Effects of Dichrostachys cinerea (l.) Wight & Arn (Fabaceae) on herbaceous species in a semi-arid rangeland in Zimbabwe

Abstract

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

Effects of Sicklebush (Dichrostachys cinerea (l.) wight and arn.shrub) Encroachment on Floristic and Vegetation Structure in Semi-arid Savannah of Southern Ethiopia

“…It is not only species richness and 1 6 1 5 7 2 1 4 8 1 1 3 1 2 4 9 1 0 3 1 1 6 5 3 1 2 0 2 1 2 9 2 7 2 3 2 2 1 7 1 9 1 8 2 4 2 5 2 6 2 8 3 2 3 composition that was negatively affected by sickle bush encroachment, but also the species diversity as encroached areas exhibited lower species diversity indices (both Shannon-Weiner diversity Index and Simpson's Index) than the non-encroached areas. This is in agreement with Mudzengi et al (2014) and Ayana (2007).…”

“…This may indicate that D. cinerea encroachment was affecting the species richness and composition of the savannah plains of NSNP in particular and that of the rift valley system in general. Our result concurs with previous researches (Mudzengi et al, 2014) in reporting the negative effect of sicklebush encroachment on species richness and composition in the savannah ecosystems. Similarly, Sirami and Monadjem (2012) reported that there is significant decrease in species richness associated with shrub cover increase, which was also complemented in our study.…”

“…The effects of D. cinerea encroachment in species richness decline, particularly to that of herbaceous species observed in this study can be explained in terms of its competitive advantage over the other species. The same justification has been drawn before (Jacoby et al 1982;Mudzengi et al, 2014). It is not only species richness and 1 6 1 5 7 2 1 4 8 1 1 3 1 2 4 9 1 0 3 1 1 6 5 3 1 2 0 2 1 2 9 2 7 2 3 2 2 1 7 1 9 1 8 2 4 2 5 2 6 2 8 3 2 3 composition that was negatively affected by sickle bush encroachment, but also the species diversity as encroached areas exhibited lower species diversity indices (both Shannon-Weiner diversity Index and Simpson's Index) than the non-encroached areas.…”

“…Ecologically unsustainable anthropogenic activities such as settlement, agriculture, overgrazing deforestation, coupled with climate change and variability, facilitate plant species encroachments, which have been an established problem of savannahs worldwide (Mudzengi et al, 2014). Savannahs are ecosystem with a continuous grass layer intermixed with a discontinuous tree and shrub layer (Van Langeveld, 2003).…”

“…Sicklebush is a woody shrub or tree that may adversely affect native herbaceous species plant vigour, basal cover and species richness (Mudzengi et al, 2014). Reduced litter covers of herbaceous and top hamper were also observed in invaded sites.…”