Changes in leaf function and canopy structure with tree age
From: Croft, H. Chen, J.M. and Noland, T. (2014) Stand age effects on Boreal forest physiology using a long time-series of satellite data. Forest Ecology and Management, 328: 202-208
Many ecosystem variables and processes show a relationship with stand age, including leaf area index (LAI), nutrient and water cycling, biomass production and photosynthesis. However, investigations into stand age dependency have typically focused on stand structure and are limited by the availability of measurement sites. This study used a measured chronosequence of 9 sites, ranging in age from 15-90 years, supported by repeated satellite-derived data from a long time series (1989-2011). The measured LAI and leaf chlorophyll chronosequence showed an excellent correspondence with the VI-derived LAI and chlorophyll over time, modelled from the satellite archive. The temporal dependency of LAI and leaf chlorophyll with stand age was quantified through the fitting of a spherical model (chlorophyll = 44 years; LAI = 22 years), after which further increases in forest age did not increase leaf chlorophyll or LAI. The differences in temporal lags indicates differences in the maturation period for leaf biochemistry and canopy physical structure, with LAI likely related to a reduction in stand density. The demonstrated stand age-dependency of leaf chlorophyll content is crucial for understanding stand age effects on photosynthetic processes and carbon assimilation, both for quantifying net primary production (NPP) within carbon budgets and for guiding forest management and harvesting strategies in light of a changing climate.
Modelled chlorophyll content (first panel) and LAI (second panel) from Landsat-derived data from 1989-2010, alongside measured ground data, where α = range value.
Mapped changes in leaf chlorophyll values from 2001-2010.