A2 Refereed review article in a scientific journal
A global framework for linking alpine-treeline ecotone patterns to underlying processes
Authors: Bader Maaike Y, Llambí Luis D, Case BradleyS, Buckley Hannah L, Toivonen Johanna M, Camarero J Julio, Cairns David M, Brown Carissa D, Wiegand Thorsten, Resler Lynn M
Publisher: WILEY
Publication year: 2021
Journal: Ecography
Journal name in source: ECOGRAPHY
Journal acronym: ECOGRAPHY
Volume: 44
Issue: 2
First page : 265
Last page: 292
Number of pages: 28
ISSN: 0906-7590
eISSN: 1600-0587
DOI: https://doi.org/10.1111/ecog.05285(external)
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/51146480(external)
Globally, treeline ecotones vary from abrupt lines to extended zones of increasingly small, stunted and/or dispersed trees. These spatial patterns contain information about the processes that control treeline dynamics. Describing these patterns consistently along ecologically meaningful dimensions is needed for generalizing hypotheses and knowledge about controlling processes and expected treeline shifts globally. However, existing spatial categorizations of treelines are very loosely defined, leading to ambiguities in their use and interpretation. To help better understand treeline-forming processes, we present a new framework for describing alpine treeline ecotones, focusing on hillside-scale patterns, using pattern dimensions with distinct indicative values: 1) the spatial pattern in the x-y plane: a) decline in tree cover, and b) change in the level of clustering. Variation along these dimensions results in more or less 'discrete' or 'diffuse' treelines with or without islands. These patterns mainly indicate demographic processes: establishment and mortality. 2) Changes in tree stature: a) decline in tree height, and b) change in tree shape. Variation along these dimensions results in more or less 'abrupt' or 'gradual' treelines with or without the formation of environmental krummholz. These patterns mainly indicate growth and dieback processes.Additionally, tree population structure can help distinguish alternative hypotheses about pattern formation, while analysing the functional composition of the ecotonal vegetation is essential to understand community-level processes, controlled by species-specific demographic processes.Our graphical representation of this framework can be used to place any treeline pattern in the proposed multi-dimensional space to guide hypotheses on underlying processes and associated dynamics. To quantify the dimensions and facilitate comparative research, we advocate a joint effort in gathering and analysing spatial patterns from treelines globally. The improved recognition of treeline patterns should allow more effective comparative research and monitoring and advance our understanding of treeline-forming processes and vegetation dynamics in response to climate warming.
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