Ecological status of species on grazing gradients on the shallow soils of the western grassland biome in South Africa

Abstract

Grasses on the shallow soils of the western grassland biome of South Africa were classified on their ecological status on the basis of their reaction to grazing. Vegetation data were gathered in such a way that those of different successional stages could be identified. An ordination technique was used to define the grazing gradient. Species abundance curves were statistically fitted to the grazing gradient and used to classify the species into decreaser and increaser categories.     

The adventive flora of New Zealand

The ecological grouping (Decreaser and Increaser groups) of individual species was determined on two topographical units in the Highland Sourveld of the Orange Free State. For this purpose gradients were selected, giving special attention to fence‐line comparisons, vegetation at different distances from watering points and ungrazed vegetation. The ecological grouping (Decreaser and Increaser groups) of species on a grazing gradient differed not only for different topographical units, but also for sub‐habitats within a certain unit. Broad standardized groupings of species into Decreaser and Increaser groups are therefore scientifically wrong and of little practical use.     

The performance of three ordination methods applied to demersal fish data sets: stability and interpretability

Abstract The performance of robust principal component analysis (RPCA), detrended correspondence analysis (DCA) and non‐metric multidimensional scaling (NMDS) with two demersal fish data sets were assessed in terms of their stability to bootstrap‐generated sample variation and the method’s ability to reflect a well‐known depth gradient. Stability was assessed for both species and site orderings and configurations, using scaled rank variance (SRV) and Spearman (ρ) and Procrustes correlations (t₀). The NMDS site and species orderings showed the highest stability. DCA performed best in terms of site ordination stability, but NMDS performed best in terms of species ordination stability. In terms of matching the expected ecological variation, NMDS was the most sensitive method for the wider‐depth gradient data and DCA was the most sensitive for the narrower‐depth gradient data. According to the sensitivity and informative power criteria associated with the stability assessment, t₀ was the best methodological approach for site ordinations, and SRV for species ordinations.     

中国沙棘在砒砂岩地区的克隆性能与环境解释

通过对砒砂岩地区不同立地类型、不同林龄的人工沙棘林克隆苗木与环境关系的对比研究,研究表明:经DCCA排序的结果显示,砒砂岩区的环境复杂多变,沙棘的克隆性能受多个环境因子的影响;林龄、坡向、土壤类型、速效钾、速效磷是所有因子中对沙棘克隆性能起决定性作用的环境因子;沙棘林从第3年开始萌蘖幼苗,5年时达到最大值,之后开始迅速下降,7-8年下降趋势较为平缓。     

Spatial pattern of a plant community in a wetland ecosystem in a semi-arid region in northwestern China

The spatial distribution characteristics of plant communities in a wetland-dry grassland ecosystem in arid and semi-arid regions in northwestern China and the main factors affecting the distribution pattern were studied. The Siertan wetland in the Haba Lake Nature Reserve was the study area. Four transect lines, each about 1 km long, were set up in the growing season along the biotope gradient in four directions: east, northeast, west and northwest. Attributes measured include frequency of occurrence, height, density, coverage, biomass and environmental soil factors. The data were analyzed using a two-way indicative species analysis (TWINSPAN), detrended correspondence analysis (DCA) and Spearman correlation coefficients. On this basis, the vegetation in the Siertan wetland was classified into three types and 14 associations. The first vegetation type was halophytic marsh vegetation, mainly distributed in the wetland zone. This type largely contains halophyte and hygric plants and its representative association is Phragmites communis + Kalidium foliatum. The second type was meadow vegetation, distributed in the ecotone. The meadow vegetation species are mainly mesophytic and their representative association is Nitraria tangutorum + Pennisetum flaccidum. The third vegetation type is grassland vegetation, which mainly consists of mesophytic and xerophytes, distributed in the arid grassland zone. The representative association of the third vegetation type is the association of Anaeurolepidium secalium + Saussurea runcinata. Correlation analysis between the axes of DCA and environmental soil factors shows that soil moisture content, organic matter, soil salt content and total nitrogen are the main environmental factors affecting the pattern of vegetation distribution along the biotope gradients from wetland to arid grassland. Other factors affecting the vegetation are microtopography and grazing pressure. Additionally, we have reported modifications and improvements to the importance value methodology. __________ Translated from Journal of Beijing Forestry University, 2008, 30(1): 6–13 [译自: 北京林业大学学报]     

Impact of logging on tree,liana and herb assemblages in a Bornean forest

In the present study, the impact of logging was assessed on the forest structure, richness, and composition of trees, lianas, and ground herbs in Indonesian Borneo. There were no significant differences in tree height, diameter, basal area, or abundance between unlogged and logged forest. Liana abundance was higher in logged than unlogged forest, but the difference was marginally nonsignificant. There was also no significant difference in the percentage cover of ground herbs. Tree species richness was similar between unlogged and logged forest, while liana species richness was higher in logged forest and herb species richness between unlogged forest. Tree and liana compositions differed significantly between unlogged and logged forest, but logging explained only a small part (<7%) of the variance in composition. In contrast to trees and lianas, ground herb composition did not differ significantly between unlogged and logged forest. Our findings indicate that the modest extraction intensity practiced did not have a severely adverse impact on forest structure or plant composition. This highlights the important role that logged forests may play in conserving biodiversity and the need to protect these forests from further disturbance.     

