Regeneration patterns of yellow cypress on down logs in mixed coniferous-broadleaf forest of Yuanyang Lake Nature Preserve, Taiwan

Abstract

The importance of down logs in forest gaps for forest development, tree regeneration, and the co-existence of yellow cypress (Chamaecyparis obtusa Sieb. & Zucc. var. formosana (Hayata) Rehder) and broadleaf trees was studied in the temperate forest of Yuanyang Lake Nature Reserve (YYL), Taiwan. On nine down logs in a plot of 0.25-ha, seedlings with diameter at breast height larger than 1cm were recorded. It was found that the species occur- ring on the sampled down logs were the same as those in the studied area. Few broadleaf trees could reach the height of 10m necessary to change the current canopy layer, which mainly consisted of yellow cypress. Regeneration of trees on down logs was sufficient to maintain the forest community, including its floristic composition, canopy structure, and species diversity. Tree seedlings of different species also varied in their distribution patterns on down logs. Yellow cypress seeds germinated on new down logs, but not on root swellings. The seedlings grew to fill gaps, while density was reduced from young to old down logs, possibly due to intra-species competition. Epiphytic bryo-phytes on new down logs seemed to provide a suitable habitat for the germination of yellow cypress seeds. In contrast, broadleaf trees grew mainly on the base and root swellings of new down logs and gradually recruited their seedlings onto other parts of older down logs. Availability of nutrient resources seemed to be the important determi-nant for the competition between seedlings of cypress and broadleaf plants. The niche partition hypothesis was employed to explain the regeneration of cypress plants in this nature preserve.