Ecological Habit Of Epiphytic Orchids In Wuzhi Mountain National Nature Reserve,Hainan Island, China

Epiphytic orchids are essential to biodiversity sustainability, water and nutrient cycling in forest ecosystems. With the habit specialities, epiphytic orchids are more prone to get endangered. Thus study of the ecological habit of epiphytic orchids is very important to the conservation of epiphytic orchids.In this research the species diversity, altitudinal distribution and ecological habit of epiphytic orchids in Wuzhi Mt. National Nature Reserve (N. N. R.), Hainan Island were studied during autumn (September2011) and spring (March2012) respectively. The results were as follows.1. Species Diversity:There’re36genera,70species of epiphytic orchids were identified in Wuzhi Mt. N. N. R. Dendrobium, Bulbophyllum and Cleisostoma were the predominant genera, and the genera having only one species summed up to26(72.22%). Only Sunipia scariosa and Dendrobium nobile contributed over10%in both the relative species frequence and abundance. The composition of species endangerment degree were:1critically endangered,19endangered,22vulnerable and28near threatened. Among all five epiphytic life-forms, the low-buds took prevalence, and no hemi-epiphytes were recognized. The Tropic Asia type is the dominant flora type in both genus and species level, which indicated strong tropical properties.2. Species Altitudinal Distribution(1) There’re61species of epiphytic orchids found among750-1867m altitudes. Sunipia scariosa counts the most frequent species even though it occurred only above1300m, whereas Dendrobium nobile, Campamulorchis thao and Bulbophyllum ambrosia were common from altitude to altitude, and D. nobile is the most abundant species.(2) Altitude from750m to1867m were grouping as6levels. The species diversity was generally declined over the increase of the altitudes except1300-1500m; species Endangered were typically found below1100m,1100-1300m contained the most richest areal-types. The distribution patterns of epiphytic life-forms showed that the low-buds were common among each altitude while the high-buds did not appear above1500m. The Closer the altitudes were, the higher the species similarity would be.3. Partitional Distribution on Individual Phorophytes(1) The differences of the species richness and the abundance of epiphytic orchids were not significant between trunk and canopy at750-1867m altitudes. The canopy partition was subdivided into inner canopy, middle canopy and outer canopy, both the species richness and the abundance in average were gradually decreased from the trunk to the outer canopy.(2) The species richness and the abundance of epiphytic orchids within each altitude level:At900-1100m, the trunk outweighed the canopy, whereas the difference was inverted at1300-1500m, and for the rest of four altitudes, the differences were not significant. Likewise, at900-1100m, both the species richness and the abundance were gradually decreased from the trunk to the outer canopy, but the differences between the trunk and the inner canopy were not significant for the rest5altitudes and the trunk outweighed either the middle canopy or the outer canopy. At750-900m, there is no significant differences between the inner canopy and the middle canopy, while for the rest altitudes, both the species richness and the abundance were greatly decreased from the inner canopy to the outer canopy.(3) Among the nine differentiated epiphytic orientation, both the species relative abundance and occurring frequence were greatly different,"circumference" accounted for the most abundant orientation, and "northern" was responsible for the highest occurring frequence.4. Relationship between Epiphytic Orchids Diversity and phorophytes species&DBH(1) The species richness of epiphytic orchids were irrelevant to the total heights of the phorophytes, trunk heights or diameter breast heights (DBH) classes, whereas, the abundance were strongly positively correlated with the total heights of the phorophytes and DBH classes, but had no relation with the trunk heights. Typically, the total heights of the phorophytes, trunk heights or diameter breast heights (DBH) classes contributed more to the abundance than the species richness.(2) In general, there’re196phorophytes recorded, which had been categorized into50species,33genera and21families. Pinus kwangtungensis, Syzygium araiocladum, Liquidambar formosana, Cyclobalanopsis championii and Gordonia hainanensis were the most popular phorophytes for both species richness and abundance of epiphytic orchids, while the phorophytes species showed no specificity with epiphytic orchids species, each epiphytic orchid had seen a broad spectrum of phorophytes.