Effects of climate on occurrence and size of large fires in a northern hardwood landscape: historical trends,forecasts, and implications for climate change in Témiscamingue,Québec

Questions: What climate variables best explain fire occurrence and area burned in the Great Lakes‐St Lawrence forest of Canada? How will climate change influence these climate variables and thereby affect the occurrence of fire and area burned in a deciduous forest landscape in Témiscamingue, Québec, Canada? Location: West central Québec and the Great Lakes‐St Lawrence forest of Canada. Methods: We first used an information‐theoretic framework to evaluate the relative role of different weather variables in explaining occurrence and area burned of large fires (>200 ha, 1959‐1999) across the Great Lakes‐St Lawrence forest region. Second, we examined how these weather variables varied historically in Témiscamingue and, third, how they may change between the present and 2100 according to different scenarios of climate change based on two Global Circulation Models. Results: Mean monthly temperature maxima during the fire season (Apr‐Oct) and weighted sequences of dry spells best explained fire occurrence and area burned. Between 1910 and 2004, mean monthly temperature maxima in Témiscamingue showed no apparent temporal trend, while dry spell sequences decreased in frequency and length. All future scenarios show an increase in mean monthly temperature maxima, and one model scenario forecasts an increase in dry spell sequences, resulting in a slight increase in forecasted annual area burned. Conclusion: Despite the forecasted increase in fire activity, effects of climate change on fire will not likely affect forest structure and composition as much as natural succession or harvesting and other disturbances, principally because of the large relative difference in area affected by these processes.     

Historic variability in fire‐generated landscape heterogeneity of subalpine forests in the Canadian Rockies

Question: This study evaluates historical changes in landscape structure and heterogeneity in subalpine forests. We use response to severe fires in 2001 and 2003, along with historical reconstructions to examine crown‐fire effects on landscape heterogeneity and to assess, comparatively, effects of fire exclusion management in the 20th century. Location: Subalpine forests of Kootenay National Park (KNP), Canadian Rockies. Methods: Using a landscape‐level model based on a fire‐origin stand age map, we reconstructed decadal burned areas within the landscape for 1750‐2000 (forming reconstructed landscapes). Landscape pattern was analysed for each reconstructed landscape map, and we compared landscape pattern indices (total area, number of patches, mean patch area, patch area variation, largest patch index, edge density, perimeter–area ratio, landscape shape index) with those in 2005 after recent large fires. Results: After large fires in 1926, connectivity of the KNP landscape increased and its diversity was quite low. After 2001 and 2003 fires, the post‐fire landscape of 2005 was highly heterogeneous in terms of size, variation, edge density and perimeter–area ratio of the remnant forest patches. Since the decline in occurrence of large fires after 1926 reflected a period of wet weather, fuel build‐up resulting from landscape homogenization within the 20th century landscape could not be attributed solely to fire exclusion. This period without fires greatly enhanced connectivity of late‐successional forests that finally burned in 2001/2003, but connectivity was within the historical range for these forests. The gradual increase in stand connectivity before recent large fires may indicate that fire exclusion was less responsible than often believed for fuel build‐up in these fire‐susceptible older forests. Conclusions: The large fires at the beginning of the 21st century are within the natural range of disturbances for this landscape, and do not stand out as “human‐induced disasters” in their effects on landscape patterns. Such stochastic large disturbances contribute to maintenance of highly heterogeneous landscape structure, which is important for many taxa and natural ecological processes. Identifying future probability of such large disturbances and their ecological roles should be incorporated into management of these dynamic, disturbance‐prone systems.     

Impacts of climate change on fire activity and fire management in the circumboreal forest

Forest fires are a significant and natural element of the circumboreal forest. Fire activity is strongly linked to weather, and increased fire activity due to climate change is anticipated or arguably has already occurred. Recent studies suggest a doubling of area burned along with a 50% increase in fire occurrence in parts of the circumboreal by the end of this century. Fire management agencies' ability to cope with these increases in fire activity is limited, as these organizations operate with a narrow margin between success and failure; a disproportionate number of fires may escape initial attack under a warmer climate, resulting in an increase in area burned that will be much greater than the corresponding increase in fire weather severity. There may be only a decade or two before increased fire activity means fire management agencies cannot maintain their current levels of effectiveness.     

