Land management practices associated with house loss in wildfires

Losses to life and property from unplanned fires (wildfires) are forecast to increase because of population growth in peri-urban areas and climate change. In response, there have been moves to increase fuel reduction—clearing, prescribed burning, biomass removal and grazing—to afford greater protection to peri-urban communities in fire-prone regions. But how effective are these measures? Severe wildfires in southern Australia in 2009 presented a rare opportunity to address this question empirically. We predicted that modifying several fuels could theoretically reduce house loss by 76%–97%, which would translate to considerably fewer wildfire-related deaths. However, maximum levels of fuel reduction are unlikely to be feasible at every house for logistical and environmental reasons. Significant fuel variables in a logistic regression model we selected to predict house loss were (in order of decreasing effect): (1) the cover of trees and shrubs within 40 m of houses, (2) whether trees and shrubs within 40 m of houses was predominantly remnant or planted, (3) the upwind distance from houses to groups of trees or shrubs, (4) the upwind distance from houses to public forested land (irrespective of whether it was managed for nature conservation or logging), (5) the upwind distance from houses to prescribed burning within 5 years, and (6) the number of buildings or structures within 40 m of houses. All fuel treatments were more effective if undertaken closer to houses. For example, 15% fewer houses were destroyed if prescribed burning occurred at the observed minimum distance from houses (0.5 km) rather than the observed mean distance from houses (8.5 km). Our results imply that a shift in emphasis away from broad-scale fuel-reduction to intensive fuel treatments close to property will more effectively mitigate impacts from wildfires on peri-urban communities.     

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

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

大兴安岭北坡火烧迹地森林郁闭度恢复及其影响因子

1987年发生在大兴安岭北坡的特大森林火灾,总过火面积达1.33×106hm2,形成了各种火烧强度区与未火烧区构成的异质镶嵌体。火烧强度、地形以及火后人类的恢复干预都不同程度地对火后森林恢复产生了影响。研究目的有二：一是为了揭示火后森林恢复状况;二是探寻火烧强度、地形以及火后更新措施等因素对火后森林恢复的影响程度。选取了位于火烧区的图强林业局中部的育英和图强两林场为研究区,选取反映森林景观质量的郁闭度指标作为研究对象,利用地理信息系统软件,将1987年火前与2000年的郁闭度等级分布图叠加,分析火后森林质量的恢复状况;利用多元线性回归法对火烧强度、海拔、坡度、坡向、坡位等地形因子以及各种更新方式对郁闭度恢复的影响程度进行了定量研究。结果显示,2000年郁闭度等级与火前相比发生了明显变化,2000年各林型郁闭度优势等级均由较高的等级4,5降为等级3;而等级1的比重也有所降低。表明,火后森林总体生长状况良好,无林地比重降低,但由于恢复时间较短,具有较高郁闭度的森林所占比重仍较低。多元线性回归显示,各因子均对火后郁闭度恢复产生了显著性影响。其中,海拔影响最大,与郁闭度等级呈正相关;其次是火烧强度,呈负相关;其它地形因子以及更新方式影响较小。     

Habitat alteration and the conservation of African primates: case study of Kibale National Park, Uganda

Tropical forests and the animals they support are being threatened by accelerating rates of forest conversion and degradation. In a continually fluctuating sociopolitical world, it is often impossible to protect areas from such conversion until the political environment is suitable to pursue conservation goals, by which time, the forests have often been converted to other uses. This reality suggests a need for inquiry into which primate species can persist after different types of disturbances and how quickly primate communities can recover from disturbance. Here we examine the persistence of primate populations in disturbed habitats by providing a case study of patterns of primate abundance in areas of Kibale National Park (766 km2), Uganda, that have been modified by different types and intensities of human activities, primarily commercial logging and agricultural clearing. Distributional surveys at 24 sites and detailed line-transect censuses at six sites demonstrate that primate populations in Kibale are often high and suggest that patterns of population change associated with disturbance are complex. Analysis of the land use coverage of Kibale reveals that abandoned farms (10.3%) and degraded forest (8.7%) now cover 146 km2. Unfortunately, we do not know what proportion of the farms were established on areas that were forest versus grassland. However, if the areas that are now abandoned farms were all once forested, this means that 79 km2 of forest has been lost. Based on density estimates from nearby sites, this would represent a loss of 52,612 monkeys and 200 chimpanzees. Populations would also have been affected by the degradation of the 66 km2 (8.7%) of forest. These estimates of the potential reductions in the primate populations that could have resulted from forest clearing and degradation illustrate the importance of protecting land. A review of the literature illustrates that the biomass of primates found within Kibale is very high in comparison to other locations and thus illustrates the importance of Kibale to regional conservation.     

