Post-fire Pine Research Articles

Post-fire Pinus radiata invasion in a threatened biodiversity hotspot forest: A multi-scale remote sensing assessment

Biological invasions are one of the most relevant factors of biodiversity loss, especially after fire disturbances. Wildfires can accelerate invasions of fire-prone species, like Pinus radiata, and dramatically alter ecosystems. However, how to assess the main impacts of this invasion process on the composition, structure, and functionality of ecosystems, including the post-fire revegetation processes, has not been fully resolved. This study aimed to evaluate the impacts of P. radiata invasion on fire-damaged forest ecosystems using combined remote sensing and in situ data, focusing particularly on changes in biodiversity, ecosystem structure, and functionality. The recovery of forest leaf area index (LAI) and the fraction of photosynthetically active radiation (FPAR) were monitored using Sentinel-2 time series products. Then the pre- and post-fire native community composition and the relationships of invasion and biodiversity with biotic and abiotic components were characterized using structural equation modeling (SEM). The postfire P. radiata density was mapped to quantify invasion intensity in three burned native forest fragments using generalized additive modeling (GAM) regressions based on UAS multispectral data. Biophysical metrics indicate that all forest fragments impacted by high, medium-high, and medium-low severity fires achieved a partial recovery of their canopy. The SEM model showed that microtopographic features and vegetation height explain native species diversity under pre-fire conditions due to their close relationship with favorable microclimatic conditions for species establishment. Vegetation height determined the abundance of P. radiata in post-fire conditions, and it negatively impacted diversity by promoting the homogenization of vegetation cover and altering diversity patterns. The general composition and abundance metrics also showed a substantial modification associated with the heavy (significant) invasion of P. radiata species. Predictive mapping of P. radiata density showed high accuracies (R2 =0.73 and explained deviation of 80%). The maps depicted an intense concentration of the invasive tree with a mean density of 76,217 individuals per ha−1 and high invasion spots with more than 176,000 individuals per ha−1. The quantification of invasion and mapping is a fundamental input for prioritizing areas and resources for a large-scale restoration program, and is a priority to avoid the loss of these highly threatened forest ecosystems.

Post-fire growth of Pinus halepensis: Shifts in the mode of competition along a precipitation gradient

Competition can intensify the struggle for resources among plants, affecting forest growth and dynamics. The intensity and mode of competition – asymmetric vs. symmetric – can change along environmental gradients and with time, impacting the response of plants to their environment, but this is seldom explicitly considered in management plans. In this study, we aim to (i) disentangle the main environmental and tree-related factors that affect post-fire Pinus halepensis sapling growth; (ii) determine which mode of competition characterizes the species post-fire regeneration; and (iii) elucidate if the mode of competition changes with time, and along climatic gradients. We sampled 148 P. halepensis saplings located in 15 sites affected by wildfires between 1987 and 2013 in Catalonia (NE Spain). We measured their radial growth at the base, and we identified their competitive environment by locating and measuring all the trees in a 3-meter-radius from our target saplings. We modelled the effect of tree size, age, climate, and competitive environment on the post-fire regeneration growth following the neighborhood theory of forest dynamics and using model comparison and information criteria to address our research questions. We used a modification from the Hegyi index to determine the prevalence of symmetric vs. asymmetric competition, and we assessed the support for models in which competition was allowed to vary with age and precipitation. The best model showed that competition, precipitation, age, and target size influenced the radial growth of P. halepensis post-fire regeneration (Akaike weight 0.66, R2 = 0.52). We found evidence that P. halepensis mode of competition is generally asymmetric but can change along a precipitation gradient: it shifts from asymmetric in drier sites to almost fully symmetrical as precipitation increases. Our findings have implications for the management of post-fire P. halepensis stands, enabling the adaptation of silvicultural prescriptions to the climatic environment. In a context of increasing water scarcity, adaptive silviculture is fundamental to foster the resilience of pinewoods to future climatic and disturbance regimes.

