| |||
Burned Sites (burned + site)
Selected AbstractsThe effects of green tree retention and subsequent prescribed burning on ground beetles (Coleoptera: Carabidae) in boreal pine-dominated forestsECOGRAPHY, Issue 5 2006Petri Martikainen We studied how two methods to promote biodiversity in managed forests, i.e. green tree retention and prescribed fire, affect the assemblages of carabid beetles. Our experiment consisted of 24 study sites, each 3,5 ha in size, which had been prepared according to factorial design. Each of the eight treatment combinations determined by the two factors explored , tree retention level (0, 10, 50 m3/ha,1 and uncut controls) and prescribed use of fire (yes/no) , was replicated three times. We sampled carabids using pitfall traps one year after the treatments. Significantly more individuals were caught in most of the burned sites, but this difference was partially reflective of the trap-catches of Pterostichus adstrictus. The fire did not increase no. of P. adstrictus in the uncut sites as much as in the other sites. Species richness was significantly affected by both factors, being higher in the burned than in the unburned sites and in the harvested than in the unharvested sites. Many species were concentrated in the groups of retention trees in the burned sites, but only a few were in the unburned sites. The species turnover was greater in the burned than in the unburned sites, as indicated by the NMDS ordinations. Greater numbers of smaller sized species and proportion of brachypterous species were present in the burned sites. Fire-favored species, and also the majority of other species that prefer open habitats were more abundantly caught in the burned sites than in the unburned sites. Dead wood or logging waste around the traps did not correlate with the occurrence of species. We conclude that carabids are well adapted to disturbances, and that frequent use of prescribed fire is essential for the maintenance of natural assemblages of carabid beetles in the boreal forest. Small retention tree groups can not maintain assemblages of uncut forest, but they can be important by providing food, shelter and breeding sites for many species, particularly in the burned sites. [source] POSTFIRE SUCCESSION IN AN ADIRONDACK FOREST,GEOGRAPHICAL REVIEW, Issue 4 2007Susy Svatek Ziegler ABSTRACT. Landscape diversity has increased with the surprising postfire establishment of aspen at upper elevations (700,945 meters above sea level) in the High Peaks of Adirondack Park in upstate New York. Tree seedlings returned quickly to the charred slopes west of Noonmark Mountain after an accidental fire consumed the forest in 1999. Aspen stands have replaced the spruce-fir-birch forests in the burned area even though mountain paper birch is expected to colonize burned sites at these elevations. Environmental conditions, historical events, and unique circumstances help explain why quaking aspen and bigtooth aspen rather than paper birch blanket the burned mountainside. Climate change over the past century to warmer, wetter conditions may have fostered this marked shift in species composition. In the unburned firebreak that people cleared to contain the flames, pin cherry has regenerated from seeds stored in the soil for nearly a century. The history of pin cherry on the site suggests that large fires or severe windthrow may have been more common in the region than was previously documented. [source] Debating the greening vs. browning of the North American boreal forest: differences between satellite datasetsGLOBAL CHANGE BIOLOGY, Issue 2 2010DOMINGO ALCARAZ-SEGURA Abstract A number of remote sensing studies have evaluated the temporal trends of the normalized difference vegetation index (NDVI or vegetation greenness) in the North American boreal forest during the last two decades, often getting quite different results. To examine the effect that the use of different datasets might be having on the estimated trends, we compared the temporal trends of recently burned and unburned sites of boreal forest in central Canada calculated from two datasets: the Global Inventory, Monitoring, and Modeling Studies (GIMMS), which is the most commonly used 8 km dataset, and a new 1 km dataset developed by the Canadian Centre for Remote Sensing (CCRS). We compared the NDVI trends of both datasets along a fire severity gradient in order to evaluate the variance in regeneration rates. Temporal trends were calculated using the seasonal Mann,Kendall trend test, a rank-based, nonparametric test, which is robust against seasonality, nonnormality, heteroscedasticity, missing values, and serial dependence. The results showed contrasting NDVI trends between the CCRS and the GIMMS datasets. The CCRS dataset showed NDVI increases in all recently burned sites and in 50% of the unburned sites. Surprisingly, the GIMMS dataset did not capture the NDVI recovery in most burned sites and even showed NDVI declines in some burned sites one decade after fire. Between 50% and 75% of GIMMS pixels showed NDVI decreases in the unburned forest compared with <1% of CCRS pixels. Being the most broadly used dataset for monitoring ecosystem and carbon balance changes, the bias towards negative trends in the GIMMS dataset in the North American boreal forest has broad implications for the evaluation of vegetation and carbon dynamics in this region and globally. [source] Effects of wildfire and permafrost on soil organic matter and soil climate in interior AlaskaGLOBAL CHANGE BIOLOGY, Issue 12 2006JENNIFER W. HARDEN Abstract The influence of discontinuous permafrost on ground-fuel storage, combustion losses, and postfire soil climates was examined after a wildfire near Delta Junction, AK in July 1999. At this site, we sampled soils from a four-way site comparison of burning (burned and unburned) and permafrost (permafrost and