High Intensity Burns Research Articles

Amplified predation after fire suppresses rodent populations in Australia’s tropical savannas

Context Changes in abundance following fire are commonly reported for vertebrate species, but the mechanisms causing these changes are rarely tested. Currently, many species of small mammals are declining in the savannas of northern Australia. These declines have been linked to intense and frequent fires in the late dry season; however, why such fires cause declines of small mammals is unknown. Aims We aimed to discover the mechanisms causing decline in abundance of two species of small mammals, the pale field rat, Rattus tunneyi, and the western chestnut mouse, Pseudomys nanus, in response to fire. Candidate mechanisms were (1) direct mortality because of fire itself, (2) mortality after fire because of removal of food by fire, (3) reduced reproductive success, (4) emigration, and (5) increased mortality because of predation following fire. Methods We used live trapping to monitor populations of these two species under the following three experimental fire treatments: high-intensity fire that removed all ground vegetation, low-intensity fire that produced a patchy burn, and an unburnt control. We also radio-tracked 38 R. tunneyi individuals to discover the fates of individual animals. Key results Abundance of both species declined after fire, and especially following the high-intensity burn. There was no support for any of the first four mechanisms of population decline, but mortality owing to predation increased after fire. This was related to loss of ground cover (which was greater in the high-intensity fire treatment), which evidently left animals exposed to predators. Also, local activity of two predators, feral cats and dingoes, increased after the burns, and we found direct evidence of predation by feral cats and snakes. Conclusions Fire in the northern savannas has little direct effect on populations of these small mammals, but it causes declines by amplifying the impacts of predators. These effects are most severe for high-intensity burns that remove a high proportion of vegetation cover. Implications To prevent further declines in northern Australia, fire should be managed in ways that limit the effects of increased predation. This could be achieved by setting cool fires that produce patchy burns, avoiding hot fires, and minimising the total area burnt.

Wildland fire management and air quality in the southern Sierra Nevada: Using the Lion Fire as a case study with a multi-year perspective on PM2.5 impacts and fire policy

Management of fire is an important and controversial policy issue. Active fire suppression has led to a backlog of fuels, limited the ecological benefits of fire, and reduced short-term smoke impacts likely delaying these emissions to future generations over a larger spatial extent. Smoke impacts can be expected to increase as fire size and intensity increase and the fuel backlog is consumed; whether through reintroduction of fire under desirable conditions or through stand replacing fire. Land Management Agencies would like to increase the use of naturally ignited fires to burn during favorable conditions as a way to reduce catastrophic fires. This study provides information about the levels of air quality impacts expected from these types of fires and discusses some of the policy controversies of managed fire that propagate inconsistencies between agencies and enter the public discourse. The Lion Fire, a primarily low intensity 8,370 ha fire that was extensively monitored for Particulate Matter less than 2.5 microns (PM2.5), is used to quantify impacts to air quality. PM2.5 monitoring sites are used to assess exposure, public health impacts, and subsequently quantify annual air quality during a year with a fire that is within the historic normal fire size and intensity for this area. Ground level PM2.5 impacts were found to be localized with 99% of the hourly Air Quality Index readings in the moderate or good category for the sites impacted by the fire. PM2.5 concentrations at sites nearest the fire were below annual federal air quality standards for PM2.5 with annual 98th percentile at the most impacted sites (Johnsondale, Kernville, and Camp Nelson) of 35.0, 34.0, and 28.0 μg m–3 respectively. Smoke impacts to PM2.5 concentrations were not found to reach the populated Central Valley. The findings suggest that this type of fire can be implemented with minimal public health impacts thus allowing an opportunity for air and fire managers to alter policy to allow additional burning in an area with severe anthropogenic air pollution and where frequent widespread fire is both beneficial and inevitable. The more extensive air quality impacts documented with large high intensity fire may be averted by embracing the use of fire to prevent unwanted high intensity burns. A widespread increase in the use of fire for ecological benefit may provide the resiliency needed in Sierra Nevada forests as well as be the most beneficial to public health through the reduction of single dose exposure to smoke and limiting impacts spatially.

