An analysis of fire frequency in tropical savannas of northern Australia, using a satellite-based fire atlas

2013 ◽  
Vol 22 (4) ◽  
pp. 479 ◽  
Author(s):  
Sofia L. J. Oliveira ◽  
M. A. Amaral Turkman ◽  
José M. C. Pereira
Keyword(s):  
Vegetation Type ◽  
Weibull Model ◽  
Fire Frequency ◽  
Northern Australia ◽  
Tropical Savannas ◽  
Probability Models ◽  
Burnt Area ◽  
Hazard Functions ◽  
Early Peak ◽  
Fire Intervals

We characterised fire frequency in western Arnhem Land, northern Australia (~24 000 km2), during the period 1990–2008, using available satellite burnt area maps. We estimated fire mortality and fire survival distributions, and hazard functions by vegetation type. We tested the performance of three probability models to study fire interval distributions: continuous and discrete Weibull, and discrete lognormal. Over the 19 year study period the mean annual area burnt was 36%. Median fire intervals ranged from 1 to 4 years. The discrete lognormal model best fitted the data, yielding non-monotonic hazard functions that peak at 2 to 3 years, making it more appropriate for fire frequency analysis in fire-prone tropical savannas than the more popular Weibull model. Open forest showed the highest flammability dependence on fuel age, and closed forest the lowest. The probability of burning as a function of time since last fire reaches an early peak and subsequently declines, due to fuel dynamics in these flammable savanna systems. Age-specific fire incidence is much higher for older vegetation patches than was suggested by earlier analysis of fire interval distributions. Fitting an appropriate model is important to characterize the observed fire frequency patterns, and make inferences for unobserved, longer fire intervals.

The short-term effects of an extensive and high-intensity fire on vertebrates in the tropical savannas of the central Kimberley, northern Australia

2008 ◽  
Vol 35 (1) ◽  
pp. 33 ◽  
Author(s):  
Sarah Legge ◽  
Stephen Murphy ◽  
Joanne Heathcote ◽  
Emma Flaxman ◽  
John Augusteyn ◽  
...  
Keyword(s):  
Species Richness ◽  
High Intensity ◽  
Fire Frequency ◽  
Northern Australia ◽  
Tropical Savannas ◽  
Short Term ◽  
Large Herbivores ◽  
Species Richness And Abundance ◽  
Species Specific ◽  
In Fire

We report the effects of an extensive (>7000 km2), high-intensity late-dry-season fire in the central Kimberley, Western Australia, on the species richness and abundance of mammals, reptiles and birds. Five weeks after the fire we surveyed 12 sites (six burnt, six unburnt); each pair of sites was closely matched for soil type and vegetation. The species richness and abundance of mammals and reptiles was greater at unburnt sites, especially for mammals (with a 4-fold difference in abundance between burnt and unburnt sites). There was an indication that reptiles immigrated into unburnt patches, but mammals did not. There were also species-specific responses to the fire: Rattus tunneyi and Pseudomys nanus were much more abundant in unburnt sites, whereas Pseudomys delicatulus was caught in equal numbers at burnt and unburnt sites. Diurnal reptiles were more abundant at unburnt sites, but nocturnal reptiles were equally common at burnt and unburnt sites. Avian species richness and overall abundance was similar between burnt and unburnt patches, although a few species showed preferences for one state or the other. The overall high trapping success for mammals (18% across all sites; 28% in unburnt patches) contrasts with the well documented mammal collapse in parts of northern Australia and seems paradoxical given that our study area has experienced the same increase in fire frequency and extent that is often blamed for species collapse. However, our study area has fewer pressures from other sources, including grazing by large herbivores, suggesting that the effects of these pressures, and their interaction with fire, may have been underestimated in previous studies.

scholarly journals Small mammals decline with increasing fire extent in northern Australia: evidence from long-term monitoring in Kakadu National Park

2015 ◽  
Vol 24 (5) ◽  
pp. 712 ◽  
Author(s):  
Michael J. Lawes ◽  
Brett P. Murphy ◽  
Alaric Fisher ◽  
John C. Z. Woinarski ◽  
Andrew C. Edwards ◽  
...  
Keyword(s):  
Small Mammals ◽  
National Park ◽  
Fire Regime ◽  
Fire Regimes ◽  
Fire Frequency ◽  
Small Scale ◽  
Northern Australia ◽  
Fire Size ◽  
Burnt Area ◽  
Fire Extent

