Abstract：
In the southeastern USA, lack of historical fire regimes often leads to hardwood encroachment into early successional plant communities and managed pine stands, reducing wildlife value and timber yields. Land managers lack information on how firing technique interacts with fire season to influence plant communities. We designed an experiment to quantify these interactions in east-central Mississippi with pairs of 4 m × 8 m plots randomly assigned a backing and heading fire in each of three seasons: February (Feb), May-June (May/Jun), and September-October (Sep/Oct). We used thermocouples to monitor fire temperature and tagged midstory trees to monitor response. We lit heading fires with an 18-25 kph wind generated by a backpack blower and backing fires into the ambient wind. Despite backing fires producing longer residence times than heading fires and raising temperature above the lethal threshold of 60 °C an average of 54 s longer, firing technique did not influence midstory response one growing season post-fire. Backing and heading fires produced similar maximum temperatures. For both firing techniques, May/Jun resulted in the highest midstory mortality rates which were 3-fold greater than Sep/Oct and 4-fold greater than Feb. Among all three fire seasons, trees with a 2.5 cm diameter at breast height (DBH) had approximately a 75% chance of top-kill which decreased to <20% as trees approached 6.5 cm DBH. We found no effects of fire season on fire temperature, rate of spread, flame height, or percent crown scorch. We found no significant interactions between fire season and firing technique. Understory analysis revealed Sep/Oct produced the greatest increase in forb coverage, May/Jun resulted in the most grass coverage, and Feb produced the most brambles (Rubus spp.). On sites with similar species, weather, and fuel conditions to ours, land managers should emphasize fire season over firing technique for midstory control and understory manipulation. Where midstory hardwood control with fire is a priority, fire return intervals should be frequent enough to prevent trees from exceeding 2.5 cm DBH to avoid trees escaping fire\'s reach. These data can help managers reduce midstory competition with crop trees and promote understory development for wildlife.
摘要：
在美国东南部,缺乏历史火灾制度往往导致硬木侵蚀早期演替植物群落和管理松树林，降低野生动物价值和木材产量。土地管理者缺乏有关射击技术如何与火灾季节相互作用以影响植物群落的信息。我们设计了一个实验来量化密西西比州中东部的这些相互作用，在三个季节中的每个季节中，一对4m×8m的地块随机分配了支持和标题火：2月（2月），5-6月（5月/6月），和9月至10月（9月/10月）。我们使用热电偶来监测火灾温度，并标记了中层树木来监测反应。我们用背包鼓风机产生的18-25公里/小时的风点燃了火焰，并向周围的风提供了火焰。尽管背火比航向火产生更长的停留时间，并且将温度升高到60°C的致命阈值以上，但平均时间延长了54秒，射击技术不会影响火灾后一个生长季节的中层反应。后退和航向火灾产生的最高温度相似。对于这两种射击技术，5月/6月导致最高的中层死亡率，比9月/10月高3倍，比2月高4倍在所有三个火灾季节中，胸高直径为2.5厘米（DBH）的树木有大约75％的顶部杀死机会，随着树木接近6.5厘米DBH，该机会降低至<20％。我们没有发现火灾季节对火灾温度的影响，传播率，火焰高度,或百分比皇冠烧焦。我们发现火灾季节和射击技术之间没有明显的相互作用。林下分析显示，9月/10月的Forb覆盖率增长最大，五月/六月导致了最多的草地覆盖率，2月产生了最多的荆棘（Rubusspp。).在物种相似的地方，天气,和我们的燃料条件，土地管理者应强调火灾季节而不是火灾技术，以进行中层控制和下层操纵。在中层硬木控制火是优先事项的地方，回火间隔应足够频繁，以防止树木超过2.5厘米的DBH，以避免树木逃离火灾。这些数据可以帮助管理者减少与农作物树木的中层竞争，并促进野生动物的林下发展。
