Is Cane Sugar Production for Biofuel a Good Practice in Semi-Arid Systems? A Special Reference to the Olifants River Catchment, Mpumalanga, South Africa

The aim of this paper is to analyse the possible impacts of proposed biofuel production at Hoedspruit in the Olifants River Catchment. These impacts are looked at in terms of availability of water and subsequent consequences on downstream users, especially the Kruger National Park that is mandated to conserve and protect biodiversity in all facets and fluxes in its area of jurisdiction. Based upon a review of experiences with biofuel production and impacts around the world, water availability for sugar cane production to support proposed biofuel production was found to be a problem in the region that has an average rainfall of only 450 mmper annum. The Olifants River system already has a deficit of about 200 million m3/a;hence the sustainability of the sugar cane based biofuel industry in the proposed area is questioned in this review. It is advised that alternative plants for the production of biofuel that may not consume large quantities of water be examined.

Competition effects in an afrotemperate forest

Background： Information about competition responses is mainly available for monospecific stands or mixed stands with a small number of species. Studies on complex multi-species and highly structured forest ecosystems are scarce. Accordingly, the objective of this study was to quantify competition effects and analyse competition responses in a species-diverse afrotemperate forest in South Africa, based on an observational study with mapped tree positions and long-term diameter increment records. Methods： The sensitivity to competition was analysed for individual species and involved the calculation of the slope of the linear relation between the value of a competition index （CI） and diameter growth as a measure of sensitivity. In a next step different competition indices were combined and tree diameters were grouped in three classes as surrogates for canopy status and ontogenetic stage. Results： Five competition indices were found to be effective in showing sensitivity to competition for a number of canopy and sub-canopy species. Significant linear regressions were fitted for 18 of a total of 25 species. Species reactions varied significantly in their sensitivity to the different CIs. The indices were classified as belonging to two groups, those that responded more to local crowding and those that are more sensitive to overtopping, which revealed species-specific sensitivities to both factors. The analysis based on diameter classes revealed that species clearly changed their sensitivity to crowding or overtopping depending on diameter. Canopy and sub-canopy species showed distinct differences in their reactions. Conclusions： The application of multiple CIs brought novel insights relating to the dynamics of afrotemperate forests. The response patterns to different competition indices that focus on crowding and overtopping are varied and tree diameter dependent, indicating that oversimplified assumptions are not warranted in the interpretation of Cl- growth relations.

Diversity and production in an Afromontane Forest

Background：This contribution evaluates the effect of forest structure and tree species diversity on plot productivity and individual tree growth in the unique Knysna forests in Southern Africa using mapped tree data from an observational study that has been re-measured over a period of 40 years.Methods：The effects of tree species diversity and forest structure on tree growth and forest production are evaluated on three levels of resolution：a） the forest community（canopy,sub-canopy species）,b） the subplots（number of trees per ha,skewness of the diameter distribution,diameter coefficient of variation） and c） the immediate neighborhood of selected reference trees（＂Mingling＂,＂Dominance＂,Aggregation＂ and ＂Size Variation＂）.Results：An analysis of the community level identified two distinct clusters,one including dominant/canopy species with the highest growth rates and a greater variation of growth,and another cluster which includes the remaining subcanopy species which have a smaller maximum size and lower rates of growth.The area-based structure variables on plot level have a highly significant effect on total basal area growth.However,the effects of forest density and species richness on productivity were not straight forward.Maximum basal area production of about 0.75 m^2/ha/year is achieved at medium levels of richness（around 20 species per ha） and medium levels of density（around 30 m^2/ha basal area） using percentile regression estimates.The relative ＂Dominance＂ of a selected reference tree had a highly significant effect on individual tree growth on all investigated species.Other neighbourhood structure variables were only occasionally significant or not significant at all.Conclusion：This contribution presents a new theoretical framework for analysing natural forests that includes community,plot and neighborhood variables of forest structure and diversity,and a first specific analysis of the structure and dynamics of the Knysna Afromontane Forest,based on a unique set of longterm observations.The species-area（SAR） model developed in this study,represents a new general approach that can be used to derive a common standard of tree species diversity for different plot sizes,the species richness per hectare.

