In the understory of an evergreen forest, how leaf traits and light availability affect whole-plant carbon balance is less investigated. We predicted that variety of leaf traits can contribute to maintain whole-plant carbon balance positive in a shaded understory, and tested it in a subtropical forest in Japan, where typhoon disturbance is relatively frequently occurred. We estimated the potential net assimilation rate (NAR) of understory sites, including typhoon-disturbed sites, by measuring photosynthetic active photon flux density (PPFD). Then, for understory saplings we applied our original ‘leaf relative growth rate’ (RGRleaf) method to simulate the whole-plant carbon balance
according to its relation to leaf mass per area (LMA), leaf lifespan (LL), net assimilation rate (NAR), and leaf
partitioning rate (LP). RGRleaf > 0 indicates positive growth. Under the fully closed canopy the potential NAR was estimated to be < 50 g glucose m-2 yr-1, where most species were predicted to have a negative RGRleaf. However, with a better NAR of the site which had likely experienced a past typhoon attack, most species would have positive RGRleaf. With those low-level NAR, neither LMA nor LL had significant relationships to RGRleaf. There, saplings’ LMA and LL showed positive relationship, but LMA tended to be smaller relative to LL compared to known global trend. With higher-level NAR, it is predicted that having smaller LMA and LL is advantageous to have large RGRleaf. We concluded that balance of the leaf traits is important to maintain positive whole plant carbon balance in the low light understory, and then, various leaf traits were valid for growth in a low light understory. The moderate shade environment brought by typhoon disturbances may help to exist species with various leaf traits.
By extending the previous investigation of the machine grading classification, this study examined the visual
grading classification to determine the size effect parameter for the size adjustment factor used to reduce the
design bending strength in the Japanese agricultural standard for sawn lumber (JAS 1083). First, by examining the relationship between the specimen depth and bending strength of various species and grades, including the machine grading classification, it was deemed realistic to adopt at present a single value for the size effect parameter for all species and grades, rather not by species and grades. Then, after comparing the size adjustment factor for the design strength for the visual grades with a 5% lower limit/design strength, it was considered logical to assume the same value for the size effect parameter of the visual grading classification as to be 0.4-0.5 that obtained from the machine grading classification. However, some problems persist, and the values of the size effect parameters need to be reexamined after accumulating bending strength data obtained from the large-diameter lumber, which will increase in the future.
To improve labor productivity, we developed an unmanned work system for the logging process in the form of an automated traveling forwarder. As the vehicle does not require a driver for a large part of operating time without reduction in the amount of production, thus resulting in increased labor productivity. The prototype has three features: 1) Traveling on a strip road and the unloading process are automated, whereas the loading of logs from a felling site is performed by workers. 2) The vehicle has an automated traveling function that uses an electromagnetic induction system, which allows switchback driving so that existing strip roads can be used. 3) By making it possible to automatically travel at the same speed as when an operator is driving, working efficiency is not reduced. The result of conducting a logging operation test using the prototype confirmed that the time required for manned work processes such as loading from felling sites was about one-third of the day. In addition, the prototype vehicle was able to travel accurately without the need to widen the existing strip road. However, it was also confirmed that a prototype equipped with an unloading mechanism will require a larger yard to store the logs because it cannot make piles. The present study showed that the unmanned logging using an automatic traveling forwarder have possibility to improve labor productivity. Further researches on automatic loading systems and ancillary work such as laying electric wires for unmanned operation are necessary.
In this study, we evaluated the distribution of weight percent gain (WPG) in the longitudinal direction of a sugi (Cryptomeria japonica D. Don) heartwood sample with a size of 100 mm (longitudinal direction) × 20 mm (radial direction) × 20 mm (tangential direction), which was acetylated using supercritical carbon dioxide (CO2). Two connected batch containers were used for the acetylation treatment. One of them contained a mixture of supercritical CO2 and acetic anhydride, which was injected into the second batch container containing a vertically fixed oven-dried wood specimen and small amount of acetic anhydride. The acetylation was performed at 120 C˚ and 10–12 MPa for 8 h using various amounts of acetic anhydride. The experiments revealed that the mixture of acetic anhydride with supercritical CO2 contributed to the acetylation on the upper side of the specimen, penetrating mainly through the upper cross section. Instead, acetic anhydride contained in the batch container with the specimen, contributed to the acetylation on the lower side of the specimen by penetrating from the bottom cross section. It was thus assumed that gaseous acetic anhydride in the batch container was pushed into the specimen by the injected supercritical CO2. Therefore, it was demonstrated that the specimen can be uniformly acetylated by adding the appropriate amount of acetic anhydride in both batch containers.
We monitored the stand structure of an old secondary lucidophyllous forest in Takaoka, Miyazaki, southwestern
Japan for 21 years (1998–2019). Based on data collected from 10 tree censuses of the 1-ha permanent plot, stem
density decreased from 1,532 stems/ha in 1998 to 1,379 stems/ha in 2019. Basal area (BA) increased from 45.74
m2/ha in 1998 to 50.97 m2/ha in 2014, but decreased during the period from 2015 to 2019 because of Castanopsis sieboldii mortality due to a number of typhoon disturbances. The average mortality rate throughout the monitoring period was 1.51%/year, which was higher than the recruitment rate for the same period (1.01%/year). The tree census in 2019 revealed the loss of some small size trees of Quercus salicina and C. sieboldii, which suggests typhoon impacts on the regeneration and species composition of this forest in the near future.
Observations of precipitation and runoff have been conducted since the inception of the Takaragawa Experimental
Watershed (Meteorological observation site: 36°51' N and 139°01' E, MSL 816-1945 m). This report describes daily precipitation and runoff from 2011 through 2016. During this period, the tipping bucket was replaced with a new one.