Growth rings in tree species from the Tana river floodplain, Kenya

Growth rings of 19 tree species obtained from the Tana riverine forests in Kenya were studied for potential usefulness in dendrochronology. Among the growth ring characteristics used to qualitatively evaluate the potential usefulness of each species for dendrochronology included: distinctiveness of ring boundaries, ring circuit uniformity, ring wedging and ring sensitivity. Five species were identified as having the most desirable growth ring characteristics and therefore presented the best opportunity to crossdate ring width series among different trees. Crossdating among different trees would lead to the development of tree ring chronologies. These species included Acacia elatior, Acacia robusta, Tamarindus indica and Newtonia hildebrandtii, common on inactive levees occurring toward the edge of the floodplain, and Rinorea elliptica, an understory species found on levees. The timing of growth ring formation and exogenous factors responsible for its formation are yet to be identified. Drought conditions during the low river flow months of August and September are thought responsible for initiation of ring formation as these species grow in a semi-arid region and are thus entirely dependent on ground water.Keywords: cross dating; tree ring analysis; marginal parenchyma; periodicity; wood anatomyJournal of East African Natural History Vol. 95 (2) 2006: pp. 181-21