Disturbance In Boreal Forest Research Articles

Long-term effects of forest fires on soil greenhouse gas emissions and extracellular enzyme activities in a hemiboreal forest

Fire is the most important natural disturbance in boreal forests, and it has a major role regulating the carbon (C) budget of these systems. With the expected increase in fire frequency, the greenhouse gas (GHG) budget of boreal forest soils may change. In order to understand the long-term nature of the soil–atmosphere GHG exchange after fire, we established a fire chronosequence representing successional stages at 8, 19, 34, 65, 76 and 179 years following stand-replacing fires in hemiboreal Scots pine forests in Estonia. Changes in extracellular activity, litter decomposition, vegetation biomass, and soil physicochemical properties were assessed in relation to carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) emissions. Soil temperature was highest 8 years after fire, whereas soil moisture varied through the fire chronosequences without a consistent pattern. Litter decomposition and CO2 efflux were still lower 8 years after fire compared with pre-fire levels (179 years after fire). Both returned to pre-fire levels before vegetation re-established, and CO2 efflux was only strongly responsive to temperature from 19 years after fire onward. Recovery of CO2 efflux in the long term was associated with a moderate effect of fire on enzyme activity, the input of above- and below-ground litter carbon, and the re-establishment of vegetation. Soil acted as a CH4 sink and N2O source similarly in all successional stages. Compared with soil moisture and time after fire, soil temperature was the most important predictor for both GHGs. The re-establishment of overstorey and vegetation cover (mosses and lichens) might have caused an increase in CH4 and N2O effluxes in the studied areas, respectively.

Wildfire severity reduces richness and alters composition of soil fungal communities in boreal forests of western Canada.

Wildfire is the dominant disturbance in boreal forests and fire activity is increasing in these regions. Soil fungal communities are important for plant growth and nutrient cycling postfire but there is little understanding of how fires impact fungal communities across landscapes, fire severity gradients, and stand types in boreal forests. Understanding relationships between fungal community composition, particularly mycorrhizas, and understory plant composition is therefore important in predicting how future fire regimes may affect vegetation. We used an extreme wildfire event in boreal forests of Canada's Northwest Territories to test drivers of fungal communities and assess relationships with plant communities. We sampled soils from 39 plots 1year after fire and 8 unburned plots. High-throughput sequencing (MiSeq, ITS) revealed 2,034 fungal operational taxonomic units. We found soil pH and fire severity (proportion soil organic layer combusted), and interactions between these drivers were important for fungal community structure (composition, richness, diversity, functional groups). Where fire severity was low, samples with low pH had higher total fungal, mycorrhizal, and saprotroph richness compared to where severity was high. Increased fire severity caused declines in richness of total fungi, mycorrhizas, and saprotrophs, and declines in diversity of total fungi and mycorrhizas. The importance of stand age (a surrogate for fire return interval) for fungal composition suggests we could detect long-term successional patterns even after fire. Mycorrhizal and plant community composition, richness, and diversity were weakly but significantly correlated. These weak relationships and the distribution of fungi across plots suggest that the underlying driver of fungal community structure is pH, which is modified by fire severity. This study shows the importance of edaphic factors in determining fungal community structure at large scales, but suggests these patterns are mediated by interactions between fire and forest stand composition.

Response of ground and rove beetles (Coleoptera: Carabidae, Staphylinidae) to operational oil sands mine reclamation in northeastern Alberta, a case study

