Burned Patches Research Articles

The impact of antecedent fire area on burned area in southern California coastal ecosystems

Frequent wildfire disasters in southern California highlight the need for risk reduction strategies for the region, of which fuel reduction via prescribed burning is one option. However, there is no consensus about the effectiveness of prescribed fire in reducing the area of wildfire. Here, we use 29 years of historical fire mapping to quantify the relationship between annual wildfire area and antecedent fire area in predominantly shrub and grassland fuels in seven southern California counties, controlling for annual variation in weather patterns. This method has been used elsewhere to measure leverage: the reduction in wildfire area resulting from one unit of prescribed fire treatment. We found little evidence for a leverage effect (leverage = zero). Specifically our results showed no evidence that wildfire area was negatively influenced by previous fires, and only weak relationships with weather variables rainfall and Santa Ana wind occurrences, which were variables included to control for inter-annual variation. We conclude that this is because only 2% of the vegetation burns each year and so wildfires rarely encounter burned patches and chaparral shrublands can carry a fire within 1 or 2 years after previous fire. Prescribed burning is unlikely to have much influence on fire regimes in this area, though targeted treatment at the urban interface may be effective at providing defensible space for protecting assets. These results fit an emerging global model of fire leverage which position California at the bottom end of a continuum, with tropical savannas at the top (leverage = 1: direct replacement of wildfire by prescribed fire) and Australian eucalypt forests in the middle (leverage ∼ 0.25).

Effect of heterogeneity in burn severity on Mexican fox squirrels following the return of fire

After decades of suppression, fire has returned to many forested areas of the western United States. Understanding responses of wildlife species to fire is essential to native species conservation because contemporary fires may not have the same effects as historical fires. Recent fires in the Chiricahua Mountains of Arizona provided an opportunity to investigate effects of fire heterogeneity on habitat selection of a native wildlife species. We used radiotelemetry to determine home ranges of Mexican fox squirrels (Sciurus nayaritensis chiricahuae) within fire-influenced forests. We then applied resource-utilisation functions to evaluate associations of use intensity within home ranges to heterogeneity of burn severity at two spatial scales. Squirrels used areas with moderate levels of burn heterogeneity at large scale more than areas of low or high heterogeneity. Squirrels used small (<0.5 ha) or narrow (<120 m) severely burnt patches, but incorporated only edges of large patches into home ranges. Use of burnt forests by Mexican fox squirrels demonstrates the complexities of fire’s effects on wildlife. Our results contribute to an understanding of the role and effect of fire in forest ecosystems and implications for wildlife conservation.

Effects of Prescribed Burning and Mechanical Bush Clearing on Ungulate Space Use in an African Savannah

AbstractSavannah ecosystems exhibit constant transitions between states dominated by trees and states dominated by a combination of trees and grasses. Transitions between these states are driven by interactions between fire and herbivory. Bush encroachment (i.e. an increase in the density of woody vegetation) is often caused by anthropogenic disturbance such as climate change, invasive plants, fire control, and livestock practices. As bush encroachment alters the dynamics between fire and herbivory, it may have significant impact on savannah ecosystems. Two of the most common measures to mitigate bush encroachment are prescribed burning and bush clearing by mechanical treatments. We studied the effects of these two mitigation measures on ungulate space use in Lapalala Wilderness, a private conservation area within the Waterberg Biosphere Reserve, northern South Africa. Burning and bush clearing affected both the overall abundance and the species composition of ungulates at particular patches, but these effects were influenced by habitat and the type of bush clearing treatment. Contrary to our expectations, most species occurred less frequently in burnt patches, and also less frequently in patches that had been bush cleared. Our results suggest that combined effects of fire and bush clearing may have positive effects on grazers and negative effects on browsers. Although our sampling design did not allow us to fully resolve interactive effects of burning and bush clearing treatments across habitats, our study highlights the fact that there are complex ecological consequences of habitat alterations in savannah ecosystems.

