Evaluation of spatial and temporal variation in fine root dynamics in a temperate mixed forest using a scanner method

ABSTRACT Understanding fine root phenology at the stand scale is crucial for elucidating how carbon and nutrient cycling in forest systems respond to climate change. This study aimed to reveal the spatio-temporal variations in the fine root phenology in a mixed temperate forest in Japan using scanner method. The spatio-temporal variation in the fine root areas was evaluated using two scales: among four plots in the stand and among four partitioned areas in the scanner image. Here, we hypothesized that root phenology would vary on both scales due to the mixture of species-specific phenologies, which means endogenous factors to have a larger impact than exogenous factors such as temperature and precipitation. The timing of the production peak varied among years, though it concentrated within a specific period of the year in all plots. In all plots, active root mortality dynamics were observed in the summer. These results suggested exogenous factors as stronger regulators of fine root production and mortality than endogenous factors. Root phenology within the scanner images is highly heterogeneous, suggesting the significance of broad observation surfaces, such as those acquired using the scanner method, in comprehending the representative phenology of root dynamics at a stand scale. This study revealed that fine root phenology had a synchronized pattern on the stand scale, even though high spatial variation existed in the scale size of the scanner. Differences in root phenology that were influenced by internal factors of the species were masked on the stand scale.