The evaluation of δ 13C isotopes of trees to determine past regeneration environments

Abstract

The effects of past regeneration environments and canopy position on δ 13C signals in leaf and wood tissue were examined. Leaves were collected from various canopy positions both inside and outside of closed forest and from gaps ranging in size from 75 to 829 m 2. Trees of known recruitment environments were cored and wood was extracted from the outer rings and from the centre of the tree. Whole tissue was converted to holocellulose for isotopic analysis. An elevation of ∼1‰ in δ 13C was associated with a conversion from whole wood to holocellulose. A regression of whole tissue vs. holocellulose produced an R 2=0.84. A significant depression in δ 13C values of leaf tissue was observed in areas under a closed canopy. Leaves sampled from open areas, or from a well-lit canopy position, had more positive δ 13C values. In gaps, δ 13C of the leaves increased with increasing gap size. The existence of a significant difference between δ 13C of inner and outer woods within a tree indicates that it is possible to distinguish between differing recruitment environments with this technique. The data indicate that the regeneration environment confers a specific isotopic signal on a tree that can be detected later in its life-span. The method can be used to determine recruitment environments and should allow for grouping of species into functional types. The potential uses of this ecological tool are important for restoration ecology and the management of forest ecosystems.