| Tetsuji Ota | Last modified date：2024.04.08 |
Associate Professor /
Forest Sciences /
Department of Agro-environmental Sciences /
Faculty of Agriculture
Papers
| 1. | Katsuto Shimizu, Tetsuji Ota, Nariaki Onda, Nobuya Mizoue, Combining post-disturbance land cover and tree canopy cover from Landsat time series data for mapping deforestation, forest degradation, and recovery across Cambodia, International Journal of Digital Earth, 10.1080/17538947.2022.2061618, 15, 1, 832-852, 2022.05, Mapping of deforestation, forest degradation, and recovery is essential to characterize country-level forest change and formulate mitigation actions. Previous studies have mainly used a simple forest/non-forest classification after forest disturbance to identify deforestation and forest degradation. However, a more flexible approach that is applicable to different forest conditions is desirable. In this study, we examined an approach for mapping deforestation, forest degradation, and recovery using disturbance types and tree canopy cover estimates from annual Landsat time-series data from 1988 to 2020 across Cambodia. We developed models to estimate both disturbance types and tree canopy cover based on a random forest algorithm using predictor variables derived from a trajectory-based temporal segmentation approach. The estimated disturbance types and canopy cover in each year were then used in a rule-based classification of deforestation, forest degradation, and recovery. The producer’s and user’s accuracies ranged from 59.1% to 72.9% and 60.8% to 91.6%, respectively, for the forest change classes of mapping deforestation, forest degradation, and recovery. The approach developed here can be adjusted for different definitions of deforestation, forest degradation, and recovery according to research objectives and thus has the potential to be applied to other study areas.. |
| 2. | Sie Thu Minn, Nobuya Mizoue, Tetsuji Ota, Evaluating ground disturbance at elephant skid trails, logging roads and log landings under the Myanmar selection system, Journal of Forest Research, 10.1080/13416979.2022.2067618, 2022.05, There has been growing interest in the practice of reduced-impact logging (RIL) to enhance various ecological services of selectively logged tropical forests. It is thus important to evaluate the effectiveness of different logging operations between RIL and conventional logging (CON). The Myanmar Selection System (MSS) has a long history and is well known for its use of elephants for skidding, which is considered one form of RIL. However, the difference in the impacts of logging operations between the MSS using elephants for skidding and machine-only-based operations commonly adopted in other countries is unknown. The present study evaluated ground disturbance along elephant skid trails, along logging roads and at log landings in four compartments logged under the MSS, comparing with reported values for CON and RIL in the other countries. The ground disturbance in the MSS compartments was, respectively, 2.1% and 0.4% in average for logging roads and log landings; it is not significantly different from that for CON and RIL (p > 0.05). In contrast, the disturbed area along elephant skid trails (0.9%) is much lower than that for CON (5.2%) and RIL (4.7%) (p |
| 3. | Khin Thu Wint Kyaw, Tetsuji Ota, Nobuya Mizoue, Geographical factors trump community factors in deforestation risk in two watershed conservation forests in Myanmar, Forests, 10.3390/f12050541, 12, 5, 2021.05, Community forestry, which is how local communities are involved in forest conservation and utilization activities, is an important forestry program in developing tropical countries. We evaluated the importance of geographical factors and community characteristics in the deforestation of community forests between 2000 and 2019 in the buffer zone of Inlay Lake Biosphere Reserve, Myanmar, using a mixed-effects logistic regression model. Distance to the nearest village, slope, and distance to the community forestry boundary were the most important variables explaining deforestation in community forests. Forests closer to human settlements and with gentle slopes faced higher risks of deforestation, presumably because such forests are more accessible. In addition, forests located far from the boundaries of community forests were more vulnerable to deforestation. Community characteristics were less important compared with geographical factors. Leadership was the most important variable among community characteristics, although not statistically significant. We conclude that deforestation depends more on forest accessibility. This indicates that the locations at which new community forests are established should receive increased consideration.. |
