Are standing dead trees (snags) suitable as climate proxies? A case study from the central Scandinavian Mountains

ABSTRACT

Standing dead trees (snags) play important roles in forest ecology by storing carbon as well as providing habitats for many species. Moreover, snags preserved for hundreds of years can provide useful data to extend tree-ring chronologies used for climatological and ecological studies beyond the lifespans of living trees. Here we examined the growth patterns of Scots pine snags from the central Scandinavian Mountains, in relation to still living trees. Using changes point analyses, we showed that a majority (74%) of the snags displayed significant negative growth changes prior (on average 17 years) to death. Change points around the same years were also seen in living trees, but they recovered their growth. The average growth reduction of snags showing negative growth changes before death was 46%. In most cases the final growth change points coincided with very cold summers, or to a lesser degree to period of cool summers. It was suggested that pines ending up as snags were less resilient than the trees which continued living, and thus not able to recover after cold summer events. Since the snag growth reductions prior to death were partly unrelated to climate, care should be taken when using such data in dendroclimatological studies.

KEYWORDS:

• Scots pine
• snags
• mortality
• climate extremes
• dendroclimatology

Acknowledgements

We acknowledge the County Administrative Board of Jämtland for providing the permission to sample trees in the studied area. We also thank Jesper Björklund for help in the field and discussions during the preparation of the manuscript, as well as comments from the editor, one anonymous reviewer and Tom Melvin, which helped improving the manuscript. It contributes to the Swedish strategic research areas Modelling the Regional and Global Earth system (MERGE), and Biodiversity and Ecosystem services in a Changing Climate (BECC), as well as the FPS COST Action FP1106 STReESS – Studying Tree Responses to extreme Events: a Synthesis. This is contribution # 37 from the Sino-Swedish Centre for Tree-Ring Research (SISTRR).

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Hans W. Linderholm http://orcid.org/0000-0002-1522-8919

Additional information

Funding

This research was supported by the Swedish Research Council [VR, grant to HWL] and the Egyptian Ministry of Higher Education and Scientific Research [ParOwn Initiatives 2012/13, grant to EF].