*2.2. Successional Stages*

The forest is free of human disturbance for 400 years according to the records of a nearby Buddhist monastery. However, according to local history, the northeast part of the plot was assumed to be established approximately 60 years ago [25]. In order to confirm that these two parts of the plot are at different age and successional stage, we took advantage of distribution of *Castanopsis chinensis* and *Pinus massoniana* in the plot. *C. chinensis* is assumed to be the foundation tree species when Dinghushan subtropical forest is close to successional climax. *P. massoniana* is a pioneer species and its prosperity suggests early successional stage.

We found that the small and large individuals of *C. chinensis* were discriminately distributed in the plot. Generally, large trees of *C. chinensis* (DBH ≥40 cm) occurred mostly in the southeast corner of the plot, while *P*. *massoniana* occurred mostly within the west part of plot (Figure 1). The west part of the plot was planted to *P*. *massoniana* and then protected for more than 60 years (since the establishment of the nature reserve). *P*. *massoniana* is now in a state of recession with *C*. *chinensis* replacing *P*. *massoniana*.

**Figure 1.** Distribution of *Castanopsis chinensis* (**a**) and *Pinus massoniana* (**b**) trees ≥ 1 cm DBH in the 20 ha DHS plot. Dot size was characterized in equal proportion of individual's DBH.

For determining the dividing line between these two parts, we calculated relative age of each 20 m × 20 m quadrat. We calculated the relative age of the biggest four trees in each quadrat, which is the dbh of each individual divided by the biggest one of the same species in DHS Plot [26]. The mean of the relative age of these four trees were taken as the relative age of the qudrate. The quadrats were classified into five groups (T1 to T5 from the youngest to the oldest) based on relative age (Figure 2). We obtained a line to separate the old-growth and the young subplots (the blue line in Figure 2). On the left of the line with light colored denoted the young patch, while on the right of the line with dark colored was the old-growth patch.

**Figure 2.** Location of successional forest (left of blue line) and mature forest (right of blue line) within the 20 ha (400 m × 500 m) plot in DHS Plot. From the oldest to the youngest: T5, T4, T3, T2, T1.