Changes in fire regime break the legacy lock on successional trajectories in Alaskan boreal forest

Predicting plant community responses to changing environmental conditions is a key element of forecasting and mitigating the effects of global change. Disturbance can play an important role in these dynamics, by initiating cycles of secondary succession and generating opportunities for communities of long‐lived organisms to reorganize in alternative configurations. This study used landscape‐scale variations in environmental conditions, stand structure, and disturbance from an extreme fire year in Alaska to examine how these factors affected successional trajectories in boreal forests dominated by black spruce. Because fire intervals in interior Alaska are typically too short to allow relay succession, the initial cohorts of seedlings that recruit after fire largely determine future canopy composition. Consequently, in a dynamically stable landscape, postfire tree seedling composition should resemble that of the prefire forest stands, with little net change in tree composition after fire. Seedling recruitment data from 90 burned stands indicated that postfire establishment of black spruce was strongly linked to environmental conditions and was highest at sites that were moist and had high densities of prefire spruce. Although deciduous broadleaf trees were absent from most prefire stands, deciduous trees recruited from seed at many sites and were most abundant at sites where the fires burned severely, consuming much of the surface organic layer. Comparison of pre‐ and postfire tree composition in the burned stands indicated that the expected trajectory of black spruce self‐replacement was typical only at moist sites that burned with low fire severity. At severely burned sites, deciduous trees dominated the postfire tree seedling community, suggesting these sites will follow alternative, deciduous‐dominated trajectories of succession. Increases in the severity of boreal fires with climate warming may catalyze shifts to an increasingly deciduous‐dominated landscape, substantially altering landscape dynamics and ecosystem services in this part of the boreal forest.     

Recent fire regime characteristics and potential natural vegetation relationships in Spain

Abstract. In heavily altered landscapes, where vegetation is not natural and where people are the main source of ignitions, relationships between fire occurrence and climate conditions may be unclear. The objective of this study was to evaluate to what extent territories with similar Potential Natural Vegetation (PNV) in peninsular Spain differ in their forest fire characteristics. From 1974 to 1994, more than 174 000 fires occurred. We used (1) the Spanish data base of forest fires, (2) a PNV map and (3) a land use map. Separate fire characteristics, based either on the number of fires occurred or the area burned, were obtained for each of the ca. 5000 grid‐cells (10 km × 10 km) into which peninsular Spain is divided in the UTM projection. Also, meteorological conditions at the time of fire ignition, cause of ignition and present forest cover were referred to the same grid‐cells as external factors potentially determinant of fire occurrence. The relationships between fire regime characteristics and PNV units were explored with Principal Components Analysis (PCA). The role of the three sets of external factors in the fire characteristics was evaluated with Redundancy Analysis (RDA). Groups of similar PNV types were clearly segregated, suggesting a gradient of fire characteristics. Higher fire incidence (higher frequencies and spatial incidence of fires, but lower proportions of grid‐cells affected by large fires) was associated with Atlantic, warm territories with deciduous forests as PNV. Intermediate fire frequency and rotation period, but with a higher relative incidence of medium and large fires occurred in Mediterranean PNV units, dominated by sclerophyllous oak forests. Low fire frequency and long rotation periods, with strong seasonal and yearly variability occurred for PNV units in the cold uplands (Fagus, Pinus, Abies, Juniperus) or in the semi‐arid, shrubby PNV units. The cause of ignition best explained the patterns of forest fire characteristics, followed by weather conditions. Our results indicate that, even in human influenced regions, climate and soil conditions exert control on the resulting forest fire characteristics, as indicated by the high segregation of the PNV types. However, the role of man was crucial in shifting the patterns of fire incidence. This was so that highest fire incidence occurred in regions that, otherwise, would be expected to have a much lower one, thus posing a serious threat for such areas. PNV maps, by providing a phytogeographical framework for characterizing forest fires, could be valuable tools for applying research results to forest fire management policies, taking properly into account the underlying determinant factors.     

