The Bangkok Metropolitan Area (BMA), of Thailand’s capital city, has approximately 1,200 kms of main and sub streets and nearly 3,000 large trees in public places. These trees need management to prevent them from potentially falling or dropping branches and so causing injury or damage to property. Unfortunately, in the BMA, very little has been done in terms of managing the street trees, with regards to their general health and vigour, and this has led to significant damage from tree failure. In order to help prioritise the BMA’s tasks, a tree risk assessment tool can be used to systematically identify the tree defects and calculate the tree risk rating. This study aimed at generating reliable data for street trees based on the Google Street View (GSV) imagery. A comparison of the GSV survey with field data indicated high levels of agreement in genus and species identification. The overall risk of stem and root could be precisely predicted using the GSV virtual surveys. Unfortunately, identifying the overall crown risk, tree defects, and sizes was difficult and the results inaccurate. In the future, advanced image capturing and processing software can improve the accuracy and precision.

Rinnamang S, Sirirueang K, Supavetch S, Meunpong P. 2020. Estimation of aboveground biomass using aerial photogrammetry from unmanned aerial vehicles in teak (Tectona grandis) plantation in Thailand. Biodiversitas 21: 2369-2376. Thailand is one of the best teak planting locations in the world. Teak is one of the most species planting and a significant source of high-value timber in Thailand. For plantation management, biomass is one of the important factors while determining the production of a plantation and also for sustainable forest management. Unmanned Aerial Vehicles (UAV) have the ability to produce 3D RGB digital images which can be used to study the plantation characteristics. This study aimed to use aerial images and photogrammetry techniques derived from unmanned aerial vehicles (UAV) to estimate teak biomass in Thong Pha Phum plantation, Kanchanaburi Province, Thailand. We conducted our study on 15-and 36-year-old teak stands, and compared the tree dimension between data obtained from field measurement and that from aerial images and photogrammetry techniques. In the 15-year-old stand, the average tree height estimated from the UAV and ground-truthing were 12.34 and 13.06 m, respectively. In the 36-year-old stand, the average tree height from the UAV and ground-truthing were 28.87 and 29.39 m, respectively. We found that in both stands, the difference between data generated from the UAV and ground-truthing data was not significant (p-value = 0.07 and 0.306, respectively). There was also a strong correspondence between tree height estimated from the UAV and that measured on the ground which is indicated by the high R2 (i.e. 0.70 and 0.64 for the 15-and 36-year-old stands, respectively). Using UAV generated data, the total biomass of 15-and 36-year-old stands was estimated to be around 42.07 t ha-1 and 67.13 t ha-1, respectively. The overall results suggest that UAV can be used as an effective tool to survey and monitor stand’s productivity in teak plantation.

The Thai forestry sector relies greatly on Eucalyptus as a raw material. The rapid expansion of plantations during the last few decades and the high demand for Eucalyptus for several purposes has led to numerous supply chain practices. A comprehensive understanding of the Eucalyptus value chain is lacking in Thailand, which has consequences for optimization, sustainability, and profitability aspects. This study analyzed actors and their activities along the value chain and estimated added value and profit margin benefit distributions. The study method involved a value chain analysis approach, whereby input data were collected from the following groups: seedling suppliers and developers, farmers and tree growers, timber traders and collectors, intermediaries, processors, wholesalers, and consumers via key informant interviews, in-depth interviews, and group discussions. The results revealed the vertical integration of Eucalyptus timber businesses, where sapling breeders were the major input suppliers with a significant role in the value chain based on the role of controlling the majority of seedling production, promoting cultivation, and ensuring the raw material supply for the pulp industry through a full-cycle membership program. Total gross marketing margin was highest (90.6%) in the path of the pulp mill industry and lowest in the path of the biomass power plant (73.4%). The profit share of growers varied between 9.9% and 26.6% depending on the path and chain. The overall benefit distribution analysis demonstrated a positive gross profit margin but minor distribution to the growers. Our study determined that decision-makers should create supportive programs, funding opportunities, and infrastructural support for research and development, capacity building, and regulation to ensure suitable benefits for all actors in the Eucalyptus timber value chain in Thailand.

Penboon C, Supavetch S, Sirirueang K, Rinnamang S, Ladpala P, Kaewgrajang T, Meunpong P. 2023. Estimation of the aboveground biomass and carbon sequestration in an urban forest remnant using aerial photogrammetry from a low-cost Unmanned Aerial Vehicle. Biodiversitas 24: 1908-1915. For low-income nations, a low-cost Unmanned Aerial Vehicle (UAV) offers an alternative to the traditional time-intensive forest survey that requires many resources. This study was conducted in the remnant forest with the dominant tree species, Dipterocarpus alatus Roxb., forming the upper canopy. Photogrammetry techniques with UAV images were used to obtain the Canopy Height Model (CHM). The results of tree height, individual tree detection, biomass, and carbon sequestration were compared between ground truthing and photogrammetry estimation. The large percentages of trees were automatically recognized. However, due to a closed forest canopy, some trees might have been left out from the actual count, leading to an undercounting of trees and an underestimation of the aboveground biomass (AGB). The photogrammetric dataset demonstrated a good tree height extraction accuracy and did not differ significantly from that determined by ground truthing (RMSE=2.59 m and 8.24%). The mean predicted height AGB from direct measurement was 24.76 tons ha-1, higher than those obtained from single- and multi-set photogrammetry, 5.41 and 17.99 tons ha-1, respectively. AGB and carbon sequestration estimated from photogrammetry were 72.66% of the ground truthing value. The accuracy of the photogrammetry results was acceptable and feasible for detecting individual tree heights, biomass, and carbon sequestration in the remnant forest. Overall, low-cost UAV could create a cost, time-efficient, and reasonably accurate local-scale forest inventory.

Accurately estimating aboveground biomass (AGB) remains a challenge due to the limitations of various measurement methods. While destructive sampling provides precise results, it is costly, labor-intensive, and environmentally unsustainable. Advances in remote sensing technologies offer efficient alternatives for AGB estimation. Our study highlights that airborne laser scanning (ALS) is more effective in assessing forest structure than detailed biomass composition. Orthophoto analysis, while applicable for rapid assessments, tends to overestimate AGB and carbon stock, particularly in dense forests. Differences in tree height measurements between ALS, orthophoto extraction, and field methods emphasize the varying precision of remote sensing techniques. Integrating ALS and orthophotos may enhance accuracy by using orthophotos for tree crown identification and ALS for height measurements. This combined approach could reduce errors in biomass estimation, especially in dense forests where traditional methods are challenging. Our findings suggest that ALS is more suitable for large-scale biomass assessments, while orthophoto data may be more effective in open forests. Field calibration remains essential to improve accuracy, particularly for orthophotos, which are influenced by environmental factors such as light, shadow, and seasonal changes.