Consequence of grazing pattern and vegetation structure on the spatial variations of net N mineralisation in a wet grassland

The aim of this study was to determine whether the spatial heterogeneity of grassland vegetation structure would lead to spatial heterogeneity in the net nitrogen mineralisation process in the soil and therefore in the quantity of mineral nitrogen available for the plants. The net nitrogen mineralisation in the soil was compared between different vegetation patches generated by grazing, on two different types of plant communities: mesophilous and meso-hygrophilous.In ungrazed conditions, the net soil nitrogen mineralisation rates did not vary significantly between the two plant communities and remained relatively constant with time. Grazing by cattle or horses appeared to have two effects on the process of net soil nitrogen mineralisation. Firstly, it significantly stimulated net nitrogen mineralisation compared to ungrazed conditions and secondly, it led to spatial heterogeneity in mineralisation rates in the grazed enclosures. This spatial heterogeneity of nitrogen available for plants occurred both between and within plant communities.In the meso-hygrophilous plant community, net nitrogen mineralisation increased with grazing pressure. We suggest that a decrease of C inputs to the soil, concomitant with increasing grazing pressure, could decrease microbial nitrogen immobilisation.By contrast, in the mesophilous plant community net nitrogen mineralisation did not vary with grazing pressure. These differences in the functional responsiveness to grazing and biomass between the two plant communities could be related to the differences in the functional traits characterizing their dominant species along the grazing gradient. In the meso-hygrophilous community, the species composition switch with grazing intensity gradient led to the replacement of the perennial plant species by annual plant species which could lead to an improvement in the litter nitrogen content and an acceleration in the litter decomposition rate. By contrast, in the mesophilous plant community, the perennial species remained dominant along the grazing intensity gradient and could explain the absence of effect on the net nitrogen mineralisation rates.We suggest that at the scale of the vegetation patch, the decrease in plant biomass linked to grazing could regulate soil microorganism activity, in relation with shift in plant functional traits which improve litter decomposability.     

Remnant grassland habitats as source communities for plant diversification in agricultural landscapes

Lately there has been a shift in Sweden from grazing species-rich semi-natural grasslands towards grazing ex-arable fields in the modern agricultural landscape. These fields normally contain a fraction of the plant species richness compared to semi-natural grasslands. However, small remnant habitats have been suggested as important for plant species diversity and conservation as they may function as refugia for grassland specialists in fragmented and highly modified agricultural landscapes. In this study, we examined whether plant communities on small remnant habitats, i.e. midfield islets, can function as sources for grassland species to disperse out into surrounding grazed ex-fields (former arable fields). We examined species richness and grassland specialists (species favoured by grazing) and their ability to colonize fields after 5 and 11 years of grazing. The fields that had been grazed for a shorter time were fairly species-poor with few grassland specialists. A longer period of grazing had a positive effect on total and small-scale species diversity in both islets and fields. Species composition became more similar with time, and the number of grassland specialists in both habitats increased. We found that grassland specialists dispersed step-wise into the fields, and the number of grassland specialists decreased with distance from the source. Our study suggests that remnant habitats, such as midfield islets, do function as a source community for grassland specialists and enhance diversification of grassland species when grazing is introduced. For long-term conservation of plant species, incorporating small refugia into larger grazing complexes may thus enhance species richness.     

放牧对植物群落特征和土壤微生物及酶活性的影响

[目的]探讨放牧对羊草群落和贝加尔针茅群落的影响,为草原土壤的保护和草原自然保护区建设提供科学依据。[方法]以呼伦贝尔草甸草原为样地,采用野外调查和实验室分析相结合的方法。[结果]在放牧干扰下,以羊草为建群种的群落所受的影响比贝加尔针茅群落小,植物群落盖度、高度和Simpson指数明显高于贝加尔针茅群,物种多样性更丰富,生长情况相对更好。羊草草原土壤全氮、全磷和有机质含量高于贝加尔针茅草原土壤。各放牧区土壤微生物数量均表现为:细菌放线菌真菌;垂直分布为0—10cm10—20cm;土壤脲酶、过氧化氢酶、转化酶活性、全N,全P和有机质等0—10cm土层的均高于10—20cm。相关分析表明,植物群落α多样性与土壤微生物数量、土壤酶活性、全N,全P和有机质等呈显著正相关。[结论]适度放牧有助于提高草甸草原羊草群落和贝加尔针茅群落α多样性、土壤微生物数量和土壤酶活性。两个群落相比较,羊草群落更适合放牧。     

