| Summary: | 碩士 === 國立臺灣大學 === 森林學系 === 81 === Basing on the patterns of radial increament, the life span of
Taiwan Hemlock can bedivided into three periods. the
establishment period starts from the formation of gap to about
25 years. The growing peroid, with intensive natural thinning,
lasts from the closure of canopy to the maturing stage of
Hemlock trees at about 250 years. Thereafter, the old-growth
period is experienced with low potential growth. These periods
correspond to the regeneration of vegetation in termsof patch
dynamics. With frequent small-scaled disturbance in the stand,
the Hemlock forest is capable of maintaining its climax state.
Six patterns of regneration niche produced by the disturbance
can be recognized. They are standing dead tree gap, tree-fall
gap, uprooting gap, small landslide gap, large gap on the main
ridge, and subcanopy tree-fall gap. Hemlock regenerations favor
the sites with soil disturbance, such as the uprooting gaps and
small landslide gaps in which many seedlings can be found.
Hemlock lacks valid advanced seedlings. No suppressed period is
evident in the radial increament. Thus Taiwan Hemlock uses
disturbed sites for regeneration niches, and is a light-
demanding species. Ohter broad-leaved species are not dependent
on canopy gaps for their regenerations, similar to the so-
called climax species. However, the subordinate hardwoods are
not capable of growing to the forest canopy, and the forest
dynamics is controlled by the growth process of Hemlock. The
dynamic cycle begins with the colonization of Hemlock seedlings
in the canopy gaps, followed by the growing and thinning of
trees, and edns in the senescence of old trees which are gap-
makers to reset the whole cycle. In accordance with the changes
of Hemlock canopy, other broad-leaved trees also develop and
regenerate under the forest.
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