Bottom-Up Variables Govern Large-Fire Size in Portugal

Large fires and their impacts are a growing concern as changes in climate and land use proceed. The study of large-fire controls remains incipient in comparison with other components of the fire regime. Improved understanding of large-fire size drivers can disclose fire–landscape relationships and inform more sustainable and effective fire management. We used boosted regression tree modeling to identify the variables influent on large-fire size (100–23,219 ha, n = 609) in Portugal (1998–2008) and quantify their relative importance, globally and across the fire-size range. Potential explanatory variables included metrics pertaining to fire weather and antecedent rainfall, burned area composition, fuel connectivity, pyrodiversity (from fire recurrence patterns), topography, and land development. Large fires seldom occurred in the absence of severe fire weather. The fire-size model accounted for 70% of the deviance and included 12 independent variables, of which six absorbed 91% of the explanation. Bottom-up influences on fire size, essentially fuel-related, largely outweighed climate–weather influences, with respective importance of 85 and 15%. Fire size was essentially indifferent to land-cover composition, including forest type, and increased with high fuel connectivity and low pyrodiversity. Relevant synergies between variables were found, either positive or negative, for example, high pyrodiversity buffered the effects of extreme weather on fire size. The relative role of fire-size drivers did not vary substantially with fire size, but fires larger than 500 ha were increasingly controlled by fuel-related variables. The extent of an individual large fire is mainly a function of factors that land-use planning and forest and fuel management can tackle.     

Climatic change and fire potential in South-Central British Columbia, Canada

The incidence and severity of forest fires are linked to the interaction between climate, fuel and topography. Increased warming and drying in the future is expected to have a significant impact on the risk of forest fire occurrence. An increase in fire risk is linked to the synchronous relationship between climate and fuel moisture conditions. A warmer, drier climate will lead to drier forest fuels that will in turn increase the chance of successful fire ignition and propagation. This interaction will increase the severity of fire weather, which, in turn, will increase the risk of extreme fire behaviour. A warmer climate will also extend fire season length, which will increase the likelihood of fires occurring over a greater proportion of the year. In this study of the North Okanagan area of British Columbia, Canada, the impacts of climate change of fire potential were evaluated using the Canadian Forest Fire Danger Rating System and multiple climate scenario analysis. Utilizing this approach, a 30% increase in fire season length was modelled to occur by 2070. In addition, statistically significant increases in fire severity and fire behaviour were also modelled. Fire weather severity was predicted to increase by 95% during the summer months by 2070 while fire behaviour was predicted to shift from surface fire‐intermittent crown fire regimes to a predominantly intermittent‐full crown fire regime by 2070 onwards. An increase in fire season length, fire weather severity and fire behaviour will increase the costs of fire suppression and the risk of property and resource loss while limiting human‐use within vulnerable forest landscapes. An increase in fire weather severity and fire behaviour over a greater proportion of the season will increase the risks faced by ecosystems and biodiversity to climatic change and increase the costs and difficulty of achieving sustainable forest management.     

Fire disturbance and forest structure in old‐growth mixed conifer forests in the northern Sierra Nevada,California