Joint Dynamics of Cowberry and Bilberry Populations in Preserved Post-Fire Pine Forests: Retrospective Forecast within the Markov Model

Joint Dynamics of Cowberry and Bilberry Populations in Preserved Post-Fire Pine Forests: Retrospective Forecast within the Markov Model

Detecting patterns of post-fire pine regeneration in a Madrean Sky Island with field surveys and remote sensing

The American Southwest is experiencing drastic increases in aridity and wildfire incidence, triggering conversion of some frequent surface forests to non-forest. Extensive research has focused on these dynamics in regional ponderosa pine forests, but we know much less about Madrean pine-oak forests, which are broadly distributed from the Sierra Madre in Mexico to the Sky Island mountain ranges in the U.S. Increased fire incidence and drought in these forests are limiting pine regeneration and driving conversion of biodiverse forests to oak shrublands. We investigated regeneration patterns in Pinus engelmannii and P. leiophylla during severe drought 10 years after the Horseshoe Two Megafire in the Chiricahua Mountains, Arizona—a follow-up to an assessment five years post-fire. In long-term plots, we examined changes in pine seedling and resprout recruitment. Past research demonstrated that topography and fire severity influenced pine recruitment across environmental gradients. We investigated here whether Landsat-8 normalized difference vegetation index (NDVI) and evapotranspiration estimated by the ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) added explanatory value to our understanding of these patterns. Conversion of Madrean pine-oak forest to oak shrublands continued 6–10 years post-fire. A dense, low oak canopy continued to coalesce in sites subject to severe fire. The importance of resprouts in P. leiophylla regeneration accelerated because these plants outgrew competing oak resprouts. Topography and fire severity (dNBR) were important predictors of 2021 patterns of pine recruitment. NDVI added explanatory value to these models, suggesting its potential in tracking forest dynamics. Evapotranspiration did not add value, likely because ECOSTRESS' larger pixel sizes and moving pixel locations created excessive subpixel heterogeneity in this highly dissected landscape. These models suggest that P. engelmannii is more drought sensitive, was more negatively affected by drought and fire, and is more at risk to shifts in climate and wildfires than P. leiophylla.

Spatial relationships of trees in middle taiga post-pyrogenic pine forest stands in the European North-East of Russia

Information on the structural organization of forest stands obtained on sample plots is the basis for long-term monitoring of post-fire pine forest structure and dynamics in the European North-East. These data can be used as a marker of native pine stands of the European taiga. Here, we studied vertical and horizontal structure in the post-pyrogenic pine forests of Vacciniosum, Vaccinioso-cladinosum and Myrtillosum site types in the boreal forest of the Komi Republic. The type of horizontal structure of uneven-aged forest stands changed with age from grouped to random one. Large trees were randomly distributed on the plot. We observed the weak aggregation of undergrowth trees (natural tree regeneration) in stands at distances of 2–6 m. Undergrowth individuals were characterized by group distribution at smaller distances than 1–2 m. Spatial relationships between large, small and codominant trees demonstrated random distribution in most cases. Undergrowth individuals did not show any competitive relations. However, we revealed a “taking off” effect between mature trees of pine and pine undergrowth. The direction of the displacement of tree crown centre projections relative to the bases of their trunks was ambiguous. The shift of the crown space towards the maximum solar radiation was detected in a thinned stand with old age and big size of trees. In other site types, no one-sided orientation of the tree crown development emerged.

Predicting natural hyperdense regeneration after wildfires in Pinus halepensis (Mill.) forests using prefire site factors, forest structure and fire severity

Postfire Pinus halepensis (Aleppo pine) regeneration is often hyperdense. The overstocked stands created by this hyperdense regeneration considerably increase the risk of biotic and abiotic disturbances, especially fires, by increasing the potential for widespread forest losses. Our aim was to understand the relation between prefire site factors (climate, geographical position, topography, soil), prefire forest structure variables and fire severity with regeneration density after fire. We specifically wondered: (1) what are the general drivers of natural regeneration in these forests after fire?; (2) what are the necessary prefire conditions for establishing Aleppo pine hyperdense regenerations (>4,000 plants/ha)? To answer these questions, we sampled 147 plots in 15 wildfires located in the Comunitat Valenciana, which were representative of Aleppo pine Mediterranean forests. We used full and partial redundancy analyses (RDAs) for variance partitioning, and a decision tree analysis to look for the key site factors that drive regeneration density after fire. We found that all the site factors measured in the study explained 34.4 % of total variation in regeneration density. Prefire site factors and fire severity together explained 28.4 % of total variability, while the measured postfire factors explained only 7.5 %. Forest structure and climate explained 8.3 % and 6.7 % of variation, respectively. Five specific site factors drove regeneration density after fire: average minimum temperature, tree density before fire, resprouting shrubs coverage before fire, soil depth and bedrock type. The conclusions of this study were: (i) the average minimum temperature was the main significant variable that classified regeneration density and split data into three significant groups of Aleppo pine burned sites; (ii) the prefire forest structure (overstorey density and understorey coverage) controls regeneration density at colder burned sites, but soil depth and bedrock can be more important at warmer sites; (iii) fire severity relates positively to pine regeneration density, but negatively to resprouting vegetation coverage after fire; (iv) overstocked stands are not expected if prefire stand density is below 100 trees/ha at colder burned sites. These results may facilitate the planning of forest management and restoration actions because it may be used to identify those areas more likely to regenerate overstocked stands when faced with a changing fire regime.