Effects of mountain pine beetle on fuels and expected fire behavior in lodgepole pine forests, Colorado, USA

In Colorado and southern Wyoming, mountain pine beetle (MPB) has affected over 1.6 million ha of predominantly lodgepole pine forests, raising concerns about effects of MPB-caused mortality on subsequent wildfire risk and behavior. Using empirical data we modeled potential fire behavior across a gradient of wind speeds and moisture scenarios in Green stands compared three stages since MPB attack (Red [1-3 yrs], Grey [4-10 yrs], and Old-MPB [～30 yrs]). MPB killed 50% of the trees and 70% of the basal area in Red and Grey stages. Across moisture scenarios, canopy fuel moisture was one-third lower in Red and Grey stages compared to the Green stage, making active crown fire possible at lower wind speeds and less extreme moisture conditions. More-open canopies and high loads of large surface fuels due to treefall in Grey and Old-MPB stages significantly increased surface fireline intensities, facilitating active crown fire at lower wind speeds (>30-55 km/hr) across all moisture scenarios. Not accounting for low foliar moistures in Red and Grey stages, and large surface fuels in Grey and Old-MPB stages, underestimates the occurrence of active crown fire. Under extreme burning conditions, minimum wind speeds for active crown fire were 25-35 km/hr lower for Red, Grey and Old-MPB stands compared to Green. However, if transition to crown fire occurs (outside the stand, or within the stand via ladder fuels or wind gusts >65 km/hr), active crown fire would be sustained at similar wind speeds, suggesting observed fire behavior may not be qualitatively different among MPB stages under extreme burning conditions. Overall, the risk (probability) of active crown fire appears elevated in MPB-affected stands, but the predominant fire hazard (crown fire) is similar across MPB stages and is characteristic of lodgepole pine forests where extremely dry, gusty weather conditions are key factors in determining fire behavior.     

Post‐fire recovery occurs overwhelmingly by resprouting in the Chaco Serrano forest of Central Argentina

In fire‐prone landscapes, differences in post‐fire regeneration by resprouting between species or sites could be far more important in explaining vegetation physiognomy and composition than seed regeneration. This is the first study exploring the relative contribution of tree resprouts and seeds to post‐fire crown volume in the Chaco Serrano forest of South America. Additionally, we compare the resprouting response among species and quantify post‐fire changes in tree composition among sites. We established 290 permanent plots distributed in three sites affected by wildfires in 2005. For all tree species in all plots we recorded survival of every individual 1 year after the fire; at the plot level, we recorded the above‐ground tree volume before and 3 years after the fire. Resprouting from the base was the main resprouting type. Survival varied between species from 73% to 100% for native species and from 7% to 100% for non‐natives. Before the fire, crown volume was similar in the three sites, and was completely lost after the fire in 92% of the plots. Three years after the fire, between 8% and 58% of crown volume was recovered. The ratio of crown recovery because of resprouts and seedlings was 1562:1. Tree composition exhibited few changes because of the high post‐fire survival of most native species. We conclude that in the semiarid Chaco Serrano ecosystem tree species regenerate mainly by resprouting. This regeneration mode should be taken into account to better understand post‐fire successional pathways of these forests, their management and the restoration of burnt forest areas.     

