Short-term Effects Of Fire Research Articles

Is pre-commercial thinning compatible with carbon sequestration? A case study in a maritime pine stand in northwestern Spain

Fire is one of the greatest potential risks to loss of stored terrestrial C (Kashian et al., 2006; van der Werf et al., 2006; Wiedinmyer and Neff, 2007) and is a loss pathway that is difficult to quantify because of the high degree of spatial and temporal variation in fire emissions (Wiedinmyer and Neff, 2007). Pulsed emissions of CO2 during fires are assumed to be partly counterbalanced via the uptake of CO2 by regrowing vegetation in the decades following fire (Wiedinmyer and Neff, 2007). In forests of the Iberian Peninsula, where wildfire is a major and frequent perturbation, the post-fire recovery rate may be important in regional scale carbon storage because carbon lost in stand-replacing fires is often a significant component of regional carbon budgets (Kashian et al., 2006; Wiedinmyer and Neff, 2007). Short-term effects of fire will be important for the carbon balance in this century because the expected higher fire frequency (Ministerio de Medio Ambiente, 2005; Vega et al., 2009) will release large amounts of carbon through combustion, and increase the forested area with negative net ecosystem production (Litton et al., 2004; Kashian et al., 2006; van der Werf et al., 2006; Wiedinmyer and Neff, 2007). Moreover, depending on the forest type, the area burned by a stand-replacing fire may not recover its pre-fire C stock for decades (Wirth et al., 2002). In postfire regenerated stands, thinning and shrub removal may have a significant impact on the magnitude of net carbon fluxes, with conversion of the ecosystem from a sink to a source of CO2 in the short term (Misson et al., 2005; Hurteau et al., 2008; Hurteau and North, 2009). In this context, it is important to quantify the effects of thinning of heavily stocked fire-origin stands on carbon accumulation in trees. Available information on this topic is still Is pre-commercial thinning compatible with carbon sequestration? A case study in a maritime pine stand in northwestern Spain

Short-Term Effects of Fire and Fire-Surrogate Treatments on Avian Nest Survival: A National-Scale Analysis

We examined the initial response of avian nest success to mechanical thinning, prescribed fire, and thinning/ prescribed fire combination treatments, designed to reduce fuel loads, at study sites throughout the continental USA as part of the National Fire and Fire Surrogate (FFS) Project. We modeled the daily nest survival of ground-, shrub-, tree-, and snag-nesting bird species to test for effects of: (1) overall treatment (2) specific treatment category (i.e., burn, thin, thin/burn); (3) time since treatment; and (4) study site. Of the 7 species examined, only 2 had top models that included effects of the FFS treatments, the remainder had either constant survival rates, or rates that varied only by study site. The Eastern Towhee had top models that included effects of treatment and study site, while the Red-bellied Woodpecker had top models that included effects of treatment category, time since treatment, and study site. All estimates of treatment, treatment category, and study site were statistically weak with confidence intervals including zero. The lack of clear response patterns observed in this study is likely a consequence of the variability inherent across forest types and taxonomic groups we examined. Forest managers should use our results cautiously and also be encouraged to facilitate opportunities for studies of avian nest survival as a function of fire-surrogate treatments that are regional specific, encompass longer time frames and larger spatial scales.

Short-Term Effects of Fire on Breeding Birds in Southern Appalachian Upland Forests

Abstract We investigated how variation in fire severity (control or no fire; low, medium, and high severity fires) and interval (1–2 years vs. 3–6 years after fires) affected habitat and avian abundance, species diversity, richness, and evenness in the southern Appalachian Mountains. Fire severity and interval had significant implications for both habitat and avian communities. Species richness within 2 years of fires was on average 26% higher in areas receiving medium and high severity treatments than in unburned control units. Species diversity and species richness were markedly greater 3–6 years after fires within high severity treatments (12 and 44%, respectively), compared to unburned controls. Relative abundance and species evenness did not vary with fire severity or time since fire. The short-term effects of low severity fires, or high severity fires with short rotation periods (≤2 years) may have limited positive effects on avian communities. Facilitation of disturbance regimes including mid to hi...

