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Fire hazard after prescribed burning in a gorse shrubland: Implications for fuel management

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... Gorse, like other shrub fuels, often burns at very high rates of spread, leading to extremely intense fires associated with high levels of fire danger. Experimental equations (Anderson and Anderson 2010;Marino et al. 2011) have been developed to predict ignition risk and fire spread in gorse shrubland, to aid decisions concerning burn prescriptions and to support fire suppression actions. Although the efficiency of prescribed fire in reducing wildfire hazard is often mentioned as a matter of fact, there are still some uncertainties regarding the protective advantages provided, which limit the use of this technique (Fernandes and Botelho 2003). ...
... Few studies have addressed the effects of fire on shrub flammability ( Marino et al. 2010;Anderson and Anderson 2010), and even fewer have investigated the fuels resulting from prescribed burning or wildfires ( Marino et al. 2011). Some authors have studied the recovery of vegetation after several fuel treatments, including prescribed burning in shrubland ( Calvo et al. 2002;Pereiras and Casal 2002;Baeza et al. 2003;Potts et al. 2010), but have not directly assessed the flammability of the resulting vegetation. ...
... Baeza et al. (2002) and De Luis et al. (2004) studied the fuel characteristics that influence fire behaviour in Mediterranean gorse shrubland of different ages, although they did not assess fuel flammability. Evaluation of flammability parameters may help forest managers and land owners, assessing the evolution of fire hazard in order to plan the frequency of prescribed burning ( Marino et al. 2011) or improving the predictive ability of forest fire behaviour models based on physical plant parameters (Sullivan 2009). ...
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• Introduction The abandonment of rural areas has led to an increase of the fire-prone European gorse (Ulex europaeus L.) communities in some regions, where prescribed burning is a technique applied to control them. Understanding flammability changes after treatments is crucial for the sustainable use of fire. • Objectives The objectives of this study were to evaluate (1) any differences in the flammability of gorse plant parts 1 and 5 years after burning and (2) the flammability of whole plants, assessing complementarities of the results between full-scale and bench-scale tests. • Results Results showed the importance of the effect of the different scales and types of methods used to determine the four components of flammability of forest fuels: (1) Ignitability was highly dependent on the type of ignition source. (2) Combustibility was more dependent on the dead fraction than on live plant part characteristics. (3) Sustainability was mainly related to physical characteristics, like air flow interaction with fuel compactness. (4) Consumability, in terms of residual mass fraction, was similar at both scales. • Conclusions The results suggest the need for intensive management of gorse shrubland to maintain them at a very young age in order to reduce flammability associated with the rapid physiological and structural changes in this kind of vegetation.
... The high amount of oil present in gorse foliage and seeds makes this plant highly flammable (Baeza et al. 2002;Madrigal et al. 2012). The gorse fire is hard to control due to the pyrophilic characteristics of the plant such as quick-burning ability and rapid-fire propagation (Marino et al. 2011;Niño et al. 2018). Thus, the gorse fire causes significant damages to human settlements and forest ecosystems. ...
... In 1936, common gorse infestation caused a catastrophic wildfire at Bandon, United State of America, and subsequently, in 1980America, and subsequently, in , 1999America, and subsequently, in , 2007America, and subsequently, in , and 2015, gorse wildfires have done notable destruction to Bandon (GAG 2019). Not only the invasive range, but the native range of the gorse is also affected due to the high flammability of this plant (Mac-Carter and Gaynor 1980;IPMIS 2000;ARMCAN 2003;Marino et al. 2011). For instance, shrub lands in Galicia, Spain where gorse is native, are under threat due to the intensified gorse wildfires (Marino et al. 2011). ...
... Not only the invasive range, but the native range of the gorse is also affected due to the high flammability of this plant (Mac-Carter and Gaynor 1980;IPMIS 2000;ARMCAN 2003;Marino et al. 2011). For instance, shrub lands in Galicia, Spain where gorse is native, are under threat due to the intensified gorse wildfires (Marino et al. 2011). The frequent gorse fires due to widespread gorse vegetation in Donegal County, Ireland affect the fauna and flora as well as human activities (DCC 2014). ...
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It is indisputable that invasive plant species strongly impact the ecosystems they invade. Many of such impacts can be negative and threaten the local species through competition, environmental change, or habitat loss. However, introduced plants may also have positive roles in the ecosystems they invade. This review extracted information from reports on common gorse (Ulex europaeus), one of the top 100 invasive plants on the earth, including its detrimental effects and potential beneficial roles in invaded ecosystems. The reduction of native fauna and flora are the main harmful effects of common gorse identified by the literature review. Soil impoverishment and fire hazards are other negative impacts reported for common gorse that could affect agricultural systems and local economies. Despite the negative impacts, reports of positive ecological services provided by common gorse also exist, e.g., as a nursery plant or habitat for endangered native animals. We also reviewed the known human uses of this plant that could support management strategies through harvest and benefit the local communities, including its use as biofuel, raw matter for xylan extraction, medicine, and food. Finally, our review identified the gaps in the literature regarding the understanding of the beneficial role of common gorse on native ecosystems and potential human uses, especially in the tropics.
... In order to assess fire hazard in the fuel complexes, flammability tests were performed in the laboratory following the experimental method proposed in Marino et al. (2011). A piece of pine wood (2 Â 2 Â 1 cm) ignited with a standard electric radiant heater (or 'epiradiator', see Marino et al. 2010 for details) was used as a point-ignition source (Fig. 1a), and was dropped in the middle of the fuel samples (Guijarro et al. 2002;Ganteaume et al. 2009;Marino et al. 2010;Madrigal et al. 2012). ...
... Nevertheless, the present results indicated that, in addition to live shrub moisture, the increase in fire initiation risk was related to a higher proportion of necromass in the shrub fuel complexes (Fig. 2a). These findings are consistent with previous studies in gorse (Ulex sp.), in which the higher fraction of necromass in older shrubs implied a higher risk of wildfire (Baeza et al. 2002;Marino et al. 2011). Moreover, the present results indicate that live shrub moisture content thresholds for initial fire propagation varied between fuel complex types associated with different fuel management. ...
... These findings are consistent with those reported by Cheney (1981), i.e. that the moisture content that allows sustained fire propagation depends on fuel characteristics, and that higher fuel loads may result in fire sustainability at higher moisture levels. However, there is a clear distinction between levels of fuel moisture that enable fire ignition only and levels leading to sustained fire propagation, with differences ranging from 17 to 25% for a specific shrub fuel complex and under the same environmental conditions Marino et al. 2011). ...
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Fuel management is commonly used to reduce fire risk in fire-prone shrubland, but information about the real efficacy of the different techniques is scarce. In this study, we assessed in the laboratory the effects of different treatment types on fire initiation risk in a mixed heathland. The effects of two mechanical treatments and of prescribed burning were compared with untreated vegetation. Flammability tests were performed in samples of the regenerated shrubs and fine ground fuels present 2 years after treatments. Results indicate that all treatments were effective in reducing fire initiation risk in regenerated shrubs, but not in fine ground fuels. Recovery of vegetation differed between treatments, and treatment type had a significant effect on flammability, mainly affecting fire sustainability. Wind speed had a minor effect on shrub fuel flammability, whereas fuel moisture had a significant effect. The flammability of fine ground fuels differed significantly depending on fuel moisture content, even at the low levels tested. Logistic models were fitted to predict successful fire sustainability, and the probability of initial propagation was obtained as a function of treatment type, fuel moisture content and fuel structural characteristics. This study provides new insights into wildfire prevention in shrubland, and compares the effectiveness of different fuel treatment techniques.
... Developing management strategies to face novel disturbance regimes associated with climate change are fundamental for mitigating their effects (Allen et al., 2013;Marino et al., 2011). Changes predicted to occur as a result of global climate-change over the next few decades are that temperate ecosystems will experience an increase in severe summer drought and wildfire frequency (Krawchuk et al., 2009). ...
... These results suggest that management strategies to keep heath/ moorlands in a "young state" with less than 20% dead-fuel may be an effective measure for reducing wildfire risk (i.e., building phase e Watt, 1947). Similar management suggestions were proposed for U. europaeus gorse in northern Spain (Marino et al., 2011). ...
... Our laboratory experiments used a representative fuel bulk density but clearly variations in this parameter may modulate fire ignition (Marino et al., 2011;Weise et al., 2005) and further research modelling this effect is needed. Other parameters such as the dead-fuel continuity or the crown base height may also influence fire initiation (Plucinski et al., 2010). ...
... Nevertheless, little is known about the extent to which forest biomass extraction for energy use reduces fire hazard (Barbour et al. 2008;Hudiburg et al. 2011;Iversen and Van Demark 2006;Mitchell et al. 2009;Neary and Zieroth 2007;Sacchelli et al. 2013). Moreover, although some studies have investigated the effectiveness of shrub fuel treatments in reducing fire risk at stand level (Marino et al. 2011(Marino et al. , 2014a, studies on the use of shrub biomass for energy purposes are scarce (Nuñez-Regueira et al. 2004;Pérez et al. 2014;Regos et al. 2016). Given the persistent uncertainty due to a lack of quantitative assessments of how forests managed for biomass extraction decrease fire risks, in a recent study Regos et al. (2016) suggested the development of new studies at finer scales to clarify this linkage. ...
... Carbon accumulation in forest stands is a dynamic process (Pasalodos-Tato et al. 2015), and thinning and understory clearing must therefore be programmed in order to maintain low canopy bulk density and low surface fuel load to make this fuel structure consistent with the sustainability of ecological processes such as regeneration of vegetation and wildlife habitats (Moritz et al. 2014, Malico et al. 2016. Fuel reduction treatments in many Mediterranean ecosystems only reduces fire hazard in the short term because shrubs recover quickly (Fernandes 2015;Fernández and Vega 2014;Marino et al. 2011Marino et al. , 2014a. Maintenance of low shrub biomass levels at landscape level by mechanical bush clearing is currently unrealistic (not profitable for biomass industry). ...
... Mean of burnt area, total area burnt (Tot) and standard deviation ( addition, these models showed high and positive values of scaled coefficients for predicting FBP variables on comparing Scenarios A and D (Fig. 3). Models P and PM are considered high risk because of the associated high ignitability and rate of fire spread of these types of vegetation (Marino et al. 2011(Marino et al. , 2014a. The area covered by these types of vegetation is increasing due to rural abandonment (Martínez et al. 2009;Ortega et al. 2012) and fireprone adaptive traits (Pausas et al. 2008), thus increasing the fire hazard and potential burnt area (Scenario B, Table 2). ...
Article
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The Mediterranean basin is a fire-prone area and is expected to continue being so according to projected climate and socioeconomic changes. Sustainable exploitation of forest biomass could have a positive effect on wildfire hazard mitigation. A modelling approach was used to compare how four different Scenarios for biomass collection for energy use affect fire behaviour and potential burnt area at landscape level under extreme meteorological conditions in a typical Mediterranean Massif. A case study of Pinus halepensis stands in Valencia (Eastern Spain) was conducted. The FARSITE simulator was used to evaluate the burnt area and fire behaviour parameters. Simulations predicted a significant increase in the burnt area and the values of most fire behaviour parameters in a Scenario of rural abandonment, relative to the current situation. Biomass management through thinning reduced canopy bulk density; however, no differences in the values of the main fire behaviour parameters were detected. Thinning and understory clearing, including biomass collection in large shrub fuel model areas, significantly reduces fire hazard. Forest biomass sustainable harvesting for energy is expected to reduce fire hazard if management includes intense modification of fuel models, comprising management of shrub biomass at the landscape level. Strong modification of forest fuel models requires intensive silvicultural treatments. Therefore, forest biomass collection for energy in the Mediterranean basin reduces fire hazard only if both tree and shrub strata are managed at landscape level.
... The high amount of oil present in gorse foliage and seeds makes this plant highly flammable (Baeza et al. 2002;Madrigal et al. 2012). The gorse fire is hard to control due to the pyrophilic characteristics of the plant such as quick-burning ability and rapid-fire propagation (Marino et al. 2011;Niño et al. 2018). Thus, the gorse fire causes significant damages to human settlements and forest ecosystems. ...
... In 1936, common gorse infestation caused a catastrophic wildfire at Bandon, United State of America, and subsequently, in 1980America, and subsequently, in , 1999America, and subsequently, in , 2007America, and subsequently, in , and 2015, gorse wildfires have done notable destruction to Bandon (GAG 2019). Not only the invasive range, but the native range of the gorse is also affected due to the high flammability of this plant (Mac-Carter and Gaynor 1980;IPMIS 2000;ARMCAN 2003;Marino et al. 2011). For instance, shrub lands in Galicia, Spain where gorse is native, are under threat due to the intensified gorse wildfires (Marino et al. 2011). ...
... Not only the invasive range, but the native range of the gorse is also affected due to the high flammability of this plant (Mac-Carter and Gaynor 1980;IPMIS 2000;ARMCAN 2003;Marino et al. 2011). For instance, shrub lands in Galicia, Spain where gorse is native, are under threat due to the intensified gorse wildfires (Marino et al. 2011). The frequent gorse fires due to widespread gorse vegetation in Donegal County, Ireland affect the fauna and flora as well as human activities (DCC 2014). ...
