Post-fire Period Research Articles

Modeling Wildfire Smoke Pollution by Integrating Land Use Regression and Remote Sensing Data: Regional Multi-Temporal Estimates for Public Health and Exposure Models

To understand the health effects of wildfire smoke, it is important to accurately assess smoke exposure over space and time. Particulate matter (PM) is a predominant pollutant in wildfire smoke. In this study, we develop land-use regression (LUR) models to investigate the impact that a cluster of wildfires in the northwest USA had on the level of PM in southern Alberta (Canada), in the summer of 2015. Univariate aerosol optical depth (AOD) and multivariate AOD-LUR models were used to estimate the level of PM2.5 in urban and rural areas. For epidemiological studies, it is also important to distinguish between wildfire-related PM2.5 and PM2.5 originating from other sources. We therefore subdivided the study period into three sub-periods: (1) Pre-fire, (2) during-fire, and (3) post-fire. We then developed separate models for each sub-period. With this approach, we were able to identify different predictors significantly associated with smoke-related PM2.5 verses PM2.5 of different origin. Leave-one-out cross-validation (LOOCV) was used to evaluate the models’ performance. Our results indicate that model predictors and model performance are highly related to the level of PM2.5, and the pollution source. The predictive ability of both uni- and multi-variate models were higher in the during-fire period than in the pre- and post-fire periods.

The Legacy of a Severe Wildfire on Stream Nitrogen and Carbon in Headwater Catchments

Large, high-severity wildfires alter the physical and biological conditions that determine how catchments retain and release nutrients and regulate streamwater quality. The short-term water quality impacts of severe wildfire are often dramatic, but the longer-term responses may better reflect terrestrial and aquatic ecosystem recovery. We followed streamwater chemistry for 14 years after the largest fire in recorded Colorado history, the 2002 Hayman Fire, to characterize patterns in nitrogen (N) and carbon (C) export. Throughout the post-fire period, stream nitrate and total dissolved N (TDN) remained elevated in 10 burned catchments relative to pre-burn periods and 4 unburned control catchments. Both the extent of fire in a catchment and wildfire severity influenced stream N concentrations. Nitrate was more than an order of magnitude higher in streams draining catchments that burned to a high extent (> 60% of their areas) compared to unburned catchments. Unburned catchments retained more than 95% of atmospheric N inputs, but N retention in burned catchments was less than half of N inputs. Unlike N, stream C was elevated in catchments that burned to a lesser extent (30–60% of their areas burned), compared to either unburned or extensively burned catchments. Remotely sensed estimates of upland and riparian vegetation cover suggest that burned forests could require several more decades before forest cover and nutrient demand return to pre-fire levels. The persistent stream N increases we report are below drinking water thresholds, but exceed ecoregional reference concentrations for healthy stream ecosystems and indicate that extensively burned headwater catchments no longer function as strong sinks for atmospheric N. Combined with increasing trends in wildfire severity and elevated N deposition, our findings demonstrate the potential for substantial post-wildfire changes in ecosystem N retention and have implications for nutrient export to downstream waters.

Temporal characterisation of soil-plant natural recovery related to fire severity in burned Pinus halepensis Mill. forests

Despite Mediterranean ecosystems' high resilience to fire, both climate and land use change, and alterations in fire regimes increase their vulnerability to fire by affecting the long-term natural recovery of ecosystem services. The objective of this work is to study the effects of fire severity on biochemical soil indicators, such as chemical composition or enzymatic activity, related to time after fire and natural vegetation recovery (soil-plant interphase). Soil samples from three wildfires occurring 3, 15 and 21 years ago were taken in the south-eastern Iberian Peninsula (semiarid climate). Sampling included three fire severity levels in naturally regenerated (and changing to shrublands) Pinus halepensis Mill. forests.In the short-term post-fire period, phosphorus concentration, electrical conductivity and urease activity were positively linked to fire severity, and also influenced β-glucosidade activity in a negative relationship. During the 15–21-year post-fire period, the effects related to medium-high fire severity were negligible and soil quality indicators were linked to natural regeneration success. The results showed that most soil properties recovered in the long term after fire (21 years).These outcomes will help managers and stakeholders to implement management tools to stabilise soils and to restore burned ecosystems affected by medium-high fire severity. Such knowledge can be considered in adaptive forest management to reduce the negative effects of wildfires and desertification, and to improve the resilience of vulnerable ecosystems in a global change scenario.

