strategy is observed for Aconitum nasutum, Cirsium simplex, Geranium sylvaticum, Hesperis voronovii, Rumex alpestris, and some other species. Two species (Achillea millefolium and Dactylis glomerata) are characterized by the competitive and stress-tolerant (CS) strategy. The stress-tolerant (S) strategy is observed for three species (Veronica filiformis, Lilium monadelphum, and Millium effusum). Finally, the mixed CSR strategy is typical for two species (Trifolium pratense and Astrantia maxima). The majority (93%) of the species studied is characterized by clear competitive traits; the contribution of this strategy type positively correlates with the average vegetative height of a species. In addition, many of the studied species (26% on average) are also characterized by some R-strategy traits. In our opinion, this fact results from a long-term grazing history of alpine plant communities in this region. The obtained results contradict the common opinion about the domination of stress-tolerant species in highlands. This contradiction may be explained by the fact that the studied subalpine meadows are located in the most favorable habitats providing competitive advantages for rapidly-growing tall-herb species. The study confirms the hypothesis that the dominated species of the subalpine tall-grass community of the northwest Caucasus are characterized by significantly (up to 95%) manifested traits of C strategy.

Degraded or Just Dusty? Examining Ecological Change in Arid Lands

AbstractThe ecological history of rangelands is often presented as a tale of devastation, where fragile drylands are irreversibly degraded through inappropriate land use. However, there is confusion about how to recognize and measure degradation, especially in low-productivity environments characterized by extreme natural variability and where abrupt and comprehensive management upheavals preclude benchmarks. These issues have important consequences for rangeland management programs, which are typically founded on presumptions of substantial and ongoing degradation from former “natural” states. We explore complementary approaches to critically assess degradation: the historical record, long-term grazing exclosures, surveys for potentially rare and sensitive plant species, and assessment of water-remote areas in relation to rare plant occurrence. Employing these approaches in inland Australia, we show that prevailing paradigms have become entrenched despite being inconsistent with empirical evidence. Our methodology can be applied to drylands with abrupt changes in management and contentious ecological narratives.