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

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 will use a mixed stand management approach to find
optimal planting designs and oversotyr thinning to balance growth
and survival of all species. Objectives are: (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 will be measured along with soil nutrient availability
and foliar nutrient content. Competition, facilitation, and
parasitism will be 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 will be used to project long-term outcomes of planting
designs and effects of overstory thinning. Results will provide
recommendations for planting designs and mid-rotation management.
They will also be used for producer training, educational
activities, and scientific presentations and publications.

(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, and (2) to evaluate the
influence of host thinning on the growth of ʻiliahi at three
years post-establishment