Post-Fire Regeneration and Diversity Response to Burn Severity in Pinus halepensis Mill. Forests

In recent decades, fire regimes have been modified by various factors such as changes in land use, global change or forest management policies. The vulnerability of Mediterranean terrestrial ecosystems is increasing due to more severe and frequent droughts. This study aimed to determine the plant response of ecosystems during the short-term post-fire period by relating alpha diversity, floristic richness and tree recruitment dynamics to burn severity 5 years after a wildfire. Our results conclude that in the short term, Pinus halepensis Mill. stands in southeastern Spain quickly recovered alpha diversity values, mainly in areas burned with low severity. We observed that moderate and high severities affected the ecosystem more significantly, showing higher values for the Shannon Index but lower for the Simpson index. Pine recruitment was higher in burned areas, and we found the highest number of Aleppo pine seedlings under a moderate burn severity. Post-fire regeneration functional groups (obligate seeders and resprouters) were promoted under moderate and high burn severity, increasing their abundance. Annual species (mainly herbs) colonized burned areas, persisting with higher presence under moderate burn severity. Restoration tools should be focused on reducing fire severity, mainly in areas at high risk of desertification, and promoting resistance, vulnerability and resilience of these ecosystems.

Characterization and evaluation of controls on post-fire streamflow response across western US watersheds

Abstract. This research investigates the impact of wildfires on watershed flow regimes, specifically focusing on evaluation of fire events within specified hydroclimatic regions in the western United States, and evaluating the impact of climate and geophysical variables on response. Eighty-two watersheds were identified with at least 10 years of continuous pre-fire daily streamflow records and 5 years of continuous post-fire daily flow records. Percent change in annual runoff ratio, low flows, high flows, peak flows, number of zero flow days, baseflow index, and Richards–Baker flashiness index were calculated for each watershed using pre- and post-fire periods. Independent variables were identified for each watershed and fire event, including topographic, vegetation, climate, burn severity, percent area burned, and soils data. Results show that low flows, high flows, and peak flows increase in the first 2 years following a wildfire and decrease over time. Relative response was used to scale response variables with the respective percent area of watershed burned in order to compare regional differences in watershed response. To account for variability in precipitation events, runoff ratio was used to compare runoff directly to PRISM precipitation estimates. To account for regional differences in climate patterns, watersheds were divided into nine regions, or clusters, through k-means clustering using climate data, and regression models were produced for watersheds grouped by total area burned. Watersheds in Cluster 9 (eastern California, western Nevada, Oregon) demonstrate a small negative response to observed flow regimes after fire. Cluster 8 watersheds (coastal California) display the greatest flow responses, typically within the first year following wildfire. Most other watersheds show a positive mean relative response. In addition, simple regression models show low correlation between percent watershed burned and streamflow response, implying that other watershed factors strongly influence response. Spearman correlation identified NDVI, aridity index, percent of a watershed's precipitation that falls as rain, and slope as being positively correlated with post-fire streamflow response. This metric also suggested a negative correlation between response and the soil erodibility factor, watershed area, and percent low burn severity. Regression models identified only moderate burn severity and watershed area as being consistently positively/negatively correlated, respectively, with response. The random forest model identified only slope and percent area burned as significant watershed parameters controlling response. Results will help inform post-fire runoff management decisions by helping to identify expected changes to flow regimes, as well as facilitate parameterization for model application in burned watersheds.

Low Evapotranspiration Enhances the Resilience of Peatland Carbon Stocks to Fire

AbstractBoreal peatlands may be vulnerable to projected changes in the wildfire regime under future climates. Extreme drying during the sensitive postfire period may exceed peatland ecohydrological resilience, triggering long‐term degradation of these globally significant carbon stocks. Despite these concerns, we show low peatland evapotranspiration at both the plot‐ and landscape‐scale postfire, in water‐limited peatlands dominated by feather moss that are ubiquitous across continental western Canada. Low postfire evapotranspiration enhances the resilience of carbon stocks in such peatlands to wildfire disturbance and reinforces their function as a regional source of water. Near‐surface water repellency may provide an important, previously unexplored, regulator of peatland evapotranspiration that can induce low evapotranspiration in the initial postfire years by restricting the supply of water to the peat surface.

