Effect of season of burning on grass recovery in the false thornveld of the eastern cape

Abstract

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.     

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.     

Fire behaviour in the Kruger National Park

Abstract

Fire research in the Kruger National Park has largely been focussed on the effect of the season and frequency of burning on the vegetation. Very little information is available on the effect of fire behaviour and in particular fire intensity, on the flora of the Park. Consequently a research project was conducted to develop statistical models for predicting fire intensity, flame height and rate of spread in the field. The devleopment of these models constitutes the initial phase of determining the relationship between fire behaviour and vegetation response.     

Veldherwinning langs paaie

The results of a trial to study the effects of periodic burning, or complete resting, on the vegetation and some soil characteristics of semi‐arid Acacia nigrescens/Combretum apiculatum savanna in eastern Botswana are discussed. Plots of 1,2 ha were burned at intervals of O (no burn control), 1,2,3,4 and 5 years from 1958 to 1980. In 1981 these were assessed for bush density by species and by height classes, for grass basal cover and botanical composition, and for soil properties. Bush density increased with increasing burning interval but complete resting suppressed seedling development. All burned plots were visibly more open than the rested plot and hence fire appears to offer the possibility of a low cost means of bush control. The changes in soil properties, grass cover and botanical composition resulting from low frequency burns were small.     

Grass defoliation affecting survival and growth of seedlings of Acacia karroo,an encroaching species in southwestern Zimbabwe

Abstract

Two experiments were conducted, one in the field and the other in the greenhouse, to investigate the effects of the intensity and frequency of grass defoliation on the survival and growth of Acacia karroo seedlings. In the greenhouse, seedlings growing with heavily clipped grasses had higher biomass production than those competing with moderately clipped grasses. Root/shoot ratios were higher in treatments with undipped grasses. There was a negative relationship between grass root production and A. karroo biomass production. The field experiment was carried out in two paddocks, one previously heavily‐grazed and the other lightly‐grazed. Grazing in both paddocks was simulated by artificial defoliation. Generally more A. karroo seedlings emerged under lightly defoliated treatments. Clipping frequency had a strong effect (P=0.066) on the survival of emerged seedlings during the wet season. There were no differences in survival rate at the end of the dry season. Though grass defoliation was shown to enhance seedling growth under controlled conditions, no evidence was found to suggest that seedling establishment during the first year is influenced by the intensity of grass defoliation.     

Preliminary observations on the ability of goats to control post‐burning regrowth in acacia nigrescens/combretum apiculatum Savanna in Botswana

Abstract

A ten hectare block which had been burned with an intense surface head fire was stocked at the rate of one goat per hectare to control the woody regrowth. After one year the block was subdivided and in one half the stocking rate increased to three goats per hectare. After two further years there was insufficient forage to sustain the high stocking rate. At this stage the bush density below two metres had been reduced by 23% and 52% in the low and high stocking rates respectively. Similarly the bush canopy below two metres had been reduced by 70% and 95%. There was greater mortality of benign browse species than of spinescent species. Adverse changes in herbaceous layer composition were recorded in the high stocking rate. Drought, stocking rate and plant tolerance to browsing are discussed in relation to management objectives.     

The influence of tree density on the grass layer of three semi-arid savanna types of southern Africa

The influence of bush density on the grass component of the herbaceous layer was investigated for three savanna veld types (Molopo Thornveld, Mixed Vaalbos Thornveld, and the Eastern Grass and Bushveld) in the Northern Cape and North-West Province of South Africa. Relationships between bush density and the density, species composition and phytomass production of the grass component were determined over a four-year period. Bush encroachment had an adverse influence on the density and production of the grass component, but not on the species composition. Fluctuations in seasonal rainfall appeared to be the most important factor governing changes in the species composition of the grass component. Bush enchroachment (2 500 tree equivalents ha^?l) decreased the potential grazing capacity by as much as 331%, 149% and 58% in the Molopo Thornveld, the Mixed Vaalbos Thornveld and the Eastern Grass Bushveld, respectively, In comparison to sites with tree densities of less than 400 tree equivalents ha^?1. In the encroached condition grazing capacities of 15, 13 and 10 ha LSU^?1 are recommended for the Molopo Thornveld, the Mixed Vaalbos Thornveld and the Eastern Grass and Bushveld, respectively. The implementation of bush control measures in all problem areas is proposed in order to restore the productivity of these areas in the long term.     

