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T.-C. Lin et al. 2010. Immediate effects of typhoon disturbance and artificial thinning on understory light environments
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In 2006, an experimental thinning on a Cryptomeria japonica plantation in central
Taiwan was initiated as an attempt to improve the structural heterogeneity and biodiversity of
the forest (Sun 2007). This was the first large and comprehensive experimental thinning in
Taiwan, and the study included assessment of a wide variety of biotic and abiotic consequences
(e.g. vertebrate and invertebrate diversity, recruitment of tree species, microclimate,
decomposition, and soil respiration) of forest management practices. Although the C. japonica
plantation under investigation is located at a moderate elevation (1500-1700 m), the study
aimed to produce recommendations for island-wide application (Sun 2007).
The objectives of the current study are to 1) characterize the forest understory light
environment before and after the experimental thinning, and 2) compare the impacts of artificial
thinning in the C. japonica plantation with those from typhoon disturbances in a mixed
evergreen hardwood forest at Fushan Experimental Forest in northeastern Taiwan (Fig. 1). In
both the C. japonica plantation and the Fushan Experimental Forest, we measured understory
light availability immediately before and after artificial thinning and typhoon disturbances to
determine whether artificial thinning results in patterns of understory light environments
comparable to those following typhoon disturbances characteristic of many low-elevation
forests in Taiwan.
2. Methodology
2.1 Study site
2.1.1 Cryptomeria japonica plantation: The Zenlun Experimental Forest
The C. japonica forest plantation is located in central Taiwan between 1500 m and 1700
m elevation. The natural vegetation in this area was clear-cut approximately 50 years ago and
replanted with C. japonica. The mean annual precipitation at the plantation is 3800 mm, and the
mean monthly temperature is 17.5 o C (Wang et al. 2007). The mean tree height was
approximately 17 m in 2006 (Chiu 2007 unpublished data).
In 2006, twelve 100 x 100 m plots were established at Zenlun Experimental Forest
following the design of large forest dynamic plots at the Center for Tropical Forest Science of
the Smithsonian Tropical Research Institute (Losos and Leigh 2004). The 12 plots were evenly
and randomly assigned to three treatments: unthinned, 25% thinning, and 50% thinning. Each
plot was divided into a grid of 100 10 x 10 m subplots, which were grouped into 25 20 x 20 m
operating plots. In the 25% thinning, one of the four subplots in each operating plot was
randomly assigned for clear-cutting; two non-adjacent subplots were randomly assigned for
cutting in operating plots assigned a 50% thinning. We established one 100-m transect
perpendicular to the elevational contours at the center of each of the 12 plots. In order to
monitor seasonal variation of understory light environment before thinning, transects at Zenlun
Experimental Forest were established one year before thinning. All transects were less than 3 m
from the edges of the thinning subplots; none of our sampling transects ran through the center of
the thinned subplots.
2.1.2 Natural forest: the Fushan Experimental Forest
The Fushan Experimental Forest is a mixed evergreen hardwood forest dominated by
Fagaceae and Lauraceae and located in northeastern Taiwan at elevations between 500 and 1200
m. Typhoons mainly occur between July and September, with infrequent typhoons as early as
May and as late as December. On average, 1.4 typhoons strike the Fushan Experimental Forest
each year (Mabry et al. 1998). The mean annual temperature at Fushan is 18.6 o C, and the mean
annual relative humidity is 96% (Hsia and Hwong 1999). The forest is multistoried with
Forest Landscapes and Global Change-New Frontiers in Management, Conservation and Restoration. Proceedings of the IUFRO Landscape Ecology
Working Group International Conference, September 21-27, 2010, Bragança, Portugal. J.C. Azevedo, M. Feliciano, J. Castro & M.A. Pinto (eds.)
2010, Instituto Politécnico de Bragança, Bragança, Portugal.