nonpermafrost). Soil organic layers (which comprise ground-fuel storage) were thicker in permafrost than nonpermafrost soils both in burned and unburned sites. While we expected fire severity to be greater in the drier site (without permafrost), combustion losses were not significantly different between the two burned sites. Overall, permafrost and burning had significant effects on physical soil variables. Most notably, unburned permafrost sites with the thickest organic mats consistently had the coldest temperatures and wettest mineral soil, while soils in the burned nonpermafrost sites were warmer and drier than the other soils. For every centimeter of organic mat thickness, temperature at 5 cm depth was about 0.5°C cooler during summer months. We propose that organic soil layers determine to a large extent the physical and thermal setting for variations in vegetation, decomposition, and carbon balance across these landscapes. In particular, the deep organic layers maintain the legacies of thermal and nutrient cycling governed by fire and revegetation. We further propose that the thermal influence of deep organic soil layers may be an underlying mechanism responsible for large regional patterns of burning and regrowth, detected in fractal analyses of burn frequency and area. Thus, fractal geometry can potentially be used to analyze changes in state of these fire prone systems. [source] Assessing burn severity and comparing soil water repellency, Hayman Fire, ColoradoHYDROLOGICAL PROCESSES, Issue 1 2006Sarah A. Lewis Abstract An important element of evaluating a large wildfire is to assess its effects on the soil in order to predict the potential watershed response. After the 55 000 ha Hayman Fire on the Colorado Front Range, 24 soil and vegetation variables were measured to determine the key variables that could be used for a rapid field assessment of burn severity. The percentage of exposed mineral soil and litter cover proved to be the best predictors of burn severity in this environment. Two burn severity classifications, one from a statistical classification tree and the other a Burned Area Emergency Response (BAER) burn severity map, were compared with measured ,ground truth' burn severity at 183 plots and were 56% and 69% accurate, respectively. This study also compared water repellency measurements made with the water drop penetration time (WDPT) test and a mini-disk infiltrometer (MDI) test. At the soil surface, the moderate and highly burned sites had the strongest water repellency, yet were not significantly different from each other. Areas burned at moderate severity had 1·5 times more plots that were strongly water repellent at the surface than the areas burned at high severity. However, the high severity plots most likely had a deeper water repellent layer that was not detected with our surface tests. The WDPT and MDI values had an overall correlation of r = ,0·64(p < 0·0001) and appeared to be compatible methods for assessing soil water repellency in the field. Both tests represent point measurements of a soil characteristic that has large spatial variability; hence, results from both tests reflect that variability, accounting for much of the remaining variance. The MDI is easier to use, takes about 1 min to assess a strongly water repellent soil and provides two indicators of water repellency: the time to start of infiltration and a relative infiltration rate. Copyright © 2005 John Wiley & Sons, Ltd. [source] Plant functional group responses to fire frequency and tree canopy cover gradients in oak savannas and woodlandsJOURNAL OF VEGETATION SCIENCE, Issue 1 2007David W. Peterson Abstract Questions: How do fire frequency, tree canopy cover, and their interactions influence cover of grasses, forbs and understorey woody plants in oak savannas and woodlands? Location: Minnesota, USA. Methods: We measured plant functional group cover and tree canopy cover on permanent plots within a long-term prescribed fire frequency experiment and used hierarchical linear modeling to assess plant functional group responses to fire frequency and tree canopy cover. Results: Understorey woody plant cover was highest in unburned woodlands and was negatively correlated with fire frequency. C4-grass cover was positively correlated with fire frequency and negatively correlated with tree canopy cover. C3-grass cover was highest at 40% tree canopy cover on unburned sites and at 60% tree canopy cover on frequently burned sites. Total forb cover was maximized at fire frequencies of 4,7 fires per decade, but was not significantly influenced by tree canopy cover. Cover of N-fixing forbs was highest in shaded areas, particularly on frequently burned sites, while combined cover of all other forbs was negatively correlated with tree canopy cover. Conclusions: The relative influences of fire frequency and tree canopy cover on understorey plant functional group cover vary among plant functional groups, but both play a significant role in structuring savanna and woodland understorey vegetation. When restoring degraded savannas, direct manipulation of overstorey tree canopy cover should be considered to rapidly reduce shading from fire-resistant overstorey trees. Prescribed fires can then be used to suppress understorey woody plants and promote establishment of light-demanding grasses and forbs. [source] Effects of fire severity in a north Patagonian subalpine forestJOURNAL OF VEGETATION SCIENCE, Issue 1 2005Thomas Kitzberger Abstract. Question: What is the relative importance of fire-induced canopy mortality, soil burning and post-fire herbivory on tree seedling performance? Location: Subalpine Nothofagus pumilio forests at Challhuaco valley (41°13'S, 71°19'W), Nahuel Huapi National Park, Argentina. Methods: We fenced and transplanted soils of three burning severities along a fire severity gradient produced