共查询到20条相似文献，搜索用时 15 毫秒
1.
Canopy fuel characteristics and potential crown fire behavior in Aleppo pine (Pinus halepensis Mill.) forests 总被引：3，自引：0，他引：3
Canopy fuel characteristics that influence the initiation and spread of crown fires were measured in representative Aleppo pine (Pinus halepensis Mill.) stands in Greece. Vertical distribution profiles of canopy fuel load, canopy base height and canopy bulk density are presented. Aleppo pine canopy fuels are characterized by low canopy base height (3.0–6.5 m), while available canopy fuel load (0.96–1.80 kg/m2) and canopy bulk density (0.09–0.22 kg/m3) values are similar to other conifers worldwide. Crown fire behavior (probability of crown fire initiation, crown fire type, rate of spread, fireline intensity and flame length) in Aleppo pine stands with various understory fuel types was simulated with the most updated crown fire models. The probability of crown fire initiation was high even under moderate burning conditions, mainly due to the low canopy base height and the heavy surface fuel load. Passive crown fires resulted mostly in uneven aged stands, while even aged stands gave high intensity active crown fires. Assessment of canopy fuel characteristics and potential crown fire behavior can be useful in fuel management and fire suppression planning. 相似文献
2.
We studied the bark beetle guild (Coleoptera: Scolytidae) in the ponderosa pine forests of northern Arizona to explore if the species assemblages and relative abundance differ between managed and unmanaged stands. Four stand conditions were assessed: (1) unmanaged stands with high tree density, (2) thinned stands, (3) thinned and burned (with prescribed fire) stands and (4) stands that had been burned by stand replacing wildfires. The study was conducted in the ponderosa pine forests of the Coconino Plateau, northern Arizona. For several decades this area has been relatively free of bark beetle outbreaks despite the current overstocked condition of many stands. We found that a similar species assemblage composed of Dendroctonus frontalis, D. brevicomis, D. valens, D. approximatus, D. ponderosae, and Ips pini occurred across all four stand conditions over 3 years of study. The population levels of all these species were endemic across all stand conditions. The non-aggressive D. approximatus and D. valens were indicator species for thinned and unmanaged stands, respectively, but this was not consistent among years. The ambrosia beetle Gnathotrichus sp. and the bark beetle predator Enoclerus sp. consistently indicated stands burned by wildfire. In addition to our field experiment, we analyzed the historical pattern of attacks of bark beetles in our area of study. Our findings suggest that the pattern of attack of D. brevicomis (the only Dendroctonus species for which attacks have been reported) and Ips spp. has been through scattered small infestations in groups of 1–10 trees. Whereas small infestations by Ips spp. are increasing, those for D. brevicomis are decreasing. Although we agree that the high density stands in northern Arizona are in an “unhealthy” condition, our results do not show that they were supporting large bark beetle outbreaks. Our results challenge the theoretical assumptions about the relationship between stand structure, tree resistance and bark beetle performance. 相似文献
3.
Mountain pine beetle, Dendroctonus ponderosae Hopkins can cause extensive tree mortality in ponderosa pine, Pinus ponderosa Dougl. ex Laws., forests in the Black Hills of South Dakota and Wyoming. Most studies that have examined stand susceptibility to mountain pine beetle have been conducted in even-aged stands. Land managers increasingly practice uneven-aged management. We established 84 clusters of four plots, one where bark beetle-caused mortality was present and three uninfested plots. For all plot trees we recorded species, tree diameter, and crown position and for ponderosa pine whether they were killed or infested by mountain pine beetle. Elevation, slope, and aspect were also recorded. We used classification trees to model the likelihood of bark beetle attack based on plot and site variables. The probability of individual tree attack within the infested plots was estimated using logistic regression. Basal area of ponderosa pine in trees ≥25.4 cm in diameter at breast height (dbh) and ponderosa pine stand density index were correlated with mountain pine beetle attack. Regression trees and linear regression indicated that the amount of observed tree mortality was associated with initial ponderosa pine basal area and ponderosa pine stand density index. Infested stands had higher total and ponderosa pine basal area, total and ponderosa pine stand density index, and ponderosa pine basal area in trees ≥25.4 cm dbh. The probability of individual tree attack within infested plots was positively correlated with tree diameter with ponderosa pine stand density index modifying the relationship. A tree of a given size was more likely to be attacked in a denser stand. We conclude that stands with higher ponderosa pine basal area in trees >25.4 cm and ponderosa pine stand density index are correlated with an increased likelihood of mountain pine beetle bark beetle attack. Information form this study will help forest managers in the identification of uneven-aged stands with a higher likelihood of bark beetle attack and expected levels of tree mortality. 相似文献
4.