Continental-scale quantification of post-fire vegetation greenness recovery in temperate and boreal North America

Knowledge and information of post-fire vegetation recovery are essential for our understanding of ecosystem stability and resilience in response to present and future disturbances. Although previous studies have examined the post-fire vegetation recovery at landscape and regional levels, the lack of continent-wide analysis limits our understanding of fire effect on vegetation recovery across ecoregions and climate zones. With advanced technology in satellite observations as well as large-scale database development, it is possible for us to explore the large-scale effect of concurrent and lagged responses of terrestrial ecosystems to fire disturbances. In this study, we investigated the recovery of vegetation greenness in the early post-fire period in North America by integrating two national-level fire perimeter datasets and multiple Moderate Resolution Imaging Spectroradiometer (MODIS) products. We developed a new algorithm to estimate fire effect on the Normalized Difference Vegetation Index (NDVI) by comparing fire pixels with their surrounding unburned pixels. Our results showed the fire effect on needleleaf trees was stronger than on other vegetation types, and the high-latitude ecoregions had larger NDVI reduction and longer recovery time than the mid-latitude ecoregions. We also found the variations in vegetation composition and fire severity can explain a large fraction of post-fire vegetation greenness recovery. Our satellite-based analysis showed a longer NDVI recovery time than the existing estimates, which indicates a stronger fire effect on ecosystems than previously thought. Findings in this study indicate that more sophisticated parameterization schemes of fire severity and post-fire vegetation recovery are needed for the vegetation-fire models to better simulate the terrestrial carbon cycling and climate-ecosystem feedbacks.

Nitrogen balance along a northern boreal forest fire chronosequence.

Fire is a major natural disturbance factor in boreal forests, and the frequency of forest fires is predicted to increase due to climate change. Nitrogen (N) is a key determinant of carbon sequestration in boreal forests because the shortage of N limits tree growth. We studied changes in N pools and fluxes, and the overall N balance across a 155-year non stand-replacing fire chronosequence in sub-arctic Pinus sylvestris forests in Finland. Two years after the fire, total ecosystem N pool was 622 kg ha-1 of which 16% was in the vegetation, 8% in the dead biomass and 76% in the soil. 155 years after the fire, total N pool was 960 kg ha-1, with 27% in the vegetation, 3% in the dead biomass and 69% in the soil. This implies an annual accumulation rate of 2.28 kg ha-1 which was distributed equally between soil and biomass. The observed changes in N pools were consistent with the computed N balance +2.11 kg ha-1 yr-1 over the 155-year post-fire period. Nitrogen deposition was an important component of the N balance. The biological N fixation increased with succession and constituted 9% of the total N input during the 155 post-fire years. N2O fluxes were negligible (≤ 0.01 kg ha-1 yr-1) and did not differ among post-fire age classes. The number and intensity of microbial genes involved in N cycling were lower at the site 60 years after fire compared to the youngest and the oldest sites indicating potential differences in soil N cycling processes. The results suggest that in sub-arctic pine forests, the non-stand-replacing, intermediate-severity fires decrease considerably N pools in biomass but changes in soil and total ecosystem N pools are slight. Current fire-return interval does not seem to pose a great threat to ecosystem productivity and N status in these sub-arctic forests.

Wildfire impact: Natural experiment reveals differential short-term changes in soil microbial communities

A wildfire which overran a sensor network site provided an opportunity (a natural experiment) to monitor short-term post-fire impacts (immediate and up to three months post-fire) in remnant eucalypt woodland and managed pasture plots. The magnitude of fire-induced changes in soil properties and soil microbial communities was determined by comparing (1) variation in fire-adapted eucalypt woodland vs. pasture grassland at the burnt site; (2) variation at the burnt woodland-pasture sites with variation at two unburnt woodland-pasture sites in the same locality; and (3) temporal variation pre- and post-fire. In the eucalypt woodland, soil ammonium, pH and ROC content increased post-fire, while in the pasture soil, soil nitrate increased post-fire and became the dominant soluble N pool. However, apart from distinct changes in N pools, the magnitude of change in most soil properties was small when compared to the unburnt sites. At the burnt site, bacterial and fungal community structure showed significant temporal shifts between pre- and post-fire periods which were associated with changes in soil nutrients, especially N pools. In contrast, microbial communities at the unburnt sites showed little temporal change over the same period. Bacterial community composition at the burnt site also changed dramatically post-fire in terms of abundance and diversity, with positive impacts on abundance of phyla such as Actinobacteria, Proteobacteria and Firmicutes. Large and rapid changes in soil bacterial community composition occurred in the fire-adapted woodland plot compared to the pasture soil, which may be a reflection of differences in vegetation composition and fuel loading. Given the rapid yet differential response in contrasting land uses, identification of key soil bacterial groups may be useful in assessing recovery of fire-adapted ecosystems, especially as wildfire frequency is predicted to increase with global climate change.