... Several studies have shown that PB application is a useful fuel management tool that reduces wildfire hazard and severity, thus, improving ecosystem resilience to wildfire, particularly in Mediterranean pine plantations [14,[16][17][18][19][20][21][22]. However, current understanding of the effects of prescribed burning on ecosystem components and processes is incomplete. ...
... 11, x FOR PEER REVIEW 9 of19261Figure 2. P. pinea plantation. Mean (+ standard deviation) values of microbial biomass C (Cmic) (A and 262 B), DNA yield (C and D), fungal mycelium (E and F), fungal fraction of Cmic (Cfung % Cmic) (G and H), 263 respiration (I and J), metabolic quotient (qCO2) (K and L), and carbon mineralization rate (CMR) (M 264 and N) in the fermentation layer (F-layer), and in the 5 cm soil underneath (S-layer) of control and 265 burned plots at different times (3 h, and 33, 89, 189, 363 d) after treatment. ...
Article
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Microbial diversity plays a crucial role in ecosystem processes, including organic matter decomposition and nutrient cycling. This research explores the effect of prescribed burning (PB) on soil microbial diversity, as well as biomass and activity in Mediterranean pine plantations. In burned and adjacent unburned plots of Pinus pinea and P. pinaster plantations of Southern Italy protected areas, the fermentation layer and the 5 cm thick layer of mineral soil underneath were sampled at intervals during the first year after PB. The experimental protocol encompassed measurements of total microbial abundance (Cmic and soil DNA), fungal mycelium, fungal fraction of Cmic, microbial activity, bacterial genetic diversity (16S rDNA PCR-DGGE), microbial metabolic quotient (qCO2), and C mineralization rate (CMR), as well as physical and chemical soil properties. PB caused only temporary (up to 3 h–32 d) reductions in Cmic, DNA amount, fungal mycelium, respiration, and CMR in the P. pinaster plantation, and had no appreciable negative effect on the microbial community in P. pinea plantation, where fire intensity was lower because of less abundant litter fuel. In either plantation, PB did not generally reduce bacterial genetic diversity (evaluated as band richness, Shannon index, and evenness), thus, also accounting for the fast recovery in microbial growth and activity after high-intensity PB in P. pinaster plantation. While confirming PB as a sustainable practice to reduce wildfire risk, also supported by data on plant community obtained in the same plantations, the results suggest that an integrated analysis of microbial diversity, growth, and activity is essential for an accurate description of PB effects on soil microbial communities.
... Several studies have shown that PB application is a useful fuel management tool that reduces wildfire hazard and severity, thus, improving ecosystem resilience to wildfire, particularly in Mediterranean pine plantations [14,[16][17][18][19][20][21][22]. However, current understanding of the effects of prescribed burning on ecosystem components and processes is incomplete. ...
... 11, x FOR PEER REVIEW 9 of19261Figure 2. P. pinea plantation. Mean (+ standard deviation) values of microbial biomass C (Cmic) (A and 262 B), DNA yield (C and D), fungal mycelium (E and F), fungal fraction of Cmic (Cfung % Cmic) (G and H), 263 respiration (I and J), metabolic quotient (qCO2) (K and L), and carbon mineralization rate (CMR) (M 264 and N) in the fermentation layer (F-layer), and in the 5 cm soil underneath (S-layer) of control and 265 burned plots at different times (3 h, and 33, 89, 189, 363 d) after treatment. ...
Article
Wildfire has historically been a major disturbance in Mediterranean European ecosystems and prescribed burning is increasingly used here to mitigate possible damage and reduce hazard. This raises the issue of a possible negative impact on soil from repeated burning treatments. We investigated the effects of a single and repeated prescribed burning on total and extractable organic C, microbial biomass C, fungal mycelium, microbial activity, metabolic quotient and C mineralization rate in the fermentation layer (F-layer) and the 5-cm soil underneath of a Pinus halepensis Mill. plantation in the Cilento, Vallo di Diano e Alburni National Park, Southern Italy. Prescribed burning was sequentially applied in 2009 and 2014 and the measurements were performed during the first year following each burning treatment. The first treatment produced short-term effects on the microbial biomass and activity of the F-layer, whereas the soil layer underneath was virtually unaffected. Surprisingly, the second treatment had negligible effects on either layer, probably because of a reduction of the understory fuel load and changes in the stand structure after the first burning. Most remarkably, fire-induced changes in the soil parameters considered were generally smaller than over-time fluctuations.
... It is known that PB, and wildfire in general, modifies vegetation structure (Baeza et al., 2002;Casals, Valor, Besalú, & Molina-Terrén, 2016), plant species composition and diversity (Clemente, Rego, & Correia, 1996;De Luis, Raventós, & González-Hidalgo, 2006;Duff, Bell, & York, 2013), but less is known on how long the effects may last and how it may affect the conservation status of a mosaic of Mediterranean dry shrub-grassland Natura 2000 habitat types (Ascoli & Bovio, 2013). PB may only temporarily affect plant communities that may recover without substantial changes in plant species abundance, diversity or functional composition (Casals et al., 2016;Marino, Guijarro, Hernando, Madrigal, & Díez, 2011). Thus, the influence of PB and specifically the duration of the effects is worth investigating to assess potential PB frequency and specify it in management plans. ...
... We show that PB is effective in reducing fire hazard in the short term, and this has also been shown in similar shrub-grassland habitat types in northern (Marino et al., 2011) and eastern ...
Article
Questions: What are the effects of time since prescribed burning on plant species composition and diversity of a mosaic of Natura 2000 shrub-grassland habitat types? Is it possible to use prescribed burning to reduce fire hazard and simultaneously maintain conservation status in such habitat types? Location: Sintra-Cascais Natural Park, Portugal Methods: We assessed differences in plant species composition, plant diversity, vegetation structure and aboveground plant biomass between plots treated with prescribed burning (2, 4 and 6 years after fire) and untreated plots in a mosaic of Natura 2000 dry shrub-grasslands, and assessed potential fire behaviour differences between treatments. Results: Plant species richness and diversity was higher 2 and 4 years after prescribed burning, in comparison with untreated plots. Cover of herbaceous species and non-resprouters was higher, and cover of shrubs was lower, but only 2 years after fire. Habitat structure and phytovolume of the indicator species Ulex jussiaei was affected negatively up to 6 years after prescribed burning, indicating changes in conservation status from Favourable to Unfavourable. Prescribed burning reduced aboveground biomass and fire simulations showed that potential fire hazard was also reduced, particularly in 2-year-old plots. Conclusions: Prescribed burning increased plant diversity on the short-term, reduced fuel loads and fire hazard, but negatively affected habitat conservation status. We show that there are potential trade-offs between fire hazard mitigation and conservation in a Natura 2000 shrub-grassland habitat type and that these must be considered during fuel management decisions.
... Prescribed burning (PB) is a vegetation management technique that is used across the world for controlling fuel load and creating spatial discontinuities in the vegetation (Agee and Skinner, 2005;Marino et al., 2011), and for achieving conservation or restoration objectives as well (Stephens et al., 2014). Various studies conducted in the MR support the interest of applying PB as a fuel management tool to reduce fire risk, limit fire intensity and severity, while improving the ecosystems' resilience to fire (Fernandes and Botelho, 2003;Piñol et al., 2005;Cassagne et al., 2011;Marino et al., 2011;Fernandes et al., 2013;Casals et al., 2016). ...
... Prescribed burning (PB) is a vegetation management technique that is used across the world for controlling fuel load and creating spatial discontinuities in the vegetation (Agee and Skinner, 2005;Marino et al., 2011), and for achieving conservation or restoration objectives as well (Stephens et al., 2014). Various studies conducted in the MR support the interest of applying PB as a fuel management tool to reduce fire risk, limit fire intensity and severity, while improving the ecosystems' resilience to fire (Fernandes and Botelho, 2003;Piñol et al., 2005;Cassagne et al., 2011;Marino et al., 2011;Fernandes et al., 2013;Casals et al., 2016). Its use is still limited to few areas in the MR, though, due to a lack of social acceptance and the remaining uncertainties about its ecological effects, its operational feasibility in a wide range of situations (e.g. ...
Article
Since the 1970s, fire regimes have been modified in the Northern Mediterranean region due to profound landscape changes mostly driven by socioeconomic factors, such as rural abandonment and large-scale plantations.Both fuel accumulation and the increasing vegetation spatial continuity, combined with the expansion of the wildland-urban interface, have enhanced fire risk and the occurrence of large wildfires. This situation will likely worsen under the projected aridity increase resulting from climate change. Higher fire recurrences, in particular, are expected to cause changes in vegetation composition or structure and affect ecosystems' resilience to fire, which may lead to further land degradation. Prescribed burning is a common fuel reduction technique used for fire prevention, but for conservation and restoration purposes as well. It is still poorly accepted in the Mediterranean region since constrained by critical knowledge gaps about, in particular, its effects on the ecosystems (soil, vegetation). We studied the short-term (10 months) effects on the understory vegetation of a spring prescribed burning conducted in a Pinus halepensis forest in Mediterranean climate (Northeastern Spain). Our results show that the understory plant community recovered after the burning without short term significant changes in either species richness, diversity, or floristic composition. Most vegetation structural characteristics were modified though. The burning strongly reduced shrub height, shrub and herbaceous percentage covers, and aerial shrub phytomass; especially its living fine fraction, thus resulting in a less flammable community. The treatment proved to be particularly effective for the short term control of Ulex parviflorus, a highly flammable seeder species. Moreover, the strong reduction of seeder shrubs frequency in relation to resprouters' likely promoted the resilience to fire of this plant community. From a fuel-oriented perspective, the burning caused a strong reduction of spatial continuity and surface fuel loads, leading to a less fire-prone fuel complex.
... In addition, several definitions of 'flammability' have been proposed by different authors. The most commonly accepted definition is that proposed by Anderson [16], which considers four components of flammability: ignitability, combustibility, sustainability and consumability [12,[17][18][19]. There are many studies on this topic, adopting several methods and conducted for various purposes, but most of these methods are based on measuring the time to ignition of a given plant sample [20]. ...
... Grazing animals have been thought to inhibit the accumulation of dead biomass through consumption of foliage [32]. Where grazing pressure is sufficient to develop grazing lawns, plants are maintained in a state of continuous regeneration [33] and the proportion of accumulated dead material can be very low, thus reducing fire risk [18]. In the study area, from 2007 to 2011, continuous and moderate goat grazing had significant effects on the phytovolume and height of the studied shrubs. ...
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In this study, we evaluated changes in the potential flammability of different Mediterranean shrub species in a pine (Pinus pinea) forest in the Doñana Natural Park (of SW Spain) as a result of goat grazing. Plant height, total biomass, fine fuel biomass and leaves/wood ratio were measured in individual plants of each species in both grazed and ungrazed areas. Moisture content, mean time of ignition, mean time of combustion, gross heat of combustion (GHC) and flammability class of the studied shrub species were determined in the laboratory. The results of this experiment showed that grazing influenced the flammability characteristics of the studied shrub species. However, the strength of this effect was insufficient to modify the flammability index of these plants, except in the case of Myrtus communis, in which grazed plants presented a lower flammability index. According to Valette’s classification, Cistus salviifolius, Halimium halimifolium and Pistacea lentiscus are flammable species, Rosmarinus officinalis is a flammable-highly flammable species, and M. communis is non-flammable. The GHC values obtained were generally “intermediate”, except for those of R. officinalis, which were classified as “high”. The flammability parameters of the study species did not show a very marked trend in relation to grazing, but the vertical structure of plants did change by presenting reduced biomass of leaves and fine twigs. This change altered the physical characteristics of these plants and possibly acted to reduce the inherent fire risk of the shrublands.
... While our methods are commonly used to analyze foliar flammability (Liodakis et al., 2011;Pausas and Moreira, 2012), we did not measure species structural characteristics (e.g., bulk density) that could contribute to fire spread (Marino et al., 2011). Our community-level measures of dead fuel load and structure could be improved by the addition of such structural data. ...
Article
The overlapping zone between urbanization and wildland vegetation, known as the wildland urban interface (WUI), is often at high risk of wildfire. Human activities increase the likelihood of wildfires, which can have disastrous consequences for property and land use, and can pose a serious threat to lives. Fire hazard assessments depend strongly on the spatial scale of analysis. We assessed the fire hazard in a WUI area of a Patagonian city by working at three scales: landscape, community and species. Fire is a complex phenomenon, so we used a large number of variables that correlate a priori with the fire hazard. Consequently, we analyzed environmental variables together with fuel load and leaf flammability variables and integrated all the information in a fire hazard map with four fire hazard categories. The Nothofagus dombeyi forest had the highest fire hazard while grasslands had the lowest. Our work highlights the vulnerability of the wildland-urban interface to fire in this region and our suggested methodology could be applied in other wildland-urban interface areas. Particularly in high hazard areas, our work could help in spatial delimitation policies, urban planning and development of plans for the protection of human lives and assets.
... Dimitrakopoulos and Papaioannou (2001) regressed linear models to relate time-to-ignition and moisture content for 24 Mediterranean species. Dimitrakopoulos et al. (2010) and Marino et al. (2011) fit models relating ignition probability and moisture content. FARSITE has produced reasonable simulations of fire spread in drought-season live brush but only after extensive calibration of a custom fuel model (Arca et al., 2007). ...
