Spatiotemporal variation of bark pH on the bole of a mature Cryptomeria japonica D. Don (Japanese cedar) tree

The agar–agar panel method identified circumferential, vertical, and temporal variations in the bark pH of a Japanese cedar tree in detail, including high-resolution distribution reflecting the bark’s microrelief.

The morphology of bark surfaces is heterogeneous on any given tree, especially rough-barked trees, often changing along a vertical gradient from top to bottom and circumferentially. This study sought to better understand the intricacies of the spatiotemporal changes of bark pH distribution on the bole of a mature Cryptomeria japonica D. Don (Japanese cedar) tree in Taiwan by using agar–agar panels. Agar–agar panels were positioned at the four cardinal directions at seven different heights along the tree bole on six separate sampling dates ( \(n = 134\) $n=134$ ) to study the temporal variation of bark pH, while an additional 48.5 agar–agar panels were arranged radially at three tree heights (in zones 2 (30 m), 4 (20 m), and 7 (5 m)) to study the circumferential variation of bark pH. The changes in bark pH were found to vary across time, direction, height, and circumferential position, presumably due to the abiotic factors (e.g., fog) prior to sampling as well as changes in bark morphological patterns around the tree bole. This study demonstrates the highly dynamic temporal and spatial variability of bark pH. In particular, bark pH was found to be lower in the furrows as compared to the bark ridges, albeit with differing pH at different times. Future work should couple the use of agar–agar panels with mathematical modeling to quantify the interrelationships among bark morphology, bark pH, solute leaching, and mass flux along the complex network of interconnected furrows and ridges of tree stems.