Question: This study evaluates how fire regimes influence stand structure and dynamics in old‐growth mixed conifer forests across a range of environmental settings. Location: A 2000‐ha area of mixed conifer forest on the west shore of Lake Tahoe in the northern Sierra Nevada, California. Methods: We quantified the age, size, and spatial structure of trees in 12 mixed conifer stands distributed across major topographic gradients. Fire history was reconstructed in each stand using fire scar dendrochronology. The influence of fire on stand structure was assessed by comparing the fire history with the age, size, and spatial structure of trees in a stand. Results: There was significant variation in species composition among stands, but not in the size, age and spatial patterning of trees. Stands had multiple size and age classes with clusters of similar aged trees occurring at scales of 113 ‐ 254 m². The frequency and severity of fires was also similar, and stands burned with low to moderate severity in the dormant season on average every 9–17 years. Most fires were not synchronized among stands except in very dry years. No fires have burned since ca. 1880. Conclusions: Fire and forest structure interact to perpetuate similar stand characteristics across a range of environmental settings. Fire occurrence is controlled primarily by spatial variation in fuel mosaics (e.g. patterns of abundance, fuel moisture, forest structure), but regional drought synchronizes fire in some years. Fire exclusion over the last 120 years has caused compositional and structural shifts in these mixed conifer forests.     

Response of subarctic vegetation to transient climatic change on the Seward Peninsula in north-west Alaska

Understanding the response of terrestrial ecosystems to climatic warming is a challenge because of the complex interactions of climate, disturbance, and recruitment across the landscape. We use a spatially explicit model (ALFRESCO) to simulate the transient response of subarctic vegetation to climatic warming on the Seward Peninsula (80 000 km²) in north‐west Alaska. Model calibration efforts showed that fire ignition was less sensitive than fire spread to regional climate (temperature and precipitation). In the model simulations a warming climate led to slightly more fires and much larger fires and expansion of forest into previously treeless tundra. Vegetation and fire regime continued to change for centuries after cessation of the simulated climate warming. Flammability increased rapidly in direct response to climate warming and more gradually in response to climate‐induced vegetation change. In the simulations warming caused as much as a 228% increase in the total area burned per decade, leading to an increasingly early successional and more homogenous deciduous forest‐dominated landscape. A single transient 40‐y drought led to the development of a novel grassland–steppe ecosystem that persisted indefinitely and caused permanent increases in fires in both the grassland and adjacent vegetation. These simulated changes in vegetation and disturbance dynamics under a warming climate have important implications for regional carbon budgets and biotic feedbacks to regional climate.     

Contrasting fire responses to climate and management: insights from two Australian ecosystems

This study explores effects of climate change and fuel management on unplanned fire activity in ecosystems representing contrasting extremes of the moisture availability spectrum (mesic and arid). Simulation modelling examined unplanned fire activity (fire incidence and area burned, and the area burned by large fires) for alternate climate scenarios and prescribed burning levels in: (i) a cool, moist temperate forest and wet moorland ecosystem in south‐west Tasmania (mesic); and (ii) a spinifex and mulga ecosystem in central Australia (arid). Contemporary fire activity in these case study systems is limited, respectively, by fuel availability and fuel amount. For future climates, unplanned fire incidence and area burned increased in the mesic landscape, but decreased in the arid landscape in accordance with predictions based on these limiting factors. Area burned by large fires (greater than the 95th percentile of historical, unplanned fire size) increased with future climates in the mesic landscape. Simulated prescribed burning was more effective in reducing unplanned fire activity in the mesic landscape. However, the inhibitory effects of prescribed burning are predicted to be outweighed by climate change in the mesic landscape, whereas in the arid landscape prescribed burning reinforced a predicted decline in fire under climate change. The potentially contrasting direction of future changes to fire will have fundamentally different consequences for biodiversity in these contrasting ecosystems, and these will need to be accommodated through contrasting, innovative management solutions.     

