Topic
Themeda
About: Themeda is a research topic. Over the lifetime, 96 publications have been published within this topic receiving 1898 citations.
Papers published on a yearly basis
Papers
TL;DR: Species abundance, plant basal area, and mortality were likewise more strongly influenced by rainfall variability than by grazing, and differences in the population dynamics of species were related to their life history attributes.
Abstract: Summary 1. The influence of inter-annual rainfall variability and cattle grazing on the abundance (density, basal area), population dynamics (recruitment, growth, survival) and population structure of the dominant perennial grasses of an African savanna was investigated from 1984 to 1989. The unpalatable Aristida bipartite and the palatable Heteropogon contortus and Themeda triandra reproduce by seed; Bothriochloa insculpta reproduces mainly by seed, but sometimes by stolons; Digitaria eriantha can be stoloniferous; Setaria incrassata has rhizomatous growth. 2. Species abundance was more responsive to rainfall variability than to grazing. Density increased in all species in response to several successive dry years because of recruitment and tuft fragmentation, but eventually decreased in a severe final drought year because of plant mortality. The response of basal cover differed between species and sites, although all species (except Digitaria) declined in the final drought year. 3. Seedling recruitment, plant basal area, and mortality were likewise more strongly influenced by rainfall variability than by grazing. Differences in the population dynamics of species were related to their life history attributes. Aristida, a prolific seed producer, was favoured by grazing because high levels of seedling recruitment could be maintained. Seedling recruitment of palatable species (Heteropogon, Themeda) and of Bothriochloa was initially increased under heavy grazing because openings were produced within the vegetation, but this was reversed by the end of the study because of a decline in available seed. There was limited seedling recruitment of Digitaria and Setaria, but recruitment of Digitaria from stoloniferous growth increased population size, although there was no expansion of Setaria clones under the conditions of this study. Themeda and Aristida seedlings attained greater size under heavy than under light grazing.
194 citations
TL;DR: The short ecotype of Themeda triandra showed many of the characteristics that defoliation induced in each individual of any clone: higher allocation to leaf area production, higher relative growth rate, higher number but smaller size of tillers, and lower leaf specific weights.
Abstract: The response to a single defoliation was studied on three clones of Themeda triandra collected in the short, mid, and tall grassland regions of the Serengeti National Park (Tanzania). These sites represent a gradient of decreasing grazing intensity. Growth, allocation pattern, and several morphometric traits were monitored during an 80-day period. Clipped plants of the short and medium clones fully compensated for the reduction of biomass, while plants of the tall clone showed overcompensation. During the first two weeks after clipping, clipped plants showed lower relative growth rates than unclipped ones, whereas the opposite was observed later on. Clipped plants compensated for the removal of leaf area by producing new leaves with lower specific weights and higher nitrogen content. They also produced more, smaller tillers. Although clipped plants mobilized nonstructural carbohydrates from roots and crowns, this did not account for a significant amount of growth. Relative growth rates of unclipped plants of the short clone were higher. The relative growth rate of the short clone diminished less after clipping, but also exhibited the lowest increase later. The tall clone was the most negatively affected early, but showed the highest compensation later. Compared to the other clones, the short ecotype showed many of the characteristics that defoliation induced in each individual of any clone: higher allocation to leaf area production, higher relative growth rate, higher number but smaller size of tillers, and lower leaf specific weights.
137 citations
TL;DR: If species composition is to be maintained in these grasslands then stocking rates must be set at low levels to cope with the combined effect of undercompensation in response to defoliation in the wet season and strong dietary preferences for grazing sensitive species.
Abstract: . The hypothesis that season of defoliation and herbivore selectivity may be as important as level of use in determining plant community response to grazing was tested in a monsoon grassland in northern Australia. Plots, dominated by the tussock grasses Themeda triandra and Chrysopogon fallax, were grazed by cattle at low, medium and high rates of utilization in either the early wet, late wet or dry seasons. Effects of grazing on species composition were greatest in the early wet season when high rates of utilization significantly reduced the proportion and occurrence of Themeda and increased the proportion of forbs. Grazing in the dry season had no significant effect on composition.
At medium and high levels of utilization in the early wet season, the pasture responded negatively to defoliation, only partially compensating for plant tissue lost to herbivory. The negative response to defoliation carried over to the next wet season when these same medium and high-grazing treatments produced only 80 % and 60 % growth, respectively, of that in treatments grazed at low levels of utilization or those grazed during the dry season. The frequency of Themeda was still lower, and that of annual grasses and non-leguminous forbs higher, in plots that had been grazed at a high rate of utilization for just eight weeks in the early wet season two years previously. Species richness and diversity were also significantly affected by this grazing disturbance. If species composition is to be maintained in these grasslands then stocking rates must be set at low levels to cope with the combined effect of undercompensation in response to defoliation in the wet season and strong dietary preferences for grazing sensitive species.
84 citations
TL;DR: The aim is to summarise and synthesis work previously undertaken and identify areas where further research is required on Themeda triandra, a perennial tussock grass endemic to Africa, Australia and Asia.
Abstract: Themeda triandra is a perennial tussock grass endemic to Africa, Australia and Asia. Within these regions it is found across a broad range of climates, geological substrates and ecosystems. Because it is widespread across these areas it has great economic and ecological value, as it is a relatively palatable species across most of its range. It is of critical importance in supporting local populations of both native and introduced herbivores, and is thus central to wildlife and livestock production, and consequently rural livelihoods. It is an important climax or subclimax species that is well adapted to fire, a common element of many areas where it is found. Inappropriate grazing management, however, can result in a decline of Themeda, as it is not well adapted to an uninterrupted, selective grazing regime. A decline in abundance of Themeda in a grassland is usually coupled to a decline in grazing value, species richness, cover and ecosystem function. In spite of its significant ecological and economic i...
76 citations
TL;DR: In this paper, the effect of a concrete environment on the following Australian native grass species: Themeda trianda, Chloris truncata and Elymus scaber was investigated.
66 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2021 | 3 |
| 2020 | 2 |
| 2019 | 1 |
| 2018 | 3 |
| 2017 | 4 |
| 2016 | 5 |