Stand-replacing Fire Research Articles

Assessing the carbon dioxide balance of a degraded tropical peat swamp forest following multiple fire events of different intensities

Tropical peat swamp forest is a unique ecosystem rich in carbon and water, accumulating a huge amount of carbon as peat. However, the huge carbon pool has been threatened by oxidative peat decomposition and fire loss mainly because of deforestation and drainage. Fire causes acute carbon dioxide (CO2) emissions through the combustion of biomass and peat. Also, fire should change the CO2 balance of postfire ecosystems. Although it is crucial to quantify CO2 balance even after a fire event to understand the total fire impact, information based on field measurement is lacking. Thus, we had measured eddy CO2 flux above a repeatedly burned degraded peat forest for about 13 years since 2004. The site was a stable CO2 source of 147−290 g C m−2 yr−1 for five years after a stand-replacing fire in 2002. Unexpectedly, a moderate-severity fire in 2009 changed the site to a CO2 sink of about −600 g C m−2 yr−1. The drastic change would have been caused by a large decrease in the decomposition of plant debris, which had accumulated since the 2002 fire but was burned by the 2009 fire. In contrast, gross primary production (GPP) remained about the same even though vegetation was damaged, mainly because year-round wet conditions caused by a La Niña event promoted the regrowth of hygrophilous herbaceous plants and were favorable to their GPP. The site also had a low-severity fire and was drained in 2014 but did not return to a CO2 source. However, the net ecosystem CO2 uptake after the 2009 fire was insufficient to recover a large amount of fire CO2 emission. If CO2 emissions from four fires in 1999, 2002, 2009 and 2014 are counted, the site is expected to owe an outstanding CO2 debt of 25 kg C m−2.

High-severity wildfire reduces richness and alters composition of ectomycorrhizal fungi in low-severity adapted ponderosa pine forests

Ponderosa pine (Pinus ponderosa) forests are increasingly experiencing high-severity, stand-replacing fires. Whereas alterations to aboveground ecosystems have been extensively studied, little is known about soil fungal responses in fire-adapted ecosystems. We implement a chronosequence of four different fires that varied in time since fire, 2 years (2015) to 11 years (2006) and contained stands of high severity burned P. ponderosa in eastern Washington and compared their soil fungal communities to adjacent unburned plots. Using Illumina Miseq (ITS1), we examined changes in soil nutrients, drivers of species richness for ectomycorrhizal (plant symbionts) and saprobic (decomposers) fungi, community shifts, and post-fire fungal succession in burned and unburned plots. Ectomycorrhizal richness was 43.4% and saprobic richness 12.2% lower in the burned plots, leading to long-term alterations to the fungal communities that did not return to unburned levels, even after 11 years. Differences in the post-fire fungal community were driven by pyrophilous, “fire-loving” fungi, including the ectomycorrhizal Ascomycete genera Pustularia and Wilcoxina, and the saprobic Basidiomycete genus Geminibasidium. Ectomycorrhizal and saprobic fungi were intimately linked to the soil environment: depth of the organic matter, total carbon, total nitrogen, and their interaction with fire predicted ectomycorrhizal richness. Whereas total carbon, time since fire, treatment, and the interaction between time since fire and treatment predicted saprobic richness. We conclude that high-severity wildfires lead to lower ectomycorrhizal richness and significantly altered ectomycorrhizal and saprobic communities in fire-adapted ecosystems, selecting resilient and fire-adapted species, such as W. rehmii and Geminibasidium sp., thus initiating post-fire succession.

Adapting a dynamic vegetation model for regional biomass, plant biogeography, and fire modeling in the Greater Yellowstone Ecosystem: Evaluating LPJ-GUESS-LMfireCF