Accessing Hunter-Gatherer site structures using Fourier transform infrared spectroscopy: applications at a Taltheilei settlement in the Canadian Sub-Arctic

The results of Fourier transform infrared spectroscopy on soils and caribou bone from a Taltheilei culture settlement in northern Canada contribute to developing micro-archaeological approaches suitable for locating and characterizing hearth and midden features on hunter-gatherer sites. A weak yet pervasive signal for montgomeryite was developed from the diagenesis of dispersed ash and caribou processing residues. Disordered calcite, carbonate hydroxylapatite, charcoal, and burned bone in two pit-house hearth deposits indicate that both wood and bone were used for fuel. Crystallinity indices and carbonate/phosphate ratios for bone indicate high intensity burning. These data, in tandem with the presence of semi-subterranean dwellings, demonstrate that this particular tundra-based encampment was occupied during cold seasons, a type of settlement behaviour previously unrecognized in the Taltheilei archaeological record. Our results confirm that Fourier transform infrared spectroscopy is an accessible, rapid, and cost effective means of discovering micro-archaeological evidence valuable for reconstructing hunter-gatherer site structures.

Why are aggregates destroyed in low intensity fire?

Soil structure is often severely affected during high intensity burning, while low intensity prescribed burning has often been thought to have a low or neutral effect on soil aggregation. In this issue of Plant and Soil, (Albalasmeh et al. 2012) report a novel mechanism of aggregate disruption during low intensity burning that may explain some contradictory results reported in previous studies. Albalasmeh et al. (2012) suggest that during rapid heating of moist soil aggregates, intra-aggregate water is vaporized and the increased pressure causes rupture of the internal bonds and leads to aggregate breakdown. This mechanism can be compared to the aggregate breakdown due to slaking, when dry aggregates are suddenly wetted or submerged in water. Identification of the reasons for the aggregate disruption at low temperatures is important for choosing optimal soil and weather conditions for prescribed fires.

Burning outcomes following aggregated retention harvesting in old-growth wet eucalypt forests

In Tasmania, Australia, aggregated retention (ARN1Abbreviations: ARN, aggregated retention; CBS, clearfell, burn and sow.1) is being implemented as an alternative to clearfelling in old-growth wet eucalypt forests. These forests have traditionally been regenerated using a high-intensity burn and aerial sowing, but the use of more complex harvesting designs makes conventional high-intensity burning difficult. In 2007, a new burning method (‘slow burning’) was developed specifically for ARN coupes. This paper compares site preparation, burning weather conditions and burning outcomes in ARN and conventional clearfell, burn and sow (CBS) coupes burnt from 2007 to 2010. ARN coupes had higher perimeter-to-area ratios than paired CBS coupes, and 8% more of the harvested area was affected by firebreaks. Although there was less burnt seedbed and more compacted seedbed in ARN coupes compared to clearfelled coupes, mean levels of receptive seedbed were adequate and are unlikely to limit regeneration success. Burn impact on unharvested forest was greater in ARN coupes, due largely to burning in the retained aggregates. Despite this, only 11% of aggregate area was burnt overall, and the current guidelines for aggregate size (most >1ha) appear sufficient to keep burn impact within acceptable thresholds. Firebreaks affected from 4–32% of the harvested area in the coupes measured in this study, and were 10m wide on average, twice the required width. To reduce soil disturbance and potential impacts on regeneration, firebreaks should be established only where absolutely necessary, and firebreak widths should be minimised wherever possible.

