Korttermyn invloed van strawwe droogte op veldtoestand en waterverbruiksdoeltreffendheid van grasveld in die sentrale Oranje‐Vrystaat

Short‐term effect of severe drought on veld condition and water use efficiency of grassveld in the central Orange Free State. The impact of an intensive drought (1982/1983 and 1983/84‐growing seasons) on botanical composition, basal cover, mortality of grazing plants and water use efficiency (WUE) of veld in good, moderate and poor condition was identified. Increaser II species were apparently more capable of surviving drought than the Decreaser species. Under optimal soil moisture conditions the Decreaser species increased and the Increaser II species decreased. During the drought extensive grass mortality took place. Veld condition plays an important role in determining mortality during drought. Decreaser species have a high water requirement for optimal WUE, while Increaser II species can reach maximum WUE with less water. Under water stress conditions Increaser II species significantly (P≤0.01) do not use the water as efficiently as do Decreaser species. The WUE under water stress conditions for veld in good, moderate and poor condition was on average, during the study period, 0.90; 0.90 and 0.40 kg ha^?1 mm^?1, respectively, and towards under optimal water conditions, 2.47; 1.67 and 0.23 kg ha^?1 mm^?1, respectively.     

Disturbances Impact on Longevity of Grass Seeds,Semi-Arid South African Rangeland

The effect of plant and soil disturbances on seed density, species richness, and seed longevity of the soil seed bank was quantified for a semi-arid rangeland, over a 5-yr period (2002/2003–2006/2007 growing seasons). The different soil and plant treatments included fire, tillage (intended as a trampling surrogate), and blocked seed rain (simulating heavy grazing). These three experimental factors were combined in a factorial arrangement. Seed responses were evaluated in the soil seed bank before the new seed set, after the first seed production event, and after the second seed production event. Before disturbance (physical impact on the plant and soil), soil seed bank was dominated by early successional species: conversely, aboveground vegetation was mainly dominated by perennial grasses. After only 4 yr of blocked seed rain, seedling emergence of Decreaser grass species ceased totally both in the field and seed bank, with lower effect on Increaser grass species. Emergence of both Decreaser and Increaser grass species decreased in the seed bank with tillage, whereas the opposite occurred in the field. By contrast, tillage increased the emergence of weeds in the seed bank. The decrease in emergence of Decreaser grass species in both seed bank and field was still evident 4 yr after the rangeland was burnt. The grass species Themeda triandra was the most sensitive to fire in terms of seedling emergence. Blocked seed rain treatment significantly decreased (P < 0.05) species richness. Regardless of treatments applied, there was poor similarity between aboveground vegetation and the associated seed bank. Differences in the soil seed bank are likely to reflect manifested properties rather than short-term changes. Several characteristics of seed banks (species composition, seed abundance, and longevity) must be considered in order to understand the dynamics of plant communities following disturbances.     

The effect of severe drought and management after drought on the mortality and recovery of semi‐arid grassveld

Abstract

The False Thornveld of the Eastern Cape experienced a particularly intense drought during the 1982/83 growing season. Extensive grass mortality took place during the drought. After the drought, recovery was particularly sensitive to the post‐drought management treatment applied. Veld that was grazed immediately after the drought recovered far more slowly than veld that was rested. This effect was still evident three years later, illustrating the considerable importance of resting semi‐arid grassveld after a drought.

Increaser I grass species present were apparently more capable of surviving drought than the Decreaser species, which in turn were more stable than the Increaser II species. Their ability to recover after the drought followed an opposite trend. On this basis, the desirability of Decreaser dominated veld, in situations that are likely to be poorly managed, is questioned.     

Adaptation of a decreaser and an increaser grass species to defoliation in semi‐arid grassveld

Abstract

Grasses have developed through natural selection to deter, escape and tolerate herbivory, and to escape and tolerate fire. In the semi‐arid grassveld of the Eastern Cape, the species Themeda triandra and Sporobolus fimbriatus have been classified as Decreaser and Increaser II plants respectively. Both species have well‐developed escape and tolerance mechanisms, although T. triandra readily tolerates defoliation only during the dormant season, while S. fimbriatus is adapted to tolerating defoliation throughout the year. Furthermore, T. triandra has only moderately developed deterrents to herbivory, in contrast to S. fimbriatus, where deterrents are well developed. It follows that the Decreaser species T. triandra is adapted to relatively frequent fire and no more than modest herbivory, while the Increaser II species, S. fimbriatus, is adapted to heavy herbivore usage, but infrequent fire.     

