Spatiotemporal Assessment of Plant Community in Mixed Deciduous Forest, Mahidol University (Kanchanaburi Campus)

Abstract

Background and Objectives: Forests are vital natural resources that support living organisms and serve as key mechanisms for maintaining ecological stability and balance, particularly through their role in carbon sequestration and storage. Global climate change and the reduction of forest areas due to human activities have made monitoring and assessing forest resources critically important. Mahidol University, Kanchanaburi Campus, located in Sai Yok District, Kanchanaburi Province, encompasses approximately 6,500 rai of land, most of which consists of mixed deciduous forest on karst topography—a highly unique ecosystem suitable for sustainable conservation. The main objectives of this study are to: (1) assess the spatiotemporal changes in plant communities, (2) evaluate changes in plant community structure and growth of mixed deciduous forest species over a 10-year period, and (3) develop spatial data layers of the mixed deciduous forest within Mahidol University, Kanchanaburi Campus.

Methodology: This study compared historical data on plant community structure (plant census) from 2014 (B.E. 2557) with current data from 2024 (B.E. 2567). Random sample plots measuring 40 m × 40 m were established within permanent study plots to collect information on species diversity and quantitative plant characteristics, such as species identity and diameter at breast height (DBH). These data were used to calculate key quantitative attributes of the plant community, including the Shannon–Wiener Diversity Index and the Importance Value Index (IVI), which was derived from relative density, relative dominance, and relative frequency to assess the status of the vegetation. Tree growth was evaluated by comparing the mean DBH of 34 previously recorded trees over the 10-year period, with statistical significance tested using a paired t-test. For assessing spatiotemporal changes, Landsat-8 satellite imagery from March 2014 and March 2024, representing the dry season, was used to classify land-use patterns. Geoinformatics technologies were employed to interpret and analyze the data to estimate land-use proportions. Differences in overall land-use change were analyzed using the Wilcoxon Signed-Rank Test. In addition, unmanned aerial vehicles (UAVs) were utilized to capture aerial photographs and generate three-dimensional (3D) forest structure models. These datasets serve as a foundation for evaluating forest structural attributes such as canopy height and density.

Results: Spatiotemporal Changes: The assessment over a 10-year period revealed that the mixed deciduous forest area (F2) increased by 76,640 m², representing 0.72% of the total area. However, statistical analysis using the Wilcoxon Signed-Rank Test indicated that overall land-use changes were not statistically significant (p-value = 0.674). The observed increase in forest area reflects the effectiveness of land management under the university’s supervision, where there has been no agricultural encroachment, unlike in other community forests on karst landscapes in Kanchanaburi Province, allowing for natural forest regeneration. Plant Community Structure and Diversity: The survey identified 37 tree species within the sample plots. The Shannon–Wiener Diversity Index was 2.94, indicating relatively low species diversity. The species with the highest Importance Value Index (IVI) was Grewia eriocarpa (52.67), which serves as a dominant species in this area. The top five species in terms of IVI were Grewia eriocarpa, Croton roxburghii, Millettia brandisiana, Sterculia pexa, and Dalbergia oliveri. Tree Growth: Comparison of 34 previously recorded trees showed an average increase in diameter at breast height (DBH) of 8.12 cm over the 10-year period, corresponding to an average annual growth rate of 0.812 cm/year. Paired t-test results confirmed a statistically significant difference in mean DBH between 2014 (B.E. 2557) and 2024 (B.E. 2567) (p-value<0.001) indicating continuous tree growth within the area. The species with the highest growth was Vitex quinata, followed by Grewia eriocarpa.

Conclusions: This spatiotemporal study demonstrates that the mixed deciduous forest on karst topography at Mahidol University, Kanchanaburi Campus, is undergoing continuous recovery. A comparison of forest structure data over the 10-year period confirmed that the original trees exhibited statistically significant growth in diameter at breast height (DBH), reflecting positive outcomes from successful land management policies that effectively prevented encroachment. However, despite this encouraging structural recovery, species diversity within the plant community remains low. The data on spatiotemporal changes and forest structure thus provide a valuable baseline tool for the university to plan forest resource management and to assess the potential for sustainable carbon sequestration.