Abrasion and burn patch synthesis for a rough and round shaped body part

Abrasion and burn patch synthesis for a rough and round shaped body part

Comparison of the Higher-Severity Fire Regime in Historical (A.D. 1800s) and Modern (A.D. 1984–2009) Montane Forests Across 624,156 ha of the Colorado Front Range

There are concerns that recent fires, following a century of land uses, are burning in dry western forests in an uncharacteristic manner with large patches of higher-severity fire affecting long-term ecosystem dynamics. For example, it is well documented that a mixed-severity fire regime predominated over montane forests of the Colorado Front Range. However, much about the historical fire regime is unknown including the size, frequency, and distribution of higher-severity fires. We addressed these questions utilizing data from the original land surveyors who recorded locations of burned timber along survey lines resulting in a coarse-scale transect of fire occurrence across 624,156 ha. We reconstructed higher-severity burn patches, size distribution, and fire rotation for the 1800s (A.D. 1809–1883) and compared to the characteristics of modern fires over a recent 26-year period (A.D. 1984–2009) taken from remotely sensed data. We found the historical geometric mean higher-severity patch was 170.9 ha and the maximum patch size was 8,331 ha; the higher-severity fire rotation was 248.7 years. In addition, we confirmed that higher-severity fires were historically less common at elevations below 2,200 m. Modern fires had a geometric mean patch size of 90.0 ha (patches >20 ha) and a maximum size of 5,183 ha; the higher-severity fire rotation was 431 years. The distributions of higher-severity patches were only 63.5% similar, as the historical distribution had fewer small patches and more large patches. The mixed-severity fire regime, historically, included a significant portion of higher-severity fire and large burn patches; modern fires appear to be within the range of historical variability.

Ecosystem Carbon Remains Low for Three Decades Following Fire and Constrains Soil CO2 Responses to Precipitation in Southwestern Ponderosa Pine Forests

The fire regime of ponderosa pine forests in the southwestern United States has shifted over the past century from historically frequent, low-intensity surface fires to infrequent, stand-replacing crown fires. We quantified plant and soil carbon (C) responses to this new fire regime and assessed interactions between changes in fire regime and changes in precipitation regime predicted by some climate models (specifically, an earlier monsoon rain season). We hypothesized that soil C pools and carbon dioxide (CO2) efflux rates would decrease initially following stand-replacing fires (due to low plant C inputs and the loss of the soil surficial organic (O) horizon), but then increase with time-after-fire (as plant C inputs increase). Water availability often limits soil biological activity in these forests, but we predicted that low soil C availability following fire would constrain soil CO2 efflux responses to precipitation. In a series of sites with histories of stand-replacing fires that burned between 2 and 34 years prior to sampling, burned patches had lower soil C pools and fluxes than adjacent unburned patches, but there was no evidence of a trend with time-after-fire. Burned forests had 7,500 g C m−2 less live plant biomass C (P < 0.001), 1,600 g C m−2 less soil total C (P < 0.001) and 90 g C m−2 less soil labile C (P < 0.001) than unburned forests. Lower soil labile C in burned patches was due to both a loss of O horizon mass with fire and lower labile C concentrations (g labile C kg−1 soil total C) in the mineral soil. During the annual drought that precedes summer monsoon rains, both burned and unburned patches had soil CO2 efflux rates ranging from 0.9 to 1.1 g CO2-C m−2 day−1. During the monsoon season, soil CO2 efflux in unburned patches increased to approximately 4.8 g CO2-C m−2 day−1 and rates in paired burned patches (3.4 g CO2-C m−2 day−1) were lower (P < 0.001). We also used field irrigation to experimentally create an earlier and longer monsoon season, and soil CO2 efflux rates at both burned and unburned plots increased initially in response to watering, but decreased to below control (plots without irrigation) rates within weeks. Watering did not significantly change cumulative growing season soil CO2 efflux, supporting our prediction that C availability constrains soil CO2 efflux responses to precipitation. This research advances our understanding of interactions among climate, fire, and C in southwestern forests, suggesting that climate-induced shifts toward more stand-replacing fires will decrease soil C for decades, such that a single fire can constrain future soil biological responses to precipitation regime changes.

