Assessment of Invasive Species Severity along the Nature Trail at the Doi Chiang Dao Biosphere Reserve, Chiang Mai Province

Background and Objectives: Doi Chiang Dao Biosphere Reserve has been officially declared as the fifth Biosphere Reserve of Thailand, representing a critically important terrestrial ecosystem due to its significant number of endangered and endemic plant species. This designation highlights its crucial role in biodiversity conservation at both national and global scales. However, the area faces increasing threats from human activities, habitat degradation, and biological invasions. Among these threats, invasive alien plant species are particularly concerning due to their rapid spread and potential to disrupt local ecosystems, negatively affecting native biodiversity. Understanding the presence and impact of invasive plants is essential for effective conservation management. Thus, this study aimed to comprehensively examine diversity, distribution, and assess the status and severity of invasive alien plants along the nature trails within the Doi Chiang Dao Biosphere Reserve in Chiang Mai Province. Methodology: The research employed a systematic sampling plot approach along a clearly defined elevational gradient. Sampling plots measuring of 1×1 m2 were systematically established every 100 meter above sea level, ranging from the lower altitudinal limits up to the higher altitudinal zones within the study area. This sampling protocol resulted in a total of 34 distinct plots covering various elevational habitats and ecosystems. Within each sampling plot, detailed data collection was performed, documenting all plant species encountered regardless of their growth forms or life histories, including herbs, shrubs, grasses, and other vegetation types. Plant data collection involved comprehensive photographic documentation, precise counts of individual plants per species, and careful specimen collection for later taxonomic identification. Subsequent plant identification was rigorously conducted using reference materials and confirmed with experts when necessary. Identified species were systematically analyzed to quantify density and abundance, calculate indices of species diversity and importance value, and classify invasive alien species according to established guidelines provided by Thailand’s Office of Natural Resources and Environmental Policy and Planning and the Department of National Parks, Wildlife, and Plant Conservation. Main Results: The detailed botanical survey identified a total of 73 plant species belonging to 64 genera and 34 families within the sampled plots, indicating a substantial degree of floristic richness and diversity with an overall diversity index of 2.672. Among these identified species, seven invasive alien plant species from seven genera and four families were specifically recognized, contributing to an invasive species diversity index of 0.647. The most significant invasive alien species identified based on their ecological impact and calculated importance values were Ageratina adenophora, Bidens pilosa, and Commelina benghalensis. Additional invasive alien plant species recorded included Tithonia diversifolia, Imperata cylindrica, Parochetus communis, Sida acuta, and Malvastrum coromandelianum. The analysis of distribution patterns revealed that invasive alien plant species were predominantly observed at elevations around 1,500 meters above sea level. At this elevation, four invasive species exhibited particularly high occurrence rates, namely Ageratina adenophora, Tithonia diversifolia, Imperata cylindrica and Bidens pilosa, each having respective importance values of 14.24%, 8.42%, 9.72%, and 4.52%, respectively. This indicated that mid-elevation zones within the reserve were particularly vulnerable to biological invasions. Assessments of invasiveness severity, based on species density and their ecological importance, demonstrated that Ageratina adenophora was classified as highly invasive, significantly threatening native plant communities. The species Bidens pilosa and Imperata cylindrica showed moderate invasiveness levels, while Sida acuta, Malvastrum coromandelianum, and Tithonia diversifolia were categorized as severely invasive, though at a slightly lesser intensity compared to Ageratina adenophora. The Parochetus communis was the least invasive species detected, presenting minimal ecological disturbance. The presence and spread of invasive alien plant species within the Doi Chiang Dao Biosphere Reserve have significant implications for biodiversity conservation. Invasive plants compete directly with native and endemic species for essential resources such as nutrients, light, water, and space, potentially disrupting native ecological processes and reducing habitat quality for local flora and fauna. Human-mediated activities, including tourism, agricultural practices, and other anthropogenic disturbances, were identified as probable contributing factors to the dispersal and proliferation of these invasive plants. Furthermore, invasive alien plants can significantly alter ecosystem functions such as nutrient cycling, hydrology, soil erosion patterns, and even increase fire susceptibility. The dominance of invasive species at mid-elevational ranges suggests ecological niches that are highly vulnerable, possibly due to disturbed habitats and favorable climatic conditions. Effective management strategies must therefore consider specific ecological dynamics, elevational gradients, and potential anthropogenic drivers to mitigate the spread and establishment of invasive plants. Conclusion: The results of this extensive study clearly indicated that invasive alien plants are widespread along the nature trails within the Doi Chiang Dao Biosphere Reserve, particularly at mid-elevation areas. Species of Ageratina adenophora emerged as the most severely invasive species, presenting an immediate and substantial threat to local biodiversity. Therefore, it is critical to establish targeted management practices, including early detection, regular monitoring, physical removal, public awareness campaigns, and strict control measures. By implementing comprehensive management strategies, stakeholders can mitigate the adverse impacts of invasive plants and effectively safeguard the ecological integrity and biodiversity of the Doi Chiang Dao Biosphere Reserve for future generations.