Stable isotopic (δ ¹⁵ N, δ ¹³ C) analysis of wood in trees growing in past and present colonies of burrow‐nesting seabirds in New Zealand. I. δ ¹⁵ N in two species of conifer (Podocarpaceae) from a mainland colony of Westland petrels ( <i>Procellaria westlandica</i> ), Punakaiki, South Island

Abstract

Abstract Marine nitrogen (N) has been traced into terrestrial and freshwater food chains at petrel (Aves: Procellariiformes) colonies on the South Island of New Zealand, but the effects of N or other marine‐derived nutrients on the productivity of mainland forests are unknown. Mean ring widths in matai (Prumnopitys taxifolia; n = 3) and rimu ( Dacrydium cupressinum; n = 2 ) trees growing in a Westland petrel ( Procellaria westlandica ) colony were 0.9–1.4 mm yr –1 , similar to ring widths reported elsewhere. However, series of much wider rings in cores showed that trees in a petrel colony can experience periods of accelerated growth. δ 15 N values of whole wood were, at 3.2–11.1%, significantly enriched in comparison to other temperate forest trees. The highest δ 15 N values were at the cambial and pith ends of different cores, so isotopic fractionation during N remobilisation is unlikely to have been significant. The radial extent of 15 N enrichment suggests that petrels have bred at the site since at least the mid 18th century.