Factors Affecting the Distribution of Wild Ungulates on a Ranch in Kenya. Preliminary Report

This paper gives a preliminary report on the factors affecting the distribution of wild ungulates on a ranch in Kenya. The study covers only one phase of an overall project on the compatabfiity of wild and domestic ungulates. The major factors considered are vegetation, water, fire, cattle grazing, hunting and animal behaviour. These factors are related to five major wild ungulate species which occur on Akira - Coke's hartebeest (kongoni), Grant's gazelle, Thomson's gazelle, eland and giraffe.

The major influence on wild ungulate densities and distribution was vegetation. The condition of vegetation was determined by rainfall, fire and grazing intensities. Generally game populations increased with cattle populations which indicated that vegetation conditions were improving during the period of this study. Overgrazing was generally detrimental to all species except to the Thomson's gazelle which was attracted to short grass areas around water, bomas and overgrazed sites. Kongoni were found usually in tall grass areas while Grant's gazelle were not as selective as Thomson's gazelle or eland. Giraffe were confined mostly to Acacia communities and eland, though found in grassland, were most frequently in high bush country where the variety of shrubs was greater.

The effects of other factors on each of the ungulates are also presented. The interrelationships of all factors are being considered as the study continues.     

Fire and Nitrogen Effects on Purple Threeawn (Aristida purpurea) Abundance in Northern Mixed-Grass Prairie Old Fields

Purple threeawn (Aristida purpurea Nutt. varieties) is a native grass capable of increasing on rangelands, forming near monocultures, and creating a stable state. Productive rangelands throughout the Great Plains and Intermountain West have experienced increases in purple threeawn abundance, reducing overall forage quality. Our objectives were to 1) reveal the effects of prescribed fire and nitrogen amendments on purple threeawn abundance and 2) assess nontarget plant response posttreatment. Season of fire (no fire, summer fire, fall fire) and nitrogen addition (0 kg N · ha^?1, 46 kg N · ha^?1, and 80 kg N · ha^?1) were factorially arranged in a completely randomized design and applied to two similar sites in southeastern Montana. We evaluated fire and nitrogen effects on purple threeawn basal cover, relative composition, and current-year biomass one growing season postfire at two sites treated during different years. Spring weather following fire treatments was very different between years and subsequently impacted community response. Initial purple threeawn biomass at both sites was 1 214 ± 46 kg · ha^?1 SEc. When postfire growing conditions were wet, current-year biomass of purple threeawn was reduced 90% and 73% with summer and fall fire, respectively. Under dry postfire growing conditions, purple threeawn current-year biomass was reduced 73% and 58% with summer and fall fire, respectively. Nitrogen additions had no effect on purple threeawn current-year biomass at either site. Current-year biomass of C₃ perennial grass doubled with nitrogen additions and was not impacted by fire during a wet spring. Nitrogen additions and fire had no effect on C₃ perennial grass current-year biomass following a dry spring. Prescribed fire appears to be a highly effective tool for reducing purple threeawn abundance on semiarid rangelands, with limited detrimental impacts to nontarget species.     

