Alpine Phenology Research

Appalachian mountain flowers, who will survive?

Those who visit the northern Appalachian Trail’s upper elevations can be greeted by spring blooms of white, pink, and purple flowers. To a hiker this is a bonus and maybe even a photo opportunity, but to the Appalachian Mountain Club’s (AMC) research staff their blooming time is of great interest. AMC has tracked flowering times of northeastern montane plants since 2004 as part of our ongoing mountain climate research and a citizen science program called Mountain Watch. Concurrently we are investigating temperature trends at upper elevations with partners from the Mount Washington Observatory, the University of New Hampshire, and Plymouth State University (Seidel et al., 2009, Murray et al., 2014). Recently AMC merged its phenology and climate data to determine if alpine plants are blooming earlier and at greater risk from late season frost.

AMC published its findings on alpine flowering times in the American Journal of Botany, Kimball et al., 2014. The study found that the advance in flower timing for three northeastern alpine species was much less compared with lower elevation plants in the region, and the small shift in flower timing did not increase the risk of frost damage.

From a previous study (Seidel et al., 2009, Murray et al., 2014) we know that the rate of increase in annual temperatures at higher elevations on Mount Washington, NH are less compared to lower elevations in the region. This contrasts with some other mountain areas globally, where higher elevation temperatures are generally increasing faster than lower elevations. But even accounting for the elevational differences in warming trend rates, this does not fully explain the large difference in flowering advancement between our study site and lower elevations in the region.

We are now investigating whether these plants have physiologically required chilling requirements during the non-growing season to trigger the next season’s growth and flowering. Many plants use both photoperiod (length of day) and spring warming temperatures (growing degree days) as primary cues for when to grow and eventually flower. This timing is especially important in alpine plants; too early a start increases flower mortality risks from late spring frost, while late flowering can result in fruit or seeds failing to mature during the short alpine growing season. Some plants use cold temperatures in the fall/winter to signal that winter has occurred and spring has yet to follow. This prevents plants from misinterpreting a fall or winter warm spell as a signal to flower out of season. Minus sufficiently cold temperatures to meet their physiological “chilling requirements”, they may delay spring flower timing to be “certain” that winter has passed and spring is here. Chilling requirements are generally not considered an important driver for cold climate plants, such as alpine or arctic tundra species, since they usually meet their chilling requirements. However our study site represents the southern distribution for our region’s arctic/alpine species. Our ongoing research is assessing whether the warmer winter temperatures result in these arctic plants failing to achieve their chilling requirements and possibly explaining why these plants flowering time are less responsive to ongoing winter and spring warming trends compared to lower elevation species in the region, i.e. advanced by only a few days as opposed to weeks.

Photographs: Diapensia by A. Bell

References:

Kimball, K. D., Davis, M. L., Weihrauch, D. M.,Murray, G. and K. Rancourt. 2014. Limited northeastern USA alpine climatic warming and modeled phenology advancement for Diapensia lapponica, (Diapensiaceae), Carex bigelowii (Cyperaceae), and Vaccinium vitis-idaea (Ericaceae). American Journal of Botany.

Seidel, T.M., Weihrauch, D.M., Kimball, K.D., Pszenny, A.A.P., Soboleski, R., Crete, E., Murray, G. 2009. Evidence of climate change declines with elevation based on temperature and snow records from 1930s to 2006 on Mount Washington, New Hampshire, USA. Arctic, Antarctic and Alpine Research.

Murray, G.L.D, Kelsey, E. and Bailey, A.R. 2014. Temperature Trends in the White Mountains, NH. Poster at American Geophysical Union San Francisco 2014 meeting. https://agu.confex.com/data/handout/agu/fm14/Paper_30216_handout_2286_0.pdf