Outbreaks of bark beetles and drought both lead to concerns about increased fire risk, but the relative importance of these two factors is the subject of much debate. We examined how mountain pine beetle (MPB) outbreaks and drought have contributed to the fire regime of lodgepole pine forests in northwestern Colorado and adjacent areas of southern Wyoming over the past century. We used dendroecological methods to reconstruct the pre-fire history of MPB outbreaks in twenty lodgepole pine stands that had burned between 1939 and 2006 and in 20 nearby lodgepole pine stands that were otherwise similar but that had not burned. Our data represent c. 80% of all large fires that had occurred in lodgepole pine forests in this study area over the past century. We also compared Palmer Drought Severity Index (PDSI) and actual evapotranspiration (AET) values between fire years and non-fire years. Burned stands were no more likely to have been affected by outbreak prior to fires than were nearby unburned stands. However, PDSI and AET values were both lower during fire years than during non-fire years. This work indicates that climate has been more important than outbreaks to the fire regime of lodgepole pine forests in this region over the past century. Indeed, we found no detectable increase in the occurrence of high-severity fires following MPB outbreaks. Dry conditions, rather than changes in fuels associated with outbreaks, appear to be most limiting to the occurrence of severe fires in these forests. 相似文献
5.
The mountain pine beetle Dendroctonus ponderosae Hopkins is endemic to lodgepole pine, Pinus contorta var. latifolia Engelmann, forests in western Canada. However, the current beetle epidemic in this area highlights the challenges faced by forest managers tasked with prioritizing stands for mitigation activities such as salvage harvesting and direct control methods. In western Canada, the operational risk rating system for mountain pine beetle is based on biological knowledge gained from a rich legacy of stand-scale field studies. Due to the large spatial (millions of hectares affected) and temporal (over 10 years) extents of the current epidemic, new research into large-area mountain pine beetle processes has revealed further insights into the landscape-scale characteristics of beetle infested forests. In this paper, we evaluated the potential for this new knowledge to augment an established system for rating the short-term risk of tree mortality in a stand due to mountain pine beetle. New variables explored for utility in risk rating include direct shortwave radiation, site index, diameter at breast height, the temporal trends in local beetle populations, Biogeoclimatic Ecosystem Classification and beetle–host interaction variables. Proportional odds ordinal regression was used to develop a model for the Vanderhoof Forest District in west-central British Columbia. Prediction on independent data was assessed with the area under the receiver operator curve (AUC), indicating good discriminatory power (AUC = 0.84) for predicting levels of mountain pine beetle-caused pine mortality. 相似文献
6.
