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This study quantified the effect of weeding frequency and weeding schedules on weeding operation time in a sugi (Cryptomeria japonica) plantation stand. A weeding operation time estimation model was developed; then the cumulative weeding operation time after six growing seasons was simulated using the developed model. The developed model included weed height, relative height of weeds to sugi, and initial planting density. The simulated cumulative weeding operation time decreased approximately 6% for each one-treatment decrease in weeding frequency. Under a three-treatment weeding frequency scenario, the simulated cumulative operation time when weeding was conducted during non-consecutive years was longer than that when weeding was conducted during three consecutive years. The results suggest that carrying out weeding treatment during consecutive years is the more effective for reduction of weeding costs. We conclude that weeding schedule as well as weeding frequency must be considered for reduction of weeding operation time.

This study investigated the effect of weeding on the height growth of planted sugi (Cryptomeria japonica) saplings in southwestern Japan. First, we developed stand-level sugi and weed annual height growth models that accounted for tree spacing, slope aspect, and mean sugi height at the end of prior growing season and mean weed height just after weeding. Then, we simulated sugi heights after the sixth growing season under 64 different weeding schedules, using the developed model to examine the effects of the weeding frequency and the timing of weeding. The selected model for sugi height growth was expressed in terms of mean sugi height, mean weed height, slope aspect, and the relative height of weeds to sugi. In the case of weeds, the selected model was expressed in terms of mean sugi height, slope aspect, and the relative height of weeds to sugi. The simulation showed that sugi height decreased approximately 20% for every one-time reduction in the number of weeding. The simulation also showed that...

Appropriate cutting cycles and annual allowable cuts are crucial to ensure sustainability of tropical selective logging, but there have been limited field data to verify long-term effects of different cutting cycles. This study reveals some evidence of forest degradation in selectively logged production forests of Myanmar, which are subject to inappropriate cutting frequency. We compared stand structure, commercial species composition, and incidence of illegal logging between two compartments with low (LCF; 1 time) and high (HCF; 5 times) cutting frequency over a recent 18 years. Prior to the latest cutting, LCF had 176 trees ha − 1 with an inverted-J shape distribution of diameter at breast height (DBH), including a substantial amount of teak ( Tectona grandis ) and other commercially important species in each DBH class. HCF prior to the latest cut had only 41 trees ha − 1 without many commercially important species. At HCF, nearly half the standing trees of various species and size were illegally cut following legal operations; this was for charcoal making in nearby kilns. At LCF, two species, teak and Xylia xylocarpa , were cut illegally and sawn for timber on the spot. More extensive and systematic surveys are needed to generalize the findings of forest degradation and illegal logging. However, our study calls for urgent reconsideration of logging practices with high cutting frequency, which can greatly degrade forests with accompanying illegal logging, and for rehabilitating strongly degraded, bamboo-dominated forests. To reduce illegal logging, it would be important to pay more attention on a MSS regulation stating that logging roads should be destroyed after logging operations.

The quality of diameter measurements for natural old-growth forest was evaluated by comparing repeated field measurements in a diameter census and tree-ring chronologies. The diameter census was repeated three times from 1973 at 10- to 19-year intervals in old-growth Cryptomeria japonica forests on Yakushima Island, Japan. The diameter growth in the three intervals between (1) first and second measurement (15–19 years), (2) second and third measurement (10–13 years), and (3) first and third measurement (28–30 years) were calculated. The diameter growth of each interval was also measured using tree-ring chronologies as a control. There were significant differences in paired t tests for diameter growth calculated from the diameter census data and from the tree-ring chronologies when the interval was 27 years. The average percentage differences (APDs) were relatively high for every interval and for all diameter classes, but the APDs for the 28- to 30-year intervals were better than the 10- to 19-year intervals. The APDs followed a rising trend with increasing diameter at breast height for every interval. In conclusion, data from an interval of >27 years is required for accurate estimation of diameter growth. Furthermore, extra care should be taken when measuring large diameter trees. The results from this study demonstrated the difficulty of using a diameter census in natural old-growth forest.