Is the grazing tolerance of mesic decreaser and increaser grasses altered by soil nutrients and competition?

An ability to tolerate recurrent defoliation likely plays a role in the compositional shift from decreaser to increaser species with overgrazing of mesic grassland, but the grazing tolerance of local species has not been extensively studied. The growth response of two decreasers, three Increaser II grasses, and an Increaser III species to frequent, severe defoliation under three levels of competition from neighbours and two levels of soil nutrients was examined in a pot trial. The effects of competition and especially nutrients markedly modified the defoliation tolerance of different species, and grazing response groups varied in the manner in which their defoliation responses were mediated by these interactions. Contrary to expectation, defoliation constrained potential productivity most in nutrient-rich, competition-free environments, probably because it exacerbates a carbon limitation on growth. However, nutrient enrichment did enable Increaser II grasses, but not other species, to better tolerate intense defoliation, explaining why they can persist on intensively grazed fertile patches and in heavily stocked grassland, such as in communal areas, where nutrients are more available. It is concluded that grazing tolerance is not a fixed property of species or grazing response groups but depends on biotic and abiotic environmental factors.     

Plant and sward response to patch grazing in the Highland Sourveld

Abstract

Selective grazing by livestock inevitably results in patch grazing. This study was initiated to determine the effects of patch grazing on (1) the vigour of a single grass species, Themeda triandra, and of the sward, and (2) sward species composition. The generally held idea that a full season's rest followed by an early spring burn would prevent preferential grazing of patch grazed areas which had developed in the seasons before the rest was also tested. The vigour of 71 triandra was estimated from etiolated growth of marked tufts while sward vigour was indexed by above‐ground herbage production (AGHP). Etiolated growth of T. triandra and AGHP of the sward within patches were negatively affected by three seasons of grazing, but a full season's rest appeared sufficient to restore both the etiolated growth of T. triandra and the AGHP of the sward to a level similar to that in the non‐patches. A full season's rest followed by spring burning did not, however, prevent preferential grazing of grazed patches which had developed in the seasons prior to the rest. Species composition within patches (characterised by Increaser II species) differed significantly from the species composition of non‐patches (characterised by Increaser I species). Patch grazing may therefore initiate the rangeland degradation process in Highland Sourveld and patch grazing may be the focus from which rangeland degradation proceeds.     

The ecological potential of the kudu for commercial production in savanna regions

Abstract

This paper considers the choice of a browsing ungulate to supplement cattle in savanna regions susceptible to problems of bush encroachment, and evaluates the kudu in particular. Relevant aspects of its ecology considered include (i) the vegetation components utilized at different seasons and in different areas, with regard to principal food species, reserve dry season species, rejected plant species and potential food limitations; (ii) social grouping patterns and home range extent; (iii) population densities, reproductive parameters, survival rates and population dynamics in relation to rainfall; (iv) impact on the vegetation of browsing and branch breakage. Features of the kudu are compared with those of other browsing ungulates, including giraffe, eland, impala and goats. It is concluded that the kudu is a prime candidate for inclusion alongside cattle in mixed species ranching enterprises in most regions of savanna vegetation.     