by a fire in 1996. Over two growing seasons we monitored soil water, direct incoming solar radiation, seedling survival, final seedling total biomass and root/shoot ratio. Additionally, we assessed severity-related changes in soil properties. Results: Incoming radiation (an indicator of the amount of canopy cover left by the fire) was the primary factor influencing spring and summer top soil water availability, first and second-year seedling survival and seedling growth. While seedling survival and soil water content were negatively affected by increased radiation, seedling final biomass was highest in very open microsites. Burned soils showed lower water holding capacity and soil carbon; however these changes did not affect topsoil water, and, contrary to expectation, there was a slight tendency toward higher seedling survival on more heavily burned soils. Herbivory significantly reduced seedling survival, but only under high-radiation conditions. While the effect of radiation on final seedling biomass was not affected by herbivory, R/S ratios were significantly reduced by herbivory in high radiation micro sites. Conclusions: Despite inducing faster aerial growth, increased radiation and herbivory in severely burned sites may effectively prevent post-fire regeneration in north Patagonian subalpine forest where seed sources are not limiting. [source] The distribution of heath balds in the Great Smoky Mountains, North Carolina and TennesseeJOURNAL OF VEGETATION SCIENCE, Issue 4 2001Peter S. White White (1982). Abstract. We used remote sensing and a geographic information system to model the distribution of evergreen shrub communities, called ,heath balds', in the Great Smoky Mountains, North Carolina and Tennessee, USA. The 421 heath balds averaged 1.8 ha in size and covered 0.3% of the landscape. They reached their greatest importance on upper slopes (92% had relative slope positions > 80), convex topography (82% occurred on sites with a curvature greater than 2.6), and elevations between 1100 and 1600 m (94% of the balds). Although heath balds were found in old-growth watersheds, the two watersheds with the greatest number of balds burned extensively after logging in the early 1900s. Bald occurrence was positively correlated with burned sites, old growth condition, and a highly acidic rock type. Heath balds showed a striking geographic pattern, with 88.1% of the area of this community found in six watersheds comprising only 35.4% of the study area. Despite similar topography, geology, and history, the eleven other watersheds had only 11.9% of the bald area while comprising 64.4% of the study area. Multivariate models showed that this community occurs on only 0.4 to 9.0% of the seemingly appropriate sites. Once established, this shrub community, with its dense evergreen canopy and thick leaf litter, is resistant to tree invasion. Both forest and shrub communities are stable on sites that are seemingly ideal for heath bald occurrence. [source] Variation in the impact of exotic grasses on native plant composition in relation to fire across an elevation gradient in HawaiiAUSTRAL ECOLOGY, Issue 5 2000Carla M. D'Antonio Abstract The impact that an exotic species can have on the composition of the community it enters is a function of its abundance, its particular species traits and characteristics of the recipient community. In this study we examined species composition in 14 sites burned in fires fuelled by non-indigenous C4 grasses in Hawaii Volcanoes National Park, Hawaii. We considered fire intensity, time since fire, climatic zone of site, unburned grass cover, unburned native cover and identity of the most abundant exotic grass in the adjacent unburned site as potential predictor variables of the impact of fire upon native species. We found that climatic zone was the single best variable for explaining variation in native cover among burned sites and between burned and unburned pairs. Fire in the eastern coastal lowlands had a very small effect on native plant cover and often stimulated native species regeneration, whereas fire in the seasonal submontane zone consistently caused a decline in native species cover and almost no species were fire tolerant. The dominant shrub, Styphelia tameiameia, in particular was fire intolerant. The number of years since fire, fire intensity and native cover in reference sites were not significantly correlated with native species cover in burned sites. The particular species of grass that carried the fire did however, have a significant effect on native species recovery. Where the African grass Melinis minutiflora was a dominant or codominant species, fire impacts were more severe than where it was absent regardless of climate zone. Overall, the impacts of exotic grass-fuelled fires on native species composition and cover in seasonally dry Hawaiian ecosystems was context specific. This specificity is best explained by differences between the climatic zones in which fire occurred. Elevation was the main physical variable that differed among the climatic zones and it alone could explain a large percentage of the variation in native cover among sites. Rainfall, by contrast, did not vary systematically with elevation. Elevation is associated with differences in composition of the native species assemblages. In the coastal lowlands, the native grass Heteropogon contortus, was largely responsible for positive changes in native cover after fire although other native species also increased. Like the exotic grasses, this species is a perennial C4 grass. It is lacking in the submontane zone and there are no comparable native species there and almost all native species in the submontane zone were reduced by fire. The lack of fire tolerant species in the submontane zone thus clearly contributes to the devastating impact of fire upon native cover there. [source] |