*2.1. Site Description*

This study was conducted at the Long-Term Research Station of Alpine Forest Ecosystem in the Bipenggou Valley (31◦14~31◦19 N, 102◦53~102◦57 E, 2458~4619 m above sea level (masl)), Li County, Southwest China, which is located in the alpine gorge area with frequent geological breaks, clear seasonal snow cover (the maximum snow depth was about 35 cm), and frequent freeze/thaw cycles [7] (Figure 1). The mean annual precipitation is approximately 850 mm, and the annual mean air temperature is approximately 3 ◦C, with maximum and minimum temperatures of 23 ◦C (July) and −18 ◦C (January), respectively. The frozen season lasts from November to April, and thaw begins in late April. This subalpine forest is dominated by Minjiang fir (*Abies faxoniana* Rehder & E.H.Wilson), larch (*Larix mastersiana* Rehder & E.H.Wilson), and cypress (*Sabina saltuaria* Rehder & E.H.Wilson), and is interspersed with shrubs of azaleas (*Rhododendron* spp.), willow (*Salix* spp.), and barberry (*Berberis sargentiana* C.K.Schneid). The herbaceous plants consist mainly of ferns (*Cystopteris montana* (Lam.) Bernh. ex Desv) [7]. The concentrations of carbon (C), nitrogen (N), and phosphorus (P) in the surface soil (5 cm depth) was 126.0, 5.8, and 1.2 g kg−1, respectively.

**Figure 1.** The investigated streams in the Bipenggou Valley, located in the upper reaches of the Yangtze River. The letters A–O indicate the 15 sampling streams [7].
