1. ¹Genome Analysis Laboratory, Department of Forest Genetics, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305-8687, Japan
2. ²Laboratory of Forest Ecology and Physiology, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya Aichi 464-8601, Japan
3. ³Ecological Genetics Laboratory, Department of Forest Genetics, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305-8687, Japan
4. ⁴Kitakyushu Museum of Natural History and Human History, 2-4-1 Higashida, Yahatahigashi-ku, Kitakyushyu, Fukuoka 805-0071, Japan

Correspondence: S Ueno, Genome Analysis Laboratory, Department of Forest Genetics, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305-8687, Japan. E-mail: saueno@ffpri.affrc.go.jp

Received 1 October 2004; Accepted 20 December 2005; Published online 1 March 2006.

Abstract

The genetic structure of Camellia japonica saplings was investigated in relation to canopy conditions in an old-growth evergreen forest in Tsushima, Japan. To elucidate effects of canopy gaps on genetic structure, a 1 ha study site was divided into 20 20 m quadrats, which were classified into a gap quadrats (GAP), closed canopy quadrats (CLS) and mixed quadrats. Five GAP quadrats and six CLS quadrats were analyzed separately. Isolation-by-distance was tested by examining the correlation between genetic distance and geographic distance. A significant positive correlation was detected for GAP quadrats, whilst that for CLS quadrats was significantly smaller and not significantly different from zero. On the other hand, an analysis using Moran's I spatial autocorrelation coefficients indicates that the genetic structure is weaker in GAP quadrats than in CLS quadrats in short distance classes. The values were significantly positive for both types of quadrat. These results, along with our field observations on flowering, suggest that canopy gaps affect the genetic structure of C. japonica saplings in two distinct ways. First, canopy gaps may promote flowering and mating in an isolation-by-distance manner within canopy gaps. Second, canopy gaps may promote seed production and resulting overlap in seed shadows may weaken fine-scale genetic structures.