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Abstract AimAlpine treeline ecotones are influenced by environmental drivers and are anticipated to shift their locations in response to changing climate. Our goal was to determine the extent of recent climate‐induced treeline advance in the northeastern United States, and we hypothesized that treelines have advanced upslope in complex ways depending on treeline structure and environmental conditions. LocationWhite Mountain National Forest (New Hampshire) and Baxter State Park (Maine), USA. TaxonHigh‐elevation tree species—Abies balsamea, Picea marianaandBetula cordata. MethodsWe compared current and historical high‐resolution aerial imagery to quantify the advance of treelines over the last four decades, and link treeline changes to treeline form (demography) and environmental drivers. Spatial analyses of the aerial images were coupled with ground surveys of forest vegetation and topographical features to ground‐truth treeline classification and provide information on treeline demography and additional potential drivers of treeline locations. We used multiple linear regression models to examine the importance of both topographic and climatic variables on treeline advance. ResultsRegional treelines have significantly shifted upslope over the past several decades (on average by 3 m/decade). Gradual diffuse treelines (characterized by declining tree density) showed significantly greater upslope shifts (5 m/decade) compared to other treeline forms, suggesting that both climate warming and treeline demography are important correlates of treeline shifts. Topographical features (slope, aspect) as well as climate (accumulated growing degree days, AGDD) explained significant variation in the magnitude of treeline advance (R2 = 0.32). Main ConclusionsThe observed advance of treelines is consistent with the hypothesis that climate warming induces upslope treeline shifts. Overall, our findings suggest that gradual diffuse treelines at high elevations may be indicative of climate warming more than other alpine treeline ecotones and thus they can inform us about past and ongoing climatic changes.
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Inclusions and exclusions in treeline definitions
Abstract Körner and Hoch's (2023) definition of “treeline” to include only forest edges that are arctic or alpine, globally distributed and thermally limited is reconsidered for the alpine, with attention to the alpine treeline ecotone. They characterize the alpine treeline and the ecotone as a single phenomenon at a single fundamental niche limit, with all other montane forest edges at realized niche limits. The framework restricts treeline and the treeline ecotone to narrow but interesting ecophysiological questions but leaves other fundamentally limited edges, those in disequilibrium with a changed temperature regime, and the extensive zone of krummholz and tree‐species seedlings now often referred to as the treeline ecotone, without terminology. Recognizing other fundamental niche limited edges as treelines, if not alpine, and defining “alpine treeline” as a zone or line within the broader “alpine treeline ecotone”, are proposed to promote synergies in research in these related systems.
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- Award ID(s):
- 1853665
- PAR ID:
- 10484137
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Journal of Biogeography
- Volume:
- 51
- Issue:
- 1
- ISSN:
- 0305-0270
- Page Range / eLocation ID:
- 54 to 56
- Subject(s) / Keyword(s):
- alpine treeline
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1111/jbi.14729
