Overstorey tree density and understorey regrowth effects on plant composition,stand structure and floristic richness in grazed temperate woodlands in eastern Australia

As natural woodlands decline in both extent and quality worldwide, there is an increasing recognition of the biodiversity conservation value of production landscapes. In low-input, low-productivity grazing systems in Australia, the modification of natural woodlands through overstorey tree and woody regrowth removal are vegetation management options used by landholders to increase native grass production for livestock grazing; however, there is little empirical evidence to indicate at what tree densities biodiversity attributes are compromised. We examined the effects of overstorey tree density and understorey regowth on the floristic composition, stand structure and species richness of eucalypt woodlands in a grazing landscape in the Traprock region of southern Queensland, Australia. We sampled 47 sites stratified according to vegetation type (Eucalyptus crebra/Eucalyptus dealbata woodland; Eucalyptus melliodora/Eucalyptus microcarpa grassy woodland), density of mature trees (<6 trees/ha; 6–20 trees/ha; >20 trees/ha), and presence/absence of regrowth. Distinct patterns in composition were detected using indicator species analysis and non-metric multidimensional scaling, with low density areas compositionally indistinguishable, although distinct from other land management units. Within vegetation type, medium tree density woodlands were compositionally similar to high density and reference woodlands. Species richness ranged from 18 to 67 species per 500 m² across all sites. No differences in total or native species richness were detected across management units; however, some differences in exotic species richness were detected. Differences in grass cover existed between low and high density management units, yet no difference in grass cover was evident between low and medium density management units. Our results suggest that medium tree densities may provide biodiversity benefits concordant with more natural areas, yet not adversely impact on pasture production. Retaining trees in grazing landscapes provides significant landscape heterogeneity and important refuges for species that may be largely excluded from open grassland habitats. Maintaining a medium density of overstorey trees in grazed paddocks can provide both production and biodiversity benefits.     

Influence of hedgerow and grassy field borders on ground beetle (Coleoptera: Carabidae) activity in fields of corn

Agricultural landscapes may be manipulated in ways that benefit predatory invertebrates by providing alternate food sources, overwintering sites, and refuge from farming activities. Ecological theory predicts that complex plant communities should support a richer community of natural enemies of pest insects than a simple plant community. A study was conducted in Iowa, USA to investigate the influence of the vegetative diversity of field boarders on the activity, species richness, and community similarities of predatory beetles occurring in corn fields.Ground beetle (Coleoptera: Carabidae) populations were compared among corn fields bounded by either complex hedges or simple grass edges. Directional pitfall traps were used to investigate activity patterns of beetles between border types and their adjacent corn fields. Beetles were trapped during four seasonal periods, based on the growth stage of corn. During corn emergence (May–June) when fields are barren, carabids were more active and species richness was higher in the corn fields bordered by woody hedges. The carabid species Scarites quadriceps, Scarites subterraneus, and Harpalus pensylvanicus, were more dominant in hedge sites as compared to grass sites at this time. Following corn–canopy closure, carabids were now more active in fields bordered by grassy edges, but beetle activity also remained high in the fields adjacent to woody hedges. Further analysis of the carabid communities by Bray–Curtis Similarity Index showed no difference among field edge types at any time of the season. Results indicate that both complex and simple field border habitats support abundant and diverse populations of carabids during most of the growing season. However, during the early growing season hedges appear to be more important than grass edges in supplying carabid beetles to corn fields. Woody hedges may serve as very important overwintering sites and as an early season refuge for predatory beetles in corn.     