历山山核桃群落数量分类与排序

应用TWINSPAN分类和DCA排序方法分析山西历山山核桃群落生态关系。结果表明:1)应用TWINSPAN将山核桃群落的35个样方划分为7个群丛,分别是山核桃-连翘-升麻群丛、山核桃-连翘+牛奶子-蓝萼香茶菜群丛、山核桃-连翘-草乌头群丛、山核桃-连翘-香薷群丛、山核桃-连翘-披针叶苔草+筋骨草群丛、山核桃-连翘-风毛菊+牛尾蒿群丛和山核桃-连翘-藜芦群丛;2)35个样方DCA排序图较好地揭示了山核桃群落的分布格局与环境梯度的关系,排序图第1轴基本反映各群丛所在生境的坡向变化,第2轴基本反映了植物群落的地形和土壤类型变化,坡向、地形和土壤类型决定了山核桃群落类型的规律性变化;3)7个群丛草本层优势种在DCA排序轴上的分布格局在很大程度上影响着群丛在DCA排序轴上的分布格局。     

果园夏季杂草数量生态学研究

2009年夏季采用1m×1m样方法对山西省太谷县的山西省农业科学院果树研究所果园夏季杂草群落进行调查,分析不同样地杂草群落的发生规律,并在此基础上,采用双向指示种分析法（CTWINS—PAN）和除趋势对应分析法（DCA）对群落进行了数量分类和排序分析。调查共发现73种杂草,属于27科62属,其中入侵杂草最多的为菊科（14种）和禾本科（11种）。TWINSPAN等级分类将该果园66个样方划分为11个群丛,分类结果较好地反映了该果园夏季杂草群落类型与环境梯度之间的关系,并在DCA二维排序图上得到较好的验证,即DCA第1轴主要反映了土壤水分的变化情况,从左到右土壤水分逐渐增多;第2轴主要反映了土壤养分的变化趋势,从上向下土壤养分逐渐减少,说明杂草群丛的分布格局与土壤水分和养分的密切关系,组成果园夏季杂草的优势种群能客观反映群落的生境特征．     

Pre-impact forest composition and ongoing tree mortality associated with sudden oak death in the Big Sur region; California

Mixed-evergreen forests of central coastal California are being severely impacted by the recently introduced plant pathogen, Phytophthora ramorum. We collected forest plot data using a multi-scale sampling design to characterize pre-infestation forest composition and ongoing tree mortality along environmental and time-since-fire gradients. Vegetation pattern was described using trend surface analysis, spatial autocorrelation analysis and redundancy analysis. Species-environment associations were modeled using non-parametric multiplicative regression (NPMR). Tanoak (Lithocarpusdensiflorus) mortality was analyzed with respect to environmental and biotic factors using trend surface analysis and multivariate regression. Mixed-evergreen forest occurs throughout the Big Sur region but is most widespread in the north, on north facing slopes, at mid-elevations near the coast. Relative basal area of the dominant tree species changes fairly predictably from north to south and from coast to interior in relation to mapped patterns of precipitation, temperature factors and soil characteristics. Most dominant tree species sprout vigorously after fire. The forests experience a mixed-fire regime in this region ranging from low severity understory burns to high severity crown fires, with the latter increasing above the marine inversion layer and at more interior locations. Ceanothus spp. can dominate mixed-evergreen sites for several decades after severe fires. All of the dominant broadleaf evergreen tree species are hosts of P. ramorum, although not all will die from infection. Tanoak mortality decreases from northwest to southeast and is significantly correlated with climate, especially growing degree days and mean annual precipitation, and with basal area of the foliar host bay laurel (Umbellularia californica) in a 0.5–1 ha neighborhood. Adaptive management of mixed-evergreen forest to mitigate P. ramorum impacts in the region will need to consider large local and regional variation in forest composition and the potentially strong interactions between climate, fire, forest composition and disease severity.     

运用模糊排序研究露天矿区人工植被土壤主要化学成分的变化

该文应用模糊数学排序方法,对矿区样地土壤中主要化学成分和植被数据进行直接梯度分析,探讨矿区土壤环境与植被分布格局及植被动态的相互关系.结果表明通过FSO多因子排序分析,在时间梯度上,土壤中有机质、N、P、K和Zn的含量随着演替时间的增加而逐渐增高,结合双因子排序分析结果得出,土壤中有机质含量与植物的分布格局重要相关,N、P、K和Zn在土壤中的含量也随着复垦时间而发生变化.而土壤pH值、电导率及Cu、Mn的含量随时间的变化规律不十分明显,说明这几种化学成分不是影响植物分布与发展演变的主要因子.模糊数学排序与DCA、DCCA结合使用,可以直观地得出多个环境因子与植物群落之间的关系.