| 4. | Thein Saung, Tual Cin Khai, Nobuya Mizoue, Tetsuji Ota, Tsuyoshi Kajisa, Condition of illegally logged stands following high frequency legal logging in bago yoma, myanmar, Forests, 10.3390/f12020115, 12, 2, 1-12, 2021.02, © 2021 by the authors. Licensee MDPI, Basel, Switzerland. The restoration of degraded forests is the focus of global attention. Effective restoration requires information on the condition of degraded forests. This study aimed to understand the conditions of illegally logged stands that had also experienced inappropriately short rotations between legal logging cycles in natural production forests in Myanmar. Four rectangular plots (each 0.64 ha) were established in 2013. The plots included illegally logged stumps in three compartments where the latest legal logging was conducted in 2011 after very short rotations between legal logging cycles (up to five harvests between 1995 and 2011, compared with a recommended 30-year logging cycle). Using data from the field measurements in 2013 on the legal and illegal stumps and living trees, we reconstructed stand structure just before and after legal logging in 2011. Before the legal logging in 2011, there were variations in stand structure and the composition of commercial species among four plots. Illegal logging (14–31 trees ha−1 ) was much higher than legal logging (0–11 trees ha−1 ). Illegal logging targeted six to nine species that were suitable for high-quality charcoal from various sized trees, while legal logging targeted one or two timber species with a diameter at breast height (DBH) larger than 58 cm. The number of remaining trees in 2013 ranged from 33 to 181 trees ha−1 . There was a negative relationship with the number of bamboo clumps, which varied from 6 to 145 clumps ha−1 . Bamboo-dominated stands with a low remaining stock of commercial trees may need active restoration such as bamboo cutting and replanting of commercial species. Bamboo cutting could generate income for the local community.. |
| 5. | Khin Thu Wint Kyaw, Tetsuji Ota, Nobuya Mizoue, Forest degradation impacts firewood consumption patterns: A case study in the buffer zone of Inlay Lake Biosphere Reserve, Myanmar, Global Ecology and Conservation, 10.1016/j.gecco.2020.e01340, 24, 2020.12, © 2020 The Author(s) Firewood is a major energy source, especially in developing countries. Because firewood is often collected from forest, forest quality may affect firewood consumption patterns. Here, we evaluated the impact of forest degradation on firewood consumption patterns in a rural area of Myanmar. Household interviews were conducted for a total of 143 households from 20 villages, and per capita consumption rates for each household were calculated. The per capita consumption rates of households that only used firewood for cooking were regressed against several potentially important factors, including an index of forest degradation. Approximately 85% of sample households used firewood for cooking. The average per capita annual firewood consumption rate for cooking was 530 kg for households that used exclusively firewood for cooking. The regression analysis clearly showed that open forest area ratio, an indicator of forest degradation, had a negative effect on per capita annual firewood consumption rate. In addition to open forest ratio, household size, elevation, and the consumption rate of firewood for drying cigar leaves were strongly related to per capita annual firewood consumption rate. However, the nearest distance to forest had a weak relationship with per capita annual firewood consumption, although previous studies have suggested that the nearest distance to forest negatively affects the firewood consumption rate. Combined with previous studies showing that fuelwood collection causes forest degradation, we conclude that forest degradation and decreases in firewood consumption mutually affected each other. Additional studies are needed to assess the role of forest degradation in maintaining local livelihoods.. |
| 6. | Keiko Fukumoto, Tetsuji Ota, Nobuya Mizoue, Shigejiro Yoshida, Yukio Teraoka, Tsuyoshi Kajisa, The effect of weeding frequency and schedule on weeding operation time: a simulation study on a sugi (Cryptomeria japonica) plantation in Japan, Journal of Forestry Research, 10.1007/s11676-019-01017-5, 31, 6, 2129-2135, 2020.12, © 2019, Northeast Forestry University. 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.. |
