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1.
Acacia nilotica is a tree of international significance both as a beneficial plant and as a species prone to thicket formation and negative impacts on savannas throughout much of its range. While fire has been identified as a useful tool for controlling negative impacts of some Acacia species in Africa, A. nilotica adult trees are apparently fire tolerant. The effects of fire on seed bank mortality, viability and germination, and on juvenile plants of this species are unknown. We undertook a study to investigate the impacts of fire on seeds and first and second year seedlings in Australian Astrebla savannas. The primary objective was to determine the effects of control burns applied during the early stages of invasion and thicket formation. Because of high rates of seedling dessication post fire in 1997, supplementary watering was undertaken until fire mortality could be measured the following year. High seed mortality occurred for seeds located either in cattle dung (100%) or on the soil surface (c. 80%). Germination of those seeds that survived was enhanced following exposure to fire. Very high fire mortality (99%) was observed among first year seedlings and moderate mortality (60%) for second year seedlings even after a low intensity burn. Negative impacts on major pasture species were minimal. The implications of these findings are discussed in relation to A. nilotica fire ecology and to the efficacy of fire as a tool for managing this species. 相似文献
2.
Forest fire frequency in Mediterranean countries is expected to increase with land cover and climate changes as temperatures rise and rainfall patterns are altered. Although the cause of many Mediterranean fires remains poorly defined, most fires are of anthropogenic origin and are located in the wildland urban interface (WUI), so fire ignition risk depends on both weather and land cover characteristics. The objectives of this study were to quantify the overall trends in forest fire risk in the WUI of the Alpes-Maritimes department in SE France over a period of almost 50 years (about 1960–2009) and relate these to changes in land cover and temperature changes. Land cover for two contrasting reference catchments (236 km2 and 289 km2, respectively) was mapped from available aerial photographs. Changes in fire risk over time were estimated using statistical relationships defined for each type of WUI, where isolated and scattered housing present a greater risk than dense and very dense housing. Summer monthly temperatures and spring and summer precipitation were quantified over the same temporal period as land cover. Finally, trends in fire frequency and burned area were analyzed over a shorter 37 year period (1973–2009) due to the lack of available fire data before 1973. Fire risk associated with WUI expansion increased by about 18%–80% over the 1960–2009 period (depending on the catchment). Similarly, mean summer minimum and maximum monthly temperatures increased by 1.8 °C and 1.4 °C, respectively, over the same period. Summer rainfall appears to decrease over time since about the 1970's but remains highly variable. Land cover and weather changes both suggest an overall increase in fire risk. However, the number of fires and burned area have decreased significantly since about 1990. This paradoxical result is due to a change in fire-fighting strategy which reinforced the systematic extinction of fires in their early stages. Technical support in the form of improved radio communication and helicopters contributed greatly to reducing fire frequency and burned area. Surveillance and legal reforms included the introduction of field patrols and restricted access to forests during high risk periods. Although this has proven highly successful in the short term, the risk of fuel load accumulation over time remains a risk which might contribute to the development of mega-fires in extreme climatic conditions in the future. 相似文献
3.
干旱和半干旱地区草地生态系统木本植物入侵及其导致的草原灌丛化已经成为全球范 围普遍发生的现象, 是草地沙化和荒漠化的一个重要标志。干旱生态系统中, 此种类型的植被变 化将对区域和全球生物地球化学循环产生显著影响。过度放牧、区域气候干旱化和自然火过程是 导致灌丛入侵和发展的主要控制因子。草原灌丛化过程中, 草地生态系统分布较为均匀的土壤养 分及相关元素在水平和垂直方向发生分异, 关键生命元素C、N、P 、S 生物地球化学循环的变化 将对全球气候变化产生显著作用。全球气候变化与草原灌丛荒漠化之间存在潜在的反馈机制, 人 类扰动的影响将使这种反馈作用变得更加迅速和灵敏。 相似文献
4.
