The vegetation of the protected plots at Thabamhlope Research Station

Westfall, R. H.; Everson, C. S.; Everson, Terry

doi:10.1016/s0022-4618(16)30141-3

Cited by 16 publications

(14 citation statements)

References 4 publications

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“…However, closed forests occur as isolated patches in grass‐dominated landscapes indicating that the climate is suitable for forest growth (Bond, 1997; O'Connor & Bredenkamp, 1997). Long‐term fire exclusion experiments have resulted in the invasion of mesic grasslands and savannas by fire‐sensitive trees causing an ecosystem switch from open to closed forest‐type vegetation (Trapnell, 1959; Westfall et al ., 1983; Titshall et al ., 2000). The effects of fire exclusion are much less marked in less productive arid grasslands and savannas, as predicted by the DGVM simulation, and there is no invasion of closed forest tree species (Shackleton & Scholes, 2000).…”

Section: Discussionmentioning

confidence: 99%

The importance of low atmospheric CO₂ and fire in promoting the spread of grasslands and savannas

Bond¹,

Midgley²,

Woodward³

2003

Global Change Biology

395

285

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The distribution and abundance of trees can be strongly affected by disturbance such as fire. In mixed tree/grass ecosystems, recurrent grass‐fuelled fires can strongly suppress tree saplings and therefore control tree dominance. We propose that changes in atmospheric [CO2] could influence tree cover in such metastable ecosystems by altering their postburn recovery rates relative to flammable herbaceous growth forms such as grasses. Slow sapling recovery rates at low [CO2] would favour the spread of grasses and a reduction of tree cover. To test the possible importance of [CO2]/fire interactions, we first used a Dynamic Global Vegetation Model (DGVM) to simulate biomass in grassy ecosystems in South Africa with and without fire. The results indicate that fire has a major effect under higher rainfall conditions suggesting an important role for fire/[CO2] interactions. We then used a demographic model of the effects of fire on mesic savanna trees to test the importance of grass/tree differences in postburn recovery rates. We adjusted grass and tree growth in the model according to the DGVM output of net primary production at different [CO2] relative to current conditions. The simulations predicted elimination of trees at [CO2] typical of the last glacial period (180 ppm) because tree growth rate is too slow (15 years) to grow to a fire‐proof size of ca. 3 m. Simulated grass growth would produce an adequate fuel load for a burn in only 2 years. Simulations of preindustrial [CO2] (270 ppm) predict occurrence of trees but at low densities. The greatest increase in trees occurs from preindustrial to current [CO2] (360 ppm). The simulations are consistent with palaeo‐records which indicate that trees disappeared from sites that are currently savannas in South Africa in the last glacial. Savanna trees reappeared in the Holocene. There has also been a large increase in trees over the last 50–100 years. We suggest that slow tree recovery after fire, rather than differential photosynthetic efficiencies in C3 and C4 plants, might have been the significant factor in the Late Tertiary spread of flammable grasslands under low [CO2] because open, high light environments would have been a prerequisite for the spread of C4 grasses. Our simulations suggest further that low [CO2] could have been a significant factor in the reduction of trees during glacial times, because of their slower regrowth after disturbance, with fire favouring the spread of grasses.

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Section: Discussionmentioning

confidence: 99%

The importance of low atmospheric CO₂ and fire in promoting the spread of grasslands and savannas

Bond¹,

Midgley²,

Woodward³

2003

Global Change Biology

395

285

View full text Add to dashboard Cite

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“…initiate thicket habitats in the absence of fire and create conditions conducive for the establishment of more shade-tolerant forest species (Manders and Richardson, 1992;Cowling et al, 1997). Similarly, thicket environments in the Drakensberg grasslands provide shaded habitats for forest tree establishment and the habitats themselves are products of fire exclusion (Westfall et al, 1983). Early successional species (e.g., H. lucida, B. salviifolia, R. tomentosa, L. sericea) establish in the grassland matrix or on rocky outcrops where they persist (Westfall et al, 1983;Smith and Tainton, 1985;Titshall et al, 2000).…”

