Spacing and Genotype on Height and Diameter Growth of Four Eucalyptus Under Short Rotation

B B Kirongo,J Hitimana,K Senelwa,L Etiegni,A S Mbelase

doi:10.7226/jtfm.18.1.1

Abstract

In this paper, the dynamic change in tree height, diameter at breast height (dbh), and ground line diameter (gld) at different density was studied. Trial sites were established in Chepkoilel and Nangili areas of western Kenya. Eight tree species (2 hybrid eucalyptus clones; GC 10 and GC 167), 1 eucalyptus local landrace, 2 agroforestry ( Grevillea robusta and Markhamia lutea ), 1 pure eucalyptus ( Eucalyptus grandis ), and 2 preferred local species ( Maesopsis eminii and Khaya nyasica ) were planted on each site. This paper however focuses on the effect of spacing on the height, dbh, and gld growth of the 4 eucalyptus genotypes viz (2 eucalyptus hybrid clones, 1 eucalyptus local landrace, and 1 pure Eucalyptus grandis). These were planted at 10 different spacings (0.6-, 0.8-, 1.0-, 1.2-, 1.4-, 1.6-, 1.8-, 2.0-, 2.2-, and 2.4-by-1.0 m; these being some of the most common spacings used by farmers) in a Nelder radial experimental design in 4 replications. Measurements of height, dbh, and gld were taken at intervals of 6 months over 3 years. The data was subjected to an analysis of variance to determine if there were statistically significant (p = 0.05) differences in tree growth with spacing levels. The results showed that tree growth was significantly influenced by spacing and genotype with the best spacing being 2.4-by-1.0 m, indicated that the relative growth rates of height dbh, gld, and increased with increasing the distance between trees but decreased with age. After 3 years the best spacing for optimal overall tree growth was 2.4-by-1.0 m and GC10 being the outstanding genotype. Of the 2 sites, trees performed better in Nangili. The results from this study further pinpoint the importance of species-site-matching using improved germplasm and planting trees at the correct spacing for optimal growth. Keywords : tree growth, spacing, eucalyptus hybrid clones, short rotation forestry, species site matching

Highlights

Short rotation forestry (SRF) is defined as the silvicultural practice of cultivating fast growing trees that reach their economically optimum size in a much shorter period
The trees in SRF are planted at spacings that allow for quick growth and easy harvesting
It suffices to note further that there being no statistically significant effect of spacing on the mean tree height does not mean that the mean tree heights at different spacing levels are the same

Summary

Introduction

Short rotation forestry (SRF) is defined as the silvicultural practice of cultivating fast growing trees that reach their economically optimum size in a much shorter period. In their publication on short rotation forestry in Kenya, Senelwa and Sims (1997) defined SRF as planted tree crops which reach economic maturity between 5–15 years. The concept of biomass production from SRF entails planting fast growing trees at higher stocking densities (sometimes greater than 3,000 stems ha-1) than those used in conventional plantation forestry practices. The objective of the high stocking density is to achieve rapid canopy closure and high productivity (Senelwa & Sims 1997). This should be carefully done to avoid excessive intra-specific competition and loss of volume and value (Kirongo 2000; Kirongo et al 2005). It has a lot of potential in reducing deforestation, destruction of natural vegetation, and meeting wood fuel requirements, especially given that it is a clean, renewable resource with numerous additional environmental benefits (e.g. carbon sequestration, soil protection against erosion resulting in positive impacts on soil fertility in farms, and increased agricultural production)

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Conclusion