Species loss caused by anthropogenic disturbance threatens forest ecosystems globally. Until 50 years ago, the major sources of boreal forest disturbance in western Canada were a combination of forest wild fire events, pest insect outbreaks, and forest timber harvesting. However, in the 1960s, when the oil boom started in Alberta, oil and gas development along with oil sands mining quickly became another major forest disturbance agent. In this case study we report the effects of operational oil sands mine reclamation on terrestrial arthropod communities and compare them with nearby burned and mature forest sites as a way to provide a benchmark from which to understand the long-term trajectory of recovery for these groups. During the summer of 2016 over 6700 epigaeic beetles were collected using pitfall traps. A total of 43 species of ground beetles and 118 species of rove beetles were collected. Epigaeic beetle assemblages differed between the reclaimed, burned, and mature forest sites. Partitioning of beta diversity in the reclaimed, burned areas and mature forests indicated that species turnover formed the largest component of diversity. Species richness patterns were similar among sites; however, cluster analysis indicated that epigaeic beetle assemblages were only 20% similar between the reclaimed and natural sites. Although ground beetles of the reclaimed area showed positive spatial autocorrelation among treatments, both ground and rove beetles showed responses to the reclamation treatments. The reclaimed areas were dominated by small- to medium-sized open-habitat eurytopic species, whereas the fire and mature forest sites were dominated by larger forest species. The reclaimed area of this case study constitutes a novel, reconstructed ecosystem that is clearly not equivalent in species assemblage to burnt stands of similar age or to mature forest stands.

Does Environment Filtering or Seed Limitation Determine Post-fire Forest Recovery Patterns in Boreal Larch Forests?

Wildfire is a primary natural disturbance in boreal forests, and post-fire vegetation recovery rate influences carbon, water, and energy exchange between the land and atmosphere in the region. Seed availability and environmental filtering are two important determinants in regulating post-fire vegetation recovery in boreal forests. Quantifying how these determinants change over time is helpful for understanding post-fire forest successional trajectory. Time series of remote sensing data offer considerable potential in monitoring the trajectory of post-fire vegetation recovery dynamics beyond current field surveys about structural attributes, which generally lack a temporal perspective across large burned areas. We used a time series of the normalized difference vegetation index (NDVI) and normalized difference shortwave infrared reflectance index (NDSWIR) derived from Landsat images to investigate post-fire dynamics in a Chinese boreal larch forest. An adjacent, unburned patch of a similar forest type and environmental conditions was selected as a control to separate interannual fluctuation in NDVI and NDSWIR caused by climate from changes due to wildfire. Temporal anomalies in NDVI and NDSWIR showed that more than 10 years were needed for ecosystems to recover to a pre-fire state. The boosted regression tree analysis showed that fire severity exerted a persistent, dominant influence on vegetation recovery during the early post-fire successional stage and explained more than 60% of variation in vegetation recovery, whereas distance to the nearest unburned area and environmental conditions exhibited a relatively small influence. This result indicated that the legacy effects of fire disturbance, which control seed availability for tree recruitment, would persist for decades. The influence of environmental filtering could increase with succession and could mitigate the initial heterogeneity in recovery caused by wildfire.

Increases in Land Surface Temperature in Response to Fire in Siberian Boreal Forests and Their Attribution to Biophysical Processes

AbstractWildfire is the most prevalent natural disturbance in boreal forests and impacts climate through biogeochemical (e.g., greenhouse gas emission from biomass burning) and biophysical (e.g., albedo [α], evapotranspiration [ET], and roughness) processes. We used satellite observations to investigate the immediate (i.e., 1 year after fire) biophysical effects of fire in Siberian boreal forests. We found that boreal forest fires have a net annual warming effect (0.0728 to 0.325 K) due to strong summer warming and weak winter cooling. Fires also increased the diurnal temperature range and seasonal amplitude. These effects are strongest in summer and significantly higher in evergreen than in deciduous coniferous forests. Decreases in ET contributed to warming effects in summer, and increases in α contributed to cooling in winter. Our results suggest that the increase in observed land surface temperature immediately following fires in boreal ecosystems is most likely due to reduced ET leading to a strong positive feedback on the surface radiative budget.

