4.3. The effect of topographic heterogeneity and
human-influence factors on conifer richness
Our results supported the positive topographic heterogeneity-diversity
relationship (see Table 1) which promotes the coexistence and
diversification of species by offering niche spaces and this agrees with
the findings of several studies (e.g. Stein et al. 2014; Lee &
Chun 2016; Shrestha et al. 2018; Sharma et al. 2019; Wanget al. 2019). Topographic heterogeneity was the main strongest
driver affecting conifers richness pattern, and this result has been
reported in several studies for tree species of Rhododerndron in
south-western China (Shrestha et al. 2018), rare woody plant
species in Inner Asian drylands (Liu et al. 2018b), and conifer
species in south-east Alaska (Bisbing et al. 2016). The high
richness of endemic conifers in
Qionglai-Minshan
and Hengduan Mountains may be rooted to the complex topography which
creates a wide range of habitats thereby providing more resources and
supporting a high number of species (Bisbing et al. 2016;
Shrestha et al. 2018). Furthermore, historically high rate of
plant diversification in south-western China was due to topographical
isolation based on a recent study of molecular phylogeny (Xing & Ree
2017; Shrestha et al. 2018). Hence, heterogeneity is thought to
have a significant effect on the structure and dynamics of plant
communities (Lee & Chun 2016; Moeslund et al. 2013). Moreover,
topographic heterogeneity is a significant effective variable used as a
proxy of habitat heterogeneity by controlling temperature, distribution
of soil water, and nutrient availability particularly at high
elevations, and thereby controlling species’ occurrence and plant
diversity in landscapes (Hofer et al. 2011; Bisbing et al.2016; Tashi et al. 2016). This supports our finding that
temperature had a negative correlation with conifer richness, but the
elevational range and soil nutrients had a strong positive correlation
(see Table 1).
The present study showed that, the negative correlation between the
human-influence factor and conifer richness was comparatively weak; it
is probably to have a significant influence in the areas with high human
population density (Panda et al. 2017). The contribution of
human-influence explained 4%, and this was greater than that of water
availability and climate seasonality indicating the significant effect
of human activity on the conifer richness of endemic-threatened species
due to logging activities (Schmiedinger et al. 2012; Venteret al. 2016), particularly Abies fargesii var.faxoniana, Abies fabri, Abies recurvate, Picea likiangensis, Picea
aurantiaca, Pinus yunnanensis, Pinus henryi, Cupressus chengiana(López-Pujol and Zhao 2004; Miao & West 2004; Threatened Conifers of
the World 2019; Farjon et al. 2019). Anthropogenic activity in
south-western China is lower than that of Europe, or northern America
maybe because most of our study conifers distributed at higher
elevations compared to Europe and America, so the human influence is
less (Schmiedinger et al. 2012; Threatened Conifers of the World
2019). In comparison, the effect of human influence factor showed less
contribution to the richness pattern than energy, topography, and soil
factors, and this finding supported by the results of Wang et al.(2010), who studied the tree species richness with tropical and
temperate affinities in China. Therefore, China provides future insight
and promising model for long-term studies of forest management.