The short-term (2 years) influence of fire burning with the wind (head fire) and against the wind (back fire) on the productivity (above-ground phytomass and litter) and fire behaviour were determined over seven growing seasons (1995/96–2001/02) in a semi-arid rangeland. The results showed that head fires had significantly greater flame height and rate of spread than back fires. Fire caused a decrease of 40.5% and 22.5% in basal cover for the first and second seasons after burning respectively. The seasonal above-ground phytomass production and litter were significantly decreased by fire over all growing seasons. Seasonal production losses due to fire varied between 225 and 430 kg ha−1. The relation between above-ground phytomass production loss due to fire, and two independent variables namely seasonal rainfall and fuel load (above-ground phytomass plus litter) before burning, were investigated. The multiple linear regression equations obtained for one (r=0.89) and 2 years (r=0.86) after a fire, can be used with great success in estimating seasonal production losses due to fire in semi-arid rangeland. 相似文献
5.
干旱和半干旱地区草地生态系统木本植物入侵及其导致的草原灌丛化已经成为全球范 围普遍发生的现象， 是草地沙化和荒漠化的一个重要标志。干旱生态系统中， 此种类型的植被变 化将对区域和全球生物地球化学循环产生显著影响。过度放牧、区域气候干旱化和自然火过程是 导致灌丛入侵和发展的主要控制因子。草原灌丛化过程中， 草地生态系统分布较为均匀的土壤养 分及相关元素在水平和垂直方向发生分异， 关键生命元素C、N、P 、S 生物地球化学循环的变化 将对全球气候变化产生显著作用。全球气候变化与草原灌丛荒漠化之间存在潜在的反馈机制， 人 类扰动的影响将使这种反馈作用变得更加迅速和灵敏。 相似文献
6.
Early dry-season prescribed fires can reduce fuel loads and thus prevent or mitigate the severity of late, high-intensity fires that spread widely in savanna ecosystems and damage woody plants. However, due to the lack of scientific knowledge regarding fuel characteristics and fire behavior in West African savannas, this practice can have effects that are diametrically opposed to those desired and may threaten the environment. There are three crucial parameters that must be considered when planning early-season prescribed fires: the ignition probability, the rate of spread of a fire and the amount of fuel consumed. In this study, 231 early-season prescribed fires were conducted in three savanna ecosystems in Senegal in order to characterize these three fundamental parameters.Logistic regression analyses revealed that fuel moisture content and relative humidity are good predictors of ignition probability. Multiple linear regressions were used to investigate the relationships between fire rate of spread, fuel consumption or fire intensity and fuel and weather conditions. Readily usable nomographs for forest managers were created based on those relationships that proved to be significant. Kruskal–Wallis tests performed to compare the observed rates of fire propagation with those predicted using BehavePlus showed no statistically significant difference between them. 相似文献
7.
We use a 31 year dataset to assess the effects of resources (rainfall, soil, relief) and disturbance (cattle browsing and fire) on regeneration and growth in a long-lived tree Acacia peuce from arid inland Australia. Temporal and spatial resource availability had an overwhelming effect on recruitment and stand density; but cattle browsing and fire limited sapling growth and stand persistence, respectively. Seedling establishment over the 31 years was effectively confined to a single prolonged high rainfall phase. Cattle browsing in productive (run-on) patches kept saplings short; while long-fenced and low cattle-use (run-off) patches provided spatial escape opportunities for sapling growth. Fire caused the death of standing plants, but it did not stimulate recruitment, and was therefore an additional limiting factor for stand persistence. Our study provided further support for the central role of prolonged large rainfall events for regeneration in long-lived arid trees, but it also emphasised how disturbance can strongly limit stand regeneration. Overall, we expect that desert trees such as Acacia peuce that are characterised by slow population dynamics will be adversely affected by climate change due to increasingly rare recruitment. Minimisation of disturbance factors will be an increasingly important requirement for the long-term persistence of this species. 相似文献
8.
Buffelgrass invasions have been documented in Australia to North America, pointing to an end result of large-scale wildfires. In heavily populated areas such as Nogales, Sonora and Tucson and Phoenix, Arizona buffelgrass populations are growing exponentially. Although much research has been conducted on buffelgrass, relatively little is known about fire behaviors produced by a buffelgrass-fueled fire. To determine which abiotic and biotic characteristics best predict fire behavior, fire-behavior characteristics were measured in four prescribed fires in southern Arizona. Given that buffelgrass is known to decrease native plant richness in other ecosystems, the relationship between buffelgrass abundance and native plant cover was evaluated. Buffelgrass fires are more intense than fires in surrounding ecosystems, even in communities with comparable fuels. There is a strong negative relationship between buffelgrass cover and native plant cover. In addition, buffelgrass appears to be invading favorable microsites rather than species-poor communities and is radiating from the former sites. Historically, fire was rare in arid regions, but with the increase in fuels and because arid regions have weather that promotes intense fire behavior, as observed in this study, managers will increasingly observe and need to mitigate hazardous fires. 相似文献
9.
