2.1 Study sites
A. faxoniana is mainly distributed in the western Sichuan
province of China, from 30°N to 35°N in latitude. Our study covered
three sites along latitudinal gradients, including the Wolong Nature
Reserve (latitude 30°53′N, longitude 102°58′E), Miyaluo Nature Reserve
(latitude 31°42′N, longitude 102°46′E), and Wanglang Nature Reserve
(latitude 33°00′N, longitude 104°01′E).
Wolong Nature Reserve is located in the western Sichuan Plateau, with
subtropical semi-humid climate, characterized by dry, cold winters and
wet, cool summers (Li et al. , 2020); the mean annual temperature
is 4.06 ◦C, and the mean annual precipitation is about
1062.8 mm. The dominant woody plant species consist of A.
faxoniana , Picea purpurea Mast, Betula albosinensisBurkill, Betula platyphylla Suk, Ribes tenue Jancz,Sorbus koehneana Schneid, and Rosa moyesii , etc. The soil
type is classified as dark brown soil in coniferous forest according to
Chinese Soil Taxonomy (Zhang, 1983), which is developed from the
weathering of slate of metamorphic rock (Taylor et al. , 2006).
Miyaluo Nature Reserve is also located in the western Sichuan Plateau,
with subtropical semi-humid climate, characterized by dry, cold winters
and wet, cool summers (Li et al. , 2013) and mean annual
temperature of 1.67 ◦C and mean annual precipitation
of 975.2 mm. The dominant tree species consists of A. faxoniana ,Abies fabri (Mast) Craib, Picea purpurea Mast, Picea
asperata Mast, Populus davidiana Dode, and Quercus
aquifolioides , etc. The main soil type is classified as dark brown soil
in coniferous forest according to Chinese Soil Taxonomy, developed from
the parental materials of phyllite, slate, and schist (Keyimu et
al. , 2020).
Wanglang Nature Reserve is located in the Himalayas -Hengduanshan
Mountains, with subtropical semi-humid climate, characterized by dry,
cold winters and wet, cool summers (Zhao et al. , 2012) and mean
annual temperature of 4.17 ◦C and mean annual
precipitation of 1021.8 mm. The dominant tree species consists ofA. faxoniana, Picea purpurea Mast, Sabina saltuaria, Sabina
squamata, and Betula albosinensis Burkill, etc. The main soil
type is classified as dark brown soil in coniferous forest according to
Chinese Soil Taxonomy, with limestone as the main parental material
(Taylor et al. , 2006).