Different Fire Frequency Impacts Over 27 Years on Vegetation Succession in an Infertile Old-Field Grassland

We examined the effect of fire on vegetation composition with the use of an experiment with four different fire frequencies (annual, 2-yr interval, 4-yr interval, and an intended control with no burning) over a 27-yr period in an infertile, old-field grassland at the Cedar Creek Ecosystem Science Reserve, located in Minnesota, United States. We measured the plant species' aboveground biomass in permanent plots in 1983, 1987, 1991, 2000, and 2010. None of these fire frequencies, even after 27 yr, had a large impact on the vegetation composition. The plant functional groups' responses to fire frequency were consistent with their respective dominant species. The most abundant C₄ grass, little bluestem (Schizachyrium scoparium Michx.), did not change in biomass with fire frequency over time. The biomass of the introduced, invasive grass, Kentucky bluegrass (Poa pratensis L.) decreased significantly with increasing fire frequency, but this decrease did not result in change to the rate and trajectory of vegetation change. Bush clover (Lespedeza capitata Michx.), the only legume in the community, strongly increased with more frequent fire, but only after 20 yr. Species richness and litter mass decreased significantly with increasing fire frequency. These small fire-induced vegetation changes contrast with large fire-induced vegetation changes in fertile grasslands. Management strategies using fire in infertile grasslands can lower Poa abundance; however, increased fire also decreased overall plant diversity.     

不同管理措施对青海湖流域高寒草地土壤养分的影响

本文通过野外采样及室内分析比较了围栏封育(FE)、传统放牧(TG)和草灌结合(CGB)3种管理措施对青海湖流域高寒草地不同土层深度土壤养分的影响。结果表明：土壤有机质、速效氮磷和硝态氮含量在不同管理措施下均随土层深度的增加而降低(P<0.05);FE有机质含量均显著高于CGB和TG (P<0.05);不同管理措施对土壤全量养分含量影响较小,主要对0~10 cm土层全氮含量产生影响,该层中FE全氮含量显著高于CGB和TG;不同管理措施对土壤速效养分含量的影响较大,主要体现在0~10 cm和10~20 cm土层,均表现为FE土壤速效养分含量最高(P < 0.05)。综上,围栏封育更有利于青海湖流域土壤养分的固持和青海湖流域退化高寒草地的恢复。     

Pros and cons of eliminating veld burning

Fire has been a factor of the environment in Africa since time immemorial and it is often caused by natural agencies such as lightning. It is maintained that there is much prejudice against veld burning, often ill‐founded. Fire has caused and maintained most of the world's grassland. When fire has been prevented plant succession has resulted in bush encroachment in the savanna and surrounding areas or in fynbos encroachment in others. Fire results in much old grass being wasted but, if this is not removed in some manner, the grazing deteriorates. Old grass can be removed by fire, mowing or grazing, using high protein supplements. The consequences of the different methods of removal, other than mowing, may be equally deleterious.     

The effect of tebuthiuron on the vegetation of the thorn Bushveld of the Northern Cape – a preliminary report

Abstract

Two formulations of tebuthiuron i.e. Graslan 20P and Graslan 40P are currently being evaluated in the Molopo area. Tebuthiuron was applied aerially at ten application rates, in combination with two application dates.

After only two seasons, the chemical has already shown a reasonable selectivity for the woody species. Of these, Acacia mellifera, A. reficiens and Grewia flava are very sensitive while A. erioloba and Dichrostachys cinérea are less sensitive and Boscia albitrunca seems almost resistant to the lower application rates (<1,0 kg a.i./ha).

The standing crop of grass on the treated plots increased by between 220 and 740 per cent. Changes in the total grass density and botanical composition can be ascribed to an increased density of Eragrostis lehmanniana.

At this stage of the trial, its selectivity in favour of the more desirable woody species, suggests that tebuthiuron shows great promise for controlling bush encroachment in the Northern Cape, although a final conclusion would only be possible 5 years after its application.     