The Influence of Fire on Rodent Abundance at the N'washitshumbe Enclosure Site, Kruger National Park, South Africa†

The relative population numbers of rodents were studied in nine habitats in and outside the N'washitshumbe enclosure site, Kruger National Park, before and after burning the firebreaks that surround the enclosure. Trap success was exceptionally high, and the field work is suspected to have coincided with a Mastomys population explosion. This genus dominated the small mammal communities before and after the burn, and never disappeared from the burnt patches. Its numbers also did not crash directly after the burn, as have been reported in most other studies. Movement from the burnt areas was observed, which may have had a significant impact on the numbers of rodents caught both inside the enclosure and in the more natural areas outside. Our study suggests that fire can be investigated as a tool to keep rodent densities down in areas where they are nuisance animals, especially when used in conjunction with models that forecast outbreaks of Mastomys. It also emphasizes the value of long-term studies informing management strategies for animal damage control and biodiversity and ecosystem conservation.

The influence of fire on rodent abundance at the N’washitshumbe enclosure site, Kruger National Park, South Africa

The relative population numbers of rodents were studied in nine habitats in and outside the N’washitshumbe enclosure site, Kruger National Park, before and after burning the firebreaks that surround the enclosure. Trap success was exceptionally high, and the field work is suspected to have coincided with a Mastomys population explosion. This genus dominated the small mammal communities before and after the burn, and never disappeared from the burnt patches. Its numbers also did not crash directly after the burn, as have been reported in most other studies. Movement from the burnt areas was observed, which may have had a significant impact on the numbers of rodents caught both inside the enclosure and in the more natural areas outside. Our study suggests that fire can be investigated as a tool to keep rodent densities down in areas where they are nuisance animals, especially when used in conjunction with models that forecast outbreaks of Mastomys. It also emphasizes the value of long-term studies informing management strategies for animal damage control and biodiversity and ecosystem conservation.

Landsat remote sensing approaches for monitoring long-term tree cover dynamics in semi-arid woodlands: Comparison of vegetation indices and spectral mixture analysis

Tree canopy cover is a major biophysical attribute of dryland ecosystems. Monitoring its long-term changes over large spatial extents is critical for understanding woody vegetation response to climate variability and global change. However, quantifying tree canopy cover with remotely sensed data remains a challenge for dryland ecosystems where vegetation is sparse and trees, shrubs, and grasses often co-exist at fine spatial scales. In this study, we developed a full SMA (spectral mixture analysis) method that regressed photosynthetic vegetation (PV), non-photosynthetic vegetation (NPV), and shade components of the SMA with dryland tree cover to monitor tree cover dynamics on a pinyon–juniper woodland landscape in Nevada, USA using Landsat TM data. We assessed 1) how well this method could estimate tree cover in both disturbed (chained and burned) and non-disturbed woodland patches and 2) how sensitive this method was to the confounding effects of climatic variations. The assessment was conducted in comparison with two other more commonly used methods that regressed NDVI or PV with tree cover. Our results showed that although PV performed better than NDVI, both methods overestimated tree canopy cover within recently disturbed woodland patches where the confounding effects of shrubs on greenness index were higher than in non-disturbed patches. The full SMA efficiently quantified variations within post-chaining patches in addition to non-disturbed patches, but overestimated tree cover within burned patches. Of the three methods tested, only full SMA showed promising capability for mitigating the confounding effects of interannual climatic variations on monitoring the woodland recovery process. Our results are generalizable to other semi-arid landscapes comprising a mosaic of small-statured trees intermixed with shrub steppe vegetation.