Ecological restoration in boreal forest modifies the structure of bird assemblages

Ecological restoration is increasingly recognised as a useful tool for biodiversity conservation in boreal forests. Most restoration methods in this environment aim to emulate natural disturbances, and thereby promote the development of key ecological structures. However, research about forest ecosystem restoration is still in its infancy and the responses of many boreal species groups remain to be described. We established a large-scale field experiment to evaluate the short-term effects of two restoration treatments – prescribed burning and gap cutting involving the creation of dead wood – on breeding bird assemblages in boreal Sweden. We censused breeding birds using territory mapping during two years in forest stands subjected to the two restoration treatments, in untreated controls and in old-growth references (nature reserves) (n=10 per treatment). Averaged over the two census years, we found 1145 territories of 36 bird species. Total bird species richness and abundance did not differ among treatments. However, prescribed burning led to clear changes in the structure of the bird assemblages. When dividing species according to four functional categorizations (migration, foraging, nesting and successional stage), we found that the abundance of long-distance migrants, ground breeders, strong cavity excavators and species preferring early-successional habitat was higher in burned stands than in untreated controls and gap-cut stands, as was the species richness of bark feeders and strong cavity excavators. In contrast, abundance of off-ground breeders and species richness of crown feeders were lower following prescribed burning than in the controls. The gap cutting treatment did not have any significant effects on the bird assemblages. Ecological restoration through prescribed burning can be a useful tool for the conservation of boreal forest birds, including the ecologically important strong cavity excavators (i.e. woodpeckers (Picidae)). Forest managers should therefore be encouraged to use prescribed burning as a restoration tool to quickly provide habitat for bird species adapted to natural disturbances in boreal forest.

Soil Respiration of the Dahurian Larch (Larix gmelinii) Forest and the Response to Fire Disturbance in Da Xing\u2019an Mountains, China

Despite the high frequency of wildfire disturbances in boreal forests in China, the effects of wildfires on soil respiration are not yet well understood. We examined the effects of fire severity on the soil respiration rate (Rs) and its component change in a Dahurian Larch (Larix gmelinii) in Northeast China. The results showed that Rs decreased with fire burning severity. Compared with the control plots, Rs in the low burning severity plots decreased by 19%, while it decreased by 28% in the high burning severity plots. The Rs decrease was mainly due to a decreased autotrophic respiration rate (Ra). The temperature sensitivity (Q10) of Rs increased after the low severity fire disturbances, but it decreased after the high severity fire disturbance. The Rs were triggered by the soil temperature, which may explain most of the Rs variability in this area. Our study, for the first time, provides the data-based foundation to demonstrate the importance of assessing CO2 fluxes considering both fire severity and environmental factors post-fire in boreal forests of China.

Carbon dioxide, methane and nitrous oxide fluxes from a fire chronosequence in subarctic boreal forests of Canada

Forest fires are one of the most important natural disturbances in boreal forests, and their occurrence and severity are expected to increase as a result of climate warming. A combination of factors induced by fire leads to a thawing of the near-surface permafrost layer in subarctic boreal forest. Earlier studies reported that an increase in the active layer thickness results in higher carbon dioxide (CO2) and methane (CH4) emissions. We studied changes in CO2, CH4 and nitrous oxide (N2O) fluxes in this study, and the significance of several environmental factors that influence the greenhouse gas (GHG) fluxes at three forest sites that last had fires in 2012, 1990 and 1969, and we compared these to a control area that had no fire for at least 100years. The soils in our study acted as sources of CO2 and N2O and sinks for CH4. The elapsed time since the last forest fire was the only factor that significantly influenced all studied GHG fluxes. Soil temperature affected the uptake of CH4, and the N2O fluxes were significantly influenced by nitrogen and carbon content of the soil, and by the active layer depth. Results of our study confirm that the impacts of a forest fire on GHGs last for a rather long period of time in boreal forests, and are influenced by the fire induced changes in the ecosystem.

