Plant Morphoecological Traits, Grass-Weed Interactions and Water Use Efficiencies of Grasses Used for Restoration of African Rangelands

Abstract

Degradation characterized by depleted vegetation cover is a serious environmental problem in African rangelands. It poses a serious threat to millions of pastoralists and agropastoralists who depend on livestock as a source of livelihood. Consequently, there has been a growing global interest to consolidate efforts to restore degraded ecosystems. For example, the UN decade of Ecosystem Restoration initiative aims at uniting the world behind a common goal of preventing, halting and reversing the degradation of ecosystems. Grass reseeding using native perennial species has been identified as one of the practical ecological strategies for restoring degraded African rangelands, enhancing vegetation cover and forage production. Knowledge of the multifaceted performance of African rangeland grasses in terms of morphoecological traits, interaction with weeds and water use efficiencies is however largely limited and often elusive. Perennial grasses indigenous to African rangelands Cenchrus ciliaris L. (African foxtail grass), Enteropogon macrostachyus (Hochst. Ex A. Rich.) Monro ex Benth. (Bush rye grass) and Eragrostis superba Peyr. (Maasai love grass), were established in an African semi-arid rangeland under natural conditions to fill this knowledge gap. Morphoecological plant traits: aboveground biomass (shoot, leaf and stem) production, plant densities, basal cover, tiller densities and plant height were measured 9 months after establishment. Interaction between the target grass species and weeds and water use efficiencies (WUE) were also determined. Enteropogon macrostachyus displayed significantly higher values for plant densities, tiller densities and basal cover, indices commonly used to estimate the potential of grasses for ecological restoration. Eragrostis superba produced the highest shoot biomass and water use efficiencies. This is attributed to its higher leafy biomass fraction. Higher aboveground biomass production of E. superba demonstrate its suitability for enhancing rangeland productivity. Cenchrus ciliaris suppressed the weeds. This is linked to its aggressive and allelopathic nature. In conclusion, the three perennial grasses displayed distinct morphoecological traits. In order to achieve successful seed-based restoration of degraded African rangelands using native perennial grasses, careful selection species to maximize on their unique traits is recommended. Ultimately, this selection process should match the desired restoration outcomes and subsequent use of the rangeland.

Effects of Weed Control Methods on Weeds and Productivity of Range Grasses in Semi-Arid Kenya

“…This is mainly due to their growth habits and the competitive nature of Cenchrus ciliaris and Eragrostis superba that limited weed growth within their vicinity. Similar results of more weed populations in E. macrostachyus have been reported by Mganga et al, (2021) but not under E. superba as is the case with this work. The probable difference could be brought about by differences in soil types and other environmental conditions influencing weed growth and prevalence.…”

“…Plant height is an effective indicator of plant performance in cultivated pastures and rangeland restoration aspects. Height has been noted to correlate well with parameters such as herbage yields in range grasses (Mganga et al, 2021) where taller plants are expected to result in higher biomass yields. More importantly, in the context of this work, structural characteristics of the perennial grasses influence weed dynamics.…”

“…Weeds can influence the quality and quantity of pastures and hayfields, reducing the forage value for livestock. In East Africa, large tracts of land in semi-arid areas are infested with weeds which compete with favorable grasses for space, light, nutrients and moisture, limiting the success of reseeding and pasture establishment (Mganga et al, 2021), consequently affecting livestock production. Some weeds in hay pastures can be poisonous (Ekwealor et al, 2019), necessitating the need for eradication before they are mowed together for baling.…”

“…Extreme weather conditions such as increased precipitation may result in an abundance of certain species and vegetation shifts including establishment, plant physiology and weed biology (Ziska, 2016). For instance, the Ipomoea species is a common weed species that mainly spreads after heavy rains in southeastern Kenya and often engulfs germinating grass seedlings (Mganga et al, 2021). It is an invasive species presently causing havoc in the Maasai pastoral grazing lands of Kenya and Tanzania through depressing herbaceous biomass productivity (Manyanza and Ojija, 2021).…”

“…Pastures used for range restoration and fodder improvement have not been spared either. For instance, pasture weeds pose the most challenge to the establishment and success of reseeding due to their competitive nature and negative grass-weed interactions (Mganga et al, 2021). Interestingly, attempts to use the same grasses to manage problematic weeds in rangelands continue to be explored (Cowie et al, 2021), highlighting the complex nature of interactions between grasses and weeds.…”