Improving Sustainable Hawaiian Sandalwood Silviculture and Endemic Species Conservation with Mixed Stand Management

View the project final report

Commodities

• Additional Plants: native plants, trees

Practices

• Crop Production: forestry, forest/woodlot management
• Education and Training: extension, focus group, on-farm/ranch research, workshop, youth education
• Natural Resources/Environment: afforestation, biodiversity, habitat enhancement
• Sustainable Communities: employment opportunities, new business opportunities, partnerships, social networks

In Hawaiʻi, endemic sandalwood (Santalum) species (“ʻiliahi” in the Hawaiian language), were over-exploited for their fragrant oils, but landowners are interested in their reforestation and restoration of associated dry forests. Because sandalwood species are root hemiparasites, restoration and silviculture of these mixed-species forests present novel challenges. Field experiments initiated in 2019 reforested abandoned pastures with ʻiliahi alongside native host species. In one experiment, ʻilahi was outplanted simultaneously with either koa (Acacia koa), a fast-growing nitrogen-fixing tree or ʻaʻalili (Dodonaea viscosa), a fast-growing shrub. All three species have important economic and cultural values. In another experiment, ʻiliahi was underplanted in a 10-year old koa plantation. We used a mixed stand management approach to find optimal planting designs and overstory thinning to balance growth and survival of all species. Objectives were: (1) to estimate the optimum ratio of ʻiliahi and host plants to balance long-term survival and growth, and (2) to evaluate the influence of overstory host thinning on growth of ʻiliahi saplings. Plant size and growth were measured along with foliar nutrient concentration. Competition, facilitation, and parasitism were estimated from models using species composition, comparative growth of individual plants within a plot, and overall growth in the plot. Individual and stand growth models were used to project long-term outcomes of planting designs and effects of overstory thinning. Results provided recommendations for planting designs and mid-rotation management. They also were used as the basis of a field day and workshop on ʻiliahi establishment and stand management.

(1) to estimate the optimum ratio of ʻiliahi and host plants in balancing competition, facilitation, and parasitism related to their long-term survival and growth, (2) to evaluate the influence of host thinning on the growth of ʻiliahi at three years post-establishment, and (3) develop a model that accounts for the relative effects of silvicultural strategies on the establishment and growth of ‘iliahi in restored tropical dry forests.