12/15/2016
Seedling Responses to Climate Warming May Slow Tree Advance Upslope
Warming and provenance limit tree recruitment across and beyond the elevation range of subalpine forest.
The Science
Using field experiments in the Rocky Mountains, scientists tested the sensitivity of emerging tree seedlings to artificial warming and watering at three locations along a mountainside to understand whether trees will be able to migrate upward in elevation as the climate changes.
The Impact
Most vegetation models assume that forest trees will track their environmental “niche” as climate warms, including upslope to higher elevations. There is little understanding, however, of climate constraints on seedlings, which are the future of the forest. The unexpected results of intensive field experiments in Colorado indicate that warming reduces the odds of seedlings establishing at and above their current upper limits, as well as in the forest, or provides no net benefit. Seeds sourced from higher-elevation trees also performed relatively poorly, suggesting that past genetic adaptation to local conditions may hinder upslope tree advances, a finding counter to current theory.
Summary
Climate warming is expected to promote upslope shifts in forests. However, common gardens sown with seeds collected from two different elevations and subjected to climate manipulations using infrared heaters and manual watering indicate that warming and local genotype may constrain tree seedling recruitment above current treeline. Negative effects of warming in forest, treeline, and alpine sites were partly offset by watering, suggesting growing season moisture may limit establishment of future subalpine forests. Greater climate sensitivity of Engelmann spruce compared with limber pine portends potential contraction in the elevational range of Engelmann spruce and changes in the composition of high-elevation Rocky Mountain forests. The greater availability of poorer-quality seed at the upper forest edge could act to further slow upslope shifts.
Principal Investigator(s)
Lara M. Kueppers
University of California, Merced, and Lawrence Berkeley National Laboratory
[email protected]
Funding
This research was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research (DE-FG02-07ER64457).
References
Kueppers, L. M., et al. “Warming and provenance limit tree recruitment across and beyond the elevation range of subalpine forest.” Global Change Biology 23(6), 2383–2395 (2016). [DOI:10.1111/gcb.13561]