Anthropogenic alteration of an environment and other disturbance regimes may enable the expansion of some native species into new geographical areas, a phenomenon observed with Dichrostachys cinerea. Five D. cinerea invaded sites, each approximately one hectare in size were assessed for the effects of D. cinerea on native herbaceous species diversity, richness, basal cover, litter cover, top hamper and plant vigour. The same attributes were studied in five uninvaded sites adjacent to, and equal in size to each invaded site. Forty herbaceous species were identified in the area. There were significant differences (P < 0.05) noted in species richness, basal cover, litter cover, top hamper, plant vigour, and species diversities between invaded and uninvaded sites, with uninvaded sites recording higher values than invaded sites. Altitude, erosion and the edaphic variables pH, N, P and K, which were included as explanatory variables, also differed significantly (P<0.05) between invaded and uninvaded sites. Of the 30 D. cinerea invaded plots established for herbaceous species assessments, 26 were positively correlated with altitude, erosion, pH, P, N and K. It is imperative to find ways of managing D. cinerea in order to reduce its adverse effects on herbaceous species.
RESEARCH ARTICLE
Launched to accelerate biodiversity conservation
A peer-reviewed open-access journalClarice Mudzengi et al. / Nature Conservation 7: 51-60 (2014) 52
Key issues of concern regarding the environmental impacts of livestock on grazing land are their effects on soil, water quality, and biodiversity. This study was carried out to determine how grazing intensity influences soil physical and chemical properties and occurrence of herbaceous plant species in dambo wetlands. Three categories of grazing intensity were selected from communal, small scale commercial and large scale commercial land. Dambos from the large scale commercial land functioned as the control. Data analysis included ANOVA and multivariate tests from CANOCO. There were significantly negative changes to soil nutrient status in communal dambos though with a higher number of rare taxa. Sodium, phosphorous, pH and infiltration rate were significant determinants of plant species occurrence. Overgrazing is threatening the productivity, stability, and ecological functioning of dambo soils in communal Zimbabwe. These dambos also require special conservation and management priorities as they contain a large number of rare plant species.
Livestock production is the major source of rural livelihoods in semi-arid regions of Southern Africa. However, nutrition is the major limiting factor of livestock production in these areas characterised by declines in rangeland productivity due to the increases in drought frequency, deliberate overstocking by farmers, and climate change and variability. For instance, the grazing resource is strongly influenced by seasonality of rainfall. Poor-quality cereal crop residues are the main dry season supplementary feed source, yet the predominant crops such as sorghum and maize are deficient in protein and other essential nutrients. Additionally, although conventional supplements, fodder crops and agro by-products are an alternative dry season supplementary feed source; they are costly and not readily available. They are also mostly based on staple food crops such as maize, creating competition in use between humans and livestock. Therefore, indigenous browse species remain a significant source of abundant and persistent animal feeds. Other innovations with the potential to improve feed availability include straw ammoniation and silages, veld reinforcement and rehabilitation, and strategic destocking. However, they are not readily adopted by farmers. There is thus a need to promote technologies that improve livestock feeds and feeding for sustainable livelihoods.
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