North American forests are threatened by changes in climate and disturbance dynamics. Current efforts to model future vegetation and fire dynamics are challenged by the lack of mechanistic representation of ecological processes, the spatial resolution to capture landscape-level heterogeneity, and the ability to model regional spatial extents. To address these gaps, a dynamic vegetation model was adapted for regional applications to the western forests of the U.S. Here we present LPJ-GUESS-LMfireCF, a dynamic vegetation model that includes the ecological processes of a dynamic global vegetation model with cohort-based forest demography (LPJ-GUESS) and a mechanistic fire module (LMfire), with a newly developed routine to simulate stand-replacing crown fires (CF). The LMfireCF fire module calculates surface fire and canopy characteristics to determine if critical conditions are met for crown fire initiation and spread, and if met, calculates crown fire effects. Adapting the model to regional applications required parameterization of dominant regional plant functional types (PFTs) and additional model adjustments related to the representation of fire. Simulations driven by historical climate data from 1980 to 2016 were made to compare the two different fire modules: the original GlobFIRM and newly created LMfireCF, and two different plant functional type (PFT) parameterizations: the original global vs. newly created regional PFTs. Model performance was evaluated by comparing simulation outputs to field and satellite-based estimates for landscape biomass distribution, dominant plant cover, fire activity, and forest regeneration. LPJ-GUESS-LMfireCF accurately represented vegetational zones with elevation and climate gradients in Yellowstone National Park (YNP). Total carbon in aboveground live vegetation within YNP simulated by LPJ-GUESS-LMfireCF with the regional PFTs overestimated satellite-based estimates by 12% (44.8 TgC vs 39.9 TgC respectively). In comparison, an LPJ-GUESS simulation using the older GlobFIRM fire module and global PFTs resulted in total carbon in aboveground live vegetation of 225 Tg C for YNP, five times the satellite-based estimates. LPJ-GUESS-LMfireCF simulated burned area and fire severity approximated satellite-based observations. Importantly, LPJ-GUESS-LMfireCF simulated the large stand-replacing fires of 1988 in Yellowstone as emergent results without model initialization of vegetation cover or fire history. LPJ-GUESS-LMfireCF simulated that 25% of the area of YNP burned in 1988, compared to 36% based on field and satellite-based estimates. However, modeled postfire regrowth was more rapid than field-based estimations, with simulated mean biomass 24 years postfire (40.1 ± 1.65 Mg ha−1) 58% greater than field estimations (25.4 ± 2.5 Mg ha−1), yet simulated mean biomass for mature forests (>100 years old without a major disturbance) was 24% less than field estimations (58.4 ± 0.8 compared to 76.6 ± 3.5 Mg ha−1). In summary, LPJ-GUESS-LMfireCF effectively simulates regional crown fire dynamics and vegetation to more accurately model regional biomass, plant biogeography, and fire activity.

The propagule doesn't fall far from the tree, especially after short-interval, high-severity fire.

Subalpine forests that historically burned every 100-300yr are expected to burn more frequently as climate warms, perhaps before trees reach reproductive maturity or produce a serotinous seedbank. Tree regeneration after short-interval (<30-yr) high-severity fire will increasingly rely on seed dispersal from unburned trees, but how dispersal varies with age and structure of surrounding forest is poorly understood. We studied wind dispersal of three conifers (Picea engelmannii, Abies lasiocarpa, and Pinus contorta var. latifolia, which can be serotinous and nonserotinous) after a stand-replacing fire that burned young (≤30yr) and older (>100yr) P. contorta forest in Grand Teton National Park (Wyoming, USA). We asked how propagule pressure varied with time since last fire, how seed delivery into burned forest varied with age and structure of live forest edges, what variables explained seed delivery into burned forest, and how spatial patterns of delivery across the burned area could vary with alternate patterns of surrounding live forest age. Seeds were collected in traps along 100-m transects (n=18) extending from live forest edges of varying age (18, 30, and >100yr) into areas of recent (2-yr) high-severity fire, and along transects in live forests to measure propagule pressure. Propagule pressure was low in 18-yr-old stands (~8seeds/m2 ) and similarly greater in 30- and 100-yr-old stands (~32seeds/m2 ). Mean dispersal distance was lowest from 18-yr-old edges and greatest from >100-yr-old edges. Seed delivery into burned forest declined with increasing distance and increased with height of trees at live forest edges, and was consistently higher for P. contorta than for other conifers. Empirical dispersal kernels revealed that seed delivery from 18-yr-old edges was very low (≤2.4seeds/m2 ) and concentrated within 10m of the live edge, whereas seed delivery from >100-yr-old edges was >4.9seeds/m2 out to 80m. When extrapolated throughout the burned landscape, estimated seed delivery was low (<49,400seeds/ha) in >70% of areas that burned in short-interval fire (<30yr). As fire frequency increases, immaturity risk will be compounded in short-interval fires because seed dispersal from surrounding young trees is limited.

