Abstract
To examine the effects of thinning intensity on wind vulnerability and regeneration in a coastal pine (Pinus thunbergii) forest, thinning with intensities of 20%, 30% and 50% was conducted in December 1997; there was an unthinned treatment as the control (total 8 stands). We re-measured the permanent sites to assess the regeneration characteristics 11 years after thinning. In the 50% thinned stand, seedlings aged from 2 to 10 years exhibited the highest pine seedling density and growth. The age composition ranged from 1–3 years with densities of 9.9 and 5.1 seedlings m−2 in 30% and 20% thinned stands; only 1-year-old seedlings with a density of 6.1 seedlings m−2 in the unthinned stand. Similar trends were found for the regeneration of broadleaved species such as Robinia pseudoacacia and Prunus serrulata. We speculate that the canopy openness and moss coverage contributed to the regeneration success in the 50% thinned stand, while the higher litter depth and lack of soil moisture induced the regeneration failure in the unthinned stand. The stands thinned at 20% or 30% were less favourable for pine regeneration than the stands thinned at 50%. Therefore, thinning with less than 30% canopy openness (20% and 30% thinned stands) should be avoided, and thinning at higher than 30% canopy openness (50% thinned stand, approximately 1500 stems ha−1 at ages 40–50 years) is suggested for increasing regeneration in the coastal pine forest. The implications of thinning-based silviculture in the coastal pine forest management are also discussed. The ongoing development of the broadleaved seedlings calls for further observations.
Highlights
The coastal forest, as a protective system along the shoreline, represents an important aspect of the natural environment
The canopy openness of the unthinned stand increased from 8.5% in March 2000 to 18.4% in 2003 and remained stable at 18.7% in 2008
Due to wind damage and self-thinning, the canopy openness of the unthinned stand increased by 18.37% in 2003 and was close to the canopy openness of the 20% and 30% thinned stands
Summary
The coastal forest, as a protective system along the shoreline (sandy soil), represents an important aspect of the natural environment. It is necessary to apply management regimes to establish and sustain the coastal forest to preserve the continuity of the protective or shelter functions. Japanese black pine (Pinus thunbergii Parl.), an evergreen species, is one of the most important tree species in coastal forests of the Japanese islands [3] and in other similar regions such as the shorelines in Shandong Province, China [4,5], because the tree species can resist pollution, salt and wind effectively [6,7]. To sustain the shelter functions of coastal pine forests, natural regeneration in accordance with modern sustainable management is considered an effective strategy for the forest ecosystems [8,9,10,11]. Thinning is the most important silvicultural measure to promote natural regeneration and maintain the continuity of shelter benefits
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