Forest crown density restoration and influencing factors in the burned area of northern Great Hing′an Mountains of China

Fire in the Great Hing′an Mountains in 1987 affected an area of more than 1.33×10⁶ hm², creating a mosaic of burn severities across the landscape, which strongly affected the postfire vegetation succession. In addition, undulate landform and anthropogenic disturbance inevitably influenced the postfire vegetation succession. In this paper, a typical area was selected for a case study, including two forest farms, covering more than 1.2×10⁵ hm². In order to reveal how the forest changed in 2000 (13 years after the fire) by comparing with 1987 (prefire) and to find out the relationship between the forest succession and the affecting factors, forest crown density was selected as the criterion, and forest type, fire severity, silviculture practice, elevation and topography gradients were designed as the affecting variables. With the support of GIS software, each variable was classified and entered into the multivariate regression model. The result showed that the forest crown density changed notably in 2000 compared with that of the prefire, and all the variables significantly affected the forest crown density. The most important affecting variable was elevation, which was positively correlated with the forest crown density. The next was fire severity, which was negatively related with the forest succession. The effects of topographic factors and silviculture practices on forest crown density were relatively small.     

Raised houses reduce mosquito bites

BACKGROUND: In many parts of continental Africa house construction does not appear to impede entry of malaria vectors and, given their generally late biting cycle, the great majority of transmission takes place indoors. In contrast, many houses in S?o Tomé, 140 km off the coast of Gabon, are raised on stilts and built of wooden planks. Building on stilts is a time-honoured, but largely untested, way of avoiding mosquito bites. Exposure may also be affected by mosquito activity times and age composition of host-seeking females. A study was therefore undertaken on the island of S?o Tomé to determine if exposure to Anopheles gambiae, the only vector on the island, varied with house construction or time of the night. METHODS: A series of all-night landing collections were undertaken out of doors at ground level, inside houses at ground level, on the verandas of, and inside houses built on stilts. The gonotrophic age of an unselected sample of insects from the first three hours of landing collection (18:00-21:00) was determined by dissection. In addition, 1,149 miniature light-trap collections were obtained from 125 houses in the study area. Numbers collected were related to house construction. RESULTS: Biting of An. gambiae took place primarily outside at ground level. Less than one third of biting occurred inside houses. Houses built on stilts had half the number of An. gambiae in them compared to those built at ground level. Conversely houses with an eaves gap had more An. gambiae in them than houses without such a gap. Gonotrophic age did not affect house entry rates in An. gambiae. House construction affected Culex quinquefasciatus less than An. gambiae. Mean density per house, derived from a series of 1,490 randomly assigned light-trap collections, was over-dispersed with 18% of houses having 70% of the vectors. CONCLUSION: House construction plays an important role in determining exposure to malaria vectors in S?o Tomé. Neighbours can have very different exposure levels. Recommendations for improvement in control are given.     

Simulating the Effects of Fire Reintroduction Versus Continued Fire Absence on Forest Composition and Landscape Structure in the Boundary Waters Canoe Area, Northern Minnesota, USA

The Boundary Waters Canoe Area (BWCA) Wilderness of northern Minnesota, USA, ememplifies how fire management and natural disturbance determine forest composition and landscape structure at a broad scale. Historically, the BWCA (>400,000 ha) was subject to crown fires with a mean rotation period of 50–100 y. Fires often overlapped, creating a mosaic of differently aged stands with many stands burning frequently or, alternatively, escaping fire for several centuries. The BWCA may never have reached a steady-state (defined as a stable landscape age-class structure). In the early 1900s, a diminished fire regime began creating a more demographically diverse forest, characterized by increasingly uneven-aged stands. Shade-tolerant species typical of the region began replacing the shade-intolerant species that composed the fire-generated even-aged stands. Red pine (Pinus resinosa) stands are relatively uncommon in the BWCA today and are of special concern. The replacement of early-to-midsuccessional species is occurring at the scale of individual gaps, producing mixed-species multiaged forests. We used LANDIS, a spatially explicit forest landscape model, to investigate the long-term consequences of fire reintroduction or continuing fire absence on forest composition and landscape structure. Fire reintroduction was evaluated at three potential mean fire rotation periods (FRP): 50,100, and 300 y. Our model scenarios predict that if fire reintroduction mimics the natural fire regime (bracketed by FRP = 50 and 100 y), it will be most successful at preserving the original species composition and landscape structure, although jack pine (Pinus banksiana) may require special management. With limited fire reintroduction, all of the extant species are retained although species dominance and landscape structure will be substantially altered. If fire remains absent, many fire-dependent species will be lost as local dominants, including red pine. The landscape appears to be in a state of rapid change and a shift in management to promote fire may need to be implemented soon to prevent further deviation from historic, presettlement conditions.     