Burning for biodiversity or burning biodiversity? Prescribed burn vs. wildfire impacts on plants, lizards, and mammals

Fire is a large-scale phenomenon that affects ecosystems in many parts of the world. Wildfires can have highly destructive effects on habitats and the biota they support, and land managers frequently use prescribed burning to reduce the extent of wildfires and to benefit biodiversity. Underpinned by the predictions of the intermediate disturbance (IDH) and patch mosaic burn (PMBH) hypotheses, small-scale prescribed fires are thought to maximize biodiversity by creating heterogeneous mixes of early-, mid-, and late-successional habitats across the landscape. However, evidence supporting the positive effects of prescribed burning for biodiversity is mixed. We conducted a before–after control–impact study assessing the effect of prescribed burns and a wildfire on the alpha and beta diversity of plants, mammals, and lizards in hummock grassland in arid central Australia. Diversity was assessed for up to one year after each fire. Applying the IDH and PMBH we predicted that (1) small-scale, patchy, prescribed burns, by increasing habitat heterogeneity, would increase the alpha diversity and decrease the beta diversity of our study taxa in burned patches and (2) wildfire, by creating large, homogeneous burned patches, would reduce the alpha diversity of the study taxa in burned patches but promote beta diversity at the landscape level due to the differing assemblages expected to inhabit the burned and unburned areas. In accordance with our predictions, we found that fires of differing spatial scale and heterogeneity affected alpha and beta diversity in different ways, but also that the effects were taxon dependent. In contrast to our predictions, we found a surprisingly high level of congruence between alpha and beta diversity within taxa. Our results provide little support for the application of the intermediate disturbance and patch mosaic burn hypotheses and highlight instead the importance of stochastic events such as rainfall in influencing biodiversity over the immediate postfire period in arid environments. We suggest that prescribed fire is of little utility for the broadscale conservation of biodiversity due to taxon-dependent and unpredictable species responses, but that it may be useful in creating fire breaks that serve to protect the habitats of fire-sensitive species from the effects of broadscale wildfire.

Post-fire succession of collembolan communities in a northern hardwood forest

Forest fire intensity can impact the survival and recovery of soil fauna at local scales. We compared three contiguous sites differing in fire history to explore post-fire succession of collembolan (Hexapoda: Apterygota) communities in a maple-oak forest in southern Québec, Canada. We found a total of 22 collembolan species from 8 families and 17 genera at sites burned 0, ∼50, and ∼100 years in the past; samples from the most recent fire were collected in both lightly and intensely burned patches. Shifts in community composition were significantly related to time since a fire disturbance, burn intensity, and consumption of litter and organic soil horizons during recent fire events. Using a trait-based approach we demonstrate that species that remain following high-intensity fire are smaller-bodied than species in unburned areas. Additional character states (eyeless, unpigmented) suggest these species are endogeaic versus epigeaic, and that litter loss associated with high-intensity fire is the main driver of collembolan community compositional changes. We suggest that understanding Collembola community dynamics in response to a fire disturbance will require a better understanding of the spatial configuration of remnant habitat patches within heterogeneous burn sites, and patterns of collembolan dispersal and recolonization in three dimensional space.

Factors affecting moorland plant communities and component species in relation to prescribed burning

Summary1. The role of prescribed burning of vegetation to manage fire risk is controversial in a variety of situations worldwide. It is becoming more topical (i) as a result of potential global warming where the risk of wildfire might increase and (ii) because fire might affect the various ecosystem services provided in a different way. Where prescribed fire is used, ecologists need to know the impact on biodiversity (post‐fire recovery) and on provisioning and regulating services such as water collection and carbon sequestration. Here, we assess the effect of prescribed burning on plant community composition and its component species at the regional scale of the Peak District, where the moorland vegetation is severely degraded.2. Species cover (%) was assessed on five moors with respect to elapsed time since prescribed burning and vegetation height. A stratified random method was used to choose burn patches covering a range of ages since burning; quadrats were then sampled randomly within these patches over a 3‐year period. Detrended correspondence analysis was used to relate species composition to significant environmental variables, and variation partitioning was used to assess their relative contribution. Response curves were produced for the major species with respect to elapsed time since burning and vegetation height.3. The species ordination produced two gradients, (i) a continuum from a graminoid‐dominated vegetation to one dominated by Erica tetralix, Vaccinium myrtillus and Rubus chamaemorus and (ii) a post‐fire growth response of the dominant species, Calluna vulgaris. Species composition was more highly correlated with vegetation height than elapsed time since burning. The environmental variables explained 15·2% of the variation.4. Calluna vulgaris was the only species to show an increasing response after burning; all others showed an increase immediately after burning, but then they either decreased or showed a unimodal/skewed response. Most other species were restricted to vegetation &lt;40 cm height and 20–25 years after burning.5. Synthesis and applications. We found two major results of importance to policy makers and land managers: (i) that prescribed burning maintains species diversity in the immediate post‐burn phase, and (ii) as the vegetation ages and increases in height, most species disappear and the vegetation becomes dominated by C. vulgaris. From a policy perspective, prescribed burning (or some other disturbance) is needed to maintain burning and a no‐burn policy will result in a low‐diversity, C. vulgaris‐dominated vegetation. As vegetation height is the easiest measure for land managers to use in judging when to burn, we recommend moorland vegetation be burned before it reaches 25 cm in height to maintain the pre‐burn complement of plant species. If the rotation allows the vegetation to become much taller (&gt;40 cm), then most species will be lost and they will have to colonize after subsequent fires from the seedbank or from the surrounding area.

