Picea is one of the most dominant conifer genera in the Northern Hemisphere and includes species which require coarse woody debris (CWD) as a seedbed for regeneration. To understand the future of forest distribution under global climate change, it is important to investigate regeneration mechanisms in Picea forests on the borders of its distribution. In the present study, we evaluated the biotic factors affecting the establishment of Picea jezoensis var. hondoensis seedlings on CWD in one of its southernmost populations in central Japan, where there is dieback of Picea forest. Amplicon sequencing of the fungal ITS1 region of rDNA obtained from wood samples showed that forest dieback increased the frequency of brown rot fungi in CWD. The frequency of brown-rotted wood, in which wood holocellulose is decayed, increased with dieback intensity. The domination of brown-rotted wood in dieback forests was negatively associated with bryophyte cover which was positively associated with Picea seedling density. Forest dieback itself also had other strong negative effects on bryophytes. Thus, linkages between dead wood and spruce seedlings via bryophytes had collapsed after the dieback event, which may partly be a reason that the spruce forest shifted to and is staying as open grassland.

云杉是北半球最主要的针叶树属之一，其中包括需要粗木屑（CWD）作为再生苗床的物种。为了了解全球气候变化下森林分布的未来，重要的是研究其分布边界上的云杉林更新机制。在本研究中，我们评估了影响云杉云杉建立的生物因素。hondoensis上CWD幼苗在日本中部，其最南端群体之一其中存在的顶梢枯死云杉森林。从木材样品中获得的rDNA真菌ITS1区域的扩增子测序表明，森林枯死增加了CWD中褐腐真菌的发生频率。棕色腐烂木材的频率随其回缩强度的增加而增加，其中棕褐色纤维素被腐烂。枯萎森林中褐色腐烂木材的优势与苔藓植物的覆盖负相关，而苔藓植物的覆盖与云杉幼苗的密度正相关。森林枯死本身也对苔藓植物具有其他强烈的负面影响。因此，枯萎事件发生后枯死木材和云杉幼苗之间通过苔藓植物之间的联系已经崩溃，这可能部分是由于云杉林向开阔的草地迁移并保持其开放状态而造成的。