Importance of riparian habitats for small mammal and herpetofaunal communities in agricultural landscapes of southern Québec

The presence of adequate riparian strips in agricultural landscapes is generally recognized to contribute to the reduction of the impacts of agricultural practices on the water quality of streams, to regularize water temperature and to help in the creation of important wildlife habitats. This study aimed at determining the importance of riparian strips in agricultural landscapes of southern Québec for small mammal and herpetofaunal communities, and verifying farmers’ general belief that these habitats become shelters for species considered as agricultural pests. Abundance, composition and diversity of communities were compared between three types of riparian strips: herbaceous, shrubby and wooded. A total of 1460 small mammals belonging to 14 species and 329 amphibians and reptiles belonging to 11 species were captured with line trapping and drift fences. The generalist species Sorex cinereus, Zapus hudsonius, Blarina brevicauda, and Bufo americanus were abundant in all three types of riparian strips. Peromyscus maniculatus, Sorex fumeus, Clethrionomys gapperi, and Rana pipiens were associated more closely to wooded strips, whereas Rana sylvatica was captured mostly in shrubby strips. The abundance of small mammals and herpetofauna increased with complexity of vegetation structure. Small mammal diversity was higher in herbaceous and wooded riparian strips, whereas the herpetofaunal community was more diverse in shrubby strips. Proportion and abundance of pest species diminished with complexity of vegetation structure, whereas insectivores increased in abundance. Maintaining woody vegetation in riparian strips should increase abundance and diversity of wildlife within agricultural landscapes where increasing development pressure is presently contributing to the conversion of such habitats to herbaceous strips. Such a management approach should also help reducing the risk of riparian strips becoming shelters for pest species.     

Subhumid pasture plant communities entrained by management

Many annual cropping lands are being converted to perennial pasture in humid and subhumid areas of the USA as the economic, social, and environmental benefits of managed grazing become evident. Recent evidence about the positive effects of plant diversity on productivity is driving farmers towards management for more complex species mixes than were promoted historically for grazed pastures, but this emphasis has highlighted a lack of understanding about plant community management in pastures. To better understand this system we examined sources of variability in the plant community of a subhumid grassland that was subjected to combinations of disturbance (graze or burn), and amendment (nitrogen, carbon, or ambient), and native grass seeding treatments over 3 years (2004 to 2006). We estimated species cover five times during the study period and ordinated these data with nonmetric multidimensional scaling (NMS). The ordination explained 80% of the variation in the plant community data set. Variance in ordination site scores was ascribed to management (disturbance, soil amendment, and native grass seeding time), the environment (year, season within year, and block), or unexplained (residual) realms with a linear mixed-effects model. The overwhelming source of variability in the plant community (62–99%) was attributed to management. Ordination results illustrated that plant groups sorted out along management gradients: burned plots were shifted towards grasses while forbs and clovers were associated with grazed plots. We demonstrate how a community-level approach can be used to evaluate management regimes in agroecosystems. Our results indicate that disturbance and soil amendments can be used to shape plant communities in subhumid grasslands for specific agronomic and conservation goals.     

Degradation of Populus euphratica community in the lower reaches of the Tarim River, Xinjiang, China

IntroductionRiparian systems are aquatic-terrestrial ecotones withunique biotic , biophysical and landscape characteristics(Gregory, 1991 ; Naiman, 1997 ; Wiens , 2002) and areshaped by fluvial geomorphic processes . Riparian plantcommunities perform an i…     

Botanical composition, soil and forage quality under different management regimes in Russian grasslands

Little is known on how management of Russian native grasslands affects botanical composition, soil and forage properties. Three fields were sampled in the V.V. Alekhin Central-Chernozem Biosphere State Reserve in the Kursk region of Russia: a native grassland (not cultivated for at least 300 years), a grazed/hay field with 4 years of annual harvest followed by 1 year of rest (periodically-cut grazed/hay field), and a yearly-cut grazed/hay field. Soil samples were collected from the top 10 cm and analyzed. Plant species were identified at the sampling sites and this plant material was used to determine total elemental analysis of forage, crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), in vitro true digestibility (IVTD) and lignin concentrations. Above-ground live and dead plant material and roots were analyzed for C, N and lignin. Soil sample analysis showed that fields were comparable in terms of soil chemical and physical properties. SOC and N contents were not statistically different in the native and yearly grazed/hay fields. Soil bulk density significantly increased as a result of utilization, from 0.80±0.09 Mg m⁻³ for the native grassland to 0.97±0.06 Mg m⁻³ for the yearly grazed/hay field. A total of 107 different plant species were recorded at the three fields. There were changes in plant composition among the fields. The native grassland field had the least number of plant species (41) followed by the yearly-cut grazed/hay field (68), and the periodically-cut grazed/hay field (87). There was a greater proportion of grass species (20%) in the native grassland field. Dead plant biomass and roots from the grazed/hay fields were higher in N and lignin concentrations. Forage mineral concentration was highest in the periodically-cut hay field. No significant differences were observed in terms of forage properties.     