Prescribed fire is an important tool in the management of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) forests, yet effects on bark beetle (Coleoptera: Curculionidae, Scolytinae) activity and tree mortality are poorly understood in the southwestern U.S. We compared bark beetle attacks and tree mortality between paired prescribed-burned and unburned stands at each of four sites in Arizona and New Mexico for three growing seasons after burning (2004–2006). Prescribed burns increased bark beetle attacks on ponderosa pine over the first three post-fire years from 1.5 to 13% of all trees, increased successful, lethal attacks on ponderosa pine from 0.4 to 7.6%, increased mortality of ponderosa pine from all causes from 0.6 to 8.4%, and increased mortality of all tree species with diameter at breast height >13 cm from 0.6 to 9.6%. On a per year basis, prescribed burns increased ponderosa pine mortality from 0.2% per year in unburned stands to 2.8% per year in burned stands. Mortality of ponderosa pine 3 years after burning was best described by a logistic regression model with total crown damage (crown scorch + crown consumption) and bark beetle attack rating (no, partial, or mass attack by bark beetles) as independent variables. Attacks by Dendroctonus spp. did not differ significantly over bole heights, whereas attacks by Ips spp. were greater on the upper bole compared with the lower bole. Three previously published logistic regression models of tree mortality, developed from fires in 1995–1996 in northern Arizona, were moderately successful in predicting broad patterns of tree mortality in our data. The influence of bark beetle attack rating on tree mortality was stronger for our data than for data from the 1995–1996 fires. Our results highlight canopy damage from fire as a strong and consistent predictor of post-fire mortality of ponderosa pine, and bark beetle attacks and bole char rating as less consistent predictors because of temporal variability in their relationship to mortality. The small increase in tree mortality and bark beetle attacks caused by prescribed burning should be acceptable to many forest managers and the public given the resulting reduction in surface fuel and risk of severe wildfire. 相似文献
7.
Thomas W. McGinnis Jon E. Keeley Scott L. Stephens Gary B. Roller 《Forest Ecology and Management》2010
Typically, after large stand-replacing fires in mid-elevation Sierra Nevada forests, dense shrub fields occupy sites formerly occupied by mature conifers, until eventually conifers overtop and shade out shrubs. Attempting to reduce fuel loads and expedite forest regeneration in these areas, the USDA Forest Service often disrupts this cycle by the logging of fire-killed trees, replanting of conifers and killing of shrubs. We measured the effects of these treatments on live and dead fuel loads and alien species and modeled potential fire behavior and fire effects on regenerating forests. Sampling occurred in untreated, logged and herbicide-treated stands throughout the Sierra Nevada in four large fire areas 4–21 years after stand-replacing fires. Logging fire-killed trees significantly increased total available dead fuel loads in the short term but did not affect shrub cover, grass and forb cover, alien species cover or alien species richness. Despite the greater available dead fuel loads, fire behavior was not modeled to be different between logged and untreated stands, due to abundant shrub fuels in both logged and untreated stands. In contrast, the herbicide treatment directed at shrubs resulted in extremely low shrub cover, significantly greater alien species richness and significantly greater alien grass and forb cover. Grass and forb cover was strongly correlated with solar radiation on the ground, which may be the primary reason that grass and forb cover was higher in herbicide treated stands with low shrub and tree cover. Repeat burning exacerbated the alien grass problem in some stands. Although modeled surface fire flame lengths and rates of spread were found to be greater in stands dominated by shrubs, compared to low shrub cover conifer plantations, surface fire would still be intense enough to kill most trees, given their small size and low crown heights in the first two decades after planting. 相似文献
8.
9.
T.E. Kolb J.K. Agee P.Z. Fulé N.G. McDowell K. Pearson A. Sala R.H. Waring 《Forest Ecology and Management》2007
We review current knowledge about the use of management treatments to reduce human-induced threats to old ponderosa pine (Pinus ponderosa) trees. We address the following questions: Are fire-induced damage and mortality greater in old than younger trees? Can management treatments ameliorate the detrimental effects of fire, competition-induced stress, and drought on old trees? Can management increase resistance of old trees to bark beetles? We offer the following recommendations for the use of thinning and burning treatments in old-growth ponderosa pine forests. Treatments should be focused on high-value stands where fire exclusion has increased fuels and competition and where detrimental effects of disturbance during harvesting can be minimized. Fuels should be reduced in the vicinity of old trees prior to prescribed burns to reduce fire intensity, as old trees are often more prone to dying after burning than younger trees. Raking the forest floor beneath old trees prior to burning may not only reduce damage from smoldering combustion under certain conditions but also increase fine-root mortality. Thinning of neighboring trees often increases water and carbon uptake of old trees within 1 year of treatment, and increases radial growth within several years to two decades after treatment. However, stimulation of growth of old trees by thinning can be negated by severe drought. Evidence from young trees suggests that management treatments that cause large increases in carbon allocation to radial xylem growth also increase carbon allocation to constitutive resin defenses against bark beetle attacks, but evidence for old trees is scarce. Prescribed, low-intensity burning may attract bark beetles and increase mortality of old trees from beetle attacks despite a stimulation of bole resin production. 相似文献
10.
