不同孔隙對海岸林樹種種子發芽之影響

Effects of Gaps in Seed Germination of Coastal Tree Species

本研究嘗試直播5種海岸林樹種海檬果、欖仁、瓊崖海棠、楝樹及台灣海桐（Cerbera manghas, Terminalia catappa, Calophyllum inophyllum, Melia azedarach and Pittosporum pentandrum）於臺灣新竹縣新豐段海岸林現場，探討不同光度及孔隙環境對種子發芽及幼苗存活之影響，並以苗圃作為對照，以評估直播於此地之成效及海岸直播造林之可行性。現場選定大孔隙、小孔隙及林下三種不同孔隙大小之林分，苗圃則設置相對光度100％、40％、20％及5％四種光度環境。經種子活力檢驗僅台灣海桐及楝樹發芽率有達一般標準，而實際於各光度及孔隙下之發芽結果顯示，各樹種在相對光度5％及小孔隙至林下者有較高之平均發芽時間，顯示若直播於光度過低之林下會拉長種子發芽速度，進而影響成苗率。楝樹為先驅樹種，在相對光度5％有顯著較低之發芽率，其餘樹種屬演替後期樹種，於相對光度及孔隙間無顯著差異。比較樹種間的發芽表現，海檬果及欖仁應受種子性質之故於二樣區之發芽率皆不高，應經適當促進並配合種子成熟期再行播種，然二者皆生長快速且存活率表現較佳，僅海檬果於大孔隙存活率有降低情形，建議海檬果較適合直播於林分小孔隙處及林下，欖仁應可直播至各孔隙處；瓊崖海棠與台灣海桐於現場發芽率低及無，以作業效益而言建議採栽植作業較有利；楝樹生長迅速，然其先驅樹種之特性，可選用於第二線林地之建立或大孔隙之補植，待順利育林成功後，再陸續於林下種植耐蔭性樹種以利其自行演替。整體而論試驗現場以海檬果有較佳之結果，可考慮作為此地造林之樹種選擇。

In this experiment we explored the effect of gap environment and light intensity on seed germination and seedling viability. We sowed the seeds of five littoral species (Cerbera manghas, Terminalia catappa, Calophyllum inophyllum, Melia azedarach and Pittosporum pentandrum) in the littoral field area in Xinfeng section, Hsinchu country, Taiwan, and in the nursery as the control. The goal is to assess the germination effect in that field area and the feasibility of seeding regeneration in littoral forest. We classified three gap types as large gap, small gap and understory in the field, and treated four light intensity treatments as 100 %, 40 %, 20 % and 5 % of sunlight in the nursery. In the seeds vitality test, only M. azedarach and P. pentandrum appeared normal vitality as generally mature seeds. As for the germination results in different light intensities and gap types, each species showed longer mean germination time (MGT) in the 5 % treatment and in the small gap to understory, indicating seeds germination time increases with insufficient light intensity and will affect tree percentage further. And considering germination rate, there were mostly no significant treatment difference in two sites except for M. azedarach in the nursery, therefore we could estimate primarily that M. azedarach is a pioneer species and the other species are mostly late-successional species. Moreover, species showing better germination and survival was estimated. That the germination rate of C. manghas and T. catappa weren't high in two sites seems to be affected by seed property. Germination rate can be enhanced through sprout promotion and time command depending on seed maturity stage. However, both species mentioned above showed fast growth and better survival, except C. manghas in the large gap that showed lower survival rate. This means small gaps or understory offer a more favorable environment condition for seeding of C. manghas, and any gap size may be suitable for seeding of T. catappa. C. inophyllum achieved its general germination rate in the nursery while showing a sharp decline in the field (T4, 5). It showed more scattered rate and longer MGT C. inophyllum, so planting regeneration might be better when considering regeneration benefit. M. azedarach is better applied for establishment of coastal second-line and replanting of large gap because of its being a pioneer species, which is beneficial for regeneration of shade-tolerant species planted subsequently in the understory. The small seed of P. pentandrum was a major restriction for seeding, so they were hardly observed in the field. Planting regeneration might be favorable for this species. In conclusion, C. manghas, having more feasibility for seeding regeneration, may be suitable as a planting species in this experimental littoral forest.