Short-term effects of fire on soil and plant nutrients in palmetto flatwoods

Fire may have different effects on the relative availability of nitrogen (N) and phosphorus (P) because N volatilization occurs at lower temperatures than P volatilization, and fire-mediated changes in soil nutrient availability may affect foliar nutrient concentrations. We assessed the short-term effects of fire on soil and plant nutrients and 15N isotopic signatures in a palmetto flatwoods ecosystem in central Florida. Fire caused a short-term increase in extractable ammonium (NH4+) and phosphate (PO43-). The increase in PO43- was greater than the increase in NH4+, resulting in a decrease in the soil extractable N:P ratio shortly after fire. Similarly, foliar %P of the palmetto Serenoa repens (W. Bartram) Small increased more than foliar %N, resulting in a decrease in foliar N:P ratios shortly after fire. Soil δ15N and the difference between foliar and soil δ15N did not vary with time since fire; however, foliar δ15N of S. repens decreased after fire. Foliar %N of Quercus geminata Small and ericaceous shrubs was positively correlated with soil extractable inorganic N, while foliar %P of S. repens was positively correlated with soil extractable PO43-. Variation in foliar δ15N after fire and the positive relationship between soil and foliar nutrients suggest that both increased soil nutrient availability and reallocation of nutrients from below- to aboveground can be important for plant nutrient status after fire in palmetto flatwoods.

Long-term decrease of organic and inorganic nitrogen concentrations due to pine forest wildfire

• Growing concerns about fires and the increase of fire frequency and severity due to climate change have stimulated a large number of scientific papers about fire ecology. Most researchers have focused on the short-term effects of fire, and the knowledge about the long-term consequences of fires on ecosystem nutrient dynamics is still scarce. • Our aim was to improve the existing knowledge about the long-term effects of wildfires on forestlabile N concentrations. We hypothesized that fires may cause an initial decline in organic and inorganic N availability, and in the amount of microbial biomass-N; this should be followed by the recovery of pre-fire N concentrations on a long-term basis. We selected a fire chronosequence in Pinus canariensis forests on La Palma Island (Canary Islands, Spain). These forests are under low anthropogenic atmospheric deposition, and forest management is completely lacking; wildfires are therefore the only significant disturbance. Soil samples were collected during the winter and spring at 22 burned and unburned plots. • Fire produced a significant decrease in microbial biomass N, mineral N and dissolved organic N. Almost 20 y after fire, pre-fire levels of N concentrations had not recovered. • These results demonstrate that P. canariensis forest soils have a lower resilience against fire than expected. The magnitude of these observed changes suggests that pine forest wildfires may induce long-term (2 decades) changes in soil and in plant primary production. Mots-cles : azote organique dissous / azote labile / biomasse microbienne / azote mineral / Pinus canariensis / incendie

Short-Term Fire Effects on Small Mammal Populations and Vegetation of the Northern Chihuahuan Desert

Fire is an important ecological factor in semidesert grass-shrub community dynamics, but there is a lack of designed field experiments documenting effects on vegetation and small mammals. We document effects of June prescribed fire on vegetation and small mammals on 20, 25-ha study areas in the Northern Chihuahuan Desert of Southern New Mexico, USA one month and one year posttreatment. Canopy cover of shrubs and grasses recovered to 68 and 27% of the preburn canopy cover, respectively, after one year. Prescribed burns during June enhanced short-term forb production by reducing competition from grasses and shrubs. Thirty thousand trap-nights yielded 1744 captures of 766 individuals of 15 small mammal species. Burns did not affect small mammal species richness and species diversity. Relative abundance of Merriam's kangaroo rats (Dipodomys merriami) was 91% greater on burned sites than on control sites one year postburn. Silky pocket mouse (Perognathus flavus) relative abundance was 221% greater on burned sites one year postburn. Chihuahuan Desert pocket mice (Chaetodipus eremicus) responded negatively to the fire, with relative abundance 170% greater on control sites (). Burning produced short-term benefits for two heteromyids, Merriam's kangaroo rats and silky pocket mice.

Changes in net N mineralization rates and soil N and P pools in a pine forest wildfire chronosequence

The concern that climate change may increase fire frequency and intensity has recently heightened the interest in the effects of wildfires on ecosystem functioning. Although short-term fire effects on forest soils are well known, less information can be found on the long-term effects of wildfires on soil fertility. Our objective was to study the 17-year effect of wildfires on forest net mineralization rates and extractable inorganic nitrogen (N) and phosphorus (P) concentrations. We hypothesize that (1) burned forest stands should exhibit lower net mineralization rates than unburned ones; (2) these differences would be greatest during the growing season; (3) differences between soil variables might also be observed among plots from different years since the last fire; and (4) due to fire-resistant geochemical processes controlling P availability, this nutrient should recover faster than N. We used a wildfire chronosequence of natural and unmanaged Pinus canariensis forests in La Palma Island (Canary Islands). Soil samples were collected during winter and spring at 22 burned and unburned plots. We found significantly higher values for net N mineralization and extractable N pools in unburned plots. These differences were higher for the winter sampling date than for the spring sampling date. Unlike extractable N and N mineralization rates, extractable P levels of burned plots exhibited a gradual recovery over time after an initial decrease. These results demonstrate that P. canariensis forest soils showed low resilience after wildfires, especially for N, and that this disturbance might induce long-term changes in ecosystem functioning.