Ungulate preference for burned patches reveals strength of fire–grazing interaction

The interactions between fire and grazing are widespread throughout fire-dependent landscapes. The utilization of burned areas by grazing animals establishes the fire–grazing interaction, but the preference for recently burned areas relative to other influences (water, topography, etc.) is unknown. In this study, we determine the strength of the fire–grazing interaction by quantifying the influence of fire on ungulate site selection. We compare the preference for recently burned patches relative to the influence of other environmental factors that contribute to site selection; compare that preference between native and introduced ungulates; test relationships between area burned and herbivore preference; and determine forage quality and quantity as mechanisms of site selection. We used two large ungulate species at two grassland locations within the southern Great Plains, USA. At each location, spatially distinct patches were burned within larger areas through time, allowing animals to select among burned and unburned areas. Using fine scale ungulate location data, we estimated resource selection functions to examine environmental factors in site selection. Ungulates preferred recently burned areas and avoided areas with greater time since fire, regardless of the size of landscape, herbivore species, or proportion of area burned. Forage quality was inversely related to time since fire, while forage quantity was positively related. We show that fire is an important component of large ungulate behavior with a strong influence on site selection that drives the fire–grazing interaction. This interaction is an ecosystem process that supersedes fire and grazing as separate factors, shaping grassland landscapes. Inclusion of the fire–grazing interaction into ecological studies and conservation practices of fire-prone systems will aid in better understanding and managing these systems.

Aboveground Macroinvertebrate Diversity and Abundance in Sand Sagebrush Prairie Managed With the Use of Pyric Herbivory

Through pyric herbivory (i.e., fire-induced grazing patterns), native grasslands were historically a spatially heterogeneous environment. It is hypothesized that the mosaic of habitats created by pyric herbivory supports a more diverse invertebrate community compared to modern range management. Patch-burn management, a pyric herbivory technique, is an application of prescribed fire and grazing whereby the timing and location of the burned and grazed patches is varied, creating a diversity of habitat conditions. Although disturbance in sandsage (Artemisia filifolium Torr.) prairie historically included fire and grazing, fire disturbance has been nearly eradicated from this ecosystem in western Oklahoma. We compared patch-burn management to traditional management (i.e., moderate grazing with no fire) in sandsage prairie to evaluate the impact of these two management regimes on aboveground invertebrates. We sampled invertebrates at 44 points in each of 3 mo (May, June, and July) with the use of Dietrick vacuum sampling. Diversity, total abundance, and abundance of seven invertebrate orders (Araneae, Diptera, Hemiptera, Homoptera, Hymenoptera, Lepidoptera, and Orthoptera) were similar between patch-burn and traditional pastures. When examined on a patch level, five invertebrate orders were also similar between their respective time since burn patch and the traditional patches. Araneae and Coleoptera abundance were higher in traditional patches, and Hemiptera abundance was higher in current-year burn patches. Our results suggest a heterogeneity-based management scheme based on pyric herbivory does not negatively impact the overall invertebrate community and may benefit a wider variety of invertebrates by providing areas of varying levels of disturbance. In comparison, homogeneous landscapes such as those created by traditional management may only benefit segments of the invertebrate community that have habitat associations with moderately disturbed or undisturbed areas. Therefore, a disturbance regime involving the interaction of fire and grazing may be valuable for maintaining biodiversity and productivity within sandsage prairie ecosystems.

