Stripe rust reactions of Australasian wheats

Summary Seedling and field reactions to four European races of stripe rust were determined for 254 wheat cultivars, mostly from Australia and New Zealand. Numerical analyses of the data employed a divisive classification procedure with termal reallocation to form 10 groups which were then further classified, ordinated and diagnosed by several procedures. The groups formed ranged from one comprising four wheats with low seedling reactions to all four rust strains and mean field rust of only 1.0%, to one comprising 105 wheats with high seedling reactions and mean field rust of 64.7%. Groups of cultivars with intermediate levels of rust resistance were classified both on relative level of overall rust and on differential reactions to rust strains. One group of 13 cultivars had moderately high seedling reactions but averaged only 1.5% rust in the field.Seedling response to gibberellic acid (GA) was also measured and diagnosed as an external attribute, along with grain type and region of origin. Principal co-ordinate analysis revealed that greater resistance to stripe rust was associated with the insensitivity to GA typical of semidwarf wheats and with an origin in northern Australia, where semidwarf wheats have been most used in the breeding program. In terms of numerical analysis of disease data in plant breeding programs, the study highlighted the advantages of using divisive classification with terminal reallocation of group members.     

火地塘林区主要景观类型地形格局及其解释

运用典范对应分析(CCA)方法分析了地形对火地塘林区主要森林景观类型分布格局的影响;同时引入每个样本的空间坐标,定量分离了地形、空间及其交互作用等因素对景观格局总体变异的影响。研究结果表明,地形、空间及其交互作用解释的植被结构变异分别为4.465%,15.659%和3.78%,总共解释了全部植被结构变异的23.906%,尚有76.094%的变异不能得到解释。     

Effect of abiotic factors on understory community structures in moist deciduous forests of northern India

Understory vegetation controls, in a significant way, the regeneration of overstory trees, carbon sequestration and nutrient retention in tropical forests. Development and organization of understory vegetation depend 3n climate, edaphic and biotic factors which are not well correlated with plant community structures. This study aimed to ~xplore the relationships between understory vegetation and abiotic factors in natural and planted forest ecosystems. A non-metric multidimensional scaling （NMS） ordination technique was applied to represent forest understory vegetation among five forest communities, i.e., a dry miscellaneous forest （DMF）, a sal mixed forest （SMF）, a teak plantation （TP）, a low-land miscellaneous forest （LMF） and a savanna area （SAV） of the Katerniaghat Wildlife Sanctuary, located in northern India. Microclimatic variables, such as photosynthetically active radiation （PAR）, air temperature （AT）, soil Lemperature （ST）, ambient atmospheric CO2 concentration, absolute air humidity （AH）, physical and chemical soil ~roperties as well as biological properties were measured. Understory species were assessed via 100 random quadrats （5 m x 5 m） in each of the five forests in which a total of 75 species were recorded encompassing 67 genera from 37 families, consisting of 32 shrubs and 43 plant saplings. DMF was the most dense forest with 34,068 understory individuals per ha of different species, whereas the lowest understory population （13,900 per ha） was observed in the savanna. Ordination and correlation revealed that microclimate factors are most important in their effect compared to ~daphic factors, on the development of understory vegetation in the various forest communities in the north of India.     

Use of multivariate techniques to identify vegetation units and monitor change on a livestock production system in a semi‐arid savanna of the eastern Cape

Species composition data of the grass layer were determined from point surveys along permanently demarcated transects. These data were separated into vegetation units using multivariate techniques. The repeatability of this classification was tested on data collected over a period of time. The results indicate that classification based on composition data collected from a single sampling period was adequate for practical purposes provided certain precautions were taken. Change in vegetation was assessed by ordering sites from repeated measurements and tracing site trajectories through ordination space. The trends along the axes were strongly correlated with assessed condition score.     

An evaluation of veld condition assessment techniques in Highland Sourveld

An evaluation of six methods used to index veld condition showed that the majority provided indices that were insensitive to long‐term grazing impact. However, certain species were found to either increase or decrease in relative abundance with an increase in grazing intensity. A key species method is therefore suggested to be a potentially sensitive approach for indexing veld condition in relation to grazing management in the Highland Sourveld.     

A comparison of some range condition assessment techniques used in southern African grasslands

Techniques currently used to assess range condition in the grassland biome of southern Africa are reviewed. The methods were used to calculate range condition indices from fire‐climax and climatic‐climax grassland data. These indices were then used to evaluate each method in terms of sensitivity (i.e. the detection of spatio‐temporal differences in index), index interpretation and efficiency, bearing in mind the objectives of each technique. The Weighted Key Species Method and Degradation Gradient Method were found to currently provide the best indices for assessing range condition. Shortcomings of the techniques are recognized and suggestions are made for the application of these methods in different vegetation types.     

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.