The influence of grassland management on ground beetles (Carabidae, Coleoptera) in Swiss montane meadows

Effects of grassland management type and intensity on carabid species richness, number of individuals and species composition were studied in the Swiss Prealps. Carabids were censused in 2001 and 2002 in 21 mown and 20 grazed meadows by means of pitfall traps.Mean species richness was significantly higher in mown plots than in grazed plots and species composition was significantly different between these two management types. Additionally, different species characteristic for mown and grazed plots were found. These results suggest that mown meadows and grazed meadows represent two habitat types for carabid beetles.Within both habitats, management intensity was quantified by fertilizing intensity, the number of cuts, cattle density and/or grazing intensity. The relationship between management intensity and the number of individuals and species was positive. Higher fertilizing intensity was the most important factor for higher species richness and had a significant influence on species composition in both habitats. Other variables positively related to the number of individuals, were the number of cuts in mown meadows and grazing intensity and altitude in grazed meadows. Additionally to fertilizing intensity, cattle density was positively related to the number of species in grazed meadows. These results illustrate that in the extensive management systems found in the Swiss Alps and Prealps, even intensively managed meadows can sustain high carabid diversity and abundance.     

丹江口库区库滨带植被土壤细菌群落多样性及PICRUSt功能预测分析

微生物是土壤元素生物地球化学循环的主要驱动力,目前库滨带植物截留和消减污染物质过程中细菌群落及其功能研究尚未清楚.本研究选取适宜丹江口库区库滨带生长的4种典型植物(草本植物香根草、芦苇、乔木植物杜梨和灌木植物假奓包叶),采用16S r DNA Miseq高通量测序技术研究根际细菌群落组成,发现其主要由变形菌门、拟杆菌门、放线菌门等31个门、343个属的细菌组成,表现出群落组成的丰富性.细菌群落分析表明香根草和芦苇细菌群落结构较为相似,但和杜梨细菌群落结构差异最大.PICRUSt功能预测分析表明,库滨带植物根际细菌主要涉及次生产物代谢的生物合成、转录、多糖生物合成和代谢、细胞生长和死亡等38个子功能,表现出功能上的丰富性.库滨带植物根际细菌代谢能力整体趋势为假奓包叶芦苇香根草杜梨.本研究初步探讨了丹江口库区库滨带不同植物根际细菌群落和功能,为丹江口水库库滨带植被构建及其水环境保护提供了参考依据.     

The role of plant leaf attributes in linking land use to ecosystem function in temperate grassy vegetation

We tested predictions of the relative changes in plant leaf traits in response to land uses in Australian eucalypt grassy ecosystems. Predictions were determined from responses observed in European landscapes in relation to disturbances associated with agricultural land uses. We measured specific leaf area (SLA) and leaf dry matter content (LDMC) across five land uses: reference sites (closest to pre-European state), native pastures (unfertilized), fertilized pastures, sown pastures (cultivated and fertilized) and enriched grassland (previously fertilized, no longer grazed). Leaves were expected to have higher SLA and lower LMDC at sites with increasing fertility and/or disturbance.The predictions were confirmed, with SLA increasing progressively in land uses associated with (1) grazing; (2) grazing and fertilization; (3) grazing, fertilization and cultivation. Values for LDMC were closely (but inversely) correlated with those of SLA. For both traits, there were relationships with available soil phosphorus but not with soil total nitrogen. The positive correlation of SLA with phosphorus was not evident above 30 mg kg⁻¹, the recommended level of phosphorus for improved pastures.Results confirm patterns of leaf-trait response to disturbance that reflect fundamental constraints to plant survival in habitats with different levels of resources and disturbances. A conservative strategy for low productivity undisturbed habitats is associated with low SLA and high dry matter content in contrast to fertile disturbed habitats which select for high SLA and low dry matter content. The changes in leaf traits across land uses resulted from species substitution rather than variation within species across sites, and most notably the replacement of native by annual exotic species as land use intensifies.Recommended fertilization rates for pasture production convert the ground layer to plants with soft, digestible leaves, that are responsive to fertilizer and desirable for livestock production. However, fertilization also drastically reduces the diversity of native plants and annual plants tend to dominate. The trade-off associated with high production includes increased vulnerability to soil erosion, due to reduced plant cover and low persistence of cover. If alternative ecosystem values such as erosion control, water quality, salinity control and biodiversity persistence are required, incentives may be needed to offset the loss of production that can be gained from fertilizer application.     

