Evergreen and ever growing – Stem and canopy growth dynamics of a temperate eucalypt forest

Abstract

Irregular growth rings and long-lived leaves present challenges to quantify stem growth and canopy dynamics of evergreen eucalypt trees, which has impeded understanding of seasonal and inter-year biomass allocation in temperate eucalypt forests. To address this knowledge gap, we examined the sub-annual dynamics of stem and canopy growth by tree canopy class of three co-occurring species over 35months in a temperate eucalypt forest of southeastern Australia. We used dendrometers to monitor basal area increments and daily terrestrial lidar scans to monitor integrated and height-specific canopy dynamics. Associations with concomitant weather data and stand-level carbon fluxes were used to enhance understanding of biomass allocation patterns.Comparisons of growth patterns indicated seasonal asynchronicity of stem and crown growth: the canopy expanded mainly in summer and early autumn, and the stems grew mainly in spring and autumn, but also to a lesser degree in winter. Eucalypts in the dominant crown classes grew all year, with growth allocated to crown expansion and thickening in the summer months, or to stem growth in all other months. Canopy volume was stable during the first part of the study period and subsequently increased by 20%. However, stratum-specific dynamics indicated a distinct seasonality of canopy turnover, characterised by volume gains at the top of the canopy and concurrent volume losses in the middle stratum during summer. Growth patterns, as either canopy expansion or stem increment, were not clearly associated with ecosystem-scale carbon dynamics. In addition, relationships of growth with climatic variables appeared to be associative rather than causative, indicating that allocation dynamics to root growth and nonstructural carbohydrate pools will be essential in explaining ecosystem carbon dynamics in temperate eucalypt forests.