Natural seeding and seedling occurrence in the Chamaecyparis forest at Chilan Mt.Area

Chamaecyparis formosensis and C. obtusa var. Formosana are two important tree species in the cloud forest zone in Taiwan. Because their wood quality and price are high, they have long been the major timbers for harvesting. But whether current harvest of snags and down logs in natural C. forest in Chilan causes negative or positive impact on Chamaecyparis regeneration, is still concerned by all parties involved in C. forest management issues. We tried to estimate natural seeding and seedling survivor patterns in the forest floors with different time spans after harvest of snags and down logs in Chilan. 3 sites along forest road 130,160 and 170 were selected to represent the sites of 1, 8 and 14years after snag and down log harvest respectively. The result indicated, the amount of seeds collected on 3 sites was not significantly different from each other but differ in germination rates. As to weeding or weeding plus soil disturbance, they did not enhance seedling occurrence and survival rate significantly. Consequently, snag and down log harvest has not negative impact on the following natural regeneration. However, C. forest has a very obvious recurring of masting year for 3-5 years, it is recommended that the harvesting operation be conducted in the masting year. Under such circumstance, the seedbed would be readily prepared, and weed or shrub competition eliminated by harvesting operation. On the other hand, the higher survival rate of seedlings on down logs indicates that leaving some large down logs on the ground is beneficial to seedling establishment. But, how many large down logs should be left need to be further studied.

台湾红桧（Chamaecyparis formosensis）与台湾扁柏（Chamaecyparis obtusa var. Formosana）是中国台湾地区云雾林带的两类重要乡土树种。因其木材品质优异、经济价值颇高，长期以来均为主要采伐用材树种。然而，在栖兰天然桧木林分中，当前对枯立木（snag）与倒木（down log）的采伐作业，是否会对桧木天然更新产生正负向影响，仍是桧木林经营相关各方共同关注的核心议题。本研究旨在评估栖兰林区开展枯立木与倒木采伐后，不同时间跨度下林地内天然落种与幼苗存活的分布模式。研究沿林道130、160及170号线选取3处样地，分别对应枯立木与倒木采伐后1年、8年及14年的恢复样地。结果显示，3处样地的收集种子总量并无显著差异，但种子发芽率存在明显区别。针对除草或除草辅以土壤扰动的处理措施，并未显著提升幼苗发生概率与存活率。据此可知，枯立木与倒木采伐并未对后续天然更新产生负面影响。不过，桧木林具有显著的3-5年周期性结实大年（masting year）特征，因此建议采伐作业宜安排在结实大年开展。此时采伐作业可同步完成苗床整理，并通过采伐清除杂草与灌丛的竞争压力。另一方面，倒木上的幼苗存活率更高，这表明留存部分大型倒木于林地内，有助于幼苗定植。但具体应留存多少大型倒木，仍有待进一步研究。