Wildfire refugia in forests: Severe fire weather and drought mute the influence of topography and fuel age

Wildfire refugia (unburnt patches within large wildfires) are important for the persistence of fire‐sensitive species across forested landscapes globally. A key challenge is to identify the factors that determine the distribution of fire refugia across space and time. In particular, determining the relative influence of climatic and landscape factors is important in order to understand likely changes in the distribution of wildfire refugia under future climates. Here, we examine the relative effect of weather (i.e. fire weather, drought severity) and landscape features (i.e. topography, fuel age, vegetation type) on the occurrence of fire refugia across 26 large wildfires in south‐eastern Australia. Fire weather and drought severity were the primary drivers of the occurrence of fire refugia, moderating the effect of landscape attributes. Unburnt patches rarely occurred under ‘severe’ fire weather, irrespective of drought severity, topography, fuels or vegetation community. The influence of drought severity and landscape factors played out most strongly under ‘moderate’ fire weather. In mesic forests, fire refugia were linked to variables that affect fuel moisture, whereby the occurrence of unburnt patches decreased with increasing drought conditions and were associated with more mesic topographic locations (i.e. gullies, pole‐facing aspects) and vegetation communities (i.e. closed‐forest). In dry forest, the occurrence of refugia was responsive to fuel age, being associated with recently burnt areas (<5 years since fire). Overall, these results show that increased severity of fire weather and increased drought conditions, both predicted under future climate scenarios, are likely to lead to a reduction of wildfire refugia across forests of southern Australia. Protection of topographic areas able to provide long‐term fire refugia will be an important step towards maintaining the ecological integrity of forests under future climate change.     

Tropical and north Pacific teleconnections influence fire regimes in pine-dominated forests of north-eastern California, USA

Aim To assess the importance of drought and teleconnections from the tropical and north Pacific Ocean on historical fire regimes and vegetation dynamics in north‐eastern California. Location The 700 km² study area was on the leeward slope of the southern Cascade Mountains in north‐eastern California. Open forests of ponderosa pine (Pinus ponderosa var. ponderosa Laws.) and Jeffrey pine (P. jeffreyi Grev. & Balf) surround a network of grass and shrub‐dominated meadows that range in elevation from 1650 to 1750 m. Methods Fire regime characteristics (return interval, season and extent) were determined from crossdated fire scars and were compared with tree‐ring based reconstructions of precipitation and temperature and teleconnections for the period 1700–1849. The effect of drought on fire regimes was determined using a tree‐ring based proxy of climate from five published chronologies. The number of forest‐meadow units that burned was compared with published reconstructions of the El Niño/Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Results Landscape scale fires burned every 7–49 years in meadow‐edge forests and were influenced by variation in drought, the PDO and ENSO. These widespread fires burned during years that were dryer and warmer than normal that followed wetter and cooler years. Less widespread fires were not associated with this wet, then dry climate pattern. Widespread fires occurred during El Niño years, but fire extent was mediated by the phase of the PDO. Fires were most widespread when the PDO was in a warm or normal phase. Fire return intervals, season and extent varied at decadal to multi‐decadal time scales. In particular, an anomalously cool, wet period during the early 1800s resulted in widespread fires that occurred earlier in the year than fires before or after. Main conclusions Fire regimes in north‐eastern California were strongly influenced by regional and hemispheric‐scale climate variation. Fire regimes responded to variation that occurred in both the north and tropical Pacific. Near normal modes of the PDO may influence fire regimes more than extreme conditions. The prevalence of widespread teleconnection‐driven fires in the historic record suggests that variation in the Pacific Ocean was a key regulator of fire regimes through its influence on local fuel production and successional dynamics in north‐eastern California.     

A review of the relationships between drought and forest fire in the United States

The historical and presettlement relationships between drought and wildfire are well documented in North America, with forest fire occurrence and area clearly increasing in response to drought. There is also evidence that drought interacts with other controls (forest productivity, topography, fire weather, management activities) to affect fire intensity, severity, extent, and frequency. Fire regime characteristics arise across many individual fires at a variety of spatial and temporal scales, so both weather and climate – including short‐ and long‐term droughts – are important and influence several, but not all, aspects of fire regimes. We review relationships between drought and fire regimes in United States forests, fire‐related drought metrics and expected changes in fire risk, and implications for fire management under climate change. Collectively, this points to a conceptual model of fire on real landscapes: fire regimes, and how they change through time, are products of fuels and how other factors affect their availability (abundance, arrangement, continuity) and flammability (moisture, chemical composition). Climate, management, and land use all affect availability, flammability, and probability of ignition differently in different parts of North America. From a fire ecology perspective, the concept of drought varies with scale, application, scientific or management objective, and ecosystem.     