Effects of Post-Fire Plant Cover in the Performance of Two Cordilleran Cypress (Austrocedrus chilensis) Seedling Stocktypes Planted in Burned Forests of Northeastern Patagonia, Argentina.

Cordilleran cypress (Austrocedrus chilensis [D.Don] Pic. Serm. et Bizarri) forests occupy 140,000 ha along a sharp environmental gradient of central Andean-Patagonia in Argentina. Every summer, about 3200 ha of these forests are affected by wildfires, taking thereafter long time to recover. To accelerate forest recovery, we determined in xeric and mesic cypress stands burned 5 and 2 year before whether survival and growth of two planted cypress seedling stocktypes are affected by plant cover and contrasting precipitation conditions. Two experiments were conducted on each site, involving 100 replicates of two seedling stocktypes, having each significantly different morphological attributes. The experiments comprised a dry and humid growing season on each site. Both stocktypes performed similarly within stands, but differently between stands. In the xeric stand, plant cover had neutral effects on seedling survival, favored seedling height growth in the dry season, and was negative on collar diameter and stem growth. In the mesic site, high plant cover favored survival and height growth, but was inconsequential for collar diameter and stem growth. In this short-term post-fire period, and independent of precipitation received during both seasons (dry or humid), plant cover appears as playing a facilitative role, having neutral or even positive effects on survival and growth of planted seedlings. During the early post-fire successional stages, and besides seedling stocktype, there was a synergistic balance between light and soil moisture that seems to benefit planted seedling performance in burned cypress forests, and especially in mesic sites.

Can anthropic fires affect epigaeic and hypogaeic Cerrado ant (Hymenoptera: Formicidae) communities in the same way?

Fire occurrences are a common perturbation in Cerrado ecosystems, and may differently impact the local biodiversity. Arthropods are one of the taxa affected by fires, and among them, ants are known as good bioindicators. We aimed to evaluate the effect of anthropic fires on epigaeic and hypogaeic ant communities (species richness and composition) in Cerrado areas with different post-fire event recovery periods. We conducted the study in four Cerrado areas during two weeks of 2012 dry season: one unburned and three at different post-fire times (one month, one and two years). We sampled ants with pitfall traps in epigaeic and hypogaeic microhabitats. We collected 71 ant morpho-species from 25 genera. In the epigaeic microhabitat we sampled 56 morpho-species and 42 in the hypogaeic microhabitat. The area with the shortest recovery time presented lower epigaeic ant species richness (4.3 ± 2.00) in comparison to the other areas (8.1 ± 2.68 species on one year area; 10.3 ± 2.66 species on two years area; 10.4 ± 2.31 species on control area), but recovery time did not affect hypogaeic ant species richness. Regarding ant species composition, fire did not directly affect hypogaeic ant species, which remained the same even one month after fire event. However, two years were not enough to reestablish ant species composition in both microhabitats in relation to our control group samples. Our study is the first to assess anthropic fire effects upon epigaeic and hypogaeic ants communities; highlighting the importance of evaluating different microhabitats, to more accurately detect the effects of anthropic disturbances in biological communities. We concluded that ant communities are just partially affected by fire occurrences, and epigaeic assemblages are the most affected ones in comparison to hypogaeic ants. Furthermore the study provides knowledge to aid in the creation of vegetation management programs that allow Cerrado conservation.

