Question: We investigated the bryophyte communities on tree boles along three altitudinal gradients located within different types of forested area to answer the following questions: (1) how many bole epiphytic bryophyte species are there; (2) what are the dominant species; (3) what are the richness patterns of epiphytic bryophyte communities along the altitudinal gradients; and (4) what are the major drivers and conservation implications of these patterns? 

Location: Three protected forested areas in sub-montane (Mengla transect:00–1400 m), montane (Zhenyuan transect: 2000–2600 m) and sub-alpine (Lijiang transect: 3200–3800 m) regions in Yunnan, SWChina. 

Method: Sixty 20 m 9 20 msampling plots were established, five at each of 12ltitudes at 200-m intervals along the transects. Species composition and cover of bryophytes were investigated from 594 subplots (each 400 cm2) on large tree boles of these plots. One-way ANOVAs were adopted to test for differences in species diversity among different transects. Multi-dimensional scaling in two dimension (MDS-2D) ordinations were conducted to assess similarity of bryophyte communities among study transects and altitudes. Canonical correspondence analysis (CCA) was applied to relate species composition to selected environmental variables. 

Results: The three protected forests in Yunnan harboured 226 epiphytic bryophyte species belonging to 101 genera and 46 families, which were essential components of biodiversity of the entire forest ecosystem. In total, 99% of bryophyte species (224 species) showed varying degrees of local rarity. Smooth mat, fan and turf dominated in the sub-montane, montane and sub-alpine forests, respectively. Significantly lower bryophyte species richness was detected in the sub-montane area, which may be partly attributed to higher temperature, limited water availability and more frequent human disturbance. Epiphytic bryophytes exhibited a hump-shaped species richness pattern with increasing altitude. Peak richness coincided with highestmoisture levels at ca. 2600 m. 

Conclusions: Based on the presence of a high diversity of bryophytes and a high percentage (99%) of locally rare species growing on tree boles, this study emphasizes the importance of conserving these forests in Yunnan. Additionally, the regional pattern of lower epiphytic bryophyte diversity in warmer, drier areas shown in this study reveals how emerging climate change threatens Yunnan’s epiphytic bryophytes.