The Alpine-Treeline Warming Experiment ran from 2008 to 2016 on Niwot Ridge above Boulder, Colorado. It combined common gardens with climate manipulations, using infrared heaters to warm soil and plant surfaces by an amount comparable to current average projections of climate warming in the year 2100. We had three basic questions we hoped to answer with the project:

  1. Will subalpine trees, currently restricted from cooler, higher elevations, move into alpine habitat and replace alpine plant species as a result of climate warming?
  2. Will subalpine trees be stressed by warmer temperatures and be less successful in their existing elevational ranges as a result of climate warming?
  3. Will ecosystem properties modify the effects of climate warming on subalpine or alpine species within and beyond their current elevational ranges?

Alpine and subalpine ecosystems are islands of biodiversity isolated from each other by surrounding lower elevation areas. The species in these ecosystems may be particularly vulnerable to a warming climate given their isolation and adaptations to very cold conditions and short growing seasons. In addition, the forest-alpine tundra ecotone is an important land cover transition. Shifts in the position of this transition zone will affect snow pack and water cycling, local temperatures, and ecosystem carbon and nutrient cycling. Shifts would also affect wildlife habitat and recreational opportunities.

Our study focused on limber pine and Engelmann spruce because they are common treeline species that occur throughout the Rocky Mountains, yet they also differ in important ways. For example, limber pine thrives in direct sunlight and can be found on exposed ridges, while Engelmann spruce is shade tolerant and more typically found on moist slopes or in valleys. We also studied lodgepole pine, which typically occurs below treeline in Colorado, and can regenerate strongly in high light and following fire.

Recruitment, or the ability of seeds to germinate and become established, is an important bottleneck for plants to pass through before successfully expanding into new areas. Similarly, if a species is going to survive where it currently grows, new recruits must be successful. Therefore this experiment studied the germination and first few years of seedling establishment and growth in field experiments and using climate controlled growth chambers. We collected seeds for our experiments from local high- and low-elevation populations of each species to assess whether population-level variation affected seedling germination, establishment, and physiology. Finally, we used spatially explicit models of tree population dynamics to extend our experimental findings to future landscapes.

Alpine plant species restricted to growing above current treeline may be particularly vulnerable to climate change. One quarter of our experimental plots are devoted to studying the effects of climate warming on alpine species phenology, productivity, and physiology to determine which species and functional groups may be most sensitive to changing climate.

PIs and Collaborators

Lara Kueppers (PI), Matt Germino, John Harte, Jeff Mitton, Margaret Torn, Dave Billesbach, Carolin Frank, Julia Klein, Noah Molotch, Keith Reinhardt, Tom Veblen, Yan Yang

Researchers and Postdocs

Ethan Brown, Ramona Butz, Andrea Campanella, Cristina Castanha, Erin Conlisk, Akasha Faist, Scott Ferrenberg, Brynne Lazarus, Andrew Moyes

Graduate Students

Manisha Anantharaman, Danielle Christianson, Meredith Jabis, Leah Meromy, Jennifer Petrzelka, Bettina Weibel, Daniel Winkler, Jennifer Wolf

Field Crews 2008-2014

Max Barlerin, Sebastien Barlerin, Megan Oldfather, Amy Farnham, Miranda Redmond, Miles Daly, Andrea Dixon

Ashley Allen, Will Baird, Jeff Beauregard, Sasha Berkowitz, Wendy Brown, John Curtis, Jeff Darrow, Karen Darrow, Jon DeCoste, Halley Finkel, Erin Flemming, Cody Foster, Alexandra Fylypovych, Rowan Gaffney, Nat Goodby, Doug Haller, Armin Howell, Katharina Knoebl, Michael Koontz, Sierra Love-Stowell, Allison Peterson, Evan Portier, Kirin Riddell, Allison Qubain, Sam Sartwell, Sunny Sawyer, Lauren Senkyr, Julia Siegrist, Anthony Slominski, Sylvia Taylor Smith, Jeff Thorburn, Cristin Walters, Jennifer Wilkening, Fabian Zust

Research Interns

Helen Dole, Daniella Rodriguez, Renee Rozaieski, Anna Szendrenyi, Melanie Wiederhold, Alan Hong, Evan Portier, Rick Thomas


Yang, Y., J. A. Klein, D. E. Winkler, A. Peng, B. E. Lazarus, M. J. Germino, K. N. Suding, J. Smith, and L. M. Kueppers. 2020. Warming of alpine tundra enhances belowground production and shifts community towards resource acquisition traits. Ecosphere 11(10): e03270. doi: 10.1002/ecs2.3270

