Bud banks of perennial savanna grasses in Botswana

Abstract

Three semi-arid savanna grasses in Botswana (Stipagrostis uniplumis, Eragrostis lehmanniana, and Aristida stipitata) were sampled to quantify their belowground bud banks during the dormant season and to estimate their relative allocation to vegetative and sexual reproduction. Bud banks of these African perennial caespitose grasses were also compared with four perennial caespitose grasses of semi-arid North American grasslands. The three African grasses each maintained approximately two buds per tiller and showed a high percentage (88-99%) of tillers producing seed. Only E. lehmanniana produced new aerial tillers from axillary buds at elevated nodes on the stem as well as from the belowground bud bank. Compared with species of North American grasslands, these African grasses produced fewer belowground buds but showed a much higher percentage of tillers producing seed. These patterns indicate relatively greater belowground meristem limitation, lower allocation to vegetative reproduction (tillering) and higher allocation to seed reproduction in these African grasses, although studies of more species are needed to assess the generality of this pattern. The management of savannas in ways that favour the maintenance of a reserve population of belowground buds may increase the ability of grasses to respond to pulses of resource availability, increase their compensatory growth capacity following grazing or drought, and decrease the invasibility of these plant communities by exotic species, whereas maintaining allocation to sexual reproduction may be important for conserving genetic variation and enhancing their capacity to adapt to environmental change.

Bud production and dynamics of flowering and vegetative tillers in Andropogon gerardii (Poaceae): the role of developmental constraints

“…The bud production per tiller of Andropogon gerardii is large in comparison with many other perennial grasses ( Cable, 1971 ;Mueller and Richards, 1986 ;Mullahey et al, 1991 ;Hendrikson and Briske, 1997 ;Hartnett et al, 2006 ;Dalgleish et al, 2008 ). Over the winter dormant season, there were approximately eight dormant mature buds per aboveground tiller.…”

Species, functional groups and community structure in seed banks of the arid Nama Karoo: Grazing impacts and implications for rangeland restoration

“…At the study sites, only the shrubs R. trichotomum and Catophractes alexandri are able to spread vegetatively to potentially produce free-living ramets. The dominating perennial grass Stipagrostis uniplumis has a dual strategy of population maintenance via both seed and vegetative buds but shows a greater resource allocation to seed reproduction (Hartnett et al, 2006).…”

Short-Term Responses of Southern African Semi-Arid Rangelands to Fire: A Review of Impact on Plants

“…This parallels the results for the Tall Grassveld of KwaZulu-Natal (AE500 mm rainfall) in South Africa (Everson, 1999), where Tristachya leucothrix Nees, C. excavatus Hochst and C. validus Stapf ex Burtt Davy become dormant when burning is infrequent, provided other forms of defoliation are not imposed. A semi-arid savanna rangeland area of Botswana (rainfall 320 mm), Hartnett et al (2006) found that Eragrostis lehmanniana Nees for example showed that each tiller maintained approximately two belowground buds during the dormant season and a high percentage of tillers flower over the season, which can explain to some extent the less variability of Eragrostis species to fire. For the higher rainfall (>500 mm) area of the semi-arid North American grasslands the opposite in terms of grass reproduction biology were found, namely the production of more vegetative buds per tiller with lower proportion of flowering tillers (Hartnett et al, 2006), which made it more sensitive to fire-perhaps also a function of tuft size.…”

“…A semi-arid savanna rangeland area of Botswana (rainfall 320 mm), Hartnett et al (2006) found that Eragrostis lehmanniana Nees for example showed that each tiller maintained approximately two belowground buds during the dormant season and a high percentage of tillers flower over the season, which can explain to some extent the less variability of Eragrostis species to fire. For the higher rainfall (>500 mm) area of the semi-arid North American grasslands the opposite in terms of grass reproduction biology were found, namely the production of more vegetative buds per tiller with lower proportion of flowering tillers (Hartnett et al, 2006), which made it more sensitive to fire-perhaps also a function of tuft size. Cymbopogon pospischilii and E. muticus are two unpalatable species that can sprout most rapidly after a fire (Snyman, 2003a;Snyman, 2014).…”