Mangrove growth rings: fact or fiction?

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.

Occurrence of seasonal water replacement in mangrove soil and the trunk growth response of Avicennia alba related to salinity changes in a tropical monsoon climate

“…Many authors have discussed the presence of growth rings in mangrove wood (Chowdhury et al, ; Menezes, Berger, & Worbes, ; Nazim, Ahmed, Shaukai, Khan, & Ali, ; Schmitz et al, ; Verheyden, Ridder, Schmitz, Beekman, & Koedam, ). Climatic conditions that cause seasonal fluctuations in soil water salinity are a prerequisite for the formation of growth rings (Robert et al, ). Thus, we hypothesize that the replacement of soil water between the rainy and dry seasons affects soil salinity and thus the growth of mangroves.…”

A Review of Sea-Level Rise Effect on Mangrove Forest Species: Anatomical and Morphological Modifications

“…In mangroves, the highly dynamic intertidal environment and the overriding ecological drivers difficult the existence of growth rings. Nevertheless, climatic conditions that result in a range of soil water salinity experienced over the year are a prerequisite for the formation of growth ring (Robert et al, 2011). Recently, annual growth rings were discovered in Rhizophora mucronata in Kenya, but the ring boundaries are indistinct and growth ring consists of a low vessel density earlywood, produced during the rainy seasons, and a high vessel density latewood, produced during the dry season.…”

Issues and Challenges of Mangrove conservation in the Anthropocene

“…The anatomical basis and reliability of annual ring formation have been submitted to severe tests, and the conclusion was that the use of growth rings for age or growth rate determinations should be evaluated on a case by case basis, and accompanied by simultaneous measurements of stem growth (Robert et al, 2011). Even in cases when no welldefined rings are formed, application of high-resolution analysis of stable isotopes ( 18 O and 13 C) has proved annual ciclycity in tree growth (Verheyden et al, 2004).…”