Quantifying multiple-site compositional turnover in an Afrotemperate forest, using zeta diversity

Background： Species turnover is typically measured by partitioning diversity components into alpha and pairwise beta diversity. However, alpha and beta components cannot express the full spectrum of multiple-site compositional turnover. To this end, zeta diversity has been proposed as an extended framework to allow complete biodiversity partitioning and to measure multiple-site species turnover. We use a zeta-diversity framework to explore the turnover and potential community assembly processes of an African Montane Forest. Methods： Using a 20 m grid, we explore the species turnover in a 4.55 ha forest plot located in the Garden Route National Park of South Africa, with 47 and 27 canopy and sub-canopy tree species in the regional poo We first calculate how zeta diversity declines and how the probability of retention of species with particular occupancies changes with increasing zeta orders （i.e. the number of sites [grid cells] involved in the calculation）. Using null models with row sums and column sums constrained respectively, we explore whether species turnover is driven by mechanisms of ecological differences （species-specific occupancies） or habitat heterogeneity （site-specific alpha diversity and thus environmental filters）. Results： The decline of zeta diversity with zeta order followed a power law; that is, the probability of retention increased with species occupancies, suggesting common species being more likely to be discovered in extra sites. The null model retaining row sums （species＇ occupancy） of the species-by-site matrix recreated perfectly the decline of zeta diversity, while the null model of habitat heterogeneity （retaining column sums） was rejected. This suggests that mechanisms driving species-specific occupancies （i.e. ecological differences between species） dictate the multi-site species turnover in the community. The spatial patterns of zeta diversity revealed little spatial structuring forces, supporting a fine-grain structure in these southern Cape forests. Conclusions： The framework of zeta diversity revealed mechanisms driving the large discrepancies in the occupancy among species that are behind the species turnover in the African Montane forest plot. Future studies could further link species turnover to spatial distance decay. Environmental filters and temporal turnover from landscape demography could bring a cohesive understanding of community assembly in these unique forest ecosystems.

Long-term effects of fire frequency and season on herbaceous vegetation in savannas of the Kruger National Park,South Africa

Aims:The long-term effects of changing fire regimes on the herbaceous component of savannas are poorly understood but essential for understanding savanna dynamics.We present results from one of the longest running(>44 years)fire experiments in savannas,the experimental burn plots(EBPs),which is located in the Kruger National Park(South Africa)and encompasses four major savanna vegetation types that span broad spatial gradients of rainfall(450–700 mm)and soil fertility.Methods:Herbaceous vegetation was sampled twice in the EBPs using a modified step-point method,once prior to initiation of the experiment(1954)and again after 44–47 years.Different combinations of three fire frequency(1-,2-and 3-year return intervals)and five season(before the first spring rains,after the first spring rains,mid-summer,late summer and autumn)treatments,as well as a fire exclusion treatment,were applied at the plot level(;7 ha each),with each treatment(n=12 total)replicated four times at each of the four sites(n=192 plots total).The effects of long-term alterations to the fire regime on grass community structure and composition were analyzed separately for each site.Important Findings:Over the 44+years duration of the experiment,fires were consistently more intense on sites with higher mean annual rainfall(>570 mm),whereas fires were not as intense or consistent for sites with lower and more variable rainfall(<510 mm)and potentially higher herbivory due to greater soil fertility.Because the plots were open to grazing,the impacts of herbivory along with more variable rainfall regimes likely minimized the effects of fire for the more arid sites.As a consequence,fire effects on grass community structure and composition were most marked for the higher rainfall sites and generally not significant for the more arid sites.For the high-rainfall sites,frequent dry season fires(1-to 3-year return intervals)resulted in high grass richness,evenness and diversity,whereas fire exclusion and growing season fires had the lowest of these measures and diverged the most in composition as the result of increased abundance of a few key grasses.Overall,the long-term cumulative impacts of altered fire regimes varied across broad climatic and fertility gradients,with fire effects on the grass community decreasing in importance and herbivory and climatic variability likely having a greater influence on community structure and composition with increasing aridity and soil fertility.

Democratization of ecosystem services--a radical approach for assessing nature's benefits in the face of urbanization

Objectives:(1)To evaluate how ecosystem services may be utilized to either reinforce or fracture the planning and development practices that emerged from segregation and eco-nomic exclusion;(2)To survey the current state of ecosystem service assessments and synthesize a growing number of recommendations from the literature for renovating ecosys-tem service analyses.Methods:Utilizing current maps of ecosystem service distribution in Bushbuckridge Local Municipality,South Africa,we considered how a democratized process of assessing ecosys-tem services will produce a more nuanced representation of diverse values in society and capture heterogeneity in ecosystem structure and function.Results:We propose interventions for assessing ecosystem services that are inclusive of a broad range of stakeholders'values and result in actual quantification of social and ecological processes.We demonstrate how to operationalize a pluralistic framework for ecosystem service assessments.Conclusion:A democratized approach to ecosystem service assessments is a reimagined path to rescuing a poorly implemented concept and designing and managing future social-ecological systems that benefit people and support ecosystem integrity.It is the responsi-bility of scientists who do ecosystem services research to embrace more complex,pluralistic frameworks so that sound and inclusive scientific information is utilized in decision-making.