Effects of climate on historical fire regimes (1451–2013) in Pinus hartwegii forests of Cofre de Perote National Park, Veracruz, Mexico

Cofre de Perote National Park (CPNP) in Veracruz, Mexico is part of the Transmexican Volcanic Belt, and its Pinus hartwegii forests reflect a balance between the various natural factors that represent the region's climatology and hydrology. Like many other areas in this region, the historical fire regimes of these forests and their relationship with climate are unknown, but are needed for sustainable management plans. The main objectives of this study were to reconstruct the historical fire regime in a Pinus hartwegii forest and decipher the influenced of climate. Our investigation focused in two study areas, Valle la Teta (VT) and Barranca Honda (BH). The VT study area was divided into three sites based on humidity and elevation: 1) Humid (VTH), 2) Dry Low (VTDL) and 3) Dry High (VTDH). The approximated area for each site was ​​30, 30, 35 and 50 ha, for VTH, VTDL, VTDH and BH, respectively. We collected 162 fire scarred samples to reconstruct the fire history for the last 550 years (1461−2013). The fire scarred samples contained 1240 fire scars, with most fires occurring in spring (95 %) or summer (5%). Prior to 1973, these sites were characterized by a frequent surface fire regime. In all four sites, the mean fire intervals ranged from 5 to 6 years (for fires that scarred ≥ 10 % of the samples) and 13–23 years (for fires that scarred ≥ 25 % of the samples). Extensive fires (≥ 10 %) coincided with significantly dry conditions based on the Standardized Precipitation Index (SPI), influenced by El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation Index (PDO). We also found a significant relationship between fire occurrence and ENSO, both in its warm phase, El Niño (21 fires ≥ 10 %) and in its cold phase, La Niña (32 fires ≥ 10 %). Synchronization of the cold phase of ENSO (La Niña) with the cold phase of the PDO (negative), facilitated severe drought conditions, resulting in fires with the greatest spatial extent. Since 1973, extensive fires have been absent from the study area most likely due to anthropogenic activities including active fire suppression. These results show a strong climate-fire relationship in these high elevation forests. The lack of fire in the last four decades is concerning and could potentially lead to unnatural stand-replacing fires, unless the historical fire regime is restored to maintain natural processes and increase forest resilience.

Effects of Post-Fire Vegetation Recovery on Soil Erosion in Vulnerable Montane Regions in a Monsoon Climate: A Decade of Monitoring

In areas with frequent fires and erosive soils under monsoon climate, we aimed to determine the long-term dynamics of soil loss during vegetation recovery and to examine elapsed time for soil stabilization. Runoff plots were installed in Pinus densiflora forests affected by stand-replacing fires on the East Coast of South Korea, which occurred in spring 2000. Runoff plots measured runoff and sediment yields for 11 years (2003–2013) during which time, vegetation cover of low-, intermediate-, and high-vegetation cover plots increased from 21 to 44%, 49% to 69%, and 87% to 95%, respectively. Vegetation was effective in preventing runoff and sediment yield. Nevertheless, to stabilize to below baseline load, it took 7 years at low and intermediate cover plots and only 3 years at high cover plots. For 7 years, 7.06 (5.2-fold) and 4.29 (3.1-fold) kg m−2 of soil were lost at the low and intermediate cover plots, respectively, compared to the high cover plots (1.37 kg m−2). Sediment loss fluctuated more than runoff following extreme rainfall events. We suggest that for the slow recovery area ( 70% cover).

Fire-catalyzed vegetation shifts in ponderosa pine and Douglas-fir forests of the western United States

Increased wildfire activity combined with warm and dry post-fire conditions may undermine the mechanisms maintaining forest resilience to wildfires, potentially causing ecosystem transitions, or fire-catalyzed vegetation shifts. Stand-replacing fire is especially likely to catalyze vegetation shifts expected from climate change, by killing mature trees that are less sensitive to climate than juveniles. To understand the vulnerability of forests to fire-catalyzed vegetation shifts it is critical to identify both where fires will burn with stand-replacing severity and where climate conditions limit seedling recruitment. We used an extensive dendrochronological dataset to model the influence of seasonal climate on post-fire recruitment probability for ponderosa pine and Douglas-fir. We applied this model to project annual recruitment probability in the US intermountain west under contemporary and future climate conditions, which we compared to modeled probability of stand-replacing fire. We categorized areas as ‘vulnerable to fire-catalyzed vegetation shifts,’ if they were likely to burn at stand-replacing severity, if a fire were to occur, and had post-fire climate conditions unsuitable for tree recruitment. Climate suitability for recruitment declined over time in all ecoregions: 21% and 15% of the range of ponderosa pine and Douglas-fir, respectively, had climate conditions unsuitable for recruitment in the 1980s, whereas these values increased to 61% (ponderosa pine) and 34% (Douglas-fir) for the future climate scenario. Less area was vulnerable to fire-catalyzed vegetation shifts, but these values also increased over time, from 6% and 4% of the range of ponderosa pine and Douglas-fir in the 1980s, to 16% (ponderosa pine) and 10% (Douglas-fir) under the future climate scenario. Southern ecoregions had considerably higher vulnerability to fire-catalyzed vegetation shifts than northern ecoregions. Overall, our results suggest that the combination of climate warming and an increase in wildfire activity may substantially impact species distributions through fire-catalyzed vegetation shifts.

