Comparing microbial colonisation and Decay Rates of Wood from Sound and Aphid-Killed Kenyan-Grown Mexican Cypress (Cupressus lusitanica)
Samples of wood from 10, 15, and 30-year old trees attacked and killed by the cypress aphid (Cinara cupressi) and sound Kenyan-grown Cupressus lusitanica trees were investigated for variations in moisture content, density and susceptibility to microbial decay. MC varied with tree age, a normal trend, and between samples from aphid-killed and sound trees. In samples from 10, 15 and 20-year old sound trees, MC was higher by 11.1%, 8.6% and 7.8% respectively, than in samples from aphid-killed trees. Similarly density varied with age, to be expected, and between samples from aphid-killed and sound trees, being 3.5%, 2.6% and 2.1% higher in samples from sound trees of the 3 age classes. Exposure to riverwater and soil revealed a pattern of microbial colonisation and degradation normal for each environment. In riverwater, samples were mainly colonised by bacteria, actinomycetes, stain fungi, and softrot fungi, bacteria and softrot fungi being the main wood degraders, but their action on samples were slow and generally moderate in severity of attack. Exposure to soil followed a similar pattern of colonisation, the principal wood decaying organisms being bacteria and softrot fungi, and to a lesser extent brown and white rot fungi. Samples from both aphid-killed and sound trees were colonised and decayed in a similar fashion, but microbial decay in the soil environment was more pronounced than in riverwater. The soil block test recorded low weight losses after 2 weeks exposure, rising to between 29% and 36% after 12 weeks, with no significant differences between weight losses in samples from aphid-killed and sound trees, or tree age. The results of the study revealed that there are no significant differences between microbial decay susceptibility of wood from aphid-killed and sound trees, and that slight differences in MC and density did not influence decay rate. Consequently, wood from aphid-killed cypress trees should not be considered as of inferior quality, in terms of decay susceptibility, by wood processors and consumers.