Soil Ph at black spruce sites at its northern limit in the Brooks Range, Alaska

Although black spruce is the dominant treeline species in the eastern boreal forest, its distribution stops several kilometers short of treeline in the Brooks Range in Alaska, and white spruce is the dominant treeline species. The explanation for this distribution is not known, but two hypotheses are plausible. First, black spruce may be less tolerant of climatic conditions near treeline than white spruce. Second, black spruce may be unable to regenerate successfully near treeline due to long intervals between fires. We are establishing permanently marked study plots along a transect from the Yukon River basin, where black spruce is the dominant species, to the foothills of the Brooks Range, where it reaches its distributional limit. We are reconstructing recruitment history of both black and white spruce at our study sites, and are reconstructing recent fire history from analysis of fire scars and stand age structures. These data are being used to parameterize matrix population models, with which we are describing patterns of population stability.

尽管黑云杉是东部北方针叶林的优势林线（treeline）物种，但在阿拉斯加布鲁克斯山脉，其分布范围距林线仍有数公里之遥，此时优势林线物种为白云杉。目前尚无针对该分布格局的合理解释，但存在两项合理假说。其一，相较于白云杉，黑云杉对林线附近的气候条件耐受性更弱；其二，受林线附近火灾间隔期过长的影响，黑云杉或无法在该区域成功完成天然更新。本研究沿一条样带设置永久标记样地，样带覆盖范围从以黑云杉为优势物种的育空河盆地，延伸至黑云杉分布上限所在的布鲁克斯山脉山麓。我们将重建研究样地内黑云杉与白云杉的更新历史，并通过分析火灾痕与林分年龄结构，还原近期火灾历史。上述数据将用于矩阵种群模型（matrix population models）的参数化工作，借此描述种群稳定性的变化格局。