Tertiary relic deciduous forests on a humid subtropical mountain, Mt. Emei, Sichuan, China

The floristic characteristics, age structure and survival modes of Tertiary-relic deciduous forests were analyzed at 1600 m on Mt. Emei (3099 m), Sichuan, China. Three plots were selected to represent typical topographies: Plot 1 at 1620 m on a scree slope, Plot 2 at 1640 m on a slope with moderately rocky soils, and Plot 3 at 1616 m on a gentle slope with less rocky soils. At Plot 1, on the scree slope, the forest was rich in species and dominated by Tertiary remnants and other deciduous trees (Davidia involucrata, Styrax hemsleyana, Cercidiphyllum japonicum var. sinense, Pterocarya hupehensis, Prunus brachypoda, Prunus padus, Tetracentron sinense and Staphylea holocarpa). The relic deciduous tree taxa Davidia, Cercidiphyllum, Tetracentron and Euptelea occupied the unstable concave slopes, where evergreen broad-leaved trees (Castanopsis platycantha and Machilus pingii) were rarely able to survive. On the relatively stable convex slopes of this plot, evergreen trees with small diameter mainly appeared in the subcanopy and shrub layers. Davidia involucrata was the dominant species in this forest. On the slope with moderately rocky soils (Plot 2), the forest was co-dominated by relic Davidia and other deciduous (Styrax and Pterocarya), and evergreen trees (Castanopsis and Machilus). On the gentle slope with less rocky soils (Plot 3), Davidia trees were found only in the subcanopy and shrub layers, and the forest was dominated by Machilus, Castanopsis, Styrax and Prunus trees. Regeneration of Davidia occurs mainly on the scree slope where landslides are most common. The age structure of the Davidia stands indicates that this species is able to survive on the unstable scree habitat due to its strong sprouting ability. The Tertiary-relic deciduous forest on the scree slope is seen to be a topographic climax forest.