This study proposed to use the approximate standard deviation as an indicator of the accuracy of an area measured by Global Navigation Satellite System (GNSS) receivers. The standard deviation of the area was derived mathematically based on the shoelace formula using the position of the vertices of the plot and the standard deviation of position errors. The approximate value of the standard deviation was calculated using measured GNSS positions and position errors, instead of theoretical true values, because GNSS cannot measure the true position and its error. This paper gives a mathematical description of the derivation of the standard deviation of the area from GNSS-derived coordinates and those errors. The degree of approximation was also evaluated using a numerical simulation. The results showed a goodness of the approximation such that the error rate of the approximate standard deviation was within ±3％ of the measured values in 90％ of the cases in the simulation. The paper also showed examples of the application of the proposed index in GNSS measurement of area.

The pinewood nematode, Bursaphelenchus xylophilus, is the causative agent of pine wilt disease (PWD). The nematode invades healthy pine trees via feeding wounds and dead pine trees via oviposition wounds made by the Japanese pine sawyer, Monochamus alternatus. We investigated the dispersal pattern of the nematodes invading Pinus thunbergii logs via oviposition wounds and the number of nematodes carried by the vector insects emerging from the logs. Trees killed by felling (felled trees) and those killed by natural infection of PWD in the field (PWD trees) were prepared, and then they were oviposited by M. alternatus. Nematode positive reaction in wood without oviposition wounds, larval frass and emergence holes of the adult insects was significantly higher in the PWD than the felled trees. Although there was no difference in the number of nematodes carried by the insects between the felled and PWD trees, the frequency of the insects carrying more than 10,000 nematodes was significantly higher in the felled than the PWD trees. Our results experimentally suggest that the nematodes invading dead trees from oviposition wounds did not tend to spread throughout the trees and that numerous nematodes were carried by the vector insect even if the trees were killed by some factor other than PWD.

This study aims at achieving the automatic extraction of attributes for influencing tree-marking decisions and decision rules, and constructing classification models for marked trees by employing machine-learning algorithms. A tree-marking exercise was conducted at a research plot comprising 184 trees with natural forest management at the University of Tokyo Hokkaido Forest, located in northern Japan. Forty-seven visual stem indicators, such as the quality and vitality of each marked tree, and diameter at breast height (DBH) were input to machine learning models as attribute data. By employing machine-learning algorithms, automatic extraction of attributes was performed and thereby applied to a feature selection algorithm for classifying marked trees and extracting decision rules, which were then incorporated in the decision-tree algorithm. Performance evaluation of the proposed model was performed with the help of the Matthews correlation coefficient (MCC) index. The obtained results indicate that the majority of the attributes that acquire a higher rank from the results of feature selection are those attributes that can identify marked trees. The top five attributes obtained from the results of feature selection were not able to classify marked trees. However, the top fifteen attributes are adequate for performing the said classification. Furthermore, the high-efficiency proposed model has been designed by adjusting various parameters associated with a machine-learning model. The constructed decision-tree comprised 26 learning models, of which one model has been employed for achieving complete classification of marked trees.

In order to reveal the genetic variation of root traits and their effect on early shoot growth, we investigated the root traits and early shoot growth of cuttings of 193 clones in Cryptomeria japonica. We quantitatively measured seven root traits (root length, root surface area, root volume, average diameter, fine root ratio, root tip density and branch density) and early shoot growth, and assessed their genetic characteristics and relationships between root traits and early shoot growth. The broad-sense heritability of root tip density and branch density was relatively high. There was a strong correlation between traits related to root amount (root length, root surface area and root volume), and these traits also correlated with branch density. Early shoot growth correlated with root length, root surface area, root volume, branch density and fine root ratio. Our results provide a useful genetic basis for root traits and suggest the importance of the root traits as factors influencing shoot growth in C. japonica.

In the summer of 2015, mass mortality of oak trees by Platypus quercivorus occurred in an evergreen broad-leaved forest in Miyazaki, Japan. To reveal the characteristics of damage, we surveyed the damaged tree species, the diameter at breast height (DBH) and the micro topography in the old evergreen broad-leaved forest dominated by Castanopsis cuspidata and C. sieboldii. Attack by P. quercivorus was observed for all 7 fagaceous species occurring in the study site. The percentages of attacked trees were higher for C. cuspidata than for Quercus glauca and Q. salicina. Attack was more often observed for trees over 33 cm DBH. Frequency distribution of DBH was different between tree species, which mostly ranged larger than 33 cm for C. cuspidata. Micro topography did not influence the occurrence of damage. We conclude that DBH was the major factor in selection by beetles and that beetles preferred larger DBH trees over 33cm.

The amendment of soil with superabsorbent polymers (SAPs) has been gaining interest in agriculture and forestry, in both dry and semi-dry lands since the late 1970s. Here, we review studies on the characterization, application, and evaluation of SAPs in forestry and revegetation fields worldwide. SAPs usually absorb amounts of pure water several hundred times their dry weight; however, their absorption capacity decreases significantly for water containing salts and SAP expansion by water is restricted to the soil pore space. Until now, the experiments with SAPs have been mainly conducted on 1) root dipping of seedlings, 2) soil water holding capacity and drought tolerance of tree seedlings, 3) field application of SAPs to planting holes, and 4) gel seeding. The water-holding capacity of the soil increases with the amount of SAP added but the effects of the SAP on soil available water content and plant growth were more evident in sandy soils than in clayey soils. The application of SAP exhibited both positive and negative effects, depending on the soil texture and tree species. Some studies show that overuse of SAPs resulted in low seedling growth rates. The limitations of SAPs included the following: reduction in water holding capacity by combined use of fertilizers, short durability of SAP effects, and lack of cost evaluation. Further systematic studies are necessary to 1) develop suitable application methods, 2) identify applicable tree species by systematic studies in dry and semidry lands, and 3) improve the SAP products.