High‐severity fire corroborated in historical dry forests of the western United States: response to Fulé et al.

Accurate assessment of changing fire regimes is important, since climatic change and people may be promoting more wildfires. Government wildland fire policies and restoration programmes in dry western US forests are based on the hypothesis that high‐severity fire was rare in historical fire regimes, modern fire severity is unnaturally high and restoration efforts should focus primarily on thinning forests to eliminate high‐severity fire. Using General Land Office (GLO) survey data over large dry‐forest landscapes, we showed that the proportion of historical forest affected by high‐severity fire was not insignificant, fire severity has not increased as a proportion of total fire area and large areas of dense forest were present historically (Williams & Baker, Global Ecology and Biogeography, 21 , 1042–1052, 2012; W&B). In response, Fulé et al. (Global Ecology and Biogeography, 2013, doi: 10.1111/geb.12136; FE) suggest that our inferences are unsupported and land management based on our research could be damaging to native ecosystems. Here, we show that the concerns of FE are unfounded. Their criticism comes from misquoting W&B, mistaking W&B's methods, misusing evidence (e.g. from Aldo Leopold) and missing substantial available evidence. We also update corroboration for the extensive historical high‐severity fire shown by W&B. We suggest that restoration programmes are misdirected in seeking to reduce all high‐severity fire in dry forests, given findings from spatially extensive GLO data and other sources.     

Post-Disturbance Plant Community Dynamics following a Rare Natural-Origin Fire in a Tsuga canadensis Forest

Opportunities to directly study infrequent forest disturbance events often lead to valuable information about vegetation dynamics. In mesic temperate forests of North America, stand-replacing crown fire occurs infrequently, with a return interval of 2000-3000 years. Rare chance events, however, may have profound impacts on the developmental trajectories of forest ecosystems. For example, it has been postulated that stand-replacing fire may have been an important factor in the establishment of eastern hemlock (Tsuga canadensis) stands in the northern Great Lakes region. Nevertheless, experimental evidence linking hemlock regeneration to non-anthropogenic fire is limited. To clarify this potential relationship, we monitored vegetation dynamics following a rare lightning-origin crown fire in a Wisconsin hemlock-hardwood forest. We also studied vegetation in bulldozer-created fire breaks and adjacent undisturbed forest. Our results indicate that hemlock establishment was rare in the burned area but moderately common in the scarified bulldozer lines compared to the reference area. Early-successional, non-arboreal species including Rubus spp., Vaccinium angustifolium, sedges (Carex spp.), grasses, Epilobium ciliatum, and Pteridium aquilinium were the most abundant post-fire species. Collectively, our results suggest that competing vegetation and moisture stress resulting from drought may reduce the efficacy of scarification treatments as well as the usefulness of fire for preparing a suitable seedbed for hemlock. The increasing prevalence of growing-season drought suggests that silvicultural strategies based on historic disturbance regimes may need to be reevaluated for mesic species.     

Winners and losers: tropical forest tree seedling survival across a West African forest–savanna transition

Forest encroachment into savanna is occurring at an unprecedented rate across tropical Africa, leading to a loss of valuable savanna habitat. One of the first stages of forest encroachment is the establishment of tree seedlings at the forest–savanna transition. This study examines the demographic bottleneck in the seedlings of five species of tropical forest pioneer trees in a forest–savanna transition zone in West Africa. Five species of tropical pioneer forest tree seedlings were planted in savanna, mixed/transition, and forest vegetation types and grown for 12 months, during which time fire occurred in the area. We examined seedling survival rates, height, and stem diameter before and after fire; and seedling biomass and starch allocation patterns after fire. Seedling survival rates were significantly affected by fire, drought, and vegetation type. Seedlings that preferentially allocated more resources to increasing root and leaf starch (starch storage helps recovery from fire) survived better in savanna environments (frequently burnt), while seedlings that allocated more resources to growth and resource‐capture traits (height, the number of leaves, stem diameter, specific leaf area, specific root length, root‐to‐shoot ratio) survived better in mixed/transition and forest environments. Larger (taller with a greater stem diameter) seedlings survived burning better than smaller seedlings. However, larger seedlings survived better than smaller ones even in the absence of fire. Bombax buonopozense was the forest species that survived best in the savanna environment, likely as a result of increased access to light allowing greater investment in belowground starch storage capacity and therefore a greater ability to cope with fire. Synthesis: Forest pioneer tree species survived best through fire and drought in the savanna compared to the other two vegetation types. This was likely a result of the open‐canopied savanna providing greater access to light, thereby releasing seedlings from light limitation and enabling them to make and store more starch. Fire can be used as a management tool for controlling forest encroachment into savanna as it significantly affects seedling survival. However, if rainfall increases as a result of global change factors, encroachment may be more difficult to control as seedling survival ostensibly increases when the pressure of drought is lifted. We propose B. buonopozense as an indicator species for forest encroachment into savanna in West African forest–savanna transitions.     

