Skip to Main Content
U.S. Forest Service
Caring for the land and serving people

United States Department of Agriculture

Home > Search > Publication Information

  1. Share via EmailShare on FacebookShare on LinkedInShare on Twitter
    Dislike this pubLike this pub


    Frost damage is among the major limitations to reforestation and forest restoration projects worldwide. Investigations of environmental and genetic effects on frost resistance have focused on boreal and temperate tree species rather than tropical trees. Koa (Acacia koa A. Gray) is a valuable tropical hardwood tree species endemic to the Hawaiian Islands, USA. Koa occurs across a wide elevational gradient, and newly planted trees are subject to winter frost at high elevations. We sought to determine whether different koa populations show variation in freeze hardiness as a cold-tolerance mechanism, and whether exposure to hardening conditions prior to frost exposure can modify koa cold-tolerance adaptation. Seeds from 13 populations of koa (Acacia koa A. Gray) were collected across an elevational range (603–2050 m) on the Island of Hawai'i. Four-month-old seedlings grown from the 13 population seed sources were divided into control (non-acclimated) and cold-acclimated treatments, maintained at 26 °C/22 °C (day/night) or exposed to gradually decreasing temperatures to 8 °C/4 °C (day/night), respectively. After six weeks, control and cold-acclimated seedlings from each population were tested for freeze tolerance by electrolyte leakage at five test temperatures ranging from 5 °C (control) to -20 °C. Treatment effects were mainly observed at the lowest test temperatures (-15 and -20 °C). A higher index of cold damage occurred in the non-acclimated seedlings for most of the populations. Several of our higher elevation populations showed greater cold tolerance than populations from lower elevations, particularly when cold-acclimated. Our results suggest that cold acclimation may increase frost hardiness in a tropical forest tree species, and that there is likely some adaptive variation in frost tolerance among populations from different elevations. Cold acclimation could be a useful tool to prepare koa seedlings to be planted in high-elevation sites prone to freezing winter temperatures.

    Publication Notes

    • Check the Northern Research Station web site to request a printed copy of this publication.
    • Our on-line publications are scanned and captured using Adobe Acrobat.
    • During the capture process some typographical errors may occur.
    • Please contact Sharon Hobrla, if you notice any errors which make this publication unusable.
    • We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.


    Ayala-Jacobo, Lilian M.; Woeste, Keith E.; Jacobs, Douglass F. 2021. Cold Acclimation Increases Freeze Tolerance in Acacia koa, a Tropical Tree Species Occurring over a Wide Elevational Gradient. Forests. 12(8): 1089. 12 p.


    Google Scholar


    cold acclimation, electrolyte leakage, forest restoration, outplanting, reforestation, seed source, target plant concept

    Related Search

    XML: View XML
Show More
Show Fewer
Jump to Top of Page