Ecological studies of epiphytic bryophytes along altitudinal gradients in Southern Thailand

Abstract

Southern Thailand is one of the richest areas in terms of biodiversity. It is a part of the Indo-Burma and Sundaland biodiversity hot spots. It also included the transition zone between Indo-Chinese and Malesian floristic regions. However, there is no data on bryophytes, despite the fact that it is an important component of epiphytic community. Even though bryophytes are, mostly, small and inconspicuous, they are important components of tropical forests, especially the montane ones, and might play the significant role in the water balance and nutrient cycling of such type of forest. As different bryophyte species might have their particular patterns of distributions along the different altitudinal areas vertically and they might have different habitat preferences due to the different potential environmental variables. In spite of that, there have been poorly studying of how do the epiphytic bryophytes distribute along an altitudinal gradient, particularly, in the paleo-tropical forests like those in the South-east Asia Mainland and how do the potential environmental variables regulate their distributions.<br /> The present dissertation is containing results of a study on diversity and ecology of epiphytic bryophytes along altitudinal gradients in Southern Thailand. The purpose of this study is to determine species richness and community composition of epiphytic bryophyte and to correlate them with some selected ecological parameters such as altitude, temperature and air humidity. In additions, the measurements of pH bark of the host trees had been achieved together with the determinations of the biomass, water storing capacity and covered percentage of epiphytic bryophytes along the altitudinal gradients in some selected less-disturbed tropical forest patches in Peninsular Thailand. It is to be noticed that this is the first comparative study on the epiphytic bryophyte in Thailand and the first study of such issue on the South-east Asian mainland as well.<br /> The first part (Chapter 3) is dealing with the biomass of epiphytic bryophytes along the altitudinal gradients from lowland to montane forests. In additions, the microclimate and the pH of the bark of host trees were measured, together with the determinations of water storing capacity of epiphytic bryophytes as well as the estimations of the biomass and water storing capacity per hectare. <br /> Biomass of epiphytic bryophytes was investigated along three altitudinal transects in Southern Thailand. i.e. Tarutao National Park (25-700 m), Khao Nan national Park (400-1300 m) and Khao Luang National Park (400-1500 m). The results had demonstrated that the dry weight of epiphytic bryophytes per surface area increased from 1.15 g/m2 in the lowland to a maximum of 199 g/m2 in the montane forests. The estimation of dry weight per hectare had increased along the transect from 2.4 to 620 kg. The water storing capacity of epiphytic bryophytes was about 1.2 to 2.4 times as much as a dry weight and was generally higher in the montane (up to 1500 l/ha) than in the lowland forests. The result showed that the biomass and water storing capacity of epiphytic bryophytes had increased with higher altitudes from lowland to montane forests at all transects. <br /> The bark pH values of host trees ranged between 3.19 and 6.84 and showed negative correlation with the altitude (r = -0.635, p < 0.05). <br /> The microclimatic measurements were performed in dry season (December to April). At each site, a data logger had placed at 1.5 m above the ground and recorded the air temperature (°C) and the relative air humidity (%RH) in 10 minute intervals. Air temperature gradually had decreased with the increasing altitude ca 0.6 °C per 100 m elevation, but the relative humidity had increased with the increasing altitude. The general pattern of the day climate was as follows: the temperature increased quickly at dawn (±6:00 am). The relative humidity decreased simultaneously. The highest temperature was recorded during the first hour in the afternoon (±1:00 pm). Late in the afternoon, the temperature had commenced to decrease again. The cooling period was rather quick after sunset for an hour (±6:00 pm) and the temperature had decreased slowly afterwards, during the rest of the night. The lowest temperatures were recorded during the early morning before sunrise. In contrast to the temperature, the highest relative humidity values were recorded in the early morning, while the lowest relative humidity values were recorded in the afternoon. This pattern may be interrupted by rainfalls and wind.<br /> The second part (Chapter 4) is paying attention to the species richness and the species composition as well as the distribution patterns of life forms of epiphytic bryophytes on tree trunks in lowland forest along the altitudinal gradient on Tarutao Island, and seeking the correlation, if any, between the epiphytic bryophyte communities and the selected physical environments concerning the bryophyte diversity of the tropical lowland forest.<br /> Epiphytic bryophytes had been collected along an altitudinal transect between 25 and 700 m a.s.l. In this study area, four 0.25 ha sampling plots were laid in approximately 200 m altitudinal intervals. A 20 × 20 cm quadrat with 5 vertical and 5 horizontal crosswire was placed on the bases of tree-trunks between 1.5 and 2 m above the ground. Within each 0.25 hectare plot, 15-20 trees with girths more than 30 cm up to 150 cm were studied. In total 61 species of epiphytic bryophytes were recorded from 75 quadrats which included 30 species of liverworts and 31 species of mosses. There is no significant difference of the bryophyte species richness between 25 m and 700 m a.s.l., however, the species composition changed markedly. Besides, the altitudinal gradient of 4 study sites had proved to be the most important factor in community differentiation of epiphytic bryophytes as indicated by DCA analysis. On one hand, the microclimate parameters might be the primary factors that correlated to the differences in diversity and species composition of bryophyte assemblages. On the other, the similarities of the host plant species were probably minor factors. Moreover, the result of TWINSPAN had shown that the communities of epiphytic bryophytes were clearly altitudinal grouping and four community types could be recognized. Furthermore, the distribution of the life forms among each bryophyte differed significantly along the altitudinal gradient. This might well explain the relationship between each epiphytic bryophyte group to its habitat. <br /> The third part (Chapter 5) is comparing the species richness, community composition and the ecology of epiphytic bryophytes in different altitudes from the lowland forest to the montane one at Khao Nan National Park, southern Thailand. It had demonstrated the distribution pattern of epiphytic bryophyte species as well as the epiphytic bryophyte communities along a given altitudinal gradient. <br /> As the same sampling method which had been explained in Chapter 3, epiphytic bryophytes were collected along an altitudinal gradient, ranged from 400 m to 1,300 m a.s.l. A total of 118 quadrats were sampled from six 0.25 ha plots. In total 138 species of epiphytic bryophytes were recorded including 83 species of liverworts and 55 species of mosses. Species richness of epiphytic bryophytes had increased with an increasing altitude. In addition, the species composition had changed significantly between altitudes. Liverworts were the important elements in terms of species numbers concerning epiphytic bryophytes. The number of liverwort species was more than that of moss species in almost all altitudes, except at the 600 m one. They performed a maximum species richness between 1,200 m and 1,300 m a.s.l. <br /> Mat and turf life forms species were the most common at all altitudes. Fan-like species were significantly the most common in a lowland forest (with low light intensity condition), whereas weft life form was a dominant one of the epiphytic bryophyte in a montane forest (with high light intensity condition). The results had shown also that the fan life form was succeeded by the weft life form at higher altitude.<br /> A quantitative analysis of the vegetation environment relationships consistently showed that the distributions of epiphytic bryophytes were affected by a complex set of factors, related to the altitudinal gradient, such as light intensity, air temperature and relative humidity. The microclimate parameters might be the primary factors that correlated to the differences in diversity and species composition of bryophyte assemblages. On the other hand, the characteristics of the host plant species (tree diameter, bark roughness) were probably minor factors. In fact, the zonation along the altitudinal gradient was clearly important in the TWINSPAN analysis with five community types could be recognized. The Sørensen’s similarity index had decreased with increasing the altitudinal distance. It is to be convinced here that the community composition of bryophytes gradually changed with the altitudinal distance.