Abstract:
A better understanding of the spatiotemporal dynamics of species composition and
biodiversity provides significant insights into the distribution patterns of biodiversity and the
prediction of biodiversity fate in a global change context. However, how species and phylogenetic
diversity change along elevational gradient with temporal scale in mountain ecosystems is largely
unknown. In this study, we used census data (2004, 2008 and 2013) of an elevational transect
(elevational range 960-2 878 m) covering eastern and western slopes of Gaoligong Mountains,
SW China, to investigate the spatiotemporal dynamics of forest arbor layer (DBH≥5 cm) species
diversity and phylogenetic diversity. The results were as follows: (1) Species diversity was humpshaped
along the elevational gradient, while the phylogenetic diversity increased with increasing
elevation. Clustering phylogenetic structure was observed at low elevations, and overdispersed or
random structure was detected at high elevations. (2) Overall, temporal species and phylogenetic
beta diversity analysis showed no significant difference among these three investigation time
points. However, we found a higher clustering of phylogenetic structure along the temporal scale.
(3) Spatial beta diversity showed that there was a significant loss of species at low elevations
(960-1 381 m) on the eastern slope, where the vegetation has been disturbed or completely
converted into farmland. The main lost species including Terminalia chebula, Quercus acutissima,Pistacia weinmanniifolia, Hovenia acerba and Ilex wattii. In contrast, the change in the western
slope is mild at low elevations, only observing species abundance increasing, which include
Cyclobalanopsis oxyodon, Symplocos chinensis, and Taiwania cryptomerioides. Therefore, we
speculate that the change in species and phylogenetic diversity of the arbor layer of subtropical
evergreen broadleaf forest may be related to succession process and climatic change in middle and
high elevations, while the communities at low elevations were seriously impacted by human
activities in the Gaoligong Mountains. The results will deepen the understanding of the
mechanisms of plant community dynamics in the Gaoligong Mountains and provide new insights
to guide precise conservation strategies in the region.