Canada lynx use of burned areas: Conservation implications of changing fire regimes

A fundamental problem in ecology is forecasting how species will react to major disturbances. As the climate warms, large, frequent, and severe fires are restructuring forested landscapes at large spatial scales, with unknown impacts on imperilled predators. We use the United States federally Threatened Canada lynx as a case study to examine how predators navigate recent large burns, with particular focus on habitat features and the spatial configuration (e.g., distance to edge) that enabled lynx use of these transformed landscapes. We coupled GPS location data of lynx in Washington in an area with several recent large fires and a number of GIS layers of habitat data to develop models of lynx habitat selection in recent burns. Random Forest habitat models showed lynx‐selected islands of forest skipped by large fires, residual vegetation, and areas where some trees survived to use newly burned areas. Lynx used burned areas as early as 1 year postfire, which is much earlier than the 2–4 decades postfire previously thought for this predator. These findings are encouraging for predator persistence in the face of fires, but increasingly severe fires or management that reduces postfire residual trees or slow regeneration will likely jeopardize lynx and other predators. Fire management should change to ensure heterogeneity is retained within the footprint of large fires to enable viable predator populations as fire regimes worsen with climate change.     

Examining forest resilience to changing fire frequency in a fire‐prone region of boreal forest

Future changes in climate are widely anticipated to increase fire frequency, particularly in boreal forests where extreme warming is expected to occur. Feedbacks between vegetation and fire may modify the direct effects of warming on fire activity and shape ecological responses to changing fire frequency. We investigate these interactions using extensive field data from the Boreal Shield of Saskatchewan, Canada, a region where >40% of the forest has burned in the past 30 years. We use geospatial and field data to assess the resistance and resilience of eight common vegetation states to frequent fire by quantifying the occurrence of short‐interval fires and their effect on recovery to a similar vegetation state. These empirical relationships are combined with data from published literature to parameterize a spatially explicit, state‐and‐transition simulation model of fire and forest succession. We use this model to ask if and how: (a) feedbacks between vegetation and wildfire may modify fire activity on the landscape, and (b) more frequent fire may affect landscape forest composition and age structure. Both field and GIS data suggest the probability of fire is low in the initial decades after fire, supporting the hypothesis that fuel accumulation may exert a negative feedback on fire frequency. Field observations of pre‐ and postfire composition indicate that switches in forest state are more likely in conifer stands that burn at a young age, supporting the hypothesis that resilience is lower in immature stands. Stands dominated by deciduous trees or jack pine were generally resilient to fire, while mixed conifer and well‐drained spruce forests were less resilient. However, simulation modeling suggests increased fire activity may result in large changes in forest age structure and composition, despite the feedbacks between vegetation–fire likely to occur with increased fire activity.     

不同区域森林火灾对生态因子的响应及其概率模型

火灾是影响森林生态系统过程的重要干扰之一,其对森林生态系统内各生态因子的响应各不相同.由于植被状况及生态环境的不同,森林火灾的时空分布特征在中国不同植被气候类型内表现不同,根据植被气候类型分类系统,将中国主要森林火灾地区划分为4个区域:东北(冷温带松林)、华北(落叶阔叶林)、东南(常绿阔叶林)和西南(热带雨林),应用遥感监测数据和地面环境数据,以时空变量、生态因子(植被生长变化指数、湿度等)为可选自变量,应用半参数化Logistic回归模型,就森林火险对不同生态影响因子的响应规律进行了分析,建立了基于生态因子的着火概率模型和大火蔓延概率模型,通过模拟及实际数据散点图、火险概率图,评估了模型应用价值.结果表明,土壤湿度及植被含水量在落叶阔叶林、常绿阔叶林、热带雨林地区对着火概率影响显著.在4个植被气候区内,土壤及凋落物湿度对大火蔓延的作用较小.在冷温带松林、落叶阔叶林、常绿阔叶林地区,植被生长的年内变化对火灾发生的影响显著,在常绿阔叶林地区,年内植被生长变化对大火蔓延的作用较小.森林火险概率与各生态因子的相关关系主要呈现出非线性.不同植被气候区内,火险概率受不同生态因子组合的影响,这与不同区域的植被状况及生态环境不同有关.在不同植被气候类型,应用时空变量、生态因子建立半参数化logistic回归模型,进行着火概率和大火蔓延概率的模拟具有可行性和实际应用能力.为进一步分析森林生态系统与火灾之间的动态关系、展开生态系统火灾干扰研究提供了理论基础.     

