Characteristics and dynamics of Alnus nepalensis dominated forests in the subtropical region of Yunnan, southwestern China

Alnus nepalensis is a deciduous broad-leaved tree species. It commonly appears in patchy distributions following the destruction of evergreen broad-leaved forests or the abandonment of agricultural land in the subtropical region of Yunnan, southwestern China. This versatile and ecologically important tree species plays a crucial role in the environment. Studying its community characteristics and succession trends is vital for understanding diverse forest types and secondary succession in the subtropical areas. Through our field vegetation investigation, we identified six forest types, i.e., 1: Alnus nepalensis deciduous broad-leaved forest; 2: Alnus nepalensis-Schima wallichii deciduous and evergreen broad-leaved mixed forest; 3: Alnus nepalensis- Pinus armandii deciduous broad-leaved and evergreen coniferous mixed forest. 4: Alnus nepalensis-Litsea monopetala deciduous and evergreen broad-leaved mixed forest. 5: Alnus nepalensis-Quercus aliena-Pinus yunnanensis deciduous broad-leaved and evergreen coniferous mixed forest. 6: Alnus nepalensis-Quercus delavayi deciduous and evergreen broad-leaved mixed forest. Among the six forest types, the Shannon-Wiener diversity ranged from 1.1 to 2.1. In all the forest types, A. nepalensis trees were predominantly found in DBHs of 10-30 cm with ages of ca. 10-30 years. Its maximum age reached ca. 95 years with a DBH of 132 cm. In central Yunnan, the successional pathways: transitioning from Alnus nepalensis-Quercus aliena- Pinus yunnanensis deciduous broad-leaved or evergreen coniferous mixed forest, Alnus nepalensis-Pinus yunnanensis-Quercus aliena mixed forest, or Alnus nepalensis deciduous broad-leaved forest, gradually shifting to Alnus nepalensis-Quercus delavayi deciduous and evergreen broad-leaved mixed forest, and ultimately progressing to Quercus delavayi evergreen broad-leaved forest.