SREL Reprint #3556

Observed compression of in situ tree stems during freezing

Ethan D. Gutmann1, John T. Van Stan II2, Jan Friesen3, Doug P. Aubrey4,5, and Jessica Lundquist6

1Research Applications Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
2Department of Geology & Geography, Georgia Southern University, Statesboro, GA, USA
3Department of Catchment Hydrology, Helmholtz Centre for Environmental Research - UFZ,
Leipzig, Germany
4Savannah River Ecology Laboratory, University of Georgia, Aiken, SC, USA
5Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA, USA
6Civil and Environmental Engineering, University of Washington, Seattle, WA, USA

Abstract: Freezing temperatures can influence the material properties of trees. Understanding how forest biometeorological interactions respond to freezing temperatures is important for forest science and management, as its effects can cascade through coupled hydrological and ecological processes including limitations on tree growth, changes to canopy interception, and influences on atmospheric turbulence. This short communication details the effect of sub-freezing temperatures on the mechanical displacement of three in situ Pinus contorta Douglas (lodgepole pine) stems during a winter season (2013–2014) at Niwot Ridge Mountain Research Station (CO, USA). Although previous research on harvested trees suggests longitudinal stem expansion should occur as temperatures decrease below freezing, we observed longitudinal compression in live stems below -3 °C that linearly correlated with sub-zero air temperatures ranging down to -22 °C. Freeze-related compression of stems frequently achieved displacement magnitudes comparable to applying 55 kN of compressive force (800 µm). Hypotheses are proposed to explain the significant mechanical displacement observed due to freezing: (1) internal gas release as freezing fronts propagate through stems; (2) short-term relocation of water via sap exudation or preferential ice crystal growth. As the observed stem compression response to freezing is substantial, future work on underlying processes and consequences is merited. The measurement technique used here may prove useful to others interested in the dynamics of stem freezing.

Keywords: Freeze avoidance; Pinus contorta; Stem compression; Stem mechanical properties

SREL Reprint #3556

Gutmann, E. D., J. T. Van Stan II, J. Friesen, D. P. Aubrey, and J. Lundquist. 2017. Observed compression of in situ tree stems during freezing. Agricultural and Forest Meteorology 243(2017): 19-24.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).