Towards recovery of an endangered Pacific island endemic: Experimental evidence for shortening juvenility of Serianthes plants using a shade and trellis system to generate vigorous growth and precocious flowering

Abstract

Conservationists aiming to establish seed orchards or restoration plantings benefit from methods that reduce tree juvenility. Previous studies suggest that seedling and sapling mortality is the major limitation to natural population recovery of the critically endangered Serianthes nelsonii. To enable effective restoration actions new methods are required to reduce sapling mortality. Ex situ experiments were used to determine if trellised, shaded growth conditions would reduce juvenility of Serianthes saplings. Serianthes kanehirae was used as a surrogate for S. nelsonii. Stem growth was trained horizontally to a wire trellis in shaded tunnels of differing lengths (0, 3, 6, 9 or 12 m). Time to reach the end of each tunnel, and subsequent vertical stem growth in full sun were recorded until flower production commenced. The shortest S. kanehirae juvenile phase occurred under 12 m tunnels, with first flower production within a year (351 ± 10 days, mean ± SE). The juvenile phase increased in duration as tunnel length shortened. The control plants did not produce flowers during the study. Horizontal trellised support of shaded stems was effective in reducing juvenile phase duration of Serianthes saplings. Serianthes seed orchards may use shaded trellises to produce seeds on young plants to rapidly boost species recovery efforts. The production of seeds in managed conservation gardens may improve recovery efforts by reducing the need to remove seeds from in situ communities. Therefore, this simple protocol may prove beneficial for both in situ and ex situ conservation of all federally listed woody plant species in the region.