Short-term effects of experimental burning on soil nutrients in the Cantabrian heathlands

The aim of this study is to determine the short-term effects of fire on nitrogen and phosphorus soil concentration in heathland sites dominated by Calluna vulgaris in the Cantabrian Mountain range (NW Spain). Three C. vulgaris heathlands sites (San Isidro, Riopinos I and Riopinos II) were selected. In June 2005, one plot (20 m × 20 m) per site was subjected to an experimental fire and the other was used as a control. Immediately after the fire, ten ash samples and ten soil samples (at a depth of 5 cm) were collected and thoroughly mixed. Soil moisture, temperature, total N, NH 4 +, NO 3 −, total P, available P and pH were determined in each sample. The quantity of ashes deposited was 300 g/m 2, with a pH of 9, low N content but higher P concentrations. Significant differences in temperature and soil moisture were detected between the fire-treated and control plots. No significant differences for soil pH, total and available P, total N and NO 3 − concentration were found between the treatments. However, the concentration of ammoniacal-N indicated a significant increase 11 months post-fire and was produced by the changes in environmental soil conditions after the fire. Our results show that low intensity fires do not modify the concentration of N and P in the soil. However, post-fire conditions favour an increase in ammoniacal-N one year later.

Short-term effects of fire and fire surrogate treatments on foraging tree selection by cavity-nesting birds in dry forests of central Washington

Dry forests of Washington are becoming increasingly susceptible to broadscale stand replacement fire and insect and disease epidemics. In response, land managers implement fuel reduction strategies. These situations could potentially affect numerous wildlife species, including cavity-nesting birds. Much information exists on nesting requirements of cavity-nesters, while little information is available on their foraging requirements, or how changes to their habitat affect foraging. We examined short-term responses of cavity-nesting birds in dry conifer forests of Washington, to fuel reduction treatments in 2004 and 2005, as part of the National Fire–Fire Surrogate Project (FFS). Our objective was to determine if altering the forest stand through mechanical thinning or prescribed burning or a combination of the two would alter foraging tree selection. We used linear logistic regression and Akaike's Information Criteria (AIC) to model foraging tree selection and to analyze the effects of treatments on foraging tree selection. Model averaged parameter estimates suggested that cavity-nesting birds selected for large diameter trees and FFS treatments had a positive impact on foraging for nuthatches and woodpeckers. Birds were more likely to be observed foraging in treated stands and the positive relationship was strongest in stands that received a combination of thinning and burning treatments. Enhanced foraging conditions in the thin–burn treatment may have resulted from a more complete removal of small trees, while the prescribed burn was so low-intensity, it did not remove many small trees. Bird groups selected for trees at least 1.6 times as large in diameter in treated stands as compared to control stands. Our results indicate activities such as thinning and burning may best enhance foraging habitat for bark gleaning species as a whole. Our data suggests that some important treatment design considerations include the removal of small trees and the retention of large trees and snags (>40 cm dbh) that provide important foraging substrate and nesting habitat.

Short-term effects of fire on arthropods in Calluna-heathlands in NW Spain

Short-term effects of fire on arthropods in Calluna-heathlands in NW Spain

Short-term effects of fire on plant cover and soil conditions in two Austrocedrus chilensis (cypress) forests in Patagonia, Argentina

On analyse ici les effets du feu a court terme sur la couverture vegetale, la temperature (0, 5, 20, et 30 cm de profondeur) et l'humidite du sol (0-16, 20-36, et 40-56 cm de profondeur) dans deux peuplements de cypres en Patagonie, Argentine, au long de deux annees. Les peuplements (Trevelin = xerique; Bolson = messique) presentent trois traitements : non-brule (UN), partiellement brule (PB) et totalement brule (CB). A Trevelin, 4 et 6 ans apres le feu, la couverture du sous-bois inferieur augmenta (CB > PB > UN) tandis que celle du sous-bois superieur diminua (CB = PB CB > UN) a chaque profondeur et a chaque date. Dans les deux peuplements, l'humidite du sol a ete nettement plus haute pour les traitements brules. Tandis que la couverture vegetale pourrait avoir des effets de protection et que l'humidite du sol n'apparait pas comme etant limitative, les hautes temperatures du sol semblent etre restrictives pour l'etablissement des cypres a la suite du feu, notamment dans les sites xeriques.

