Winter climatic comparison between France and New Zealand: effects of frost damage on populations of Leptospermum scoparium JR et G Forst grown at three locations in France

Abstract

Ornamental cultivars of Leptospermum scoparium, a species indigenous to New Zealand and Australia, have restricted horticultural use in France because of limited cold hardiness. In New Zealand wild populations of the species are widely distributed across 14 degrees of latitude and from the coast to 1 400 m above sea level. Existing ornamental cultivars appear to have been derived from plants collected at lower latitude and low altitude sites. Populations representing the latitudinal and altitudinal range of L scoparium (fig 1) in New Zealand were grown at Angers, Landerneau and Fréjus to test their adaptation to a range of habitats in France. Plants were set out in the field before the 1987/1988 winter at all sites and also in spring 1988 at Angers. Plant death in the first year was attributed to drought stress at transplanting, frost in the 1987/1988 winter, and high soil pH in the range 7-8 at Fréjus which caused widespread chlorosis. Because of this chlorosis, detailed observations on cold damage were made for only the Angers and Landerneau plantings after the 1988/1989 winter (tables I, II). During this winter the lowest screen minimum temperature at Angers was -5.6 ° C (-9.1 ° C grass minimum) and at Landerneau -3.5 ° C (fig 2). Cold damage was much greater at Landerneau suggesting the climate of Angers produced more effective cold hardening. At the evaluation sites in France cold damage was significant for low latitude coastal populations, and negligible for South Island montane populations of L scoparium (figs 4, 5). Spring bud movement at Angers was most advanced for high latitude populations, but was retarded for montane populations (fig 6). These results are discussed with reference to temperature and day length regulation of cold hardiness. Comparison of the temperature regimes of the colder zones of the South Island, New Zealand, and the temperate zones of France (figs 3a, 3b, 3c) show these to be sufficiently similar to envisage the increased use of New Zealand plants in the horticulture of western Europe. To enable this increased use, other factors beside temperature limitations such as soil permeability and soil acidity will have to be considered. © 1991.