Fire is a critical component of the Earth system, and substantially influences land surface, climate change, and ecosystem dynamics. To accurately predict the fire regimes in the 21st century, it is essential to understand the historical fire patterns and recognize the interaction among fire, human, and environment factors. Until now, few efforts are put on the studies regarding to the long-term fire reconstruction and the attribution analysis of anthropogenic and environmental factors to fire regimes at global scale. To fill this knowledge gap, we developed a 0.5°× 0.5°data set of global burned area from 1901 to 2007 by coupling Global Fire Emission Database version 3 with a process-based fire model and conducted factorial simulation experiments to evaluate the impacts of human, climate, and atmospheric components. The average global burned area is 442 × 10 4 km 2 yr À1 during 1901-2007 and our results suggest a notable declining rate of burned area globally (1.28 × 10 4 km 2 yr À1 ). Burned area in tropics and extratropics exhibited a significant declining trend, with no significant trend detected at high latitudes. Factorial experiments indicated that human activities were the dominant factor in determining the declining trend of burned area in tropics and extratropics, and climate variation was the primary factor controlling the decadal variation of burned area at high latitudes. Elevated CO 2 and nitrogen deposition enhanced burned area in tropics and southern extratropics but suppressed fire occurrence at high latitudes. Rising temperature and frequent droughts are becoming increasingly important and expected to increase wildfire activity in many regions of the world.

In 1973, a study was established in south-central Alabama, U.S.A., to determine the effects of hardwood control treatments on understory succession and overstory growth in natural stands of longleaf pine (Pinus palustris Mill.). The treatments were seasonal biennial burns and a no-burn check, each combined with three supplemental hardwood control treatments (one-time chemical, periodic mechanical, and untreated check). Green vegetation less than 1 cm DBH and organic litter were destructively sampled to determine the effects of 23 years of treatments on understory vegetation and identify changes in this community since last sampled in 1982. Among the hardwood control treatments, the only significant differences occurred in the shrub and green biomass (total of tree, shrub, woody vine, and herbaceous species masses) component of the understory. There were significant differences for all vegetation components when comparing the burning to no-burn treatment. Green biomass estimates were variable but showed an increase for all but two of the 12 treatment combinations when compared to 1982 biomass. The major change occurred in the accumulation of organic litter, which increased 119% when averaged across all treatments. The chemical treatment did not eliminate any species when compared with the other hardwood control treatments.

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Data were collected on open-grown loblolly pine (Pinustaeda L.), longleaf pine (Pinuspalustris Mill.), and shortleaf pine (Pinusechinata Mill.) and analyzed to provide predictive equations of crown width and maximum potential basal area growth for crown competition and growth and yield models. The measurements were taken on 115 open-grown loblolly pine trees and 76 shortleaf pines in southeastern Arkansas. The longleaf pine data consisted of 81 open-grown trees from southern Alabama, Georgia, and Florida. A circle and an ellipse were tested as geometric models of the vertically projected crown. No significant differences between the tree shapes were found based on analyses of length and azimuth of the largest crown diameter, and the circle was chosen as an appropriate model. This indicated that only the distance between trees, not their orientation to one another, need be included in models of crown competition based on crown contact. Predictive equations of mean crown width based on diameter at breast height were fitted for each species for use in models of crown competition. A Chapman–Richards growth rate function with an intercept term was fit to periodic annual inside-bark basal area growth based on initial inside-bark basal area to provide empirical estimates of maximum basal area growth rates for growth and yield modeling of the given species. Additionally, equations to predict double bark thickness as a function of diameter at breast height were fit for each species to facilitate the use of the equations with outside-bark measurements of diameter.

Abstract. Fire affects numerous aspects of plant growth and anatomy, particularly in those species adapted to persist in fire-prone environments. A key aspect of tree survival is rapid accumulation of protective bark within fire return intervals. We compared bark accumulation in five co-occurring hardwood species within a longleaf pine (Pinus palustris) ecosystem in the mountains of northeastern Alabama, USA. Sampled species included blackjack oak (Quercus marilandica), sand hickory (Carya pallida), common persimmon (Diospyros virginiana), rock chestnut oak (Quercus montana), and red maple (Acer rubrum). Using bark thickness and inside bark diameter measurements taken at 20-cm intervals along the main stem of saplings (average age 4-5 years) we found that, while average wood diameter did not differ across species, significant differences occurred in the ratio of bark to wood. Bark comprised over half (bark:wood ¼ 0.55) of the basal diameter of blackjack oak, which was 33, 43, and 63 greater than the bark:wood ratio of sand hickory and rock chestnut oak, common persimmon, and red maple, respectively. Bark taper revealed that while other species allocated similarly to bark along the length of their stem, blackjack oak allocated much more at its base (in the flaming zone) and relatively less as height increased. Red maple, a commonly cited invader during fire-free intervals, invested the least in bark thickness and, with rock chestnut oak, had an average height and height:diameter ratio significantly greater than blackjack oak and all other species, respectively. These results confirm the adaptive importance of bark thickness to enhancing species survival in frequent fire regimes.