Key message

Flower to fruits × and seed-to-seedling were the most critical transition in the early regeneration cycle of pure and mixed Nothofagus forests, both in coastal and mountain geographic locations. Within mixed forest, the deciduous N. pumilio shows better recruitment performance (e.g., highest transition probabilities) than the evergreen N. betuloides. The evergreen species fails to recruit in the mixed coastal forests for two of the three analysed cohorts, which implies an advantage of N. pumilio over N. betuloides that must be further examined. However, N. betuloides in average value had a higher probability of reaching 2-year survivor in mixed forest.

Abstract

Transition from flower to seedling encompasses major processes that define the success of the tree regeneration, and consequently, its study is crucial in the context of forest management. Here, we analysed the transition probability of the reproductive cycle of two Nothofagus species, which formed pure and mixed forests in coastal and mountain geographic locations of Tierra del Fuego (Argentina). Pure deciduous N. pumilio (Np), pure evergreen N. betuloides (Nb), and mixed N. pumilio–N. betuloides (M) forests in coasts and mountains (3 forest types × 2 geographic locations × 20 replicas = 120 replicas) were evaluated. Reproductive structures (female flowers, fruits, seeds, sound seeds, emerged seedlings and surviving seedlings up to 2 years) were studied since 2012–2018. Our results suggested that transition probabilities from flower to surviving seedlings varied inter-annually between N. pumilio and N. betuloides. The hazard ratio in the transition showed an influence of the cohorts and the geographic location on N. pumilio, while forest type and geographic location influenced on N. betuloides. Flower to fruits and seed to seedling were the most critical process in all forest types and locations. Cumulative transition probabilities (female flowers to 2-year-old seedlings) for N. pumilio were 0.3–46.2% in Np and 1.4–30.2% in M, and pure and mixed forests reached similar probabilities only in cohort 3. For N. betuloides, these were 2.8–24.4% in Nb and 0.0–6.5% in M. Both Nothofagus species showed a better performance of pure forests in mountains (15.9–46.2% Np; 3.8–24.8% Nb) than in coasts (0.3–16.1% Np; 2.8–5.3% Nb). Through this integrated approach, considering the full reproductive cycle, it is possible to quantify the influence of canopy composition and inter-annual variability in natural forest dynamic, and allows to identify the critical stages of tree recruitment in pure and mixed Nothofagus forests.

中文翻译：

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推断火地岛沿海和山地森林中 Nothofagus pumilio 和 N. betuloides 的种群动态趋势：通过几个生殖周期从开花到幼苗存活的对比

关键信息

花到果实 × 和种子到幼苗是沿海和山地地理位置的纯和混合Nothofagus森林早期更新周期中最关键的过渡。在混交林中，落叶N. pumilio显示出比常绿N. betuloides更好的补充性能（例如，最高的过渡概率）。对于三个被分析的队列中的两个，常绿物种未能在混合沿海森林中招募，这意味着N. pumilio优于N. betuloides，必须进一步检查。然而，在混交林中，N. betuoides达到 2 年存活率的概率较高。

摘要

从花到幼苗的过渡包括决定树木再生成功的主要过程，因此，其研究在森林管理的背景下至关重要。在这里，我们分析了在火地岛（阿根廷）的沿海和山区地理位置形成纯林和混交林的两种Nothofagus物种生殖周期的过渡概率。纯落叶N. pumilio (Np)、纯常绿N. betuloides (Nb) 和混合N. pumilio – N. betuloides(M) 评估了海岸和山区的森林（3 种森林类型 × 2 个地理位置 × 20 个副本 = 120 个副本）。自 2012-2018 年以来，研究了生殖结构（雌花、果实、种子、健全种子、出苗和存活幼苗长达 2 年）。我们的结果表明，在N. pumilio和N. betuloides之间，从花到存活幼苗的过渡概率每年都在变化。在过渡风险比显示队列和所述地理位置的影响N. pumilio，而森林类型和地理位置上影响N. betuloides. 花到果实和种子到幼苗是所有森林类型和位置中最关键的过程。N. pumilio 的累积过渡概率（雌花到 2 年生幼苗）在 Np 中为 0.3-46.2%，在 M 中为 1.4-30.2%，纯林和混交林仅在队列 3 中达到相似的概率。对于N. betuloides，这些是在Nb的2.8-24.4％和0.0-6.5％在M.两个假山毛榉物种在山区（15.9–46.2% Np；3.8–24.8% Nb）比在海岸（0.3–16.1% Np；2.8–5.3% Nb）表现出更好的纯林性能。通过这种综合方法，考虑到完整的繁殖周期，可以量化天然森林动态中冠层组成和年际变化的影响，并可以确定纯和混合Nothofagus森林中树木补充的关键阶段。