Topographic position amplifies consequences of short-interval stand-replacing fires on postfire tree establishment in subalpine conifer forests

Stand-replacing fires burned at 100 to 300-year intervals for millennia in subalpine conifer forests of western North America, but forests are burning more frequently as climate warms. Postfire tree regeneration is reduced when young forests reburn before recovering from previous fires or when drought occurs during postfire years. However, whether seedling vulnerabilities to harsh microclimate conditions may be amplified in short-interval (<30 years) fires is unclear. We conducted a field experiment to answer three questions: (1) How do germination, survival, and establishment of lodgepole pine (Pinus contorta var. latifolia) and Douglas-fir (Pseudotsuga menziesii var. glauca) vary by aspect following high-severity, short-interval fires? (2) What environmental factors control germination, survival, and establishment of both species? (3) Based on our experimental evidence, what proportion of available seed would be expected to establish across landscapes that burned in these short-interval fires? One year postfire, we planted seeds of both species in north-facing, south-facing and flat plots at four sites across the Greater Yellowstone Ecosystem (Wyoming, USA). Soil microclimate was monitored continuously. Seed germination and seedling survival were measured every two weeks during the following growing season and at the beginning and end of the second growing season. Germination did not vary with aspect but increased with early-season soil moisture and temperature. Survival and establishment were low on south-facing aspects (<1% of seeds established for both species) and declined with warmer soil temperatures and drier soils. For lodgepole pine, we predicted establishment rates of <1% of available seed over 25% of the reburned landscape. Soil temperatures in short-interval fires were 2˚C warmer than similar areas of long-interval fire, with maximum temperatures frequently exceeding 40 °C. Topographic variation will mediate the consequences of short-interval fire for seedling establishment, leading to patchier tree regeneration as climate warming raises the likelihood of short-interval fires.

Fire as a driver of wood mechanical traits in the boreal forest

In boreal forests where the fire return interval is long, the high structural variability of stands may affect wood traits. Here, we build on earlier work that revealed a difference in wood mechanical traits of black spruce between regular (regenerated from fire in the last 200 years) and irregular (undisturbed by fire for at least 200 years) stands. This study aimed to identify the ecological drivers of this variation in wood traits. To do so, we first sought to corroborate existing results on the effects of stand structure induced by the time since the last stand-replacing fire (TSLF) on wood mechanical stiffness in the eastern boreal forest of Canada. Results confirmed that black spruce from regular stands tend to produce wood with higher modulus of elasticity (MOE) than those from irregular stands. For both regular and irregular stands, we compared a set of linear models that were defined a priori to determine the structural and site productivity variables having the largest influence on MOE. The ‘growth efficiency index’ (aboveground woody biomass production per unit leaf area) was the best predictor of MOE variation among regular stands. For irregular stands, the model with TSLF as the sole explanatory variable was a better predictor of MOE than any other candidate model. However, we did not find strong evidence of a direct relationship between TSLF and wood traits, since our best models explained a relatively small proportion of the variance. Our results suggest that differences in wood traits could be attributable to the seed or layer origin of the trees and/or to the length of time trees remain in the understory. We propose that intensive wood production strategies focus on stands of the first post-fire cohort.