| 7. | Katsuto Shimizu, Tetsuji Ota, Nobuya Mizoue, Accuracy assessments of local and global forest change data to estimate annual disturbances in temperate forests, Remote Sensing, 10.3390/RS12152438, 12, 15, 2020.08, © 2020 by the authors. Forest disturbances are generally estimated using globally available forest change maps or locally calibrated disturbance maps. The choice of disturbance map depends on the trade-offs among the detection accuracy, processing time, and expert knowledge. However, the accuracy differences between global and local maps have still not been fully investigated; therefore, their optimal use for estimating forest disturbances has not been clarified. This study assesses the annual forest disturbance detection of an available Global Forest Change map and a local disturbance map based on a Landsat temporal segmentation algorithm in areas dominated by harvest disturbances. We assess the forest disturbance detection accuracies based on two reference datasets in each year. We also use a polygon-based assessment to investigate the thematic accuracy based on each disturbance patch. As a result, we found that the producer's and user's accuracies of disturbances in the Global Forest Change map were 30.1-76.8% and 50.5-90.2%, respectively, for 2001-2017, which corresponded to 78.3-92.5% and 88.8-97.1%, respectively in the local disturbance map. These values indicate that the local disturbance map achieved more stable and higher accuracies. The polygon-based assessment showed that larger disturbances were likely to be accurately detected in both maps; however, more small-scale disturbances were at least partially detected by the Global Forest Change map with a higher commission error. Overall, the local disturbance map had higher forest disturbance detection accuracies. However, for forest disturbances larger than 3 ha, the Global Forest Change map achieved comparable accuracies. In conclusion, the Global Forest Change map can be used to detect larger forest disturbances, but it should be used cautiously because of the substantial commission error for small-scale disturbances and yearly variations in estimated areas and accuracies.. |
| 8. | The influence of sampling grid resolution and understory on forest structure estimation from terrestrial laser scanning Naoki Suematsu, Tetsuji Ota, Katsuto Shimizu, Keiko Fukumoto, Nobuya Mizoue, Akio Inoue, Haruka Kitazato,Hideo Kusano, Hirofumi Kai and Yasushi Omasa: The influence of sampling grid resolution and understory on forest structure estimation from terrestrial laser scanning. Jpn. J. For. Plann. 54: 45~54, 2020 This study investigated the effects of sampling grid resolution and understory on tree stem detection and diameter at breast height（DBH）, tree height,and stem volume estimation from terrestrial laser scanning（TLS）. We established six rectangular plots. Within three plots,we removed the understory before scanning. The TLS data were acquired using a 5 m sampling grid. Four sampling-grid resolutions were tested by changing the combinations of TLS data used for registration of scans. The results showed that the understory and/or a coarser grid resolution negatively affected the registration of TLS, detection of stems, and estimation of DBH, tree height, and volume. . |
| 9. | Tetsuji Ota, Pichdara Lonn, Nobuya Mizoue, A country scale analysis revealed effective forest policy affecting forest cover changes in Cambodia, Land Use Policy, 10.1016/j.landusepol.2020.104597, 95, 2020.06, © 2020 Elsevier Ltd Considerable proportions of the remaining global forest areas are currently harboured in tropical countries. Reducing deforestation in this region is important to help mitigate climate change. Effective forest conservation approach is needed to reduce deforestation and degradation in these countries. Here, we investigated the forest conservation effect of community forests and protected areas using country scale data in Cambodia. In addition to these two forest conservation approaches, we also evaluated the effectiveness of protected forests, which are similar to protected areas but managed by different authorities. We compared deforestation between 2006 and 2016 in areas under the three forest conservation approaches and a non-conserved area by applying the inverse probability of treatment weighting with the propensity score minimizing confounding effects. The results showed that community forest, protected areas, and protected forest significantly decreased deforestation compared with non-conserved forests. Out of the three forest conservation approaches, protected forest was the most effective and community forest was the least effective. We conclude that all of the policies we evaluated are effective for forest conservation but the effectiveness varies depending on the approach. Our findings also suggest that the authority managing the given approach plays an important part in its effectiveness.. |
