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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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Immediate effects of typhoon disturbance and artificial thinning on
understory light environments in two subtropical forests in Taiwan
Teng-Chiu Lin 1* , Kuo-Chuan Lin 2 , Jeen-Liang Hwong 2 & Hsueh-Fang Wang 3
1
Department of Life Science, National Taiwan Normal University, Taiwan
2
Taiwan Forestry Research Institute, Taiwan
3
Department of Geography, National Taiwan University, Taiwan
Abstract
We compared changes in understory light environments immediately following two typhoons,
and artificial thinning (25% and 50% of stems removed) in two subtropical forests. Both
typhoon disturbance and artificial thinning enhanced understory light availability in Taiwan, but
the enhancement following thinning, 42%, was considerably greater than that following typhoon
disturbance, < 25%. Understory light availability increased 45% and 120% after 25% and 50%
thinning, respectively. The diffuse nature of canopy disruption following typhoon disturbance
relative to the patchy and binary canopy removal associated with artificial thinning was likely
the reason for their very different impacts on understory light environments. It appears that
artificial thinning with more than 25% of stems removed increases understory light availability
to a level that does not naturally occur in low-elevation forests so that forest development
following artificial thinning is likely to be different from that following typhoon disturbance.
Keywords: typhoon disturbance; artificial thinning; understory light environment; Fushan
Experimental Forest
1. Introduction
The availability of light to understory plants is critical in determining patterns of the understory
plant community (Fahey and Puettmann 2007). Because light availability beneath undisturbed
forest canopies is typically low, enhancing understory light availability can increase the growth
and survival of both shade-tolerant and -intolerant tree seedlings (Chazdon and Fetcher 1984;
Oliver and Larson 1996). Disturbances that lead to enhancement of understory light availability
create opportunities for seedlings to grow into the mid-canopy and overstory and therefore play
a key role in determining the structure and function of forest ecosystems. Although artificial
thinning may create spatial and temporal heterogeneities in the understory light environment
and promote the growth of understory plants (Yanai et al. 1998; Wang et al. 2008), the
comparison of its impacts with wind disturbances, to our knowledge, has not been adequately
documented. Such comparisons are critical to evaluate whether artificial thinning results in
patterns and processes that are comparable to those following natural disturbances.
Typhoons are the most common natural disturbance in many low-elevation, subtropical
forest ecosystems, such as those in Taiwan with an average of three to four typhoons striking
Taiwan annually (Wu and Kuo 1999). Any silvicultural practice that intends to maintain natural
levels of light heterogeneity and species diversity in low-elevation forests must consider the role
that typhoon disturbance plays in regulating natural patterns and processes of these ecosystems.
* Corresponding author. Tel.: +886-2-7734-6240 - Fax: +886-2-2931-2904
Email address: tclin@ntnu.edu.tw
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.