*2.1. Study Sites*

This study was conducted at two selected sites in subtropical China. One is located at Huitong Forest Ecological Station in Hunan Province (26◦52N, 109◦42E), and the other at Datian Experimental Forest Farm in Fujian Province (25◦45N, 117◦33E) (Figure S1). Both sites are approximately 1000 km away from each other but have a similar humid, mid-subtropical, monsoonal climate with the average annual temperatures of 15~18 ◦C and average annual precipitation of 1350~1450 mm. The zonal vegetation is evergreen broadleaved forest; but establishing forests by plantation is more pronounced, and this has occupied more than 90% due to logging. The altitudes of both sites are 500–600 m ASL, soil types belong to red soil, but are classified as Oxisol in Hunan Province and Humic Planosol in Fujian Province, respectively, according to the FAO classification system. Chinese fir has become the most important a fforestation tree due to its fast-growing, easy processing, and wide utilization in both provinces [24].

### *2.2. Experimental Design and Investigation*

At each selected site from both provinces, we randomly established total eight plots (circles with 200-m<sup>2</sup> size); At each site of both provinces, there are four plots in pure Chinese fir plantations and four plots in mixed plantations with a broadleaved tree species (*Michelia macclurei* in Hunan Province or *Schima superba* in Fujian Province), respectively, which are located on the mid-slope with the slopes ranging from 25◦ to 30◦. Both *M. macclurei* and *S. superba* are native evergreen tree species, and widely afforested as pure or mixed forest due to rapid growth characteristic. In Hunan Province, both stand types were established in 1983 and common managemen<sup>t</sup> practices were used in the early stages of the

two stand types, including weeding and thinning. In Fujian Province, both stands were established in 1991 and similarly managed, such as weed-controlling during the first three years and thinning during the first 10 years (for more details see [23]). All sixteen selected plots were independently distributed in different hills, and generally far away, with more than 500 m between two plots of the same stand type.

In May 2013, the diameter at breast-height (DBH) and species of trees with a DBH > 2 cm were measured and recorded in all plots of both sites. The stand basal area was obtained at plot level. Meanwhile, general stand characteristics, including stem density, shrub density, and herb cover were investigated (See Table 1).

**Table 1.** Stand characteristics (means and standard errors, *n* = 4) of pure Chinese fir plantations (PP) and its mixed plantations with a broadleaved tree species (MP) at two sites located in Hunan and Fujian provinces of China.


Note: The broadleaved tree species are *Michelia macclurei* and *Schima superba* in Hunan and Fujian provinces, respectively.