Early impacts of harvesting and burning disturbances on vegetation communities in the Warra silvicultural systems trial, Tasmania, Australia

Impacts on the understorey vegetation of a range of silvicultural alternatives to clearfelling in lowland Eucalyptus obliqua wet forest were studied over a decade in the Warra silvicultural systems trial in southern Tasmania. The treatments were clearfell with understorey islands, patchfell, stripfell, dispersed retention, aggregated retention, and single-tree/small-group selection. High intensity burning, low intensity burning and no burning were variously applied as part of these treatments. Three understorey types were studied, including one wet sclerophyll community and two rainforest communities. Wherever burning occurred across the research trial, the regenerating vegetation was floristically wet sclerophyll with an incipient composition consistent with that of the pre-harvest wet sclerophyll community. Sites previously occupied by rainforest understoreys retained occasional rainforest elements, but the regeneration was overwhelmingly sclerophyll in nature. There were no consistent differences in the floristic composition of the regenerating vegetation, after burning or harvesting disturbance, that could be attributed to the silvicultural system. However, field observations and the results of a related, subsequent study suggest that, in designing silvicultural trials similar to the present one, close attention should be paid to the size of quadrats in relation to the level at which disturbance impacts are operating. The response of the vegetation at edges created by the treatments, and in the undisturbed forest beyond, supports the finding that edge effects on the vascular flora extend for less than 10 m into the undisturbed forest.

Spatial heterogeneity of understory vegetation and soil in an Alaskan upland boreal forest fire chronosequence

In this study we characterized spatial heterogeneity of soil carbon and nitrogen pools, soil moisture, and soil pH of the first 15 cm of the soil profile; depth of the organic horizon; forest floor covers; and understory vegetation abundances in three sites (1999, 1987 and 1920 wildfires) of a boreal forest chronosequence of interior Alaska. We also investigated the cross-dependence between understory vegetation distribution and soil characteristics. Our results showed higher microbial respiration rates and microbial biomass in the oldest site and greater net N mineralization rates in the mid-successional site. Although spatial heterogeneity was absent at the scale studied for the majority of soil variables (60%), understory vegetation abundances and forest floor cover, spatial heterogeneity decreased with time after fire for the depth of organic horizon, soil microbial biomass, N mineralization rates and feathermoss cover. Our results also showed that increasing time after fire decreased the number of correlations between understory vegetation and soil characteristics while it increased between forest floor covers and soil characteristics. Overall, our study suggest that fire initially creates a patchy mosaic of forest floor cover, from fire hot spots, where high intensity burning exposes mineral soil, to practically unburned areas with intact mosses and lichens. As time since fire passes, forest floor cover and soil characteristics tend to become more uniform as understory species fill in severely burned areas.

Predicting the post-fire establishment and persistence of an invasive tree species across a complex landscape

The reintroduction of pre-European fire regimes has allowed the entry of many invasive plant species into fire-dependant ecosystems of North America. However, the environmental factors that favor the post-fire establishment of these species across complex landscapes are not well understood and the initial establishment of invasive species does not necessarily result in long-term persistence. To evaluate the post-fire establishment and persistence of disturbance-dependent invasive plants, we studied the invasion of Paulownia tomentosa (princess tree, an early-successional species introduced from Asia) across three burns in the southern Appalachian Mountains. Based upon classification tree analysis, the presence/absence of P. tomentosa 2 years after burning was most strongly related to the cover of residual vegetation, topographic shading, and moisture availability. Spatial application of classification tree models to repeated survey data showed that P. tomentosa established across a wide range of microsites 2 years after burning. However, predicted habitat for P. tomentosa decreased by 63% 4 years after fire and by 73% 6 years after fire. Following its initial widespread establishment, P. tomentosa only persisted on xeric and exposed topographic positions that experienced high intensity burning. However, the sites where it persisted include rare community types that contain two endangered plant species that depend upon fire for successful reproduction. The control of P. tomentosa on these ecologically important sites may require special attention from land managers.

