Abstract A widely accepted paradigm in forest ecology proposes that patterns of relative abundance among mature forest trees are largely influenced by biotic and abiotic processes that operate most intensely during the earliest life-cycle stages. Therefore, traits expressed early in development such as germination and seedling establishment may be under strong selective pressure from the environment, and their adjustment to changing climates may ultimately influence species’ responses to global climate change. Here we used different environments established across altitude in an old-growth temperate Patagonian forest as a natural laboratory, and studied the Nothofagus obliqua and N. pumilio regeneration response – seedling emergence and survival –to different climatic scenarios, inside and outside their natural distribution range. These are two iconic species of sub-Antarctic forests, which co-exist in contrasting and non-overlapping thermal niches. Whereas N. obliqua is predominant in the warmer and lower environments at 650–850 m above sea level (a.s.l.), N. pumilio inhabits the colder and higher montane environments, above 1000 m a.s.l. By sowing germinated seeds of both species at different altitudes in the forest – 680, 930 and 1340 m a.s.l. – we were able to distinguish the environmental influence on seedling emergence from its influence on germination. Our results show that the local environment had a major effect on seedling survival, and a minor influence on emergence. Overall, regeneration of both species showed a temporal window of stronger environmental susceptibility, which comprised the process of emergence, and in the particular case of N. obliqua, the first month of post-emergence growth. Survival ability was influenced by the ontogenetic stage of the seedling, evidencing stronger environmental resistance and higher probability of survival after the first year of growth. Interestingly, we found inter-specific differences in survival dynamics and the final number of surviving seedlings, which may reflect species-specific physiological adaptations and tolerance to abiotic stress. However, the performance of both species was favored in relatively colder environments inside their natural ranges. This indicates that present climatic conditions in the lower zones of the gradient exert physiological constraints at seedling stage, even in N. obliqua, which shows high abundance of adult trees at these altitudes. Results reported here were consistent across two independent experiments and will be discussed in the context of forest regeneration in present and future climatic scenarios.

中文翻译：

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不同自然环境对安第斯山脉南部两种不同海拔不同山毛榉物种再生动态的影响

摘要 森林生态学中一个被广泛接受的范式提出，成熟林木的相对丰度模式在很大程度上受生命周期最早阶段最强烈的生物和非生物过程的影响。因此，在发育早期表现出来的性状，如发芽和幼苗建立，可能会受到来自环境的强烈选择压力，它们对气候变化的调整可能最终影响物种对全球气候变化的反应。在这里，我们使用在古老的温带巴塔哥尼亚森林中跨海拔建立的不同环境作为自然实验室，并研究了 Nothofagusobliqua 和 N. pumilio 的再生反应——幼苗的出现和存活——对不同气候场景的自然分布范围内外. 这是亚南极森林的两个标志性物种，它们共存于对比和非重叠的热生态位中。斜纹猪笼草在海拔 650-850 米 (asl) 的温暖和低海拔环境中占主导地位，而 N. pumilio 则栖息在海拔 1000 米以上的寒冷和高山环境中森林——海拔 680、930 和 1340 米——我们能够区分环境对幼苗出苗的影响和对萌发的影响。我们的结果表明，当地环境对幼苗成活有主要影响，对出苗影响较小。总体而言，这两个物种的再生显示出更强的环境敏感性的时间窗口，其中包括出现的过程，在特殊情况下，N.obliqua，出现后增长的第一个月。存活能力受幼苗个体发育阶段的影响，证明在生长的第一年后具有更强的环境抵抗力和更高的存活概率。有趣的是，我们发现生存动态和存活幼苗的最终数量存在种间差异，这可能反映了物种特定的生理适应和对非生物胁迫的耐受性。然而，这两个物种的表现在其自然范围内相对较冷的环境中受到青睐。这表明梯度较低区域的当前气候条件在幼苗阶段施加了生理限制，即使在 N. obliqua 中，在这些海拔高度显示成年树的丰度。