Article
Wildfire models serve many purposes, from highly empirical operational models that provide decision support for fighting active fires to physical models which provide insights about fire behavior. The fuel structure of live fuels is usually complex and while leaf-scale fuel placement and behavior can significantly impact bulk fire behavior, a model has not previously been developed to investigate these effects. While a detailed treatment of fuel structure is typically outside the scope of empirical and semi-empirical models, physical and semi-physical models often provide some detail about the fuel, especially as it relates to fluid dynamics. However, these models do not typically resolve the behavior of leaf-scale particles, including their individual flames, and the interactions between flames and neighboring particles and flames. A model was created which models leaf-scale biomass as fuel particles, 3 - 6 cm lengths for chamise (Adenostoma fasciculatum) and Utah juniper (Juniperus osteosperma) and whole leaves for manzanita (Arctostaphylos glandulosa). The designated fuel particles were burned in a laboratory flat-flame burner system to determine ignition and flame characteristics of fuel particles and correlated with their physical characteristics. These experiments were used in a semi-empirical multi-particle fire spread simulator. Fuel particle locations are assigned based on L-systems, a branch of fractal theory. Fuel particle parameters are assigned based on correlations to laboratory measurements of samples. One or more fuel particles are ignited, producing flames in the model. The fire propagates through the shrub when flames from burning particles engulf neighboring leaves, which in turn ignite according to experimentally correlated preheat times. Neighboring flames synergistically interact. Convective heat transfer mechanisms are embedded in the model due to the nature of the experiments and the representation of flames in the model. The shrub models for manzanita, chamise and juniper were studied parametrically. Shrub-scale burn experiments performed on chamise and manzanita in a wind tunnel were then compared to model simulations. Simulation predictions of flame height, fraction of shrub burned, burn time, burn path and flame angle were analyzed, demonstrating the simulator's sensitivity to moisture content, wind speed and amount of fuel. This model uniquely enables the study of fuelflame and flame-flame interactions and how specific fuel placement and plant structure impacts fire spread. It also provides insight into the role convection plays in live shrub fires.
... With the exception of more arid and wind-sheltered environments, the dependency of burn probability on time, i.e. on fuel accumulation, is moderate at best in Mediterranean-type shrublands (Fernandes, Loureiro, Magalhães, Ferreira, & Fernandes, 2012;Moritz, Keeley, Johnson, & Schaffner, 2004;O'Donnell, Boer, McCaw, & Grierson, 2011;Oliveira, Pereira, & Carreiras, 2012;Van Wilgen et al., 2010). Shrublands are crown fire systems -implying that fire control is difficult at relatively mild weather conditions -and their structure and flammability recover fast after disturbance (Marino, Guijarro, Hernando, Madrigal, & Díez, 2011). In forests, and although understorey and ladder fuels take longer to recover, litter is determinant for fire spread and typically returns to its pre-treatment levels in 2-5 years (Fernandes & Botelho, 2003), except in certain short-needled conifer forests where fire spread is a self-limited process . ...
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Modified, more severe fire regimes are developing in the Mediterranean basin as a result of changes in land use and climate. Current fire management privileges fire suppression and tends to ignore land management issues, which may further accelerate the transition to a more fire-prone future and magnify the problem. Fire-smart management aims to control the fire regime by intervening on vegetation (fuel) to foster more fire-resistant (less flammable) and/or fire-resilient environments. Scientific knowledge supporting the creation and maintenance of fire-smart wildlands is critically reviewed, considering the landscape and the forest stand scales. Fuel management strategies (isolation, structural modification, and type conversion) are discussed in regards to their current and future potential to buffer the effects of global change on the extent and severity of fires. Uncertainty in the outcomes of fire-smart management arises mainly from insufficient understanding of the relative weights of fuel and weather-drought on the fire regime. Likewise, linkage between global change processes and the fire regime is not straightforward. Shrublands and, in general, open and dry vegetation types will prevail even more in future landscapes. Decrease in biomass will limit fire incidence over parts of the Mediterranean. However, the fire regime will be largely driven by weather, advising concentration of fuel management efforts in wildland–urban interfaces and in forests and their vicinity; decrease of landscape fire severity rather than area burned as the objective; prescribed burning as the treatment of choice, except in the wildland-urban interface; and focus on forest types that are fire-resilient irrespective of flammability.
... 10,11,22,26 However, periods of strong drought stress associated to future climate change scenarios could result in considerable lower values of average shrub moisture, which may lead to increased fire potential in this type of community. 27 Despite recent works that have demonstrated the relevance of live FMC when predicting ignition and fire sustainability in shrub fuels in laboratory, [28][29][30] and in the field, 31 there are very few laboratory studies addressing combined live and dead shrub moisture effect on fire ROS. ...
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Fuel bulk density and fuel moisture content effects on fire rate of spread were assessed in shrub fuels, comparing experimental data observed in outdoor wind tunnel burns and predictions from the physically-based model FIRETEC. Statistical models for the combined effects of bulk density and fuel moisture content were fitted to both the experimental and the simulated rate of spread values using non-linear regression techniques. Results confirmed a significant decreasing effect of bulk density on rate of spread in a power law in both laboratory burns and simulations. However, experimental data showed a lesser effect than simulations, suggesting a difference in the effective drag. Fuel moisture content effect was highly consistent, showing a similar exponential relationship with rate of spread in laboratory and in simulations. FIRETEC simulations showed similar orders of magnitude with predictions of two field-based empirical models, finding a significant correlation between rate of spread values. The study confirms the efficacy of the combined approach through experimental data and simulations to study fire behaviour.
... Because of its recent adoption as a wildfire-fighting tool (Salgueiro, 2010), it has not been possible to examine the effect of repeated prescribed fire on the soil. Fire intervals in shrublands might need to be just 2–3 years to maintain low fuel loads (Cassagne et al., 2011; Marino et al., 2011), contrasting with traditional, much longer prescribed fire intervals (typically 7 years in Portugal) associated with forage quality maintenance (Rego et al., 1988). Concern has been expressed about repeat-fire impacts on soil degradation (Carreira and Niell, 1995; de Koff et al., 2006; González-Pelayo et al., 2010) and soil losses were found by Campo et al. (2006) almost to double in quantity following low-intensity burning of shrub vegetation on bounded plots in south-east Spain, which had been previously burned 8 years earlier. ...
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Prescribed fire (or a controlled burn) is a management tool used in wildfire-prone areas to reduce the fuel load of living and dead biomass, while attempting to keep disturbance of the ground surface and soil to a minimum. We know that wildfire, particularly of moderate or extreme severity, can cause important changes to the chemical and physical properties of soil, typically leading to a reduction in aggregate stability, surface roughness and water storage capacity, and an increase in overland flow. It has also been shown that wildfire disturbance can cause major loss of soil, particularly at plot and hillslope scales. There is less information on soil losses at catchment scales, but it is known that losses particularly of organic-rich fine sediment and nutrients can undergo hillslope to channel transfer, where they can affect water quality. Far less research has been carried out into the effects of prescribed fire on soil and nutrient losses at all scales, but particularly at catchment scales. This paper considers the impact of an experimental fire (equivalent to a severe prescribed fire) on soil and nutrient losses. These losses have been monitored at a range of scales (small rainfall simulation plots, long-term erosion plot, erosion plot, hillslope sediment traps (sediment fences) and catchment) before and after the fire in a 10-ha catchment near Góis, central Portugal, which forms part of the 5-year DESIRE research programme concerning desertification and its mitigation at a range of study sites worldwide. The catchment has steep slopes covered mainly with scrub vegetation ranging from c. 0.15 to 2m in height. The soil is thin, stony and highly water repellent. Long-term pre-burn erosion rates are known from a c. 10-year record of soil losses from a small erosion plot (8 x 2m in size) and sediment accumulation in the weir pool of a subcatchment gauging station. Rainfall simulations carried out under dry and wet antecedent conditions before and after the fire, eroded soil collected in sediment fences installed in strategic locations on the catchment slopes and suspended sediment and bedload determinations at the catchment gauging station provide the evidence for pre- and post-fire erosional losses. Comparison with wildfire effects is provided by instrumented scrub-covered hillslopes burnt in early summer 2008 in the same area. In addition to monitoring soil losses in the small catchment, losses of selected nutrients in eroded soil and runoff together with determinations of pre- and post-fire vegetation cover, fuel loads and soil water repellency have been determined. The soil degradational implications are discussed and placed in the context of the literature on prescribed fire and wildfire impacts from elsewhere in the Mediterranean and from further afield.
... Overall, our results demonstrate a decrease in SBD as shrub height increases that seems consistent with the decrease detected with age in different shrub ecosystems [68,74,[78][79][80]. This is important because fire rate of spread is expected to change with changes in bulk density [81]. ...
Article
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Bulk density for shrubs and tree crowns is an important variable, useful for many purposes, namely estimations for biomass and carbon sequestration and potential fire behavior prediction. In the latter case, bulk density is required to predict the rate of spread and intensity of crown fires. However, bulk density information is scarce. The estimation of bulk density is crucial to help choosing proper pyrosilviculture options to decrease fire susceptibility. Due to the similar environmental conditions and fuel characteristics in Portugal and Spain, we modelled bulk density for the most common woody species in all the Iberian Peninsula. We used 10 different shrub type formations and a set of tree species or groups common to both countries. Equations for bulk density, in both forest canopy and understory layers, were fitted as a function of biometric variables commonly used in forest inventories for the selected species. Standardized estimates of bulk density can be associated with data from the National Forest Inventories from Portugal and Spain, to estimate biomass of the forest ecosystems and to evaluate potential fire behavior involving tree canopies and shrubs.
... Because of its recent adoption as a wildfire-fighting tool (Salgueiro, 2010), it has not been possible to examine the effect of repeated prescribed fire on the soil. Fire intervals in shrublands might need to be just 2-3 years to maintain low fuel loads (Cassagne et al., 2011;Marino et al., 2011), contrasting with traditional, much longer prescribed fire intervals (typically 7 years in Portugal) associated with forage quality maintenance (Rego et al., 1988). Concern has been expressed about repeat-fire impacts on soil degradation (Carreira and Niell, 1995;de Koff et al., 2006;González-Pelayo et al., 2010) and soil losses were found by Campo et al. (2006) almost to double in quantity following low-intensity burning of shrub vegetation on bounded plots in south-east Spain, which had been previously burned 8 years earlier. ...
... Gorse stands also present lower abundance and diversity of ground-dwelling arthropods than unburned, floristically more diverse heathlands [8]. Although prescribed burning has proven to be effective to reduce fuel amount in common gorse (Ulex europaeus) shrublands of Galicia, fire hazard increased again after only three years after burning [57]. ...
Article
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In the northwest of the Iberian Peninsula, characterized by its humid climate, large rural areas are being abandoned, mostly in less-favoured areas covered by heathlands, which present a low nutritive quality for livestock production. The high combustibility of these shrublands is driving a high wildfire incidence with negative environmental and economic effects. In this review, some aspects on wildfire occurrence and the potential of grazing livestock to reduce woody phytomass and fire risk in heathland-dominated areas whilst maintaining quality production and preserving biodiversity are summarized. Heathlands may be partially improved—converted to grassland—to better meet animals’ nutritional requirements while acting as ‘natural’ firebreaks. The specific grazing behaviour offers the opportunity to combine different domestic herbivores (mixed grazing) to achieve sustainable systems utilizing heterogeneous resources. Cattle, sheep, goats, and horses may have a role in the provision of different ecosystem services such as food production and biodiversity conservation. Genotype x environment interactions shape the ability of animals to cope with poor vegetation conditions, with smaller species and breeds performing better than larger animals. Goats and horses are indicated to arrest woody encroachment. Sustainable grazing systems are affordable in heathland–grassland mosaics by selecting appropriate livestock species and breeds for quality production, thus favouring rural economies and lowering fire risk.
... A basic scientific understanding of the ecological impacts of this fuel treatment exists for different Spanish ecosystems, and could be used to avoid the potential negative effects (Fontúrbel et al. 1995;Vega et al. 2000Vega et al. , 2005Calvo et al. 2002;Pereiras and Casal 2002;Vadilonga et al. 2008). Some recent studies provide useful information on the effects of prescribed burning on plant flammability and fire behaviour, which is crucial for the integration of this method in fuel management planning (Baeza et al. 2002;Marino et al. 2011;Madrigal et al. 2012). Experts consider that fire can be an effective tool for fuel management when properly managed and regulated (S11, S14). ...
Article
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Spain is one of the Mediterranean countries most severely affected by wildfires during the last 30 years, despite enhanced fire suppression efforts. At present, forest area is increasing more in Spain than in any other European country, and also has one of the highest densities of fire ignitions. However, forest management plans have been developed for only 13% of Spanish forest areas. The objective of the present study was to assess the role of forest fuel management for wildfire prevention in Spain. Different fuel management techniques, including mechanical treatments, prescribed burning and controlled grazing, were considered. A quantitative SWOT (Strengths, Weaknesses, Opportunities and Threats) analysis was performed, based on a thorough documentation review and on the opinions of forest fire experts. Results enabled the identification of obstacles that hinder the implementation of effective fuel management, and suggested strategic recommendations to overcome them. New opportunities related to rural development activities (e.g. promotion of ‘FIRESMART’ products) would be highly relevant in fire-prone forest areas. These opportunities should provide additional funding for sustainable forest management and could foster fuel management activities that would directly involve and benefit rural populations.
