Effects of gap-model thinning intensity on the radial growth of gap-edge trees with distinct crown classes in a spruce plantation

Radial growth responses of gap-edge trees to GT intensity greatly depends on microclimate condition (soil temperature and PAR) within gaps and their abilities in competing and utilizing the limited resources. Gap-model thinning (GT) is an effective management technique to improve the productivity of dense monoculture plantation. However, how GT intensity influence inter- and intra-annual radial growth of the gap-edge trees remains an open question. In order to explore this question, we implemented an experiment with four treatments (control and gap sizes of 74, 109, and 196 m(2)) in a 30-year-old spruce (Picea asperata) plantation in 2008. We used dendrochronological method to explore dynamic of the basal area increment (BAI) of gap-edge trees (n = 127) from 2009 to 2012 after GT treatments. We found that effects of GT on the BAI of gap-edge trees highly depended on GT intensity and their crown classes. The large gaps significantly increased the BAI of gap-edge trees and further the latewood growth responded more sensitively than the earlywood, whereas the influences of the small and intermediate gaps were weak; the large gaps effectively improved the BAI of the dominant trees, following by the intermediate, but not for the suppressed trees. Our results also displayed that the earlywood increment was strongly related to the soil temperature in spring and the latewood formation was influenced by the photosynthetically active radiation in autumn. It was eventually concluded that dynamic radial growth of gap-edge trees were driven by the improved microclimate caused by GT and their abilities in competing and utilizing resources. The present study highlights the importance of setting appropriate GT intensity and choosing the felled trees in GT operation.