Determinants of flammability in savanna grass species

1. Tropical grasses fuel the majority of fires on Earth. In fire-prone landscapes, enhanced flammabil-ity may be adaptive for grasses via the maintenance of an open canopy and an increase in spa-tiotemporal opportunities for recruitment and regeneration. In addit ion, by burning intensely butbriefly, high flammability may protect resprouting buds from lethal temperatures. Despite thesepotential benefits of high flammability to fire-prone grasses, variation in flammability among grassspecies, and how trait differences underpin this variation, remains unknown.2. By burning leaves and plant parts, we experimentally determined how five plant traits (biomassquantity, biomass density, biomass moisture content, leaf surface-area-to-volume ratio and leaf effec-tive heat of combustion) combined to determine the three components of flammability (ignitability,sustainability and combustibility) at the leaf and plant scales in 25 grass species of fire-pr one SouthAfrican grasslands at a time of peak fire occurrence. The influence of evolutionary history onflammability was assessed based on a phylogeny built here for the study species.3. Grass speci es differed significantly in all components of flammability. Accounting for evolution-ary history helped to explain patterns in leaf-scale combustibility and sustainability. The five mea-sured plant traits predicted components of flammability, particularly leaf ignitability and plantcombustibility in which 70% and 58% of variation, respectively, could be explained by a combina-tion of the traits. Total above-ground biomass was a key drive r o f combustibility and sustainabi litywith high biomass species burning more intensely and for longer, and producing the highest pre-dicted fire spread rates. Moisture content was the main influence on ignitability, where speci es withhigher moisture conten ts took longer to ignite and once alight burnt at a slower rate. Bioma ss den-sity, leaf surface-area-to-volume ratio and leaf effective heat of combustion were weaker predictorsof flammability components.4. Synthesis. We demonstrate that grass flammability is predicted from easily measurable plant func-tional traits and is influenced by evolutionary history with some components showing phylogeneticsignal. Grasses are not homogenous fuels to fire. Rather, species differ in functional traits that inturn demonstrably influence flammability. This diver sity is consistent with the idea that flammabilitymay be an adaptive trait for grasses of fire-prone ecosystems

Long-term effects of fire frequency and season on herbaceous vegetation in savannas of the Kruger National Park, South Africa

Aims: The long-termeffects of changing fire regimes on the herbaceous component of savannas are poorly understood but essential for understanding savanna dynamics. We present results from one of the longest running (>44 years) fire experiments in savannas, the experimental burn plots (EBPs), which is located in the Kruger National Park (South Africa) and encompasses four major savanna vegetation types that span broad spatial gradients of rainfall (450–700mm) and soil fertility. Methods: Herbaceous vegetation was sampled twice in the EBPs using a modified step-point method, once prior to initiation of the experiment (1954) and again after 44–47 years. Different combinations of three fire frequency (1-, 2- and 3-year return intervals) and five season (before the first spring rains, after the first spring rains, mid-summer, late summer and autumn) treatments, as well as a fire exclusion treatment, were applied at the plot level (;7 ha each), with each treatment (n = 12 total) replicated four times at each of the four sites (n = 192 plots total). The effects of long-term alterations to the fire regime on grass community structure and composition were analyzed separately for each site. Important Findings: Over the 44+ years duration of the experiment, fires were consistently more intense on sites with higher mean annual rainfall (>570 mm), whereas fires were not as intense or consistent for sites with lower and more variable rainfall (<510 mm) and potentially higher herbivory due to greater soil fertility. Because the plots were open to grazing, the impacts of herbivory along with more variable rainfall regimes likely minimized the effects of fire for the more arid sites. As a consequence, fire effects on grass community structure and composition were most marked for the higher rainfall sites and generally not significant for the more arid sites. For the high-rainfall sites, frequent dry season fires (1- to 3-year return intervals) resulted in high grass richness, evenness and diversity, whereas fire exclusion and growing season fires had the lowest of these measures and diverged the most in composition as the result of increased abundance of a few key grasses. Overall, the long-term cumulative impacts of altered fire regimes varied across broad climatic and fertility gradients, with fire effects on the grass community decreasing in importance and herbivory and climatic variability likely having a greater influence on community structure and composition with increasing aridity and soil fertility

Composition of woody species in a dynamic forest-woodland-savannah mosaic in Uganda: implications for conservation and management

Forest¿woodland¿savannah mosaics are a common feature in the East African landscape. For the conservation of the woody species that occur in such landscapes, the species patterns and the factors that maintain it need to be understood. We studied the woody species distribution in a forest¿woodland¿savannah mosaic in Budongo Forest Reserve, Uganda. The existing vegetation gradients were analyzed using data from a total of 591 plots of 400 or 500 m2 each. Remotely sensed data was used to explore current vegetation cover and the gradients there in for the whole area. A clear species gradient exists in the study area ranging from forest, where there is least disturbance, to wooded grassland, where frequent fire disturbance occurs. Most species are not limited to a specific part of the gradient although many show a maximum abundance at some point along the gradient. Fire and accessibility to the protected area were closely related to variation in species composition along the ordination axis with species like Cynometra alexandri and Uvariopsis congensis occurring at one end of the gradient and Combretum guenzi and Lonchocarpus laxiflorus at the other. The vegetation cover classes identified in the area differed in diversity, density and, especially, basal area. All vegetation cover classes, except open woodland, had indicator species. Diospyros abyssinica, Uvariopsis congensis, Holoptelea grandis and all Celtis species were the indicator species for the forest class, Terminalia velutina and Albizia grandbracteata for closed woodland, Grewia mollis and Combretum mole for very open woodland and Lonchocarpus laxiflorus, Grewia bicolor and Combretum guenzi for the wooded grassland class. Eleven of the species occurred in all cover classes and most of the species that occurred in more than one vegetation cover class showed peak abundance in a specific cover class. Species composition in the study area changes gradually from forest to savannah. Along the gradient, the cover classes are distinguishable in terms of species composition and vegetation structure. These classes are, however, interrelated in species composition. For conservation of the full range of the species within this East African landscape, the mosaic has to be managed as an integrated whole. Burning should be varied over the area with the forest not being burnt at all and the wooded grassland burnt regularly. The different vegetation types that occur between these two extremes should be maintained using a varied fire regim

Effect of season of burning on grass recovery in the False Thornveld of the Eastern Cape.

