Water stress as a factor influencing the distribution of the ericoid shrub Philippia evansii in the Natal Drakensberg mountains, South Africa

Xylem pressure potential (Ψp) was measured in Philippia evansii plants growing on a cool, south aspect and a warm, valley bottom site. There were no significant differences in the minimum Ψp values (min Ψp) between sites during the day despite differences in the water vapour pressure deficit (VPD). It is deduced that P. evansii plants are sensitive to water loss with Ψp values stabilizing at ca − 1100kPa by the control of transpirational flux. In spite of the higher VPD measured at the warmer site, pre-dawn values of Ψp (base Ψp) were more negative at the cool site. Since plants were experiencing water stress on the cool southern slopes at night, it appears that conditions on the northern slopes would be too dry for colonization by P. evansii plants. It is concluded that the indirect effects of radiation on the water balance are important factors controlling the distribution of P. evansii

Número mínimo de medições para a avaliação acurada de características agronômicas de pinhão-manso

Resumo: O objetivo deste trabalho foi identificar o método mais eficaz para estimar coeficientes de repetibilidade em progênies de meios-irmãos de pinhão-manso (Jatropha curcas) e predizer o número mínimo de medições necessárias para algumas características agronômicas da oleaginosa. Avaliaram-se 18 famílias de meios-irmãos, em delineamento de blocos ao acaso, com três repetições, de 2009 a 2013. Nesse período, as seguintes características foram avaliadas: altura de plantas, diâmetro do caule, número de ramos por planta, projeção da copa na linha, projeção da copa na entrelinha e produtividade de grãos. O coeficiente de repetibilidade (r) foi estimado a partir de diferentes estratégias: análise de variância; análise dos componentes principais (ACP), com base na matriz de correlações (CPCOR); ACP, com base na matriz de variâncias e covariâncias fenotípicas (CPCOV); e análise estrutural, com base na matriz de correlações. A estratégia CPCOV proporciona estimativas mais acuradas do coeficiente de repetibilidade e do número de medições necessárias (no mínimo quatro) para avaliação acurada (mínimo 80%) das características, devido ao comportamento cíclico das progênies

The influence of season on the suppression by Pteridium aquilinum leaf extracts of root growth in Avena fatua: a possible influence on the distribution of Philippia evansii

Philippia evansii has colonized south aspect sites extensively but has been less successful in the valley bottoms, despite the growth rate of valley bottom plants being significantly greater than that of south aspect plants.Pteridium aquilinum is dominant in the valley bottoms and fronds are shown to contain water extractable phytotoxins which inhibit radicle extension in Avena fatua L. It is suggested that these toxins have contributed to the slow rate of colonization of valley bottom sites by P. evansii

Topo-edaphic environment and forest plantation disturbance explain patterns of grassland species richness, composition and structure in an agro-ecological landscape, Maputaland, South Africa

Grasslands of the Maputaland coastal plain are biologically diverse and provide a variety of ecosystems services. Yet grasslands in this region are vulnerable to continuing development by plantation forestry that provides economic benefits to local communities. In order to provide a framework for land use that maintains grassland heterogeneity in complex agro-ecological systems, this paper characterises the main relations between grassland species composition, the physical environment and forestry plantation disturbance. Grassland species composition corresponded with landscape position and soil organic carbon. Grasslands occurring in infertile, elevated landscape positions were the most diverse having a greater richness of tufted graminoids, herbaceous forbs and geoxylic suffrutices than grassland occurring in low-lying dystrophic sites, which were dominated by rhizomatous and stoloniferous graminoids. Previously afforested grasslands (i.e. secondary grassland) were species poor, lacked keystone grasses, such as Themeda triandra, were dominated by a few species of rhizomatous or stoloniferous grasses and had been colonised by pioneer or ruderal forbs. Grassland species composition affects the provision of ecosystem services so to maintain a full complement of these attributes, grassland landscapes in Maputaland should comprise intact grasslands that cover both elevated and low-lying topographic positions

Topo-edaphic environment and forestry plantation disturbance affect the distribution of grassland forage and non-forage resources, Maputaland, South Africa

Grasslands are integral to rural livelihoods in southern Africa, because they provide hydrological regulation services and a variety of plant resources, including livestock fodder, medicines, and food products. To ensure ongoing provision of these resources in rapidly developing rural landscapes, an understanding of the relationships between grassland species composition and ecosystem services is required. This study examines the provision of grassland forage and non-forage resources across five grassland types in relation to environmental determinants of site topography, soil conditions, and plantation-forestry disturbance. Grasslands characteristic of low-lying and fertile landscape positions were dominated by nutritious lawn grasses and therefore tended to complement rangeland practices, whereas grasslands associated with elevated areas or infertile conditions were diverse in species composition and consequently provided the majority of plant medicines, spiritual resources, fruit-beverage resources, oils, and craft materials. Secondary grassland, resulting from forestry plantation abandonment, had moderate forage potential and limited non-forage resources. Our results provide a simple framework for approaching grassland resource classification, grassland conservation and land use management on the Maputaland coastal plain

Quantifying the water balance of Mfabeni Mire (iSimangaliso Wetland Park, South Africa) to understand its importance, functioning and vulnerability

Peatlands occurring in regions with high rates of total evaporation (ET), matching or exceeding precipitation (P) during seasonal dry periods or longer-term dry spells, are dependent on sustained groundwater flows to ensure peat accumulation. The objective of this study was to quantify the water balance of Mfabeni Mire in South Africa over one year, and thereby define its contribution to downstream and adjacent ecosystems and identify risks and consequences likely to arise from future shifts in the water balance. P (1,031 mm) and ET (1,053 mm) dominated the water balance measured from May 2008 to April 2009. These were followed by groundwater inflows (14 mm), stream outflow (9 mm) and storage change (-3 mm, a net loss in water stored in the mire) with the smallest flux being groundwater outflow (0.3 mm). There were differences in the seasonal patterns of ET from the two dominant plant communities (swamp forest and sedge/reed fen), which probably resulted from their significantly different canopy structures. Limiting factors for ET were low vapour pressure deficit and cloud cover. Although the water balance of Mfabeni Mire was dominated by and equally split between ET and P, it still contributed a small efflux to downstream ecosystems by streamflow. Its value in a landscape where seasonality and long-term dry periods are major ecological drivers lies in its damping effect on climatic variability. This creates a more stable environment for adjacent aquatic ecosystems by contributing to a steady groundwater condition. Mires occurring in areas that experience dry periods, where water stress frequently threatens biodiversity, should be recognised as assets in natural resource management; and their potential to support adjacent ecosystems should be protected through planning and conservation practices. Management of the area should include careful consideration of any proposed changes in land use or encouragement of one plant community at the expense of another, as such changes will alter the equilibrium of the water balance. Mfabeni Mire is particularly vulnerable through the impact of adjacent commercial forestry, which has impacted river and estuary management over the last 80 years and depleted groundwater levels in the surrounding aquifers

The water use of selected fruit tree orchards (volume 2) : technical report on measurement and modelling

Final report to the water research commission and department of agriculture, forestry and fisheries. The water use of selected fruit tree orchards (Volume 2) : technical report on measurements and modelling