An examination of stocking and early growth in the Warra silvicultural systems trial confirms the importance of a burnt seedbed for vigorous regeneration in Eucalyptus obliqua forest

Clearfelling of wet eucalypt forest followed by high intensity burning and aerial sowing, a silvicultural system designed to mimic the natural dynamic of sporadic regeneration following cataclysmic disturbance, has attracted criticism for not maintaining the structural diversity that is associated with natural disturbance. A silvicultural systems trial was established at the Warra Long-Term Ecological Research site in southern Tasmania to explore alternatives to clearfelling in tall wet eucalypt forest. Stocking, density and growth of the seedling regeneration were monitored for up to 3 years after harvesting and regeneration treatments were applied from 1998 to 2007. The treatments were clearfell with understorey islands, a patchfell, stripfell, dispersed retention, aggregated retention, and single-tree/small-group selection. High intensity burning, low intensity burning and no burning were variously applied as part of these treatments. The nature of the seedbed in each coupe was related to the harvesting and regeneration treatment. Where high intensity burns were applied there was a higher proportion of burnt seedbed available than in coupes where low intensity burns were applied. The highest seedling densities and fastest early seedling growth rates occurred on the hottest burnt seedbeds. The lowest seedling densities occurred on unburnt and undisturbed seedbeds and the slowest early growth rates occurred on unburnt and compacted seedbeds. Treatments that created the most burnt seedbed had the highest seedling densities and the fastest seedling growth. Aggregated retention is considered the most promising alternative to clearfelling. Because high intensity burns as applied to clearfell burn and sow coupes cannot be conducted in aggregated retention coupes as they would probably burn the aggregates, the lower proportion of burnt seedbed will, on average, result in lower seedling density and growth, and may compromise longer term productivity compared to clearfelled and high intensity-burnt coupes. If aggregated retention is to be successfully applied, as measured by the density and height growth of the regeneration, finding ways of successfully and consistently burning such coupes post-harvesting will be essential.

Short-term response of reptiles and amphibians to prescribed fire and mechanical fuel reduction in a southern Appalachian upland hardwood forest

We compared the effects of three fuel reduction techniques and a control on the relative abundance and richness of reptiles and amphibians using drift fence arrays with pitfall and funnel traps. Three replicate blocks were established at the Green River Game Land, Polk County, North Carolina. Each replicate block contained four experimental units that were each approximately 14 ha in size. Treatments were prescribed burn (B); mechanical understory reduction (M); mechanical + burn (MB); and controls (C). Mechanical treatments were conducted in winter 2001–2002, and prescribed burns in March 2003. Hot fires in MB killed about 25% of the trees, increasing canopy openness relative to controls. Leaf litter depth was reduced in B and MB after burning, but increased in M due to the addition of dead leaves during understory felling. The pre-treatment trapping period was short (15 August–10 October 2001) but established a baseline for post-treatment comparison. Post-treatment (2002–2004), traps were open nearly continuously May–September. We captured a total of 1308 species of 13 amphibians, and 335 reptiles of 13 species. The relative abundance of total salamanders, common salamander species, and total amphibians was not changed by the fuel reduction treatments. Total frogs and toads (anurans) and Bufo americanus were most abundant in B and MB; however, the proximity of breeding sites likely affected our results. Total reptile abundance and Sceloporus undulatus abundance were highest in MB after burning, but differed significantly only from B. Mean lizard abundance in MB was highest in 2004 and higher than in other treatments, but differences were not statistically significant. Our results indicate that a single application of the fuel reduction methods studied will not negatively affect amphibian or reptile abundance or diversity in southern Appalachian upland hardwood forest. Our study further suggests that high-intensity burning with heavy tree-kill, as in MB, can be used as a management tool to increase reptile abundance – particularly lizards – with no negative impact on amphibians, at least in the short-term.

Changes in sediment loads and discharge from small mountain catchments following wildfire in south eastern Australia