Four treatments (control, burn-only, thin-only, and thin-and-burn) were evaluated for their effects on bark beetle-caused mortality in both the short-term (one to four years) and the long-term (seven years) in mixed-conifer forests in western Montana, USA. In addition to assessing bark beetle responses to these treatments, we also measured natural enemy landing rates and resin flow of ponderosa pine (Pinus ponderosa) the season fire treatments were implemented. All bark beetles were present at low population levels (non-outbreak) for the duration of the study. Post-treatment mortality of trees due to bark beetles was lowest in the thin-only and control units and highest in the units receiving burns. Three tree-killing bark beetle species responded positively to fire treatments: Douglas-fir beetle (Dendroctonus pseudotsugae), pine engraver (Ips pini), and western pine beetle (Dendroctonus brevicomis). Red turpentine beetle (Dendroctonus valens) responded positively to fire treatments, but never caused mortality. Three fire damage variables tested (height of crown scorch, percent circumference of the tree bole scorched, or degree of ground char) were significant factors in predicting beetle attack on trees. Douglas-fir beetle and pine engraver responded rapidly to increased availability of resources (fire-damaged trees); however, successful attacks dropped rapidly once these resources were depleted. Movement to green trees by pine engraver was not observed in plots receiving fire treatments, or in thinned plots where slash supported substantial reproduction by this beetle. The fourth tree-killing beetle present at the site, the mountain pine beetle, did not exhibit responses to any treatment. Natural enemies generally arrived at trees the same time as host bark beetles. However, the landing rates of only one, Medetera spp., was affected by treatment. This predator responded positively to thinning treatments. This insect was present in very high numbers indicating a regulatory effect on beetles, at least in the short-term, in thinned stands. Resin flow decreased from June to August. However, resin flow was significantly higher in trees in August than in June in fire treatments. Increased flow in burned trees later in the season did not affect beetle attack success. Overall, responses by beetles to treatments were short-term and limited to fire-damaged trees. Expansions into green trees did not occur. This lack of spread was likely due to a combination of high tree vigor in residual stands and low background populations of bark beetles. 相似文献
11.
Extensive ponderosa pine (Pinus ponderosa Dougl. ex Laws.) mortality associated with a widespread severe drought and increased bark beetle (Coleoptera: Curculionidae, Scolytinae) populations occurred in Arizona from 2001 to 2004. A complex of Ips beetles including: the Arizona fivespined ips, Ips lecontei Swaine, the pine engraver beetle, Ips pini (Say), Ips calligraphus (Germar), Ips latidens (LeConte), Ips knausi Swaine and Ips integer (Eichhoff) were the primary bark beetle species associated with ponderosa pine mortality. In this study we examine stand conditions and physiographic factors associated with bark beetle-caused tree mortality in ponderosa pine forests across five National Forests in Arizona. A total of 633 fixed-radius plots were established across five National Forests in Arizona: Apache-Sitgreaves, Coconino, Kaibab, Prescott, and Tonto. Prior to the bark beetle outbreak, plots with mortality had higher tree and stocking compared with plots without pine mortality. Logistic regression modeling found that probability of ponderosa pine mortality caused by bark beetles was positively correlated with tree density and inversely related with elevation and tree diameter. Given the large geographical extent of this study resulting logistic models to estimate the likelihood of bark beetle attack should have wide applicability across similar ponderosa pine forests across the Southwest. This is particularly true of a model driven by tree density and elevation constructed by combining all forests. Tree mortality resulted in significant reductions in basal area, tree density, stand density index, and mean tree diameter for ponderosa pine and for all species combined in these forests. Most of the observed pine mortality was in the 10–35 cm diameter class, which comprise much of the increase in tree density over the past century as a result of fire suppression and grazing practices. Ecological implications of tree mortality are discussed. 相似文献
12.