Fire history and management as determinant of patch selection by foraging herbivores in western Serengeti, Tanzania

Although the use of fire as a management tool has increased during the past decades in East African savannas, there is insufficient knowledge about herbivores' utilization of areas with different fire history. We therefore examined large mammal herbivores' preference for patches that differed in fire history to test whether herbivores would non-randomly select patches according to availability. Our study area was the East African Serengeti ecosystem. Animals were recorded along transects at monthly intervals from May 2001 to April 2006, and data on the burnt and non-burnt areas along transects were extracted from existing fire maps. The prediction was tested using chi-square goodness-of-fit test, and selection ratio as a preference index for patch types. Our results show that African buffalo persistently occurred in non-burnt patches, whereas browsers (Giraffe and Kirk's dik-dik) and mixed feeders (Grant's gazelle and impala) were often seen in non-burnt patches but also used burnt patches. Grazer species (Thompson's gazelle, topi, wildebeest and Burchell's zebra) favoured patches burnt in the current year compared to non-burnt patches. For all species together, patches burnt repeatedly were least selected compared to those that were burnt only once in 3 years. The outcome of this study suggests that annual burning of the same patches is not optimal for biodiversity maintenance and ecosystem functioning.

Mapping burned areas from Landsat TM/ETM+ data with a two-phase algorithm: Balancing omission and commission errors

Maps of burned area have been obtained from an automatic algorithm applied to a multitemporal series of Landsat TM/ETM+ images in two Mediterranean sites. The proposed algorithm is based on two phases: the first one intends to detect the more severely burned areas and minimize commission errors. The second phase improves burned patches delimitation using a hybrid contextual algorithm based on logistic regression analysis, and tries to minimize omission errors. The algorithm was calibrated using six study sites and it was validated for the whole territory of Portugal (89,000 km 2) and for Southern California (70,000 km 2). In the validation exercise, 65 TM/ETM+ scenes for Portugal and 35 for California were used, all from the 2003 fire season. A good agreement with the official burned area perimeters was shown, with kappa values close to 0.85 and low omission and commission errors (< 16.5%). The proposed algorithm could be operationally used for historical mapping of burned areas from Landsat images, as well as from future medium resolution sensors, providing they acquire images in two bands of the Short Wave Infrared (1.5–2.2 μm).

Fire severity and seed source influence lodgepole pine (Pinus contorta var. murrayana) regeneration in the southern cascades, Lassen volcanic National Park, California

Rocky Mountain lodgepole pine, (Pinus contorta var. latifolia) regenerates quickly after high severity fire because seeds from serotinous cones are released immediately post-fire. Sierra lodgepole pine (P. contorta var. murrayana) forests burn with variable intensity resulting in different levels of severity and because this variety of lodgepole pine does not have serotinous cones, little is known about what factors influence post-fire regeneration. This study quantifies tree regeneration in a low, moderate, and high severity burn patch in a Sierra lodgepole forest 24 years after fire. Regeneration was measured in ten plots in each severity type. In each plot, we quantified pre- and post-fire forest structure (basal area, density), counted and aged tree seedlings and saplings of all species, and measured distance to the nearest seed bearing tree. There was no difference in the density of seedlings and saplings among severity classes. Distance and direction to the nearest seed bearing lodgepole pine were the best predictors of lodgepole seedling and sapling density in high severity plots. In contrast to Rocky Mountain lodgepole pine, regeneration of Sierra lodgepole pine appears to rely on in-seeding from surviving trees in low or moderate severity burn patches or live trees next to high severity burn patches. Our data demonstrate that Sierra lodgepole pine follows stand development pathways hypothesized for non-serotinous stands of Rocky Mountain lodgepole pine.

