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Wildland fires have a multitude of ecological effects in forests, woodlands, and savannas across the globe. A major focus of past research has been on tree mortality from fire, as trees provide a vast range of biological services. We assembled a database of individual-tree records from prescribed fires and wildfires in the United States. The Fire and Tree Mortality (FTM) database includes records from 164,293 individual trees with records of fire injury (crown scorch, bole char, etc.), tree diameter, and either mortality or top-kill up to ten years post-fire. Data span 142 species and 62 genera, from 409 fires occurring from 1981-2016. Additional variables such as insect attack are included when available. The FTM database can be used to evaluate individual fire-caused mortality models for pre-fire planning and post-fire decision support, to develop improved models, and to explore general patterns of individual fire-induced tree death. The database can also be used to identify knowledge gaps that could be addressed in future research.

Overstory trees serve multiple functions in grassy savannas. Past research has shown that understory species can vary along gradients of canopy cover and basal area in savannas. This variation is frequently associated with light availability but could also be related to other mechanisms, such as heterogeneity in soil and litter depth and fire intensity. Several savanna studies have found differences in understory plant functional groups within the local environment near trees versus away from them in canopy openings. Although small‐scale variation is known to be high in southeastern U.S. pine savannas, patterns in understory species diversity have not been examined at the scale of individual overstory pine trees in this system. We conducted an observational study of the relationship between understory plant communities and proximity to individual pine trees in xeric and mesic pine savannas in frequently burned sites (1–3 year intervals). We recorded the plant community composition in plots adjacent to tree boles (basal) or outside crown driplines (open). Within each environment, raw species richness was significantly greater in open locations, where light transmittance was greater. In contrast, rarified species richness did not differ. Multivariate analyses showed that community composition differed significantly between basal and open plots. One native, woody species in each environment, Serenoa repens (W. Bartram) Small in mesic and Diospyros virginiana L. in xeric, was more abundant in basal plots. In mesic environments, eight species had greater occurrence in open plots. In xeric environments, four understory forbs were more abundant in open plots. Our results support previous research indicating that individual pine trees are associated with significant variation in understory vegetation in pine savannas. [ABSTRACT FROM AUTHOR]

Duff fires (smouldering in fermentation and humus forest floor horizons) and their consequences have been documented in fire-excluded ecosystems but with little attention to their underlying drivers. Duff characteristics influence the ignition and spread of smouldering fires, and their spatial patterns on the forest floor may be an important link to the heterogeneity of consumption observed following fires. We evaluated fuel bed characteristics (depths, bulk densities, and moisture) of duff in a long-unburned longleaf pine (Pinus palustris Mill.) forest and corresponding spatial variation across [10.sup.0] to [10.sup.3] m scales. Fermentation and humus horizon depths both varied (~100% coefficient of variation) but with moderate to strong spatial autocorrelation at fine scales. Fermentation bulk density varied less than humus bulk density, which varied considerably at fine scales. Fermentation horizons held more moisture (average 49%-172%) and were much more variable than humus following rainfall, which remained stable and relatively dry (average 28%-62%). Humus moisture was moderately auto-correlated at fine scales, but fermentation moisture was highly variable, showing no evidence of spatial autocorrelation under dry, intermediate, or wet conditions. Observations from this study highlight the underlying spatial variability in duff, informing future sampling and fire management efforts in these long-unburned coniferous forests. Key words: fire exclusion, fuel heterogeneity, fuel moisture, longleaf pine, spatial autocorrelation. Les feux d'humus (feux couvant dans l'horizon de fermentation et la couche d'humus de la couverture morte) et leurs consequences ont ete documentes dans des ecosystemes oU le feu etait exclu mais peu d'attention a ete accordee a leurs causes sous-jacentes. Les caracteristiques de l'humus influencent l'allumage et la propagation des feux couvant et leur configuration spatiale dans la couverture morte pourrait avoir un lien important avec l'heterogeneite de la combustion observee a la suite des feux. Nous avons evalue les caracteristiques des lits de combustibles (profondeur, densite apparente et teneur en humidite) dans l'humus d'une foret de pin des marais (Pinus palustris Mill.) qui n'a pas brule depuis longtemps et les variations spatiales correspondantes a des echelles de [10.sup.0] a [10.sup.3] m. La profondeur de l'horizon de fermentation et celle de la couche d'humus variaient (coefficient de variation d'environ 100 %) mais avec une autocorrelation spatiale moderee a forte aux echelles fines. La densite apparente de l'horizon de fermentation etait moins variable que celle de la couche d'humus qui variait considerablement aux echelles fines. L'horizon de fermentation avait une teneur en humidite plus elevee (49-172 % en moyenne) et etait beaucoup plus variable que la couche d'humus apres une pluie, laquelle demeurait stable et relativement seche (28-62 % en moyenne). La teneur en humidite de l'humus etait moderement autocorrelee aux echelles fines mais celle de l'horizon de fermentation etait tres variable et ne montrait aucun signe d'autocorrelation spatiale en conditions seche, intermediaire ou humide. Les observations faites dans le cadre de cette etude font ressortir la variabilite spatiale sous-jacente dans l'humus et seront utiles pour orienter les efforts futurs d'echantillonnage et de gestion du feu dans ces forets de coniferes qui n'ont pas brule depuis longtemps. [Traduit par la Redaction] Mots-cles: exclusion de feu, heterogeneite des combustibles, teneur en humidite des combustibles, pin des marais, autocorrelation spatiale., Introduction Forest floor fuels are dominant drivers of ignition and surface fire behavior and of ecological effects that result from burning. The partially decomposed fermentation (Oe) and humus (Oa) horizons [...]

