Braziunas Kristin H, Hansen Winslow D, Seidl Rupert, Rammer Werner, Turner Monica G
Department of Integrative Biology, University of Wisconsin-Madison, Birge Hall, 430 Lincoln Drive, Madison, WI 53706, United States.
Institute of Silviculture, Department of Forest and Soil Sciences, University of Natural Resources and Life Sciences (BOKU) Vienna, Peter Jordan Strasse 82, 1190 Wien, Austria.
For Ecol Manage. 2018 Dec 15;430:460-471. doi: 10.1016/j.foreco.2018.08.034. Epub 2018 Aug 29.
High-severity, infrequent fires in forests shape landscape mosaics of stand age and structure for decades to centuries, and forest structure can vary substantially even among same-aged stands. This variability among stand structures can affect landscape-scale carbon and nitrogen cycling, wildlife habitat availability, and vulnerability to subsequent disturbances. We used an individual-based forest process model (iLand) to ask: Over 300 years of postfire stand development, how does variation in early regeneration densities versus abiotic conditions influence among-stand structural variability for four conifer species widespread in western North America? We parameterized iLand for lodgepole pine ( var. ), Douglas-fir ( var. ), Engelmann spruce (), and subalpine fir () in Greater Yellowstone (USA). Simulations were initialized with field data on regeneration following stand-replacing fires, and stand development was simulated under historical climatic conditions without further disturbance. Stand structure was characterized by stand density and basal area. Stands became more similar in structure as time since fire increased. Basal area converged more rapidly among stands than tree density for Douglas-fir and lodgepole pine, but not for subalpine fir and Engelmann spruce. For all species, regeneration-driven variation in stand density persisted for at least 99 years postfire, and for lodgepole pine, early regeneration densities dictated among-stand variation for 217 years. Over time, stands shifted from competition-driven convergence to environment-driven divergence, in which variability among stands was maintained or increased. The relative importance of drivers of stand structural variability differed between density and basal area and among species due to differential species traits, growth rates, and sensitivity to intraspecific competition versus abiotic conditions. Understanding dynamics of postfire stand development is increasingly important for anticipating future landscape patterns as fire activity increases.
森林中高严重程度、不频繁发生的火灾会在数十年至数百年间塑造林分年龄和结构的景观镶嵌格局，而且即使在同龄林分中，森林结构也可能有很大差异。林分结构的这种变异性会影响景观尺度的碳和氮循环、野生动物栖息地的可用性以及对后续干扰的脆弱性。我们使用基于个体的森林过程模型（iLand）来探讨：在火灾后300年的林分发育过程中，早期更新密度的变化与非生物条件相比，如何影响北美西部广泛分布的四种针叶树种林分间的结构变异性？我们针对美国大黄石地区的黑松（变种）、花旗松（变种）、白云杉和亚高山冷杉对iLand进行了参数化。模拟以林分更替火灾后更新的实地数据为初始条件，并在无进一步干扰的历史气候条件下模拟林分发育。林分结构以林分密度和断面积来表征。随着火灾后的时间增加，林分结构变得更加相似。对于花旗松和黑松，断面积在林分间的收敛速度比树木密度更快，但对于亚高山冷杉和白云杉则不然。对于所有树种，由更新驱动的林分密度变化在火灾后至少持续99年，对于黑松，早期更新密度决定了林分间217年的变化。随着时间的推移，林分从竞争驱动的收敛转变为环境驱动的发散，其中林分间的变异性得以维持或增加。由于树种特性、生长速度以及对种内竞争与非生物条件的敏感性不同，林分结构变异性驱动因素的相对重要性在密度和断面积之间以及树种之间存在差异。随着火灾活动增加，了解火灾后林分发育动态对于预测未来景观格局变得越来越重要。
