孔隙對海岸林更新樹種之影響

Abstract

為供臺灣西北部海岸林混合造林或林下更新等措施作參考，本研究擬針對二大項目標試驗：一、選擇新竹縣新豐鄉新豐段及桃園縣新屋鄉蚵殼港段之海岸林調查林分現況，以從中評估目前更新之必要性及可能具適生潛力之樹種；二、嘗試以海檬果 (Cerbera manghas)、欖仁 (Terminalia catappa) 及瓊崖海棠 (Calophyllum inophyllum) 為直播材料種於新豐段現場，並以苗圃作為對照，再者於蚵殼港段大孔隙處的現有栽植苗作生長調查，探討這些樹種對不同孔隙環境之適應，進而評估於此地造林之成效。 林分現況調查結果：林分組成皆以木麻黃 (Casuarina spp.) 為主，且已呈現衰退趨勢，朴樹 (Celtis sinensis) 有機會成為穩定族群但數量不多，可以人為方式促進更新，而黃槿及 (Hibiscus tiliaceus) 林投 (Pandanus odoratissimus) 生長良好，可混植於木麻黃林下營造成複層林模式。 直播及栽植試驗結果：依據三樹種於苗圃之試驗，形態特性上海檬果及欖仁在全光有較佳之生長量，瓊崖海棠為全光至相對光度20 % 環境較佳；光合特性上海檬果及欖仁皆以全光環境之最大淨光合速率顯著最高，瓊崖海棠於光度環境間無顯著差異；葉綠素螢光特性在全光環境下海檬果稍受影響但黎明Fv/Fm值顯示仍屬健康，其他二者無受影響。綜合結果三者可適合全光至相對光度20 % 間，然瓊崖海棠於全光下也無較佳之生長表現。而進一步對照現場試驗，海檬果發芽率及生長量皆低於苗圃海檬果，且存活率在大孔隙較低，顯示海檬果在環境惡劣處可能無法適應高光，欖仁及瓊崖海棠則發芽率甚低。 整體而言三樹種於海岸林分更新作業上，海檬果較適合直播於小孔隙，相對光度約40 % 至20 %，欖仁可直播於空曠地至各孔隙處，相對光度約20 % 以上，惟仍需有效提高二樹種發芽率；而二者栽植苗整體適應情況佳，因此也可以栽植方式種植。瓊崖海棠可嘗試與欖仁同樣之光度環境但較適合採栽植作業。而其餘栽植樹種也可作為此地區更新之選擇，較建議從林分內緣處建立以提高造林成功率。

To offer the reference of mixed forest or forest understory regeneration for coastal forest in northwest Taiwan, we directed at two objective to study: First, we investigated stand condition in coastal forest in Xinfeng section, Hsinchu county and Kekegang section, Taoyuan county, then estimated the essentiality of regeneration and the adaptive species; second, we selected seeds of the Cerbera manghas, Terminalia catappa and Calophyllum inophyllum as sowing materials, then sowed the seeds at Xinfeng field, and nursery as the control group. Moreover, we investigated transplanting seedlings at large gap in Kekegang section. To explore the adaptation of these experimental species in the different gap environment and the results of forestation of these species further. The results of stand condition: Casuarina spp. were the major species but they showed signs of deterioration. Celtis sinensis might have an opportunity of becoming a stable population but it was deficient in quantity. This suggested that artificial manner could promote the assignments of regeneration. Furthermore, Hibiscus tiliaceus and Pandanus odoratissimus showed the greater growth performance so it could plant in the understory to construct a multistoried forest The experiment results of the sowing seedlings and the transplanting seedlings: In the nursery’s seedling, the characteristics of morphology indicated the C. manghas and T. catappa had better growth at the full light, C. inophyllum had better growth at the relative light environment of 20 % to the full light; the characteristics of photosynthesis indicated the C. manghas and T. catappa showed the greater net photosynthetic rate at the full light, and C. inophyllum had similar values between the light environment treats; the characteristics of chlorophyll fluorescence indicated the C. manghas was slightly influenced at the full light but it was still healthy according to Fv/Fm of predawn, T. catappa and C. inophyllum were not influenced. Summarizing the above results, seedlings of three species were suitable at the light environment of 20 % to the full light, but C. inophyllum couldn’t have better growth at the full light. Contrast to the field’s seedling further, sowing seedlings of the C. manghas performed lower germination percentage and morphological sections than the nursery’s seedlings, and lower survival rate at large gap. This indicated that C. manghas might not adapt to high light in harsh environments. Germination percentage of the T. catappa and C. inophyllum was very low. Summarizing the sowing seedlings results, C. manghas was suitable for sowing to small gap which were in the light of 20 % to 40 % and T. catappa was suitable for sowing to gap or open site which were above the light of 20 % when implementing understory regeneration for coastal forest, but it required on the premise that effectively improvement of the germination percentage; moreover, C. manghas and T. catappa had good adaptation, hence they were also suitable for planting. C. inophyllum was also suitable in the same light environment with T. catappa, but it was more proper for planting. The other transplanting seedlings could be used for regeneration in the region. To improve successful probability, it suggested that transplanting seedlings planted in the interior of stand from the start.