Variation in the Phenology of Natural Populations of Montane Shrubs in New Zealand

SUMMARY (1) Variation in flowering time of individuals in one population of each of three species of shrub was recorded over two growing seasons in montane scrub-grassland in the South Island of New Zealand. (2) There was considerable variation in flowering time within each popuLlation, but the flowering rank-order of individuals in different years was positively correlated. (3) Variation in flowering time was poorly correlated witlh the dLuration of flowering and the number of flowers and fruits per plant, except that variation in flowering time in Discaria toumatou (Rhamnaceae) was weakly positively correlated with the percentage fruit set in 1976-77. If both earlier and later flowering plants showed reduced fruit set this would suggest stabilizing selection, but there is no indication of such a pattern. Weak and inconsistent directional phenotypic selection for flowering time can be demonstrated for these two species however. (4) In the warm, dry summer of 1977-78, Leptospermum scoparium (Myrtaceae) and Dracophyllumn spp. (Epacridaceae) flowered on average 9 days and 5 days earlier respectively and for 17 and 8 days shorter duration than in the cool, damp summer of 1976-77. Further, L. scoparium plants had a lower production of flowers and fruits in the second season in comparison with the first season. Plants of Discaria toumatou also flowered earlier in 1977-78, but the duration of flowering and flower and fruit production was greater in 1977-78 than in the 1976-77 season. (5) Patterns of variation in flowering time are also apparent among adjacent populations depending on altitude and on the major geographical units of the range of species. Variation in flowering time both at the individual and the population level may be an important adaptation by which selection and physiological mechanisms increase reproductive success.