Discontinuous DBH–height relationship of Cryptomeria japonica on Yakushima Island: effect of frequent typhoons on the maximum height

Abstract

The mountain zone of Yakushima Island is covered with a mixed conifer-broadleaved forest dominated by old-growth Cryptomeria japonica (L.f.) D. Don trees. Even though Yakushima Island has been frequently struck by typhoons with wind velocities exceeding 55 m s À1 , the Cr. japonica trees in the mountain zone have survived for thousands of years without fatal damage. To evaluate the effect of storms on tree growth, the relationships between the stem diameter at breast height (DBH) and the heights of Cr. japonica and coexistent tree species were investigated. Two models based on an expanded allometric equation and a discontinuous piecewise allometric equation, respectively, to represent DBH-height relationships were evaluated. In all plots, the DBH-height relationship of Cr. japonica was discontinuous between small DBH and large DBH individuals. The tops of the large DBH individuals of Cr. japonica were lost to strong winds. However in each instance, they occupied the highest position in the canopy, even if they had lost their tops. In contrast, the DBH-height relationships of subcanopy broadleaved species were continuous in many plots and the equilibrium heights of the dominant broadleaved species were similar and almost in the same order regardless of the canopy heights of Cr. japonica. These results revealed a constant vertical structure in the Cr. japonica forest on Yakushima Island. Our results demonstrate a vertical niche segregation in the forest under high wind pressures and such vertical structure enables effective use of forest space and increases the basal area density.

Estimating Tree Height and Diameter at Breast Height (DBH) from Digital Surface Models and Orthophotos Obtained with an Unmanned Aerial System for a Japanese Cypress (Chamaecyparis obtusa) Forest

“…The literature indicates that DBH height trajectory may differ depending on leaf amounts [43]. Light availability and wind play roles in tree architecture [34,35,44], as does water availability [45]. Therefore, instead of estimating DBH from tree heights, we focused on estimating it from the canopy structure.…”

“…Digital surface models (DSMs) and ultra-fine resolution orthophotos can be directly utilized to estimate tree heights and canopy size. Usually, these data are difficult to extract correctly because the height of a tree depends on site conditions (higher/lower stem density; [33]), decreased interpretation of surface area at dense forest sites [30], or even exposure to light and wind [34,35]. In addition, directly estimating parameters in lower layers, such as DBH (Diameter at Breast Height), from DSM or orthophotos is also difficult because of tree canopies, particularly in dense forest environments.…”

Comparing 30-year diameter censuses and tree-ring chronologies in natural old-growth Cryptomeria japonica forest on Yakushima Island, Japan

“…The accuracy of measurements of large trees in natural old-grown forests needs to be improved; in particular, special attention should be paid to trees with an average DBH that is much larger than 50 cm, as were measured in this study. Previous studies in our study area have analyzed stand structure using census data (Yoshida and Imanaga 1990;Takashima 2009, Takashima et al 2009). These studies did not deal with the DBH increment of individual trees calculated from time-series census data, which was found to be problematic in the present study.…”

“…1). Study plots were covered in natural, uneven-aged, mixed, conifer-broadleaved forest dominated by C. japonica (Takashima 2009). Study plots were located between 850 and 1,250 m a.s.l.…”

“…Therefore, this study focused on 30 years of diameter census and tree-ring chronologies from natural oldgrowth Cryptomeria japonica forest on Yakushima Island, which includes trees of a few hundred years in age. There are some previous studies using census data in our study area (Yoshida and Imanaga 1990;Takashima 2009;Takashima et al 2009;Yoshida and Imanaga 1990). However, some problems may arise and create difficulties each time a census is conducted, such as minus or exaggerated growth.…”