Regeneration on CWD is generally a characteristic of cool-temperate to boreal forest conifers in forest ecosystems throughout Europe ( Hofgaard, 1993 Bače et al., 2012), the Pacific coast of North America ( Harmon and Franklin, 1989), and East Asia ( Kubota et al., 1994 Nakagawa et al., 2003). These coniferous species successfully regenerate at safe sites, which are most often decaying logs and areas of coarse woody debris (CWD) ( McCullough, 1948 Harmon, 1987 Suzuki et al., 1987 Nakamura, 1992), and some are so strongly dependent on CWD for their establishment that they are highly susceptible to changes in the environment. Sub-boreal conifer forests are widely distributed throughout the northern hemisphere, including North America, northern Europe, and western Siberia, and are mainly dominated by the genera Picea, Abies, and Tsuga. Therefore, it is possible that the colonization history of mature trees present on the study site might differ from that of the current offspring. This indicated that inbreeding depression, stochastic loss, or eradication of establishment sites by local disturbances alone could not explain the lack of FSGS among mature-stage trees. However, the results for the FSGS were significant for all simulated data sets. We calculated values for simulated offspring generated under three sets of conditions i.e., by removing (i) inbred individuals, (ii) randomly chosen individuals, and (iii) all individuals on the specific fallen logs. We ran a simulation to examine the hypothesis that the FSGS could be eliminated by demographic thinning during life history processes. In contrast to the results for the early stages, mature-stage trees showed no significant FSGS. These results indicated that genetically related seedlings and saplings regenerated on the same or nearby fallen logs. Furthermore, the estimation of dispersal kernels indicated the frequent occurrence of short-distance seed dispersal. We also found a significant FSGS in early life-stages based on a decline in the kinship coefficient calculated between individuals over shorter to longer spatial distances. A STRUCTURE analysis of seedlings and saplings established on fallen logs revealed that genetically related individuals were spatially localized between adjacent logs. The FSGS of the established seedlings and later growth stages was investigated using 11 nuclear simple sequence repeat loci. To understand the fine-scale spatial genetic structure (FSGS) of this species, a 5-ha plot was established in central Hokkaido, and 531 individual trees were categorized into four life-stages (seedling, sapling, juvenile, and mature) on the basis of age and size. In northern Japan, the sub-boreal conifer species Picea jezoensis is completely dependent on coarse woody debris for seedling establishment. 3Education and Research Center, The University of Tokyo Forests, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, JapanĬonifers in northern forests, such as fir and spruce, preferably regenerate on coarse woody debris, including fallen logs, stumps, and snags.2Asian Natural Environmental Science Center, The University of Tokyo, Tokyo, Japan.1Hokkaido Research Center, Forestry and Forest Products Research Institute, Forest Research and Management Organization, Sapporo, Japan. Keiko Kitamura 1, Atsushi Nakanishi 1, Chunlan Lian 2 and Susumu Goto 3*
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