EFFECT OF PROTECTION ON PLANT COMMUNITY DYNAMICS IN THE MEDITERRANEAN ARID ZONE OF SOUTHERN TUNISIA: A CASE STUDY FROM BOU HEDMA NATIONAL PARK

Ecosystems protected from heavy grazing impacts, such as national parks and refuges, are generally considered to sustain higher plant species diversity and better ecosystem composition and structure compared to heavily grazed areas. To evaluate the impact of livestock grazing, we sampled vegetation characteristics from two areas having different grazing intensity levels. The first site has high protection from grazing and is located inside the Bou Hedma National Park in Southern Tunisia. The second site has a low protection from grazing and is situated within an open area located immediately outside the park boundary where human populations and their livestock have unrestricted access to ecosystem resources. Total plant cover, density, perennial species cover and their contribution were compared between the two grazing level sites. Results show that considerable positive effects occur in the areas protected from grazing. As compared to the overgrazed (open) sites. Several species known for their high palatability, such as Cenchrus ciliaris L., Salvia aegyptiaca L., Echiochilon fruticosum Desf. and Helianthemum sessiliflorum Desf., are more abundant inside the park than outside. These results are very important for managers to apply this technique as a tool for increasing the resilience of arid ecosystems, qualified very vulnerable to climate change. Copyright © 2011 John Wiley & Sons, Ltd.     

How does grazing intensity affect different vegetation types in arid Succulent Karoo, South Africa? Implications for conservation management

The Knersvlakte in the Succulent Karoo Biome (South Africa) is known for its high plant diversity and endemism. In the course of establishing a conservation area there, we assessed baseline data for future management. We investigated the effects of grazing on the vegetation in terms of species diversity and composition as well as reproduction of selected species. Data were sampled on four adjacent farms, which were ungrazed, moderately or intensively grazed by sheep and goats. The data were collected in 27 quartz and 24 non-quartz plots, representing two major habitat types of the region. Within each of the 1000-m² plots, 100 subplots of 400 cm² size were sampled. ANOVAs revealed that species richness and abundance of endemic species on quartz fields decreased with grazing. Abundance of annuals did not increase significantly due to grazing. Fidelity analyses indicated that species composition differed between grazing intensities and that the ungrazed and moderately grazed plots both contained unique locally endemic habitat specialists. Reproduction of two endemic dwarf shrubs Drosanthemumschoenlandianum and Argyrodermafissum (both Aizoaceae) increased under moderate grazing, which in the case of D.schoenlandianum was interpreted as an effect of grazing. We attribute the low number of seedlings and annuals on the moderately grazed farm to lower seasonal rainfall on these plots. From a conservation perspective, no or moderate grazing appear to be necessary to preserve plant diversity and vegetation patterns, and their underlying processes.     

宁东矿区天然植物群落特征及其与土壤理化性质的关系

[目的] 研究宁东矿区天然植物群落特征与土壤理化性质的关系,为宁东矿区植被重建过程中植物种的选择提供科学依据。[方法] 以宁东矿区6种典型的天然植物群落和土壤为研究对象,采用野外调查结合室内试验的方法,对比分析不同群落的植物群落特征及其与土壤理化性质的关系。[结果] 宁东矿区6种天然植物群落共调查到植物55种,隶属于15科48属,集中分布于菊科、豆科、藜科和禾本科4科。细枝岩黄耆（Hedysarum scoparium）+柠条锦鸡儿（Caragana korshinskii）—白莲蒿（Artemisia sacrorum）群落灌木层植被盖度和高度在6个群落中均最高,其数值分别为48%和202.54 cm,灌木物种柠条锦鸡儿在其中5个群落中均有分布且生长良好。灌木层Patrick丰富度指数与土壤碱解氮、砾石含量、速效钾和有机质呈正相关,与pH值呈负相关;草本层植物种Patrick丰富度指数与土壤有机质、田间持水量和速效磷呈正相关关系。[结论] 宁东矿区煤矸石山植被重建时,对于覆土土质为壤质砂土或砂质壤土,优先选择柠条锦鸡儿、细枝岩黄耆、黑沙蒿（Artemisia ordosica）和沙拐枣（Calligonum mongolicum）等灌木树种;覆土土质为少砾质砂土时选沙冬青（Ammopiptanthus mongolicus）和柠条锦鸡儿;覆土土质为多砾质砂土时可选藏锦鸡儿（Caragana tibetica）、裸果木（Gymnocarpos przewalskii）和胡枝子（Lespedeza bicolor）等灌木物种。土壤容重对灌木物种多样性贡献率较大,土壤田间持水量和有机质对草本植物多样性贡献率较大。     

