Twig Elongation Patterns of Chamaecyparis lawsoniana

Abstract

Twig elongation was measured during two growing seasons for 12 native populations of saplings of Chamaecyparis lawsoniana and for co-occurring saplings of Pseudotsuga menziesii, Tsuga heterophylla, or Abies concolor at some sites. Growth of lateral branches of C lawsoniana was always early, and sometimes completed more quickly, on the hot and open sites but was always late and brief on the colder ones; moderate coastal sites had more prolonged elongation centered in midsummer The rate of growth increased with the rise in daytime air temperature in the spring, with populations at cold sites responding most to rising temperature Rates of growth after the peak were not related to temperature. Early growth cessation of populations in open, hot sites occurred despite their high predawn water potentials. Twig elongation of Pinaceae associated with C lawsoniana was of shorter duration than for Chamaecyparis Pseudotsuga in the mixed-evergreen zone was more responsive to temperature than was C. lawsoniana Phenology of rooted cuttings of four populations of C lawsoniana grown in a garden varied much less than did saplings studied in the field; no phenological differences were significant Genetic variability of phenology of C lawsoniana is smaller than that of competing Pinaceae Its phenological pattern appears to be important in restricting C lawsoniana to sites with dependable summer moisture and perhaps in determining its northern range limit.