Ecostress Water Balance and Topography Drive Post-Fire Pine Regeneration Patterns in a Madrean Pine-Oak Forest in the Arizona Sky Islands

Ecostress Water Balance and Topography Drive Post-Fire Pine Regeneration Patterns in a Madrean Pine-Oak Forest in the Arizona Sky Islands

A Simple Conservation Tool to Aid Restoration of Amphibians following High-Severity Wildfires: Use of PVC Pipes by Green Tree Frogs (Hyla cinerea) in Central Texas, USA

Amphibians are the most threatened vertebrate class based on the IUCN Red List. Their decline has been linked to anthropogenic activities, with wildfires being among the most conspicuous agents of habitat alterations affecting native amphibians. In 2011, the most destructive wildfire in Texas history occurred in the Lost Pines ecoregion of central Texas, USA, burning 39% of the 34,400 ha forest and drastically decreasing available habitats for many native wildlife species, including the green tree frog (Hyla cinerea). We investigated use of PVC pipes as artificial refuges for green tree frogs in different habitats within this post-fire pine forest. We monitored green tree frog use of small (diameter 38.1-mm, 1.5 inch) and large (diameter 50.8-mm, 2 inch) pipes located adjacent to, and 5 m from, ponds in burned and unburned areas over a 5-month period. We caught 227 frogs, 101 (24 adults and 77 juveniles) in burned and 126 (61 adults, 63 juveniles, and 2 unknown) in unburned areas. A relationship between pipe use by adults and/or juveniles and pipe location in burned versus unburned areas was found, but pipe use by adults and/or juveniles and pipe size were independent. Pipe use by adults and/or juveniles and pipe size were also independent. Juveniles were more frequently observed in pipes located adjacent to ponds. Our results confirmed that PVC pipes merit consideration as a simple, inexpensive, conservation tool to aid in restoration of green tree frog populations after high-severity wildfires. Such artificial refuges may be particularly important for survival of juveniles in severely altered post-fire habitats.

Forest Biomass Collection from Systematic Mulching on Post-Fire Pine Regeneration with BioBaler WB55: Productivity, Cost and Comparison with a Conventional Treatment

Post-wildfire regenerated Mediterranean pine stands have a high risk of wildfire recurrence. Preventive clearings are frequently applied in a mix of systematic and selective ways, being a potential biomass source using technologies such as the collector-bundler BioBaler WB55. Our research aimed to compare the BioBaler with a chain mulcher performing systematic mulching of 50% vs. 67% of stand surface over 11.4 ha dominated by Pinus pinaster Ait. regenerated after a severe wildfire. Time studies included the machinery GPS follow-up and the weighing of each produced bale. Environmental aspects were also assessed. A regression curve related BioBaler weight productivity (odt·Workh−1) to pine biovolume (cover (%) average tree height, m). Surface productivity (stand ha·Workh−1) was greater for both technologies when a lower percentage of the total surface was cleared, but less than theoretically predicted. The BioBaler’s economic balance, including the cost of further selective clearing and the income from biomass selling, was costlier than that of the mulcher—in the most representative strata, 475 EUR·ha−1 vs. 350 EUR·ha−1. Under the studied conditions, BioBaler was not economically competitive with the conventional treatment, its main constraint being low collection efficiency (31% of the standing biomass in the cleared surface, 5.33 out of 17.1 fresh tonnes·ha−1).

Increased canopy seed-storage in post-fire pine invaders suggests rapid selection mediated by fire

Exotic species storing seeds in the canopy (serotinous species) can experience a clear advantage in fire-prone communities that lack native taxa with such fire-resistant traits. In addition, selection in the new environment can potentially increase the frequency of fire-adapted characteristics such as serotiny. We studied the potential role of fire favoring the serotinous, non-native conifer Pinus radiata in NW Patagonia. We characterized the degree of serotiny (percentage of serotinous cones) and the size of the canopy seed bank in the unburned plantation and in stands of trees recruited after a fire 30 years ago as a proxy for invasion potential. Fire had a positive effect, increasing serotiny in post-fire P. radiata stands. Post-fire recruited cohorts showed higher serotiny levels and a larger canopy seed bank compared with plantations. Our study suggests that fire-linked traits like serotiny may be subjected to a rapid, fire-driven selection process in fire-adapted species such as P. radiata invading fire-prone ecosystems. Thus, increased serotiny can lead to higher postfire invasion densities, which in turn create a positive feedback loop in invaded areas under recurrent fires.