Water utilization patterns around isolated Acacia karroo trees in the False Thornveld of the eastern Cape

The effect of various vegetation treatments on two soil moisture regimes (i.e. the proportion of the experimental period where the soil had sufficient water for: (a) growth, and (b) to keep the plants turgid in the vicinity of experimentally isolated A. karroo trees) was monitored over a two‐year period. Removal of all vegetation had the greatest effect on soil moisture, increasing the moisture regime by around 200%. Grass removal had the next most significant effect, increasing moisture regimes within 9 m of the tree by around 100%. Removal of the tree had the smallest significant effect, increasing the moisture regime by less than 20%. There was no significant difference in the moisture regime surrounding trees with heights ranging between 1,4 m and 2,5 m, or where various combinations of tree and/or grass defoliations were implemented. We conclude that water supply to the trees is enhanced when soil water extraction is reduced (e.g. during winter or when the sward is harmed) and argue that this may be a mechanism of accelerating bush encroachment in semi‐arid savannas.     

The effect of thirty years of burning on the Highland Sourveld of Natal

Abstract

A veld condition assessment was used to determine the effect of past burning treatments on the species composition of Highland Sourveld at Cathedral Peak. Veld condition scores in grassland protected from fire were significantly lower than where veld had been burnt or burnt and grazed at regular intervals. Frequent defoliation was found to maintain the grassland composition largely unchanged over a period of 30 years. Individual species were found to react strongly to defoliation frequency.     

Postfire Succession in Big Sagebrush Steppe With Livestock Grazing

Prescribed fire in rangeland ecosystems is applied for a variety of management objectives, including enhancing productivity of forage species for domestic livestock. In the big sagebrush (Artemisia tridentata Nutt.) steppe of the western United States, fire has been a natural and prescribed disturbance, temporarily shifting vegetation from shrub–grass codominance to grass dominance. There is limited information on the impacts of grazing to community dynamics following fire in big sagebrush steppe. This study evaluated cattle grazing impacts over four growing seasons after prescribed fire on Wyoming big sagebrush (Artemisia tridentata subsp. Wyomingensis [Beetle & Young] Welsh) steppe in eastern Oregon. Treatments included no grazing on burned and unburned sagebrush steppe, two summer-grazing applications after fire, and two spring-grazing applications after fire. Treatment plots were burned in fall 2002. Grazing trials were applied from 2003 to 2005. Vegetation dynamics in the treatments were evaluated by quantifying herbaceous canopy cover, density, annual yield, and perennial grass seed yield. Seed production was greater in the ungrazed burn treatments than in all burn–grazed treatments; however, these differences did not affect community recovery after fire. Other herbaceous response variables (cover, density, composition, and annual yield), bare ground, and soil surface litter did not differ among grazed and ungrazed burn treatments. All burn treatments (grazed and ungrazed) had greater herbaceous cover, herbaceous standing crop, herbaceous annual yield, and grass seed production than the unburned treatment by the second or third year after fire. The results demonstrated that properly applied livestock grazing after low-severity, prescribed fire will not hinder the recovery of herbaceous plant communities in Wyoming big sagebrush steppe.     

Semiarid Rangeland Is Resilient to Summer Fire and Postfire Grazing Utilization

Most wildfires occur during summer in the northern hemisphere, the area burned annually is increasing, and fire effects during this season are least understood. Understanding plant response to grazing following summer fire is required to reduce ecological and financial risks associated with wildfire. Forty 0.75-ha plots were assigned to summer fire then 0, 17, 34 or 50% biomass removal by grazing the following growing season, or no fire and no grazing. Root, litter, and aboveground biomass were measured before fire, immediately after grazing, and 1 yr after grazing with the experiment repeated during 2 yr to evaluate weather effects. Fire years were followed by the second driest and fifth wettest springs in 70 yr. Biomass was more responsive to weather than fire and grazing, with a 452% increase from a dry to wet year and 31% reduction from a wet to average spring. Fire reduced litter 53% and had no first-year effect on productivity for any biomass component. Grazing after fire reduced postgrazing grass biomass along the prescribed utilization gradient. Fire and grazing had no effect on total aboveground productivity the year after grazing compared to nonburned, nongrazed sites (1 327 vs. 1 249 ± 65 kg · ha^-1). Fire and grazing increased grass productivity 16%, particularly for Pascopyrum smithii. The combined disturbances reduced forbs (51%), annual grasses (49%), and litter (46%). Results indicate grazing with up to 50% biomass removal the first growing season after summer fire was not detrimental to productivity of semiarid rangeland plant communities. Livestock exclusion the year after summer fire did not increase productivity or shift species composition compared to grazed sites. Reduction of previous years' standing dead material was the only indication that fire may temporarily reduce forage availability. The consistent responses among dry, wet, and near-average years suggest plant response is species-specific rather than climatically controlled.     

