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Research article - Peer-reviewed, 2020

Mosses modify effects of warmer and wetter conditions on tree seedlings at the alpine treeline

Lett, Signe; Teuber, Laurenz M.; Krab, Eveline J.; Michelsen, Anders; Olofsson, Johan; Nilsson, Marie-Charlotte; Wardle, David A.; Dorrepaal, Ellen


Climate warming enables tree seedling establishment beyond the current alpine treeline, but to achieve this, seedlings have to establish within existing tundra vegetation. In tundra, mosses are a prominent feature, known to regulate soil temperature and moisture through their physical structure and associated water retention capacity. Moss presence and species identity might therefore modify the impact of increases in temperature and precipitation on tree seedling establishment at the arctic-alpine treeline. We followedBetula pubescensandPinus sylvestrisseedling survival and growth during three growing seasons in the field. Tree seedlings were transplanted along a natural precipitation gradient at the subarctic-alpine treeline in northern Sweden, into plots dominated by each of three common moss species and exposed to combinations of moss removal and experimental warming by open-top chambers (OTCs). Independent of climate, the presence of feather moss, but notSphagnum, strongly supressed survival of both tree species. Positive effects of warming and precipitation on survival and growth ofB. pubescensseedlings occurred in the absence of mosses and as expected, this was partly dependent on moss species.P. sylvestrissurvival was greatest at high precipitation, and this effect was more pronounced inSphagnumthan in feather moss plots irrespective of whether the mosses had been removed or not. Moss presence did not reduce the effects of OTCs on soil temperature. Mosses therefore modified seedling response to climate through other mechanisms, such as altered competition or nutrient availability. We conclude that both moss presence and species identity pose a strong control on seedling establishment at the alpine treeline, and that in some cases mosses weaken climate-change effects on seedling establishment. Changes in moss abundance and species composition therefore have the potential to hamper treeline expansion induced by climate warming.


Arctic; Betulapubescens; bryophytes; climate change; Pinussylvestris; plant interactions; precipitation; treeline expansion

Published in

Global Change Biology
2020, volume: 26, number: 10, pages: 5754-5766
Publisher: WILEY

Authors' information

Lett, Signe
Umea Univ
Teuber, Laurenz M.
Ernst Moritz Arndt Univ Greifswald
Umeå University
Swedish University of Agricultural Sciences, Department of Soil and Environment
Michelsen, Anders
Univ Copenhagen
Olofsson, Johan
Umea Univ
Nilsson, Marie-Charlotte (Nilsson Hegethorn, Marie-Charlotte)
Swedish University of Agricultural Sciences, Department of Forest Ecology and Management
Swedish University of Agricultural Sciences, Department of Forest Ecology and Management
Nanyang Technological University (NTU)
Dorrepaal, Ellen
Umea Univ

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SDG13 Climate action

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