Spatial assessment of nitrogen content in canopy leaf is important to understand the spatial variability of nitrogen cycle in forest ecosystem, because leaf nitrogen closely relate to quality and quantity in litterfall, nutrient cycle and plant nutrient uptake. This study aims to develop and analyze the assessment method to estimate spatial distribution of nitrogen content in canopy leaf in natural forest with heterogeneous species composition and complexed canopy structure using unmanned aerial vehicle (UAV) with digital camera through Structure from Motion (SfM). The study was conducted in a natural cool-temperate mixed forest in Uryu experimental forest, Hokkaido University located in northern Hokkaido, Japan. Digital image for single leaf in dominated 8 tree species (2 evergreen coniferous and 6 deciduous broad-leaved species) and Sasa dwarf bamboo as understory vegetation were taken to analyze the relationship to leaf nitrogen content using various RGB indicators. There were significant correlations between RGB indicators and leaf nitrogen content in coniferous and broad-leaved tree (with Sasa understory), respectively. We developed a method to estimate the spatial distribution of each vegetation using the aerial digital images taken from UAV derived digital surface model (DSM) and their seasonal differences between leave on and off periods. Spatial distribution of nitrogen content in canopy leaf was mapped from the relationship between the RGB indicators and leaf nitrogen content on the vegetation map. From this result, spatial dynamics in nitrogen cycling of forest ecosystem can be visualized and mapped out to help to understand detail locational difference.

Vertical ¹³⁷Cs distribution in the barks of Japanese cedar (Cryptomeria japonica) trees in the initial phase after the Fukushima Dai-ichi Nuclear Power Plant accident was investigated in several forests in Fukushima prefecture in 2012. 12 trees that were felled in 7 forests were used in the present study. ¹³⁷Cs concentration in bark samples taken at various heights were determined using a NaI spectrometer. In order to compare the vertical ¹³⁷Cs distribution in the bark of each tree, ¹³⁷Cs concentration was normalized to that at the lowest height from the ground. An increase of ¹³⁷Cs concentration from the bottom to the tree top was clearly observed for 9 trees. The inner barks were almost constant at any vertical positions. Large part of the ¹³⁷Cs in the barks existed in the outer barks. These results indicated that the vertical distribution of the outer ¹³⁷Cs contamination on the barks in 2012 had a common ¹³⁷Cs concentration profiles against the tree top with the different contamination levels of the forests and different height of the tree.

To quantitatively clarify the distinct impact of forest clearing, soil movement was investigated using sediment trap boxes in and out of the cutover area. After collecting and studying the data related to the micro-topography, slope inclination and floor cover percentage, the difference of soil movement and seasonal changes were evaluated at 30 points in 6 plots. The amount of soil movement changed after the seasonal precipitation events, where the winter season was less than summer typhoon season, and both were less than the rainy season prior to summer owing to the brunt of only two typhoons. The data showed the largest value during the typhoon season, especially in a plot that was severely disturbed by heavy machinery. Steep forest plots also displayed rather large values in soil amount. By contrast, regardless of the amount of precipitation, the plots primarily covered with understory vegetation demonstrated low values similar to the plots located on gentle slopes in forests. Considering the relationship between the amount of soil movement, slope inclination, floor cover percentage and soil thickness; the understory vegetation was shown to have a significant influence on soil movement. However, when the floor cover percentage was approximately 50% or below, the amount of soil movement was more dependent on slope inclination and soil thickness.