Abstract. Fire frequency in 21 forest planning regions of Portugal during the period 1975-2005 was estimated from historical burnt area maps generated with semi-automatic classification of Landsat Thematic Mapper (TM) satellite imagery. Fire return interval distributions were modelled with the Weibull function and the estimated parameters were used to calculate regional mean, median and modal fire return intervals, as well as regional hazard functions. Arrangement of the available data into three different time series allowed for assessment of the effects of minimum mapping unit, time series length and use of censored data on the Weibull function parameter estimates. Varying the minimum mapping unit between 5 and 35 ha had a negligible effect on parameter estimates, whereas changing the time series length from 22 to 31 years substantially affected the estimates. However, the strongest effect was caused by censored data. Its exclusion led to substantial overestimation of fire frequency and of burning probability dependence on fuel age. We estimated a countrywide mean fire interval of 36 years and an annual burnt area of 1.2%. Regional variations in fire frequency descriptors were interpreted in terms of land cover and land use practices that affect the contemporary fire regime in Portugal.

Covering almost a quarter of Brazil, the Cerrado is the world’s most biologically rich tropical savanna. Fire is an integral part of the Cerrado but current land use and agricultural practices have been changing fire regimes, with undesirable consequences for the preservation of biodiversity. In this study, fire frequency and fire return intervals were modelled over a 12-year time series (1997–2008) for the Jalapão State Park, a protected area in the north of the Cerrado, based on burned area maps derived from Landsat imagery. Burned areas were classified using object based image analysis. Fire data were modelled with the discrete lognormal model and the estimated parameters were used to calculate fire interval, fire survival and hazard of burning distributions, for seven major land cover types. Over the study period, an area equivalent to four times the size of Jalapão State Park burned and the mean annual area burned was 34%. Median fire intervals were generally short, ranging from three to six years. Shrub savannas had the shortest fire intervals, and dense woodlands the longest. Because fires in the Cerrado are strongly responsive to fuel age in the first three to four years following a fire, early dry season patch mosaic burning may be used to reduce the extent of area burned and the severity of fire effects.

Frequent and extensive fires are becoming increasingly common throughout the tropical savannas of northern Australia. This fire regime has been implicated in both habitat alteration and losses of biodiversity. Granivorous birds are particularly affected because of the effect of fire on grass seed availability. The endemic Gouldian finch (Erythrura gouldiae) has experienced population declines in recent decades, potentially in response to changed fire regimes. Using breeding data from monitored artificial nest-boxes, this study examined the choice of breeding site by Gouldian finches in response to several attributes of the prevailing fire regime. The fire regime was characterised using remote sensing analysis of annual fire scars. Time since last fire and fire frequency were the most useful predictors of breeding site occupancy. Gouldian finches favoured recently burnt sites (previous dry season), but also sites that were infrequently burnt (return time of 2–3 years). Consequently, under the current regime of many frequent fires, Gouldian finches move among breeding sites and display low seasonal site fidelity. Our findings provide support for the notion that the Gouldian finch favours a fine-grain patch-mosaic fire regime and that contemporary large-scale fire regimes are likely contributing to their decline.

Understanding fine-scale fire patchiness has significant implications for ecological processes and biodiversity conservation. It can affect local extinction of and recolonisation by relatively immobile fauna and poorly seeddispersed flora in fire-affected areas. This study assesses fine-scale fire patchiness and severity, and associated implications for biodiversity, in north Australian tropical savanna systems. We used line transects to sample burning patterns of ground layer vegetation in different seasons and vegetation structure types, within the perimeter of 35 fires that occurred between 2009 and 2011. We evaluated two main fire characteristics: patchiness (patch density and mean patch length) and severity (inferred from char and scorch heights, and char and ash proportions). The mean burned area of ground vegetation was 83% in the early dry season (EDS: May to July) and 93% in the late dry season (LDS: August to November). LDS fires were less patchy (smaller and fewer unburned patches), and had higher fire severity (higher mean char and scorch heights, and twice the proportion of ash) than EDS fires. Fire patchiness varied among vegetation types, declining under more open canopy structure. The relationship between burned area and fire severity depended on season, being strongly correlated in the EDS and uncorrelated in the LDS. Simulations performed to understand the implications of patchiness on the population dynamics of fire-interval sensitive plant species showed that small amounts of patchiness substantially enhance survival. Our results indicate that the ecological impacts of high frequency fires on fire-sensitive regional biodiversity elements are likely to be lower than has been predicted from remotely sensed studies that are based on assumptions of homogeneous burning. interval-sensitive plant species showed that small amounts of patchiness substantially enhance survival. Our results indicate that the ecological impacts of high frequency fires on fire-sensitive regional biodiversity elements are likely to be lower than has been predicted based on assumptions of homogeneous burning derived from remotely sensed studies.

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.