Invasive plant species of savanna rangelands: Are they a threat or an opportunity?

Abstract

Invasive and less palatable plant species are prevalent on most rangelands. Finding ways of utilising them should be a research priority. This study evaluated the threats and potential uses of invasive plant species as livestock feed resources. The evaluation was done over four stages. The first stage involved gathering the farmer perceptions in communal farming system, through a pretested semi-structured questionnaires on changes in quality of grazing, carrying capacity and the abundance of invasive plant species. The second stage was done through botanical field measurements and a survey in the three farming systems to confirm the issues raised by farmers in the first study. The collected data were analysed for threats and effects of the perceived changes in the rangelands. Predominant invasive plant species determined in the first and second stage of the study were evaluated for potential uses as animal feeds by determining their nutritive value. The third and fourth stages involved determining the best stage of growth for harvesting and conserving of these forages, analysing the nutrient composition, digestibility and determining how the performance of animals will be affected when fed on the harvested biomass. Data collected and measured were analysed using various procedures of SAS. Farmers reported that they were observing a widespread increase in woody and invasive plant species such as Lantana camara, Helichrysum kraussii, and thickets of Dichrostachys cinerea and Vachellia species. They also revealed that they were noticing the establishment of less palatable grass species such as Hyparrhenia filipendula, Hyperthelia dissoluta, and Sporobolus pyramidalis. Range condition assessment in the three farming systems also showed that communal grazing management was more detrimental to all rangeland parameters measured followed by small-scale commercial system, with commercial grazing management producing desirable results on rangeland productivity. Lantana camara, Hyparrhenia filipendula, and Hyperthelia dissoluta were nutritionally characterised in terms of crude protein (CP), acid detergent fibre (ADF), neutral detergent fibre (NDF) levels and apparent digestibility coefficient and the results showed that they have great potential of being used as animal feeds. L. camara from different locations did not differ significantly at (P> 0.05) in CP but differed in total extractable phenolics, according to site of harvesting. Harvesting H. filipendula and H. dissoluta eight to ten weeks from the onset of the rain season and conserving as silage or hay produced high quality roughage for livestock. In animal feeding trial, animals fed graded levels of L. camara biomass (5%, 10%, 15%, 20%, and 25%) completed the 22 days of feeding trial and without signs of ill health. The rate of microbial nitrogen production and efficiency on microbial nitrogen supply for growth was not significantly different at low rate of inclusion. The result suggested that dried L. camara biomass was safe to use up to 15% inclusion level in diets, beyond which it lowers voluntary feed intake. Increased utilisation of invasive plant species may control their rate of spread in invaded rangelands. Large quantities of L. camara, H. filipendula, and H. dissoluta biomass may be used to bridge the perennial feed deficit in both quality and quantity in tropical and subtropical agro ecosystems during the dry season of the year. Furthermore, harvesting and conserving these species will reduce the risk associated with the occurrence of high intensity wildfire fuelled by the presence of large quantities of biomass from these invasive plant species. These results confirmed that invasive plant species can be used as animal feed and contribute towards sustainable livestock production.ii