Evaluating a State-and-Transition Model Using a Long-Term Dataset

State-and-transition models (STMs) are used in natural resource management to describe ecological site scale response to natural and anthropogenic disturbances. STMs are primarily based for expert opinion and literature reviews, lacking analytical testing to support vegetation community dynamics, thresholds, and state changes. We developed a unique approach, combining ordination and permutation MANOVA (perMANOVA) with raw data interpretation, to examine vegetation data structure and identify thresholds for a STM. We used a long-term monitoring dataset for an ecological site on the Santa Rita Experimental Range, Arizona. Basal cover of perennial grasses and canopy cover of shrubs and cacti were measured on permanent transects beginning in 1957. Data were grouped by drivers identified by the STM including species invasion, grazing, drought, and mesquite treatment. Ordination by nonmetric multidimensional scaling described the structure of the data. PerMANOVA was used to test for differences between groups of sample units. Analyses of combined key species (Lehmann's lovegrass and mesquite [Prosopis velutina Woot.]) and nonkey species patterns demonstrated an irreversible transition and occurrence of a structural threshold due to Lehmann's lovegrass invasion, as well as a short-term reversible transition (restoration pathway) following mesquite treatment. Sensitivity analysis, in which key species were removed from the dataset, showed that the relative composition of nonkey species did not differ between states previously defined by the key species. This apparent disconnect between dynamics of key and nonkey species may be related to changes in the functional attributes that were not monitored during this time series. Our analyses suggest that, for this ecological site, transition to a Lehmann's lovegrass state occurs when basal cover of this species exceeds 1–2%, which often occurs within 6 yr of its arrival. Evaluation of the restoration pathway showed a recrossing of the threshold within 6 yr of treatment and when mesquite canopy cover exceeded 10%.     

草坪草对氟污染的反应及氟污染区草坪草种的选择

贵州瓮福磷肥厂厂区因氟化氢(HF)污染,草坪成坪后3个月内就出现氟化氢污染伤害症状。在比较试验后发现,草坪草对氟污染的反应不同,用草坪植被指数作属性进行聚类分析,将15种试验草坪草划分成了不敏感,较不敏感和敏感3个反应类型,以草坪草叶片含硫量和草坪植被指数作属性进一步聚类,划分出了强抗性,中抗性和弱抗性3个抗性类型。     

Geographical patterns based on faunal types of breeding birds and mammals in China

We collected available chorological data of birds and mammals in China and assigned faunal types. The 19 sub‐regions of the zoogeographical regions of China were used as operative geographical units. Matrices of the geographical units using the species number of each faunal type were then constructed. Based on the matrices we clustered the geographical units using a hierarchical cluster analysis The results of the faunal divisions according to the cluster analysis were illustrated in a geographic information system (GIS). When 19 geographical units were clustered into two clusters, the boundary of the two clusters corresponded to that of the Palearctic and Indomalayan (Oriental) realms in the recent division of Chinese fauna. When the geographical units were clustered into eight clusters, the sub‐region Southern Yunnan Hilly became an idiographic cluster. As a result, Southern Yunnan hilly should be regarded as a region rather than a sub‐region at the same level as Southwest region, Central China region and South China region. The differences in the distribution patterns of birds and mammals among the units in the Indomalayan (Oriental) realm were more complicated than those in Palearctic realm. A few differences of the cluster analysis results based on the faunal types were found between the bird and mammal species. These differences might result from the different ecological and geographical distribution patterns of these two animal categories.     

草原植被恢复对矿区排土场土壤线虫群落多样性的影响

矿区排土场是草原被开垦利用的产物,植被恢复对已破坏草原生态系统具有重要意义。线虫是草原地下生态系统的主要组成部分,对土壤环境反应敏感,可作为一种良好的指示性生物。通过对人工植被恢复8年、人工植被恢复4年、无植被恢复4年的矿区排土场和自然状态下的天然草地中0~10 cm和10~20 cm土层中线虫的数量、种类和群落结构多样性开展研究,旨在揭示草原植被恢复对矿区排土场土壤线虫的影响。结果表明：试验区共分离出土壤线虫51个属,不同草原植被恢复方式影响土壤线虫种类及优势度,不同恢复方式下土壤线虫的优势属有一定差异;草原植被恢复方式影响土壤线虫数量及营养类群,不同草原植被恢复方式下土壤线虫数量及属数从大到小依次为：人工恢复8年>人工恢复4年>天然草地>无恢复4年;人工恢复4年区及8年区捕食/杂食类线虫数量高于无恢复区,整个地下土壤线虫多样性增大;无恢复4年区的H′多样性指数显著（P<0.05）低于其他3种处理,反映出草原植被恢复对土壤线虫群落成熟稳定的作用,揭示了土壤恢复状况。研究结果为矿区排土场生态恢复措施的选择和实施提供了理论依据。     

