Widespread forest dieback is a phenomenon of global concern that requires an improved understanding of the relationship between tree growth and climate to support conservation efforts. One priority for conservation is the Atlas cedar (Cedrus atlantica), an endangered species exhibiting dieback throughout its North African range. In this study, we evaluate the long-term context for recent dieback and develop a projection of future C. atlantica growth by exploring the periodic variability of its growth through time. First, we present a new C. atlantica tree-ring chronology (1150–2013 CE) from the Middle Atlas mountains, Morocco. We then compare the new chronology to existing C. atlantica chronologies in Morocco and use principal components analysis (PCA) to isolate the common periodic signal from the seven longest available records (PCA7, 1271–1984 CE) in the Middle and High Atlas portions of the C. atlantica range. PCA7 captures 55.7% of the variance and contains significant multidecadal (˜95 yr, ˜57 yr, ˜21 yr) periodic components, revealed through spectral and wavelet analyses. Parallel analyses of historical climate data (1901–2016 CE) suggests that the multidecadal growth signal originates primarily in growing season (spring and summer) precipitation variability, compounded by slow-changing components of summer and winter temperatures. Finally, we model the long-term growth patterns between 1271–1984 CE using a small number (three to four) of harmonic components, illustrating that suppressed growth since the 1970s – a factor implicated in the dieback of this species – is consistent with recurrent climatically-driven growth declines. Forward projection of this model suggests two climatically-favourable periods for growth in the 21st century that may enhance current conservation actions for the long-term survival of the C. atlantica in the Middle and High Atlas mountains.

中文翻译：

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过去 850 年中西北非阿特拉斯雪松生长的数十年变化：对枯死和濒危物种保护的影响


广泛的森林枯死是一种全球关注的现象，需要更好地了解树木生长与气候之间的关系，以支持保护工作。保护的重点之一是阿特拉斯雪松（Cedrus atlantica），这是一种濒临灭绝的物种，在整个北非分布范围内都出现枯死现象。在这项研究中，我们评估了最近顶枯病的长期背景，并通过探索其生长随时间的周期性变化来预测未来的 C. atlantica 生长。首先，我们提出了来自摩洛哥中阿特拉斯山脉的新的 C. atlantica 树轮年表（公元 1150-2013 年）。然后，我们将新的年表与摩洛哥现有的 C. atlantica 年表进行比较，并使用主成分分析（PCA）从中阿特拉斯和高阿特拉斯部分的七个最长可用记录（PCA7，公元 1271-1984 年）中分离出共同的周期信号。 C. atlantica范围。 PCA7 捕获了 55.7% 的方差，并包含通过光谱和小波分析揭示的显着的数十年（~95 年、~57 年、~21 年）周期分量。对历史气候数据（1901-2016 CE）的并行分析表明，数十年增长信号主要源于生长季节（春季和夏季）降水变化，再加上夏季和冬季温度的缓慢变化。最后，我们使用少量（三到四个）谐波分量对公元 1271 年至 1984 年之间的长期生长模式进行建模，说明自 1970 年代以来生长受到抑制（与该物种枯死有关的一个因素）与经常性的生长一致气候驱动的增长下降。 该模型的前瞻预测表明，21 世纪有两个气候有利的生长时期，这可能会加强当前的保护行动，以确保中阿特拉斯山脉和高阿特拉斯山脉的 C. atlantica 的长期生存。