Analysis and prediction of growth, grazing impacts, and economic production of Acacia koa

Thesis (Ph. D.)--University of Hawaii at Manoa, 1995.Includes bibliographical references.Microfiche.xiv, 176 leaves, bound 29 cmKoa (Acacia koa) is a valuable native hardwood which is the focus of a complex set of land-use issues in Hawaii. We conducted an integrated research program to investigate: 1) impacts of cattle grazing on koa growth and on the pest Passiflora mollissima, 2) koa growth and stand development, and 3) the effects of koa shade on pasture productivity and forage quality. Results were synthesized into a computer model to project stand development. Long-term projections were used to evaluate the economic feasibility of koa production under different management scenarios. Two non-destructive methods for monitoring leaf area removal by cattle were tested versus harvest. Estimates of projected canopy area using color slides and grid-counting correlated well with leaf area and provided a simple and reliable method, while the LiCor LAI-2000 was more variable. In a grazing experiment, survival of koa saplings over 3 cm diameter was high, but diameter increment was reduced in proportion to the fraction of leaf area removed. Diameter growth was reduced by trampling and was increased by grass removal. Repeated grazing would be necessary to control P. mollissima. Analysis of permanent growth plots showed that larger trees grew faster and suppressed the growth of smaller trees. Mortality was a function of diameter increment. Higher site quality reduced competition, allowing mid-ranking trees faster growth and longer survival. Light absoption by koa canopies was strongly affected by solar angle, in response to the vertical phyllode orientation. Kikuyu grass (Pennisetum clandestinum) growth was reduced in proportion to light interception by the koa canopy. The synthesis of field results into a stochastic, non-spatial, gap-scale model showed that maturing koa stands converged towards similar merchantable volumes despite large variations in initial stocking density. Simulation of silvopastoral systems showed that grazing reduced tree leaf area index and harvestable volumes, but increased grass production. Based on projected volumes of koa under different management options, and using current real property tax rates in Hawaii, silvopastoral production of koa should yield positive cash flows and higher economic returns than either monoculture koa production or grazing only