Topoedaphic Variability and Patch Burning in Sand Sagebrush Shrubland

Patch burning is the deliberate application of fire to a management unit in a heterogeneous manner, resulting in the heterogeneous distribution of grazing animal impact. The application of patch burning typically has been discussed within a framework of imposing heterogeneity on a homogeneous landscape or management unit, yet most landscapes and management units are actually distinguished by an inherent level of heterogeneity. Within landscapes and management units, differing topography and soils interact to create patterns of contrasting patches, also known as topoedaphic sites. Thus, introduction of a heterogeneous disturbance such as patch burning on a landscape or management unit is more accurately described as the imposition of one layer of heterogeneity onto a pre-existing layer of heterogeneity. We examined effects of patch burning on vegetation structure and animal distribution across contrasting topographical sites in sand sagebrush (Artemisia filifolia Torr.) shrubland of the southern Great Plains in North America. Landscapes at our study site were characterized by an inherent amount of heterogeneity in vegetation structure due to variability in topoedaphic sites, and the patch burning treatment superimposed additional heterogeneity that was constrained by topoedaphic characteristics. Shrub-dominated sites were more dependent on patch burning for heterogeneity of vegetation structure than sites dominated by short grasses. Distribution patterns of cattle (Bos taurus) were not significantly different across treatments, though they followed patterns similar to previous studies. We demonstrated that heterogeneity was dependent on topoedaphic patterns and the application of patch burning management for heterogeneity was dependent on the inherent variability of a landscape.     

Identification and selection of benchmark sites on litholitic soils of the western grassland biome of South Africa

Abstract

An approach to identify benchmarks for different ecological situations in the grassland biome is described. The approach is illustrated by using information on vegetation change, role of habitat factors and the relative palatability differences between the species of the vegetation on shallow soils of the litholitic complexes in the western parts of the grassland biome. The information was obtained from the ordination and interpretation of vegetation and habitat data gathered at different distances from watering points and in vegetation under different grazing pressures.     

Allometric Estimates of Aboveground Biomass Using Cover and Height Are Improved by Increasing Specificity of Plant Functional Groups in Eastern Australian Rangelands

Plant aboveground biomass (AGB) is a useful metric to assess ecosystem functioning, and its sensitivity to changing environmental conditions provides insight into potential global change impacts. Allometric estimates of AGB using vegetation characteristics such as plant cover or height provide nondestructive biomass proxies for repeated measurements but can introduce uncertainty to estimates. We estimated the relationship between both plant cover and a cover·height index and AGB for 15 plant species from six sites to identify the most reliable approach to estimate biomass nondestructively in semiarid eastern Australian rangelands. Estimates were made by grouping species at four different levels of specificity, to test whether generic estimates were more robust than grouping species based on life history and morphological characteristics. Estimates were then tested on a 1.5-m² plot at each site for validation. In all cases, models were highly significant (P < 0.001) with adjusted R² values ranging from 0.42 to 0.96 for cover models and 0.38 to 0.98 for cover·height index models. We found the addition of height improved model fits in four groups while reducing model fits in two groups. The error around AGB estimates for cover·height index−based models ranged from −66.8 to 4% (absolute mean 35%). Cover-based models had errors between −13.4% and 53% (absolute mean 14.2%). For cover-based estimates of AGB in validation plots, grouping plants by plant functional types (PFTs) increased accuracy (absolute mean error 17.3%) compared with estimates using data from all 15 species (absolute mean of 65.2%). Overall cover was a useful surrogate to estimate AGB (with the exception of one site, accuracy ranged from −2.3% to 11.5%), while height (thought to be a surrogate for canopy characteristics) provided benefit in a few circumstances. We suggest that future research should test additional nondestructive proxies and group species based on PFTs to improve AGB estimates using allometry.     