Jabis, M., D. Winkler, and L. M. Kueppers. 2020. Warming acts through earlier snowmelt to advance but not extend alpine community flowering. Ecology 101 (9): e03108. doi: 10.1002/ecy.3108

Jabis, M. D., M. J. Germino, and L. M. Kueppers. 2020. Colonisation of the alpine tundra by trees: alpine neighbours assist late-seral but not early-seral conifer seedlings. Plant Ecology and Diversity, doi: 10.1080/17550874.2020.1762134

Brodersen, C., M. Germino, D. Johnson, K. Reinhardt, W. Smith, L. Resler, M. Bader, A. Sala, L. Kueppers, G. Broll, D. Cairns, K. Holtmeier, and G. Wieser. 2019. Seedling survival at timberlines critical to conifer mountain forest elevation and extent. Frontiers in Forests and Global Change 2:9, doi: 10.3389/ffgc.2019.00009.

Mohan, J. E., S. Wadgymar, D. E. Winkler, J. Anderson, P. Frankson, R. Hanifin, K. Benavides, L. M. Kueppers and J. Melillo. 2019. Plant Reproductive Fitness and Phenology Responses to Climate Warming: Results from Native Populations, Communities and Ecosystems. pp. 61-102 in Ecosystem Consequences of Soil Warming: Microbes, Vegetation, Fauna and Soil Biogeochemistry, J. Mohan, ed.

Winkler, D. E., K. C. Lubetkin, A. A. Carrell, M. D. Jabis, Y. Yang, and L. M. Kueppers. 2019. Responses of alpine plant communities to climate warming, pp. 297-346 in Ecosystem Consequences of Soil Warming: Microbes, Vegetation, Fauna and Soil Biogeochemistry, J. Mohan, ed.

Winkler, D. E., R. J. Butz, M. J. Germino, K. Reinhardt, and L. M. Kueppers. 2018. Snowmelt timing regulates community composition, phenology, and physiological performance of alpine plants. Frontiers in Plant Science, 9: 1140, doi: 10.3389/fpls.2018.01140.

Carper, D. L., A. A. Carrell*, L. M. Kueppers, and C. Frank. 2018. The effects of climate change on above- and belowground bacterial endophytic communities in subalpine conifer seedlings establishing across an elevation gradient. Plant and Soil, 428(1), 335-352, doi: 10.1007/s11104-018-3682-x.

Baker, E. A. G., J. L. Wegrzyn, U. U. Sezen, T. Falk, P. E. Maloney, D. R. Vogler, C. Jensen, J. Mitton, J. Wright, B. Knaus, H. Rai, R. Cronn, D. Gonzalez-Ibeas, H. A. Vasquez-Gross, R. A. Famula, J.-J. Liu, L. M. Kueppers, and D. B. Neale. 2018. Comparative transcriptomics among four white pine species. G3: Genes, Genomes, Genetics, doi: 10.1534/g3.118.200257.

Kueppers, L.M., A. Faist, S. Ferrenberg, C. Castanha, E. Conlisk, and J. Wolf. 2017. Lab and field warming similarly advance germination date and limit germination rate for high and low elevation provenances of two widespread subalpine conifers. Forests. 8(11), 433, doi:10.3390/f8110433.

Conlisk, E., C. Castanha, M. Germino, T. Veblen, J. Smith, A. Moyes, and L. M. Kueppers. 2017. Seed origin and warming constrain lodgepole pine recruitment, slowing the pace of population range shifts. Global Change Biology, 24(1): 197-211, doi: 10.1111/gcb.13840.

Lazarus, B., C. Castanha, M. Germino, L. M. Kueppers, and A. B. Moyes. 2017. Growth strategies and threshold responses to water deficit modulate effect of warming on tree seedlings from forest to alpine. Journal of Ecology, 106(2): 571-585, doi: 10.1111/1365-2745.12837.

Conlisk, E., C. Castanha, M. Germino, T. T. Veblen, J. Smith, and L. M. Kueppers. 2017. Declines in low elevation subalpine tree populations outpace high elevation population expansion with warming. Journal of Ecology 105(5): 1347–1357, doi:10.1111/1365-2745.12750.

Kueppers, L.M., E. Conlisk, C. Castanha, A. Moyes, M. Germino, P. de Valpine, M. S. Torn, and J. B. Mitton. 2017. Warming and provenance limit tree recruitment across and beyond the elevation range of subalpine forest. Global Change Biology 23(6): 2383-2395, doi:10.1111/gcb.13561.