Effect of nitrogen application,seeding rate and defoliation height on mixtures of Trifolium vesiculosum cv Amclo and Lolium multiflorum cv Midmar: I. dry matter production,crude protein content and crude protein production*

Abstract

The interaction between Trifolium vesiculosum cv Amclo and Lolium multiflorum cv Midmar was measured in a field trial, in terms of dry matter production, crude protein content and crude protein production. The treatments included in the field trials were five different seeding rates of the grass component, four rates of nitrogen application and two defoliation heights. Total DM production of the mixtures differed only slightly, and height of defoliation had, likewise, little effect on the DM production. N application tended to increase the yield of pure grass as well as the grass component of the mixtures. Crude protein content and crude protein production of the mixtures were markedly increased by nitrogen application, largely due to effective uptake of nitrogen by the grass component. However, the highest crude protein production, achieved by an application of 240 kg N/ha to both mixtures and pure grass swards, did not differ appreciably from the amount produced by pure clover receiving no nitrogen fertilizer.     

Long-Term Effects of Fire,Livestock Herbivory Removal,and Weather Variability in Texas Semiarid Savanna

We examined how the occurrence and structure of grasses and woody plants changed after 12 yr of a fire season manipulation and removal of livestock herbivores. Applying high intensity fires in the summer preserved the structural integrity of this semiarid live oak (Quercus virginiana Mill.) savanna while decreasing or eliminating numerous problematic plants in the understory and overstory, such as prickly pear cactus (Opuntia spp.), sacahuista (Nolina texana S. Watson), Ashe juniper (Juniperus ashei J. Buchholz), Pinchot's juniper (J. pinchotii Sudw.), and honey mesquite (Prosopis glandulosa Torr.). In the less intense repeat winter burning treatments, undesirable woody plants were generally maintained at pretreatment levels in the overstory but all woody plants except Ashe juniper increased in the understory. Alternatively, areas excluded from fire in the control treatment rapidly transitioned from a grass-tree codominated savanna environment to one that is heavily dominated by woody plants. In the grass community, the most frequently occurring grass species in the winter burn treatment differed from summer burn and control treatments, whereas the summer burn treatment was not different from the control. Of the herbaceous plants, only little bluestem (Schizachyrium scoparium &lsqb;Michx.] Nash) responded to fire treatments. Little bluestem increased in the winter burn treatment, remained fairly constant in the summer burn treatment, and decreased in the control. Other grasses varied largely as a function of annual weather variability, the removal of livestock, and legacy effects resulting from pre-existing variability. These findings suggest that fire can reduce or eliminate woody plant species that threaten the stability of live oak savannas while having little long-term effect on grasses desired by rangeland managers.     

Influence of bushdumps on the herbaceous understorey in a mesic Eastern Cape savanna

Abstract

Studies of the effects of woody vegetation on herbaceous vegetation in southern Africa have focused almost exclusively on savannas with isolated trees with no attention given to multi‐species bushclump savannas. The influence of multi‐species bushdumps on herbaceous vegetation was investigated in a mesic savanna in the Eastern Cape. Development of bushdumps appeared to reduce herbaceous production underneath the clumps by up to 90%. The herbaceous layer underneath the bushdumps was distinctly different to that of the open grassland and it also had slightly higher quality compared to that of grassland. Effective bush control measures are warranted if these savanna areas are to sustain beef and mutton production as is currently the case.