The ignition and combustion of forest floor duff are poorly understood yet have been linked to soil heating and overstory tree mortality in many temperate coniferous forests. Research to date has focused on the characteristics of duff that facilitate ignition and spread, including fuel moisture, mineral content, and depth. Field observations suggest that the presence of pine cones on and within the forest floor might facilitate ignition of intermixed forest floor fuels. We investigated the effect of cone fuel additions on the ignition of underlying forest floor from fuels collected in long-unburned longleaf pine (Pinus palustris Mill.) forests in northern Florida, USA. Fuels were wetted to threshold gravimetric moisture contents to evaluate the relative effect on ignition. In stark contrast to fuel beds without cones, in which duff ignition only occurred in 17% of samples, those with cones added ignited the underlying duff 94% of the time. Flame heights were 40% taller and flaming duration was 47% longer in fuel beds with cones. Where present, pine cones act as vectors of ignition for forest floor fuels, and their role in fires deserves more attention to enhance our understanding of forest floor combustion. Resume: Bien qu'on sache peu de choses au sujet de l'allumage et de la combustion de l'humus dans la couverture morte, le rechauffement du sol et la mortalite des arbres de l'etage dominant ont ete mis en cause dans plusieurs forets de coniferes temperees. A ce jour, la recherche s'est concentree sur les caracteristiques de l'humus qui facilitent l'allumage et la propagation, incluant la teneur en humidite, la teneur en mineraux et l'epaisseur des combustibles. Les observations sur le terrain indiquent que la presence de cones de pin dans la couverture morte et en surface pourrait faciliter l'allumage du melange de combustibles dans la couverture morte. Nous avons etudie l'effet de l'ajout de cones en tant que combustible sur l'allumage de la couverture morte sous-jacente a l'aide de combustibles preleves dans les forets de pin des marais (Pinus palustris Mill.) qui n'ont pas brule depuis longtemps dans le nord de la Floride, aux Etats-Unis. Les combustibles ont ete humidifies jusqu'au seuil de saturation selon la teneur en eau gravimetrique pour evaluer l'effet relatif sur l'allumage. Contrastant nettement avec les lits de combustibles exempts de cones dans lesquels l'allumage de l'humus est survenu dans seulement 17 % des echantillons, l'allumage de l'humus sous-jacent s'est produit 94 % du temps dans ceux qui contenaient des cones. Les flammes etaient 40 % plus hautes et la duree de l'embrasement 47 % plus longue dans les lits de combustibles contenant des cones. Ou ils sont presents, les cones de pin agissent comme vecteurs d'allumage des combustibles dans la couverture morte et leur role en lien avec les feux merite d'etre davantage etudie afin d'ameliorer notre comprehension de la combustion de la couverture morte. [Traduit par la Redaction], Introduction Long-term smoldering combustion of forest floor duff in coniferous forests has a wide range of impacts (Miyanishi 2001; Varner et al. 2005). So-called 'duff fires' smolder in fermentation (Oe) [...]