河岸草本缓冲带对模拟径流中污染物的净化

选择华北地区3种常见草本植物——狗牙根、虎尾草和天堂草,通过人工配水模拟地表径流,在北京潮白河河岸设置径流试验,研究河岸带宽度、水力负荷和进水浓度对不同缓冲带截污能力的影响。结果表明:模拟径流中污染物均随缓冲带沿程距离增加有降低趋势,且前段下降较快,后段下降逐渐趋缓。SS的去除主要发生在沿程前3 m,TP和COD的去除主要发生在前6 m,TN的去除主要发生在9 m以内。若缓冲带的宽度设置受限,为保证一定的截污效果,宽度不应小于9 m。狗牙根、虎尾草和天堂草缓冲带在沿程15 m处对NH_4~+-N的去除率分别为50.6%、32.0%和40.4%,总体上狗牙根和天堂草对N、P的去除能力优于虎尾草。不同水力负荷和进水浓度下,草本缓冲带均能有效截留径流中的SS,去除率均在70%以上,而NH_4~+-N的去除受进水浓度的影响较大。由于模拟径流中NO_3~--N和溶解性磷(DP)进水浓度低于1 mg/L,缓冲带对两者的去除效果较差,特别是虎尾草缓冲带,出现了出水浓度高于进水的情况。     

Mollusc communities in Bulgarian fens: predictive power of the environment,vegetation, and spatial structure in an isolated habitat

Mollusc communities of previously unexplored Bulgarian fens were studied in order to determine and generalise the patterns of species richness and composition along the mineral richness gradient. The aim was also to compare predictive values of the environment, vegetation and spatial structure. Altogether, 44 mollusc species were recorded at 40 treeless fen sites. Species richness varied from 0 to 18 species per site, and it was positively associated with the mineral gradient and negatively with altitude. However, the best predictor was obtained using plant species composition. All explanatory variables had higher effect on land snails than on the entire mollusc assemblage (including aquatic species). Species richness and abundance were significantly and positively correlated with the species composition turnover; the communities were highly nested, with poor sites having subsets of the fauna found in the richest. The main direction of mollusc species turnover was highly associated with that observed for vegetation, and the main gradient of plant species composition was able to explain nearly 20% of total variation in mollusc data. We found that spatial structure explained by far the highest proportion of independent variation, which reflected the high level of geographical isolation of Bulgarian fens and regional differences independent of any environmental variation. Our results demonstrate (1) the general role of mineral richness gradient for structuring mollusc communities in fens, (2) the pivotal indicator role of plant species composition in predicting species composition of mollusc communities, despite being trophically independent and (3) the effect of isolation and origins of the habitat on species composition: most species have wide geographical distributions within the habitat type, and geographical patterns within Bulgaria may have a stochastic element.     