Jacob M. Griffin 《Forest Ecology and Management》2011,261(6):1077-1089
Widespread bark beetle outbreaks are currently affecting multiple conifer forest types throughout western North America, yet many ecosystem-level consequences of this disturbance are poorly understood. We quantified the effect of mountain pine beetle (Dendroctonus ponderosae) outbreak on nitrogen (N) cycling through litter, soil, and vegetation in lodgepole pine (Pinus contorta var. latifolia) forests of the Greater Yellowstone Ecosystem (WY, USA) across a 0-30 year chronosequence of time-since-beetle disturbance. Recent (1-4 years) bark beetle disturbance increased total litter depth and N concentration in needle litter relative to undisturbed stands, and soils in recently disturbed stands were cooler with greater rates of net N mineralization and nitrification than undisturbed sites. Thirty years after beetle outbreak, needle litter N concentration remained elevated; however total litter N concentration, total litter mass, and soil N pools and fluxes were not different from undisturbed stands. Canopy N pool size declined 58% in recent outbreaks, and remained 48% lower than undisturbed in 30-year old outbreaks. Foliar N concentrations in unattacked lodgepole pine trees and an understory sedge were positively correlated with net N mineralization in soils across the chronosequence. Bark beetle disturbance altered N cycling through the litter, soil, and vegetation of lodgepole pine forests, but changes in soil N cycling were less severe than those observed following stand replacing fire. Several lines of evidence suggest the potential for N leaching is low following bark beetle disturbance in lodgepole pine. 相似文献
13.
14.
Benjamin L. VanderWeide David C. Hartnett 《Forest Ecology and Management》2011,261(9):1530-1538
Fire, climatic variability, and grazing by large herbivores have historically limited woody vegetation in the tallgrass prairie region of North America to gallery forests in protected areas along rivers and streams. Fire, in particular, has been a strong selective pressure against woody vegetation. Consequently, we expect that dominant tree species in these forests have developed mechanisms for tolerating periodic surface fires. Susceptibility of trees to fire damage depends in part on key properties of bark which influence heat transfer to the vascular cambium, including thickness, density, and moisture content. An historical (1983) survey of Konza Prairie Biological Station in northeast Kansas, USA indicated that gallery forests were co-dominated by Quercus macrocarpa and Quercus muehlenbergii, while Celtis occidentalis occurred as an important sub-dominant species. Populus deltoides, Gleditsia triacanthos, and Juniperus virginiana were relatively uncommon. To test the hypothesis that historically dominant gallery forest tree species are more resistant to fire damage than uncommon species, fire was applied to the bark of 10 individuals of each of these six species under conditions mimicking surface fires (400 °C for 120 s). Maximum temperature at the vascular cambium, bark thickness, bark moisture content, and bark density were measured. Trees were considered fire-resistant if the vascular cambium temperature remained below the thermal cell death threshold, 60 °C, throughout the treatment. Using logistic regression, bark thickness was found to be a significant predictor of lethal cambium temperatures (P = 0.002), while neither bark density nor moisture content were significantly related to lethal cambium temperature (P = 0.279 and P = 0.131, respectively). Across species, a minimum bark thickness of approximately 8.6 mm was necessary to maintain the vascular cambium temperature below 60 °C. Trees that produce thick bark quickly in juvenile size classes (P. deltoides, Q. macrocarpa, and Q. muehlenbergii) experienced lower temperatures at the vascular cambium than those which do not develop thick bark with increasing diameter (C. occidentalis, G. triacanthos, and J. virginiana). Ranking these tree species by either the DBH or age needed to develop the minimum protective bark thickness largely agreed with ranking based on historical relative importance. As fire frequency and intensity decrease in remnant tallgrass prairie of North America as a result of habitat fragmentation, fire suppression, and changing land management, fire-sensitive species may increase in relative importance in gallery forests because of increased juvenile survival. 相似文献
15.