Fire is an important disturbance agent for terrestrial ecosystems, particularly in tropical and subtropical regions where its occurrence is controlled by multiple biophysical and anthropogenic variables. We assessed the temporal and spatial patterns of active fire detections (MODIS product MCD14ML) in the Caribbean region of Colombia between 2003 and 2015, using time series, cross-correlation, hot spot and density techniques. We also assessed the environmental envelope of active fires by evaluating the effect of multiple biophysical and anthropogenic variables on fire presence/absence using generalized linear models (GLMs). Results show that fires follow a clear intra-annual cycle, with 86% of fire events taking place during the region's main dry season (December–March). There is also inter-annual variability related to the Tropical North Atlantic (TNA) quasi-decadal climatic oscillation. Active fires exhibit a distinctive spatial pattern, with regional hotspots. The set of variables that best explain fire presence/absence include biophysical (TNA, temperature annual range, dry quarter precipitation), anthropogenic (minimum distance to towns and roads) and composite (NDVI) variables. The extensive and ongoing land cover transformation of this region, from forest to pasture and agriculture, will likely increase the extent of burned areas and future carbon fire emissions to the atmosphere. 相似文献
10.
《Journal of Arid Environments》1999,41(1):27-35
The effect of both a non-prescribed summer fire and grazing at high stocking rate following fire on plant community composition, the frequency of occurrence of bare soil, grasses and shrubs, species diversity and biomass of herbaceous forage were evaluated for three growing seasons after fire. Changes in community composition occurred as a consequence of both fire and grazing. Communities were dominated by unpalatable shrubs and grasses in unburned sites as a result of a long history of overgrazing. Fire contributed to a conversion of those shrublands to communities with a more favourable balance between woody and herbaceous species. The frequency of palatable grasses and herbaceous forage biomass increased by a factor ofc. 3 at the expense of woody vegetation. Grazing after fire had significant positive (i.e. decrease in undesirable grasses) and negative (i.e. increase in bare soil) effects. 相似文献
11.
A perennial forage grass, Agropyron desertorum was sown under the canopies of four shrub species or in open areas to test for facilitation during seedling establishment in an arid rangeland in Karnakh, Northeast Iran. Height, area and volume of shrubs were measured. Microclimate conditions and seedling establishment were assessed three times within two consecutive growing seasons. Near surface light intensity and air temperature were lower under shrubs, which led to initially higher soil moisture and grass establishment under the canopy of some shrub species. The leguminous shrub (Astragalus gossypinus) showed facilitation during moderate stress (summer 2009), but shifted to a negative effect during the severe drought (summer 2010). Competition, possibly for light, reduced the establishment of Agropyron seedlings under the cushion-like shrub (Acantholimon prostegium). Salsola arbusculiformis and Artemisia kopetdaghensis respectively showed a neutral and a facilitation effect in the first season, but a combined effect of allelopathy and drought led to the high mortality of Agropyron seedlings under their canopy. In conclusion in this arid rangeland, shrubs may facilitate establishment of understory plants under moderate drought stress, and for non-resource factors (light and temperature), but these positive effects are suppressed due to competition under severe drought conditions. 相似文献
12.
