NOAA/WDS Paleoclimatology - Esper - Mount Smolikas EHS13 - PIHE - ITRDB GRC041

We present the longest high-elevation tree-ring width dataset in the Mediterranean reaching back to the 6th century CE. The network includes 101 living and 92 relict Pinus heldreichii Christ trees from four differently exposed sites in the 2100-2200 m a.s.l. elevation range of Mt. Smolikas in the Pindus Mountains in Greece. Though the sites were all sampled within a distance of <1 km, inter-site correlations are surprisingly low (r1550-2014 = 0.65-0.87), indicating site exposure might affect tree-ring formation. We here explore the consequence of exposure differences on the climate signals in an eastern Mediterranean treeline ecotone. Temporally stable growth/climate relationships reveal similar seasonal patterns among the four sites, but differences in signal strength. P. heldreichii growth at Mt. Smolikas is significantly controlled by temperature in April (r1951-2014 = 0.33-0.50) and precipitation in June-July (r1951-2014 = 0.23-0.42), which emphasizes the overall importance of an early growth onset and subsequent moisture conditions. The association between stem growth and April climate is strongest in the South-facing stand, supporting the significance of higher insolation rates at this thermally privileged site. Strongest summer precipitation signals are found in the NE-facing stand, where trees seem to benefit least from an early growth onset and where reduced meltwater supply may enhance the dependency on early summer precipitation. The significance of spring temperature on tree growth in all four sites constrains the emergence of a distinct summer precipitation signal in the Mt. Smolikas high elevation ecotone. Exploration of the site-specific influences on a new millennium-long tree-ring width dataset is an important step towards an improved understanding of long-term climate variability in the Eastern Mediterranean. Site-related differences in climate sensitivity in the high-elevation tree-ring network at Mt. Smolikas indicate that both temperature and precipitation during different seasons could potentially be reconstructed if distinct site exposures (S versus NE) are considered.

本研究构建了地中海地区迄今最长的高海拔树轮宽度（tree-ring width）数据集，其时间跨度可追溯至公元6世纪。该数据集网络涵盖希腊品都斯山脉斯莫利卡斯山海拔2100~2200米（a.s.l.，above sea level）区间内的4个不同坡向（exposure）样地，包含101株活立木与92株残遗海氏松（Pinus heldreichii Christ）。尽管所有样地的采样范围均不足1千米，但样地间相关系数竟极低（1550-2014年时段r值为0.65~0.87），表明坡向差异可能对树轮形成存在影响。
本研究聚焦东地中海林线交错带（treeline ecotone），探讨坡向差异对气候信号的调控效应。时序稳定的生长-气候（growth-climate）关系显示，4个样地的季节生长模式相近，但信号强度存在差异。斯莫利卡斯山的海氏松生长显著受4月气温（1951-2014年时段r值为0.33~0.50）与6-7月降水（1951-2014年时段r值为0.23~0.42）调控，这凸显了生长季早期启动及后续水分条件的整体重要性。南向林分（stand）的树干生长与4月气候的关联强度最高，印证了该热优势样地较高日照辐射（insolation）的关键意义。东北向林分则呈现出最强的夏季降水信号，该林分的树木似乎从早期生长启动中获益最少，且融水（meltwater）补给减少可能进一步增强其对初夏降水的依赖。4个样地均存在春季气温对树木生长的显著调控作用，这限制了斯莫利卡斯山高海拔林线交错带中独立夏季降水信号的有效提取。
针对这一全新的千年尺度树轮宽度数据集开展样地特异性影响分析，是增进东地中海长期气候变异规律认知的重要环节。斯莫利卡斯山高海拔树轮网络中存在的样地特异性气候敏感性（climate sensitivity）差异表明，若考虑不同坡向（南向与东北向）的差异，便可分别重建不同季节的气温与降水数据。