| 10. | Katsuto Shimizu, Tetsuji Ota, Nobuya Mizoue, Detecting forest changes using dense Landsat 8 and Sentinel-1 time series data in tropical seasonal forests, Remote Sensing, 10.3390/rs11161899, 11, 16, 2019.01, The accurate and timely detection of forest disturbances can provide valuable information for effective forest management. Combining dense time series observations from optical and synthetic aperture radar satellites has the potential to improve large-area forest monitoring. For various disturbances, machine learning algorithms might accurately characterize forest changes. However, there is limited knowledge especially on the use of machine learning algorithms to detect forest disturbances through hybrid approaches that combine different data sources. This study investigated the use of dense Landsat 8 and Sentinel-1 time series data for detecting disturbances in tropical seasonal forests based on a machine learning algorithm. The random forest algorithm was used to predict the disturbance probability of each Landsat 8 and Sentinel-1 observation using variables derived from a harmonic regression model, which characterized seasonality and disturbance-related changes. The time series disturbance probabilities of both sensors were then combined to detect forest disturbances in each pixel. The results showed that the combination of Landsat 8 and Sentinel-1 achieved an overall accuracy of 83.6% for disturbance detection, which was higher than the disturbance detection using only Landsat 8 (78.3%) or Sentinel-1 (75.5%). Additionally, more timely disturbance detection was achieved by combining Landsat 8 and Sentinel-1. Small-scale disturbances caused by logging led to large omissions of disturbances; however, other disturbances were detected with relatively high accuracy. Although disturbance detection using only Sentinel-1 data had low accuracy in this study, the combination with Landsat 8 data improved the accuracy of detection, indicating the value of dense Landsat 8 and Sentinel-1 time series data for timely and accurate disturbance detection.. |
| 11. | Effect of weeding frequency, slope aspect and initial tree density on the mortality and accidental cutting of planted Sugi (Cryptomeria Japonica) trees : A case study in the Kagoshima University Research Forest, southwestern Japan. |
| 12. | Tetsuji Ota, Miyuki Ogawa, Nobuya Mizoue, Keiko Fukumoto, Shigejiro Yoshida, Forest Structure Estimation from a UAV-Based Photogrammetric Point Cloud in Managed Temperate Coniferous Forests, FORESTS, 10.3390/f8090343, 8, 9, 2017.09, Here, we investigated the capabilities of a lightweight unmanned aerial vehicle (UAV) photogrammetric point cloud for estimating forest biophysical properties in managed temperate coniferous forests in Japan, and the importance of spectral information for the estimation. We estimated four biophysical properties: stand volume (V), Lorey's mean height (HL), mean height (HA), and max height (HM). We developed three independent variable sets, which included a height variable, a spectral variable, and a combined height and spectral variable. The addition of a dominant tree type to the above data sets was also tested. The model including a height variable and dominant tree type was the best for all biophysical property estimations. The root-mean-square errors (RMSEs) for the best model for V, HL, HA, and HM, were 118.30, 1.13, 1.24, and 1.24, respectively. The model including a height variable alone yielded the second highest accuracy. The respective RMSEs were 131.74, 1.21, 1.31, and 1.32. The model including a spectral variable alone yielded much lower estimation accuracy than that including a height variable. Thus, a lightweight UAV photogrammetric point cloud could accurately estimate forest biophysical properties, and a spectral variable was not necessarily required for the estimation. The dominant tree type improved estimation accuracy.. |
| 13. | Katsuto Shimizu, Oumer S. Ahmed, Raul Ponce-Hernandez, Tetsuji Ota, Zar Chi Win, Nobuya Mizoue, Shigejiro Yoshida, Attribution of Disturbance Agents to Forest Change Using a Landsat Time Series in Tropical Seasonal Forests in the Bago Mountains, Myanmar, FORESTS, 10.3390/f8060218, 8, 6, 2017.06, In 2016, in response to forest loss, the Myanmar government banned logging operations for 1 year throughout the entire country and for 10 years in specific regions. However, it is unclear whether this measure will effectively reduce forest loss, because disturbance agents other than logging may have substantial effects on forest loss. In this study, we investigated an approach to attribute disturbance agents to forest loss, and we characterized the attribution of disturbance agents, as well as the areas affected by these agents, in tropical seasonal forests in the Bago Mountains, Myanmar. A trajectory-based analysis using a