Tree Growth Rings in Tropical Peat Swamp Forests of Kalimantan, Indonesia

Abstract

Tree growth rings are signs of the seasonality of tree growth and indicate how tree productivity relates to environmental factors. We studied the periodicity of tree growth ring formation in seasonally inundated peatlands of Central Kalimantan (southern Borneo), Indonesia. We collected samples from 47 individuals encompassing 27 tree species. About 40% of these species form distinct growth zones, 30% form indistinct ones, and the others were classified as in between. Radiocarbon age datings of single distinct growth zones (or "rings") of two species showing very distinct rings, Horsfieldia crassifolia and Diospyros evena, confirm annual growth periodicity for the former; the latter forms rings in intervals of more than one year. The differences can be explained with species-specific sensitivity to the variable intensity of dry periods. The anatomical feature behind annual rings in Horsfieldia is the formation of marginal parenchyma bands. Tree ring curves of other investigated species with the same anatomical feature from the site show a good congruence with the curves from H. crassifolia. They can therefore be used as indicator species for growth rate estimations in environments with weak seasonality. The investigated peatland species show low annual growth increments compared to other tropical forests.

The growth ring concept: seeking a broader and unambiguous approach covering tropical species

“…Thus, most dendrochronologists consider the criterion of tangential continuity in deciding whether rings are distinct or not (e.g. Schweingruber, ; Worbes et al ., ). Less frequently, tangentially discontinuous rings may be annual (Glock, ).…”

“…Presumably these views were the result of the seductive conviction of a reliable means for discovering the age of trees and reconstructing past climates, the attraction of having a robust, well‐defined and general law which can be applied to the formation of growth rings in all plants, comparable to the physical laws of Isaac Newton, or simply the prevailing view that considered Europe the cradle of world knowledge because of its political, cultural and scientific hegemony. The assumption of rings being essentially annual is part of the myths so created, as was the widely accepted opinion that tropical species do not exhibit growth rings (Worbes et al ., ).…”

“…The growth ring as conceived by dendrochronologists and anatomists of temperate regions is an imposed model of well‐marked, tangentially continuous and annual rings. This pattern also corresponds to a small percentage of species with growth rings in the tropics, and has predominated in studies in the past and present for historical reasons and because of its applications (Worbes & Fichtler, ; Brienen et al ., ; Schöngart et al ., ; Worbes et al ., ). However, when the tropical origin and diversification of angiosperms is taken into account (Philippe et al ., ; Soltis et al ., ), it is probable that the first species with growth rings did not follow this model nor do the great majority existing today.…”

“…Sonsin et al ., ; Silva et al ., ), would possibly be described as indistinct or absent by anatomists of temperate regions (e.g. Worbes, Herawati & Martius, ).…”

“…The degree of distinction of growth rings may vary with the magnification at which the wood is observed. Those which are well defined macroscopically may be difficult to identify microscopically (Malavassi, ; Worbes & Fichtler, ; Worbes et al ., ) and vice versa (Sonsin et al ., ).…”