Warm-wet climatic conditions are widely regarded as conducive to remarkable tree growth, alleviating climatic pressures. However, the notable decline in tree growth observed in the southern edge of boreal forests has heightened concerns over the spatial-temporal dynamics of forest decline. Currently, attaining a comprehensive grasp of the underlying patterns and their propelling factors remains a formidable challenge. We collected tree ring samples from a network of 50 sites across the Greater Xing'an Mountains. These samples were subsequently grouped into two distinct clusters, designated as Groups A and B. The percentage change of growth (GC, %) and the proportion of declining sites were utilized to assess forest decline. The decline in tree growth within Larix gmelinii forests exhibits significant regional variation, accompanied by temporal fluctuations even within a given region. Group A exhibited a pronounced increase in frequency (59.26%) of occurrences and encountered more severe declines (21.65%) in tree growth subsequent to the 1990s, contrasting sharply with Group B, which observed lower frequencies (20.00%) and relatively less severe declines (21.02%) prior to the 1980s. The primary impetus underlying the opposite radial growth increments observed in Larix gmelinii trees from the interplay between their differential response to temperatures and wetter climatic conditions, which is significantly influenced by varying stand densities. In cold-dry conditions, low-density forests may experience soil water freezing, exacerbating drought conditions and thereby inhibiting tree growth, in Group B. Trees growth in high-density stands is restrained by warm-wet conditions, in Group A. These results provide new insights into the variability at the southern edge of the boreal forest biome with different responses to density and climate.

中文翻译：

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北方森林中树木生长下降到暖湿条件与林分密度有关


暖湿气候条件被广泛认为有利于树木显着生长，减轻气候压力。然而，在北方森林南部边缘观察到的树木生长显着下降，这加剧了人们对森林衰退的时空动态的担忧。目前，全面掌握基本模式及其推动因素仍然是一项艰巨的挑战。我们从大兴安岭的 50 个站点网络收集了树木年轮样本。这些样本随后被分为两个不同的集群，分别命名为 A 组和 B 组。利用生长百分比变化 （GC， %） 和下降地点的比例来评估森林衰退。落叶松森林内树木生长的下降表现出显着的区域差异，即使在给定区域内也伴随着时间波动。A 组出现的频率 （59.26%） 显着增加，并且在 1990 年代之后树木生长的下降幅度更大 （21.65%），与 B 组形成鲜明对比，B 组观察到较低的频率 （20.00%） 和相对不那么严重的下降 （21.02%）在 1980 年代之前。在 Larix gmelinii 树中观察到的相反径向生长增量的主要动力来自它们对温度和更潮湿气候条件的不同响应之间的相互作用，这受到不同林分密度的显着影响。在 B 组中，在寒冷干燥条件下，低密度森林可能会经历土壤水冻结，加剧干旱条件，从而抑制树木生长。在 A 组中，高密度林分中的树木生长受到暖湿条件的限制。 这些结果为北方森林生物群落南部边缘的变化提供了新的见解，这些变化对密度和气候的反应不同。