The effects of ENSO and the North American monsoon on mast seeding in two Rocky Mountain conifer species

We aimed to disentangle the patterns of synchronous and variable cone
production (i.e., masting) and its relationship to climate in two conifer
species native to dry forests of western North America. We used cone
abscission scars to reconstruct ca. 15 years of recent cone production in
Pinus edulis and Pinus ponderosa, and used redundancy analysis to relate
time series of annual cone production to climate indices describing the
North American monsoon and the El Niño Southern Oscillation (ENSO). We
show that the sensitivity to climate and resulting synchrony in cone
production varies substantially between species. Cone production among
populations of P. edulis was much more spatially synchronous and more
closely related to large-scale modes of climate variability than were
populations of P. ponderosa. Large-scale synchrony in P. edulis cone
production was associated with the North American monsoon and we
identified a dipole pattern of regional cone production associated with
ENSO phase. In P. ponderosa, these climate indices were not strongly
associated with cone production, resulting in asynchronous masting
patterns among populations. This study helps frame our understanding of
mast seeding as a life history strategy and has implications for our
ability to forecast mast years in these species.

本研究旨在解析北美西部干旱森林原生的两种针叶树的同步性与波动型球果结实（即结实大年，masting）模式，及其与气候的关联。本研究通过球果脱落痕重建了近15年来皮尼翁松（Pinus edulis）和西黄松（Pinus ponderosa）的球果结实序列，并采用冗余分析（redundancy analysis）将年度球果结实时间序列与表征北美季风（North American monsoon）及厄尔尼诺南方涛动（El Niño Southern Oscillation, ENSO）的气候指数进行关联。研究结果表明，不同物种对气候的敏感性及其导致的球果结实同步性存在显著差异。相较于西黄松种群，皮尼翁松种群的球果结实在空间上具有更强的同步性，且与大尺度气候变率模态的关联更为紧密。皮尼翁松球果结实的大尺度同步性与北美季风相关，且本研究识别出了与厄尔尼诺南方涛动相位相关的区域球果结实偶极模式。而西黄松的球果结实与上述气候指数关联性较弱，其种群间呈现出异步的结实大年模式。本研究有助于构建我们对作为生活史策略的种子大年现象的认知框架，同时对预测这两个物种的结实大年年份具有重要参考价值。