Burn Severity and Post-Fire Erosion Control Affect Post-Fire Woody Plant Recruitment

As wildfires become more frequent and severe in the United States, effective post-fire intervention is increasingly important for soil and plant conservation. Erosion control is often necessary after wildfire, but methods vary in effectiveness and impacts on vegetation. Little is known about the effects of hydroseed, an erosion control product, on post-fire plant recovery trajectories. Hydroseed was applied to control erosion of sandy soils after the 2011 wildfire in the Lost Pines region of Texas. Pre-fire, the region was dominated by loblolly pine (Pinus taeda), an obligate-seeder, and resprouting oak species, including sand post oak (Quercus margaretta). We investigated the effects of hydroseed and burn severity on pine and oak recovery in Bastrop State Park, within the Lost Pines. Forty-six permanent plots were surveyed 1999–2015; hydroseed was applied to 15 plots post-fire. Hydroseed inhibited P. taeda regeneration in the first post-fire year but had no subsequent effect on P. taeda seedling numbers, and no effect on Q. margaretta resprout numbers in any year. P. taeda seedling numbers were greatest in lower burn severity plots in the first post-fire year and increased following high rain in 2015. Q. margaretta resprout numbers were greatest in higher burn severity plots in the first post-fire year only. Our results suggest that hydroseed may reduce initial post-fire pine recruitment but is unlikely to permanently alter long-term woody plant community recovery in this region; burn severity may be a more important factor. Further research is warranted to examine the effects of hydroseed on herbaceous plant communities.

Effect of Herbaceous Layer Interference on the Post-Fire Regeneration of a Serotinous Pine (Pinus pinaster Aiton) across Two Seedling Ages

Herbaceous vegetation is a major source of interference with the regeneration of woody species. This is particularly the case after forest fires, as a dense herbaceous layer usually regenerates naturally. Although the competitive effect of the herbaceous vegetation upon tree seedlings has been widely studied, there are still gaps in knowledge for management related to the effect of tree seedling age and size on the outcome of the interaction. In this study, we seek to determine the response of maritime pine (Pinus pinaster Aiton) seedlings to herbaceous competition at two different seedling ages. For that, two treatments of herbaceous competition were implemented, namely unweeded (no action around pine seedlings) and weeded (herbaceous cover removed around pine seedlings). Treatments were conducted twice (2 and 4 years after the fire), and we monitored seedling survival and growth at the end of each growing season. The treatments were implemented across three adjacent landscape units that differed in the management of burned wood and that are representative of common post-fire scenarios: no intervention, salvage logging, and an intermediate degree of intervention. Weeding increased seedling survival from 44.7% to 67.8% when seedlings were 2 years old, but had no effect for four-year-old seedlings, which showed 99% survival. Seedling growth also increased in the weeding treatment, but only slightly. Moreover, growth (and survival for two-year-old seedlings) was strongly correlated with initial seedling size, particularly in the case of two-year-old seedlings. Initial pine seedling height was strongly and positively correlated with the height of the herbaceous layer, supporting the existence of microsite features that promote plant growth above competitive effects. The results support that management actions conducive to foster post-fire pine forest restoration in this Mediterranean ecosystem should reduce herbaceous competition at early stages after fire (second or third year) and focus on larger seedlings.

Functional activity of soil microbial communities in post-fire pine stands of Tolyatti, Samara oblast

The state of microbial communities in gray-humus soils (Eutric Fluvic Arenosols (Ochric)) of pine stands in the city of Tolyatti after forest fires of 2010 is analyzed. It is shown that fires exert negative effects on the structure and metabolic activity of microbial communities in the postpyrogenic soils. The content of the carbon of microbial biomass and the intensity of microbial respiration in the upper organic horizons of the post-fire plots decrease by 6.5 and 3.4 times, respectively, in comparison with those in the soils of background plots. However, the fire has not affected the studied microbiological parameters of the soils at the depths of more than 10 cm. The maximum content of the carbon of microbial biomass carbon and the maximum intensity of microbial respiration have been found in the subsurface AY2 and АС horizons two–three years the fire. An increase in the microbial metabolic quotient (the ratio of soil respiration to microbial biomass) attests to the disturbance of the ecophysiological state of soil microbial communities after the pyrogenic impact.

