YIELD OF <em>GREVILLEA</em> <em>ROBUSTA</em> IN THE MAIZE FIELDS OF KENYA

Authors

  • J. Miina & T. Pukkala

Keywords:

Agroforestry, competition index, spatial model, individual-tree model, simulation model, silky oak, silver oak, Zea mays

Abstract

The study developed individual-tree diameter and height models for Grevillea robusta growing in the maize fields of central Kenya. This type of agroforestry farming has become very popular in the central highlands of Kenya, producing both staple food and wood for various purposes. The yield of wood of this
kind of production system is most probably very significant but little investigated. This study used tree-level data from 24 temporary plots to model the dependence of tree diameter on tree age and competition by other trees. Competition was described with a competition index computed from the distances and diameters of neighbour trees. Another model was developed for predicting the tree height from tree age and diameter. The diameter model explained 65% of the variation in diameter if tree age was the only predictor and 68% if competition index was used as another predictor. The height model explained 82% of the variation in tree height. The models were utilised in a simulation model, which was run for two different initial stands, one representing a regular and the other an irregular spatial distribution of trees. In the case simulations covering 30 years, the mean annual volume increment of the rather sparse Grevillea robusta stands in agroforestry fields (about 200 trees ha-1) ranged from 8 to 24 m3 ha year-1. The highest yield for wood was obtained when the stand volume was left to increase significantly from its initial value, indicating that the current growing stock volumes are clearly too low for
maximal wood production. However, higher stand volumes would most probably
significantly decrease maize yields.

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Published

2022-08-23

How to Cite

J. Miina & T. Pukkala. (2022). YIELD OF <em>GREVILLEA</em> <em>ROBUSTA</em> IN THE MAIZE FIELDS OF KENYA. Journal of Tropical Forest Science (JTFS), 14(4), 485–498. Retrieved from https://jtfs.frim.gov.my/jtfs/article/view/1305

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