Static and dynamic controls on fire activity at moderate spatial and temporal scales in the Alaskan boreal forest

AbstractWildfire, a dominant disturbance in boreal forests, is highly variable in occurrence and behavior at multiple spatiotemporal scales. New data sets provide more detailed spatial and temporal observations of active fires and the post‐burn environment in Alaska. In this study, we employ some of these new data to analyze variations in fire activity by developing three explanatory models to examine the occurrence of (1) seasonal periods of elevated fire activity using the number of MODIS active fire detections data set (MCD14DL) within an 11‐day moving window, (2) unburned patches within a burned area using the Monitoring Trends in Burn Severity fire severity product, and (3) short‐to‐moderate interval (<60 yr) fires using areas of burned area overlap in the Alaska Large Fire Database. Explanatory variables for these three models included dynamic variables that can change over the course of the fire season, such as weather and burn date, as well as static variables that remain constant over a fire season, such as topography, drainage, vegetation cover, and fire history. We found that seasonal periods of high fire activity are associated with both seasonal timing and aggregated weather conditions, as well as the landscape composition of areas that are burning. Important static inputs to the model of seasonal fire activity indicate that when fire weather conditions are suitable, areas that typically resist fire (e.g., deciduous stands) may become more vulnerable to burning and therefore less effective as fire breaks. The occurrence of short‐to‐moderate interval fires appears to be primarily driven by weather conditions, as these were the only relevant explanatory variables in the model. The unique importance of weather in explaining short‐to‐moderate interval fires implies that fire return intervals (FRIs) will be sensitive to projected climate changes in the region. Unburned patches occur most often in younger stands, which may be related to a greater deciduous fraction of vegetation as well as lower fuel loads compared with mature stands. The fraction of unburned patches may therefore increase in response to decreasing FRIs and increased deciduousness in the region, or these may decrease if fire weather conditions become more severe.

Silviculture to sustain productivity in black spruce paludified forests

Fire is considered the major disturbance in boreal forests. Nonetheless, in several areas logging has become the primary driver of forest dynamics. In many areas of the boreal forest, stands may undergo paludification (i.e. the accumulation of thick, poorly decomposed organic layers over the mineral soil) in the prolonged absence of fire, which reduces forest productivity. Whereas high-severity fires (HSF) may restore forest productivity by burning the soil organic layer (SOL), low-severity fires (LSF) mainly burn the soil surface and do not significantly reduce SOL thickness. In the Clay Belt region of eastern Canada, an area prone to paludification, forest stands have historically been harvested by clearcutting (CC), but concerns about the protection of soils and tree regeneration lead to the replacement of CC by careful logging (CL). Whereas CC disturbs the SOL and is thought to favor tree growth, CL has little impact on the SOL. Furthermore, it has been suggested that prescribed burning after clearcut (CCPB) could also be used to control paludification. Using a retrospective approach, this study sought to understand how CC, CL, and CCPB compare to LSF and HSF with respect to soil properties, SOL thickness, vegetation ground cover, tree nutrition, and stand height in paludified black spruce stands of the Clay Belt region. HSF led to significantly taller trees than CL and LSF, but did not differ from CC and CCPB. Foliar N was significantly higher in HSF and CCPB sites relative to CL and LSF, with an intermediate value in CC sites. Ground cover of Rhododendron groenlandicum was significantly lower in HSF and CC sites relative to LSF, with intermediate values in CL and CCPB sites. Sphagnum spp. ground cover was significantly lower in HSF and CCPB sites relative to CL, with intermediate values in CC and LSF sites. High-severity fire sites had a significantly thinner SOL than the four other disturbances. Finally, regression tree analysis showed that SOL thickness represented the best predictor of tree height, whereas segmented regression showed that tree height was negatively correlated to SOL thickness and revealed a cut-off point circa 23cm, which suggests that tree growth is impeded beyond this threshold. These results support the idea that management strategies intending to regenerate paludified forests should primarily aim at reducing organic layer thickness, either through mechanical disturbance or combustion.

