Wisconsin Department of Natural Resources, Division of Forestry, 2801 Progress Road, Madison, Wisconsin, 53716, USA.
Rocky Mountain Tree-Ring Research, 2901 Moore Lane, Fort Collins, Colorado, 80526, USA.
Ecology. 2019 Nov;100(11):e02839. doi: 10.1002/ecy.2839. Epub 2019 Aug 21.
A key challenge to maintaining resilient landscapes is adapting to and maintaining dynamic ecological processes. In fire-dependent ecosystems, this includes identifying and defining mechanisms through which fire influences forest structure and functionality. Interpretations of tree patterns via land survey records in the Lake States have often highlighted the importance of infrequent moderate to extreme disturbance events. However, historical survey methods are limited to observing higher severity disturbances and over large landscapes, thus it is not clear if the origin, structure, and forcing factors for either patterns or processes are adequately quantified by these methods. We used dendrochronological methods to determine how fire history and stand structure, including cohort structure, tree density, and spatial patterning, are linked within Lake States mixed conifer forests in Wisconsin. We found relatively short mean fire return intervals (MFRIs) ranging from 6 to 13 yr with little variation in fire frequency among sites. Current densities of red-pine-dominated forests are 4-37 times historical (ca. 1860) densities (mean 12×) and almost entirely spatially random, whereas historically forests were spatially aggregated at stand scales. Stands also contained multiple and/or loosely defined cohort structures suggesting very different controls operating historically than currently. Heterogeneity that helped maintain ecosystem resilience in these ecosystems historically came from frequent fire disturbance processes that affected stand-scale forest resistance. This was likely the historical dynamic across fire-adapted transitional pine forests of the Lake States.
维持弹性景观的一个关键挑战是适应和维持动态生态过程。在依赖火灾的生态系统中，这包括确定和定义火灾影响森林结构和功能的机制。在湖泊州的土地调查记录中对树木模式的解释经常强调了不频繁的中度到极端干扰事件的重要性。然而，历史调查方法仅限于观察更高的严重程度的干扰，并且在较大的景观上，因此不清楚这些方法是否充分量化了模式或过程的起源、结构和驱动因素。我们使用树木年代学方法来确定威斯康星州湖泊州混合针叶林中的火灾历史和林分结构（包括群结构、树木密度和空间格局）之间的关系。我们发现相对较短的平均火灾间隔期（MFRIs）范围为 6 至 13 年，各地点之间的火灾频率变化很小。目前红松主导的森林的密度是历史上（约 1860 年）密度的 4-37 倍（平均 12 倍），几乎完全是空间随机的，而历史上的森林在林分尺度上是空间聚集的。林分还包含多个和/或定义不明确的群结构，表明历史上的控制与当前的控制非常不同。在这些生态系统中，有助于维持生态系统弹性的异质性来自于频繁的火灾干扰过程，这些过程影响了林分尺度的森林抵抗力。这可能是湖泊州适应火灾的过渡松树林的历史动态。
