Time-dependence of forage quality for large herbivores in seasonally dry tropical forests, Western Thailand

Abstract

Forage quality serves as a key indicator of habitat health in protected areas. In the buffer zone of the Huai Kha Khaeng World Heritage Site, a critical habitat for endangered herbivores of Thailand, limited data on forage quality hampers effective habitat management for large herbivores. This study examines seasonal variations in forage quality in the seasonally dry forests of Western Thailand based on 6 surveys conducted in 2018–2019. A nutritional analysis of 55 dominant forage species (12 forbs, 16 shrubs, and 27 tree seedlings) revealed a prolonged annual period (~8–9 months) of low forage quality. Peak nutritive content occurred at the start of the rainy season (April to June), with crude protein (CP) highest in April (16.9%) and lowest in February (10.4%). Forbs consistently provided higher CP (peaking at 16.1% in August), while shrubs contributed more fiber, with neutral detergent fiber (NDF) and acid detergent fiber (ADF) levels rising from 39.9% and 28.8% in April to 45.6% and 38.6% in the late rainy season. Acid detergent lignin (ADL) levels were lowest in April (11.8%) and peaked in August (16.3%). Seasonal shifts in forage quality were reflected in the proportion of species in high-quality (A1) and lower-quality (B1–D3) classes. The A1 forage peaked in April (56.3%, 9 species) but declined sharply by August (8.3%, 1 species). During the dry season, medium- and low-quality forage (B1, C1, D1) predominated. These findings emphasize that integrating forage quality dynamics into habitat management planning can play a key role in supporting the ecological needs of large herbivores and sustaining their long-term populations.