Small mammal (<2 kg) numbers have declined dramatically in northern Australia in recent decades. Fire regimes, characterised by frequent, extensive, late-season wildfires, are implicated in this decline. Here, we compare the effect of fire extent, in conjunction with fire frequency, season and spatial heterogeneity (patchiness) of the burnt area, on mammal declines in Kakadu National Park over a recent decadal period. Fire extent – an index incorporating fire size and fire frequency – was the best predictor of mammal declines, and was superior to the proportion of the surrounding area burnt and fire patchiness. Point-based fire frequency, a commonly used index for characterising fire effects, was a weak predictor of declines. Small-scale burns affected small mammals least of all. Crucially, the most important aspects of fire regimes that are associated with declines are spatial ones; extensive fires (at scales larger than the home ranges of small mammals) are the most detrimental, indicating that small mammals may not easily escape the effects of large and less patchy fires. Notwithstanding considerable management effort, the current fire regime in this large conservation reserve is detrimental to the native mammal fauna, and more targeted management is required to reduce fire size.

How hot? How often? Getting the fire frequency and timing right for optimal management of woody cover and pasture composition in northern Australian grazed tropical savannas. Kidman Springs Fire Experiment 1993–2013

2014 ◽  
Vol 36 (4) ◽  
pp. 323 ◽  
Author(s):  
Robyn A. Cowley ◽  
Mark H. Hearnden ◽  
Karen E. Joyce ◽  
Miguel Tovar-Valencia ◽  
Trisha M. Cowley ◽  
...  
Keyword(s):  
Fire Regime ◽  
Vegetation Type ◽  
Fire Frequency ◽  
Perennial Grasses ◽  
Tropical Savannas ◽  
Heteropogon Contortus ◽  
Pasture Degradation ◽  
Annual Grasses ◽  
Woody Cover ◽  
The Impact

A long-term (1993–2013) experiment in grazed semiarid tropical savannas in northern Australia tested the impact of varying the frequency (every 2, 4 and 6 years) and season (June – EDS versus October – LDS) of fire compared with unburnt controls on woody cover and pasture composition, in grassland and open woodland. Over an 18-year period, woody cover increased by 4% (absolute) in the woodland even with the most severe (i.e. frequent, late dry season) fire treatments. With less severe or no fire, woody cover increased by 12–17%. In the grassland, woody cover remained static when subjected to LDS fires every 2 or 4 years, but increased by 3–6% under other fire treatments, and by 8% when unburnt. Major shifts in understorey species composition occurred at both sites regardless of fire regime. The effect of fire on herbage mass and composition was compounded by higher grazing after fires. The herbage mass of perennial grasses declined and that of annual grasses and forbs increased following early or frequent fires. Brachyachne convergens, Gomphrena canescens and Flemingia pauciflora increased in response to fire while Aristida latifolia and Heteropogon contortus decreased. Four-yearly LDS fire provided the most effective management of woody cover and pasture composition. Although EDS fire is recommended for biodiversity management and reducing greenhouse gas emissions in wet tropical savannas, on grazed pastoral land, it can promote woodland thickening and pasture degradation. Optimal fire management, therefore, depends on vegetation type, land use and the prevailing seasonal timing and frequency of fire.

Correlates of grass-species composition in a savanna woodland in northern Australia

2009 ◽  
Vol 57 (1) ◽  
pp. 10 ◽  
Author(s):  
K. A. Scott ◽  
S. A. Setterfield ◽  
A. N. Andersen ◽  
M. M. Douglas
Keyword(s):  
Species Composition ◽  
Vegetation Structure ◽  
Spatial Scales ◽  
Fire Frequency ◽  
Grass Species ◽  
Northern Australia ◽  
Tropical Savannas ◽  
Environmental Characteristics ◽  
Savanna Woodland ◽  
Litter Cover

Environmental features associated with the distribution of grass species are poorly known in tropical savannas, particularly at smaller spatial scales. The present study aimed to determine the relative influence of 11 environmental characteristics on grass-species composition in a savanna woodland in northern Australia. Environmental characteristics relating to woody-vegetation structure and soil, plus the long-term (14-year) fire frequency, were documented along an environmental gradient and compared with grass-species composition. Differences in grass-species composition, as well as richness and evenness, were related to differences in vegetation structure and edaphic characteristics. In particular, grass-species composition was most strongly related to plant-available moisture, the density of woody plants in the midstorey (2.0–9.99 m height), and canopy and litter cover. Grass-species richness and evenness were extremely low in areas where midstorey density, canopy cover and litter cover were high, and where soil moisture content in the root zone of grasses was low. Differences in fire frequency also influenced grass-species composition, with areas that had experienced lower fire frequency during the previous 14 years having lower density of the annual grass Sorghum intrans (F.Muell. ex Benth.) and the perennial grass Heteropogon triticeus (R.Br.) Stapf, and increased dominance of the perennial Eriachne triseta Nees ex Steud. The results of the present study demonstrate a complex interplay between bottom-up environmental factors and top-down processes such as fire, as determinants of grass-species composition in tropical savannas.

