2.2 Vegetation characterization and phenology
The forest in the ECNNR was divided into four habitat types: cliff face,
slope, mountain peak, and valley-floor flatland. These habitats were
analyzed using stratified random sampling methods. We sampled 18 plots
(20 × 20 m) within the main study site, including four plots that were
located in the valley-floor flatland, nine on slopes, two on cliff
faces, and three on mountain peaks. These plots were located in the core
area of the langurs’ home range, which included more than 4% of the
langurs’ annual home range (unpublished data). Within these plots, all
the trees with a ≥ 3 cm diameter at breast height (DBH) were tagged. In
addition, to evaluate the dominance of each species within a plot, the
re each lative density (RD), relative frequency (RF), and relative
coverage (RC) were calculated for species as follows (Burton et al.,
2005):
RD = number of individuals of the species i /total number of
individuals in all the plots;
RF = number of plots with the species i/ total number of plots;
RC = sum of the basal area of species i /sum of the basal areas of
all the species.
Based on previous studies of langurs (Zhou et al., 2006) and our
two‐month pilot study, 32 plant food species were selected for phenology
monitoring. Then, 10 individuals of each species were randomly selected
and tagged in the main study area, and a total of 320 trees were
monitored. In addition, the data from the vegetation surveys and plant
phenology were combined to obtain appropriate estimates of food
availability. During the monthly phenology surveys, all the tagged trees
were visually inspected for the presence of young leaves, flowers, and
fruit, and their abundance (% of crown cover) was scored with a
five‐point scale: 0, absent; 1, 0.1–25%; 2, 25.1–50%; 3, 50.1–75%;
and 4, 75.1–100%. The monthly food availability index (FAI) was
calculated for the main food items (young leaves, flowers, and fruits)
by integrating the density, basal area, and phenology score of the plant
species. The formula was as follows:
\(\text{FAI}=\sum_{\text{i\ }=\ 1}^{n}D_{i}B_{i}P_{i}\),
where Di is the density of the tree species i (number of
stems/ha), Bi is the average basal area of tree species i(m2/ha), and Pi is the mean phenology score of
the particular food item in the crown of species i in a given
month (Albert et al., 2013).