Strategic analysis of forest vulnerability to risk related to fire: an example from the coniferous boreal forest of Quebec

As fire is a major disturbance in boreal forests, it is now recognized that it has to be taken into account in forest management planning. Moreover, as the time of exposure to fire is related to stand productivity, combining information on productivity and fire should help in assessing the potential to sustainably manage forests. We present a method to assess potential vulnerability to the risk of fire and illustrate it in the boreal coniferous forest of Quebec. This method takes into account some sources of uncertainty related to the estimation of productivity and fire risk. Spatialization of stand productivity from growth and yield curves allowed us to compute the area comprised of productive stands of each district with or without considering fire risk. Results showed that productive area is generally decreasing with decreasing degree-days, increasing elevation, or in relation to surficial geology. Furthermore, districts with moderate to good productivity were found to be vulnerable to fire when burn rates were greater than 0.333%·year–1. Our innovative approach allowed us to assess the vulnerability of the districts to fire and could be helpful in many regions in the context of a projected increase in future area burned under climate change.

Spatial simulation of the effect of fire and harvest on aboveground tree biomass in boreal forests of Northeast China

Fire and timber harvest are two major forest disturbances in boreal forests. Predicting the dynamics of boreal forest biomass requires accounting for both of those effects. Related stochasticity and other uncertainties can produce great variation in predicted responses of forests to fire and timber harvest. In this study, we investigated the effects of fire and timber harvest on landscape-level predictions of the tree component of stand biomass in a boreal forest landscape in Northeast China. We used a forest landscape model (LANDIS PRO) to predict the tree biomass over three time intervals (0–50, 50–150, and 150–300 years). We then compared the simulated results of fire and timber harvest and their interactions with observed biomass and its spatial distribution over short-, mid-, and long-term intervals. For additional prediction comparisons, we observed uncut, unburned stands (i.e., the succession-only scenario). Compared to the succession-only scenario, we found that predicted biomass was reduced by 3.8 ± 2.1, 9.1 ± 3.6, and 11.2 ± 5.1 tons/ha in fire-only, harvest-only, and combined fire and harvest scenarios, respectively. Our results indicated that the effect of harvest on biomass exceeded that of fire, and that the interaction of fire and harvest was more effective in reducing biomass than the effects of fire or harvest separately. Biomass predictions that did not consider effects of fire and timber harvest tended to inflate biomass estimates. The spatial distribution of tree biomass moreover changed with simulation period. These results have important implications in designing prescriptions for improving forest sustainability.

Mapping a burned forest area from Landsat TM data by multiple methods

Forest fire is one of the dominant disturbances in boreal forests. It is the primary process responsible for organizing the physical and biological attributes of the boreal biome, shaping landscape diversity and influencing biogeochemical cycles. The Greater Hinggan Mountain of China is rich in forest resources while suffers from a high incidence of forest fires simultaneously. In this study, focusing on the most serious forest fire in the history of P. R. China which occurred in this region, we made use of two Landsat-5 TM (Thematic Mapper) images, and proposed to map the overall burned area and burned forest area by multiple methods. During the mapping, the fire perimeter, as well as rivers, roads and urban areas were first extracted and masked visually, and then four indices of Normalized Difference Vegetation Index, Enhanced Vegetation Index, Vegetation Fractional Cover and Disturbance Index were calculated. For each index, the optimal threshold for separating burned from unburned forest area was determined using their histograms. For comparison, threshold segmentation using single-band reflectance was performed, in addition to a Maximum Likelihood Classifier (MLC) based supervised classification of all features and forest area alone; their accuracies were also evaluated and analysed. Among all the methods compared here, mapping by EVI threshold segmentation proved to be optimal by the comparisons of overall accuracy (99.78%) and the kappa coefficient (0.9946). Finally, the calculated burned area and burned forest area were compared with the values from official statistics. Compared with the classical methods used to report official statistics on burned areas, the remote sensing-based mapping is more objective and efficient, less labour- and time-consuming, and more repeatable.