Fine-scale Patchiness of Burns in a Mesic Eucalypt Savanna Differs with Fire Season and Sorghum Abundance

Canopy tree populations in the eucalypt savannas of northern Australia consistently show bottlenecks in the transition of young trees to the canopy layer. This is most likely due to frequent fires, where young trees are caught in a 'fire trap', suffer topkill and regenerate from underground tissues year after year. Little is known of fire behaviour at the spatial scale of individual juvenile trees. This paper presents field measurements of small-scale, 10 cm (microsite), burn patterns and patch sizes following set fires in the early dry season, late dry season, and wet season. Fire treatments were repeated in plots dominated by a native annual grass (Sorghum) and in others with little or none of this grass. Both late dry season and wet season fires left few or no microsites unburnt, regardless of understorey type. With early dry season fire, however, understorey type made a difference: 47% of the microsites were left unburnt in plots with little or no Sorghum compared to only 5% in Sorghum-dominated plots. Further, the early dry season fire pattern was very patchy, resulting in both large and small areas of burnt vegetation. In Sorghum-dominated plots, more than half the patches were greater or equal 10 m in size and only a third were < 3 m in size, whereas in plots with little or no Sorghum, 99% of burnt patches were < 10 m in size, and 41% were < 0.5 m in size. Thus, only a regime of early dry season fire with little or no Sorghum in the understorey creates potential 'windows of escape' for juvenile trees. The study has implications for management of savanna trees by fire.

Allometric scaling predicts preferences for burned patches in a guild of East African grazers

The high herbivore diversity in savanna systems has been attributed to the inherent spatial and temporal heterogeneity related to the quantity and quality of food resources. Allometric scaling predicts that smaller-bodied grazers rely on higher quality forage than larger-bodied grazers. We replicated burns at varying scales in an East African savanna and measured visitation by an entire guild of larger grazers ranging in size from hare to elephant. We found a strong negative relationship between burn preference and body mass with foregut fermenters preferring burns to a greater degree than hindgut fermenters. Burns with higher quality forage were preferred more than burns with lower quality forage by small-bodied grazers, while the opposite was true for large-bodied grazers. Our results represent some of the first experimental evidence demonstrating the importance of body size in predicting how large herbivores respond to fire-induced changes in plant quality and quantity.

Spatial and temporal variability of fires in relation to ecosystems, land tenure and rainfall in savannas of northern South America

AbstractFire is a predominant factor forcing global terrestrial biomass dynamics, with more than 30% of the land surface showing frequent burning, particularly in the tropics, where it mostly affects savannas ecosystems annually. Savannas, which cover approximately 269 million ha in South America, play a major role in the global carbon cycle. They are affected by increasing human pressures and global climate change. Using satellite data, this study quantifies vegetation burning in the Colombian Llanos savannas for the period 2000–2008, and analyzes how fire spatial pattern, frequency and extent vary with ecosystem type, land tenure and rainfall. On average 2.75±0.5 million ha (24±4.2%) of the savannas burn each year. Burned area is highly variable, with 3.4 million ha burned in 2002–2003 and &lt;1.9 million ha in 2005–2006. However, during the 2000–2008 period near of 3.7 million ha (33.5%) of the savannas never burned. Compared with the average 8–10 years of fire return time for the tropics and subtropics, these savannas burn twice as often. In addition, the average burn size figure for tropical and subtropical grassland savannas (with &lt;5% trees) of 7000 ha (median 5000 ha), is about seven times the average burned patch size we found in our study. Fires predominate in the well‐drained high plain savannas, lowest figures occurring along the Andean foothills, in forested areas and in pasture and croplands. Annual proportion burned varies with land tenure, being highest in National Parks. This study is the first complete regional map of fire disturbance in a South American savanna. This detailed regional data provides a unique opportunity for increasing the accuracy of global carbon emission calculations.