Population dynamics across latitudes of black spruce 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树种，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，此时优势林线树种为白云杉。目前尚无定论解释这一分布格局，但存在两种合理假说。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差；其二，由于火灾间隔周期较长，黑云杉或无法在林线附近完成成功更新。本研究正沿一条样带设立永久标记样地，样带覆盖范围从黑云杉占优势的育空河流域，延伸至黑云杉分布边界所在的布鲁克斯山脉山麓地带。本研究正重建研究样地内黑云杉与白云杉的更新历史，并通过分析火疤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的参数校准，借此阐释种群稳定性格局。