Post-fire vegetative dynamics as drivers of microbial community structure and function in forest soils

Soil microorganisms have numerous functional roles in forest ecosystems, including: serving as sources and sinks of key nutrients and catalysts of nutrient transformations; acting as engineers and maintainers of soil structure; and forming mutualistic relationships with roots that improve plant fitness. Although both prescribed and wildland fires are common in temperate forests of North America, few studies have addressed the long-term influence of such disturbances on the soil microflora in these ecosystems. Fire alters the soil microbial community structure in the short-term primarily through heat-induced microbial mortality. Over the long-term, fire may modify soil communities by altering plant community composition via plant-induced changes in the soil environment. In this review, we summarize and synthesize the various studies that have assessed the effects of fire on forest soil microorganisms, emphasizing the mechanisms by which fire impacts these vital ecosystem engineers. The examples used in this paper are derived primarily from studies of ponderosa pine-dominated forests of the Inland West of the USA; these forests have some of the shortest historical fire-return intervals of any forest type, and thus the evolutionary role of fire in shaping these forests is likely the strongest. We argue that the short-term effects of fire on soil microflora and the processes they catalyze are transient, and suggest that more research be devoted to linking long-term plant community responses with those of the mutually dependent soil microflora.

Short-term effects of fire and forest thinning on truffle abundance and consumption byNeotamias speciosusin the Sierra Nevada of California

In many western North American forests, prescribed burning and mechanical thinning are widely used to reduce fuels and restore stand conditions after a century of fire suppression. Few studies have followed the relative impacts of these treatments on the production and consumption of truffles in forest ecosystems, particularly in the Sierra Nevada of California. Using a full-factorial completely randomized design, we examined the short-term impacts of prescribed burning (no burn and burn), mechanical thinning (no thin, light thin, and heavy thin), and combinations of these treatments on the production of truffles and their consumption by lodgepole chipmunks (Neotamias speciosus Merriam) in a mixed-conifer forest of the southern Sierra Nevada of California. Truffle frequency, biomass, and species richness were lower in thinned or burned plots than controls, as was the frequency and generic richness of truffles in the diet of N. speciosus. Truffle frequency, biomass, and species richness, and truffle consumption by N. speciosus were lower in heavily thinned and thinned and burned plots than in those exclusively burned. These results suggest that either thinning or burning can reduce short-term truffle production and consumption, and potentially the dispersal of ectomycorrhizal spores by small mammals. Moreover, truffles decreased with treatment intensity, suggesting heavy thinning and higher burn intensity, particularly when applied together, can significantly affect short-term truffle abundance and small mammal consumption.

Short-term effects of fire on soil nitrogen availability in Mediterranean grasslands and shrublands growing in old fields

In three different plant communities growing in Mediterranean old fields we studied the short-term changes in soil nitrogen availability that occur after the fire. Two of these communities were grasslands with great capacity of resprouting and contrasted N availability, one dominated by Brachypodium retusum, and the second one dominated by B. retusum and the N fixing shrub Genista scorpius. The third community was an obligate seeder community (shrubland) with low N availability and was dominated by Rosmarinus officinalis. We selected six plots for each type of vegetation and therefore performed 18 experimental fires. During fires we measured temperatures at the soil surface. Maximum temperature recorded during fire and time–temperature integral were used as indexes of fire severity. During the 6 months following fires we measured Net N mineralization and plant uptake by field incubations using the resin-core technique in paired burnt and control plots. Fire severity increased with plant biomass. In grasslands heating of the soil surface increased with plant biomass up to a limit of 1 kg m −2 of above-ground biomass. For high biomass a large proportion of heat released during fire was probably transmitted to the atmosphere or to the deeper soil horizons. The increase of soil mineral N was larger in fires of greater severity. Most mineral nitrogen released to the soil during fire was ammonia. Increases of ammonia post-fire depends on the temperatures measured on the soil surface while increases of the less volatile N form (nitrate) were related to the amount of burnt biomass and were highly dependent on the type of vegetation. The amount of nitrogen released to soil during fire represented a small proportion of the N mineralized during the 6 months following fire and thus the amount of nitrogen mineralized per unit of N released during fire was very different across the different types of vegetation. In grasslands fire induced changes in N mineralization decreased as fire severity increased. In contrast, in shrublands we observed the opposite trend. Differences in potentially mineralizable and in net mineralization N between unburnt grasslands and shrublands could account for this fact. Despite the depression in nitrification that we observed in grasslands between 40 and 80 days after the fire, high nitrate concentration in the soil during that period increased N leaching in burnt plots. No plant uptake was detected at that time. In grasslands the onset of plant uptake in burnt plots was delayed as compared to control. Cumulative changes in N did not depend on the burnt biomass in grassland communities, but it did in the seeder community. On the contrary, soil temperatures measured during fires related to changes in N observed in grasslands but not in the seeder community. It appears therefore, that post-fire N mineralization and leaching in grasslands may have been driven by the changes induced by heating the soil surface while in shrublands it may have been driven by the quantity of ash deposited on the soil surface.

