Comparative responses of the Savanna grasses Cenchrus ciliaris and Themeda triandra to defoliation

Hodgkinson, Ken C.; Ludlow, M. M.; Mott, J. J.; Baruch, Zdravko

doi:10.1007/bf00378238

Cited by 66 publications

(50 citation statements)

References 13 publications

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“…The large proportion of biomass allocated to leaves and less selfshading due to a lower leaf area/plant area ratio increased growth capacity in Hyparrhenia. High biomass production of invader African grasses has also been found in other tropical grasslands and it has been proposed as one of the main features contributing to their high competitive potential Hodgkinson et al 1989;Bilbao and Medina 1990;Klink 1994;Williams and Black 1994;Baruch 1996). Despite its higher peak biomass, the initial seasonal growth of Hyparrhenia was slower than that of Trachypogon.…”

Section: Discussionmentioning

confidence: 96%

Effects of fire and defoliation on the life history of native and invader C 4 grasses in a Neotropical savanna

Baruch

Bilbao

1999

Oecologia

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African grasses, introduced into Neotropical savannas to improve forage quality, have spread successfully and displaced native plants. To understand their competitive relationships, we compared biomass production and allocation, plant architecture and phenology, net photosynthesis (Pn), water relations, and nutrient content under fire and simulated herbivory between two C grasses, the native Trachypogon plumosus and the introduced Hyparrhenia rufa from a seasonal savanna in Venezuela. All variables were strongly influenced by the rainfall regime. Hyparrhenia produced bigger plants (in mass and size) with a large proportion of mass (>75%) allocated to leaves and culms. Its biomass production was more affected by fire than by defoliation. In contrast, Trachypogon was more affected by defoliation than by fire which promoted a flush of leaf growth even in the dry season. Fire caused up to 85% mortality in Hyparrhenia but none in Trachypogon where it increased inflorescence production. However, fire promoted abundant seed germination and fast seedling growth in Hyparrhenia, enabling it to colonize new areas. During the growing season Trachypogon had higher Pn and lower leaf water potential (Ψ) than Hyparrhenia but differences among treatments were not significant for either grass. Pn of Trachypogon ceased at a lower Ψ (-3.0 MPa) than in Hyparrhenia (-2.0 MPa), indicating its higher tolerance to water stress. During the dry season, Trachypogon leaves remained alive and retained low Pn. Leaf nutrient content was higher during the rainy season in both species. Differences in Pn could not explain the higher seasonal biomass production of Hyparrhenia. However, its water stress evasion strategy, larger biomass allocated to leaves, abundant germination and fast seedling growth appeared to be responsible for the success of Hyparrhenia as an invader of Neotropical savannas.

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Section: Discussionmentioning

confidence: 96%

Effects of fire and defoliation on the life history of native and invader C 4 grasses in a Neotropical savanna

Baruch

Bilbao

1999

Oecologia

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“…Ritchie and Wolfe's (1994) simulation model of herbivory by deer, elk, and cattle predicted different plant community composition under different management schemes, and illustrated the importance of indirect effects on community level results of herbivory. Differences in the effects of herbivory on survival, growth, recruitment, and/or regeneration of different plant species have frequently been presented (Hodgekinson et al 1989;De Steven 1991;Auld 1995;Hulme 1996;Tiver and Andrew 1997). Some researchers have used exclosure studies similar to the one presented here to determine effects of different herbivores on plant species and community composition (for example , Bowers 1993;Auld 1995;Freudenberger 1995;Hulme 1996).…”

Section: Differential Effects Of Herbivoresmentioning

confidence: 93%

Survival, growth, and escape from herbivory are determined by habitat and herbivore species for three Australian woodland plants