Parametric Study of Possible Railgun Radiation in Postfire Stage

Railgun represents a game-changing weapon for the U.S. Navy, with its development approaching maturity; the electromagnetic (EM) compatibility with other onboard electronics is becoming interesting. Railgun is powered by a gigawatts class pulsed power supply, and due to the nature of its design, considerable remnant energy is still applied to the railgun when the projectile leaves the barrel. If the plasma or debris formed inside the barrel is ejected along with the projectile, a conductive channel may form, which acts as a virtual antenna, and it can radiate the remaining energy as EM waves into the air. In this paper, we try to investigate the far-field EM radiation pattern and near-field electric field intensity after the projectile leaves the muzzle in four cases: case 1 is a bell-shaped plasma at $\omega _{\mathrm{ pe}} = 1$ MHz; case 2 is the same plasma at $\omega _{\mathrm{ pe}} = 100$ MHz; case 3 is a pillar-shaped plasma at $\omega _{\mathrm{ pe}} = 100$ MHz; and case 4 is the effect of a muzzle shunt resistor. The plasma is assumed to be about 5 m high, and is formed on top of the muzzle and behind the projectile, and a 1-kV voltage excitation source with frequencies ranging from 100 MHz to 1 GHz is located at the breech to excite the railgun and plasma combination. Three field probes located 10 m away from the projectile are set up to record the field intensities. We simulate the frequency response of this system with a finite-difference time-domain code. The results show that the plasma is not a very good radiator, and the field coming out of the muzzle is contained in a region near the muzzle because of the plasma. The EM radiation in the postfire period is not as strong as in the firing process.

The influence of fire on the assemblage structure of foraging birds in grasslands of the Serra da Canastra National Park, Brazil.

Grasslands are the most threatened physiognomies of the Cerrado biome (Brazilian savanna), a biodiversity hotspot with conservation as a priority. The Serra da Canastra National Park protects the most important remnants of the Cerrado's southern grasslands, which are under strong anthropogenic pressure. The present study describes the structure of bird assemblages that directly use food resources in burned areas, comparing areas affected by natural fire to the areas where controlled fires were set (a management strategy to combat arson). The tested null hypothesis was that different bird assemblages are structured in a similar manner, regardless of the post-fire period or assessed area. Between December/2012 and January/2015, 92 species were recorded foraging in the study areas. The results indicate that both types of burnings triggered profound and immediate changes in bird assemblages, increasing the number of species and individuals. Natural fires exhibited a more significant influence on the structure (diversity and dominance) than prescribed burnings. Nevertheless, all the differences were no longer noticeable after a relatively short time interval of 2-3 months after prescribed burnings and 3-4 after natural fires. The findings may help the understanding of prescribed burnings as a management strategy for bird conservation in grasslands.

High stocks of coarse woody debris in a tropical rainforest, East Kalimantan: Coupled impact of forest fires and selective logging

Forest fires coupled with logging have now become one of the most extensive causes of forest degradation, affecting the balance between carbon emissions and sequestration in lowland tropical forests in Southeast Asia. Being transient pools of disturbance-killed trees, coarse woody debris (CWD) stocks play a key role in the carbon budget of such disturbed forests. Here, we investigated for the first time how logging affects the CWD input during and following a fire and, consequently, post-fire CWD stocks. Measurements were made at a permanent site in Bukit Soeharto Education Forest (BSEF) in East Kalimantan, Indonesia. This site consisted of plots that had been subjected to three different logging intensities (HF: heavily felled, trees with diameter at breast height (DBH) ⩾30cm were felled; LF: lightly felled, trees with DBH ⩾50cm were felled; UF: unfelled), all of which were burned by a fire that occurred during a drought associated with the El Niño Southern Oscillation in 1998, shortly after logging. CWD mass were measured in 2012, following 14years of monitoring the CWD inputs. The average CWD mass across the three logging treatments was 89Mgha−1, which is higher than the reported values for undisturbed forests but within the recorded range for recently disturbed forests. The amount of CWD inputs due to tree death during the fire was similar among the three treatments. However, there was a large difference in the CWD input in the post-fire period. In UF plots, large CWD inputs lasted for 2years following the fire due to delayed tree death, whereas in HF and LF plots, where the above-ground biomass had greatly reduced by selective logging, no further large CWD inputs occurred after the fire. Consequently, the CWD stocks in the HF and LF plots were 50–60% lower than those in the UF plots. A simulation predicted that these CWD inputs during and shortly after the fire still constitute a large proportion of the CWD stocks in 2012, suggesting that the CWD pool is a rather durable carbon store in BSEF. In the HF and LF plots, there was few large diameter CWD pieces, reflecting the selective logging of large diameter trees, whereas, in the UF plots, there were large standing dead and uprooted trees. Since the larger diameter CWD pieces are persist in the forest for a longer time continuing to store carbon and to provide habitats for diverse wild life, selective logging could have large impacts on forest ecology and function not only by decreasing the total CWD inputs and stocks but also by decreasing the large diameter CWD pieces.