Understory vegetation responses to simulated mountain pine beetle attack and salvage logging in grey attack stage lodgepole pine stands

Disturbances are an integral part of forest ecosystems and drive successional change. The boreal forest is adapted to stand-replacing fires, which have different ecological impacts than less severe disturbances, such as insect attacks. In recent years, mountain pine beetle (MPB), a bark beetle native to western North America, has undergone an unprecedented range expansion into lodgepole pine forests in west-central Alberta, Canada. MPB influences understory microclimatic conditions and above- and below-ground resources, but does not have the direct impacts on ground vegetation and the forest floor that normally accompany wildfire. The objective of this study was to quantify vegetation responses to MPB in forests for which this is a novel disturbance. Our replicated field experiment included an untreated control, medium and high tree mortality (simulated MPB-attack through stem injection of herbicide), and harvesting to simulate salvage logging. We used univariate and multivariate analyses to examine responses of understory vegetation to these treatments from pre- to seven years post-treatment. The severity of disturbance determined the magnitude of vegetation changes. Only the simulated salvage logging resulted in immediate changes post-treatment. Seven years post-treatment, vascular plant richness increased along the gradient of treatment severity. Total vegetation cover declined in the short term after salvage logging but then returned to pre-treatment levels. Notably, graminoid cover increased with the high-mortality MPB and salvage logging treatment, and remained higher in these two treatments, seven years post-treatment. Changes in species composition were most dramatic for salvage logging followed by the high mortality and then the medium mortality treatments; by seven years post-treatment there were indications that communities were beginning to recover to their pre-treatment composition. Feathermosses were indicative of the untreated control, shade-tolerant species increased their relative abundance in the medium mortality treatment, both shade-tolerant and intolerant species increased their relative abundance in the high mortality treatment, and disturbance-adapted, shade-intolerant species (including lodgepole pine) were indicators of salvage logging. We conclude that stands experiencing medium levels (~50%) of MPB-caused mortality will demonstrate resistance (change less or more slowly) and/or resilience (recover to the pre-disturbance condition more quickly) as compared to those experiencing high levels (~100%) of mortality, which show changes in understory composition that might influence stand successional trajectories. Effects of salvage logging will be much more dramatic than those of the MPB attack. Our results can help inform decisions on management or rehabilitation of stands post-MPB attack.

Timing and structure of vegetation, fire, and climate changes on the Pacific slope of northwestern Patagonia since the last glacial termination

By virtue of its location in the southern mid-latitudes, northwestern Patagonia (40°-44°S) offers the opportunity to unravel the mechanisms involved in the initiation and propagation of paleoclimate signals of hemispheric and global significance. Of particular importance is deciphering the evolution of the Southern Westerly Winds (SWW) considering their influence at continental, zonal, hemispheric, and global scale. Here I present a multi-decadal record from Lago Proschle, a small closed-basin lake located on the Pacific slope of northwestern Patagonia, to examine the timing and structure of vegetation, fire, and climate change along a continuum since the onset of the Last Glacial Termination (T1). The record shows rapid glacier recession during T1, reaching the western Andean foothills in ∼400 years or less. Nothofagus-dominated forests established between ∼17.4–17 ka, followed by closed-canopy North Patagonian Rain Forests (NPRF) with shade-tolerant thermophilous trees between ∼16.3–15.4 ka. These changes suggest an abrupt warming trend and an increase in precipitation at ∼16.3 ka, associated with a northward shift of the SWW. Subsequent increases in cold-tolerant hygrophilous trees between ∼15.4–12.8 ka imply a shift to cold, more humid conditions during the Antarctic Cold Reversal, suggesting stronger SWW influence. This was followed by stand-replacing fires brought by a sudden decline in summer precipitation at ∼12.8 ka, associated with a millennial-scale southward shift of the SWW which was contemporaneous with the onset of the Younger Dryas. Dominance of thermophilous, summer-drought tolerant Valdivian rainforest trees and high fire activity ensued between ∼10.3–7.8 ka, suggesting peak warmth and overall decline in annual precipitation associated with weakening of the SWW during the early Holocene. A multi-millennial cooling and wetting trend started at ∼7.8 ka, brought by stronger SWW influence, followed by recurrent, centennial-scale variations in temperature and precipitation starting at ∼6.4 ka. Deforestation, fire, and spread of non-native herbs by Chilean/European settlers began during the late 18th century. Abrupt vegetation changes in the Lago Proschle record were driven by rapid climate changes over the last 17,400 years amplified, in some instances, by fire disturbance.