Foy Lake in northwestern Montana provides a record of annual-to-decadal-scale landscape change. Sedimentary charcoal and pollen analyses were used to document fire and vegetation changes over the last 3800 years, which were then compared to similar records from AD 1880 to 2000. The long-term record at Foy Lake suggests shifts between forest and steppe as well as changes in fire regime that are likely the result of climate change. Fire activity (inferred from the frequency of charcoal peaks) averaged 18 fire episodes/1000 years from 3800 to 2125 cal year BP, and increased from 16 fire episodes/1000 years at 2125 cal year BP to 22 episodes/1000 years at 750 cal year BP, a period when the pollen data suggest that steppe vegetation yielded to increasing patches of forest cover. Between 2125 and 750 cal year BP, increased forest cover produced more background charcoal than before and after this period, when vegetation was dominated by steppe. Between 750 and 75 cal year BP steppe has expanded and fire episode frequency averaged 33 episodes/1000 years, increasing to a maximum of 40 episodes/1000 years at ca. 300 cal year BP and then decreasing to present levels. Since AD 1880, the pollen record indicates an increase in shrubs and grasses from AD 1895 to 1960 as a result of vegetation changes associated with timber harvesting and livestock grazing. No fires have been documented in the Foy Lake watershed since AD 1880. Charcoal from the extralocal fires of AD 1910, burning over 4,111,249 ha in Idaho, Montana, and Wyoming, however, is present in Foy Lake. Between AD 1970 and 2000, increased arboreal pollen in the record is consistent with observations that the forest has become more closed. The activities of Euro–Americans have led to a decline in forest cover between AD 1880 and 1970, followed by a recent increase as trees are now growing in areas previously occupied by steppe. Euro–Americans are likely the cause of a reduction in fire activity in watershed since AD 1880. 相似文献
13.
In Mediterranean ecosystems, fire influences plant population dynamics and changes plant community structure by affecting germination and establishment of seeder shrubs. Fabiana imbricata is a long-lived seeder shrub with a broad distribution in South America. In Northwestern Patagonia grasslands there are many records of F. imbricata recruitment after fires. We hypothesized that recruitment is promoted by: 1) soil erosion that exposes deeply buried seeds; 2) direct fire effects such as heat that could break seed dormancy; 3) indirect fire effects (i.e. increase of light availability and elimination of allelopathic substances) and 4) water availability in spring. In field conditions, we tested the effects of shading and soil disturbance on F. imbricata recruitment and seed availability and distribution in the soil profile. Under controlled conditions, we investigated the influence of leaf leachate, light, heat and water on seed germination and seedling emergence. Seed germination was inhibited by leachate, and seedling emergence was inhibited by seed heated to 80 °C and 120° for 5 min. F. imbricata seedlings only emerged in germination treatments that simulated wet and very wet spring conditions. Fire and postfire wind that favor seed exposure, combined with high precipitation early in the growing season, would be necessary for successful shrub recruitment. When F. imbricata shrubland colonizes the grassland, it strongly modifies local vegetation structure, reduces species richness and increases fuel loads. F. imbricata is a key species in the ecosystem specially related to fire regime. Information on the postfire regeneration of this species would provide valuable knowledge of the changes in biomass accumulation in a fire-prone Mediterranean ecosystem. 相似文献
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15.
Roads extend throughout savannas, yet few studies have quantified their effects on adjoining woody vegetation structure. Airborne LiDAR imagery collected over 168 experimental fire plots in the Kruger National Park, all bounded by graded firebreak roads, provided an opportunity to study if, and to what extent, roads influence woody vegetation structure under different rainfall, geologic and fire conditions. In 91.7% of the plots, woody canopy cover was higher on the edges of roads compared to areas farther away. The increase was most pronounced within 5 m of the road edge, but was detectable 10–15 m from the edge. On average, the area within 15 m from the road had approximately 6% and 2% higher woody vegetation cover than areas further than 15 m from the edge on wetter granitic and drier basaltic savanna landscapes, respectively. Increased edge effects on woody cover were observed even in fire exclusion plots, suggesting that non-fire processes, likely altered hydrological regimes, may be the underlying reason for woody encroachment. This study illustrates that roads cause selective woody plant thickening in savannas, even in areas without road edge management, and therefore careful consideration should be paid on how road edges are managed and when roads are planned. 相似文献
16.