Landsat time series was performed to detect change pixels. After the aggregation process that grouped adjacent change pixels in the same year as patches, a change attribution was implemented using the spectral, geometric, and topographic information of each patch via random forest modeling. The attributed agents of change include "logging", "plantation", "shifting cultivation", "urban expansion", "water invasion", "recovery", "other change", and "no change". The overall accuracy of the attribution model at the patch and area levels was 84.7% and 96.0%, respectively. The estimated disturbance area from the attribution model accounted for 10.0% of the study area. The largest disturbance agent was found to be logging (59.8%), followed by water invasion (14.6%). This approach quantifies disturbance agents at both spatial and temporal scales in tropical seasonal forests, where limited information is available for forest management, thereby providing crucial information for assessing forest conditions in such environments.. |
| 14. | Katsuto Shimizu, Raul Ponce-Hernandez, Oumer S. Ahmed, Tetsuji Ota, Zar Chi Win, Nobuya Mizoue, Shigejiro Yoshida, Using Landsat time series imagery to detect forest disturbance in selectively logged tropical forests in Myanmar, CANADIAN JOURNAL OF FOREST RESEARCH, 10.1139/cjfr-2016-0244, 47, 3, 289-296, 2017.03, Detecting forest disturbances is an important task in formulating mitigation strategies for deforestation and forest degradation in the tropics. Our study investigated the use of Landsat time series imagery combined with a trajectory-based analysis for detecting forest disturbances resulting exclusively from selective logging in Myanmar. Selective logging was the only forest disturbance and degradation indicator used in this study as a causative force, and the results showed that the overall accuracy for forest disturbance detection based on selective logging was 83.0% in the study area. The areas affected by selective logging and other factors accounted for 4.7% and 5.4%, respectively, of the study area from 2000 to 2014. The detected disturbance areas were underestimated according to error assessments; however, a significant correlation between areas of disturbance and numbers of harvested trees during the logging year was observed, indicating the utility of a trajectory-based, annual Landsat imagery time series analysis for selective logging detection in the tropics. A major constraint of this study was the lack of available data for disturbances other than selective logging. Further studies should focus on identifying other types of disturbances and their impacts on future forest conditions.. |
| 15. | Kazuki Ito, Tetsuji Ota, Nobuya Mizoue, Shigejiro Yoshida, Kotaro Sakuta, Akio Inoue, Satoshi Ito, Hiroyuki Okada, Differences in growth responses between Cryptomeria japonica and Chamaecyparis obtusa planted in group selection openings in Kyushu, southern Japan, Journal of Forest Research, 10.1080/13416979.2017.1283978, 22, 2, 126-130, 2017.02, We quantified the differences in growth responses between Cryptomeria japonica and Chamaecyparis obtusa trees in approximately 0.1-ha group selection openings in southern Japan. We measured the position, height (H), and diameter at ground level (D) of 6- and 13-year-old C. japonica and C. obtusa trees that were planted in two respective openings. The annual H and D growth of C. japonica increased until trees were 10 and 8 m, respectively, distant from the nearest edge of the opening. For C. obtusa, the annual H and D growth increased slightly until the trees were 6 m distant from the nearest edge, but they did not significantly differ between 6 and 18 m distant from the nearest edge. While the shortest distance from the edge explained 63% and 50% of the variationsal H and D growth, respectively, of C. obtusa. Our result demonstrates that C. obtusa is less sensitive to edge effects than C. japonica. We conclude that C. obtusa is likely to be more suitable than C. japonica for planting within 0.1-ha group openings, as it will result in faster early stage growth, with less variation, within the openings.. |
| 16. | Keiko Fukumoto, Tetsuji Ota, Nobuya Mizoue, Shigejiro Yoshida, Yukio Teraoka, Tsuyoshi Kajisa, The effect of weeding frequency and timing on the height growth of young sugi (Cryptomeria Japonica) in southwestern Japan, Journal of Forest Research, 10.1080/13416979.2017.1322347, 22, 3, 204-207, 2017.01, 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 earlier, rather than later, weeding yielded better sugi growth. In conclusion, not only weeding frequency but also weeding schedules are important for sugi height growth.. |