Historical,Observed, and Modeled Wildfire Severity in Montane Forests of the Colorado Front Range

Large recent fires in the western U.S. have contributed to a perception that fire exclusion has caused an unprecedented occurrence of uncharacteristically severe fires, particularly in lower elevation dry pine forests. In the absence of long-term fire severity records, it is unknown how short-term trends compare to fire severity prior to 20^th century fire exclusion. This study compares historical (i.e. pre-1920) fire severity with observed modern fire severity and modeled potential fire behavior across 564,413 ha of montane forests of the Colorado Front Range. We used forest structure and tree-ring fire history to characterize fire severity at 232 sites and then modeled historical fire-severity across the entire study area using biophysical variables. Eighteen (7.8%) sites were characterized by low-severity fires and 214 (92.2%) by mixed-severity fires (i.e. including moderate- or high-severity fires). Difference in area of historical versus observed low-severity fire within nine recent (post-1999) large fire perimeters was greatest in lower montane forests. Only 16% of the study area recorded a shift from historical low severity to a higher potential for crown fire today. An historical fire regime of more frequent and low-severity fires at low elevations (<2260 m) supports a convergence of management goals of ecological restoration and fire hazard mitigation in those habitats. In contrast, at higher elevations mixed-severity fires were predominant historically and continue to be so today. Thinning treatments at higher elevations of the montane zone will not return the fire regime to an historic low-severity regime, and are of questionable effectiveness in preventing severe wildfires. Based on present-day fuels, predicted fire behavior under extreme fire weather continues to indicate a mixed-severity fire regime throughout most of the montane forest zone. Recent large wildfires in the Front Range are not fundamentally different from similar events that occurred historically under extreme weather conditions.     

Metapopulation dynamics of a beetle species confined to burned forest sites in a managed forest region

Despite increasing awareness of the theoretical importance of habitat dynamics on metapopulations, only a few empirical studies have been conducted. We aimed to increase our understanding of how patch size, dynamics and connectivity affect colonization–extinction dynamics and the occurrence patterns of a beetle (Stephanopachys linearis), which breeds only in burned trees, existing as dynamic habitat patches that have become rare in managed forest landscapes. We assessed species’ presence/absence twice in all known habitat patches (i.e. > 1 ha sites where forest fires had occurred during the previous 2–15 yr) in a 200 × 150 km region of central Sweden, dominated by managed boreal forest. Evaluated over six years, the colonization rate was 47% and the local extinction risk was 65%. Probability of colonization increased with patch size (number of suitable trees in a site) and connectivity to occupied patches within 30 km, and decreased with increasing time since fire. Local extinction risk decreased with habitat patch size but increased, unexpectedly, with connectivity. Occurrence increased with patch size and decreased with increasing time since fire. At a regional scale, S. linearis tracks the fire dynamics by colonising sites with burned trees and by becoming extinct at rates which make the species rare at sites where burnt trees are more than eight years old. In managed boreal forest landscapes, a large proportion of sites may be created by prescribed burning (in our study area: 82%), and consequently human decisions strongly affect the future amount of habitat for fire‐dependent species and its spatial distribution. Stephanopachys linearis uses burned sites more often if more trees are retained and, to some extent, if sites are concentrated in those parts of a region that already support high population densities of the species.     