Summary A severe wildfire burnt over 1 million ha of forested land in southeastern Australia in early 2003. Included in the burnt area were two 136 and 244 ha hydrologic research catchments in the East Kiewa valley that had been decommissioned following a 10 year study, and an adjacent larger (10,050 ha) gauged catchment, the West Kiewa River. The three catchments were re-instrumented to measure discharge and suspended sediment fluxes at 15 min timesteps, with additional measurement of bedload at the East Kiewa sites. Analysis of annual rainfall–discharge relationships and of flow duration curves for the first 2 post-fire water years indicated annual flow increases of around 65–75% for Slippery Rock Creek in both post-fire water years and 40% and 76–94% for Springs Creek in 2003–2004 and 2004–2005, respectively. The flow impacts on the less severely burnt West Kiewa River were far more subdued, and did not exceed pre-fire variability in annual flows. Flow duration curve analysis did not indicate changed runoff generating processes at the daily timescale, with the curves shifting upward uniformly over the flow regime. Total sediment exports increased by factors of 8–9 (up to 2.96 t ha−1 yr−1) from the East Kiewa catchments in year 1 after the fire, diminishing to a 2–4-fold increase in year 2. Flow increases accounted for much of the year 2 exports as suspended sediment concentrations decreased toward pre-fire levels. Post-fire suspended load exports from the larger West Kiewa catchment were much lower per unit area, probably reflecting the smaller area of high intensity burn, less intensive burning of riparian areas and possible scale effects. The results were observed under near-average rainfall conditions, with the exception of one short duration high intensity storm that produced almost 50% of the combined sediment loads from the East Kiewa catchments.

Managing forests infested by spruce beetles in south-central Alaska: Effects on nitrogen availability, understory biomass, and spruce regeneration

In Alaska, an outbreak of spruce beetles ( Dendroctonus rufipennis) recently infested over one million hectares of spruce ( Picea spp.) forest. As a result, land management agencies have applied different treatments to infested forests to minimize fire hazard and economic loss and facilitate forest regeneration. In this study we investigated the effects of high-intensity burning, whole-tree harvest, whole-tree harvest with nitrogen (N) fertilization, and conventional harvest of beetle-killed stands 4 years after treatment, as well as clear-cut salvage harvest 6 years after treatment. We measured available soil ammonium and nitrate and estimated N loss from leaching using in situ cation and anion resin exchange capsules. We also assessed spruce regeneration and responses of understory plant species. Availability and losses of N did not differ among any of the management treatments. Even a substantial application of N fertilizer had no effect on N availability. Spruce regeneration significantly increased after high-intensity prescribed burning, with the number of seedlings averaging 8.9 m −2 in burn plots, as compared to 0.1 m −2 in plots that did not receive treatment. Biomass of the pervasive grass bluejoint ( Calamagrostis canadensis) was significantly reduced by burning, with burn plots having 9.5% of the C. canadensis biomass of plots that did not receive treatment. N fertilization doubled C. canadensis biomass, suggesting that N fertilization without accompanying measures to control C. canadensis is the least viable method for promoting rapid spruce regeneration.

Predicted effects of prescribed burning and harvesting on forest recovery and sustainability in southwest Georgia, USA

A model-based analysis of the effect of prescribed burning and forest thinning or clear-cutting on stand recovery and sustainability was conducted at Fort Benning, GA, in the southeastern USA. Two experiments were performed with the model. In the first experiment, forest recovery from degraded soils was predicted for 100 years with or without prescribed burning. In the second experiment simulations began with 100 years of predicted stand growth, then forest sustainability was predicted for an additional 100 years under different combinations of prescribed burning and forest harvesting. Three levels of fire intensity (low, medium, and high), that corresponded to 17%, 33%, and 50% consumption of the forest floor C stock by fire, were evaluated at 1-, 2-, and 3-year fire return intervals. Relative to the control (no fire), prescribed burning with a 2- or 3-year return interval caused only a small reduction in predicted steady state soil C stocks (⩽25%) and had no effect on steady state tree wood biomass, regardless of fire intensity. Annual high intensity burns did adversely impact forest recovery and sustainability (after harvesting) on less sandy soils, but not on more sandy soils that had greater N availability. Higher intensity and frequency of ground fires increased the chance that tree biomass would not return to pre-harvest levels. Soil N limitation was indicated as the cause of unsustainable forests when prescribed burns were too frequent or too intense to permit stand recovery.