Section: Forest Successionmentioning

confidence: 99%

“…Similarly, thicket environments in the Drakensberg grasslands provide shaded habitats for forest tree establishment and the habitats themselves are products of fire exclusion (Westfall et al, 1983). Early successional species (e.g., H. lucida, B. salviifolia, R. tomentosa, L. sericea) establish in the grassland matrix or on rocky outcrops where they persist (Westfall et al, 1983;Smith and Tainton, 1985;Titshall et al, 2000). These early successional species share several life history traits that include fire tolerance, the capacity to coppice in response to fire and the ability to colonise grassland (Westfall et al, 1983;Smith and Tainton, 1985).…”

Section: Forest Successionmentioning

confidence: 99%

“…Early successional species (e.g., H. lucida, B. salviifolia, R. tomentosa, L. sericea) establish in the grassland matrix or on rocky outcrops where they persist (Westfall et al, 1983;Smith and Tainton, 1985;Titshall et al, 2000). These early successional species share several life history traits that include fire tolerance, the capacity to coppice in response to fire and the ability to colonise grassland (Westfall et al, 1983;Smith and Tainton, 1985). They do not necessarily initiate forest succession and cannot be considered true forest species.…”

Section: Forest Successionmentioning

confidence: 99%

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Role reversal in the stand dynamics of an angiosperm–conifer forest: Colonising angiosperms precede a shade-tolerant conifer in Afrotemperate forest

Adie¹,

Lawes²

2009

Forest Ecology and Management

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“…Clumps reduce herbaceous production considerably (Archer 1995, Mordelet and Menaut 1995, Jarvel and O'Connor 1999, thereby reducing competition and excluding or weakening fire (Hochberg et al 1994). This should promote forestscrub species, which are well recorded to be fire intolerant (Westfall et al 1983, Titshall et al 2000. Individuals growing within the interior of a clump are protected from browsing (Hester et al 2006).…”

Section: Facilitationmentioning

confidence: 99%

Bush clump succession in grassland in the Kei Road region of the Eastern Cape, South Africa

O’Connor

Chamane

2012

African Journal of Range & Forage Science

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Bush encroachment is a vegetation dynamic of global interest. This study describes the pattern of succession of bush clumps in the Eastern Cape, South Africa, using a space-for-time substitution. Clumps formed following establishment of mainly Acacia karroo in grassland through nucleation via animal dispersal. A total of 49 tree or shrub species were recorded in 40 clumps. With increasing clump size, there was a corresponding increase in woody basal area, species richness and diversity, but not evenness. Correspondence analysis showed that the pattern of compositional variation was closely related to clump size; differences resulting from clump establishment disappeared as clumps developed. Population size structure of 20 (of 21) species was dominated by small individuals, indicating that regeneration has increased over time. Coddia rudis was prolific on a clump periphery; Scutia myrtina and A. karroo were dominant within clumps. Seven shrub and nine tree species were encountered more frequently within a clump than on its periphery. All species other than A. karroo had fruits suited to dispersal by birds or mammals. The overall pattern of bush clump succession shows close parallels with that initiated by invasion of Prosopis glandulosa into grassland in Texas, USA.

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The vegetation of the protected plots at Thabamhlope Research Station

Cited by 16 publications

References 4 publications

The importance of low atmospheric CO₂ and fire in promoting the spread of grasslands and savannas

The importance of low atmospheric CO₂ and fire in promoting the spread of grasslands and savannas

Role reversal in the stand dynamics of an angiosperm–conifer forest: Colonising angiosperms precede a shade-tolerant conifer in Afrotemperate forest

Bush clump succession in grassland in the Kei Road region of the Eastern Cape, South Africa

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The vegetation of the protected plots at Thabamhlope Research Station

Cited by 16 publications

References 4 publications

The importance of low atmospheric CO2 and fire in promoting the spread of grasslands and savannas

The importance of low atmospheric CO2 and fire in promoting the spread of grasslands and savannas

Role reversal in the stand dynamics of an angiosperm–conifer forest: Colonising angiosperms precede a shade-tolerant conifer in Afrotemperate forest

Bush clump succession in grassland in the Kei Road region of the Eastern Cape, South Africa

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Product

Resources

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The importance of low atmospheric CO₂ and fire in promoting the spread of grasslands and savannas

The importance of low atmospheric CO₂ and fire in promoting the spread of grasslands and savannas