Biogeochemical impacts of wildfires over four millennia in a Rocky Mountain subalpine watershed.
Biogeochemical impacts of wildfires over four millennia in a Rocky Mountain subalpine watershed.
复制标题
四千年来落基山亚高山流域野火的生物地球化学影响。
作者：
P. Dunnette;P. Higuera;K. McLauchlan;Kelly M. Derr;C. Briles;Margaret H Keefe
野火可以显著改变森林的碳(C)储存和氮(N)有效性，但野火的长期生物地球化学遗产却鲜为人知。我们从美国科罗拉多州的一片亚高山森林中获取了一份湖泊沉积物的火灾和生物地球化学记录，以检验过去4250年来由火灾引起的十年尺度生态系统变化的性质、规模和持续时间。高分辨率记录包含34起火灾，其中包括分水岭内的13起高严重性事件。在严重火灾之后，沉积氮稳定同位素比率(δ15N)和堆积密度增加，碳和氮浓度下降--反映了森林底板的破坏、陆地碳和氮的损失以及侵蚀。火后20-50年持续的低沉淀物C：N表明对湖泊的陆地有机质补贴减少。火后50-70年的低沉积δ为15N，与C和N的恢复一致，表明在林分发展过程中陆地N的有效性正在减少。火灾后的变化幅度通常与推断的火灾严重程度直接相关。我们的结果支持对森林演替C和N积累的现代研究，并表明了亚高山森林野火显著的、持久的生物地球化学影响。然而，即使几千年来反复发生的高强度火灾可能也不会耗尽碳或氮库存，因为在几个世纪的高强度火灾之间，可以进行足够的生物质回收。
Wildfires can significantly alter forest carbon (C) storage and nitrogen (N) availability, but the long-term biogeochemical legacy of wildfires is poorly understood. We obtained a lake-sediment record of fire and biogeochemistry from a subalpine forest in Colorado, USA, to examine the nature, magnitude, and duration of decadal-scale, fire-induced ecosystem change over the past c. 4250 yr. The high-resolution record contained 34 fires, including 13 high-severity events within the watershed. High-severity fires were followed by increased sedimentary N stable isotope ratios (δ15N) and bulk density, and decreased C and N concentrations--reflecting forest floor destruction, terrestrial C and N losses, and erosion. Sustained low sediment C : N c. 20-50 yr post-fire indicates reduced terrestrial organic matter subsidies to the lake. Low sedimentary δ15N c. 50-70 yr post-fire, coincident with C and N recovery, suggests diminishing terrestrial N availability during stand development. The magnitude of post-fire changes generally scaled directly with inferred fire severity. Our results support modern studies of forest successional C and N accumulation and indicate pronounced, long-lasting biogeochemical impacts of wildfires in subalpine forests. However, even repeated high-severity fires over millennia probably did not deplete C or N stocks, because centuries between high-severity fires allowed for sufficient biomass recovery.