Mid-term and scaling effects of forest residue mulching on post-fire runoff and soil erosion

Mulching is an effective post-fire soil erosion mitigation treatment. Experiments with forest residue mulch have demonstrated that it increased ground cover to 70% and reduced runoff and soil loss at small spatial scales and for short post-fire periods. However, no studies have systematically assessed the joint effects of scale, time since burning, and mulching on runoff, soil loss, and organic matter loss. The objective of this study was to evaluate the effects of scale and forest residue mulch using 0.25m2 micro-plots and 100m2 slope-scale plots in a burnt eucalypt plantation in central Portugal. We assessed the underlying processes involved in the post-fire hydrologic and erosive responses, particularly the effects of soil moisture and soil water repellency.Runoff amount in the micro-plots was more than ten-fold the runoff in the larger slope-scale plots in the first year and decreased to eight-fold in the third post-fire year. Soil losses in the micro-plots were initially about twice the values in the slope-scale plots and this ratio increased over time. The mulch greatly reduced the cumulative soil loss measured in the untreated slope-scale plots (616gm−2) by 91% during the five post-fire years. The implications are that applying forest residue mulch immediately after a wildfire can reduce soil losses at spatial scales of interest to land managers throughout the expected post-fire window of disturbance, and that mulching resulted in a substantial relative gain in soil organic matter.

A 6 year longitudinal study of post-fire woody carbon dynamics in California’s forests

We examined the dynamics of aboveground forest woody carbon pools — live trees, standing dead trees, and down wood — during the first 6 years following wildfire across a wide range of conditions, which are characteristic of California forest fires. From repeated measurements of the same plots, we estimated change in woody carbon pools as a function of crown fire severity as indicated by a post-fire index, years since fire, pre-fire woody carbon, forest type group (hardwood vs. softwood), elevation, and climate attributes. Our analysis relied on 130 U.S. national forest inventory plots measured before and 1 year after fire, with one additional remeasurement within 6 years after fire. There was no evidence of net change in total wood carbon, defined for this study as the wood in standing trees larger than 12.7 cm diameter at breast height and down wood larger than 7.6 cm in diameter, over the post-fire period in any of the three severity classes. Stands that burned at low severity exhibited considerable shifts from live to standing dead and down wood pools. In stands that burned at moderate severity, live wood decreased significantly whereas no net change was detected in standing dead or down wood. High severity fire burning resulted in movement from standing dead to down wood pools. Our results suggest that the carbon trajectories for stand-replacing fires may not be appropriate for the majority of California’s forest area that burned at low to moderate severities.

Impact of Land Cover Change Induced by a Fire Event on the Surface Energy Fluxes Derived from Remote Sensing

Forest fires affect the natural cycle of the vegetation, and the structure and functioning of ecosystems. As a consequence of defoliation and vegetation mortality, surface energy flux patterns can suffer variations. Remote sensing techniques together with surface energy balance modeling offer the opportunity to explore these changes. In this paper we focus on a Mediterranean forest ecosystem. A fire event occurred in 2001 in Almodóvar del Pinar (Spain) affecting a pine and shrub area. A two-source energy balance approach was applied to a set of Landsat 5-TM and Landsat 7-EMT+ images to estimate the surface fluxes in the area. Three post-fire periods were analyzed, six, seven, nine, and 11 years after the fire event. Results showed the regeneration of the shrub area in 6–7 years, in contrast to the pine area, where an important decrease in evapotranspiration, around 1 mm·day−1, remained. Differences in evapotranspiration were mitigated nine and 11 years after the fire in the pine area, whereas significant deviations in the rest of the terms of the energy balance equation were still observed. The combined effect of changes in the vegetation structure and surface variables, such as land surface temperature, albedo, or vegetation coverage, is responsible for these variations in the surface energy flux patterns.

