Reconstruction of forest change in highland Thailand: Evidence of anthropogenic disturbance, agriculture, and ecological restoration

Abstract

This study presents a high-resolution palynological reconstruction of late Holocene forest dynamics in Sri Nan National Park, Northern Thailand, to inform nature-based restoration strategies. Through stratigraphic analysis of a 140 cm sediment core, 22 subsamples were examined for pollen, spores, and non-pollen palynomorphs (NPPs), supported by Bayesian age–depth modeling. The palynological assemblages reveal three distinct ecological zones spanning ∼2800 calibrated years before present (cal BP) to the present, delineating a progressive transition from low-impact conditions to an increasingly anthropogenically modified agroecosystem. Zone I (∼2800–1600 cal BP) constitutes a low-count, preservation-limited interval in which palynomorph richness and abundance are minimal and arboreal pollen is restricted to a single horizon; consequently, forest dominance or disturbance status cannot be substantiated. Zone II (∼1600–800 cal BP) is a data-adequate, pre-intensification interval with elevated arboreal-to-non-arboreal ratios and low-to-moderate disturbance indicators, and is adopted as the most defensible ecological reference condition. Zone III (∼800 cal BP–present) registers high frequencies of cultivated and ruderal taxa (Zea mays, Poaceae), abundant fungal remains, and microbial proxies, reflecting intensive maize cultivation and ecological degradation. The persistent presence of Pseudoschizaea spp., testate amoebae, and arbuscular mycorrhizal fungi across the sequence underscores the significance of biological activity, hydrological variation, and human impact. These findings define defensible ecological reference conditions (anchored in Zone II) and provide a framework for context-specific restoration. This study demonstrates the utility of palynology in guiding evidence-based, biodiversity-centered, and temporally informed nature-based solutions (NbS) for forest restoration, particularly in degraded montane landscapes where socio-ecological legacies complicate recovery pathways.