A. P. Dimitrakopoulos I. D. Mitsopoulos D. I. Raptis 《European Journal of Forest Research》2007,126(4):555-561
Nomographs that calculate the threshold values of surface fire parameters which lead to crown fire initiation were created
by linking two separate fire behavior models: Van Wagner’s crown fire ignition criteria and Byram’s surface fire model. The
nomographs were also based on the existing surface (fuel load, fuel heat content) and canopy (foliar moisture content, live
crown base height) fuel models of Aleppo (Pinus halepensis Mill.) pine forests of Mediterranean Greece. The most important fire parameters for crown fire initiation that are calculated
by the nomographs are the critical flame length and the forward spread rate of the surface fire. These parameters are readily
observable in the field during fires. The nomographs provide a judicious way to assess whether a crown fire is likely to occur
in a conifer forest stand. Although the fire behavior models used had limited testing and are based on certain assumptions,
yet they are widely applied in forestry practice worldwide, as a basis for justified fire prevention and suppression planning. 相似文献
16.
David A. Perry Paul F. HessburgCarl N. Skinner Thomas A. SpiesScott L. Stephens Alan Henry TaylorJerry F. Franklin Brenda McCombGreg Riegel 《Forest Ecology and Management》2011,262(5):703-717
Forests characterized by mixed-severity fires occupy a broad moisture gradient between lower elevation forests typified by low-severity fires and higher elevation forests in which high-severity, stand replacing fires are the norm. Mixed-severity forest types are poorly documented and little understood but likely occupy significant areas in the western United States. By definition, mixed-severity types have high beta diversity at meso-scales, encompassing patches of both high and low severity and gradients in between. Studies of mixed-severity types reveal complex landscapes in which patch sizes follow a power law distribution with many small and few large patches. Forest types characterized by mixed severity can be classified according to the modal proportion of high to low severity patches, which increases from relatively dry to relatively mesic site conditions. Mixed-severity regimes are produced by interactions between top-down forcing by climate and bottom-up shaping by topography and the flammability of vegetation, although specific effects may vary widely across the region, especially the relation between aspect and fire severity. History is important in shaping fire behavior in mixed-severity landscapes, as patterns laid down by previous fires can play a significant role in shaping future fires. Like low-severity forests in the western United States, many dry mixed-severity types experienced significant increases in stand density during the 20th century, threatening forest health and biodiversity, however not all understory development in mixed-severity forests increases the threat of severe wild fires. In general, current landscapes have been homogenized, reducing beta diversity and increasing the probability of large fires and insect outbreaks. Further loss of old, fire tolerant trees is of particular concern, but understory diversity has been reduced as well. High stand densities on relatively dry sites increase water use and therefore susceptibility to drought and insect outbreaks, exacerbating a trend of increasing regional drying. The need to restore beta diversity while protecting habitat for closed-forest specialists such as the northern spotted owl call for landscape-level approaches to ecological restoration. 相似文献
17.
Since the first terpenoid synthase cDNA was obtained by the reverse genetic approach from grand fir, great pro-gress in the molecular genetics of terpenoid formation has been made with angiosperms and genes encoding a monoterpene synthase, a sesquiterpene synthase, and a diterpene synthase. Tree killing bark beetles and their vectored fungal pathogens are the most destructive agents of conifer forests worldwide. Conifers defend against attack by the constitutive and inducible production of oleoresin that accumulates at the wound site to kill invaders and both flush and seal the injury. Although toxic to the bark beetle and fungal pathogen, oleoresin also plays a central role in the chemical ecology of these boring insects. Re-cent advances in the molecular genetics of terpenoid biosynthesis provide evidence for the evolutionary origins of oleoresin and permit consideration of genetic engineering strategies to improve conifer defenses as a component of modern forest bio-technology. This review described enzymes of resin biosynthesis, structural feathers of genes genomic intron and exon or-ganization, pathway organization and evolution, resin production and accumulation, interactions between conifer and bark beetle, and engineering strategies to improve conifer defenses. 相似文献
18.
