Population structure and regeneration dynamics of Firmiana major, a dominant but endangered tree species

Firmiana major (Malvaceae) is a dominant tree species endemic in arid-hot and arid-warm valleys in Southwest China. Human disturbance, mainly the use of its bark to produce rope, caused a sharp decline in F. major populations before 1980s. The plant was declared extinct in 1998 but reappeared in 2001. Knowledge of population structure, regeneration characteristics, and current threats is fundamental for its conservation and recovery. In this study, we conducted field surveys and identified fourteen F. major localities, including eleven new localities. Fewer than 4,000 individuals were present in six populations. In four populations, the recruitment of new plants was low, while the other two populations had positive regeneration of seedlings and saplings. Grazing pressure might have caused a reduction in the number of younger trees. The case found in a national nature reserve proved that in situ protection over decades was essential in restoring and regenerating F. major (Panzhihua population). Although sprouting can promote F. major regeneration, it didn't revert the decline of the populations. The number of individuals and occupancy are highly likely to decline in the near future. Therefore, F. major falls into the Vulnerable (VU) category and should be classified as a Plant Species with Extremely Small Populations (PESEP) of China. The conservation implications and actions were introduced.