林下秸秆覆盖种植大球盖菇对苦驴河源头坡地清水产流的影响

[目的]探索秸秆覆盖种植大球盖菇模式对经济林(尤其是刚刚荒改坡的经济林)清水产流和改土控草的影响,为坡地水源涵养、生态保育、控草保肥提供技术支撑。[方法]在派河上游苦驴河的源头,选取2组不同种类的坡地经济林,利用秸秆覆盖种植大球盖菇技术,在大球盖菇生长的不同时期对该区域坡地水质、土壤有机质和杂草多样性进行分析。[结果]采用秸秆覆盖种植大球盖菇的技术,平均能有效降低该地区水中总氮42.68%～50.47%,总磷45.72%～46.74%和悬浮物(SS)33.41%～36.58%的含量,同时增加土壤有机质的含量,平均增长了10.17%～16.42%,减少该区域杂草多样性和种类,有效降低了该地水肥流失,可在较短时间内无害且快速地增加该区域清水产流能力。[结论]采用秸秆覆盖种植大球盖菇的技术,能有效降低坡地径流水中总氮、总磷和SS的含量,同时增加土壤有机质的含量,减少该区域杂草多样性和种类,起到控制水肥和水土流失作用,在当年荒改坡的坡地上,该作用更加明显。     

Grazing as a management tool in dune grasslands: Evidence of soil and scale dependence of the effect of large herbivores on plant diversity

In nature management, the introduction of large herbivores into human-influenced grasslands is thought to be effective to maintain or enhance plant diversity. In order to test the validity of this assumption, we studied the effect of grazing by large herbivores on plant species richness and community heterogeneity across a soil acidity gradient at different spatial scales in dry coastal dune grasslands in western Belgium and north-western France. The effect of grazing on plant richness varied with scale and soil acidity. Grazing had a predominantly positive effect on plant species richness in all habitats at the small scale (0.25 × 0.25 m). However, at site scale (8 × 8 m) it had only positive effects in grasslands with higher soil pH (6-7.4). Similarly, grazing resulted in a homogenization of grassland vegetation at lower pH, while heterogeneity increased with grazing on soil with higher pH. In general, grazing increased the number of rare species, independent of soil pH. The results confirm that the impact of grazing on plant diversity depends on the scale considered and that the effects further depend on soil acidity which was correlated to biomass production at the given soil pH range in this study. Although grazing seems an appropriate management tool to maintain and even enhance plant biodiversity under many circumstances, it may negatively affect plant species richness, where soil resources limit plant biomass production.     

Grazing intensity and environmental factors effects on species composition and diversity in rangelands of Iran

The aim of this study was to analyze the effects of grazing, precipitation and temperature factors on plant species dynamics (diversity and composition) in the semi-steppe of Isfahan semi-arid rangelands, Iran. The effects of Sheep grazing were studied in a controlled experiment along grazing gradient with seven intensities (from very heavily grazed to nongrazed) during six consecutive years (2006–2011). The results show that plant species dynamics varied among years, but were only slightly affected by grazing intensity. Since the experimental years were much dryer than the long term average, the abiotic constraints may have overridden any grazing effect. The differences among the years were predominantly determined by the abiotic factors of temperature and precipitation. Most of the variations in species dynamics and coexistence between the C₄ and C₃ species were explained by seasonal weather conditions, i.e., temperature and precipitation regimes during the early season (March-June). The dominant C₃ species, Poa bulbosa, was highly competitive in March-June at low and high temperature and rainfall levels, respectively. In contrast, the most common C₄ species Cynodon dactylon benefited from high and low early season temperature and rainfall levels, respectively. However, biomass of P. bulbosa was positively correlated with temperature in March, when effective mean temperature ranges from 0 to 5°C and thus promotes vernalization and vegetative sprouting. Our results suggest that, over a six-year period, it is temporal variability in temperature and precipitation rather than grazing that determines vegetation dynamics and species distributions in grazed semi-steppe ecosystems. Our results also support that the variability in the dominant species biomass, rather than diversity, determine ecosystem functioning. This study provides fundamental knowledge on the complex interaction of climate, vegetation, and grazing.     