不同微地形固定沙丘地上植被、土壤种子库和土壤含水量的分布特征

通过野外调查和室内培养的方法对盐池荒漠草原区不同微地形固定沙丘地上植被、土壤种子库和土壤含水量进行了调查,并研究了地上植被、土壤种子库和土壤含水量的空间分布特征及其关系以及微地形对土壤种子库及地上植被物种类型、物种密度、相似性和土壤种子库物种多样性的影响。结果表明,1)固定沙丘土壤种子库和地上植被物种数、密度、相似性、土壤种子库物种丰富度指数及土壤含水量、地上植被覆盖度和土壤种子库储量都呈现出底坡＞下部坡位＞中部坡位＞上部坡位＞顶坡的趋势,且土壤含水量、地上植被覆盖度和土壤种子库储量三者之间显著正相关(P0.05);2)土壤种子库物种多样性指数和均匀性系数随坡位变化呈现出波动状态。     

牦牛粪沉积下高寒草甸植物群落种间关联研究

植物群落构成和种间关联,反映物种在空间上的分布及相互依存和制约关系。为探究牦牛粪沉积和植被斑块互作下草地植物群落演变趋势及稳定性机制,以青藏高原东北缘高寒草甸禾草/杂类草斑块和嵩草/杂类草斑块为对象,分析牦牛粪沉积下两种斑块中主要植物种的重要值(IV)、Jaccard种间关联指数和Spearman秩相关系数的变化规律。结果表明,1)粪沉积使禾草/杂类草斑块的建群种扁穗冰草的IV增加和西北针茅的IV降低,嵩草/杂类草斑块的建群种线叶嵩草的IV降低;2)禾草/杂类草斑块中,粪沉积(DP)和对照(CK)的正负关联种对比为0.61和0.63,显著联结种对为6.6%和6.4%;嵩草/杂类草斑块中,DP和CK的正负关联种对比为0.90和0.72,显著联结种对为2.8%和14.5%;且二者显著联结的种对多存在于优势种或亚优势种与伴生种之间;3)两种斑块中多数种对间联结性弱,群落处于不稳定阶段;粪沉积使嵩草/杂类草斑块的稳定性增强,利于禾草/杂类草斑块的演变;4)依据优势种对环境的适应方式和主导生态因子,将两种斑块的群落植物种划分为喜阳耐旱植物、喜阴喜湿植物和喜阳喜湿植物三大生态种组。     

塔里木河下游生态输水对草地恢复的影响

结合塔里木河下游生态输水,通过对植被和地下水的监测,分析了输水对下游草地恢复的影响。结果显示:随着生态输水,塔里木河下游输水河道附近地下水位大幅升高,下游草地也出现明显的生态恢复,主要表现在植被种类和草地覆盖度的变化。但是由于不同草本植物对地下水位的适应程度不同,距河道不同距离植物响应的程度不同。而对于因河水漫溢出现的恢复区,其植被种类和覆盖度表现与因地下水升高而恢复的区域差异较大,说明不同输水方式对草地生态恢复的影响程度不同。     

皖北石灰岩山地不同植被恢复模式对植物群落物种组成及多样性的影响

通过研究皖北石灰岩山地生态系统的植被群落,分析不同植被恢复群落的组成、结构、多样性和生活型组成,进而阐明石灰岩山地生态系统植被恢复模式对群落结构特征以及植物物种多样性的影响。结果表明:研究区有54种植物,隶属26科54属。侧柏(Platycladus orientalis)+构树(Broussonetia papyrifera)人工混交林有植物种类16科26种,分别占总数的61.5%和48.1%。酸枣(Ziziphus jujuba var. spinosa)+牡荆(Vitex negundo var. cannabifolia)灌丛和荩草(Arthraxon hispidus)+牡荆草灌丛植物种类分别为32和33种,分别占调查总物种数的59.3%和61.1%。不同植被恢复群落生活型也有差异。侧柏+构树人工混交林群落高位芽植物占优势,而酸枣+牡荆灌丛和荩草+牡荆草灌丛则以地面芽植物所占比例较大。分析表明,多样性指数、均匀度指数和优势度指数均表现为侧柏+构树混交林>酸枣+牡荆灌丛>荩草+牡荆草灌丛,但物种丰富度表现为荩草+牡荆草灌丛>酸枣+牡荆灌丛>侧柏+构树混交...