... Campo et al. 2006;González-Pelayo et al. 2010). Given that such management might need to be applied on a relatively frequent basis in order to maintain a sufficiently low fuel load (Cassagne et al. 2011;Marino et al. 2011), especially under expected future increased summer temperatures causing probably greater wildfire risk (Badía and Martí 2008;Harding et al. 2009), this possibility of a substantial impact might apply throughout much of the Mediterranean region. However, differences between the Tresminas study site examined here and previous studies in the Mediterranean with respect to vegetation type and prescribed fire procedures need to be considered. ...
Article
In order to decrease the risk of severe wildfire, prescribed fire has recently been adopted in Portugal and elsewhere in the Mediterranean as a major tool for reducing the fuel load instead of manual or mechanical removal of vegetation. There has been some research into its impact on soils in shrublands and grasslands, but to date little research has been conducted in forested areas in the region. As a result, the impact of prescribed fire on the physico-chemical soil characteristics of forest soils has been assumed to be minimal, but this has not been demonstrated. In this study, we present the results of a monitoring campaign of a detailed pre- and post-prescribed fire assessment of soil properties in a long-unburnt P. pinaster plantation, NW Portugal. The soil characteristics examined were pH, total porosity, bulk density, moisture content, organic matter content and litter/ash quantity. The results show that there was no significant impact on the measured soil properties, the only effect being confined to minor changes in the upper 1 cm of soil. We conclude that provided the fire is carried out according to strict guidelines in P. pinaster forest, a minimal impact on soil properties can be expected.
... When the altered burning and grazing regimes persist over time, plant communities dominated by U. gallii or B. rupestre may become trap communities, constituting alternative stable states, with very low capability to evolve to other successional stages (Beisner et al., 2003;Pausas and Bond, 2019). After seven years of grazing exclusion, the spreading of both species in diverse grasslands not only leads to community degradation but also to the accumulation of great amounts of highly flammable above-ground biomass (Canals et al., 2017;Marino et al., 2011;Reyes et al., 2009). Consequently, given the current global warming scenario, these fuel accumulations increases the hazard of spontaneous wildfires in mountains (Galiana and Lázaro, 2010;Reyes et al., 2009). ...
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Over millennia, the combination of controlled burnings and extensive grazing has maintained mosaic landscapes and preserved mountain grasslands in southern Europe. In the last century, deep socio-economic changes have led to an abandonment of traditional uses, to a general decline of the domestic herbivory and to a misuse of burning practices. This study aims to quantify how the decoupling of burning and grazing regimes affects in the long-term the structure, diversity and dynamics of high-mountain, shrub-encroached grasslands. In spring 2012, four treatments (burned-grazed, burned-ungrazed, unburned-grazed and unburned-ungrazed) were set up at three sites in the Special Area of Conservation Roncesvalles-Selva de Irati, in southwest Pyrenees. During seven years, we monitored floristic composition and the height of the native tall-grass Brachypodium rupestre in four plots at each site. In the burned plots, we surveyed the resprout of the dominant shrub Ulex gallii and the dynamics of recovering of the herbaceous vegetation. Plant communities evolved differently in grazed and ungrazed plots. Extensive grazing, despite being lower than in previous decades, maintained plant diversity and limited shrub encroachment. The total absence of grazing fostered the encroachment of U. gallii at two sites and the expansion of B. rupestre at the other site. When B. rupestre cover was greater than 60%, the encroachment of U. gallii was reduced. This research highlights the competition that occurs between shrubs and tall-grasses in the absence of grazing, and the modulating effect exerted by the burnings and the site-specific features. Understanding local plant dynamics is the first step to design the most appropriate practices that help to preserve diversity at the landscape and the community level in high-mountain grasslands of south Europe.
... Fuel load and bulk density are fuel properties that vary spatially and are well known to be critical determinants of flammability at scales of plant parts through to entire vegetation communities (e.g. Murphy & Russell-Smith 2010;Madrigal et al. 2011;Marino et al. 2011;Hoffmann et al. 2012). Both fuel load and bulk density are integral components of classical and enduring fire behavior models. ...
Article
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Factors governing landscape-scale flammability are poorly understood, yet critical to managing fire regimes. Studies of the extent and severity of the 2003 Australian alpine fires revealed marked differences in flammability between major alpine plant communities, with the occurrence and severity of fire greater in heathland compared to grassland. To understand this spatial variation in landscape flammability, we documented variation in two physical properties of fuel – load and bulk density – at the life-form and plant community scale. We measured the load (mass per unit area) and bulk density (mass per unit volume) of fine fuels (<6 mm) at 56 sites across the Bogong High Plains, southeastern Australia. Fine fuel load was positively correlated with shrub cover, and fine fuel bulk density was negatively correlated with shrub cover. Furthermore, fine fuel load and bulk density were accurately predicted using simple measures of canopy height and shrub cover. We also conducted a burning experiment on individual shrubs and snowgrass (Poa spp.) patches to assess comparative differences in flammability between these life-forms. The burning experiment revealed that shrubs were more flammable than snowgrass as measured by a range of flammability variables. Consequently, our results indicate that treeless alpine landscapes of southeastern Australia are differentially flammable because of inherent life-form differences in both fine fuel load and bulk density. If shrub cover increases in these alpine landscapes, as projected under climate change, then they are likely to become more flammable and may experience more frequent and/or severe fires.
... Fire as a management tool has been met with limited success [42]. Whilst sustained hot burns e↵ectively remove above-ground cover, plants exposed to insu cient heat are able to rapidly re-sprout from roots and exposed stems [73][74][75][76][77]. Furthermore, the eradication of aboveground vegetation stimulates the germination of seeds stored in the soil seed bank [16,26]. ...
Article
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Gorse (Ulex europeus L.) is a woody legume and invasive woody weed that has been introduced to temperate pastoral landscapes worldwide. Despite the apparent cosmopolitan distribution of gorse across much of the temperate agroecological landscapes of the world, research and practice pertaining to the management of gorse has been largely constrained to single-treatments, regions, or timeframes. Gorse eradication has been widely attempted, with limited success. Using the PRISMA (preferred reporting items for systematic reviews and meta-analysis) method and a quasi-metanalytical approach, we reviewed the seminal ~299 papers pertaining to gorse management. We identified (i) the ecological characteristics of the species that predispose gorse to behaving invasively, and (ii) the success of management actions (from a plant ecological life history perspective) in reducing weed vigour and impact. A broad ecological niche, high reproductive output, propagule persistence, and low vulnerability to pests allow for rapid landscape exploitation by gorse throughout much the world. Additionally, there are differences in flowering duration and season in the northern and southern hemisphere that make gorse particularly pernicious in the latter, as gorse flowers twice per year. The implications of these life history stages and resistance to environmental sieves after establishment are that activity and efficacy of control is more likely to be favourable in juvenile stages. Common approaches to gorse control, including herbicides, biological controls, and fire have not been ubiquitously successful, and may in fact target the very site resources—sward cover, soil stability, hydrological balance—that, when degraded, facilitate gorse invasion. Ongoing seedling regeneration presents difficulties if eradication is a goal, but facilitated competition may reduce costs via natural suppression. Mechanical methods of gorse removal, though highly successful, induce chronic soil erosion and land degradation and should hence be used sparingly.
... Because of its recent adoption as a wildfire-fighting tool (Salgueiro, 2010), it has not been possible to examine the effect of repeated prescribed fire on the soil. Fire intervals in shrublands might need to be just 2-3 years to maintain low fuel loads (Cassagne et al., 2011;Marino et al., 2011), contrasting with traditional, much longer prescribed fire intervals (typically 7 years in Portugal) associated with forage quality maintenance (Rego et al., 1988). Concern has been expressed about repeat-fire impacts on soil degradation (Carreira and Niell, 1995;de Koff et al., 2006;González-Pelayo et al., 2010) and soil losses were found by Campo et al. (2006) almost to double in quantity following low-intensity burning of shrub vegetation on bounded plots in south-east Spain, which had been previously burned 8 years earlier. ...
Article
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Prescribed (controlled) fire has recently been adopted as an important wildfire-fighting strategy in the Mediterranean. Relatively little research, however, has assessed its impacts on soil erosion and soil quality. This paper investigates hillslope-scale losses of soil, organic matter and selected nutrients before and after a 'worst-case scenario' prescribed fire in a steep, shrub-vegetated catchment with thin stony soil in central Portugal. Comparison is made with soil erosion measured: (1) on a nearby hillslope burned by wildfire and monitored at the hillslope scale and (2) on long-unburned terrain at small-plot, hillslope- and catchment-scales. Hillslope-scale pre- and post-fire soil erosion was recorded over periods of 6weeks to 5months for (1) 9.5months pre-fire and 27months post-fire in the prescribed fire catchment, and (2) c. 3years post-fire at the wildfire site. Organic matter content, pH, total N, K2O, P2O5, Ca2+ and Mg2+ were measured in the eroded sediment and in pre- and post-prescribed fire surface soil. Results indicate that: (1) both the prescribed fire and the wildfire caused expected marked increases in erosion compared with unburned terrain; and (2) the hillslope-scale post-prescribed fire soil losses (up to 2.41tha-1yr-1) exceeded many reported plot-scale post-prescribed fire and post-wildfire erosion rates in the Mediterranean. As a comparison, post-fire erosion for both fire types was less than that caused by some other forms of common soil disturbance (e.g. types of tillage) and even that on undisturbed shrubland in low rainfall areas of the region. Total estimated post-prescribed fire particulate losses of organic matter and nutrients represent only 0.2-2.9% of the content in the upper 2cm of soil, suggesting only a modest fire effect on soil quality, although this may reflect in part a lack of extreme rainfall events following the fire. The longer-term implications for soil conservation of repeated prescribed fire in the Mediterranean are explored and future research priorities identified.
... However, 5 year after treatments understory fuel load in treated areas was still significantly lower than in control. Moreover, treatments yielded a decrease in the percentage of dead understory fine fuel load related to total fine understory fuel load, providing the fuel complex with higher moisture content (Marino et al. 2011;Santana and Marrs 2014). The response in the 1 and 10 h for fuel categories is consistent with that observed for other conifer species (e.g. ...
Article
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Pinus pinaster Ait., a prominent component of the western Mediterranean forest, is a species currently suffering a high wildfire pressure and consequently becoming a prime candidate for fuel reduction treatments. However, little is known about the efficiency and longevity of modification of the fuel complex structure for fire hazard reduction treatments in this type of forest. We examined how different levels of intense thinning plus mastication altered canopy and undercanopy fuel structure in a representative forest stand in northern central Spain and its recovery for the next 5 years. We also evaluated the midterm effect on potential fire behaviour. Five years after treatments, canopy bulk density and canopy fuel load were still significantly lower than in untreated areas. After that time, understory cover and height and available undercanopy fuel load had still not reached values similar to those in untreated areas, although undercanopy available fuel complex had similar bulk density to that in untreated areas. The treatments were efficient in reducing the crown fire susceptibility in the study period, and even 5 years after treatments modelled active crown fire did not occur in treated areas.
... While our methods are commonly used to analyze foliar flammability (Liodakis et al., 2011;Pausas and Moreira, 2012), we did not measure species structural characteristics (e.g., bulk density) that could contribute to fire spread (Marino et al., 2011). Our community-level measures of dead fuel load and structure could be improved by the addition of such structural data. ...
... A sharp reduction of livestock grazing has occurred in the area during the last decades, which has favoured shrub encroachment and gorse expansion in particular. Gorse is a low palatable N 2 -fixing shrub that develops tall and dense covers with high fuel loads, which are very flammable and have a high calorific power (Elvira and Hernando, 1989;Marino et al., 2011). Therefore, prescribed, winter burnings are promoted and financially supported by the local government with amelioration purposes, in order to promote diversity by the entry of new species and to decrease the risk of uncontrolled fires that may affect valuable nearby forests. ...
Article
Rural depopulation, abandonment of traditional land uses and decrease of extensive stockfarming is accelerating shrub encroachment in mountain areas. In NW Spain, gorse (Ulex gallii Planch.) is expanding, developing dense shrublands that accumulate high fuel-loads, ignite easily and persist during long periods as alternate stable states. Under this scenario, traditional bush-to-bush farming fires are being replaced by high fuel-load burnings performed by specialised teams to reduce fuels and promote mosaic landscapes. This research analyses the effects on soil function and nitrogen (N)-cycling of these new generation of prescribed fires practiced under similar conditions to traditional fires (winter time, moist soils), but differing in the biomass and the continuity of the surface burnt. The results showed significant changes in N-cycle parameters, such as increases in inorganic N and dissolved organic nitrogen (DON), but declines in N microbial biomass and urease activity. At the ecosystem level, potential N losses were high because the pulse of water-soluble forms, DON and nitrate, following fire overlaps with periods of low biological N retention by microorganisms and plants. Although most effects were similar to those observed in traditional burnings done in the same region, the primary concern is the high potential for DON losses following prescribed burning in highly gorse-encroached areas. In N-limited ecosystems, a crucial issue is to attain an equilibrium between frequent burnings, which may prevent an optimal recovery of the soil function, and uneven burnings, which burn high amounts of accumulated fuel and increase the risk of removing large quantities of dissolved N from the ecosystem in a unique fire event. Overall, the use of different techniques combined with fire are needed to promote and consolidate desired changes in dense gorse lands.