Effects of grazing by horses and/or cattle on the diversity of coastal grasslands in western France

In the coastal grasslands of western France, extensive mixed grazing by cattle and horses has been practised for many centuries. The vegetation of these old embanked grasslands varies along a topographical gradient with a hygrophilous plant community in low-lying depressions seasonally flooded, a mesophilous community on high level flats that are never flooded, and a meso-hygrophilous community on slopes where the soil remains saline. Recently, fewer horses have been grazed on these pastures and so a 6-year study was designed to investigate the effects of monospecific and mixed grazing by horses and cattle on plant community structure, composition and diversity. Mixed grazing produced the most species-rich and structurally diverse swards. Mixed grazing enhanced the development of rosette, sub-halophyte and halophyte species where the soil is saline, due to additive effects between the two herbivore species. Mixed grazing also limited the strongly competitive Elymus repens and Agrostis stolonifera on horse latrine areas, cattle grazing, thus showing a compensatory effect. The combination of additive and compensatory effects with mixed grazing could be used to manage plant diversity, heterogeneity in vegetation structure and communities of conservation value at the scale of the grassland ecosystem.     

Effects of Grazing Intensity on Soil and Vegetation Properties in a Mediterranean Rangeland

Grazing modifies the aboveground soil and plants of rangeland ecosystems. This study was conducted to determine the effects of various grazing intensity levels on soil bulk density, soil pH, soil electrical conductivity (EC), soil total organic carbon (TOC), aboveground biomass production, plant community richness (N), and vegetation diversity (H) in Gian Rangeland, Hamedan Province, Iran. Soil and vegetation samplings were conducted based on the randomized systematic method. Soil and vegetation samplings were carried out along 100-m-long transects placed at 100, 200, 400, 800, and 1600 m running perpendicular to six sheep corrals. The effects of various grazing intensities on studied parameters were detected by analysis of variance (ANOVA) (at α = 0.05). Results of this study indicated the soil bulk density, EC, TOC, aboveground biomass production, plant community richness, and vegetation diversity values were altered significantly at different distances from the sheep corrals. However, soil pH was not significantly affected by various grazing intensities.     

藏北高寒草甸土壤线虫群落对围封及自由放牧的响应

为了解放牧干扰对藏北高寒草甸的影响,以及连续围封措施对草地的恢复作用,2013—2015年连续3年对那曲县围封、自由放牧天然高寒草甸土壤线虫群落进行取样调查及数据分析。结果表明:围封、放牧样地的线虫个体数量在年际间的变化均较明显,植食性线虫是整个线虫群落个体数量变化的主要贡献者;围封样地的线虫个体密度、多样性指数H′、丰富度指数SR,以及优势度指数λ的年际变化幅度均大于放牧样地;食细菌性线虫个体数量及线虫通路比值(NCR)表明放牧样地的有机质转化效率高于围封样地;成熟度指数(MI)、植物寄生线虫指数(PPI)分析表明,所研究区域经5年围封,高寒草甸生态系统稳定性没有明显的提高,相反,现有放牧强度维持或者增加了线虫群落的物种多样性,利于物种共存和草地生态系统稳定性的维持。     

围封对荒漠草原物种多样性和功能多样性的影响

为揭示荒漠草原区域围封对不同土壤生境物种多样性和功能多样性的影响,以荒漠草原不同土壤生境下围封（15年、10年、6年）和放牧（15年、6年、5年）的草地植物群落为研究对象,基于方差分析和主成分分析的基础上,通过函数拟合分析,探讨植物物种多样性与功能多样性之间的关系。结果表明：（1）围封相对于自由放牧条件,灰钙土生境植物功能多样性显著增加（P<0.05）。随着封育年限的增加,物种多样性呈显著降低趋势（P<0.05）,功能多样性未发生显著变化（P>0.05）;风沙土生境植物功能多样性和物种多样性未发生显著变化（P>0.05）。（2）功能离散度表征的功能多样性与物种丰富度关系可用二次多项式Y=aX²+bX+c形式表示,随着封育年限的增加,二者的相关系数在灰钙土和风沙土生境均呈增加趋势。荒漠草原物种多样性与功能多样性整体正相关,且符合二次函数关系,物种多样性可以用来反映植物群落功能多样性的水平高低,但这种替代作用受封育年限和放牧的影响,随着封育年限增加,物种多样性反映功能多样性水平的能力增加,在未来荒漠草原多样性与生态系统功能关系及维持机制中,需要同时考虑多样性的多维度特征以及不同土壤生境类型。     

