Mixed stand management between ‘iliahi and host plants in Hawaiian-restored tropical dry forests

Abstract

This dissertation aimed to assess the development and tradeoffs of key interactions between ‘iliahi (Hawaiian sandalwood, Santalum paniculatum) and host plants at the forest stand level. This was designed to fill knowledge gaps in ‘iliahi ecology and to recommend silviculture strategies for ‘iliahi restoration. Survey experiment was conducted to explore ‘iliahi-host plants interaction at the community stand level in a Hawaiian-restored tropical dry forest. Results found the interaction between ‘iliahi and host plants not only related to facilitation but also included competition and parasitism, wherein these interactions occurred simultaneously. Competition increased facilitation but mitigated parasitism. The levels of facilitation-parasitism crossed at a basal area of 24 m2 ha-1 which indicate an optimum level of competition to stabilize ‘iliahi-host interactions and lead to their balanced growth. Maintaining the ideal competition through silviculture intervention like targeted thinning seems to be required to optimum the growth of both species. Our study also realized that the magnitude of ‘iliahi-host interactions was also related to the proportion of both species at the forest stand. A host:’iliahi ratio of 2:1 was required to balanced competition, facilitation, and parasitism. This ratio can be considered for planting and maintenance to support long-term survival and growth of ‘iliahi and host plants. Pre-establishing hosts before planting 'iliahi and maintaining a host:'iliahi ratio of 2:1 are recommended to maximize establishment of ʻiliahi and long-term survival of all species and to optimize individual species and forest stand growth by optimizing 'iliahi-host interactions. This recommendation not only helps to preserve ‘iliahi and host plants in Hawai’i but also may support sandalwood conservation globally and represents alternative silviculture system to simple plantation models.