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.     

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.     

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.