A Suitable Site for in situ (On-farm) Management of Plant Diversity in Traditional Agroecosystems of Western Himalaya in Uttaranchal State: A Case Study

There is a growing realisation world over that the introduction of modern agriculture has to be supplemented with measures to conserve biodiversity in situ if yield gains are to be stabilized. Hence, there is a growing interest from agricultural development specialists and conservation biologists for understanding the socioeconomic factors determining the conservation of biodiversity in situ. The present study was conducted with the objective of understanding the in situ (on-farm) conservation of agrobiodiversity in traditional agroecosystems taking the Urgam valley in north-western Himalaya of India, as a case study. An inventory was made of traditional crops and wild economic species for subsistence, and the structure of forest resource base, traditional knowledge related to resource management and use. Institutional and scientific challenges for in situ (on-farm) management of crop diversity were studied and are discussed in this paper. Complementarity of in situ (on-farm) conservation with ex situ conservation together with crop improvement in such marginal areas are suggested.     

巨尾桉工业原料林下植物多样性与土壤因子的关系

采用野外调查与室内分析相结合的方法,研究了巨尾桉工业原料林下植物多样性、土壤因子的变化特征以及二者之间的关系。结果表明,物种丰富度指数是草本层最高,而Simpson指数,Shannon—Wiener指数和均匀度指数是灌木层最高。巨尾桉林地土壤水分含量的变化规律为:母质层淀积层腐殖质层,有机质、水解氮、有效磷和速效钾含量的变化规律为:腐殖质层淀积层母质层。腐殖质层、淀积层和母质层的土壤水分含量、有机质含量与灌木层或草本层丰富度指数、多样性指数和均匀度指数无显著相关性;腐殖质层速效钾含量与草本层Simpson指数极显著相关;淀积层速效钾含量与灌木层Simpson指数极显著相关;水解氮与灌木层及草本层以Simpson指数为基础的均匀度指数,以Shannon—Wiener指数为基础的均匀度指数极显著相关;母质层土壤各因子含量与灌木层或草本层多样性指数无显著相关。研究结果为巨尾桉林的可持续经营管理提供理论基础和科学依据。     

Estimating nutritive values of Jasminum fruticans L. plant species in northern rangelands of Golestan province

Information on different rangeland plants' nutritive values on different plant parts and for various habitats is important in rangelands management. Effects of different plant parts (stems and leaves) of the Jasminum fruticans L. plant species on forage quality indicators were investigated in two regions in 2015. Plant samples were collected from Sharlogh rangelands and cultivated in the Research and Education Center of Agricultural and Natural Resources (RECANR) in Iran with completely randomized design with three replications in each plant sample. The plant leaves and stems samples were oven-dried at 80°C for 24 hr, and then analyzed for crude protein (CP), crude fiber (CF), dry matter (DM), ether extract (EE), crude ash (CA), metabolizable energy (ME), and mineral elements, including calcium (Ca) and phosphorus (P). Results showed that the forage quality indicators in different regions were statistically significant, except for the CA. Also, nutritive values differed significantly (p < 0.01) between different plant parts, except ME parameter. Results also indicated that J. fruticans due to its high tissue CP content is a valuable source of forage for livestock.     

