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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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Rapid migration of Mongolian oak into the southern Asian boreal forest
Abstract The migration of trees induced by climatic warming has been observed at many alpine treelines and boreal–tundra ecotones, but the migration of temperate trees into southern boreal forest remains less well documented. We conducted a field investigation across an ecotone of temperate and boreal forests in northern Greater Khingan Mountains of northeast China. Our analysis demonstrates that Mongolian oak (Quercus mongolica), an important temperate tree species, has migrated rapidly into southern boreal forest in synchrony with significant climatic warming over the past century. The average rate of migration is estimated to be 12.0 ± 1.0 km decade−1, being slightly slower than the movement of isotherms (14.7 ± 6.4 km decade−1). The migration rate of Mongolian oak is the highest observed among migratory temperate trees (average rate 4.0 ± 1.0 km decade−1) and significantly higher than the rates of tree migration at boreal–tundra ecotones (0.9 ± 0.4 km decade−1) and alpine treelines (0.004 ± 0.003 km decade−1). Compared with the coexisting dominant boreal tree species, Dahurian larch (Larix gmelinii), temperate Mongolian oak is observed to have significantly lower capacity for light acquisition, comparable water‐use efficiency but stronger capacity to utilize nutrients especially the most limiting nutrient, nitrogen. In the context of climatic warming, and in addition to a high seed dispersal capacity and potential thermal niche differences, the advantage of nutrient utilization, reflected by foliar elementomes and stable nitrogen isotope ratios, is also likely a key mechanism for Mongolian oak to coexist with Dahurian larch and facilitate its migration toward boreal forest. These findings highlight a rapid deborealization of southern Asian boreal forest in response to climatic warming.
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- Award ID(s):
- 2021898
- PAR ID:
- 10589864
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Global Change Biology
- Volume:
- 30
- Issue:
- 1
- ISSN:
- 1354-1013
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1111/gcb.17002
