| Summary: | 碩士 === 國立臺灣大學 === 森林環境暨資源學研究所 === 96 === This research is to investigate the microenvironment character of plantation and that under the influence of thinning. The experimental site of Cyptomeria Japonica plantation belonging to Nantou Forest District Office, Forestry Bureau was selected. 12 plots, each plot is one hectare, were taken in this experimental site that was treated by 0%, 25% and 50% thinning intensity with four duplications. Also, a weather station was set at open location near experimental site. Data include air temperature, relative humidity, photosynthetic active radiation (PAR), and soil temperature etc. of plots and weather station were collected from May 2006 to April 2008 that to compare the microenvironment difference between plots and weather station, and to compare that of plots before and after thinning.
Forest canopy can impede largely solar radiation incident upon forest land in daytime. Before thinning, from May 2006 to May 2007, observed data of 12 plots and weather station was compared that reveal monthly amount of PAR in plantation was about 1/10~1/4 as that of weather station and was less variation in month. Forest canopy can impede radiation energy input and output, which introduces energy exchange lagging in tree space. So, daily absolute temperature difference of plantation was lower than that of weather station, especially in summer. In observed period, yearly average air temperature of plots was higher 0.35 °C than weather station. Besides, relative humidity of plots changes smoothly in a day, which was usually higher than weather station, especially in winter. Others, Soil energy in plantation had longer exothermic state but at weather station had longer endothermic state.
After thinning, being completed on September 2007, microenvironment character of plot was affected and varied. When thinning intensity increases, more sunlight go through gap that introduces PAR increase obviously. Monthly amount of PAR in plots with 50% thinning intensity were about twice than that with 25% thinning intensity, and fourfold than that with control plot. Thinning also increase the chance of sunlight incident upon forest land directly. The result was that air temperature and daily absolute temperature difference increase but relative humidity decreases. Also, soil temperature of above 30 cm depth was change evidently after thinning, and increased more evidently in 50% thinning intensity plot. Besides, in December with soil energy at exothermic state, it revels that soil temperature near surface of thinning plot was lower than that of control plot.
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