Litterfall dynamics in a mixed conifer‐angiosperm forest in northern New Zealand

Abstract

SummaryLitterfall in a mixed conifer‐angiosperm temperate forest in northern New Zealand was traced for 5 years to determine the patterns of litter production and turnover for conifer and angiosperm components of the forest. Basal area and above‐ground biomass was shared approximately equally between conifer (mostly Agathis australis; New Zealand kauri) and angiosperm species (plus tree ferns). The five‐year mean annual litterfall, excluding macro‐litter, was 7.76± 0.39(SEM) t ha−1 and ranged from 6.77±0.70 t ha−1 in 1983–4 to 8.79±1.00 t ha−1 in 1987–8. Mean monthly litterfall showed a strong seasonal pattern with low rates in winter and early spring, increasing to a peak in early autumn. There were major differences in the nature and timing of litterfall between the conifer and angiosperm fractions. Angiosperm leaf litter reached a maximum in early summer, while conifer litterfall showed highest rates for leaves, twigs and cone scales in late summer‐autumn. Conifer reproductive structures (strobili and cone scales) contributed from 13 to 21% of total litterfall, a value high relative to other temperate forests. However, conifer leaf turnover was low relative to that for the angiosperms.Size of the microlitter store was 16.16±1.97 t ha−1 prior to conifer cone fall, and 18.70±2.02 t ha−1 following it, and conifer litter made up 76–78% of the total litter store. The estimated mean annual decomposition constant, k, was 0.39 overall, 0.33 for conifer leaf litter and 0.71 for angiosperm leaf litter, values which agree well with previously published rates for decomposition in this forest stand. Differences in the costs of biomass production and rates of turnover, as measured by litterfall and decomposition, may help to explain the functional coexistence of conifers and angiosperms in mixed forests.