Differential responses of Bolivian timber species to prescribed fire and other gap treatments

We followed the establishment and growth response of 13 commercial tree species to canopy opening, above-ground biomass removal, and experimental burns of low and high intensities in a lowland dry forest in Bolivia. Three patterns of response to treatments were observed among the most abundant commercial tree species. (1) Shade-intolerant species regenerated mostly from seed and had the highest survival and growth rates following high-intensity burns. (2) Shade-tolerant species were abundant in gap control and plant removal treatments. Treatments had little effect on the height growth of these species. (3) Individuals of root sprouting species were most abundant following plant removal and low-intensity burn treatments. Treatments had little effect on the height growth of these species. The wide variation in species’ responses to gap treatments found in this study not only reinforces the concept that species are distributed along a continuum of shade-tolerance levels, but that other aspects of species’ biology, such as seed dispersal type or sprouting behavior, further differentiate regeneration strategies. The variety of regeneration strategies found among the species at this forest site will require a flexible management scheme that mixes more intensive silvicultural treatments such as prescribed burning with less intensive treatments.

Prescribed under-canopy burning inPinus patulaplantations of the Mpumalanga highveld: The effects of fire on tree growth

The effect of controlled undercanopy burning on tree growth has been studied under 16-year-old Pinus patula trees in Mpumalanga. Three fire intensity treatments and a control “no-burn” treatment, were applied to 1 ha plots. Average fuel depth was 42cm with a mean fuel load of 14.3 tons/ha. Fuel load was reduced by 15%, 30% and 60% in the three intensity burns. Fire intensity parameters were calculated using the BEHAVE fire behaviour prediction and fuel modeling system. Fireline intensity was predicted to be 134, 277 and 761kW/m for low, medium and high intensity experimental burns, respectively. Bark scorch height was found to be significantly greater in the plots under the high intensity burn treatment than in the low and medium intensity treatments. Most trees experienced scorch damage to between 0 and 40% of the crown volume. There was a significant negative effect on tree growth after a period of 36 months in the high intensity burn treatment. A low level (3 dead trees in sample of 360) of mortality occurred. This study showed clearly that undercanopy burning, at a low intensity, could significantly reduce fuel loads without resulting in decreased tree growth. It is recommended that this approach should be explored at an operational scale. Keywords : Pinus patula , prescribed burning, growth, fire intensity Southern African Forestry Journal No. 204 2005: 3-13

Commercial tree regeneration 6 years after high-intensity burns in a seasonally dry forest in Bolivia

The effects of three site-preparation treatments (high-intensity burn, low-intensity burn, and mechanical cleaning with machetes and chainsaws) on the regeneration of commercial tree species, composition and structure of competing vegetation, and soil chemical and structural properties were evaluated in a seasonally dry forest in southeast Bolivia. Six years after controlled burns, the high-intensity burn treatment had the both the highest density and the tallest individuals of shade-intolerant commercial tree species. Competing vegetation was also less dominant in the high-intensity burn treatment relative to other treatments. However, high-intensity burns were not beneficial for commercial tree species with shade-tolerant or intermediate regeneration. Soil analyses revealed that certain changes in soil texture and soil chemistry (e.g., Ca and Mg concentrations and cation exchange capacity) caused by high-intensity burns persisted 6 years after the fires. These findings confirm that this suite of shade-intolerant commercial species requires very intense disturbances for their regeneration. However, several ecological, economic, and social barriers currently preclude the management-scale application of prescribed fire in Bolivia. More research is needed on cost-effective treatments to improve regeneration.

Does clearfell, burn and sow silviculture mimic the effect of wildfire? A field study and review using litter beetles

The ecological effects of clearfell harvesting followed by high intensity burning are sometimes thought to mimic wildfire, the major natural disturbance regime in Tasmanian wet forests. We investigated whether the litter-inhabiting beetle populations in logged and burnt regeneration forest resembled those in forest regenerating following natural wildfire. Pitfall trapping and habitat assessment were conducted at three pairs of adjacent 33-year-old logging and wildfire regeneration sites. In total, 6128 beetles were collected, representing 179 morphospecies in 30 families. The beetle assemblages in logging and wildfire treatments could not be distinguished. However, beetle populations did differ subtly between sites. One Aleocharinae (Staphylinidae) morphospecies and one Carabidae species were more abundant at one of the three site pairs. Multivariate analyses of common species indicated that the litter beetle assemblages differed significantly between sites, and this was partially related to their degree of geographical separation. Environmental factors considered indicative of logging impacts did not differ between wildfire and logging regeneration treatments. Temporal and landscape scale differences between logging and the natural disturbance regime and changes to logging practices since these study sites were harvested may have negative impacts on litter beetles in the future. Changes to current harvesting practices are recommended to better mimic the natural disturbance regime and thus improve conservation of forest biodiversity.

