Warming and the dependence of limber pine (Pinus flexilis) establishment on summer soil moisture within and above its current elevation range
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Continued changes in climate are projected to alter the geographic distributions of plant species, in part by affecting where individuals can establish from seed. We tested the hypothesis that warming promotes uphill redistribution of subalpine tree populations by reducing cold limitation at high elevation and enhancing drought stress at low elevation. We seeded limber pine (Pinus flexilis) into plots with combinations of infrared heating and water addition treatments, at sites positioned in lower subalpine forest, the treeline ecotone, and alpine tundra. In 2010, first-year seedlings were assessed for physiological performance and survival over the snow-free growing season. Seedlings emerged in midsummer, about 5–8 weeks after snowmelt. Low temperature was not observed to limit seedling photosynthesis or respiration between emergence and October, and thus experimental warming did not appear to reduce cold limitation at high elevation. Instead, gas exchange and water potential from all sites indicated a prevailing effect of summer moisture stress on photosynthesis and carbon balance. Infrared heaters raised soil growing degree days (base 5 °C, p < 0.001) and August–September mean soil temperature (p < 0.001). Despite marked differences in vegetation cover and meteorological conditions across sites, volumetric soil moisture content (θ) at 5–10 cm below 0.16 and 0.08 m3 m−3 consistently corresponded with moderate and severe indications of drought stress in midday stem water potential, stomatal conductance, photosynthesis, and respiration. Seedling survival was greater in watered plots than in heated plots (p = 0.01), and negatively related to soil growing degree days and duration of exposure to θ < 0.08 m3 m−3 in a stepwise linear regression model (p < 0.0001). We concluded that seasonal moisture stress and high soil surface temperature imposed a strong limitation to limber pine seedling establishment across a broad elevation gradient, including at treeline, and that these limitations are likely to be enhanced by further climate warming.
KeywordsLimber pine Treeline Experimental warming Moisture stress
This research was supported by the Office of Science (BER), U.S. Department of Energy. We thank the Mountain Research Station and Niwot Ridge LTER at the University of Colorado, Boulder for logistical support. M. Barlerin, S. Barlerin, J. Beauregard, J. Darrow, S. Ferrenberg, S. Love-Stowell, A. Peterson, and K. Riddell set up and/or maintained the treatment and microclimate sensing infrastructure, and D. Billesbach, D. Christensen, and J. Norris assisted with microclimate data retrieval, quality assurance, and archiving. J.B. Curtis, M. Daly, A. Faist, A.P. Farnham, H. Finkel, E. Flemming, C. Foster, R. Gaffney, A. Howell, A. Qubain, M. Redmond, A. Slominski, S. Sawyer, S. Taylor Smith, and F. Zust collected and sowed seeds and/or conducted germination and survival surveys. Thanks to K. Reinhardt for valuable discussions and helpful feedback on early drafts of the manuscript. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
- Adams HD, Guardiola-Claramonte M, Barron-Gafford GA, Villegas JC, Breshears DD, Zou CB, Troch PA, Huxman TE (2009) Temperature sensitivity of drought-induced tree mortality portends increased regional die-off under global-change-type drought. Proc Natl Acad Sci USA 106:7063–7066PubMedCrossRefGoogle Scholar
- Atkin OK, Evans JR, Siebke K (1998) Relationship between the inhibition of leaf respiration by light and enhancement of leaf dark respiration following light treatment. Funct Plant Biol 25:437–443Google Scholar
- Atkin OK, Millar AH, Gardestrom P, Day DA (2000) Photosynthesis, carbohydrate metabolism and respiration in leaves of higher plants. In: Leegood RC, Thomas E, Von Caemmerer S (eds) Photosynthesis: physiology and metabolism. Kluwer, Dordrecht, pp 153–175Google Scholar
- Engler R, Randin CF, Thuiller W, Dullinger S, Zimmermann NE, AraÚJo MB, Pearman PB, Le Lay G, Piedallu C, Albert CH, Choler P, Coldea G, De Lamo X, DirnbÖCk T, GÉGout JC, GÓMez-GarcÍA D, Grytnes J-A, Heegaard E, HØIstad F, NoguÉS-Bravo D, Normand S, PuŞCaŞ M, SebastiÀ M-T, Stanisci A, Theurillat J-P, Trivedi M-R, Vittoz P, Guisan A (2011) 21st century climate change threatens mountain flora unequally across Europe. Glob Change Biol 17:2330–2341CrossRefGoogle Scholar
- IPCC (2007) Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, CambridgeGoogle Scholar
- Lepper MG (1980) Carbon dioxide exchange in Pinus flexilis and P. strobiformis (Pinaceae). Madrono 27:17–24Google Scholar
- Mayr S (2007) Limits in water relations. In: Wieser G, Tansz M (eds) Trees at their upper limit: treelife limitation at the alpine timber line. Springer, Berlin, pp 145–162Google Scholar
- Moen J, Aune K, Edenius L, Angerbjörn A (2004). Potential effects of climate change on treeline position in the Swedish mountains. Ecol Soc 9(1):16Google Scholar
- NWCC. (2012). “Natural Resources Conservation Service, National Water and Climate Center.” from http://www.wcc.nrcs.usda.gov
- Wieser G (2007a) Climate at the upper treeline. In: Wieser G, Tansz M (eds) Trees at their upper limit: treelife limitation at the alpine timber line. Springer, Berlin, pp 19–36Google Scholar
- Wieser G (2007b) Limitation by an lnsufficient carbon assimilation and allocation. In: Wieser G, Tansz M (eds) Trees at their upper limit: treelife limitation at the alpine timber line. Springer, Berlin, pp 79–129Google Scholar