Department of Environmental Science, Policy, and Management, 137 Mulford Hall, MC number 3114, University of California, Berkeley, California 94720, USA.
Ecol Appl. 2011 Jan;21(1):122-36. doi: 10.1890/09-2004.1.
Predictions of future fire activity over Canada's boreal forests have primarily been generated from climate data following assumptions that direct effects of weather will stand alone in contributing to changes in burning. However, this assumption needs explicit testing. First, areas recently burned can be less likely to burn again in the near term, and this endogenous regulation suggests the potential for self-limiting, negative biotic feedback to regional climate-driven increases in fire. Second, forest harvest is ongoing, and resulting changes in vegetation structure have been shown to affect fire activity. Consequently, we tested the assumption that fire activity will be driven by changes in fire weather without regulation by biotic feedback or regional harvest-driven changes in vegetation structure in the mixedwood boreal forest of Alberta, Canada, using a simulation experiment that includes the interaction of fire, stand dynamics, climate change, and clear cut harvest management. We found that climate change projected with fire weather indices calculated from the Canadian Regional Climate Model increased fire activity, as expected, and our simulations established evidence that the magnitude of regional increase in fire was sufficient to generate negative feedback to subsequent fire activity. We illustrate a 39% (1.39-fold) increase in fire initiation and 47% (1.47-fold) increase in area burned when climate and stand dynamics were included in simulations, yet 48% (1.48-fold) and 61% (1.61-fold) increases, respectively, when climate was considered alone. Thus, although biotic feedbacks reduced burned area estimates in important ways, they were secondary to the direct effect of climate on fire. We then show that ongoing harvest management in this region changed landscape composition in a way that led to reduced fire activity, even in the context of climate change. Although forest harvesting resulted in decreased regional fire activity when compared to unharvested conditions, forest composition and age structure was shifted substantially, illustrating a trade-off between management goals to minimize fire and conservation goals to emulate natural disturbance.
对加拿大北方森林未来火灾活动的预测主要是根据气候数据做出的，假设天气的直接影响将单独作用于燃烧变化。然而，这种假设需要明确的测试。首先，最近燃烧过的区域在短期内再次燃烧的可能性较小，这种内源性调节表明，在区域气候驱动的火灾增加情况下，存在自我限制的负生物反馈的潜力。其次，森林采伐正在进行，植被结构的变化已被证明会影响火灾活动。因此，我们利用包括火灾、林分动态、气候变化和皆伐采伐管理相互作用的模拟实验，测试了在北方混合林没有生物反馈或区域采伐驱动的植被结构变化调节的情况下，火灾活动将由火灾天气变化驱动的假设。我们发现，用加拿大区域气候模型计算的火灾天气指数预测的气候变化增加了火灾活动，这是预期的结果，我们的模拟结果表明，区域火灾增加的幅度足以对随后的火灾活动产生负反馈。我们举例说明了，当气候和林分动态被纳入模拟时，火灾起始和燃烧面积分别增加了 39%（1.39 倍）和 47%（1.47 倍），而当仅考虑气候时，分别增加了 48%（1.48 倍）和 61%（1.61 倍）。因此，尽管生物反馈以重要方式减少了燃烧面积的估计，但它们次于气候对火灾的直接影响。然后，我们表明，该地区正在进行的采伐管理改变了景观组成，导致火灾活动减少，即使在气候变化的情况下也是如此。虽然与未采伐条件相比，森林采伐导致区域火灾活动减少，但森林组成和年龄结构发生了重大变化，说明了在最大限度减少火灾的管理目标和模仿自然干扰的保护目标之间存在权衡。
