Editor’s Choice: Ice caves and treeline dynamics

The Editor’s Choice article for Volume 107 Issue 2 is a study by Leunda et al. about long-term treeline dynamics. Associate Editor Bérangère Leys has taken a closer look at the paper in the blog post below…

Ecosystem responses to climate change is a great concern and a lot of effort has been made to better frame the future consequences of a temperature rise on vegetation dynamics (Sobrino et al. 2004; McMahon et al. 2011; López-Merino et al. 2012), including migration and survival.

Armeña A294_ice deposit_2015

A long-term approach to this research question is important, and model outputs can help put into context ecosystem responses to ancient climate variations, including both warmer and cooler climatic conditions (Heiri, Tinner & Lotter 2004; Renssen et al. 2009; Saltré et al. 2013a). While considerable attention has been focused on plant responses to future climate change (Chuine 2010; Saltré et al. 2013b), the lack of a long‐term (millennial) perspective on tree line shifts in Mountain forest ecosystems, such as the Alps and the Pyrenees, has prevented understanding the underlying ecosystem dynamics and processes.

The Editor’s Choice paper for this issue assesses for the first time in the Pyrenees, tree line dynamics and ecosystem resilience to climate changes 5,700–2,200 years ago. Maria Leunda and colleagues combined palaeoecological proxies (fossil pollen, spores, conifer stomata, and plant macrofossils) from an ice cave deposit located in the alpine belt c. 200 m above current tree line.

From their experiment, the authors found that the subalpine forests were generally more widely distributed during the last 5700 years, due to overall warmer temperatures than today. For example, today’s situation is different to how it was 2000 years ago as only alpine meadows are present which could suggest that the climatic or human disturbances resulted in the depression treelines and timberlines of species such as Pinus uncinata and Betula. In light of these results, the long‐term Pyrenean tree line ecotone sensitivity suggests that rising temperatures could trigger future mountain pines and birches expansions to higher elevations, potentially replacing other arctic–alpine plant species.

The impact of global change on alpine ecosystems, and specifically on treeline communities, has already been detected, as treelines are slightly expanding and timberlines are thickening at the subalpine belt. We look forward to seeing further reconstructions of ecosystem responses to past climate variability in order to establish whether these patterns are generalizable to other parts of the Pyrenees and also the Alps! Ice archives are however severely endangered by rising temperatures and more scientific attention is needed in order to rescue their untapped scientific information. Stay tuned!

Bérangère Leys, Journal of Ecology Associate Editor

You can also read the Pyrenean Institute of Ecology (IPE-CSIC) press release for this paper from October 2018.

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