Effectiveness of Restoration Treatments for Reducing Fuels and Increasing Understory Diversity in Shrubby Mixed-Conifer Forests of the Southern Rocky Mountains, USA

Exclusion of natural surface fires in warm/dry mixed-conifer forests of the western U.S. has increased potential for stand-replacing crown fires and reduced resilience of these systems to other disturbances, such as drought and insect attack. Tree thinning and the application of prescribed fire are commonly used to restore more resilient ecological conditions, but currently, there is a lack of long-term data with which to evaluate restoration treatment effectiveness in forest types where resprouting shrubs dominate understory communities. At a mixed-conifer site in southwestern Colorado, we compared forest structure and understory vegetation responses to three restoration treatments (thin/burn, burn, and control) over 10 years in a completely randomized and replicated experiment. Forest density, canopy cover, and crown fuel loads were consistently lower, and crown base height was higher, in thin/burn than burn or controls, but the effects diminished over time. Ten years following treatment, &gt;99% of all plant species within both treatments and the control were native in origin. There were no differences between treatments in understory richness, diversity, cover, or surface fuels, but graminoid cover more than doubled in all treatments over the 15-year monitoring period. Similarly, there was more than a 250% increase post-treatment in shrub density, with the greatest increases in the thin/burn treatment. In addition, we saw an increase in the average shrub height for both treatments and the control, with shrub stems &gt;80 cm becoming the dominant size class in the thin/burn treatment. Conifer seedling density was significantly lower in thin/burn compared with burn and control treatments after 10 years. Taken together, these conditions create challenges for managers aiming to reestablish natural fire patterns and sustain mixed-conifer forests. To limit the dominance of resprouting shrubs and facilitate conifer regeneration after overstory thinning and prescribed fire, managers may need to consider new or more intensive approaches to forest restoration, particularly given current and projected climate change.

Disturbance history modulates how litter and herbaceous cover influence conifer regeneration after fire

Climate-driven increases in disturbance frequency and extent augment the potential for compounded disturbances. Drawing on well-studied forests that experienced successive disturbances, we asked: (1) how does post-fire cover of litter, herbaceous cover and bare ground vary between stands affected by combinations of blow-down, insect outbreak, and fire? (2) How do post-fire relationships between ground cover and conifer regeneration vary with recent disturbance history? We measured ground cover and conifer regeneration from 2003 to 2014 following stand-replacing fires in 2002. Burned stands were either blown down in 1997, affected by a 1940s Dendroctonus rufipennis (spruce beetle; SB) outbreak, or neither. Implementing mixed-effects models, we measured the relationships between pre-fire stand attributes (structural stage, canopy dominance and combination of disturbances) and post-fire ground cover and between post-fire ground cover and conifer regeneration. Fire-only stands had more litter and herbaceous cover post fire than other stands (P&amp;lt;0.05). Fir regeneration increased with litter in stands that only burned, but decreased with litter in stands that were first blown down. Similarly, pine and fir regeneration increased with herbaceous cover after fire-only, but did the opposite in stands affected by the SB outbreak. Pre-fire legacies can modulate the effects of ground cover on plant regeneration.

Fire history in Andean Araucaria–Nothofagus forests: coupled influences of past human land-use and climate on fire regimes in north-west Patagonia

Historical fire regimes are critical for understanding the potential effects of changing climate and human land-use on forest landscapes. Fire is a major disturbance process affecting the Andean Araucaria forest landscape in north-west Patagonia. The main goals of this study were to reconstruct the fire history of the Andean Araucaria–Nothofagus forests and to evaluate the coupled influences of climate and humans on fire regimes. Reconstructions of past fires indicated that the Araucaria forest landscape has been shaped by widespread, stand-replacing fires favoured by regional interannual climate variability related to major tropical and extratropical climate drivers in the southern hemisphere. Summer precipitation and streamflow reconstructions tended to be below average during fire years. Fire events were significantly related to positive phases of the Southern Annular Mode and to warm and dry summers following El Niño events. Although Euro-Chilean settlement (1883–1960) resulted in widespread burning, cattle ranching by Pehuenche Native Americans during the 18th and 19th centuries also appears to have changed the fire regime. In the context of climate change, two recent widespread wildfires (2002 and 2015) affecting Araucaria forests appear to be novel and an early indication of a climate change driven shift in fire regimes in north-west Patagonia.