Summary In central Cambodia, rapid growing non-endemic species are planted for future timber production. However, less is understood about the impact of the introduction of non-endemic species on the transpiration characteristics of the forest, which has been composed of native species that adapted to the highly seasonal environments. Sap flux of two native and one non-endemic tree species in central Cambodia was measured to reveal its seasonal trends and variability in the Monsoon Asia region. Measurements were carried out in a 10- to 15-year-old forest in the dry and rainy seasons that were defined by differing rainfall patterns. The seasonal trend in depth to water table differed from that of rainfall; groundwater table depth reached zero late in the rainy season and increased gradually after the onset of the dry season. The ratio of sap flux to an equilibrium evaporation condition of the native species, Popel ( Shorea roxburghii ), showed a sharp decline at the end of the dry season, whereas that of a non-endemic species, eucalyptus ( Eucalyptus camaldulensis ), decreased in the mid rainy season while Tbeng ( Dipterocarpus obtusifolius ) did not show a clear trend. The ratio of sap flux to an equilibrium evaporation was negatively correlated with the depth to water table in Popel, but was positively correlated in eucalyptus, possibly because of the negative effects of flooding. In addition to the large seasonal variation, intra-species variation in sap flux was also large and was a major controlling factor for tree-level water uptake at this young forest site in both dry and rainy seasons. In conclusion, the transpiration characteristics of this forest were species-specific and were controlled more by the fluctuating depths to groundwater rather than the onset of the rainy/dry seasons defined by rainfall events.

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−1, 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.

Our objective was to investigate the differences in the spectral trajectory of the LANDSAT Thematic Mapper with stand volume development between Japanese larch (Larix kaempferi) and Japanese oak (Quercus mongolica var. crispula) in the experimental forest of Kyushu University, Hokkaido, Japan. We used nonlinear regression and a categorical variable to investigate the relationship between spectral reflectance factor and stand volume for each forest type. This research showed that the reflectance factor of Japanese larch and Japanese oak reached saturation and that both forest types had different spectral trajectories with stand development. In addition, we found that middle of development stage (stand volume was between 100 and 200 m3/ha) of each forest type had similarity in reflectance factor.

To detect non-thinned stands using very-high-resolution imagery, we assessed the relationship between the texture statistics derived from the gray level co-occurrence matrix (GLCM) and the density of Cryptomeria japonica stands. Because it was difficult to make the condition, like stand age and slope, consistent using real images and stands, simulated images were used. The results showed that each texture statistic had a unique pattern of variation, owing to stand density. Moreover, the amount of thinning affected the texture statistics. Because the values of the texture statistics varied according to the amount of it even if the stand density was the same, it was indicated that it was difficult to predict stand density using the texture derived from GLCM. Nevertheless, it should be possible to extract stands that have not been thinned using the texture statistics from very-high-resolution imagery, especially the homogeneity and the angular second moment.

Ecological communities including tropical rainforest are rapidly changing under various disturbances caused by increasing human activities. Recently in Cambodia, illegal logging and clear-felling for agriculture have been increasing. Here, we study the effects of logging, mortality and recruitment of plot trees on phylogenetic community structure in 32 plots in Kampong Thom, Cambodia. Each plot was 0.25 ha; 28 plots were established in primary evergreen forests and four were established in secondary dry deciduous forests. Measurements were made in 1998, 2000, 2004 and 2010, and logging, recruitment and mortality of each tree were recorded. We estimated phylogeny using rbcL and matK gene sequences and quantified phylogenetic α and β diversity. Within communities, logging decreased phylogenetic diversity, and increased overall phylogenetic clustering and terminal phylogenetic evenness. Between communities, logging increased phylogenetic similarity between evergreen and deciduous plots. On the other hand, recruitment had opposite effects both within and between communities. The observed patterns can be explained by environmental homogenization under logging. Logging is biased to particular species and larger diameter at breast height, and forest patrol has been effective in decreasing logging.