不同烈度林火干扰下呼中国家级自然保护区森林各碳库储量的动态变化

本研究通过FireBGCv2模型,模拟不同烈度林火干扰下未来100年呼中自然保护区森林各碳库的动态变化特征,以探究森林不同碳库对火干扰的响应规律,为保护区森林可燃物的管理提供科学依据。结果表明: 林火干扰显著降低了保护区森林碳储量,且林火烈度越大,碳储量降低越多。火干扰影响森林各碳库储量的变化,也改变了森林总碳库的分配特征。林火干扰对各碳库碳储量的影响表现为:林火干扰使活立木、半腐殖质层碳储量降低,使粗木质残体碳储量在模拟前、中期增加,在模拟后期降低,灌草碳库碳储量在模拟后期增加。林火烈度越大,活立木、灌草碳库碳储量越低,枯立木和粗木质残体碳库碳储量越高。林火干扰对总碳库分配的影响表现为:林火干扰后,灌草、枯立木、粗木质残体和土壤碳库占比增加,活立木、半腐殖层碳库在总碳库中的占比减小。林火烈度越大,灌草碳库占比越小,粗木质残体碳库占比越大,烈度对其他碳库占比影响较小。枯落物的周期性变化规律为: 20年达到高值,然后10年内降到低值,这一发现为确定森林可燃物处理的时间间隔提供了有力的依据,建议在大兴安岭地区每隔20年进行一次计划火烧,以合理保护该地区的森林资源。     

Rapid expansion of lichen woodlands within the closed-crown boreal forest zone over the last 50 years caused by stand disturbances in eastern Canada

Aim Our two main goals are first to evaluate the resilience of the boreal forest according to latitude across the closed‐crown forest zone using the post‐disturbance distribution and cover of lichen woodlands and closed‐crown forests as a metric, and second to identify the disturbance factors responsible for the regeneration and degradation of the closed‐crown forest according to latitude since the 1950s. Location The study area extends between 70°00′ and 72°00′ W and throughout the closed‐crown forest zone, from its southern limit near 47°30′ N to its northern limit at the contact with the lichen woodland zone at around 52°40′ N. Methods Recent (1972–2002) and old (1954–1956) aerial photos were used to map the distribution of lichen woodlands across the closed‐crown forest zone. Forest disturbances such as fire, spruce budworm (Choristoneura fumiferana (Clemens)) outbreak, and logging were recorded on each set of aerial photos. Each lichen woodland and stand disturbance was validated by air‐borne surveys and digitized using GIS software. Results Over the last 50 years, the area occupied by lichen woodlands has increased according to latitude; that is, 9% of the area that was occupied by closed‐crown forests has shifted to lichen woodlands. Although logging activities have been concentrated in the same areas during the last 50 years, the area covered by logging has increased significantly. Outbreaks by the spruce budworm occurred predominantly in the southern (47°30′ N to 48°30′ N) and central (48°53′ N to 50°42′ N) parts of the study area, where balsam fir stands are extensive. In the northern part of the study area (51°–52°40′ N), extensive fires affected the distribution and cover of closed‐crown forests and lichen woodlands. Main conclusions Over the last 50 years, the area occupied by closed‐crown forests has decreased dramatically, and the ecological conditions that allow closed‐crown forests to establish and develop are currently less prevalent. Fire is by far the main disturbance, reducing the ability of natural closed‐crown forests to self‐regenerate whatever the latitude. Given the current biogeographical shift from dense to open forests, the northern part of the closed‐crown forest zone is in a process of dramatic change towards the dominance of northern woodlands.     