scholarly journals A spatial and temporal assessment of fire regimes on different vegetation types using MODIS burnt area products

Bothalia ◽  
2016 ◽  
Vol 46 (2) ◽  
Author(s):  
Nokuphila L.S. Buthelezi ◽  
Onisimo Mutanga ◽  
Mathieu Rouget ◽  
Mbulisi Sibanda
Keyword(s):  
Vegetation Type ◽  
Fire Regimes ◽  
Fire Frequency ◽  
Fire Season ◽  
Burned Area ◽  
Vegetation Types ◽  
Remotely Sensed Data ◽  
Burnt Area ◽  
Coastal Belt ◽  
Kwazulu Natal

Background: The role of fire in maintaining grassland diversity has been widely recognised; however, its effect in KwaZulu-Natal grasslands is still rudimentary. In that regard, understanding fire regimes of different vegetation types in KwaZulu-Natal is a critical step towards the development of effective management strategies that are specific to each vegetation type. Objective: To assess the effect of different vegetation types on fire regimes in KwaZulu-Natal using moderate resolution imaging spectroradiometer (MODIS) burnt fire products. Method: Ten years of fire data for four different vegetation types (Ngongoni Veld, KwaZuluNatal Sandstone Sourveld, Eastern Valley Bushveld and KwaZulu-Natal Coastal Belt) were extracted from the MODIS products and used as a basis to establish three parameters: annual burnt areas, fire season and fire frequency. The total burnt area within each vegetation type over the 10-year period was quantified. Results: The KZN Sandstone Sourveld had a high-burnt area of 80% in 2009 with KwaZuluNatal Coastal Belt having the least burnt area of less than 5%. Ngongoni Veld and the KwaZuluNatal Sandstone Sourveld had the highest fire frequency, while the coastal region had low fire frequencies. Results showed high fire prevalence during the late period of the dry season (which extends from June to August) across all the vegetation types. Conclusion: This study underscores the potential of remotely sensed data (MODIS burned area products) in providing a comprehensive view of fire patterns in different vegetation types

Determinants of spatial variation in fire return period in a semiarid African savanna

2011 ◽  
Vol 20 (4) ◽  
pp. 540 ◽  
Author(s):  
T. G. O'Connor ◽  
C. M. Mulqueeny ◽  
P. S. Goodman
Keyword(s):  
Spatial Variation ◽  
Return Period ◽  
Vegetation Type ◽  
Fire Frequency ◽  
Fuel Load ◽  
Annual Rainfall ◽  
Vegetation Types ◽  
Terrestrial Vegetation ◽  
African Savanna ◽  
Data Set

Fire pattern is predicted to vary across an African savanna in accordance with spatial variation in rainfall through its effects on fuel production, vegetation type (on account of differences in fuel load and in flammability), and distribution of herbivores (because of their effects on fuel load). These predictions were examined for the 23 651-ha Mkuzi Game Reserve, KwaZulu-Natal, based on a 37-year data set. Fire return period varied from no occurrence to a fire every 1.76 years. Approximately 75% of the reserve experienced a fire approximately every 5 years, 25% every 4.1–2.2 years and less than 1% every 2 years on average. Fire return period decreased in relation to an increase in mean annual rainfall. For terrestrial vegetation types, median fire return periods decreased with increasing herbaceous biomass, from forest that did not burn to grasslands that burnt every 2.64 years. Fire was absent from some permanent wetlands but seasonal wetlands burnt every 5.29 years. Grazer biomass above 0.5 animal units ha–1 had a limiting influence on the maximum fire frequency of fire-prone vegetation types. The primary determinant of long-term spatial fire patterns is thus fuel load as determined by mean rainfall, vegetation type, and the effects of grazing herbivores.

