Control of Flowering and Factors Affecting Phenology of Endemic Low-Elevation Tree Species at Hawai'i Ka'ūpūlehu.

Native dry forest habitat is one of the most threatened and rare ecosystems in the Hawaiian Islands. The Ka'ūpūlehu Dry Forest Preserve, on the west coast of Hawai'i Island, is one of the few remaining intact examples of this low elevation habitat. To aid restoration efforts, flowering phenology of nine native species was estimated monthly from 2001 to 2007. Some species flowered prolifically, others seldom. Two dioecious tree species are in the survey, one only has female flowering trees, the second has both male and female trees. Each gender is treated as a separate species, making ten study "species." The effects of a number of abiotic factors (precipitation, temperature, photoperiod, and insolation) have on flowering are analyzed. Results indicate that flowering phenology of eight species is highly periodic, often correlating with photoperiodism or insolation. Four species are classified as short-day plants, four as long-day plants, and two as neutral-day plants. Both neutral-day species flowered continuously. Critical day length for flowering was determined for four light-dependent flowering species. The amount of precipitation prior to flowering, termed critical rain lag, was determined for seven species. During a multiyear drought, flowering periodicity was found not to depend on precipitation, rainfall only modified the degree of flowering. Several species had significantly more flowering during drought and ceased flowering during wet years. This analysis offers a unique finding of photoperiod the dominant abiotic driver and precipitation secondary, both combining to regulate flowering of dry forest native species. [ABSTRACT FROM AUTHOR]