Simulating riparian disturbance: Reach scale impacts on aquatic habitat in gravel bed streams

Large wood governs channel morphology, as well as the availability of in-stream habitat, in many forested streams. In this paper, we use a stochastic, physically based model to simulate wood recruitment and in-stream geomorphic processes, in order to explore the influence of disturbance history on the availability of aquatic habitat. Specifically, we consider the effects of fire on a range of stream sizes by varying the rate of tree toppling over time in a simulated forest characterized by a tree height of 30 m. We also consider the effects of forest harvesting with various riparian buffer sizes, by limiting the lateral extent of the riparian stand. Our results show that pulsed inputs of wood increase the availability and variability of physical habitat in the postfire period; reach-averaged pool area and deposit area double in small streams, while side channels increase by over 50% in intermediate-sized channels. By contrast, forest harvesting reduces the availability of habitat within the reach, though the effects diminish with increasing buffer size or stream width; in laterally stable streams the effects are minimal so long as buffer width is large enough for key pieces to be recruited to the reach. This research emphasizes the importance of natural disturbance in creating and maintaining habitat heterogeneity and shows that scenario-based numerical modeling provides a useful tool for assessing the historical range of variability associated with natural disturbance, as well as changes in habitat relevant to fish. It can be also used to inform forest harvesting and management.

Recovery of understory vegetation biomass and biodiversity in burned larch boreal forests in Northeastern China

ABSTRACTRecovery of biomass and biodiversity of forest understory vegetation after fire disturbance has been widely studied; however, how this relationship changes and what are the determinants at different post-fire stages in larch boreal forests are still unclear. We investigated a chronosequence of 81 understory plots in larch boreal forests that were disturbed by fires in 1987 (S5), 1992 (S4), 1996 (S3), 2002 (S2), or 2007 (S1). Analysis of variance was conducted to test the differences of biodiversity and biomass among various post-fire stages. Different regression models were used to fit the relationship between biomass and biodiversity, while factors influencing this relationship were identified by boosted regression tree analysis. Results showed that total understory biomass increased from 2.51 t ha−1 in S1 to 8.47 t ha−1 in S3 and declined to 5 t ha−1 in S5. Similar dynamics were also found between species richness and species diversity. Positive linear correlations linked biomass and biodiversity throughout most of the post-fire periods. Slope and stand density were the two most important factors influencing the secondary succession of understory vegetation after fire. Geographical factors and overstory competition determine the orientation of vegetation recovery, and the impacts of climate on vegetation are muted after fire disturbances.

Molecular characterization of wildfire impacts on organic matter in eroded sediments and topsoil in Mediterranean eucalypt stands

Wildfires can increase soil erosion due to the destruction of the vegetation and changes in soil organic matter (SOM) quantity and quality. This fact is especially dramatic in the case of Mediterranean ecosystems. Therefore, the major goal of the present study was to achieve a better understanding of the short-term effects of wildfires on the quantity and quality of organic matter (OM) in the topsoil of burnt Mediterranean eucalyptus plantations in north-central Portugal.Wildfire had a large impact on slope-scale sediment losses, as they were approximately 30 times higher at the burnt site than at the unburnt site over the first 25months after the fire. The pH and total nitrogen (TN) content of the burnt topsoil showed a noticeable increase immediately after the wildfire, whereas the total organic carbon (TOC) content revealed the opposite behavior. However, the TOC content showed a partial recovery during the subsequent two years after the fire. The sediments eroded after the fire were consistently more acidic and richer in TOC and TN than the burnt topsoil; they also revealed less pronounced changes with time-since-fire compared with the burnt topsoil.Analytical pyrolysis analyses indicated that the fire resulted in an enrichment of aromatic compounds, nitrogen (N) constituents, lignin-derived compounds and polysaccharides. The latter is best explained with the input of partially charred OM, ash and decaying parts of plants killed by the fire. The thermal transformation of SOM caused the thermal breakdown and cracking of n-alkane compounds, as was revealed by the increase of the ratio of short-to-long chains and the alteration of the typical odd-over-even carbon predominance indexes. The relative abundance of specific biomarkers for vegetation and, in particular for Eucalyptus globulus, such as terpenoids eucalyptol and globulol decreased drastically or even disappeared from the pyrolysates of the burnt topsoil. These fire-induced changes in the quality of topsoil OM persisted during the whole post-fire period of 25months. In general, the Py–GC/MS results pointed out that during the first two years after the fire the recovery of the topsoil OM quality was practically negligible.