Effects of an Intense Wildfire in a Mexican Oak-Pine Forest

Abstract An oak-pine forest burned by intense wildfire in April, 1996, and a companion unburned area were sampled 1 month and 1 yr postfire in La Michilía Biosphere Reserve, Durango, Mexico. Up to 90% of the trees were killed or top-killed in the burned area, but larger trees tended to survive, so basal area was only reduced by 66%. Top-killing was relatively higher among fire-susceptible oaks and lower among fire-resistant pines. However, oaks were strong resprouters both in the canopy and at the base of top-killed trees. Damage codes based on crown scorch and bole char were highly accurate when predicting that a tree would die but substantially overestimated survivors. Most tree regeneration was top-killed in the fire, but oak sprout density was 700% that of the unburned area by 1 yr postfire. Manzanita shrubs also resprouted vigorously. Herbaceous production and cover were lower after the first postfire growing season in the burned area than the unburned area. Woody fuels and forest floor depth were also reduced. Although short-term fire effects indicate that the forest ecosystem has moved closer toward a savanna condition, remnant seed trees and sprouting trees are expected to maintain forest cover. Future herbaceous production is likely to increase in response to overstory mortality. Quantification of fire effects is helpful for supporting short-term management decisions since oak-pine forests cover millions of hectares in northern Mexico. As a long-term management strategy, however, we suggest that restoring the frequent, low-intensity fire regime may be desirable for ecological and economic reasons. For. Sci. 46(1):52-61.

Short‐term effects of fire and competition on growth and plasticity of the yellow pitcher plant, Sarracenia alata (Sarraceniaceae)

Although recurrent fires are widely assumed to reduce competitive interference of plants of pine savannas, rarely has this assumption been tested explicitly. This 2-yr study reports on the interactive effects of fire and neighbors on short-term growth responses and plasticity in allocation patterns of a carnivorous plant, the yellow pitcher plant, Sarracenia alata. This species relies upon pitfall traps (pitchers) to attract and capture insects to obtain nutrients. Neighbors reduced the growth rate of individual ramet transplants (phytometers) in one but not both years of the study. The effect of neighbors on total (i.e., both above- and belowground) productivity of phytometers was not reduced by a winter fire. Neighbors had a greater effect on large plants than on small plants. Although fire did not affect the growth rate of phytometers in the short term, allocation patterns were greatly altered by both neighbors and fire. Allocation to pitchers increased at the expense of belowground organs following fire and in the absence of neighbors at the unburned site. Results of the current study suggest that adult pitcher plants may tolerate competition from neighboring vegetation by reducing allocation to costly pitchers during years without fire.

Short-term Effects of Fire on Soil Properties in Pinus densiflora Stands

This study was performed to investigate a short time change (one week after fire) on soil properties due to the fire inPinus densiflora Sieb. et Zucc stands of the Kosung area in Kangwon Province in Korea. Twenty seven sampling plots [16 burned (8 low intensity fire, 8 high intensity fire) and 11 unburned plots] were chosen. Mineral soil samples from three depths (0–5, 5–15, and 15–25 cm) under the forest floor were collected. Forest fire in the area affected soil chemical properties. Soil pH, total nitrogen, available phosphorus, potassium, calcium, and magnesium in the surface soil (0–5 cm) of the burned area compared with the unburned area increased, but there was no marked change in the subsurface soil (5–25 cm). Organic matter, total nitrogen, available phosphorus, and exchangeable cations in the surface soil were generally lower in the high than in the low intensity fire areas. This indicates that these nutrients on the high intensity fire may be volatilized. The results suggest that change in soil chemical properties in the area was restricted mainly to the surface soil and was different between the high and the low intensity fire types.