Tree community structural development in young boreal forests: A comparison of fire and harvesting disturbance

Although natural disturbance-based management systems support the use of clearcut harvesting as a means of emulating fire disturbance in boreal forest, there are continual concerns and uncertainties over the degree to which clearcutting alters forest ecosystem dynamics relative to wildfire. Here, we sampled 56 and 47 post-fire and post-harvest stands, respectively, to examine early tree community structural development in young boreal mixedwood forests in central Canada. We find that tree species diversity is higher immediately following clearcut harvesting compared with stand-replacing crown fire. We attribute this primarily to protection of advanced regeneration, suitable regeneration substrates, and propagule availability of shade-tolerant conifer species following harvesting compared with fire. Although both disturbances promoted early successional species, harvesting resulted in higher regeneration densities of late-successional conifers (Picea mariana (Mill.) and Abies balsamea (L.) Mill.). Vertical height structure variation was higher after fire than harvesting, likely a result of spatial heterogeneity in burn severity. Although tree heights, corrected for stand age, did not differ between disturbances for Populus tremuloides Michx. and Pinus banksiana Lamb., they were shorter for Betula papyrifera Marsh. and taller for late-successional conifers following harvest. Higher tree species richness, regeneration densities, and tree heights of late-successional conifer species indicate that clearcut harvesting can potentially accelerate succession in boreal mixedwood forests; however, harvesting can reduce height structural variability. Furthermore, leaving Betula papyrifera to satisfy the policy requirement for green tree retention can negatively affect its post-harvest regeneration and growth.

Rates of Disturbance vary by data resolution: implications for conservation schedules using the Alberta Boreal Forest as a case study

Investigations of biophysical changes on earth caused by anthropogenic disturbance provide governments with tools to generate sustainable development policy. Canada currently experiences one of the fastest rates of boreal forest disturbance in the world. Plans to conserve the 330 000 km(2) boreal forest in the province of Alberta exist but conservation targets and schedules must be aligned with rates of forest disturbance. We explore how disturbance rate, and the accuracy with which we detect it, may affect conservation success. We performed a change detection analysis from 1992 to 2008 using Landsat and SPOT satellite image data processing. Canada's recovery strategy for boreal caribou (Rangifer tarandus caribou) states that ≤35% of a caribou range can be either burned or within 500 m of a man-made feature for caribou to recover. Our analyses show that by 2008 78% of the boreal forest was disturbed and that, if the current rate continues, 100% would be disturbed by 2028. Alberta plans to set aside 22% for conservation in a region encompassing oil sands development to balance economic, environmental, and traditional indigenous land-use goals. Contrary to the federal caribou recovery strategy, provincial conservation plans do not consider wildfire a disturbance. Based on analyses used in the provincial plan, we apply a 250 m buffer around anthropogenic footprints. Landsat image analysis indicates that the yearly addition of disturbance is 714 km(2) (0.8%). The higher resolution SPOT images show fine-scale disturbance indicating that actual disturbance was 1.28 times greater than detected by Landsat. If the SPOT image based disturbance rates continue, the 22% threshold may be exceeded within the next decade, up to 20 years earlier than indicated by Landsat-based analysis. Our results show that policies for sustainable development will likely fail if governments do not develop time frames that are grounded by accurate calculations of disturbance rates.