Allcock

Hik

2004

Oecologia

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To understand how plant communities are structured by herbivory it is essential to investigate the roles of different herbivores and the responses of a variety of plant species in different habitats. We examined the effects of mammalian herbivores on survival and growth of transplanted seedlings of two native trees (Eucalyptus albensand Callitris glaucophylla), and one native grass (Themeda australis) in white box ( E. albens) woodlands in eastern Australia over 3 years. Herbivores were manipulated using four fencing treatments that successively excluded livestock, macropods, and rabbits from woodland and grassland (cleared pasture). Survival was highest in the absence of mammalian herbivores and in woodlands, and patterns differed among plant species. Survival of T. australis was low, especially in grasslands, and mortality by overgrowth was common in ungrazed treatments. All plant species were taller in fenced plots, and differences between treatments were greater in grassland. Rabbits and livestock had the greatest influence on C. glaucophylla, while T. australis and E. albens were most affected by livestock and macropods. We used field data to parameterize stage-classified matrix models to predict escape from herbivory (escape height >100 cm) for tree species. Reduced herbivory increased the proportion of individuals reaching escape height after 15 years. Rate of escape was greater in grassland, and this faster growth appeared to counteract much of the negative impact of herbivores. While T. australis was unable to escape herbivory, larger, ungrazed individuals were more likely to flower and therefore contribute to the maintenance of the population. Our results show that habitat and herbivore species strongly influence the effect of herbivory on vegetation.

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“…Individual parameters are too numerous to cite, but examples may be classified within groups of ecological processes: plant phenology and biomass (e.g., Ndawula-Senyimba, 1972;McNaughton, 1985;O_Connor and Pickett, 1992;Seagle and McNaughton, 1993;Satorre et al, 1996), plant allometrics and growth (e.g., Fourie and Roberts, 1977;Hodgkinson et al, 1989;Coughenour et al, 1990;Tewari, 1996), ungulate energetics and growth (e.g., Stafford Smith et al, 1985;Murray, 1995), wildlife and livestock populations (e.g., Campbell and Borner, 1995;Boshe, 1997;Kijazi et al, 1997;NCAA, 1999), habitat relationships (e.g., Sinclair and Gwynne, 1972;Western, 1975;Boshe, 1997), grazing and climatic effects (e.g., Mwalyosi, 1992;O_Connor, 1994;Gowda, 1997;Tapson, 1997;Norton-Griffiths, 1979), and pastoralist status and decision making (e.g., Homewood et al, 1987;Bekure et al, 1991;Homewood and Rodgers, 1991;McCabe, 1997;McCabe et al, 1997b;Galvin et al, 2000).…”

Section: Parameterizing the Modelmentioning

confidence: 99%

Cultivation and Conservation in Ngorongoro Conservation Area, Tanzania

et al. 2006

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Ngorongoro Conservation Area (NCA), Tanzania, contains renowned wildlife, an expanding human population, and cultivation by Maasai agro-pastoralists and nonMaasai agriculturalists. We used integrated assessments to explore some effects of cultivation on livestock, resident wildlife, and people. Using a Landsat image from 2000, we mapped 3,967 ha [9,803 acres (ac)] of cultivation within NCA, or 39.7 km 2 of the 8,283 km 2 conservation area. Using integrative ecosystem (Savanna) and household (PHEWS) models, we assessed effects of: up to 50,000 ac (20,234 ha) of cultivation; cultivation concentrated into two blocks totaling 10,000 ac (4,047 ha) and 20,000 ac (8,094 ha) that may be more palatable to tourists; and human population growth. Simulations with from 10,000 to 50,000 ac in cultivation showed no large changes in ungulate populations relative to there being no cultivation. When cultivation was altered to be in two blocks, some wildlife populations changed (≤15%) and ungulate biomass remained the same. When cultivation was increased linearly with human population, poor households needed 25% of their diets to come from relief as populations tripled, because livestock could not increase significantly. Our results indicate that having <1% of NCA in cultivation, in its current distribution, is not overly detrimental to wildlife or livestock populations, and is important to Maasai well-being.

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Comparative responses of the Savanna grasses Cenchrus ciliaris and Themeda triandra to defoliation

Cited by 66 publications

References 13 publications

Effects of fire and defoliation on the life history of native and invader C 4 grasses in a Neotropical savanna

Effects of fire and defoliation on the life history of native and invader C 4 grasses in a Neotropical savanna

Survival, growth, and escape from herbivory are determined by habitat and herbivore species for three Australian woodland plants

Cultivation and Conservation in Ngorongoro Conservation Area, Tanzania

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