The influence of fire frequency on the structure and botanical composition of savanna ecosystems

Savannas cover 60% of the land surface in Southern Africa, with fires and herbivory playing a key role in their ecology. The Limpopo National Park (LNP) is a 10,000 km² conservation area in southern Mozambique and key to protecting savannas in the region. Fire is an important factor in LNP's landscapes, but little is known about its role in the park's ecology. In this study, we explored the interaction between fire frequency (FF), landscape type, and vegetation. To assess the FF, we analyzed ten years of the Moderate resolution Imaging Spectroradiometer (MODIS) burned area product (2003–2013). A stratified random sampling approach was used to assess biodiversity across three dominant landscapes (Nwambia Sandveld‐NS, Lebombo North‐LN, and Shrubveld Mopane on Calcrete‐C) and two FF levels (low—twice or less; and high—3 times or more, during 10 years). Six ha were sampled in each stratum, except for the LN versus high FF in which low accessibility allowed only 3 ha sampling. FF was higher in NS and LN landscapes, where 25% and 34% of the area, respectively, burned more than three times in 10 years. The landscape type was the main determinant of grass composition and biomass. However, in the sandy NS biomass was higher under high FF. The three landscapes supported three different tree/shrub communities, but FF resulted in compositional variations in NS and LN. Fire frequency had no marked influence on woody structural parameters (height, density, and phytomass). We concluded that the savannas in LNP are mainly driven by landscape type (geology), but FF may impose specific modifications. We recommend a fire laissez‐faire management system for most of the park and a long‐term monitoring system of vegetation to address vegetation changes related to fire. Fire management should be coordinated with the neighboring Kruger National Park, given its long history of fire management. Synthesis: This study revealed that grass and tree/shrub density, biomass, and composition in LNP are determined by the landscape type, but FF determines some important modifications. We conclude that at the current levels FF is not dramatically affecting the savanna ecosystem in the LNP (Figure 1). However, an increase in FF may drive key ecosystem changes in grass biomass and tree/shrub species composition, height, phytomass, and density.     

The relative importance of intrinsic and extrinsic factors in the decline of obligate seeder forests

Forests that regenerate exclusively from seed following high‐severity fire are particularly vulnerable to local extinction if fire frequency leaves insufficient time for regenerating plants to reach sexual maturity. We evaluate the relative importance of extrinsic (such as fire weather and climate cycles) and intrinsic (such as proneness to fire due to stand age and structural development) factors in driving the decline of obligate seeder forests. We illustrate this using obligate seeding alpine ash (Eucalyptus delegatensis) forests in the montane regions of Victoria, Australia, that were burnt by megafires in 2003 (142,256 ha) or 2007 (79,902 ha), including some twice‐burnt areas (11,599 ha). Geospatial analyses showed only a small effect of stand age on the remote sensing estimates of crown defoliation, but a substantial effect of forest fire weather, as measured by forest fire danger index (FFDI). Analysis of meteorological data over the last century showed that 5‐year increases in FFDI precede cycle major fires in the E. delegatensis forests. Such strong extrinsic climate/weather driving of high‐severity fires is consistent with the ‘interval squeeze model’ that postulates the vulnerability of obligate seeder forests to landscape‐scale demographic collapse in response to worsening fire weather under climate change.     