... In any case, it is also necessary to continue monitoring all these parameters over time in order to determine how long it takes for the resulting shrub formation to reach the pre-harvest fire risk level. The scarce studies undertaken in shrubland within the Mediterranean area point to an average timespan of approximately 4-5 years for a significant return to pre-harvest fire risk, depending on the type of shrub formation [13,41]. Hence, further research is needed to assess the temporal effects of this treatment on fire behavior in the mid to long term at the study sites. ...
Article
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Mechanized harvesting of shrub formations as part of sustainable forest management not only helps reduce the risk of forest fires in Mediterranean environments but also provides economic benefit from the extracted biomass, contributing to the development of the bioeconomy. However, these mechanized operations require an environmental impact assessment to identify the short-term impacts, both positive and negative. This is especially important in the Mediterranean basin given the specific climatic conditions which exist. In this study, the environmental impact of mechanized shrub harvesting is analyzed in relation to (i) changes in biodiversity and in the presence and growth of species; (ii) physical and chemical properties of the soil; and (iii) changes in forest fire risk. For this purpose, a pre-harvest inventory was conducted and post-harvest monitoring schedules of 1-and 2-year durations were established in three characteristic Mediterranean shrubland formations located in the northern-central area of the Iberian Peninsula. Our results reveal that the recovery rates in biodiversity indices after harvesting were very high, with values ranging from 30 to 70% depending on the site. Two years after harvesting, the species coverage was similar to the pre-harvest scenario in some locations, although not with regards to height, the ericaceous species being those with the greatest sprouting capacity. Significant changes in the physical and chemical properties of soils were also observed. In this regard, negative impacts such as soil compaction or slight acidification were identified at some sites. However, positive effects were also found such as an increment in carbon and nitrogen content after harvesting, along with increased litter quantity a year from the clearing operation due to biomass residue left on the ground after harvesting. Furthermore, mechanical harvesting effectively modified fire behavior in all the shrub formations 2 years after clearing, with a notable reduction in fire risk at all the studied sites.
... Beyond the dissimilar intra-annual patterns of fire activity captured, we found that large fires were linked to different fuel models at fire ignition stage in the four zones identified, which had implications for fuel management in Spain. Our northwest fuels (fuel models 5), basically heath and gorse shrublands of, respectively, Erica australis L. and Pterospartum tridentatum (L.) Willk., and Ulex europaeus L., have been identified as hazardous by previous works, and treatments by prescribed burning, clearing and mastication are currently under discussion in terms of both efficiency and ecological effects (Fernandez et al., 2015;Marino et al., 2011). Fuels in the North zone are linked to pastures and rangelands (fuel models 1, 2) and glue gum plantations (Eucalyptus globulus Labill., fuel model 7), facing similar needs of analysis regarding best treatments, i.e. mechanical or chemical (Mirra et al., 2017). ...
Article
The area affected by wildfires is experiencing an overall decrease in the Mediterranean European region. However, there is no clear trend associated to the incidence of large fire events, which continue to pose an important threat to assets-at-risk, while debates on control by meteorological or fuel drivers are ongoing. Understanding the underlying spatial and temporal patterns of large-fire drivers is of critical importance for a more efficient and science-based management, and specifically for improving wildfire season definition and informing fuel management. Taking advantage of the reliable wildfire data available in Spain, we analyzed large fires (>100 ha) in the period 2010-2015 to outline homogenous spatial-temporal regions in terms of the influence of the main drivers of large-fire activity: temperature, wind speed, slope, distance to populated places and roads, and proximity to agricultural lands. We combined Geographically Weighted Logit Regression (GWLR) models to parameterize the marginal influence of the drivers, with optimized hierarchical clustering to define uniform regions in terms of the underlying driving factors. These regions were subsequently analyzed for monthly distribution of fire occurrence and associated fuel models. We identified four different zones in terms of drivers' features, capturing dissimilar intra-annual patterns of fire activity and affected fuels: one covering the Mediterranean and two along the northern coast, and a fourth aggregation in the hinterlands that seems to act as transition area. The Mediterranean and hinterland were linked to weather-related summer ignitions, late and early summer respectively. The northern cluster gathers most winter fires starting in remote locations under steep slopes and strong wind conditions. The northwestern cluster accounts for most of the fire activity in Spain, related to complex relief and shrub-type fuels.
... For example, harvesting biomass could also be an important management strategy for diminishing fuel continuity and wildfire hazard, the main disturbance in this type of Mediterranean ecosystems (Kitzberger and Veblen 1999), as has been largely studied for the Mediterranean basin (Madrigal et al. 2016). Our results agree that biomass harvesting in these ecosystems only reduces fire hazard in the short term because shrubland species recover quickly (Marino et al. 2011(Marino et al. , 2014Fernández and Vega 2014;Fernandes 2015;Madrigal et al. 2016) and mainly by a large bulk of fine fuels. In fact, our results show that increasing harvesting intensity of biomass (and potentially diminishing fuel continuity) produces a major production of fine fuel in the short term (potentiality increasing flammability); thus, this trade-off shows that the management of these communities for fire hazard reduction needs more complex solutions as previous works have discussed (Madrigal et al. 2016). ...
Article
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Forest biomass with energy purpose is gaining importance. Although there is a lot of information about afforestation for energy purpose, native resource management for biofuel production is a less studied topic. Consequently, generating information about management of local forest types that have potential for providing biomass for energy, such as resprouting shrublands, becomes a priority objective. We evaluated the effects of harvesting intensity on coppice growth in three resprouting shrublands with contrasting site conditions in northern Patagonia (Argentina). At each site, three harvesting treatments in strips of increasing width were randomly assigned to six permanent plots of 31.5 × 45 m during 2013–2014. Four years after, we measured resprouts (number and size of stems) of the five native dominant species. We found that almost all species responded to harvesting intensity by enhancing the coppice growth rates. Nonetheless, species showed different strategies for resource obtention. When analyzing at the community level, the response to harvesting intensity was consistent among the hillside sites, but conservative in the valley bottom site with the worst environmental conditions. Due to the high response of these species to harvesting intensity, we conclude that intense shrubland management for biomass commercialization could be a viable option depending on site conditions.
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Se estudian los regimenes selvícolas más adecuados para la utilización energética y maderable de las masas de pino carrasco (Pinus halepensis) del Macizo del Caroig, partiendo de los datos de un inventario LIDAR y de una revision bibliográfica amplia sobre la especie. Se proporcionan datos sobre los sistemas de aprovechamiento más adecuados, sus rendimientos y costes estimados para los distintos tipos de masas forestales inventariadas, se estudia la influencia de esos tratamientos sobre el riesgo de incendios forestales y se recomiendan prácticas para reducer su incidencia y gravedad a través de selvicultura preventiva e infraestructuras de defensa optimizadas mediante algoritmos basados en lógica fuzzy. Se proporcionan también datos sobre transformación energética y características de los combustibles.
Thesis
The increase in extraction of biomass from cultivated forests could negatively affect soil fertility because of high nutrient exportations. Nitrogen, an essential nutrient, is one of the most limiting factors for global forest growth. Therefore, soil nitrogen availability plays a key role in the stability or the increase in forest productivity, and suggests that fertilisation would be a necessary practice. However, in order to avoid the environmental concerns associated with the use of chemical fertilisers, an alternative coming from agroecology could integrate nitrogen-fixing species into the cropping system. This ecological option was successfully applied in forestry in mixed tree plantations associating nitrogen-fixing trees with non-fixing trees. Nevertheless, the innovating technic using nitrogen-fixing shrubs as an intercrop in forestry has to be further studied. The overarching objective of the thesis consists in improving our knowledges about the functioning of intensively managed forest ecosystems including fixing species in oligotrophic soil. To do that, we studied biotic interactions and nutriments biochemical cycles in a young maritime pine plantation (production tree), intercropped with European gorse (nitrogen-fixing species), in the Landes de Gascogne region (SW of France). We also assessed whether a gorse intercropping could maintain or increase the forest production in this forest range. Several forest trials, corresponding to various growth stages of the tested forest itinerary, were conducted in the field with conventional itineraries. Results showed that gorse understorey growth increases both light and water competition with pine. Light competition occurs in the first three to four years after trial installation, with for pine a preferential growth allocation to stem height, at the expense of diameter growth. Competition for water occurs prior to four to five years, with an increase in pine mortality and a decrease in pine water potentials during drought events in summer. However, the pine nitrogen content is increased and competition for soil nutrients, such as phosphorus, is absent throughout this time. After understorey crushing, carried out around five to six years, pines recover the production delay in two years. This is due both to an alleviation of the interspecific competition from the gorse and to a lasting nitrogen fertiliser effect, sustained by the mineralisation of crushed gorse plant material. More precisely, this mixing technique promotes nitrogen fertility and carbon storage in soil, without subsequent nitrate pollution. Further studies will be needed to show a possible gain for forestry production in the longer term. At a local scale, we recommend managers to delay the first understorey control in the case of an abundant gorse understorey. Trials in similar ecosystems could create new opportunities to apply this fertilisation technique in other forest regions.
Article
The increasing concern regarding fire in the wildland-urban interface (WUI) around the world highlights the need to better understand the flammability of WUI fuels. Research on plant flammability is rapidly increasing but commonly only considers a single fuel scale. In some cases, however, different fuel scales (e.g. leaf and litter bed) have greater influence on fire, for instance, when it spreads from the litter bed to the lower canopy. Examining fuel flammability at these different scales is necessary to better know the overall flammability but also provides insights into the drivers of flammability. To investigate if leaf and litter bed flammability differed, laboratory experiments were conducted on 15 species (native or exotic) commonly found in the WUI of south-eastern France. Species were ranked and the association of fuel characteristics with flammability sought at both scales. For most species, leaf and litter bed flammability differed because of strong fuel characteristics (e.g. leaf thickness or litter bulk density), entailing differences in rankings based on fuel scale and potentially leading to a misrepresentation of flammability of the species studied. Favouring species with lower flammability at both scales in the WUI, especially near housing, may help reduce undesired effects during wildfires.
Article
Among plant characteristics promoting flammability, terpenes have received little attention, especially regarding the vegetation surrounding housing. Here, mono-, sesqui- and diterpenes were screened in live and dead leaves of ornamental species found in wildland–urban interfaces (WUIs) of south-eastern France. Terpene content and composition were compared among species and between fuel types. Their influence on flammability was assessed through several variables and compared with that of leaf thickness and moisture content. Six of the 17 species examined contained terpenes. Terpene diversity and content differed among species but not between fuel types. Mono-, sesqui- and diterpenes (especially the highly concentrated compounds) were involved to varying degrees in both leaf and litter flammability. Their effects could be opposite according to the flammability variable and the fuel type considered. Leaf sesquiterpene content and litter total terpene content had the strongest influence on maximum combustion temperature; the former also mainly drove leaf flaming duration. The other flammability variables were more strongly associated with either moisture content or leaf thickness. Our findings highlight the idea that fire management in the WUI must also acknowledge the potential for ornamental species containing terpenes, such as Pinus halepensis, to affect fire behaviour.
