Biodiversity and Stability in Tropical Savannas

Silva, Juan F.

doi:10.1007/978-3-642-78969-4_9

Cited by 9 publications

(6 citation statements)

References 22 publications

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“…Annual RIR estimated from the data presented in Table 1 are well within the range of the estimations based on the data from San Jose and Fariñas (Silva, 1996). If these rates of increase were constant, all areas feasible to be invaded by trees would soon be forested.…”

Section: Discussionsupporting

confidence: 78%

“…Annual rates of increase calculated from data on densities from the monitoring reported in San José & Fariñas (1991), changed drastically. In the interval between 1983 and 1986, the annual rate of increase of most species was 0.01 or lower (Silva, 1996).…”

Section: Discussionmentioning

confidence: 99%

“…They are related not only to water availability (Medina & Silva, 1990), kind of substrate (Trollope et al ., 1998) and soil depth (San José & Fariñas, 1983), but also to other less prominent factors, such as the episodic and chronic disturbances and small‐scale heterogeneities (Van de Koppel & Prins‐Herbert, 1998; Gomez‐Sal et al ., 1999). It is very difficult to disentangle the effects of fire regime from these and other factors, as they are strongly interdependent and interact with each other (Silva, 1996). O’Connor (1985) reviewed seventy‐two long‐term experiments conducted in southern African savannas to conclude that it is not possible to draw a clear picture of the driving forces of savanna structure from those experiments because of the various defects in experimental design.…”

Section: Discussionmentioning

confidence: 99%

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Increase in the woody component of seasonal savannas under different fire regimes in Calabozo, Venezuela

Silva

Zambrano

Fariñas

2001

Journal of Biogeography

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Aim We tested the hypothesis that exclusion from ®re and cattle is responsible for the increase in tree cover in open savanna vegetation.Location Four plots in open savanna vegetation from the Calabozo region in central Venezuela were studied. Plot A was located in a Biological Station (EBL) that was excluded from ®re and cattle between 1961 and 1991, with only two burning events in 1964 and 1968. The other plots (B, C, D) were located within 2 km distance from A, in neighbouring farms with soils similar to those in A but under various regimes of land use and ®re frequency.Methods We measured the cover of isolated trees, small tree groups and groves of each plot in 1960 and 1977 using geographic information system (GIS) and digitalized aerial photographs. Additionally, the plots were located in the ®eld and the open grassland was sampled in 1995 for species composition and density of stems above 20 cm height. Information on land use was obtained surveying people at the farms.Results There was an increase in the woody component of all plots during the 17-year interval (1960±1977). Total woody cover in the four plots as a whole increased from 4.5% to 17.9%. All three components measured, groves, tree groups and isolated trees, increased despite differences in land use and ®re frequency between plots. Contrary to our expectations, the ®eld survey performed in 1995 showed that ®re-sensitive species were abundant in the open savanna in plots B, C and D, which were not excluded. Plot B, with the most intense agricultural use showed the highest rate of woody increase, and plot C, under extensive cattle ranching, was second. The results also showed that woody cover increased by aggregation from single trees and small tree groups into groves. As a consequence of these changes, savanna physiognomy changed from open to dense savanna parkland with a woody cover reaching over 25% in one of the four plots.Conclusions The results agree with other reported increases in woody cover in savannas under exclusion or with annual ®res during the same time period in Africa (Dauget & Menaut, 1992). Our results support evidence from previous studies showing that ®re and grazing are only part of a complex system of interacting factors affecting the structure of savanna communities.

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Section: Discussionsupporting

confidence: 78%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Increase in the woody component of seasonal savannas under different fire regimes in Calabozo, Venezuela

Silva

Zambrano

Fariñas

2001

Journal of Biogeography

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“…Nevertheless, the relationship between environmental factors, such as soil quality and fire, and functional diversity is a question rarely addressed in natural communities and especially for woody species. Soil and fire are the major determinants of plant community structure and composition in neotropical savannas (Silva 1996;Lehmann et al 2011). Recurrent fires modify many soil properties, such as the concentration of available nutrients, amount of organic matter, toxic elements, and soil texture (Kennard & Gholz 2001;González-Pérez et al 2004;Silva & Batalha 2008).…”

Section: Introductionmentioning

confidence: 99%

Influence of fire history and soil properties on plant species richness and functional diversity in a neotropical savanna

2013

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Differences in plant species richness and composition are associated with soil properties and disturbances such as fire, which can therefore be key determinants of species occurrence in savanna plant communities. We measured species richness, using nine plant functional traits and abundance to calculate three functional diversity indices. We then used model selection analyses to select the best model for predicting functional diversity and richness based on soil variables at sites with three different fire frequencies. We also calculated the community-weighted mean of each trait and used ordination to examine how traits changed across fire frequencies. We found higher species richness and functional dispersion at sites that were more fertile and where fire was frequent, and the opposite at such sites where fire was infrequent. However, soil properties influenced functional evenness and divergence only where fire was infrequent, with higher values where soils were poorer. Fire can change functional traits directly by hindering development of plants and indirectly by altering competition. Different fire frequencies lead to different plant-soil relationships, which can affect the functioning of tropical savanna communities. Functional diversity components and functional identity of the communities are both affected by fire frequency and soil conditions. Keywords: cerrado; complementarity; fertility effect; plant traits; soil nitrogen Acta Botanica Brasilica 27(3): 490-497. 2013.

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“…The restoration speed of a clearfelled savanna mainly depends on the rainfall (resilience is much higher in moist savannas than in arid ones), on the regeneration capacity of the dominating woody species and their fire resistance and also on the specific fire regime. According to SILVA (1996) tree seed that do not germinate do not survive and there is no apparent seed bank in the savanna soil. Consequently, seedling recruitment depends on current seed production, which is almost nil in a clearfelled savanna.…”

Section: Methodsmentioning

confidence: 99%

The use of fire in the environmental rehabilitation on the sites of a former refugee camp at Benaco, Tanzania

Bloesch

2001

Schweizerische Zeitschrift Fur Forstwesen

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The enormous wood requirements of about 450 000 Rwandan refugees in northwestern Tanzania led to the depletion of the wood resources in the surrounding savannas in an area of about 500 km2. The natural regeneration of the woody plants was endangered by frequent fierce late dry-season fires. Since total fire exclusion of the vast area was not feasible, early-burning was prescribed which is less destructive to woody regeneration than the hotter late burns and which prevents the more destructive late dry-season fires. The techniques of controlled burning are explained.

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Biodiversity and Stability in Tropical Savannas

Cited by 9 publications

References 22 publications

Increase in the woody component of seasonal savannas under different fire regimes in Calabozo, Venezuela

Increase in the woody component of seasonal savannas under different fire regimes in Calabozo, Venezuela

Influence of fire history and soil properties on plant species richness and functional diversity in a neotropical savanna

The use of fire in the environmental rehabilitation on the sites of a former refugee camp at Benaco, Tanzania

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