Season of burning is one of the most controversial questions concerning the use of fire in veld management. In the summer rainfall areas of South Africa the generally accepted rule of burning only after the first spring rains has proven ineffectual when using fire to control bush encroachment because the fires are too cool when burnt at this time. It was therefore decided to investigate the effect of burning on the regrowth of grass when applied during mid-winter, spring, late spring and early summer. The results showed that burning when the grass was dormant (mid-winter) had no deleterious effect on the recovery of grass when compared with burning after the first spring rains (spring). Conversely burning when the grass was actively growing (early summer) seriously retarded its regrowth.Language: EnglishKeywords: burning; Burning seasons; bush encroachment; control; eastern cape; false thornveld; fire regime; fires; Grass recovery; grasses; management; rainfall; recovery; regrowth; Savanna; south africa; summer rainfall area; Veld mamagement; veld managemen

Fire behaviour - A preliminary study.

There is a serious deficiency in knowledge concerning the behaviour of fires in South Africa. Arising from this, an investigation was initiated to characterise the behaviour of head and back fires under a variety of environmental conditions. The results showed that head fires had a significantly greater rate of spread, length of flame and overall intensity than back fires. However, at ground level back fires were more intense and had a significant depressive effect on the recovery of the grass, resulting in lower yields. These results demonstrate the value of knowledgte about fire behaviour in veld management; it is recommended that fire behaviour and its effect on vegetation always be taken cognisance of in any future research on fire in relation to vegetation.Keywords: behaviour; botany; environmental conditions; fire; fire behaviour; fire ecology; fires; grass; grasses; management; rate of spread; recovery; south africa; vegetation; veld; veld management; yiel

Recommended terms, definitions and units to be used in fire ecology in South Africa.

In South Africa there is no well developed nomenclature available for describing the various aspects of burning that are pertinent to the field of fire ecology. A set of terms and definitions, based on a review of the world literature and adapted where necessary, has been proposed in an effort to overcome this problem. The terms have been grouped into those that describe general aspects of fire ecology and those that relate to fire behaviour and related parameters.Keywords: burning; ecology; fire behaviour; fire ecology; nomenclature; south africa; terminolog

Controlling bush encroachment with fire in the savanna areas of South Africa.

The savanna areas of South Africa can be divided into the moist and arid savanna types according to the availability of soil moisture. Bush encroachment is a serious veld management problem in all the savanna areas and veld burning is a potential eradication technique in situations with an adequate grass cover to support an intense fire. In the moist savannas fire per se can be used to control bush encroachment but in the arid savannas it has the role of maintaining trees and shrubs at an available height and in acceptable state for browsing animals. Intense head fires applied at the end of the dormant season are used for bush eradication. The frequency of burning is relatively high in the moist savannas but is very low in the arid savannas, being usually limited to years with above average rainfall when adequate grass fuel loads can be accumulated. Veld burning provides an attractive economic and energy saving technique of solving the problem of bush encroachment in the savanna areas of South Africa.Keywords: arid savanna; browsing; burning; bush encroachment; control; fire; fires; frequency of burning; fuel load; grass cover; management; savanna; soil moisture; south africa; technique; veld burning; veld managemen

Appendix:Veld en aangeplante weidingsbestuurterminologie in suidelike Afrika.

Keywords: afrikaans; botany; ecology; grazing; pasture management; southern africa; terminology; veld; veld managemen

Use of key grass species for assessing veld condition in the Eastern Cape.

The current technique used in the Eastern Cape for assessing veld condition and trend assumes that the operator is able to identify all the grass species in the sample site. This is a serious limitation to its use by extension officers, consultants and farmers. Data from the Dohne Sourveld and the False Thornveld of the Eastern Cape were used successfully to identify the minimum number of key grass species required to assess the condition and trend of the veld.Keywords: botany; disturbance history; dohne sourveld; eastern cape; false thornveld; grass; grasses; south africa; veld conditio

Veld management in the communal areas of Ciskei.

Veld management in Ciskei is based predominantly on a communal land tenure system, and livestock is produced under a `Group Ranch' system. Stocking rates are excessively high and consequently veld degradation is severe, resulting in a lowered carrying capacity and low efficiency indicators such as weaning percentage. A solution to the continued degradation of the veld depends on the commitment of the government to a development strategy which addresses factors such as freehold tenure, education and the provision of incentive for profitable productionLanguage: EnglishKeywords: Bush encroachment; Ciskei; Communal areas; Group Ranch system; Land tenure systems; Overstocking; Veld degradation; Veld development; Veld management; Veld rehabilitation; carrying capacity; degradation; grazing; land tenure; management; selective grazing; veld condition; livestock; rehabilitation; socio-economic; production; stocking rates; land use; south africa; botan