FOREST PLANTATION SPECIES SELECTION FOR WESTERN SAMOA¹

E.H. Nile, Research Forester
Western Samoa Forestry Division
Department of Agriculture, Forests and Fisheries
P.O. Box 1874
Apia, Western Samoa

The independent state of Western Samoa lies between 13° and 14° South of the equator in the South Pacific. There are four inhabited islands with an area of 2,900 km² and a population of approximately 160,000. The islands of Samoa are of recent volcanic origin. Annual rainfall varies from 2300 to 5500 mm, with an annual relatively dry period of three months.

Exotic timber introductions began in the 19th century with the planting of Tectona grandis as boarders in coconut plantations. In the 1950's forest investigations began with the introduction and planting of small blocks of several timber species. In 1967 a forest act was passed by parliament and reforestation of logged-over areas began in 1972. The indigenous forests are expected to be depleted by the turn of the century which will coincide with the commencement of plantation harvesting. The Forestry Division of the Department of Agriculture, Forests and Fisheries presently manages nine blocks of customary lease and government property totaling 10,000 hectares. Approximately 4,300 hectares are stocked, with the dominant species being Swietenia macrophylla and Eucalyptus deglupta. The current rate of reforestation is 800 ha/year using a mix of open planting and line planting techniques.

Species and silvicultural research began in 1968 with a species elimination trial, a replicated species elimination trial in 1970, followed by 20 trials in 1971 – 1978, testing many species under different ecological conditions and methods of reforestation. In all over 130 species were introduced and tested in the period from 1968 to 1984, with approximately 50 species surviving today in tree form.

Selection of species for reforestation is a major decision with long ranging implications. This decision is complicated by the fact that some species have very good initial growth and stem characteristics, but might have a poor wood quality; other species are slow starting, but might be very marketable in the future. In order to aid this decision and reduce subjectivity in the process, Dixon (1970) outlined a system to rate species for their suitability as plantation timbers for Samoa. The species were to be rated in the following categories:

This analysis was done by Levingston (1973) and by Neuteboom (1977). In 1988 the species selection, point score system was modified and an evaluation conducted on 47 species.

In contrast to the earlier evaluations, the 1988 evaluation placed a higher value on wood quality and weed competition suppression, and reduced the weight of stem form and seed acquisition. Additionally each category was subdivided into minor components to obtain an accurate value for each species.

The majority of the trees observed for this evaluation were 10 to 30 years old. As the trials age, a more accurate evaluation can be made as different traits are revealed. Some species that were rated highly in the early evaluations dropped due to pathological problems, while others developed a good form later, and rose in the evaluation.

The point rating is merely a comparison between species as their growth is expressed in Samoa, and are only applicable for Samoa. Using this system elsewhere would require observation of the species in the particular area in question.

Wood characteristics of Samoan grown material of eight of the species have been tested and the remaining species were rated based on published data of timbers from their native source. As utilisation studies are conducted the evaluation should be updated.

Table 1. Point score evaluation, in descending order of preference

These ratings give the general suitability for plantation species in Samoa. The three main use categories for Samoan plantation timbers are: (1) export quality cabinet timbers, (2) domestic utility timbers, and (3) pole species used in round form. Selection of a species from the top-rated trees for planting on an individual site should be made considering the ecological factors of the site and the suitability of a species for that site.

This exercise has provided a useful tool for management decision making. It has also proved useful to increase the awareness of some minor species, and point out weaknesses of major species. A major concern that has arisen out of this exercise is the lack of good genetic base for Swietenia macrophylla. As a result the Samoan Forestry Division is working to rectify this problem.

REFERENCES

DIXON, R.G. (1970) Species Trials and Investigations for Forestry Development. Silvicultural Circular No. 1. Department of Forestry. Western Samoa. 26 pp.

LEVINGSTON, R. (1973) Investigation of Tree Species and Reforestation Suitable for Western Samoa. FAO Report. FAO, Rome 114 pp.

NEUTEBOOM, J.H. (1977) Report on Silvicultural Research and Reforestation Activities in Western Samoa. FAO Project Working Paper 4. WEST/68/004. FAO, Rome 55 pp.

NILE, E.H. (1988) Notes of Forest Research and Reforestation in Western Samoa, 1978–1988. Forestry Division. Department of Agriculture Forestry, and Fisheries. Western Samoa. 123 pp.

Table 2. Point Score for Selection of Tree Species for Plantations in Western Samoa

Table 3. Species rating 1988 according to the outlined evaluation system

Western Samoa Forestry Division

Eucalyptus urophylla at Masamasa, Savaii, Western Samoa 1988.

The tree is 15 years and 9 months old. Height is 32 m and diameter at breast height is 52 cm.

¹ Manuscript received January 1989