| 17. | Tual Cin Khai, Nobuya Mizoue, Tsuyoshi Kajisa, Tetsuji Ota, Shigejiro Yoshida, Using a tree-based approach to evaluate logging damage in a tropical mixed deciduous forest of Myanmar Comparison with cases in Cambodia, Journal of Forest Research, 10.1080/13416979.2017.1302545, 22, 3, 185-190, 2017.01, Logging damage to residual trees is an important parameter when considering the sustainability of selective logging in tropical natural forests. Here, we applied a proposed tree-based approach to evaluate logging damage in a tropical mixed deciduous forest in Bago Yoma, Myanmar and compared the cases with semi-evergreen forests of Cambodia. The logging damage was assessed in twenty 0.1-ha plots, each of which contained the stump and crown of one felled tree, and multinomial logistic regression was used to quantify the probability of the felled tree causing severe, slight, or no damage to residual trees. In both cases of Myanmar and Cambodia, severe damage was dependent on the size of the residual and felled trees, while slight damage was independent of the size of felled trees. There was no slight damage of residual trees with ≥50 cm diameter at breast height (DBH) in Myanmar, whereas slight damage increased with residual tree size in Cambodia and in tropical rain forests of other countries. This difference could be attributed to the sparseness of standing trees (98 trees ha−1) in our study site in Myanmar, which made it easier to control the felling direction to avoid damage to larger residual trees. Additionally, the probability of increasingly severe damage with increasing DBH of the felled trees was higher in Myanmar than in Cambodia; one of the reasons may be the steeper terrain at the Myanmar site.. |
| 18. | T. C. Khai, N. Mizoue, T. Kajisa, T. Ota, S. Yoshida, Effects of directional felling, elephant skidding and road construction on damage to residual trees and soil in Myanmar selection system, INTERNATIONAL FORESTRY REVIEW, 10.1505/146554816819501718, 18, 3, 296-305, 2016.09, Reduced-impact logging (RIL) is widely expected to maximize conservation values of selectively logged tropical forests; however, there remains a lack of supporting data to confirm the effectiveness of individual RIL practices. This study evaluates the extent of damage to residual stands and soil caused by directional felling, elephant skidding, and road construction in a tropical mixed deciduous forest under the Myanmar Selection System (MSS). The felling damage number was consistently larger for bamboo clumps than for trees over the range of felled tree size and felling intensity. Soil disturbed by road construction made up 4.6% of the 9-ha study area, but no visible damage to residual trees and soil from elephant skidding was found three months after the operation. Directional felling toward bamboos and elephant skidding of MSS are effective as RIL practices, producing the lowest level of damage to residual trees and soil as compared with other RIL studies.. |
| 19. | Katsuto Shimizu, Raul Ponce-Hernandez, Oumer S. Ahmed, Tetsuji Ota, Zar Chi Win, Nobuya Mizoue, Shigejiro Yoshida, The effects of topographic correction and gap filling in imagery on the detection of tropical forest disturbances using a Landsat time series in Myanmar, INTERNATIONAL JOURNAL OF REMOTE SENSING, 10.1080/01431161.2016.1201230, 37, 16, 3655-3674, 2016.08, In this study, we evaluated the effects of topographic correction and gap filling of Landsat Enhanced Thematic Mapper Plus (ETM+) images on the accuracy of forest change detection through a trajectory-based approach. Four types of Landsat time series stacks (LTSS) were generated. These stacks resulted from combinations of topographically corrected and uncorrected imagery combined with gap-filled and unfilled stacks. These combinations of stacks were then used as input into a trajectory-based change detection. The results of change detection from trajectory-based analysis using these LTSS were compared in order to assess the effects of both topographic correction and gap-filling procedures on the ability to detect forest disturbances. The results showed that overall accuracies of change detection were improved after gap filling (10.5% and 7.5%), but were only slightly improved after topographic correction (3.6% and 0.6%). Although the gap-filling process introduced some uncertainty that might have caused false change detection, the number of pixels whose detection of disturbance was enhanced after gap filling exceeded those detecting false change. The results also showed that the topographic correction did not contribute much to improve the change detection in this study area. However, topographic correction has a potential to increase the accuracy of change detection in areas of more rugged terrain and steep slopes. This is because a direct relationship between the slope of the topography with topographic correction and an enhanced detection of disturbance in pixels from year to year was observed in this study. For robust change detection, we recommend that a gap-filling process should be included in the trajectory-based analysis procedures such as the one used in this study where a single image per year is used to characterize change. We also recommend that in areas of rugged terrain, a topographic correction in the image pre-processing should be implemented.. |
