| Summary: | 博士 === 國立臺灣大學 === 森林學研究所 === 90 === Variation in Vegetation Structure and Composition in Different
Micro-landforms and Regeneration Niches of a Steep Forest Plot
in the Fushan Experimental Forest, Northern Taiwan
Summary
The variation of vegetation structure and composition among micro-landforms and regeneration niches were examined in a 2-ha plot established on a slope extending from the mountain crest to bottomland in an evergreen broadleaf forest in the Fushan Experimental Forest, northern Taiwan. Seven micro-landforms (crest, upper slope, lower slope, foot slope-bottomland, smooth gully, steep gully, and landslide) and 3 regeneration niches (low-gap, high-gap, closed canopy) were recognized in this plot. Vegetation structure (represented by vegetation height profile, average canopy height, basal area of woody plants, and density of woody plants) and areas of gaps were compared among different micro-landforms. The chi-square test was used for demonstrating the association of certain species with different micro-landforms or regeneration niches.
There was significant difference in vegetation structure among micro-landforms. The vegetation developed better (higher average canopy height, larger basal area and density of woody plants) on the crest and upper slope where the effective soil was deeper and the inclination was flatter. In contrast, there were greater areas of canopy gaps recorded in the steep gully, foot slope-bottomlands and landslide patches where the effective soil was shallower due to soil erosion. Standing dead trees tend to aggregate on the crest and upper slope, while snapped and uprooted trees show no obvious aggregation. In conclusion, the regime of soil disturbance is the predominant factor influencing the vegetation structure and distribution of canopy gaps among different micro-landforms.
Ninety-nine woody species were recorded in 2 ha plot, and most of them significantly adapted to certain micro-landform (92 species) or regeneration niche (76 species). Many rare species tend to appear in the gap and/or micro-landform with frequent soil disturbance, such as lower slope, foot slope-bottomland, steep gully and landslide; and most of them are shade-intolerant. In contrast, common species often appear in closed canopy patch and/or the micro-landform with slight soil disturbance, such as crest and upper slope; and most of them are shade-tolerance species. There are more rare species in 2 ha plot while fitting to the lognormal distribution curve, and many rare species are shade-intolerant. Many rare species occurred in micro-landforms and/or gaps in which the soil is frequently disturbed. As a result, the α diversity in the plot is increased.
According to the regeneration niche selection among life stages, canopy tree (17 species) could be grouped into 4 categories. At sapling stage (dbh< 5 cm), most of canopy species (11 species) tend to exist in area of closed canopy; at young tree stage(5 cm≦dbh≦20 cm), most of canopy species (10 species) are evenly distribute among 3 regeneration niches. The regeneration niche adaptation may be modified at different life stages for some canopy species.
The species turnover rate between crest and foot slope-bottomland is 77.7%, which is much higher than that between low-gap and closed canopy. Therefore, the differentiation of micro-landform contributes more to β diversity than that of regeneration niche. In conclusion, micro-landform and regeneration niche differentiation is important mechanism for maintaining woody species diversity at local scale.
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