Measuring changes in landscape pattern from satellite images: Short-term effects of fire on spatial diversity

Satellite images can be considered a very convenient tool to measure landscape patterns since they provide a digital mosaic of the spatial arrangement of landcovers. This paper describes a practical application of several indices frequently used in landscape ecology to measure changes in the spatial mosaic as a result of large fires. These indices were computed from Normalized Difference Vegetation Index images of Landsat Thematic Mapper and Advanced Very High Resolution Radiometer data acquired before and after a large fire affecting the Mediterranean coast of Spain in 1991. The following landscape pattern indices were computed: standard deviation of spatial profiles, spatial auto-correlation, texture, number of patches, diversity, compactness and fractal dimension. To avoid potential bias in the results, these indices were calculated for several scenarios. The modification of the study area limits and spatial resolutions of the images, the measurement scale and the number of categories were tested in this study. All the indices computed showed a short-term increase in spatial homogeneity after the fire. Spatial auto-correlation increased, while texture, number of patches and mean diversity decreased. Compactness was reduced and fractal dimension increased, which also suggests that the fire created more elongated and complex forms. These effects were observed in both high- and low-resolution images.

Fire and topographic effects on decomposition rates and N dynamics of buried wood in tallgrass prairie

Decay rates and N dynamics of wood in soils of annually burned and unburned tallgrass prairie were measured over a 3-y period. Wooden dowels were placed at upland, mid-slope and lowland sites in two annually burned and two unburned watersheds. After 3 y, an average of only 15% of initial wood mass remained in burned watersheds, while 34% remained in unburned watersheds. Topographic position also significantly affected decay rates, with dowels decaying faster in the shallow-soil, upland sites and slope sites than in the deep-soil, lowland sites. This pattern is opposite of that generally observed for plant productivity (i.e. greater at lowland sites compared to uplands), and suggests that the controls of belowground decomposition and plant productivity are dissimilar. Dowels in both burned and unburned watersheds showed significant increases in N concentration over 3 y. Topographic position did not affect N concentration in the residual dowel material. Burn treatment, however, did affect N concentration, with dowels decomposing in burned watersheds having a higher average N concentration (0.5% after 3 y exposure) than dowels in unburned watersheds (0.43%). Relatively rapid decay rates resulted in net release of N, despite increased N concentration in the residual material. Faster net N release on the annually burned watershed was due to faster mass loss, since there were no differences in the rate of increase in N concentration per unit mass lost. Surface soil temperatures on burned prairie following spring fire usually exceed those on unburned prairie. However, average monthly summer soil temperatures (May–August) at a 10 cm depth in burned and unburned plots during the study were not statistically different and could not explain decay rate differences. Additionally, one of our unburned watersheds was accidentally burned during the first year of the study. Surprisingly, there were no significant differences in rates of wood decay between that watershed and the other unburned watershed. This suggests that indirect effects of annual fire (i.e. changes in the composition of soil flora and fauna) may override the short-term effects of fire (i.e. changes in soil temperature and moisture) on belowground decomposition in tallgrass prairie.

Fluctuations of rodent populations in response to rainfall and fire in a central Australian hummock grassland dominated by Plectrachne schinzii

Fluctuations in the composition and abundance of a small-mammal assemblage were studied in a hummock grassland dominated by Plectrachne schinzii at Watarrka National Park from 1988 to 1993. During this period an experiment was conducted to examine the short-term effects of fire on the rodents. We caught three species of rodent (Pseudomys hermannsburgensis, Notomys alexis and Mus domesticus). All species reached their greatest density in spring 1989 during an exceptionally wet period that extended from mid- 1988 to 1990. P. hermannsburgensis was the most abundant species and showed a 10-fold fluctuation in numbers over the sample period; N. alexis was the next most abundant species and showed a 5-fold increase but the population took longer to decline. M. domesticus was recorded only during the period of high rainfall. The number of M. domesticus was significantly less on the burnt plots than on the unburnt plots. Neither P. hermannsburgensis nor N. alexis showed significant differences between burnt and unburnt plots. This study illustrates the impact of rainfall events on the composition and density of small-mammal populations in spinifex grasslands in central Australia. Our results lead to the prediction that rodent populations will achieve densities in the order of 10 individuals ha-' or more in regions that experience three consecutive 6-month periods each with rainfall at 150% of the long-term average. This sequence apparently needs to follow a dry period where rainfall is no more than 85% of the long-term annual average for two consecutive 12-month periods.