SamenvattingThough assumed for a long time to be absent in tropical trees, several studies unveiled
growth rings in these trees and for the first time in mangroves by Verheyden et al.,
(2004) the presence and annual nature of rings in Rhizophora mucronata was noted.
Furthermore, understanding the dynamics behind wood production and its interaction
with the environment would provide important information for setting up
management plans for silvicultural practices. The main aim of this study therefore
was to explore wood formation in six Kenyan mangrove species and to gain insight in
its relationship with the environment.
Cambial marking (pinning) was done in six mangrove tree species (Sonneratia alba,
Bruguiera gymnorrhiza, Ceriops tagal, Lumnitzera racemosa, Heritiera littoralis and
Xylocarpus granatum) in May 2005 and February 2006 in Gazi bay, Kenya. These
were later cut down in June 2006 dried and brought to Xylarium of the Royal
Museum for Central Africa, Tervuren, Belgium as part of the wood collection. In the
laboratory, they were sawed into transverse sectioned discs, sanded then viewed both
macroscopically and microscopically for counting and determination of clarity of
rings, anatomy of the growth ring borders as well as radial increment measurement.
X. granatum and L. racemosa had very clear rings with well defined borders. While
merging unclear rings was a common phenomenon in S. alba and B. gymnorrhiza, H.
littoralis had exceptionally thick bark and as a result the cambial marking was too
shallow to create a proper reaction leading to imprecision in ring count and radial
growth measurement. C. tagal had clear rings but periodicity could not be defined due
to lack of ring formation during the study period (slow growth). Radial increment was
found to be non uniform over the study period and varying in the different study sites.
Further, the negative effect of Salagenia discata pest on radial growth of S. alba was
shown to display a threshold level below which the attack was not reflected on wood
production. The study thus concluded that X. granatum and L. racemosa both have
potential for use in dendrochronology and that many factors including precipitation,
salinity and phenology all play an integral role in manipulating radial growth to
various degrees in the different species.
|Nico Koedam (Promotor), Nele Schmitz (Co-promotor) & Hans Beeckman (Co-promotor)