The Composition And Biomass Of Epiphytic Materials And Their Relationships With Ecological Factors In Xujiaba Region From Ailao Mountain, Yunnan

Epiphytes are organism that grows non-parasitically on its hosts, which constituent important component in tropical and subtropical forest ecosystems, and they perform many irreplaceable ecological functions such as facilitating water and nutrient cycling and sustaining biodiversity. The present study examined:1) epiphytic bryophytes’ species composition and biodiversity among forests under different successional stages;2) the edge effect on epiphytes;3) the distribution of vascular epiphytes and their biomass along the canopy gradient; 4) the influence of ecological factors, including atmospheric relative humidity, host bark traits and etc, on the species composition and distribution pattern of epiphytes;5) how bryophytes from other substrate contribute to the biodiversity of epiphytic bryophyte community. The major results are as follows:1. This region habored rich flora of epiphytes. There were altogether 176 epiphytic bryophytes recored from 38 families and 83 genera, in which Homaliodendron flabellatum (Sm.) Fleisch, Plagiochila arbuscula (Brid. ex Lehm.) Lindenb., H. scalpellifolium (Mitt.) Fleisch., Floribundaria walkeri (Ren. et Card.) Broth, and Neckera crenulata Hedw. appeared to be dominante species in terms of number of quadrats occuppied. Totally 67 species of vascular epiphytes coming from 26 families and 41 genera were listed from the whole canopy, among which Polypodiodes subamoena (Clarke) Ching, Lepisorus scolopendrium (Ham. ex D. Don) Menhra et Bir, Araiostegia perdurans (Christ) Cop. and Polypodiastrum argutum (Wall. ex Hook.) Ching were dominant species by frequencies.2. The epiphytic bryophyte species composition between old-growth and secondary forests were rather different. Several life forms showed pronounced habitat preferences:the frequencies of fan [moss] and rough mat [liverwort] had decreased significantly in secondary forests, while the frequencies of turf [moss] had increased accordingly. Theβdiversity indices were dramatically reduced in secondary forests, especially in Secondary Alnus Forest, which is during the early stage of succession. Althought secondary forests were less capable of performing certain ecological functions as compared to old-growth ones, forests consisted from patches under different successional stages had created a combination of diversified habitats, which turned out to be rather crucial in sustaining epiphyte biodiversity. Sinskea phaea (Mitt.) Buck and Homaliodendron flabellatum were identified as indicator species for Old-growth dwarf mossy forest (ODMF) and Old-growth Lithocarpus forest (OLF) respectively. In addition, Neckera crenulata were indicative of Secondary Populus forest (SPF), while Brachythecium noguchii Tak., Pterobryopsis acuminate (Hook.) Fleisch., Spruceanthus semirepandus (Nees) Verd., Tayloria subglabra (Griff.) Mitt. and Frullania bolanderi Aust. were detected as indicator species for SAF.3. Edge effects had significantly influenced the biomass of epiphytes, coverage of epiphytic bryophytes, and density of epiphytic ferns along the edge-interior gradient. But edge effect had not affected the species richness of epiphytes across edge transects mainly due to uniformed atmospheric humidity in this region. However, edge effect had shaped the species compositon of epiphytes in transects near forest edge. The overall similarity coefficient between 10m and 80m transects were merely 0.506. Turf-life-formed (P<0.001) and weft-life-formed epiphyic bryophytes exhibited significant differences, where weft preferred habitats in forest interior and turf appeared more in transects near forest edge..4. Bryophytes, dead organic matter (DOM) and vascular plants were the major component of epiphytic material in the present study area, in which vascular plants (ca.47.0%) and bryophytes (ca.43.4%) contributed the largest proportion of the epiphytic biomass composition. There were "power function" relationships between epiphytes and their associated DOM with host DBH. It is then deduced the total biomass of epiphyte in OLF were 10.33 t·ha-1 from empirical regression functions. 80.6% of the total biomass was spatially aggregated in the section between 10m and 22m above ground. There were significant correlations between the biomass of DOM and the biomass of vascular plant and bryophytes, which well illustrated the significance of DOM in maintaining epiphyte biodiversity.5. The water-holding capacity influenced pendant in epiphytic bryophytes;the roughness of host barks affected the distribution pattern of turf; the the mass of woody debris (WD) positively correlated with the distribution of weft; and "canopy illumination index" regulated the distribution of dendroid. CCA ordination on the distribution of vascular epiphytes suggested that the majority epiphytes were not "nutrient-limited", and there were mutual benefical relationships between DOM and Polypodiodes subamoena, Araiostegia perdurans (Christ) Cop., Vitlaria plurisulcata Ching and Arthromeris lehmanni (Mett.) Ching.6) WD was especially important in sustaining the biodiversity of epiphytic bryophytes. The mass of WD clearly affected the distribution pattern of weft-life-fromed species in epiphytic bryophytes as whole, and nearly all epixylic species (ca.96.4%) were capable of transforming into facultative epiphytes, by dwelling on nearby host trees. Further quantitative analysis implied that the direction of bryophyte dispersal between these two substrate (WD and host trunk) was mutual.