Book review: Look northward to the boreal, the home of many migrating birds

ISSN 1948‐6596 news and update book review Look northward to the boreal, the home of many migrating birds Boreal birds of North America: A hemispheric view of their conservation links and significance, by Jeffrey V. Wells (editor), 2011, Studies in Avian Biology No. 41, University of California Press, 136 pp. £30.95 (Hardback) ISBN: 9780520271005; http://www.ucpress.edu/ To many people, the term “boreal forest” evokes an image of a vast, cold, and inaccessible wilder‐ ness far from home. Most of us live south of the boreal, and when we think of bird diversity we tend to look toward the tropics, where species diversity is high and species range size tends to be small, placing many species under threat of extinc‐ tion due to human‐caused habitat destruction. This book provides an eye‐opening look to the north, strongly demonstrating the importance of North America’s boreal forest to avian biodiversity both there and throughout the Americas via sea‐ sonal migration. The book also shows that, while being one of the largest wilderness areas left on the planet, the boreal forest is under growing threat. Despite its small size for an edited volume (9 chapters totaling 125 pages), this book presents a remarkably balanced and comprehensive over‐ view of the biogeography, ecology, and conserva‐ tion of the boreal birds of North America. Most chapters focus on broad biogeographic patterns; these include contributions on the threats to the boreal forest, the global role of the boreal in sus‐ taining bird populations, the use of survey data in geospatial modeling of bird abundance, and the role of boreal migrants in winter bird communities far to the south. These are supplemented by con‐ tributions that focus on geographically more nar‐ row areas, including chapters on waterfowl con‐ servation in the western boreal forest, boreal landbird migrants in eastern North America, and boreal migrants in the tropical Andes. Finally, two contributions provide examples of in‐depth re‐ search on two species that have experienced alarming declines: surf scoters and rusty black‐ birds. The mix of broad‐scale overviews with fo‐ cused looks at individual species in decline leaves the reader with a remarkably rich understanding of the importance of the boreal forest and the research being undertaken (and needed in the future) to better understand and protect its avi‐ fauna. Some remarkable statistics emerge from this book. Spanning from interior Alaska across the continent to Newfoundland, North America's boreal forest covers 5.9 million km 2 , representing 25% of remaining intact forests on Earth. Over 300 bird species regularly breed there, accounting for 43% of all species that regularly occur in Canada and/or the U.S. The total number of adult boreal breeders is estimated at somewhere between 1.65 and 3 billion, accounting for 30% of all breed‐ ing landbirds of Canada and the U.S., 38% of wa‐ terfowl, and 30% of shorebirds. Between 3 and 5 billion adults and immature birds migrate south from the boreal every fall; during the northern winter, they play important ecological roles in North, Central, and South America, where they can comprise up to 50% of the species composi‐ tion in some feeding guilds. While the above num‐ bers are impressive, the threats to boreal birds are as well. From 1966 to 1994, Saskatchewan’s boreal plain was deforested at a rate of 0.89% per year, three times the global rate of deforestation, and rates of boreal forest disturbance due to oil and gas exploration, hydropower projects, agricul‐ ture, and other industrial development are also alarming. One of the strengths of this book is that it goes beyond the presentation of patterns, and argues for a subtle change in conservation values. While traditional approaches to conservation have emphasized rarity and endemism in prioritizing conservation efforts, Wells and Blancher (p. 8) advance the idea that “some regions have a high stewardship responsibility for maintaining species that are still abundant.” This point is well taken, frontiers of biogeography 4.3, 2012 — © 2012 the authors; journal compilation © 2012 The International Biogeography Society

Changes in Soil Fungal Communities, Extracellular Enzyme Activities, and Litter Decomposition Across a Fire Chronosequence in Alaskan Boreal Forests

Wildfires are a pervasive disturbance in boreal forests, and the frequency and intensity of boreal wildfires is expected to increase with climate warming. Boreal forests store a large fraction of global soil organic carbon (C), but relatively few studies have documented how wildfires affect soil microbial communities and soil C dynamics. We used a fire chronosequence in upland boreal forests of interior Alaska with sites that were 1, 7, 12, 24, 55, ~90, and ~100 years post-fire to examine the short- and long-term responses of fungal community composition, fungal abundance, extracellular enzyme activity, and litter decomposition to wildfires. We hypothesized that post-fire changes in fungal abundance and community composition would constrain decomposition following fires. We found that wildfires altered the composition of soil fungal communities. The relative abundance of ascomycetes significantly increased following fire whereas basidiomycetes decreased. Post-fire decreases in basidiomycete fungi were likely attributable to declines in ectomycorrhizal fungi. Fungal hyphal lengths in the organic horizon significantly declined in response to wildfire, and they required at least 24 years to return to pre-fire levels. Post-fire reductions in fungal hyphal length were associated with decreased activities of hydrolytic extracellular enzymes. In support of our hypothesis, the decomposition rate of aspen and black spruce litter significantly increased as forests recovered from fire. Our results indicate that post-fire reductions in soil fungal abundance and activity likely inhibit litter decomposition following boreal wildfires. Slower rates of litter decay may lead to decreased heterotrophic respiration from soil following fires and contribute to a negative feedback to climate warming.