Thomas Saladyga 《自然地理学》2013,34(5):404-422
AbstractFire history reconstructions provide fire managers with valuable information regarding historical fire regime dynamics. Yet, in the Central Hardwood Forest Region (CHF), there is an absence of dendroecological studies where frequent wildfires have persisted into the twenty-first century. This study presents the first documented tree-ring reconstruction of fire history in the Pennsylvania anthracite coal-producing region. An approximately 150-year fire chronology was developed from fire-scarred pitch pine (Pinus rigida) and sassafras (Sassafras albidum) collected on Spring Mountain in Schuylkill County. Principal component analysis and k-means cluster analysis were used to identify four fire regime clusters based on interacting fire and non-fire parameters. Results indicate that fires occurred under a variety of moisture conditions and that a mid-twentieth century increase in fire activity on Spring Mountain was associated with the collapse of the regional anthracite industry and possibly amplified by the 1960s drought. Fires continue to burn on Spring Mountain in the twenty-first century, contrary to the dominant pattern of fire exclusion across the CHF. Future research needs are highlighted regarding historical fire regime dynamics and cultural ties to landscape burning in the Pennsylvania Anthracite Region. 相似文献
17.
The detection of vegetation fires using remote sensing has proven useful for highlighting areas undergoing rapid conversion in humid forests, but not in tropical dry forest (TDF). To further understand this relationship, we explored the correlation between MODIS Active Fires and forest cover change at local scales using 3 × 3 km sampling grids in three TDF landscapes in Bolivia; Mexico, and Brazil. Our analysis showed no single overall correlation among sites between the frequency of fires reported by the MODIS Active Fire Mapping product and forest cover change. Also, aggregated patterns of fire occurrence in Brazil and Bolivia did not correspond to areas with high percentage of forest loss, which indicates that the fire/deforestation relationship in TDF is not apparent in a simple fire frequency map. However, statistically significant correlations were found in sampling boxes with 50–60%, 50–70%, 50–95% forest cover at “initial state” of the time series in the Mexican site, Bolivian site and Brazilian site, respectively. Our findings suggest that complex interactions between anthropogenic fire-use, satellite-detected fires, and deforestation in highly fragmented TDF landscapes are difficult to describe at regional scales and might only be possible to analyze using finer resolution sampling grids. 相似文献
18.
在全球变暖趋势下,林火的频率和烈度都呈上升趋势,对林火进行准确的预警成为当前中国森林防火亟待解决的紧迫问题。当前全球最常用的火灾天气等级系统是加拿大森林火险天气指数系统(FWI),本研究介绍了其原理、基本结构、发展过程,着重介绍了FWI系统在世界范围内的校准及应用情况,对中国如何建立更适用于中国火灾特点的FWI系统提出了建议。 相似文献
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20.
Fallout radionuclide tracers identify a switch in sediment sources and transport-limited sediment yield following wildfire in a eucalypt forest 总被引：2，自引：0，他引：2
S.N. Wilkinson P.J. Wallbrink G.J. Hancock W.H. Blake R.A. Shakesby S.H. Doerr 《Geomorphology》2009,110(3-4):140-151
Fire can alter sediment sources and transport rates in river basins, changing landforms and aquatic habitats and degrading downstream water quality. Variability in the response between environments, between fires, and with time since fire makes predicting the catchment-scale effect of individual fires difficult. This study applies the fallout radionuclides 137Cs and 210Pbxs to trace the sources and transport of fine sediment through a river network following a wildfire of moderate to extreme severity in the 629-km2 eucalypt-forested Nattai River water-supply catchment near Sydney, Australia. The tracer analysis showed that post-fire erosion caused a switch in fine (< 10 µm) sediment sources from 80% subsoil derived from gully and river bank erosion to 86% topsoil derived from hillslope surface erosion. The fine sediment phosphorus content increased 4–10 fold over pre-fire levels. Annual post-fire sediment yields estimated from suspended solids rating curves were 109–250 times higher than they would have been without fire. A large additional amount of sediment remained stored within the river network for at least four years, particularly in lower-gradient reaches. Analysis of a sediment core showed that surface erosion following a previous fire had supplied at least 29% of total catchment sediment yield over the past 36 years. It is concluded that wildfire can alter catchment sediment budgets in two ways. Firstly, a spatially-diffuse pulse of elevated erosion is associated with moderate or intense rainfall events in post-fire years. Secondly, pulses of elevated catchment sediment yield are driven by the timing and river sediment transport capacity of runoff events. Severe post-fire erosion and high interannual hydrologic variability can result in large sediment stores persisting within the river network for many years. Fallout radionuclide tracers are shown to be useful in quantifying fine sediment sources and transport dynamics following wildfire, and the contribution of wildfire to catchment sediment yield. 相似文献