Adaptive Management Lessons for Serianthes nelsonii Conservation

Abstract

The literature covering the biology, ecology, horticulture, and conservation of the critically endangered tree Serianthes nelsonii Merr. was reviewed. The roots, stems, and leaves of this charismatic legume tree revealed highly plastic traits and responded positively to horticultural manipulations to improve the quality of container-grown transplants. Pre-sowing seed treatments of seed coat scarification and 1 h of imbibition generated 85% to 90% germination at a temperature optimum of 26 °C. Adventitious root formation on air layers and successful unions on approach grafts were 100%. Seedling and sapling growth was maximum under 25% to 50% sunlight transmission, limited irrigation to ensure adequate root zone aeration, repetitive stem tip pruning to increase root:shoot quotient, and thigmic stress to retain an orthotropic orientation of stems. In situ regeneration on Guam was substantial but recruitment from seedling to sapling was nil. High quality leaf litter chemistry enabled rapid decomposition, and soils beneath the tree exhibited unique chemical traits that increased ecosystem health by creating spatial heterogeneity. The greatest unanswered questions focus on plant mortality. Research is needed to determine the reasons for the mortality of in situ seedlings, mortality within transplantation projects on Guam, and the mortality of 60% of the mature in situ tree population during the 26-year implementation of the national recovery plan. Horticultural researchers are ideally positioned to answer these urgent questions.

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

“…Funding a knowledgeable ecologist to more comprehensively study all distance and density components of community competition will be required to mitigate the ongoing recruitment failures. Decades of successful production of container-grown nursery plants in Guam have been characterized by post-transplant sapling death (Marler et al, 2021). Post-transplant monitoring research by a community ecologist with skills to tease apart the net-positive and net-negative biotic and abiotic interactions within the restoration sites will be required to stop this form of mortality.…”

“…The decades of failures to advance toward the goal of 2000+ mature trees within four managed sites have unfolded without the involvement of published academic scientists in the field work following transplantation from conservation nurseries (Marler et al, 2021). This has led to the current absence of knowledge concerning what has caused the mortality.…”

“…This S. nelsonii knowledge concerning the use of shade to increase stem extension rates and decrease stem strength was exploited in a shaded trellis system to generate excessive primary stem growth of Serianthes seedlings. The limitations on S. nelsonii research imposed by federal handling permits has led to the use of Serianthes kanehirae Fosberg as a surrogate for conservation research to aid in recovery of S. nelsonii (Marler et al, 2021). Canopy and inflorescence appearance is similar for these two species (Figure 1).…”

Talking with Strangers: Improving Serianthes Transplant Quality with Interspecific Companions

“…The national recovery plan for S. nelsonii [21] called for goals that have not been adequately addressed [22]. More research directed toward the reasons for the inadequate progress is urgent.…”

“…Research on conservation of this species has been deficient, so knowledge of root growth and behavior is minimal. The slow progress on the 1994 national recovery plan [21] includes a long-term pattern of widespread mortality of saplings after they are removed from a conservation nursery setting and placed in natural, competitive closed forest habitats [22]. Experiments with surrogate genotypes are important for improving conservation knowledge for species which are critically threatened, and may involve substitution by congenerics or other closely related taxa for manipulative studies [23,24].…”