| 20. | Tual Cin Khai, Nobuya Mizoue, Tsuyoshi Kajisa, Tetsuji Ota, Shigejiro Yoshida, Stand structure, composition and illegal logging in selectively logged production forests of Myanmar: Comparison of two compartments subject to different cutting frequency, GLOBAL ECOLOGY AND CONSERVATION, 10.1016/j.gecco.2016.06.001, 7, 132-140, 2016.07, 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. (C) 2016 The Authors. Published by Elsevier B.V.. |
| 21. | Tetsuji Ota, Tsuyoshi Kajisa, Nobuya Mizoue, Shigejiro Yoshida, Gen Takao, Yasumasa Hirata, Naoyuki Furuya, Takio Sano, Raul Ponce-Hernandez, Oumer S. Ahmed, Heng Sokh, Vuthy Ma, Eriko Ito, Jumpei Toriyama, Yukako Monda, Hideki Saito, Yoshiyuki Kiyono, Sophal Chann, Nang Ket, Estimating aboveground carbon using airborne LiDAR in Cambodian tropical seasonal forests for REDD plus implementation, JOURNAL OF FOREST RESEARCH, 10.1007/s10310-015-0504-3, 20, 6, 484-492, 2015.12, We developed an empirical model to estimate aboveground carbon density with variables derived from airborne Light Detection and Ranging (LiDAR) in tropical seasonal forests in Cambodia, and assessed the effects of LiDAR pulse density on the accurate estimation of aboveground carbon density. First, we tested the applicability of variables used for estimating aboveground carbon density with the original LiDAR pulse density data (26 pulse m(-2)). Aboveground carbon density was regressed against variables derived from airborne LiDAR. Three individual height variable models were developed along with a canopy density model, and three other models combined canopy height and canopy density variables. The influence of forest type on model accuracy was also assessed. Next, the relationship between pulse density and estimation accuracy was investigated using the best regression model. The accuracy of the models were compared based on seven LiDAR point densities consisting of 0.25, 1, 2, 3, 4, 5 and 10 pulse m(-2). The best model was obtained using the single mean canopy height (MCH) model (R-2 = 0.92) with the original pulse density data. The relationship between MCH and aboveground carbon density was found to be consistent under different forest types. The differences between predicted and measured residual mean of squares of deviations were less than 1.5 Mg C ha(-1) between each pulse density. We concluded that aboveground carbon density can be estimated using MCH derived from airborne LiDAR in tropical seasonal forests in Cambodia even with a low pulse density of 0.25 pulse m(-2) without stratifying the study area based on forest type.. |
| 22. | Tetsuji Ota, Miyuki Ogawa, Katsuto Shimizu, Tsuyoshi Kajisa, Nobuya Mizoue, Shigejiro Yoshida, Gen Takao, Yasumasa Hirata, Naoyuki Furuya, Takio Sano, Heng Sokh, Vuthy Ma, Eriko Ito, Jumpei Toriyama, Yukako Monda, Hideki Saito, Yoshiyuki Kiyono, Sophal Chann, Nang Ket, Aboveground Biomass Estimation Using Structure from Motion Approach with Aerial Photographs in a Seasonal Tropical Forest, FORESTS, 10.3390/f6113882, 6, 11, 3882-3898, 2015.11, [URL], We investigated the capabilities of a canopy height model (CHM) derived from aerial photographs using the Structure from Motion (SfM) approach to estimate aboveground biomass (AGB) in a tropical forest. Aerial photographs and airborne Light Detection and Ranging (LiDAR) data were simultaneously acquired under leaf-on canopy conditions. A 3D point cloud was generated from aerial photographs using the SfM approach and converted to a digital surface model (DSMP). We also created a DSM from airborne LiDAR data (DSML). From each of DSMP and DSML, we constructed digital terrain models (DTM), which are DTMP and DTML, respectively. We created four CHMs, which were calculated from (1) DSMP and DTMP (CHMPP); (2) DSMP and DTML (CHMPL); (3) DSML and DTMP (CHMLP); and (4) DSML and DTML (CHMLL). Then, we estimated AGB using these CHMs. The model using CHMLL yielded the highest accuracy in four CHMs (R-2 = 0.94) and was comparable to the model using CHMPL (R-2 = 0.93). The model using CHMPP yielded the lowest accuracy (R-2 = 0.79). In conclusion, AGB can be estimated from CHM derived from aerial photographs using the SfM approach in the tropics. However, to accurately estimate AGB, we need a more accurate DTM than the DTM derived from aerial photographs using the SfM approach.. |