山地河流水电开发对河岸带植物群落特征的影响

为充分了解水电开发对山地河流河岸带植物群落特征的影响,于2014年采用植被常规调查方法,在九龙江源头河流地村溪依次设置RS(源头)、PL(皮寮)、HKU和HKD(环坑水坝上游和下游)、GXU和GXD(高厦水坝上游和下游)6个样地,分析其物种多样性、相似性等的变化特征. 结果表明:①水坝建成后,水坝上游和下游流速、水位及河宽存在显著差异(P<0.05). ②沿河流纵向的自由流动河段,Shannon-Wiener多样性指数和Pielou均匀度指数均随与源头距离的增加而增大,分别由0.30±0.24、0.22±0.17增至0.87±0.20、0.38±0.03;Simpson优势度指数随与源头距离的增加而减小,HKU样地Simpson优势度最低,仅为0.20±0.10;受水电开发影响河段,水坝上游样地的Shannon-Wiener多样性指数和Pielou均匀度指数均高于水坝下游样地,而Simpson优势度低于水坝下游样地. ③沿河流横向,河岸带不同断面植物群落多样性都符合中度干扰假说,水坝建设对河流横向物种多样性的影响不显著;Shannon-Wiener多样性指数和Pielou均匀度指数变化总体上变化趋势一致,均表现为先升后降. ④相似性分析表明,沿河流纵向,水坝上、下游样地间物种相似性相对较高,不同组样地之间高地物种相似性最高的是HKU-HKD(0.270 3),河岸带物种相似性最高的是RS-PL(0.612 2);沿河流横向,HKU(0.392 9)、HKD(0.372 5)和GXD(0.348 8)样地的高地-河岸带物种相似性相对较高,GXU(0.173 9)样地的高地-河岸带物种相似性最低,表明水电开发导致水坝下游河岸带植物主要来源于本地种子库而非区域种子库. 结果显示,水电开发是造成河岸带植物群落发生变化的主导因子,导致水坝下游河岸带和高地物种组成趋向同质化,土地利用格局、河岸带及周围的人类干扰同样会影响河岸带植物群落的多样性和相似性.      

南京外秦淮河河岸带原生植被初步调查

对南京外秦淮河河岸带原生植被进行了初步调查.外秦淮河河岸带原生植被共有28科、50属、53种,其中漂浮植物4种,占7.55%,沉水植物1种,占1.89%,挺水和湿生植物13种,占24.53%,陆生草本和藤本植物24种,占45.28%,乔木和灌木11种,占20.75%.在概括外秦淮河自然环境和分析原生植被主要特征的基础上,提出在进行河岸带植被群落重建时应注重闸下段河岸带植被群落的重建,增加沉水植物、浮叶植物和观赏性植物的种植.另外,植被群落可按河道垂向的常水位以下区域、变化水位区域和洪水位以上区域来构建.     

乐安河-鄱阳湖湿地植物群落分布及其环境影响因子

于2012年平水期(4月)、丰水期(8月)和枯水期(11月)对乐安河自上游至下游及入鄱阳湖区域内湿地植物群落分布和水土环境因子进行调查,分析乐安河不同水期湿地植物群落的分布特征,通过DCCA(detrended canonical correspondence analysis,除趋势典范对应分析)探讨不同水期植物群落分布特征与环境因子间的定量关系. 结果表明:3个水期内共观测到湿地植物167种,不同水期植物种类及组成结构均具有显著差异. 其中平水期湿地植物102种,分属于33科75属;枯水期71种,分属于27科53属;丰水期种类最少,为55种,分属于20科42属. 乐安河上游处于未受矿山开采影响的对照区域内,水生植物群落分布主要受河流自然环境因素的影响. 对于受重金属酸性污染影响较严重的区域,DCCA排序结果显示,水土环境中pH和Cu、Pb、Cd等重金属含量是影响植物群落分布的重要因素. 其中,上游湿地植物群落分布主要受Cu含量和pH的影响;中、下游主要受水、土环境中重金属Pb、Cd的复合污染以及pH的影响. 乐安河湿地植物群落分布与环境因子间具有明显的对应关系,DCCA法能准确识别影响湿地植物群落分布的关键环境因子.      