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Les incendies de forêts se propagent au sein d’un combustible dont les caractéristiques physiques affectent le comportement, au même titre que les conditions atmosphériques et topographiques. Après une présentation des caractéristiques de la propagation d’un feu et des différents modèles de propagation, nous étudions le comportement du feu dans des combustibles homogènes en fonction de leurs caractéristiques physiques avec le modèle FIRETEC. Cette étude met en évidence un impact significatif de la fraction volumique (qui exprime la densité du combustible) sur la vitesse de propagation et l’intensité du feu. La vitesse de propagation décroît avec la fraction volumique ; cette tendance est validée par quelques données expérimentales de feux de litières. Par ailleurs, le comportement du feu peut passer de « wind-driven » à « plume dominated » selon la fraction volumique. En présence de canopée, cette dernière pilote également le seuil de propagation entre « torching » et « crowning ». Son fort impact sur le comportement justifie la pertinence de notre interrogation concernant l’effet de l’hétérogénéité spatiale du combustible, qui se traduit par des variations spatiales de la fraction volumique. Nous proposons ensuite une approche originale, inspirée de la bibliographie sur le rayonnement solaire dans les canopées, pour aborder les problèmes d’homogénéisation du combustible dans le calcul du transfert radiatif. Elle souligne l’influence de certaines caractéristiques du combustible (coefficient d’absorption local) et de l’hétérogénéité spatiale (recouvrement, taille des hétérogénéités) sur l’échauffement radiatif qui pilote une partie du comportement du feu. Lors de la propagation, les végétations les plus hétérogènes induisent une diminution de l’irradiance moyenne du combustible par rapport aux combustibles hétérogènes. Une distribution insuffisamment détaillée de la structure spatiale tend donc à augmenter la vitesse de propagation. Dans les canopées, une description de l’enveloppe des houppiers et la définition d’un coefficient d’agrégation à l’échelle de la pousse s’avèrent suffisantes pour une évaluation précise du transfert radiatif. Concernant les strates arbustives, une formule permet d’évaluer l’importance des effets attendus de l’hétérogénéité. Lorsque ceux-ci sont importants, une méthode d’homogénéisation est proposée. Dans un troisième temps, le calcul des écoulements en présence de canopée est abordé sous la forme d’une résolution explicite de la turbulence (large eddy simulation). Un travail de validation du modèle est proposé, sur la base de données expérimentales recueillies dans la littérature. Ces résultats illustrent l’influence significative de grandes coupures de combustible sur la nature des écoulements. Une investigation systématique des effets de l’hétérogénéité de la végétation sur l’écoulement est ensuite conduite. Pour une biomasse donnée, les résultats obtenus mettent en évidence que l’hétérogénéité du combustible induit une augmentation de la vitesse de l’écoulement moyen par rapport aux configurations homogènes. Les effets obtenus sont d’autant plus importants que le recouvrement et la taille des hétérogénéités sont élevés et que les agrégats de végétation sont denses. Une description à l’échelle des houppiers s’avère suffisante pour reproduire les écoulements au sein des canopées ; elle n’est nécessaire que lorsque le recouvrement est inférieur à 50 %. Enfin, nous étudions les effets de l’hétérogénéité de manière globale à l’échelle du paysage. Elle intégre l’ensemble des caractéristiques sur lesquelles l’hétérogénéité du combustible peut agir, y compris la source de chaleur. Elle confirme qu’une homogénéisation du combustible est à proscrire dans le cas des faibles recouvrements, alors que celle-ci ne pose pas de problème dans le cas de recouvrements élevés. Cependant, on observe une différence de comportement selon le type d’écosystème envisagé : dans le pin Maritime, l’homogénéisation se traduit par une augmentation de l’intensité et des dégâts, alors que c’est le contraire pour le pin d’Alep, qui est moins dense. Le recouvrement apparaît comme une grandeur cruciale pour la description du combustible à l’échelle de la parcelle. En effet, si une réduction du recouvrement de 75 à 50 % ne modifie pas significativement le comportement du feu, une réduction à 25 %, voire même à 0 % (suppression de la strate arborée) réduit très significativement les intensités prédites. Par ailleurs, la sévérité du feu diminue de manière importante lorsque l’on réduit le recouvrement. Cependant, les diminutions d’intensité et de sévérité s’accompagnent d’une inclinaison progressive du panache, qui induit des températures plus élevées en avant du front, qui peuvent être préjudiciables à la lutte. L’augmentation de la taille des hétérogénéités et des distances entre les agrégats induit une diminution de la sévérité du feu dans le cas de l’écosystème à pin maritime. D’autres résultats suggèrent que cette diminution pourrait être plus significative pour des recouvrements voisins de 50 %. Le travail s’achève sur une courte synthèse des différents enseignements de notre travail présentant une utilité pour le gestionnaire. Elle inclut les études appliquées réalisées, qui mettent en évidence l’applicabilité des modèles physiques. Quelques préconisations quant aux échelles appropriées à la description du combustible sont fournies, selon le type de modèle. Certains résultats concernant les écoulements sur les coupures sont appliqués à la pratique du brûlage dirigé. Le document s’achève sur quelques recommandations quant à la réalisation des coupures de combustible.
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The objective of this study was the assessment of the probability of ignition and moisture of extinction of the annual herbaceous species Slender Oat (Avena barbata Pott. ex Link) in Greece. Multiple ignition tests were conducted in situ with a drip torch during two fire seasons, with simultaneous monitoring of the weather conditions. Stepwise logistic regression was applied to assess the probability of ignition based on plant moisture content and meteorological parameters. Fuel moisture content was determined to be the only statistically significant (P < 0.0001) parameter and, therefore, it was the only variable kept in the analysis. The logistic model correctly predicted fire ignition in 93.6% of the tests and 50% ignition probability was determined at 38.5% oven-dried weight (ODW) plant moisture content. Moisture of extinction (i.e. probability of ignition at 1%) was calculated at 55.5% ODW. Furthermore, classification tree analysis was applied to determine the independent variables that explain the variability in ignition probability. Wind speed was found to have an effect on ignition probability only at relatively high (>30% ODW) fuel moisture contents. Assessment of the ignition potential and moisture of extinction of grass fuels is a prerequisite for reliable fire danger prediction.
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Shrubland are one of the main communities affected by wildland fires, both in forested and unforested areas. However, empirical models predicting fire behaviour in these communities are scarce. One reason explaining the lack of knowledge is the difficulty of obtaining data to develop these kinds of models. Wind tunnel experimental fires have been carried out in different shrubland fuel complexes (Ulex europaeus L. and Pterospartum tridentatum (L.) Willk.) collected in Galicia (NW Spain). Rate of spread data recorded in the laboratory tests have been compared with predictions from existing empirical models. The relationship between the rate of spread values observed in the wind tunnel and the values predicted by different empirical equations obtained in field experimental burns is highly significant, although models overestimate the values observed in the wind tunnel. Nevertheless, the high correlation (r between 0.86 and 0.99) allows both values to be considered proportional. Even if the laboratory scale is a limiting factor to study fire behaviour, these experiments are simpler, safer and less expensive than the ones carried out in the field. Therefore, laboratory experiments could be an important complementary source of information to field studies in order to further the understanding of fire behaviour in shrubland fuel complexes.
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Factors affecting ignition thresholds of the litter layer of shrubland vegetation were investigated using reconstructed litter beds in a laboratory. The factors investigated were fuel moisture content (FMC), litter type (primarily species), pilot ignition source, and wind. Litter beds made from 11 different litter types were ignited with point ignition sources. Litter from Allocasuarina nana (Sieber ex Spreng.) L.A.S. Johnson was used as the standard type across all experiments. Successful ignition was defined as fire spreading a fixed distance from the ignition point. Ignition success was modelled as a logistic function of FMC. Litter type had a major effect on ignitibility. The bulk density of the litter bed and the surface area of litter per volume of litter bed provided reasonably good predictors of the effect of litter type on ignition success. Low-density litter beds ignited at higher FMCs than dense litter beds. The two densest litter beds failed to ignite with the procedures used here. The ignition sources tested had significantly different effects on ignition success. Larger ignition sources were able to ignite wetter fuels than smaller sources. The presence of wind was found to have a different effect on ignition success depending on the location of the ignition source with respect to the litter bed. Wind decreased ignition success when the ignition source was located on top of the litter bed, but aided ignition when the ignition source was located within the litter bed.
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Fire-spread was measured on 121 grass fires in a 2500 ha experimental site in the Northern Territory, Australia. Selected plots were harvested to alter the height, load and bulk density of the fuel-bed. Fires were lit from a line and allowed to travel up to 400 m down-wind. Fire-spread was correlated with fuel, weather and fireshape variables using multiple regression techniques. Wind speed had most effect on fire-spread. The influence of the other variables was examined after a model for wind speed and moisture content had been fitted. Fuel load did not influence fire-spread. Fires in natural swards burnt 18% faster than fires in cut grass, but this increase could not be fully explained by changes in the height or bulk density of the fuel bed. Grass type characterised either by species group or by surface-area-to-volume ratio of the fuel particle, did not appear to significantly influence fire-spread. Differences in spread rates between the two grasses were attributed to differences in grass curing. The influence of grass curing appeared to be less than indicated by published models. Models of fire-spread in grasslands currently in use need to be revised. Ignition line length was a significant variable influencing fire-spread and this must be taken into consideration when using experimental fires to validate theoretical models or develop empirical models from field observations.
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Since the early 1990s, Mediterranean gorse shrublands have expanded significantly in the Mediterranean regions of Spain mainly as a result of the increase in the frequency and extension of forest fires. Mediterranean gorse (Ulex parviflorus), which has been described as a degradation stage of forest communities after fire, has also been described as a fire-prone community. Thus, its presence increases the risk that new fires might occur. In spite of this evidence, there is little information on both the composition and structural characteristics of these communities or the relationship that might exist between these vegetation characteristics and fire behaviour. In this paper we present the results of a characterization of the vegetative structure (plant density, specific composi- tion, biomass fractions, and horizontal and vertical fuel distribution) in Mediterranean gorse. We also analyse fire behaviour using indicators obtained at different scales. Our results show mature Mediterranean gorse shrublands to be communities with high biomass values (3000-4000 g m−2) and high horizontal and vertical vegetation con- tinuity, in which the proportion of fine dead fuel fractions with low moisture content is around 50% of the total phytomass present. Ulex parviflorus is the dominant species and its degree of dominance is a key element in the behaviour of fire. Both the fire-line intensity values and the fire severity values observed can be considered high with respect to those observed in other Mediterranean communities, thus confirming Mediterranean gorse as a high-risk community.
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Forest fire ignition potential was investigated in Picea abies (L.) Karst. (Norway spruce) and Pinus sylvestris L. (Scots pine) dominated stands of 0, 15, 30-45, and 40-60 years of age. A series of small-scale (< 0.5 m(2)) ignition tests were carried out in experimental plots on 61 different days in June, July, and August. Ignition success percentages were analyzed in relation to stand structural properties, preclassified stand types, and the output of the Canadian Fire Weather Index system. In addition, the number of average stand-type-specific fire days was estimated based on weather data (June-August) for southern Finland for the years 1991-2002. Factors in stand structure that significantly correlated with the ignition success percentage were canopy depth and leaf area index, the correlation coefficients being -0.575 (p < 0.005) and -0.582 (p < 0.005), respectively. In Pinus sylvestris dominated stands, ignition tests produced self-sustained surface fires in 32.0%, 24.0%, and 19.3% of cases in 0-, 15-, and 30- to 45-year age classes, respectively. In Picea abies dominated sites conditions were favorable for fire in 12.0% and 4.6% of trials in the 0- and 40- to 60-year age classes, respectively. The output of the FWI-system correlated well with the ignition success in June and July but poorly in August. Based on the 12-year time series analysis, there were on average per year 27, 18, and 14 potential fire days in 0-, 15-, and 30- to 45-year-old Pinus sylvestris stands, and 10 and 4 potential fire days in 0- and 40- to 60-year-old Picea abies stands, respectively. We concluded that the dominance of Picea abies or Pinus sylvestris and stand age appear to modify the ignition conditions significantly and should be used as threshold indicators in fire occurrence predictions.
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Evolutionary and paleoecological studies suggest that fires are natural in the Mediterranean basin. However, the important increase in the number of fires and area burned during the 20th century has created the perception that fires are disasters. In the present paper, we review to what extent fires are generating ecological disasters in the Mediterranean basin, in view of current fire regimes and the long-term human pressure on the landscapes. Specifically, we review studies on post-fire plant regeneration and soil losses. The review suggests that although many Mediterranean ecosystems are highly resilient to fire (shrublands and oak forest), some are fire-sensitive (e.g. pine woodlands). Observed erosion rates are, in some cases, relatively high, especially in high fire severity conditions. The sensitive ecosystems (in the sense of showing strong post-fire vegetation changes and soil losses) are mostly of human origin (e.g. extensive pine plantations in old fields). Thus, although many Mediterranean basin plants have traits to cope with fire, a large number of the ecosystems currently found in this region are strongly altered, and may suffer disasters. Post-fire disasters are not the rule, but they may be important under conditions of previous human disturbances.
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Mechanical treatments are traditionally used to modify the fuel complex in shrubland, but information about their actual effectiveness in reducing the risk of wildfire initiation is scarce. The effects of two mechanical fuel treatments (shrub clearing with crushing and manual removal) on flammability in a shrubland community in north-western Spain were compared. Three months after treatment, laboratory tests using a point-ignition source were conducted on the fine dead fuels to analyse the effect of type of treatment and fuel moisture content (FMC) under two conditions: (1) flaming; or (2) glowing + wind ignition source. Fuel load effect within each treatment was also studied. Time-to-ignition, flaming duration, number of burnt sides of the sample and fuel consumption ratio were assessed. Logistic models were developed to assess ignition and sustained combustion probabilities. Type of treatment and FMC significantly affected flammability under both experimental conditions tested. Slow smouldering was observed in fuels subjected to shrub clearing and removal, whereas crushing fuels were rapidly burnt with flaming phase combustion. In general, shrub clearing and removal appeared to be more effective in reducing wildfire hazard in these shrubland communities.
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Current fire models are designed to model the spread of a linear fire front in dead, small-diameter fuels. Fires in predominantly living vegetation account for a large proportion of annual burned area in the United States. Prescribed burning is used to manage living fuels; however, prescribed burning is currently conducted under conditions that result in marginal burning. We do not understand quantitatively the relative importance of the fuel and environmental variables that determine spread in live vegetation. To address these weaknesses, laboratory fires have been burned to determine the effects of wind, slope, moisture content and fuel characteristics on fire spread in fuel beds of common chaparral species. Four species (Adenostoma fasciculatum, Ceanothus crassifolius, Quercus berberidifolia, Arctostaphylos parryana), two wind velocities (0 and 2 m s −1) and two fuel bed depths (20 and 40 cm) were used. Oven-dry moisture content of fine fuels (<0.63 cm diameter) ranged from 0.09 to 1.06. Seventy of 125 fires successfully propagated the length (2.0 m) of the elevated fuel bed. A logistic model to predict the probability of successful fire spread was developed using stepwise logistic regression. The variables selected to predict propagation were wind velocity, slope percent, moisture content, fuel loading, species and air temperature. Air temperature and species terms were removed from the model for parsimony. The final model correctly classified 94% of the observations. Comparison of results with an empirical decision matrix for prescribed burning in chaparral suggested some agreement between the laboratory data and the empirical tool.
