Growing a native hardwood species within teak plantations, which can be harvested after just a few years, gives growers early returns as well as facilitating thinning of the plantation. Research in Solomon Islands with native flueggea showed minimal competition between the two tree species, lending support to this approach.
Teak, which is non-native in Solomon Islands, produces high-value timber which is in strong demand globally. Best practice is to begin with dense stocking and then to thin the trees after the first few years, that is, removing some to allow the others to make best use of the resources and grow to maximum size. However, smallholder growers in Solomon Islands are often reluctant to cut any of the trees early, as they feel they are losing potential value. A proposed solution is to plant fewer teak trees and mix them with another tree species that has value when harvested earlier. The native tree flueggea is a promising candidate – it is a hardwood species much in demand locally for building houses and fencing. But before promoting this idea, it is important to understand whether the flueggea trees will compete with the teak trees, which might reduce the teak’s growth rate.
This paper reports an experiment to assess competition between these two tree species for nitrogen – one of the main nutrients needed for plant growth. The research team used an isotope of nitrogen that could be traced from when it was added to the soil, to uptake by and then movement through the plants. They concluded that there was minimum competition between the trees during the first four years, indicating that the two species could be grown together in an agroforestry system.
This was collaborative research involving Griffith University in Brisbane, the Ministry of Forestry and Research and SPE Analytical, both in Honiara, and the Instituto de Ecología, Xalapa, Mexico.
Reference: V.W. Vigulu, T.J. Blumfield, F. Reverchon, Z.H. Xu and S. S. Tutua (2017) Competition for nitrogen between trees in a mixed-species plantation in the Solomon Islands. Australian Forestry, Vol. 80, No. 3, pp. 135–142. DOI: 10.1080/00049158.2017.1326093
The open-source publication of the above paper is part of wider initiative by ACIAR to disseminate the results of its projects as widely as possible. The move towards supporting open access is in line with ACIAR’s thinking on free and fair knowledge sharing in pursuit of more productive and sustainable agricultural systems.