拉萨温性草原土壤原生动物群落对不同放牧强度的响应

探究土壤原生动物对拉萨河谷温性草原不同放牧强度的响应，可以动态监测草原生态系统的环境变化，为保护青藏高原草原生态环境提供科学依据。本研究选取5年围封的温性草原进行为期3年的放牧试验，于2018年9月采取不同放牧强度下的土壤样品进行土壤原生动物培养和鉴定（非淹没培养法、活体观察法）。结果表明：供试样地共鉴定出土壤原生动物46属，隶属于2门、12纲、21目和36科；不同放牧强度下的土壤原生动物主要类群为旋毛纲（Spirotrichea）；不同放牧强度下土壤原生动物多样性指数（H、E、C、M）无显著差异（P>0.05）；Jaccard相似性指数在极不相似到中等不相似之间；样地B3（禁牧）单独聚为一类，说明其空间异质性较大；全氮是影响土壤原生动物分布的主要环境因子，土壤湿度、速效钾、电导率等环境因子共同影响不同放牧强度下土壤原生动物物种组成和分布。     

Conservation value of the herbaceous vegetation in hedgerows - does organic farming make a difference?

The aim was to compare and test differences in the conservation value of hedge bottom vegetation on organic and conventional farms. The studied hedgerows (28 organic and 28 conventional) were on average 14 years old and established in the same way, except that organic hedgerows were established and managed without use of pesticides. We investigated three sample plots of 10 m² in all hedgerows together with a set of 13 explanatory variables. There were no differences in soil texture between hedgerow types but organic farms had higher pH and lower conductivity. Organic farms had higher total N values, which are explained by a slightly higher content of organic matter. There was highly significant interaction between farming type and neighbouring crop type according to soil phosphate concentration. Significantly more plant species were found in the organic hedgerows. The species compositions in organic hedgerows appeared significantly more similar to semi-natural communities when compared with other plant communities. We conclude that organic farming is slightly superior with regard to conservation of herbaceous diversity of hedgerows in intensively cultivated agricultural landscapes. The possible reasons for this are discussed.     

Grazing management of calcareous grasslands and its implications for the conservation of beetle communities

Calcareous grasslands are an important habitat for floral and faunal communities in the UK and Europe. Declines due to changes in management, scrub invasion and agricultural improvement have left much of the remnants of this habitat in a degraded and fragmented state. Grazing, by cattle or sheep, is one of the main management practices used to maintain and improve the floral and faunal quality of calcareous grassland. The long-term impacts of different grazing regimes, however, are poorly understood, particularly in terms of the invertebrate communities. This study contrasted the impacts of recently introduced and long-term sheep or cattle grazing on beetle communities present on one of the largest areas of calcareous grassland in Europe, the Salisbury Plain military training Area, UK. No effects of grazing management on beetle abundance, species richness or evenness were found, but plant diversity and overall percentage cover of grasses did influence beetle diversity. Proportions of the total number of individuals and overall species richness within beetle guilds (predatory, phytophagous, flower/seed feeders, root feeders and foliage feeders) were strongly influenced by both the duration and type of grazing animal. At the species level, beetle community structure showed significant differences between ungrazed, long-term cattle and long-term sheep grazing treatments. Changes in plant community structure were found to influence beetle community structure. The significance of these results is discussed in terms of the long-term impacts of grazing on beetle community structure, and the benefits of different grazing regimes for the conservation management of calcareous grasslands.     

Effect of biochar on the growth of Poncirus trifoliata (L.) Raf. seedlings in Gannan acidic red soil

Soil acidification has become a serious problem for citrus cultivation in China. As a soil amendment, biochar is expected to increase soil pH as well as soil fertility. In this study, we assessed the effect of biochar on Trifoliate orange, the most frequently used citrus rootstock, in a pot experiment using acidic red soil from the Gannan citrus production area. Plant height and shoot diameter of Poncirus trifoliata (L.) Raf. seedlings increased significantly after biochar was added to soils. This positive effect was further evidenced by the increased plant biomass and leaf net photosynthetic rate. The root system architecture (RSA) was evaluated based on root length, root surface area, root volume and root tip. Biochar amendment significantly increased the total absorptive surface area of the root system. Due to the significant role of arbuscular mycorrhizal fungi (AMF) in citrus root nutrient uptake, the AMF colonization and community in Poncirus roots were investigated. The AMF colonization rate was not significantly affected by biochar, whereas AMF diversity increased upon biochar treatment. In addition, the biochar treatment resulted in increases in soil pH, organic matter and mineral nutrients. Together, our results suggest that the positive effects of biochar on the growth performance of Poncirus seedlings can be attributed to the substantial augmentation of soil fertility, increased soil pH, optimized RSA and improved AMF species composition.