Recruitment of black and white spruce 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（black spruce）是东部寒温带森林的优势林线树种，但在阿拉斯加布鲁克斯山脉（Brooks Range），其分布范围距林线仍有数公里之遥，该区域的优势林线树种为白云杉（white spruce）。目前尚无定论可解释该分布格局，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弱；其二，受较长的火灾间隔周期影响，黑云杉可能无法在林线附近成功完成自然更新。本研究正沿一条样带设立永久标记样地，样带起点为黑云杉占优势的育空河流域（Yukon River basin），终点为黑云杉达到分布极限的布鲁克斯山脉山麓地带。本研究正重建两个树种在各样地的种群补充历史，并通过分析火烧痕与林分年龄结构，还原近期火灾历史。上述数据正被用于对矩阵种群模型（matrix population model）进行参数化，并借助该模型阐释种群稳定性的变化格局。