Increased heat resistance in mycelia from wood fungi prevalent in forests characterized by fire: a possible adaptation to forest fire

Forest fires have been the major stand-replacing/modifying disturbance in boreal forests. To adapt to fire disturbance, different strategies have evolved. This study focuses on wood fungi, and a specific adaptation to forest fire: increased heat resistance in their mycelia. Fifteen species of wood fungi were selected and a priori sorted in two groups according to their prevalence in fire-affected environments. The fungi were cultivated on fresh wood and exposed to 100, 140, 180, 220 °C for 5, 10, 15, 20 and 25 min. under laboratory conditions. A clear difference was found among the two groups. Species prevalent in fire-affected habitats had a much higher survival rate over all combinations of time and temperature compared to species associated with other environments. Thus, the results indicate that fire adaptation in terms of increased heat resistance in mycelia occurs in some species of wood fungi. Such adaptation will influence the ecology and population dynamics of wood fungi, as well as having implications for best practices during restoration fires.

Wildfire and forest harvest disturbances in the boreal forest leave different long-lasting spatial signatures

Aims Natural disturbances leave long-term legacies that vary among landscapes and ecosystem types, and which become integral parts of successional processes at a given location. As humans change land use, not only are immediate post-disturbance patterns altered, but the processes of recovery themselves are likely altered by the disturbance. We assessed whether short-term effects on soil and vegetation that distinguish wildfire from forest harvest persist over 60 years after disturbance in boreal black spruce forests, or post-disturbance processes of recovery promote convergence of the two disturbance types.

Edge effects of wildfire and riparian buffers along boreal forest streams

Summary1. Clearcutting and wildfire are the two major edge‐creating disturbances in boreal forests. While clearcutting retains at least a 30 m buffer, wildfires burn close to streams killing most of the trees and potentially creating a different edge structure. Different edge structures are likely to support different plant assemblages. The riparian buffer and fire edge structures and their effects on plant assemblages are unknown, but they have implications for forest management that aims to harvest trees and conserve biodiversity by emulating natural disturbance.2. We hypothesized that environmental filters created by post‐fire residual structures at the fire edge will support a different plant assemblage than the buffer edge. We further hypothesized that the fire edge with a weaker environmental filter because of post‐fire residual structures and proximity to streams will result in lower depth of edge effects (DEEs) and magnitude of edge effects (MEEs) than buffer edges.3. We determined the structure of canopy trees, understorey cover and the near‐ground microclimate by sampling 576 (5 × 10 m) and 1820 (1 × 1 m) quadrats along 96 transects beside 24 streams near Thunder Bay, Canada. We determined DEEs and MEEs by comparing edge variables with reference forests. We used repeated measures/factorialanovas with Tukey’spost hoctests to determine DEEs andmanovafor MEEs.4. The average microclimatic DEEs extended 8 m into the buffer but only 2·5 m from the fire edge. Similarly, the DEEs for plant life‐forms extended 20 m from the buffer edge and 5 m from the fire edge. At the fire edge, the structural MEEs were significantly higher, but the microclimatic MEEs were lower than the buffer edge. We found no significant difference in the overall life‐form MEEs, but shrubs, shade‐tolerant herbs and grasses were increased at the buffer edge and decreased at the fire edge.5. Synthesis and applications. We discovered that the ecological structure at buffer and fire edges in boreal forests creates different environmental filters supporting different plant assemblages. Lower structural and microclimatic DEEs and MEEs at the fire edge result from (i) edge location, (ii) intact shrub layer and (iii) disturbance‐resilient riparian vegetation. We suggest that replacing the conventional sharp edges of the riparian clear‐cut buffer with ‘feathered’ edges by selective harvesting of trees will create wider edges mimicking wildfire legacy and will help to emulate natural disturbance for conserving biodiversity.