Euro-American logging practices, intensive grazing, and fire suppression have increased the amount of carbon that is stored in ponderosa pine (Pinus ponderosa Dougl. Ex Laws) forests in the southwestern United States. Current stand conditions leave these forests prone to high-intensity wildfire, which releases a pulse of carbon emissions and shifts carbon storage from live trees to standing dead trees and woody debris. Thinning and prescribed burning are commonly used to reduce the risk of intense wildfire, but also reduce on-site carbon stocks and release carbon to the atmosphere. This study quantified the impact of thinning on the carbon budgets of five ponderosa pine stands in northern Arizona, including the fossil fuels consumed during logging operations. We used the pre- and post-treatment data on carbon stocks and the Fire and Fuels Extension to the Forest Vegetation Simulator (FEE-FVS) to simulate the long-term effects of intense wildfire, thinning, and repeated prescribed burning on stand carbon storage.The mean total pre-treatment carbon stock, including above-ground live and dead trees, below-ground live and dead trees, and surface fuels across five sites was 74.58 Mg C ha−1 and the post-treatment mean was 50.65 Mg C ha−1 in the first post-treatment year. The mean total carbon release from slash burning, fossil fuels, and logs removed was 21.92 Mg C ha−1. FEE-FVS simulations showed that thinning increased the mean canopy base height, decreased the mean crown bulk density, and increased the mean crowning index, and thus reduced the risk of high-intensity wildfire at all sites. Untreated stands that incurred wildfire once within the next 100 years or once within the next 50 years had greater mean net carbon storage after 100 years compared to treated stands that experienced prescribed fire every 10 years or every 20 years. Treated stands released greater amounts of carbon overall due to repeated prescribed fires, slash burning, and 100% of harvested logs being counted as carbon emissions because they were used for short-lived products. However, after 100 years treated stands stored more carbon in live trees and less carbon in dead trees and surface fuels than untreated stands burned by intense wildfire. The long-term net carbon storage of treated stands was similar or greater than untreated wildfire-burned stands only when a distinction was made between carbon stored in live and dead trees, carbon in logs was stored in long-lived products, and energy in logging slash substituted for fossil fuels. 相似文献
19.
Phillip J. van Mantgem Nathan L. StephensonEric Knapp John BattlesJon E. Keeley 《Forest Ecology and Management》2011,261(6):989-994
The capacity of prescribed fire to restore forest conditions is often judged by changes in forest structure within a few years following burning. However, prescribed fire might have longer-term effects on forest structure, potentially changing treatment assessments. We examined annual changes in forest structure in five 1 ha old-growth plots immediately before prescribed fire and up to eight years after fire at Sequoia National Park, California. Fire-induced declines in stem density (67% average decrease at eight years post-fire) were nonlinear, taking up to eight years to reach a presumed asymptote. Declines in live stem biomass were also nonlinear, but smaller in magnitude (32% average decrease at eight years post-fire) as most large trees survived the fires. The preferential survival of large trees following fire resulted in significant shifts in stem diameter distributions. Mortality rates remained significantly above background rates up to six years after the fires. Prescribed fire did not have a large influence on the representation of dominant species. Fire-caused mortality appeared to be spatially random, and therefore did not generally alter heterogeneous tree spatial patterns. Our results suggest that prescribed fire can bring about substantial changes to forest structure in old-growth mixed conifer forests in the Sierra Nevada, but that long-term observations are needed to fully describe some measures of fire effects. 相似文献