Postfire recruitment failure in Scots pine forests of southern Siberia

Wildfire disturbances effect changes in vegetation communities that in turn influence climate. Such changes in boreal forest ecosystems can persist over decadal time scales or longer. In the ecotone between boreal forest and steppe in the region southeast of Lake Baikal in southern Siberia, shifts between the two vegetation types may be precipitated by variations in site specific conditions, as well as disturbance characteristics such as fire frequency and severity. Warmer, drier conditions in the region have been associated with a decrease in fire return intervals and greater burn severity that may, in turn, drive conversion of forests to steppe vegetation at a greater rate than has occurred prior to the onset of warming and drying. Stand-replacing fires in Pinus sylvestris stands in southern Siberia may lead to recruitment failure postfire, particularly on southwest to west-facing slopes, which are more often dominated by grasses. This study uses a combination of field data and remotely sensed indices of vegetation and moisture to distinguish between recruitment pathways in southern Siberia, and to study the influence of factors related to soils, topography, fire severity and winter snow cover on these.We expected that recruitment success would be associated with lower burn severity (higher NBR), higher greenness (NDVI) and moisture (NDMI), and winter snow (NDSI) postfire. We also expected phenological characteristics to differ among recruitment paths. Prior to burning, our sites are broadly similar in terms of remotely sensed indices of moisture (NDMI), vegetation (NDVI), and winter fractional snow cover (NDSI), but recruitment failure sites are generally drier and less green postfire. Initial differences in greenness and moisture among sites characterized by abundant recruitment (AR), intermediate recruitment (IR) and recruitment failure (RF) become more pronounced over the initial decades postfire. The earliest separability of AR and RF sites using remotely sensed indices occurs in the winter months 3–4 years postfire, during which time NDSI is highest for AR sites and lowest for RF. Although seasonality was important with regard to distinguishing among AR, IR and RF index values, the timing of phenological events such as start and end of season did not differ significantly among the sites.

Cambio postincendio en la estructura y composición del estrato arbóreo y carga de combustibles en un bosque de Pinus douglasiana de México

En los bosques de pino con un régimen histórico de incendios superficiales frecuentes de baja severidad, bajo condiciones extremas del estado del tiempo o a consecuencia de la supresión del fuego, la severidad de los incendios puede incrementar. La respuesta de la vegetación a eventos de incendios severos se estudió en una cronosecuencia postincendio de 8 años, 28 años y 60 años en un bosque dominado por Pinus douglasiana en México. La densidad de árboles con diámetro &gt; 2.5 cm y su área basal alcanzaron valores de 1095 árboles ha-1 ± 609 árboles ha-1 y 10.0 m2 ha-1 ± 2.2 m2 ha-1 a los 8 años; a los 28 años el área basal (44.6 m2 ha-1 ± 3.0 m2 ha-1) fue cercana a la de los rodales de 60 años (49.0 m2 ha-1 ± 6.4 m2 ha-1). Los pinos mantuvieron el mayor valor de importancia con el tiempo postincendio, se observó la formación de un subdosel de latifoliadas tolerantes a la sombra y un aumento en la riqueza y diversidad de especies; también se documentó que periodos largos sin incendios incrementan la carga de combustibles superficiales ligeros (66.0 Mg ha-1 ± 5.5 Mg ha-1 en los sitios de 28 años y 61.5 Mg ha-1 ± 4.6 Mg ha-1 en los sitios de 60 años) y modifican el comportamiento del fuego (velocidad de propagación de 1.3 m s-1 a 4.1 m s-1 y la longitud de la llama de 0.7 m a 1.7 m entre los rodales de 8 años y los de 28 años y 60 años combinados). El manejo de los bosques de pino debe considerar el balance entre objetivos de conservación biológica y mitigación del peligro de incendios de alta severidad.

