Mangrove growth rings: fact or fiction? |
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Authors: | Elisabeth M R Robert Nele Schmitz Judith Auma Okello Ilse Boeren Hans Beeckman Nico Koedam |
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Institution: | (1) Laboratory for Plant Biology and Nature Management (APNA), Vrije Universiteit Brussel (VUB), Pleinlaan 2, 1050 Brussels, Belgium;(2) Laboratory for Wood Biology and Xylarium, Royal Museum for Central Africa (RMCA), Leuvensesteenweg 13, 3080 Tervuren, Belgium;(3) Kenya Marine and Fisheries Research Institute (KMFRI), Headquarter and Mombasa Station, P.O. Box 81651 080100, Mombasa, Kenya;(4) Institute of Botany (210), University of Stuttgart-Hohenheim, 70593 Stuttgart, Germany;(5) Research Group Ecosystem Management, Research Institute for Nature and Forests (INBO), Kliniekstraat 25, 1070 Brussels, Belgium |
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Abstract: | The analysis of tree rings in the tropics is less straightforward than in temperate areas with a demarcated unfavourable winter
season. But especially in mangroves, the highly dynamic intertidal environment and the overriding ecological drivers therein
have been a reason for questioning the existence of growth rings. This study aimed at casting light on growth rings in mangroves.
In six mangrove species growing in Gazi Bay, Kenya (Sonneratia alba, Heritiera littoralis, Ceriops tagal, Bruguiera gymnorrhiza, Xylocarpus granatum and Lumnitzera racemosa), the occurrence of growth rings was examined. Growth rate of each species was determined based on a 1-year period using
the cambial marking technique. The effect of climate was furthermore considered by comparing the results with a number of
wood samples originating from contrasting climatic regions. We can conclude that for growth rings to appear in mangroves more
than one condition has to be fulfilled, making general statements impossible and explaining the prevalent uncertainty. Climatic
conditions that result in a range of soil water salinity experienced over the year are a prerequisite for the formation of
growth rings. For species with an anatomy characterized by indistinct ring boundaries, this should be combined with a growth
rate of at least 0.3 mm/year. The use of growth rings for age or growth rate determinations should thus be evaluated on a
case by case basis. |
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