Heat stress effects on the germination of Brachychiton populneus (Schott & Endl.) from Al-Jabal Al-akhdar area, Libya

Optimum temperatures play a crucial role in improving seed germination and seedling establishment for both tropical and non-tropical trees, and they are essential for developing effective strategies for vegetation restoration. The present study investigated the effect of heat stress on the germination and seedling growth of Brachychiton populneus (Schott & Endl.). Germination tests were conducted over one month under three constant temperature conditions (20, 30, and 40 °C) and one alternating temperature regime (25–35 °C; 12 h/temperature), after soaking seeds in distilled water for 12 and 24 hours.  Results indicated that the heat stress negatively affects germination percentage, mean germination time, mean daily germination, seedling length, seedling vigor index, fresh and dry seedling weight, and seedling moisture percentage. The optimum germination condition is observed at the alternating temperature (25–35 °C) after 24 hours of soaking, which yields the highest germination percentage (93.3%) and the shortest mean germination time (3.75 days). The results showed that the minimum germination temperatures for B. populneus seeds were 20°C, and the maximum (40°C). This study concludes that B. populneus seeds exhibit better germination performance under alternating temperatures, highlighting the species’ adaptability to fluctuating thermal environments and providing valuable insights for its propagation and restoration in heat-prone regions.