Firescape ecology: how topography determines the contrasting distribution of fire and rain forest in the south‐west of the Tasmanian Wilderness World Heritage Area

Aim To test the hypothesis that ‘islands’ of fire‐sensitive rain forest are restricted to topographic fire refugia and investigate the role of topography–fire interactions in fire‐mediated alternative stable state models. Location A vegetation mosaic of moorland, sclerophyll scrub, wet sclerophyll eucalypt forest and rain forest in the rugged, fire‐prone landscapes of south‐west Tasmania, Australia. Methods We used geospatial statistics to: (1) identify the topographic determinants of rain forest distribution on nutrient‐poor substrates, and (2) identify the vegetation and topographic variables that are important in controlling the spatial pattern of a series of very large fires (> 40,000 ha) that were mapped using Landsat Thematic Mapper (TM) satellite imagery. Results Rain forest was more likely to be found in valleys and on steep south‐facing slopes. Fires typically burned within highly flammable treeless moorland and stopped on boundaries with less flammable surrounding vegetation types such as wet sclerophyll forest and rain forest. Controlling for the effect of vegetation, fires were most likely to burn on flats, ridges and steep north‐facing slopes and least likely to burn in valleys and on steep south‐facing slopes. These results suggest an antagonism between fire and rain forest, in which rain forest preferentially occupies parts of the landscape where fire is least likely to burn. Main conclusions The distribution of rain forest on nutrient‐poor substrates was clearly related to parts of the landscape that are protected from fire (i.e. topographic fire refugia). The relative flammability of vegetation types at the landscape scale offers support to the proposed hierarchy of fire frequencies (moorland > scrub > wet sclerophyll > rain forest) that underpins the ecological models proposed for the region. The interaction between fire occurrence and a range of topographic variables suggests that topography plays an important role in mediating the fire–vegetation feedbacks thought to maintain vegetation mosaics in south‐west Tasmania. We suggest that these fire–topography interactions should be included in models of fire‐mediated alternative stable vegetation states in other fire‐prone landscapes.     

Diversity patterns of plant functional types in relation to fire regime and previous land use in Mediterranean woodlands

Abstract. We explore patterns of diversity of plant functional types (PFTs) in Mediterranean communities subjected to landscape‐scale fire disturbances in a mosaic of uncultivated and old fields stands. We use regenerative and growth form attributes to establish two sets of PFTs of perennial species living in shrublands and pine forests of NE Spain. We test the following hypotheses: 1. Fire frequency decreases regenerative PFTs diversity by negatively selecting attributes with low regenerative efficiency. 2. Fire history has more influence on regenerative than on growth form PFTs. 3. The lowest diversity of growth form PFTs will be in old fields without recent fires. We surveyed stands of different combinations of fire and land use histories. Fire history included areas without fires in the last twenty years (unburned), sites burned in 1982 (1‐burned), and sites burned in 1982 and 1994 (2‐burned). Land use histories considered terraced old fields, and uncultivated stands on stony soils. We analysed patterns of PFT abundance and diversity at the stand level, and across the landscape (among stands absolute deviations from sample medians of the relative cover of PFTs). At the stand level, fire had more influence on the diversity patterns of regenerative PFTs than on growth form PFTs. Fire decreased the diversity of regenerative PFTs, due to the elimination of the species without effective mechanisms to post‐fire regeneration. This effect was not observed across the landscape, but seeders showed more variation in stands with longer history without fire. Land use contributed to explain the diversity patterns of growth form PFT (i.e. the number of growth form PFTs was lower in uncultivated, unburned sites), but it did not influence regenerative PFTs diversity. Patterns of PFTs diversity reflect the response to ecological processes operating at the landscape level. Overall, regenerative and growth form PFTs appear to be more sensitive to the fire history than to the past land use.