Variability of tree-ring δ 13C in Taiwan fir: Growth effect and response to May–October temperatures

Abstract

We have analyzed the β 13C of tree-ring cellulose in three radial directions from a 120-year old (1873–1992) Taiwan fir ( Abies Kawakamii (Hayata) Ito) growing on the margin of a relatively open forest at an elevation of approximately 3,844 m in southern Taiwan. The overall δ 13C trend increases from approximately −24.0‰ to −22.4‰ to 1950, then drops sharply and fluctuates around an averaged value of −23.2‰ to 1992. Moreover, values of δ 13C in different radial directions reveal a greater variability before 1950 than those after 1950 with the maximal and averaged amplitudes of 1.62‰ vs. 1.30‰ and 0.70 ± 0.36‰ vs. 0.55 ± 0.31‰, respectively. A plot of annual increase in ring-area further shows that the growth of Taiwan fir has essentially stabilized in 1950. This synchronous change in 1950 points to a possible growth control on the observed variability of δ 13C before 1950. The variation in δ 13C from 1950 to 1992, however, is found to correlate inversely to the mean May–October temperatures and a response coefficient of −0.46‰ °C −1 is derived. Additional analysis of δ 13C across five consecutive rings reveals that δ 13C can vary up to 1.5‰ and becomes heavier from the early to the late woods. Such seasonal variations further appear to be different among individual rings. In view of these results, we conclude that apart from the commonly observed increase in tree-ring δ 13C of forest trees due to the canopy effect, a similar increasing trend can also be seen in the coniferous trees and may be attributed to an accompanying decrease in the stomatal conductance with tree age. We further propose that an adequate estimate of the response of tree-ring δ 13C to climatic and/or environmental changes must be performed on trees during stable growth.