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. ...本研究旨在厘清北美西部干旱森林本土两种针叶树种的球果产量同步性与波动模式（即大年结实 (masting)）及其与气候的关联。我们通过球果脱落痕 (cone abscission scars) 重建了单叶松 (Pinus edulis) 与黄松 (Pinus ponderosa) 近15年的球果产量序列，并采用冗余分析 (redundancy analysis) 将年度球果产量的时间序列与表征北美季风 (North American monsoon) 和厄尔尼诺-南方涛动 (ENSO) 的气候指数进行关联分析。研究结果表明，不同树种对气候的敏感性及其所导致的球果产量同步性存在显著差异。相较于黄松种群，单叶松种群的球果产量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。单叶松球果产量的大尺度同步性与北美季风存在关联，我们还识别出与ENSO位相相关的区域球果产量偶极格局 (dipole pattern)。……