Leucaena Leucoce2hala (Lam.) de Wit For Wood Production

Abstract

A series of 10 spacing and variety x spacing trials were established in Hawaii, Taiwan and Nepal to study biomass production of Leucaena leucocephala as a function of population, environment and variety. Six of these trials were spacing studies involving 12-populations ranging from 2500-80.000 stems/ha in an augmented block design. Three trials were variety and variety x spacing studies utilizing 5 arboreal leucaena varieties and 3 spacings. One trial was installed to study the effect of age and spacing on form and volume of leucaena stems. Ten samples and 4 reps were found to be satisfactory for both height and diameter measurements. Biomass yields of leucaena in Hawaii sites were high, with a maximum of 152.7 fresh ton/ha at 4 years at the Kauai site, produced in four years at a 1m x 0.5m spacing. Very close spacings had higher wood biomass yields at young ages, but on a 4-year rotation populations in the range of 10,000-20,000 stems per hectare were superior on good sites. Dry leaf production was also greatest at close spacings, with 10 dry tons/ha produced at 40,000 stems/ha. Per-hectare branch weight was found to be independent of spacing, with populations in the range of 5000-40,000 stems/ha producing equal amounts of branchwood. Increasing population decreased both height and diameter growth of leucaena. Average height of 1m x 1m and 1m x 2m spacings of 4 year plantings on 2 Hawaiian sites exceeded 10m. Closer spacings had smaller average heights. Diameter growth was affected more by spacing than height at all sites. Diameter and height development at spacings between 5000-40,000/ha generally followed linear patterns between the ages of 1 - 4 years. No significant variety x spacing interaction was detected for growth parameters of 5 giant leucaena varieties at two Hawaiian locations. This was verified in the Taiwan trial, where 4 giant varieties were tested. Tree volume equations regressing measured volume against diameter breast height (d) basal diameter (bd), total plant height (h) and their squares, logs and interactions were derived for ages ranging from 0.5 - 4.0 years. Log transformations of d and h fit the data well, and removed the effect of high variances associated with trees of great volume. Linear models utilizing the d2 h interaction term were also satisfactory. International use of Kanazawa's formula (V = 0.5d2 h) was recommended. Specific gravity and moisture content was affected by season, with the summer months decreasing moisture content and raising specific gravity values. Average per-tree values for specific gravity and moisture content were .41 and .51 respectively. Calorific values of leucaena did not appear to vary much with age and position on tree. Average value of 3 positions on trees, 4 spacings and 5 ages was 4635 cal/g.