基于MODIS卫星火点的浙江省林火季节变化及驱动因子

研究林火变化趋势和驱动因子,可为林火预防和管理提供科学依据。本研究基于MODIS卫星火点数据,结合气象(日平均风速、日平均温度、日相对湿度、气温日较差、日累计降水)、人为(到公路距离、到铁路距离、到居民点距离、人口密度、人均GDP)、地形和植被因素(高程、坡度、植被覆盖度),运用趋势分析法、Logistic回归模型,对浙江省2001—2016年林火变化趋势和驱动因子进行研究。结果表明: 浙江省春、夏季林火呈显著上升趋势,秋、冬季林火呈先上升后下降趋势,秋季下降趋势显著。浙江省各季节林火预测模型拟合度均较高,模型预测准确率分别为75.8%(春季)、79.1%(夏季)、74.7%(秋季)和79.6%(冬季)。浙江省春、夏季林火发生与变化受气象、人为、地形和植被因素的显著影响;秋、冬季林火发生与变化主要受气象因素影响。在影响因素复杂、高火险区域分散的春、夏季,林火管理应重点加强人为活动管理和防火宣传教育;在秋、冬季,可通过在高火险区集中分布的西南地区增设瞭望塔和监控设备进行监测和管理。     

Limited Edge Effects Along a Burned‐Unburned Bornean Forest Boundary Seven Years after Disturbance

Large parts of the everwet tropics have been burned, leaving many unburned–burned forest edges. Here we studied a Bornean forest edge to determine: (1) how unburned and burned forest differ in vegetation structure, diversity, composition and plant functional traits 7 yr after fire, and (2) if these variables showed significant edge effects. Environmental and inventory data from 120 plots (0.01 ha each), covering both sides of a ～1.3 km forest boundary were sampled. Differences in vegetation structure, diversity, composition and plant functional traits were analyzed in relation to disturbance type (Mann–Whitney tests) and edge distance (partial correlation analysis that controlled for confounding effects of elevation, slope and fire intensity). Seven years after fire, burned forest differed significantly from unburned forest in most measured variables while few significant edge effects were detected, i.e., there existed a sharp delimitation between the two forest types. The regeneration of the burned forest depended almost entirely on in situ recruitment with little input of late successional species from the neighboring old growth forest. On the other hand, old growth forest showed few signs of edge degradation. A possible explanation for these results might be related to the absence of a mast fruiting event during these first 7 yr of forest recovery, resulting in low levels of late successional species seed input into the burned forest, combined with the quick development of a closed canopy in the burned forest by early successional species that shielded the unburned forest from adverse edge effects.     

基于GIS的大兴安岭森林火险区划

以黑龙江省大兴安岭图强林业局育英林场和奋斗林场为研究区,以GIS技术为支撑,选取植被类型、海拔、坡度、坡向和离居住区远近作为主要林火影响因子,采用因子加权叠置法,对研究区森林火险情况进行了定量评价,将火险等级分为无、低、中、高和极高5类.结果表明,无、低、中、高和极高火险区分别占研究区的0.37%、0.63%、38.67%、58.63%和1.70%,符合正态分布;中及以上火险区占60.33%,说明研究区森林火灾管理任务仍相当繁重;森林火险等级的地域分异明显,中部高四周低,在不同林火影响因子上的分异十分明显;火险等级与1987年的火烧强度具有较强的一致性,说明火险区划结果具有较高的可靠性,可为林业部门进行森林火灾管理提供有价值的参考.     

Topographic Variation in Structure of Mixed-Conifer Forests Under an Active-Fire Regime

Management efforts to promote forest resiliency as climate changes have often used historical forest structure and composition to provide general guidance for fuels reduction and forest restoration treatments. However, it has been difficult to identify what stand conditions might be fire and drought resilient because historical data and reconstruction studies are generally limited to accurate estimates only of large, live tree density and composition. Other stand features such as smaller tree densities, dead wood, understory structure, regeneration, and fuel loads have been difficult to quantify, estimate how they may vary across a landscape, or assess how they would be affected by fire under current climate conditions. We sampled old-growth, mixed-conifer forests with at least two low-intensity fires within the last 65?years in 150 plots at 48 sample sites ranging over 400?km of the Sierra Nevada. Recent fire history had the strongest influence on understory conditions with small tree density decreasing and shrub cover increasing with the increased intensity and frequency of fire associated with upper-slope and ridge-top locations. In contrast, stand structures associated with large, overstory trees such as total basal area, canopy cover, and the abundance of large snags and logs increased in topographic locations associated with more mesic, productive sites regardless of fire history. In forests with restored fire regimes, topography, fire and their interaction influence productivity and burn intensity, creating the structural heterogeneity characteristic of frequent-fire forests.