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Firebrands or embers are produced as trees and structures burn in wildland–urban interface (WUI) fires. It is believed that firebrand showers created in WUI fires may ignite vegetation and mulch located near homes and structures. This, in turn, may lead to ignition of homes and structures due to burning vegetation and mulch. Understanding the ignition events that are due to firebrands is important to mitigate fire spread in communities. To assess the ignition propensity of such materials, simulated firebrands of uniform geometry, but in two different sizes, were allowed to impinge on fuel beds of shredded hardwood mulch, pine straw mulch, and cut grass. The moisture content of these materials was varied. Firebrands were suspended and ignited within the test cell of the Fire Emulator/Detector Evaluator (FE/DE) apparatus. The FE/DE was used to investigate the influence of an air flow on the ignition propensity of a fuel bed. Ignition regime maps were generated for each material tested as a function of impacting firebrand size, number of deposited firebrands, air flow, and material moisture content.
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We investigated the likelihood that short-duration sustained flaming would develop in forest ground fuels that had direct contact with a small and short-lived flame source. Data from 1027 small-scale experimental test fires conducted in field trials at six sites in British Columbia and the North-West Territories between 1958 and 1961 were used to develop logistic regression models for ten fuel categories that represent unique combinations of forest cover, ground fuel type, and in some cases, season. Separate models were developed using two subsets of independent variables: (1) weather variables and fuel moisture measurements taken at the site of the test fire; and (2) Canadian Fire Weather Index (FWI) system components calculated from weather observations recorded at a nearby station. Results indicated that models developed with FWI system components were as effective as models developed with site variables at predicting the probability of short-duration sustained flaming in most fuel categories. FWI system components were not useful for predicting sustained flaming in spring grass fuels and had limited usefulness for modelling the probability of sustained flaming in aspen leaf ground fuels during summer conditions. For all other fuel categories, FWI system components were highly effective substitutes for site variables for modelling the probability of sustained flaming.
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The hypothesis that high and low intensity human-made fires can produce ecologically different effects in the Chilean matorral is examined. We compared the abundance of naturally established seedlings under shrubs burned by low and high intensity fires on five north and five south facing slopes. On south facing slopes, we found 54shrubs burned by low intensity fires and only 4shrubs burned by high intensity fires. In contrast, north facing slopes had approximately the same number of shrubs burned by low and high fire intensity fires (24 versus 19, respectively). We only found seedlings under shrubs burned by low intensity fires and most of them were of Muehlenbeckia hastulata and Trevoa trinervis. Also viable seeds were only found under shrubs burned by low intensity fires. Results indicate that fire intensity can be an important factor determining species distribution patterns in the matorral.
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Resprouting from subterranean structures is a principal method of vegetative regeneration that many shrub species show after a disturbance. This study, therefore, aims to determine the resprouting capacity and intensity of six dominant species in an Atlantic shrubland area located in the NW of the Iberian Peninsula and compare their resprouting and germinating strategies. Resprouting intensity is measured using three variables: individual probability of resprouting, number of resprouts and length of these sprouts in three plant-age classes. The intensity for each species was calculated using a simple index (IRI) that included the three measured variables. All studied species, excepting Erica umbellata, could resprout. According to the IRI values, there are three groups of species: strong resprouters (Ulex europaeus, Ulex minor and Pterospartum tridentatum), weak resprouters (Ulex micranthus and Genista triacanthos) and non-resprouters (E. umbellata). The germination of strong resprouters is highly stimulated by fire. Frequent disturbances remove the non- and weak resprouter populations and promote the strong resprouter ones.
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Fuel management techniques are commonly used in shrublands to reduce wildfire risk. However, more information about the ecological effects of these treatments is needed by managers and ecologists. In an effort to address this need, we performed a replicated (4 replicates per treatment) 48-ha experiment in northern California chaparral dominated by Adenostoma fasciculatum to determine the effects of two fuel reduction types (prescribed fire and mastication) and three different seasons of treatment (fall, winter, and spring) on shrub cover, height, and seedling density. Exclosures (2.5m2 each) were also used to assess herbivory effects. By the third post-treatment year, prescribed fire treatments had higher shrub cover (71±2%) than mastication (43±4%). There was no treatment effect on shrub height, species richness, or composition. Seedling density was initially higher in prescribed fire treatments (31±4 seedlingsm−2) than mastication (3±0 seedlings m−2); however, prescribed fire treatments experienced substantial mortality, especially spring burning, resulting in lower densities 3years after treatments (18±0seedlings m−2 after fall and winter fire compared to 2±0 seedlings m−2 after spring fire). A. fasciculatum remained the dominant shrub species after the treatments, and Ceanothus cuneatus recruitment was higher in fall burning. Deer herbivory only affected shrub height, especially in masticated units, resulting in heights of 55±2cm in unexclosed areas compared to 66±4cm inside exclosures by the third post-treatment year. Overall, our findings suggest that fuel treatments play an important role in shrubland community dynamics, at least in the short-term, with implications for re-treatment frequency, community structure, and wildlife habitat. KeywordsPrescribed burning-Mastication-Resprouting-Fire hazard-Herbivory-Chamise- Adenostoma fasciculatum - Ceanothus cuneatus
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Wildfire hazard abatement is one of the major reasons to use prescribed burning. Computer simulation, case studies, and analysis of the fire regime in the presence of active prescribed burning programs in forest and shrubland generally indicate that this fuel management tool facilitates fire suppression efforts by reducing the intensity, size and damage of wildfires. However, the conclusions that can be drawn from the above approaches are limited, highlighting the need for more properly designed experiments addressing this question. Fuel accumulation rate frequently limits prescribed fire effectiveness to a short post-treatment period (2–4 years). Optimisation of the spatial pattern of fire application is critical but has been poorly addressed by research, and practical management guidelines are lacking to initiate this. Furthermore, adequate treatment efforts in terms of fire protection are constrained by operational, social and ecological issues. The best results of prescribed fire application are likely to be attained in heterogeneous landscapes and in climates where the likelihood of extreme weather conditions is low. Conclusive statements concerning the hazard-reduction potential of prescribed fire are not easily generalised, and will ultimately depend on the overall efficiency of the entire fire management process.
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A series of laboratory fire experiments were conducted in fuel beds consisting of either excelsior (wood wool), or 6.35 mm sticks, or a mixture of these. Tests were done both with and without wind. Various characteristics of the fire, including rate of spread and fireline intensity, were compared with predictions from the Rothermel model. The behavior of the mixed fuel fires, compared to that of the fires in the constituent fuels, did not agree well with the predictions of the model. We conclude that, in order to model the behavior of fire in mixed fuels, the Rothermel model needs modification.
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A series of tests were conducted under laboratory conditions to assess, on the one hand, the capacity of several fuel beds to be ignited by firebrands and to sustain a fire and, on the other hand, the capability of different types of firebrands to ignite fuel beds,. Fuel beds and firebrands were selected amongst the most common in Southern Europe. Regarding fuel bed flammability, results show that grasses are more flammable than litters and, amongst litters, Pinus species are the most flammable. The increase of bulk density and FMC involves an increase of the time-to-ignition, and a decrease of the other flammability parameters. The capability of firebrands to ignite fuel beds is higher when the firebrands drop in flaming phase and with no air flow than in glowing phase with air flow. Logistic regression models to predict fuel bed ignition probability were developed. As a whole, results show a relationship between ignition probability of fuel bed and type or weight of firebrands. Pinus pinaster cone scale, Pinus halepensis cone scale, Eucalyptus globulus leaf and bark can have ignition probabilities at least twice higher than bark of Pines when fallen in flaming combustion.
Thesis
The process of spotting whereby burning firebrands are transported by convection and wind to ignite new fires ahead of the source fire is significant both economically and in terms of exposure of fire crews to dangerous situations. Spotting behaviour recorded in Australia is the worst in the world in terms of spotfire distance and concentration and this has been attributed to features of eucalypt bark types. This thesis is the first comprehensive firebrand investigation of any bark. It briefly examines selected firebrand characteristics of Eucalyptus diversicolor, E. marginata and E. bicostata and examines in detail the aerodynamic and combustion characteristics and fuel bed ignition potential of Eucalyptus obliqua...
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The main purpose of this study is to model the relationship between simulated human-caused fires and biophysical variables related to meteorological factors and fuel properties in Taiwan red pine forests. The experiment was carried out from August to December 1998 in the Dajashi National Forest. Three to 5 days were randomly selected to conduct the experiment monthly. Ignitions were performed hourly by igniting wooden matches and dropping them simultaneously onto a fuel bed within the period from 9 a.m. to 4 p.m. on each sampling day. A logistic model was chosen to analyze the tests. One hundred and nine trials were conducted, and 46 of these trials were successful ignitions. Univariate and multivariate regression analyses were used respectively to fit the model. Results show that the best individual predictors were moisture content of pine needles (R2 = 0.83) and relative humidity (R 2 = 0.82) in univariate regression analysis. Three variables, fuel moisture content of pine needles, wind speed, and fuel shading, fit the multivariate model (R2 = 0.93). Results indicate that the equations can be used to help predict fire danger in Taiwan red pine forests.
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In maquis and garrigue, the tendency towards stability shows itself as a general succession towards woodland. Use of a triangular diagram, where woody plants (W), herbaceous vegetation (H) and bare soil-rock-litter (S) form the 3 axes, shows how succession normally shifts a site location on the diagram towards the W apex, while grazing moves it towards to H apex and ploughing towards to S apex. The vegetation responses implied by such shifts are examined in terms of changes in floristic richness, in vegetation cover, in vertical structure and in above-ground phytomass, with reference to old-field succession and the effects of fire and grazing on Quercus coccifera garrigue. Maquis and garrigue are shown to be post-cultivation stages, but also states of degradation. Management is seen as aiming for maintenance or promotion of spontaneous re-establishment of forest.-P.J.Jarvis
Article
Since the early 1990s, Mediterranean gorse shrublands have expanded significantly in the Mediterranean regions of Spain mainly as a result of the increase in the frequency and extension of forest fires. Mediterranean gorse (Ulex parviflorus), which has been described as a degradation stage of forest communities after fire, has also been described as a fire-prone community. Thus, its presence increases the risk that new fires might occur. In spite of this evidence, there is little information on both the composition and structural characteristics of these communities or the relationship that might exist between these vegetation characteristics and fire behaviour. In this paper we present the results of a characterization of the vegetative structure (plant density, specific composition , biomass fractions, and horizontal and vertical fuel distribution) in Mediterranean gorse. We also analyse fire behaviour using indicators obtained at different scales. Our results show mature Mediterranean gorse shrublands to be communities with high biomass values (3000–4000 g m −2) and high horizontal and vertical vegetation continuity , in which the proportion of fine dead fuel fractions with low moisture content is around 50% of the total phytomass present. Ulex parviflorus is the dominant species and its degree of dominance is a key element in the behaviour of fire. Both the fire-line intensity values and the fire severity values observed can be considered high with respect to those observed in other Mediterranean communities, thus confirming Mediterranean gorse as a high-risk community.
Article
In many landscapes, an important fire management objective is to reduce the negative impacts from unplanned fires on people, property and ecological values. In Australia, there exists an inherent assumption that high spatial variability in fire ages and hence fuel loads will have negative effects on both the incidence and spread of subsequent fires, and will enhance ecological values. A recent study using the process-based computer simulation model FIRESCAPE-SWTAS predicted several relationships between prescribed burn treatment levels and spatial patterning and management objectives in south-west Tasmania, Australia. The present study extended this investigation to additionally explore the effects of prescribed burning treatment unit size on unplanned fire incidence and area burned both in the general landscape and specifically in fire-intolerant vegetation. Simulation results suggest that treatment level had the greatest influence on modifying fire effects, whereas treatment unit size had the least effect. The model predicted that all three parameters interacted to determine the mean annual area burnt by unplanned fires. In fire-intolerant vegetation, treatment unit size did not influence the incidence of unplanned fires and the area burnt by unplanned fires in these communities. Where significant differences were evident, fire risk was reduced by higher treatment levels, deterministic spatial patterns of burning units, and smaller burning unit sizes.
Article
The response of woody species to experimental burning, cutting andploughing was studied for a period of twelve years in a shrub community in NWSpain. The treatments represent the perturbations most frequently imposed bymanon these shrub communities throughout history. The response to burning is muchfaster than the response to cutting. The response to ploughing is slower due tothe regeneration mechanism that species use: germination. In general, thedominant species, Erica australis, influences theregeneration patterns of the rest of the species, which make up the community.There is a significant increase in the cover of woody species until the fourthyear, and of herbaceous species until the third year. Subsequently,Erica australis attains dominance, returning to itsoriginal spatial occupancy and cover values, removing the herbaceous speciesandnegatively influencing the growth of woody ones like Halimiumumbellatum, Halimium alyssoides and Quercuspyrenaica. Both Erica australis andChamaespartium tridentatum regenerated by sprouting in theburnt and cut plots, and by germination in the ploughed plot.Arctostaphylos uva-ursi only recovers after burning andploughing. Halimium alyssoides, Halimium umbellatum, Ericaumbellata and Calluna vulgaris regenerate bygermination in the three plots. Differences in cover values and spatialoccupancy during the first years of succession tend to be eliminated twelveyears after treatment and most of the species tend to recover their initialcover values. These shrubland communities have a high degree of resilience dueto the strong sprouting potential of the component species.