Winkler, D. E., K. J. Chapin, and L. M. Kueppers. 2016. Soil moisture mediates alpine life form and community productivity responses to warming. Ecology 97(6): 1553-1563, doi:10.1890/15-1197.1.

Reinhardt, K., M. J. Germino, L. M. Kueppers, J. -C. Domec, J. Mitton. 2015. Linking carbon and water relations to drought-induced mortality in Pinus flexilis seedlings. Tree Physiology 35: 771-782 doi: 10.1093/treephys/tpv045.

Moyes, A. B., M. J. Germino, and L. M. Kueppers. 2015. Moisture rivals temperature in limiting photosynthesis by trees establishing beyond their cold-edge range limit under ambient and warmed conditions. New Phytologist 207: 1005-1014 DOI: 10.1111/nph.13422.

Meromy, L., N. P. Molotch, M. Williams, K. Musselman, and L. M. Kueppers. 2015. Snowpack-climate manipulation using infrared heaters in subalpine forests of the Southern Rocky Mountains, USA. Agricultural and Forest Meteorology 203: 142–157, DOI:10.1016/j.agrformet.2014.12.015.

Suding, K., E. Farrar, A. King, L. M. Kueppers, and M. Spasojevic. 2015. Vegetation change at high elevation: Scale-dependence and interactive effects on Niwot Ridge. Plant Ecology & Diversity 8: 713-725, DOI:10.1080/17550874.2015.1010189.

Moyes, A.B., Castanha, C., Germino, M.J. and Kueppers, L.M. 2013. Warming and the dependence of limber pine (Pinus flexilis) establishment on summer soil moisture within and above its current elevation range. Oecologia, 171:271-282, DOI: 10.1007/s00442-012-2410-0.

Castanha, C., Torn, M.S., Germino, M.J., Weibel, B. and Kueppers, L.M. 2013. Conifer seedling recruitment across a forest-to-alpine tundra gradient and effects of provenance. Plant Ecology and Diversity. 6(3-4): 307-318. doi:10.1080/17550874.2012.716087.

Harte, J. and Kueppers, L.M. 2012. Insight from integration. Nature, 485(7399): 449.

Mitton, J. and Ferrenberg, S. 2012. Mountain pine beetle develops an unprecedented summer generation in response to climate warming. The American Naturalist, 179(5): E163-E171. DOI: 10.1086/665007.

Reinhardt, K., Castanha, C., Germino, M.J. and Kueppers, L.M. 2011. Ecophysiological variation in two provenances of Pinus flexilis seedlings across an elevation gradient from forest to alpine. Tree Physiology, 31(6): 615-625.


Jabis, M. D. 2018. Climate Change Impacts in Alpine Plant Communities. PhD Dissertation, Environmental Science, Policy and Management, University of California, Berkeley. ProQuest ID: Jabis_berkeley_0028E_18505. Merritt ID: ark:/13030/m5qz78pg.

Christianson, D. S. 2016. Fine-scale Environmental Variation in Mountain Landscapes: Quantitative approaches, influences on tree recruitment, and implications for scientific visualization.  PhD Dissertation, Energy and Resources Group, University of California, Berkeley. ProQuest ID: Christianson_berkeley_0028E_15910. Merritt ID: ark:/13030/m53n6r8t.

Winkler, D. 2013. A multi-level approach to assessing alpine productivity responses to climate change, M.S. Thesis, Environmental Systems, University of California, Merced. ProQuest ID: Winkler_ucmerced_1660M_10013. Merritt ID: ark:/13030/m5029zdf.

Meromy, L. 2012. Subalpine snowpack-climate manipulation and modeling experiment at Niwot Ridge, CO and Valles Caldera National Preserve, NM, M.A. Thesis, Geography, University of Colorado, Boulder.

Petrzelka, J. 2011. The Effects of a Climate Manipulation Experiment on Snow Properties, Snow Surface Energy Balance, and Soil Temperature and Moisture Along an Elevation Gradient on Niwot Ridge, Colorado, M.A. Thesis, Geography, University of Colorado, Boulder.

Wolf, J. 2011. Response of Pinus flexilis James seedlings to simulated climate change through gas exchange rates, phenology and morphology, M.S. Thesis, Environmental Systems, University of California, Merced. ProQuest ID: 2011_jwolf. Merritt ID: ark:/13030/m5v69h52.