Post-fire fuel succession in a rare California, USA, closed-cone conifer

BackgroundIncreasing frequency and size of wildfires over the past few decades have prompted concerns that populations of obligate seeding species may be vulnerable to repeat, short-interval fires that occur prior to these species reaching maturity. The susceptibility of populations to this risk is partially dependent on the amount and characteristics of fuel loading over time and their influence on fire behavior and effects. This study characterized fuel dynamics and modeled fire behavior across a time-since-fire chronosequence in stands of the rare, serotinous conifer, Baker cypress (Hesperocyparis bakeri [Jeps.] Bartel), ranging in age between 3 and 147 years post fire.ResultsLitter and fine woody fuel loading (1- to 100-hour) were highest in the 10-year-old and 147-year-old stands, while coarse fuel loading (1000-hour) peaked in the 10-year-old stand and subsequently decreased with time since fire. Duff loading consistently increased with time since fire. Cone production had not occurred in the first 10 yr of stand development. Foliar moisture content in Baker cypress was inversely correlated with stand age, and older foliage had lower moisture content than younger foliage. Modeled surface fire behavior was highest in the 10-year-old and 107-year-old stands in accordance with higher litter, fine woody fuel, or shrub fuel accumulation. While foliar moisture content was higher in younger stands and influenced the critical fireline intensity, we did not observe changes in fire type.ConclusionsFine-fuel loading in Baker cypress stands followed a U-shaped pattern over time (first decreasing, then stable, then increasing), consistent with findings in other forests with stand-replacing fire regimes. Our results indicated that early-successional stages of Baker cypress forests have sufficient fuels to allow for the spread of wildfire and 10-year-old stands could burn with substantive fire behavior prior to cone production. Whenever possible, we recommend suppressing wildfire in stands less than 20 yr old to avoid substantial decreases or local extirpation of these rare Baker cypress populations. Our results highlight the importance of knowing the cone production patterns, fuel dynamics, and corresponding fire behavior over the development of obligate-seeder species to assess the risk of population loss due to short-interval fires.

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.

Decreased snowpack and warmer temperatures reduce the negative effects of interspecific competitors on regenerating conifers

The persistence and distribution of species under changing climates can be affected by both direct effects of the environment and indirect effects via biotic interactions. However, the relative importance of direct and indirect climate effects on recruitment stages is poorly understood. We conducted a manipulative experiment to test the multiway interaction of direct and competition-mediated effects of climate change on vegetation dynamics. Following stand-replacing fire in California mixed-conifer forest, we seeded two conifer species, Pinus ponderosa and Abies concolor, in two consecutive years, one relatively normal and the other with an unusually wet and snowy winter followed by a hot summer. We additionally manipulated snow amount and competitive environment for both years. We found the effects of the snowpack treatment were contingent upon other abiotic factors (year of seeding) and biotic factors (shrub competition). Under ambient snowpack, shrubs reduced recruitment of P. ponderosa seedlings, but this negative effect disappeared with reduced snowpack. Additionally, the effects of shrubs on seedlings differed between cohorts and by life stage. In a warmer future, decreased snowpack may increase seedling emergence, but hotter and drier summers will decrease seedling survival; the effects of shrubs on conifers may become less negative as temperatures increase.

Modelling Lichen Abundance for Woodland Caribou in a Fire-Driven Boreal Landscape

Woodland caribou (Rangifer tarandus caribou) are reliant on Cladonia spp. ground lichens as a major component of their diet and lichen abundance could be an important indicator of habitat quality, particularly in winter. The boreal forest is typified by large, stand-replacing forest fires that consume ground lichens, which take decades to recover. The large spatial extent of caribou ranges and the mosaic of lichen availability created by fires make it challenging to track the abundance of ground lichens. Researchers have developed various techniques to map lichens across northern boreal and tundra landscapes, but it remains unclear which techniques are best suited for use in the continuous boreal forest, where many of the conflicts amongst caribou and human activities are most acute. In this study, we propose a two-stage regression modelling approach to map the abundance (biomass, kg/ha) of Cladonia spp. ground lichens in the boreal forest. Our study was conducted in Woodland Caribou Provincial Park, a wilderness-class protected area in northwestern Ontario, Canada. We used field sampling to characterize lichen abundance in 109 upland forest stands across the local time-since-fire continuum (2–119 years-since-fire). We then used generalized linear models to relate lichen presence and lichen abundance to forest structure, topographic and remote sensing attributes. Model selection indicated ground lichens were best predicted by ecosite, time-since-fire, and canopy closure. Lichen abundance was very low (&lt;1000 kg/ha) across the time-since-fire continuum in upland forest stands with dense tree cover. Conversely, lichen abundance increased steadily across the time-since-fire continuum in upland forest stands with sparse tree cover, exceeding 3000 kg/ha in mature stands. We interpolated the best lichen presence and lichen abundance models to create spatial layers and combined them to generate a map that provides a reasonable estimation of lichen biomass (R2 = 0.39) for our study area. We encourage researchers and managers to use our method as a basic framework to map the abundance of ground lichens across fire-prone, boreal caribou ranges. Mapping lichens will aid in the identification of suitable habitat and can be used in planning to ensure habitat is maintained in adequate supply in areas with multiple land-use objectives. We also encourage the use of lichen abundance maps to investigate questions that improve our understanding of caribou ecology.