Impacts of fire radiative flux on mature Pinus ponderosa growth and vulnerability to secondary mortality agents

Recent studies have highlighted the potential of linking fire behaviour to plant ecophysiology as an improved route to characterising severity, but research to date has been limited to laboratory-scale investigations. Fine-scale fire behaviour during prescribed fires has been identified as a strong predictor of post-fire tree recovery and growth, but most studies report these metrics averaged over the entire fire. Previous research has found inconsistent effects of low-intensity fire on mature Pinus ponderosa growth. In this study, fire behaviour was quantified at the tree scale and compared with post-fire radial growth and axial resin duct defences. Results show a clear dose–response relationship between peak fire radiative power per unit area (W m–2) and post-fire Pinus ponderosa radial growth. Unlike in previous laboratory research on seedlings, there was no dose–response relationship observed between fire radiative energy per unit area (J m–2) and post-fire mature tree growth in the surviving trees. These results may suggest that post-fire impacts on growth of surviving seedlings and mature trees require other modes of heat transfer to impact plant canopies. This study demonstrates that increased resin duct defence is induced regardless of fire intensity, which may decrease Pinus ponderosa vulnerability to secondary mortality agents.

Fire-scars and polymodal age-structure provide evidence of fire-events in an Aleppo pine population in southern France

Aleppo pine (Pinus halepensis Mill.) is adapted to fire, the most important disturbance in Mediterranean ecosystems. This species is known to be sensitive to fire and is usually killed when burned, but has a powerful regenerative capacity following burning. Sometimes, however, pines survive within burned areas, suggesting a certain potential for recording fire events in terms of age-structure and eventually scars. In the present study, fire scars on Aleppo pine trunks were used to construct a 150-year fire record in a burned forest in southern France. Four fires were detected with a mean fire return interval of 27 years: minimum 13 years and maximum 45 years. The age structure of the Aleppo pine population was analyzed on the basis of dated fire-scars in order to test the role of fire in creating the polymodal structure of the pine population. Results show the presence of multiple “cohorts” (subpopulations) of Aleppo pine. There appear to have been several pulses of tree recruitment, with the two largest cohorts corresponding to regeneration after the 1919 and 2000 fires. Other fires were recognized based on fire scars but these were not associated with obvious post-fire pine recruitment. Regeneration success is likely to depend on fire severity and on the length of fire-free intervals. Fire history and associated age-structure can thus be reconstructed using Aleppo pine stands.

Reserves of carbon in the organic matter of postfire pine forests in the southwest of the Baikal region

A change in the mass and composition of organic matter in the phytomass and soil of pine forests affected by mid-intensity and high-intensity fires is considered. It is shown that a mid-intensity fire did not catastrophically affect the pool of carbon in the middle-aged pine forests of the subtaiga forest-steppe and the taiga higher belt areas in the southwest of the Baikal region. Five years after a high-intensity fire, the carbon reserves in a mature taiga pine forest remain 20% lower than in an unaffected pine forest. Compared with the reference figures, the mass of C and soil cover in the stand phytomass decreased by 18 and 63%, respectively. In the easily mineralizable fraction of organic matter, the reserves of carbon decreased by half owing to burnout of waste wood (by 64%) and root detritus (by 50% compared with the reference tree stand figures).

A GIS-based integrated approach predicts accurately post-fire Aleppo pine regeneration at regional scale

This study investigates post-fire natural regeneration of Aleppo pine (Pinus halepensis) forests at Ilia region (Peloponnesus, Greece) following the catastrophic fire of 2007. The objective of this study is the prediction of P. halepensis post-fire regeneration at a regional scale through an integrated geographic information systems (GIS) model as a basis for post-fire management plans. The model was developed in three interconnected stages: (1) field data collection, (2) development of two prediction models (based on interpolation of field data and multi-criteria evaluation (MCE) that combined factors known to affect regeneration), and (3) combination of applied models using Bayesian statistics. Post-fire pine regeneration presented high variation among the studied plots. Redundancy analysis revealed the positive effect of fallen branches and a negative correlation with altitude. Both modeling approaches (geostatistical and MCE) predicted the post-fire pine regeneration with high accuracy. A very significant correlation (r = 0.834, p < 0.01) was found between the combined final model and the actual number of counted seedlings, illustrating that less than 10 % of the studied area corresponds to sites of very low post-fire pine regeneration. The combination of GIS models increased the prediction success of different levels of pine regeneration. Low-altitude areas with low grass cover overlying tertiary deposits were proved the most suitable for pine regeneration, while stands developing on limestone proved least suitable. The proposed methodology provides management authorities with a sound tool to quickly assess Aleppo pine post-fire regeneration potential.

