Restoration Ecology
Volume 8 Issue 2 Page 161  - June 2000
doi:10.1046/j.1526-100x.2000.80023.x

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Moderating Night Radiative Cooling Reduces Frost Damage to Metrosideros polymorpha Seedlings Used for Forest Restoration in Hawaii

Paul G. Scowcroft¹,² Frederick C. Meinzer³ Guillermo Goldstein⁴ Peter J. Melcher⁴ Jack Jeffrey⁵

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Abstract

Winter frosts caused by radiative cooling were hypothesized to limit successful reintroduction of Hawaiian plants other than Acacia koa to alien-dominated grasslands above 1700 m elevation. We determined, in the laboratory, the temperature at which irreversible tissue damage occurred to Metrosideros polymorpha leaves. We also conducted a field study of this species to determine if (1) leaf damage was correlated with sub-zero leaf temperatures, (2) radiative cooling could be moderated by canopies of A. koa, and (3) low soil temperatures contributed to seedling damage. The last was evaluated by thermally buffering seedlings with water-filled bladders placed at their base to keep roots warm, or by installing a radiation shield to reduce early morning transpiration when water uptake from cold soils would be least. Leaf temperatures were monitored between midnight and 7:00 a.m. using fine-wire thermocouples, and leaf damage was recorded monthly. In the laboratory, supercooling protected leaves from mild sub-zero temperatures; irreversible tissue damage occurred at about 8°C. In the field, leaf damage was strongly correlated with degree-hours below freezing. Unprotected seedlings suffered the greatest leaf damage. Those sheltered under A. koa trees rarely experienced temperatures below 3°C, and damage was minimal. Shaded and thermally buffered seedlings suffered less damage than unprotected plants, probably due to elevated leaf temperatures rather than improved water relations. Using A. koa or artificial devices to reduce radiative cooling during winter nights should enhance establishment of M. polymorpha in high-elevation rangeland.

Affiliations

¹Institute of Pacific Islands Forestry, Pacific Southwest Research Station, USDA Forest Service, 1151 Punchbowl St., Room 323, Honolulu, HI 96813, U.S.A.

³Hawaii Agriculture Research Center , 99-193 Aiea Heights Drive, Suite 300, Honolulu, HI 96701, U.S.A. 4Department of Botany , University of Hawaii, 3190 Maile Way, Honolulu, HI 96822, U.S.A.

5Hakalau Forest National Wildlife Refuge , USDI Fish and Wildlife Service, 32 Kinoole St., Suite 101, Hilo, HI 96720, U.S.A.

Correspondence

² Address correspondence to P. G. Scowcroft.