喀斯特锑矿植被恢复区植物多样性及群落稳定性

了解喀斯特锑矿区植物群落结构及稳定性对生态恢复和群落构建具有重要意义,本研究以贵州晴隆大厂镇锑矿植被恢复区(锑矿区)为研究对象,并选择锑矿区周边未被破坏的植物群落作为对照区展开研究. 基于样方法对锑矿区和对照区进行植被调查,分析了植物物种多样性及群落(群落、乔木层、灌木层和草本层)的Godron稳定性. 结果表明:锑矿区植物共22种,分属14科18属,且有16种为草本植物,低于对照区的30科53属68种;豆科(Leguminosae)、禾本科(Poaceae)、菊科(Compositae)、蔷薇科(Rosaceae)和荨麻科(Urticaceae)各有2~4种,且以被子植物的双子叶植物为主(共11科13属17种),占总物种数的77.27%. 锑矿区优势植物以亮叶桦(Betula luminifera)、苎麻(Boehmeria nivea)、密蒙花(Buddleja officinalis)、茅莓(Rubus parvifolius)、水麻(Boehmeria penduliflora)和插田泡(Rubus coreanus)为主;对照区优势植物以亮叶桦、油桐(Vernicia fordii)、杨树(Populus simonii)、响叶杨(Populus adenopoda)和香樟树(Cinnamomum camphora)为主. 锑矿区与对照区乔灌植物的密度间差异不显著(P>0.05),但锑矿区植物高度101~130 cm、131~200 cm和>200 cm的物种数显著低于对照区(P<0.05). 锑矿区乔木层和灌木层物种丰富度和Shannon-Wiener指数显著低于对照区(P<0.05),物种丰富度分别比对照区显著降低了82.8%和89.5%(P<0.05),Shannon-Wiener指数分别比对照区显著降低了100%和94.8%(P<0.05). Godron稳定性分析结果表明,锑矿区植物群落不稳定. 综上,锑矿区物种组成简单,物种多样性低且不稳定,处于植被演替早期阶段.      

浙江沿海无居民海岛植物群落物种组成及多样性

无居民海岛是自然资源的宝库,人类活动对无居民海岛的影响日益剧烈,掌握它们的植物群落物种组成和多样性现状有利于进行海岛植被多样性的监测和保护。本文运用植物群落生态学方法,对浙江沿海5个无居民海岛的植被物种组成及多样性进行了研究。结果如下:(1)调查区域共记录到高等植物77科,166属,226种,其中草本151种,木本植物75种。基于双向指示种分析方法(TWINSPAN)分析,将该区域植物群落分为17个类型。(2)17个群落的物种Shannon指数均在1.91?—?2.60,Pielou指数(均匀度指数)值在0.80附近浮动,Margalef指数(丰富度指数)在1.86?—?3.80,各个群落的丰富度指数与多样性指数变化趋势大体一致,与群落均匀度无明显关系。植物区系成分多样,主要为泛热带成分和北温带成分。本研究可为我国沿海无居民海岛的资源保护及其开发利用提供科学数据。     

Sown species richness and realized diversity can influence functioning of plant communities differently

Biodiversity–ecosystem functioning experiments (BEF) typically manipulate sown species richness and composition of experimental communities to study ecosystem functioning as a response to changes in diversity. If sown species richness is taken as a measure of diversity and aboveground biomass production as a measure of community functioning, then this relationship is usually found to be positive. The sown species richness can be considered the equivalent of a local species pool in natural communities. However, in addition to species richness, realized diversity is also an important community diversity component. Realized diversity is affected by environmental filtering and biotic interactions operating within a community. As both sown species richness and the realized diversity in BEF studies (as well as local species pool vs observed realized richness in natural communities) can differ markedly, so can their effects on the community functioning. We tested this assumption using two data sets: data from a short-term pot experiment and data from the long-term Jena biodiversity plot experiment. We considered three possible predictors of community functioning (aboveground biomass production): sown species richness, realized diversity (defined as inverse of Simpson dominance index), and survivor species richness. Sown species richness affected biomass production positively in all cases. Realized diversity as well as survivor species richness had positive effects on biomass in approximately half of cases. When realized diversity or survivor species richness was tested together with sown species richness, their partial effects were none or negative. Our results suggest that we can expect positive diversity–productivity relationship when the local species pool size is the decisive factor determining realized observed diversity; in other cases, the shape of the diversity–functioning relationship may be quite opposite.     