| 23. | Shizu Itaka, Shigejiro Yoshida, Nobuya Mizoue, Tetsuji Ota, Atsushi Takashima, Tsuyoshi Kajisa, Comparing 30-year diameter censuses and tree-ring chronologies in natural old-growth Cryptomeria japonica forest on Yakushima Island, Japan, JOURNAL OF FOREST RESEARCH, 10.1007/s10310-014-0476-8, 20, 2, 255-262, 2015.04, 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.. |
| 24. | Tetsuji Ota, Oumer S. Ahmed, Steven E. Franklin, Michael A. Wulder, Tsuyoshi Kajisa, Nobuya Mizoue, Shigejiro Yoshida, Gen Takao, Yasumasa Hirata, Naoyuki Furuya, Takio Sano, Sokh Heng, Ma Vuthy, Estimation of Airborne Lidar-Derived Tropical Forest Canopy Height Using Landsat Time Series in Cambodia, REMOTE SENSING, 10.3390/rs61110750, 6, 11, 10750-10772, 2014.11, In this study, we test and demonstrate the utility of disturbance and recovery information derived from annual Landsat time series to predict current forest vertical structure (as compared to the more common approaches, that consider a sample of airborne Lidar and single-date Landsat derived variables). Mean Canopy Height (MCH) was estimated separately using single date, time series, and the combination of single date and time series variables in multiple regression and random forest (RF) models. The combination of single date and time series variables, which integrate disturbance history over the entire time series, overall provided better MCH prediction than using either of the two sets of variables separately. In general, the RF models resulted in improved performance in all estimates over those using multiple regression. The lowest validation error was obtained using Landsat time series variables in a RF model (R-2 = 0.75 and RMSE = 2.81 m). Combining single date and time series data was more effective when the RF model was used (opposed to multiple regression). The RMSE for RF mean canopy height prediction was reduced by 13.5% when combining the two sets of variables as compared to the 3.6% RMSE decline presented by multiple regression. This study demonstrates the value of airborne Lidar and long term Landsat observations to generate estimates of forest canopy height using the random forest algorithm.. |
| 25. | Estimation of Growth Rates Based on Tree-ring Analysis of Cryptomeria japonica on Yakushima Island, Japan. |
| 26. | Tetsuji Ota, Nobuya Mizoue, Shigejiro Yoshida, Influence of using texture information in remote sensed data on the accuracy of forest type classification at different levels of spatial resolution, JOURNAL OF FOREST RESEARCH, 10.1007/s10310-010-0233-6, 16, 6, 432-437, 2011.12, We evaluated the influence of texture information from remote sensed data on the accuracy of forest type classification at different spatial resolutions. We used 4-m spatial resolution imagery to create five different sets of imagery with lower spatial resolutions down to 30 m. We classified forest type using spectral information alone, texture information alone, and spectral and texture information combined at each spatial resolution, and compared the classification accuracy at each resolution. The classification and regression tree method was used for classification. The accuracy of all three tests decreased slightly with lower spatial resolution. The accuracy with the combined data was generally higher than with either the spectral or texture information alone. At most resolutions, the lowest accuracy was with texture information alone. However, there was no clear difference in accuracy between the combined data and spectral data alone at 25- and 30-m spatial resolution. These results indicate that adding texture information to spatial information improves the accuracy of forest type classification from very high resolution (4-m spatial resolution) to medium resolution imagery (20-m spatial resolution), but this accuracy improvement does not appear to hold for relatively coarse resolution imagery (25- to 30-m spatial resolution).. |
| 27. | Ota, T., Mizoue, N., Yoshida, S., Fourier transform analysis of very high resolution remote sensed imagery shows potential for estimating stand density of regular-spaced planted forests, Journal of forest planning, 16, 1-7, 2010.09. |
| 28. | Murakami, T., Ota, T., Kajisa, T., Mizoue, N., Yoshida S., Detection of Clear-Cut Areas Using the Image Differencing Method with LANDSAT/TM Data, Asian Journal of Geoinformatics, 10, 11 - 19, 2010.03. |
| 29. | The relationship between the density of Cryptomeria japonica stands and texture statistics derived from very high resolution imagery : The research using simulated very-high-resolution imagery. |
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