Toward a mechanism for eastern North American forest mesophication: differential litter drying across 17 species.
Toward a mechanism for eastern North American forest mesophication: differential litter drying across 17 species.
复制标题
建立北美东部森林中温化机制：17 个物种的凋落物干燥差异。
作者：
Jesse K. Kreye;J. Varner;J. Hiers;J. Mola
长期的防火已经改变了北美许多森林生态系统的生态功能。对火敏感的树种入侵美国东南部以前的热源山地森林，导致地表燃料的戏剧性变化，这些燃料被认为会降低植物群落的可燃性。可燃性降低或“中间相变”的机理一直缺乏实证研究。在这里，我们通过量化来自东南部17个树种的叶凋落物床的水分保持(响应时间和初始水分容量)来评估降低易燃性的潜在机制，这些树种跨越了广泛的耐火性范围。K-均值聚类分析得出四个物种组：一个由八个物种组成的快速干燥组；一个吸收很少水分但解吸缓慢的五个物种组；一个吸收大量水分但解吸速度很快的两个物种组；以及一个吸收大量水分并缓慢干燥的两个物种组。火敏感树种被划分为失水慢的类群，耐火树种倾向于聚集在快速干燥类群中。主成分分析表明，叶片的几个性状与吸水率和干燥速率相关。表面积大的薄叶树种：体积吸收的水分最多，而卷曲的大树叶的干燥速度最快。由于火敏感物种入侵导致凋落物燃料的戏剧性变化，产生了积极的反馈，减少了点火窗口，从而促进了美国东南部高原火敏感物种的生存、持久和持续入侵。
Long-term fire exclusion has altered ecological function in many forested ecosystems in North America. The invasion of fire-sensitive tree species into formerly pyrogenic upland forests in the southeastern United States has resulted in dramatic shifts in surface fuels that have been hypothesized to cause reductions in plant community flammability. The mechanism for the reduced flammability or "mesophication" has lacked empirical study. Here we evaluate a potential mechanism of reduced flammability by quantifying moisture retention (response time and initial moisture capacity) of foliar litter beds from 17 southeastern tree species spanning a wide range of fire tolerance. A k-means cluster analysis resulted in four species groups: a rapidly drying cluster of eight species; a five-species group that absorbed little water but desorbed slowly; a two-species group that absorbed substantial moisture but desorbed rapidly; and a two-species cluster that absorbed substantial moisture and dried slowly. Fire-sensitive species were segregated into the slow moisture loss clusters while fire-tolerant species tended to cluster in the rapid drying groups. Principal-components analysis indicated that several leaf characteristics correlated with absorption capacity and drying rates. Thin-leaved species with high surface area : volume absorbed the greatest moisture content, while those with large, curling leaves had the fastest drying rates. The dramatic shifts in litter fuels as a result of invasion by fire-sensitive species generate a positive feedback that reduce the windows of ignition, thereby facilitating the survival, persistence, and continued invasion of fire-sensitive species in the uplands of the southeastern United States.