Responses to mechanical wounding and fire in tree species characteristic of seasonally dry tropical forest of Bolivia

Short-term responses to stem wounding were measured over a 60-day period on six tree species found in seasonally dry tropical forest in Bolivia. Three types of wounds were inflicted to simulate mechanical bark damage and bark damage caused by low- and high-intensity fires. Extent of wood discoloration associated with wounding varied with wound type and severity, with high-intensity burns associated with the greatest amount of discoloration, low-intensity burns the least, and mechanical wounds intermediate. Two thin-barked species produced a distinct ligno suberised boundary zone in the bark earlier than thicker barked species; however, all species produced a distinct wound periderm by 60 days postwounding. The amount of wood discoloration associated with wounding appeared to be independent of the thickness of the lignosuberized boundary zone. Bark thickness provided a useful measure of species' resistance to wood discoloration with low-intensity burns but not with high-intensity burns where bark occasionally separated from the cambium or developed cracks and fissures. Variability in short-term responses to wounding and other factors may result in differences in the composition and abundance of microorganisms that colonize the wounds, with implications for reductions in wood quality and decay development.

Confronting complexity: fire policy choices in South African savanna parks

Changes in ecological concepts and a new focus on biodiversity as a central objective have led to changes in fire policies in South African savanna parks. Prescribed burning using fixed fire intervals is being replaced by systems that promote more variable fire regimes and greater management flexibility. Three policy alternatives have been proposed for Kruger National Park: a lightning fire policy, patch mosaic burning, and burning based on ecological criteria. There is no agreement as yet on which policy to adopt. However there is growing consensus on the use of a management system using 'thresholds of potential concern' to evaluate the outcome of different policies. These thresholds have been established for numerous indicators, help focus monitoring activities, and guide managers on the need for active intervention. We discuss the applicability of the policy alternatives for preventing successional change from savanna to forest and promoting grazing lawns and their associated grazers. We conclude that none of the current policies is universally applicable. A prescriptive program of frequent, high intensity burns will be required in mesic savannas to prevent succession to forests. In arid savannas, fire regimes designed to promote variable fire frequencies and fire sizes would be preferred to maintain greater diversity of grassland swards and grazer communities. The lessons learned from fire policy debates in South African savannas are of wider relevance for managing conservation areas elsewhere.

Fire intensity, slopewash and bio‐transfer of sediment in eucalypt forest, Australia

AbstractSediment movement (slopewash and bio‐transfer), runoff, and organic matter movement (mainly leaf litter, ash and charcoal) were monitored on ten plots for a six‐month period following bushfires in eastern Australia in the 1990s. Plots were installed in areas which had experienced high, moderate and low intensity burns. Although between‐plot variability was high, slopewash and organic matter amounts were greatest on the intensely burnt areas, and progressively less on moderate and low intensity burns. In contrast, most leaf litter input from scorched leaf fall was derived from, and collected in, moderately burnt areas. Bio‐transfer of sediment (direct downslope surface movement produced by faunal activity) occurred mainly by ant mounding, and was more than ten times greater on moderately burnt areas than on plots having high or low intensity burns. Bio‐transfer accounted for approximately 36 per cent of total sediment collected, with this material being recorded least often and in smallest quantities on areas of high intensity burns. Bio‐transfer by ant mounding and animal scratchings contributed loose surface sediment for transport by overland flow, disproportionately increasing total sediment movement to plot aprons in areas of moderate intensity burns. Copyright © 2002 John Wiley & Sons, Ltd.