Periglacial Research Section, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Potsdam, 14473, Germany.
Institute of Earth and Environmental Science, University of Potsdam, Potsdam, 14476, Germany.
Ecology. 2017 Sep;98(9):2343-2355. doi: 10.1002/ecy.1887. Epub 2017 Aug 22.
Arctic and alpine treelines worldwide differ in their reactions to climate change. A northward advance of or densification within the treeline ecotone will likely influence climate-vegetation feedback mechanisms. In our study, which was conducted in the Taimyr Depression in the North Siberian Lowlands, w present a combined field- and model-based approach helping us to better understand the population processes involved in the responses of the whole treeline ecotone, spanning from closed forest to single-tree tundra, to climate warming. Using information on stand structure, tree age, and seed quality and quantity from seven sites, we investigate effects of intra-specific competition and seed availability on the specific impact of recent climate warming on larch stands. Field data show that tree density is highest in the forest-tundra, and average tree size decreases from closed forest to single-tree tundra. Age-structure analyses indicate that the trees in the closed forest and forest-tundra have been present for at least ~240 yr. At all sites except the most southerly ones, past establishment is positively correlated with regional temperature increase. In the single-tree tundra, however, a change in growth form from krummholz to erect trees, beginning ~130 yr ago, rather than establishment date has been recorded. Seed mass decreases from south to north, while seed quantity increases. Simulations with LAVESI (Larix Vegetation Simulator) further suggest that relative density changes strongly in response to a warming signal in the forest-tundra while intra-specific competition limits densification in the closed forest and seed limitation hinders densification in the single-tree tundra. We find striking differences in strength and timing of responses to recent climate warming. While forest-tundra stands recently densified, recruitment is almost non-existent at the southern and northern end of the ecotone due to autecological processes. Palaeo-treelines may therefore be inappropriate to infer past temperature changes at a fine scale. Moreover, a lagged treeline response to past warming will, via feedback mechanisms, influence climate change in the future.
全球范围内的北极和高山树线对气候变化的反应不同。树线生态交错带的北移或密集化可能会影响气候-植被反馈机制。在我们的研究中，我们在北西伯利亚低地的泰梅尔低地进行了一项综合实地和模型研究，帮助我们更好地理解整个树线生态交错带（从封闭森林到单棵树苔原）对气候变暖的反应所涉及的种群过程。利用来自七个地点的林分结构、树木年龄、种子质量和数量的信息，我们研究了种内竞争和种子可利用性对最近气候变暖对落叶松林分的具体影响。实地数据表明，森林-苔原的树木密度最高，平均树木大小从封闭森林到单棵树苔原逐渐减小。年龄结构分析表明，封闭森林和森林-苔原中的树木已经存在了至少 240 年。除了最南端的地点外，所有地点的过去建立都与区域温度升高呈正相关。然而，在单棵树苔原，从 krummholz 到直立树木的生长形式的变化，始于约 130 年前，而不是建立日期，已经被记录下来。种子质量从南向北减小，而种子数量增加。LAVESI（落叶松植被模拟器）的模拟进一步表明，相对密度的变化强烈响应于森林-苔原的变暖信号，而种内竞争限制了封闭森林的密集化，种子限制阻碍了单棵树苔原的密集化。我们发现，对最近气候变暖的反应的强度和时间存在显著差异。虽然森林-苔原林分最近密集化，但由于自生态过程，在生态交错带的南端和北端，繁殖几乎不存在。因此，古树线可能不适合在精细尺度上推断过去的温度变化。此外，过去变暖对树线的滞后反应将通过反馈机制影响未来的气候变化。