Tree Mortality following Prescribed Fire and a Storm Surge Event in Slash Pine (Pinus elliottiivar.densa) Forests in the Florida Keys, USA

In fire-dependent forests, managers are interested in predicting the consequences of prescribed burning on postfire tree mortality. We examined the effects of prescribed fire on tree mortality in Florida Keys pine forests, using a factorial design with understory type, season, and year of burn as factors. We also used logistic regression to model the effects of burn season, fire severity, and tree dimensions on individual tree mortality. Despite limited statistical power due to problems in carrying out the full suite of planned experimental burns, associations with tree and fire variables were observed. Post-fire pine tree mortality was negatively correlated with tree size and positively correlated with char height and percent crown scorch. Unlike post-fire mortality, tree mortality associated with storm surge from Hurricane Wilma was greater in the large size classes. Due to their influence on population structure and fuel dynamics, the size-selective mortality patterns following fire and storm surge have practical importance for using fire as a management tool in Florida Keys pinelands in the future, particularly when the threats to their continued existence from tropical storms and sea level rise are expected to increase.

From monospecific to mixed forest after fire?: An early forecast for the montane belt of Majella, Italy

Alternative hypotheses on post-fire successions of monospecific European beech (Fagus sylvatica L.) and black pine (Pinus nigra Arnold) forests are investigated. The research area is located in the centre of the Apennine montane belt, Italy and covers portions of the Roccamorice and Lettomanoppello municipalities within the Majella National Park. Temporal moderate-resolution (MODIS) and spatial mid-resolution (ASTER) imagery are combined for the assessment of the 2007-fire features. Tree seedlings were surveyed on the ground in post-fire forests and their unburnt equivalents during September 2008. The satellite imagery analysis provides records on spread, intensity, location and extent of the forest fires. The evidence suggests an abandoned farmland fire spreading secondarily uphill into the forests.The early post-fire beech forest manifests primarily beech seedlings and beech sprouts, rarely interspersed with seedlings of maples (Acer spp.) and manna-ash (Fraxinus ornus L.), indicating a low probability of succession to mixed forest. The post-fire pine plantation appears to convert to a manna-ash bush-woodland, whereas the unburnt pine manifests succession to a mixed forest with beech and maples. Based on our findings, specific fire control and silvicultural interventions are recommended.

Influence of coarse wood and pine saplings on nitrogen mineralization and microbial communities in young post-fire Pinus contorta

Nitrogen (N) limits productivity in many coniferous forests of the western US, but the influence of post-fire structure on N cycling rates in early successional stands is not well understood. We asked if the heterogeneity created by downed wood and regenerating pine saplings affected N mineralization and microbial community composition in 15-yr old lodgepole pine ( Pinus contorta var. latifolia) stands established after the 1988 fires in Yellowstone National Park (Wyoming, USA). In three 0.25-ha plots, we measured annual in situ net N mineralization in mineral soil using resin cores ( n = 100 per plot) under pine saplings, downed wood (legacy logs that survived the fire, and fire-killed trees that had fallen and were contacting or elevated above the ground), and in bare mineral soil. Annual in situ net N mineralization and net nitrification rates were both greater in bare mineral soil (8.4 ± 0.6 and 3.6 ± 0.3 mg N kg soil −1 yr −1, respectively) than under pine saplings, contact logs, or elevated logs (ca. 3.9 ± 0.5 and 0.8 ± 0.1 mg N kg soil −1 yr −1, respectively). Net nitrification was positively related to net N mineralization under all treatments except for elevated logs. In laboratory incubations using 15N pool dilution, NH 4 + consumption exceeded gross production by a factor of two in all treatments, but consumption and gross production were similar among treatments. Contrary to our initial hypothesis, microbial community composition also did not vary among treatments. Thus, two- to three-fold differences in in situ net N mineralization rates occurred despite the similarity in microbial communities and laboratory measures of gross production and consumption of NH 4 + among treatments. These results suggest the importance of microclimate on in situ annual soil N transformations, and differences among sites suggest that broader scale landscape conditions may also be important.