Ecol Appl. 2014 Jul;24(5):976-89. doi: 10.1890/13-1426.1.
Previous studies have found negligible effects of single prescribed fires on coarse woody debris (CWD), but the cumulative effects of repeated low-intensity prescribed fires are unknown. This represents a knowledge gap for environmental management because repeated prescribed fires are a key tool for mitigating wildfire risk, and because CWD is recognized as critical to forest biodiversity and functioning. We examined the effects of repeated low-intensity prescribed fires on the attributes and stocks of (fallen) CWD in a mixed-species eucalypt forest of temperate Australia. Prescribed fire treatments were a factorial combination of two seasons (Autumn, Spring) and two frequencies (three yearly High, 10 yearly Low), were replicated over five study areas, and involved two to seven low-intensity fires over 27 years. Charring due to prescribed fires variously changed carbon and nitrogen concentrations and C to N ratios of CWD pieces depending on decay class, but did not affect mean wood density. CWD biomass and C and N stocks were significantly less in Fire than Control treatments. Decreases in total CWD C stocks of -8 Mg/ha in Fire treatments were not balanced by minor increases in pyrogenic (char) C (-0.3 Mg/ha). Effects of prescribed fire frequency and season included significantly less C and N stocks in rotten CWD in High than Low frequency treatments, and in the largest CWD pieces in Autumn than Spring treatments. Our study demonstrates that repeated low-intensity prescribed fires have the potential to significantly decrease CWD stocks, in pieces of all sizes and particularly decayed pieces, and to change CWD chemical attributes. CWD is at best a minor stock of pyrogenic C under such fire regimes. These findings suggest a potential trade-off in the management of temperate eucalypt forests between sustained reduction of wildfire risk, and the consequences of decreased CWD C stocks, and of changes in CWD as a habitat and biogeochemical substrate. Nonetheless, negative impacts on CWD of repeated low-intensity prescribed fires could be lessened by fire intervals of 10 rather than three years (to decrease losses of decayed CWD), and fires in moist rather than dry conditions (to conserve large CWD).
先前的研究发现，单次规定火烧对粗木质残体（CWD）的影响可以忽略不计，但重复的低强度规定火烧的累积效应尚不清楚。这代表了环境管理方面的一个知识空白，因为重复的规定火烧是降低野火风险的关键工具，而且 CWD 被认为对森林生物多样性和功能至关重要。我们研究了重复的低强度规定火烧对澳大利亚温带混合树种桉树森林中（倒下的）CWD 属性和储量的影响。规定火烧处理是两个季节（秋季、春季）和两个频率（三年一次高频率、十年一次低频率）的因子组合，在五个研究区域重复进行，涉及 27 年来两到七次低强度火烧。规定火烧引起的炭化会根据腐朽等级而改变 CWD 碎片的碳和氮浓度以及 C 与 N 的比率，但不会影响平均木材密度。与对照处理相比，火烧处理的 CWD 生物量和 C 和 N 储量显著减少。火烧处理的总 CWD C 储量减少了 8 Mg/ha，但由于少量的热解（炭）C 增加（0.3 Mg/ha）而未得到平衡。规定火烧频率和季节的影响包括，在高频处理中腐朽的 CWD 的 C 和 N 储量显著低于低频处理，在秋季处理中最大的 CWD 碎片的 C 和 N 储量显著低于春季处理。我们的研究表明，重复的低强度规定火烧有可能显著减少 CWD 储量，包括所有大小和特别是腐朽的 CWD 碎片，以及改变 CWD 的化学属性。在这种火灾制度下，CWD 充其量只是热解 C 的一个较小储量。这些发现表明，在管理温带桉树森林时，在持续降低野火风险与减少 CWD C 储量以及 CWD 作为栖息地和生物地球化学基质的变化的后果之间，存在潜在的权衡。尽管如此，通过将火灾间隔延长至 10 年而不是 3 年（以减少腐朽 CWD 的损失），以及在潮湿而不是干燥的条件下进行火灾（以保存大的 CWD），可以减轻重复的低强度规定火烧对 CWD 的负面影响。