Predicting spatial patterns of fire on a southern California landscape

2008 ◽  
Vol 17 (5) ◽  
pp. 602 ◽  
Author(s):  
Alexandra D. Syphard ◽  
Volker C. Radeloff ◽  
Nicholas S. Keuler ◽  
Robert S. Taylor ◽  
Todd J. Hawbaker ◽  
...  
Keyword(s):  
Spatial Patterns ◽  
Southern California ◽  
Vegetation Type ◽  
Fire Hazard ◽  
Fire Regimes ◽  
Fire Frequency ◽  
Fuel Loading ◽  
Landscape Characteristics ◽  
Management Actions ◽  
Fire Ignitions

Humans influence the frequency and spatial pattern of fire and contribute to altered fire regimes, but fuel loading is often the only factor considered when planning management activities to reduce fire hazard. Understanding both the human and biophysical landscape characteristics that explain how fire patterns vary should help to identify where fire is most likely to threaten values at risk. We used human and biophysical explanatory variables to model and map the spatial patterns of both fire ignitions and fire frequency in the Santa Monica Mountains, a human-dominated southern California landscape. Most fires in the study area are caused by humans, and our results showed that fire ignition patterns were strongly influenced by human variables. In particular, ignitions were most likely to occur close to roads, trails, and housing development but were also related to vegetation type. In contrast, biophysical variables related to climate and terrain (January temperature, transformed aspect, elevation, and slope) explained most of the variation in fire frequency. Although most ignitions occur close to human infrastructure, fires were more likely to spread when located farther from urban development. How far fires spread was ultimately related to biophysical variables, and the largest fires in southern California occurred as a function of wind speed, topography, and vegetation type. Overlaying predictive maps of fire ignitions and fire frequency may be useful for identifying high-risk areas that can be targeted for fire management actions.

scholarly journals A New Flexible Bathtub-Shaped Modification of the Weibull Model: Properties and Applications

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Qinghu Liao ◽  
Zubair Ahmad ◽  
Eisa Mahmoudi ◽  
G. G. Hamedani
Keyword(s):  
Weibull Distribution ◽  
Hazard Rate ◽  
Likelihood Estimation ◽  
Estimation Procedure ◽  
Weibull Model ◽  
Rate Function ◽  
Model Parameters ◽  
Hazard Functions ◽  
Practical Applications ◽  
Nonnested Models

Many studies have suggested the modifications and generalizations of the Weibull distribution to model the nonmonotone hazards. In this paper, we combine the logarithms of two cumulative hazard rate functions and propose a new modified form of the Weibull distribution. The newly proposed distribution may be called a new flexible extended Weibull distribution. Corresponding hazard rate function of the proposed distribution shows flexible (monotone and nonmonotone) shapes. Three different characterizations along with some mathematical properties are provided. We also consider the maximum likelihood estimation procedure to estimate the model parameters. For the illustrative purposes, two real applications from reliability engineering with bathtub-shaped hazard functions are analyzed. The practical applications show that the proposed model provides better fits than the other nonnested models.

scholarly journals Resilience of the boreal forest in response to Holocene fire-frequency changes assessed by pollen diversity and population dynamics

2010 ◽  
Vol 19 (8) ◽  
pp. 1026 ◽  
Author(s):  
Christopher Carcaillet ◽  
Pierre J. H. Richard ◽  
Yves Bergeron ◽  
Bianca Fréchette ◽  
Adam A. Ali
Keyword(s):  
Boreal Forest ◽  
Boreal Forests ◽  
Frequency Control ◽  
Regional Scale ◽  
Fire Regimes ◽  
Fire Frequency ◽  
Frequency Changes ◽  
Fire Intervals ◽  
In Fire

The hypothesis that changes in fire frequency control the long-term dynamics of boreal forests is tested on the basis of paleodata. Sites with different wildfire histories at the regional scale should exhibit different vegetation trajectories. Mean fire intervals and vegetation reconstructions are based respectively on sedimentary charcoal and pollen from two small lakes, one in the Mixedwood boreal forests and the second in the Coniferous boreal forests. The pollen-inferred vegetation exhibits different trajectories of boreal forest dynamics after afforestation, whereas mean fire intervals have no significant or a delayed impact on the pollen data, either in terms of diversity or trajectories. These boreal forests appear resilient to changes in fire regimes, although subtle modifications can be highlighted. Vegetation compositions have converged during the last 1200 years with the decrease in mean fire intervals, owing to an increasing abundance of boreal species at the southern site (Mixedwood), whereas changes are less pronounced at the northern site (Coniferous). Although wildfire is a natural property of boreal ecosystems, this study does not support the hypothesis that changes in mean fire intervals are the key process controlling long-term vegetation transformation. Fluctuations in mean fire intervals alone do not explain the historical and current distribution of vegetation, but they may have accelerated the climatic process of borealisation, likely resulting from orbital forcing.

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