Article
Experimental testing of a mathematical model showed that radiant heat transfer accounted for no more than 40% of total heat flux required to maintain rate of spread. A reasonable prediction of spread was possible by assuming a horizontal convective heat transfer coefficient when certain fuel and flame characteristics were known. Fuel particle size had a linear relation to residence time of the flame while fuel bed porosity influenced burning rate. Burning regimes of liquid pool fires(turbulent, transitional, and laminar) appeared to also apply to moving fires in solid fuels. (Author)
Article
Heathlands in the northwest of Spain have been traditionally used by domestic herbivores as a food resource. However, their abandonment in the past decades has promoted a high incidence of wildfires, threatening biodiversity. Sheep and goats exhibit different grazing behavior, affecting rangelands dynamics in a different way, but the botanical and structural composition may also affect such dynamics. The aim of this article was to compare the grazing effects of sheep and goats on three different heathland types: previously burned grass- or gorse (Ulex gallii Planchon)-dominated and unburned heather (Erica spp.)- dominated shrublands. Two grazing treatments (sheep or goats) were applied in each vegetation type in a factorial design with two replicates (12 experimental plots). A small fenced area was excluded from grazing in each plot (control treatment). The experiment was carried out from 2003 to 2006, and the grazing season extended from May to October–November. Plant cover, canopy height, and phytomass amount and composition were assessed in each plot. Results showed that goats controlled shrub encroachment, phytomass accumulation, and canopy height more than sheep in either burned grass– and gorse– and unburned heather–dominated shrublands. It was accompanied by a higher increase of herbaceous species under goat grazing. Nevertheless, plant dynamics showed different trends between the three vegetation types studied. Grazing effects were more important in previously burned grass-dominated heathlands than in unburned heather-dominated shrublands. At the end of the experiment (May 2006), shrub cover, height, and woody phytomass were significantly higher in the ungrazed enclosures than in the grazed plots. Small ruminant grazing, especially with goats, is proposed as an efficient tool to reduce shrub encroachment and woody phytomass accumulation in heathlands, thus reducing fire hazard, although these grazing effects depend on heathland composition.
Article
The acceleration phase of a forest fire, from ignition to the equilibrium rate of spread, is perhaps the most important phase of fire behavior because often it represents the only time period in which suppression efforts could be effective. A series of experimental fires in a wind tunnel were conducted to evaluate this acceleration phase. Two types of fuel and a total of three fuel loadings and four wind speeds were tested. The results were analyzed as distance/time data, and a predictive equation produced of the form: Distance = β0 x Timeβ1 The derivative of this equation relating rate of spread at a specific elapsed time since ignition compares favorably with theoretical acceleration model curve forms. The elapsed time required to achieve an equilibrium rate of spread was constant for each fuel type over the range of conditions tested. For. Sci. 37(5):1314-1337.
Article
Experimental burns were conducted on 36 plots in mixed conifer logging slash in northern Idaho to investigate consumption of duff and woody fuel. Fires were conducted in spring and fall, in YUM (yarded unmerchantable material) and non-YUM dearcuts and seed-tree cuts. Preburn duff depth averaged 3.8 cm and consisted of a shallow layer of decomposing litter, averaging 2 cm, interspersed with deep pockets of rotten wood averaging 13 cm. Preburn total woody fuel quantities ranged from 63 to 193 t/ha. Regression relationships between fuel consumption and fuel characteristics were developed. Duff depth reduction was related to preburn duff depth and to a lesser extent, duff moisture content. Percent duff consumption and mineral soil exposure were related negatively to duff moisture and positively to large fuel (diameter > 7.6 cm) diameter reduction. Diameter reduction of large fuel pieces was positively related to preburn diameter and negatively related to measured moisture content. Consumption of rotten material was greater than that of sound material. These relationships were compared to other empirical fuel consumption models and a theoretical model in predicting our fuel consumption. The relationships presented here can be used to predict duff and woody fuel consumption from prescribed burning in logging slash in the mixed conifer type of the northern Rocky Mountains. For. Sci. 37(6):1550-1566.
Article
Question: Is it possible to model the germinative and resprouting behaviour of plant species in Atlantic shrublands and woodlands in relation to fire intensity? Is it possible to recognise different functional regenerative types in these plant species?Location: Galicia, NW Iberian Peninsula.Methods: We explored the patterns of germination and resprouting plant responses in relation to different intensities of fire using data from 37 trees, shrubs and herbaceous species growing in Atlantic shrublands and woodlands.Results: Synthesizing their germinative and resprouting behaviour, we created two graphical models: the Functional Germinative Model (FGM) and the Functional Sprouting Model (FSM). Integrating the germinative and resprouting responses, and taking into account fire intensity, we created the Functional Regenerative Model (FRM), which predicts the post-fire recuperation of the populations of each species. The FRM has been validated with data from four Atlantic communities. We identified four plant functional regenerative types (PFRT) for Atlantic forest vegetation and we propose three intensities of response.Conclusions: The extracted models (FGM, FSM and FRM) and the grouping of species in four PFRTs could be applicable to more Atlantic species, to disturbance ecology in general and to population, community and landscape management.
Article
Patterns of disconnected fuel treatment patches that overlap in the heading fire spread direction are theoretically effective in changing forward fire spread rate. The analysis presented here sought to find the unit shape and pattern for a given level of treatment that has the maximum effect on forward spread rate. This occurs when the treatment units cause the fire to spread through them at the same rate as it spreads around them. Simulations suggested that these treatment patterns reduce the spread rate or fireline intensity over much of the area burned, even outside the treatment units where the fire was forced to flank. The ideal patterns are theoretically scale independent, allowing for flexible application across heterogeneous landscapes. The topology of these patterns has implications for designing landscape-level fuel treatment patterns and for understanding spatial dynamics of fuel patterns across landscapes. FOR. SCI. 47(2):219–228.
Article
a b s t r a c t Fuel reduction in the wildland–urban interface is a widely used international strategy for assisting human communities regarding wildfire threats, but very little research has examined whether certain fuel reduction methods and their seasonal timing promote nonnative invasion. To address this issue, we evaluated nonnative and native plant response to five of the most commonly-practiced shrubland fuel reduction methods in Mediterranean climates, including (a) fall prescribed fire, (b) winter prescribed fire, (c) spring prescribed fire, (d) fall mastication (slashing) and (e) spring mastication. Treatments were rep-licated four times in mature northern California chaparral and surveyed for three years after treatment; treatment type was randomly assigned. We found that the effects of treatment type (fire/mastication) were more apparent than the effects of treatment season (fall/winter/spring), but there were some differ-ences among seasons of prescribed fire. Mastication treatments had the highest number of nonnative invasive species. Mastication treatments also had 34% higher nonnative annual grass abundance than the fire treatments. Winter and spring prescribed fire treatments were most resistant to nonnative inva-sion since these areas had the fewest nonnative species, lowest nonnative species abundances, and high-est relative proportions of native plants. In shrublands where controlling nonnative annual grass is an important objective, managers should consider cool season prescribed fire as a viable fuel reduction treatment. In cases where prescribed fire is not feasible, mastication provides an alternative that can exacerbate nonnative grass production in the short term but may maintain native plant seedbanks over the long term if the site remains undisturbed for several decades. Results from this study could be appli-cable to other areas of Mediterranean shrublands.
Article
The response of Erica australis to experimental burning, cutting and ploughing treatments was studied in two heathland communities where it was dominant. The treatments represent those most frequently originated by humans on these heathland communities throughout history. The response of this species in a community where it is dominant and there is no strong interspecific competition was also compared to that produced by it in a community where there is competition. It can be observed that the response to burning and cutting treatments is very similar with very fast spatial occupation in the first few years. From the point of view of time cover values increased in a pronounced manner during the first few years and this increase was stabilized from the fourth year. However, from this moment on a greater increase in this species' maximum height is evident. The response to ploughing is slower according to recovery mechanism (seedlings). Recovery is comparatively less in the area where there is no strong competition than in that where it exists between species.
Article
Recovery after experimental burning and cutting in a shrubland of Cistus laurifolius in NW Spain has been studied. The community was homogeneous prior to the disturbances, and tended to recover through a process of autosuccession. It was tested whether in a small space (two 100 m2 plots) there was a greater similarity among individual subplots (12) in five consecutive years, or among the five subplots considered in each plot in the same year. By comparing space and time beta diversity using analysis of variance, no significant differences were observed, which indicates that temporal changes are not of a greater magnitude than space heterogeneity, even on such a small scale. Changes in time are characterized by an increase in cover by woody species, mainly Cistus laurifolius, or a decrease in the diversity and richness of species. Space heterogeneity (differences between subplots) does not seem to be determined by environmental gradients, since the sampling surface is very small, and may be due to the effect of some annual or perennial species, which are not dominant and only appear in some subplots, probably due to random dispersal.
Article
Vegetation clearing is a fuel control technique used to reduce the risk of fires in fire-prone shrublands (e.g. Ulex parviflorus (gorse) shrublands). Nonetheless, its efficacy can be undermined as much by the reproductive strategies of the different species as by the structural organization of their phytomass. In our research we tested the hypothesis that effective control of Ulex parviflorus could be limited by the vertical dead/live shoot distribution and that this distribution could affect posterior growth. We applied clearing as a fuel-control technique in three juvenile shrublands. For the following 4 years, we studied the effects of this clearing application by measuring several structural variables of the individuals involved. At the end of the study we compared the structure of treated individuals with that of untreated ones.The clearing treatment eliminated only 46% of the population. The large dependence shown between cutting height and dead shoot height in relation to treatment effectiveness (individual mortality) suggests that applying the clearing treatment below the dead shoot level rather than above it would increase effectiveness considerably. In response to the loss of phytomass, the individuals that survived the clearing treatment increased their weight by a factor of 5 in the second year. This would explain the rapid re-establishment of the relation between phytomass and basal diameter after 2 years. Significantly larger values of phytomass and basal diameter showed a compensatory growth by the fourth year. These results show that clearing is not effective in young shrublands since it generates Ulex parviflorus-dominated shrublands in a short period of time. Temporal changes in the vertical dead/live shoot distribution are seen as a key morphological variable in the effectiveness of using clearing to control this species.
Article
Prescribed burning in chaparral, currently used to manage wildland fuels and reduce wildfire hazard, is often conducted under marginal burning conditions. The relative importance of the fuel and environmental variables that determine fire spread success in chaparral fuels is not quantitatively understood. Based on extensive experimental study, a two-dimensional numerical model for vegetation fire spread was developed to simulate laboratory-scale fires. This model is based on a detailed description of the complex heat transfer processes and a simple combustion mechanism contributing to the ignition of solid fuel and fire spread. The fuel bed is described as a porous medium, and the heterogeneous nature of foliage and branch is considered via specific physical properties such as surface area-to-volume ratio, density, and volume fraction. The burning of solid fuel is computed by solving mass and energy equations, including the effects of drying, pyrolysis, and char combustion and the exchanges of mass, momentum, and energy with the surrounding gas. The effects of wind, slope, fuel moisture content, fuel bed arrangement, environmental temperature, and humidity are considered in the numerical model. Computations were performed to compare successful and unsuccessful fire spread cases to highlight the effects of various factors. Numerical results were consistent with the experimental observations of the transition between no fire spread and spread under different fuel and environmental conditions. The simulated heat transfer processes and combustion mechanism in the fuel bed are helpful in identifying factors that determine fire spread success. It was found that the relative importance of modeled convective and radiative heat transfer processes to ignition of solid fuel differed with particle location, and could be switched depending on the wind speed, terrain slope, and fuel bed arrangement.
Article
There is a debate on which factor, fuel accumulation or meteorological variability, is the fundamental control of the occurrence of large fires in Mediterranean-type ecosystems. Its resolution has important management implications, because if the fuel hypothesis proves to be right, then fire-exclusion would enhance the occurrence of large wildfires, and prescribed-fires would be a useful tool to fight them. On the other hand, if large fires were just a direct consequence of some extreme weather situations, neither fire-exclusion nor prescribed fire would have any influence on the size of wildfires. Here we present a simple model of vegetation dynamics and fire spread over homogeneous areas intended to treat quantitatively this issue. In particular, we wanted to address the following questions: (1) What is the effect that different fire fighting capacities have on the total area burnt and, especially, on large fires? (2) What is the effect that different levels of prescribed fire have on the area burnt in wildfires and, especially, in large fires? The model incorporates meteorological variability, different rates of fuel accumulation, number of ignitions per year, fire-fighting capacity, and prescribed burning. The model was calibrated with fire regime data (mean fire size, annual area burnt, and fire size distribution) of Tarragona (NE Spain) and Coimbra (Central Portugal), and it accurately reproduced both data sets, while allowing for multiple behavioural models and prediction uncertainties within the GLUE methodology. Results showed that for a given region, with its particular characteristics of climate, number of ignitions, and vegetation flammability, there was a fairly constant annual area burnt for different fire-fighting capacities. However, higher fire-fighting capacities resulted in a slightly higher proportion of large fires. There was also a quite constant annual area burnt (prescribed and wild fires together) for different prescribed fire intensities in each region. However, the total amount and proportion of large fires decreased as the prescribed burning intensity increased. So, according to the model, it seems that the total area burnt will be more or less the same despite any effort to reduce it by extinguishing fires or by using prescribed burning. Nevertheless, the effect of the fire exclusion policy slightly enhances the dominance of large fires, whereas the use of prescribed fires greatly reduces the importance of large fires.