不同草皮缓冲带对径流污染物的去除效果试验研究

选择上海地区常见的5种草皮植被,利用自行设计的试验装置构建草皮缓冲带,模拟上海地区农业面源污染和降雨特征,进行缓冲带污染物净化效果试验研究。结果表明,草皮的存在明显提高缓冲带对污染物的净化效果,并且能增强缓冲带土壤的渗透能力;百慕大缓冲带对径流SS的截留能力最强,平均去除率达到71.86%;草皮缓冲带对渗流水营养物质的净化效果明显高于径流,渗流水TN、TP平均去除率以白花三叶草最高,分别为58.27%和60.49%;综合考虑降雨特征和污染物净化效果等因素,百慕大、白花三叶草和高羊茅等3种草皮,可以作为上海地区缓冲带草皮植被的优先选择种类。     

Runoff water quality from manured riparian grasslands with contrasting drainage and simulated grazing pressure

Globally, management of grazed riparian areas is critically important to agricultural sustainability and environmental quality. However, the potential impacts of riparian grazing management on water quality are not well-documented, particularly in the southeastern USA. The objective of this work was to determine sediment and nutrient export under simulated rainfall from poorly drained and well-drained riparian soils where heavy or light grazing pressure by cattle was simulated. Plots were established on stands of existing vegetation to create grazing pressure treatments of (a) light-use (full ground cover, uncompacted), and with stands modified to establish (b) heavy-use (bare ground, compacted) treatments. Vegetation on poorly drained soils consisted of several typical wetland species (e.g., Pontederia cordata L., Juncus coriaceus Mackenzie) in the southeastern USA, whereas mixed tall fescue (Festuca arundinacea Schreb.)–dallisgrass (Paspalum dilatatum Poir.) stands were the dominant vegetation on well-drained soils. Runoff volume was generally greater from heavy-use than from light-use for poorly drained soils and for well-drained soils. Greater runoff volume was also observed from poorly drained soils compared to well-drained soils for both light-use and for heavy-use treatments. Light-use plots were remarkably effective at minimizing export of total suspended solids (TSS) on both soils (<30 kg ha⁻¹). Mean total Kjeldahl P (TKP) export was fourfold greater from heavy-use plots than from light-use plots on both soils. While export of nitrate-nitrogen (NO₃-N) was unaffected by grazing pressure and soil drainage, mean ammonium-nitrogen (NH₄-N) and total N (TN) export from poorly drained heavy-use plots was greater than fivefold that from well-drained light-use plots. Results indicate that livestock heavy-use areas in the riparian zone may export substantial TSS and nutrients, especially on poorly drained soils. However, when full ground cover is maintained on well-drained soils, TSS and nutrient losses may be limited.     

Pasture management under goat grazing on Canary Islands

Tenerife pastures in the Teno plateau are under a goat grazing management system, and the number of goats has increased by 70% in the past 10 years. This plant community was sampled during 4 years (1992, 1993, 1994 and 1999) over a 10-year period, using ten 0.25 m² plots to reveal changes in species composition, soil nutrient content, and biomass nutrient content over time and relate these variables to changes in management and understand aspects of the dynamics of these pastures.The results revealed no changes in biomass nutrient composition over the sampling period; however, biomass protein content was related to changes in species composition. Soil phosphorus content increased in the last sampling year and was related to an average species richness decrease in the plots. Results suggest that the increase in soil phosphorus and the decrease in species richness are related to the increase in goat grazing intensity. At the end of the studied period, species with a higher protein content increased in importance in the species composition. The restoration of pastures degraded by agriculture or overgrazing is required to provide a larger area for grazing and to ensure sustainable management of these protected areas.