高雄多納崩塌地耐陰樹種苗木之更新動態、生長及生理活動

高雄多納林道8.7km處，於2009年莫拉克颱風時發生崩塌。經歷10年自然演替後，此崩塌地某些區域已恢復成次生林，優勢植群為陽性先驅樹種，但也有耐陰樹種苗木建立。台灣山區地質脆弱且夏季常有豪雨侵襲，若崩塌地未經適當管理可能持續崩塌，故有以人為加速崩塌地植群恢復之必要。因此本研究之目的為了解多納崩塌地植群演替現況，特別關注耐陰樹種苗木的更新動態及生長狀況，並探討耐陰樹苗的生理活動在乾季時是否會顯著受抑制。這些生態學基本資訊可提供日後藉生態復育方式加速此崩塌地植群演替之科學依據。本研究於2017年7月在多納崩塌地設立了四個面積各0.25 ha的大樣區，每隔2~6個月調查所有耐陰樹苗的數量及植株高度。2019年2月調查時，四個大樣區內共有樹苗851株，包含陽性樹種苗木18種481株，以及耐陰樹種苗木34種370株。耐陰樹種苗木所佔比例(43%)已逐漸接近陽性樹種苗木(57%)，顯示本崩塌地已逐漸脫離演替初期階段。本研究在一年半調查期間耐陰樹苗共新增178株，死亡127株，淨增加51株。黑星紫金牛、小梗木薑子、台灣格柃及樟葉槭苗木具有較高的相對高生長率，可優先做為崩塌地次生林的復育樹種。本研究也測定樣區內耐陰樹苗乾季及雨季的黎明前葉部水勢及淨光合作用率，結果發現乾季後期崩塌地次生林植群競爭水分情形明顯，可能令林下樹苗可用的水資源較欠缺，故樣區樹木較密集處的耐陰樹苗大多有較低之黎明前葉部水勢。本研究樣區乾季後期因為林木落葉，使樹苗可利用之光資源提升，且小芽新木薑子、小梗木薑子、菲律賓樟及樟葉槭在乾季後期並未遭受明顯缺水逆境，故此4種樹苗在乾季後期仍可維持和雨季相似的淨光合作用率，顯示可度過乾旱時期，將來有可能成為冠層樹木而取代現有陽性樹種。本研究的耐陰樹種苗木雖可在演替10年之穩定崩塌地有良好的生長及生理表現，但樣區的樹苗數量仍低於台灣其他崩塌地。故可藉人為方式引入耐陰樹種苗木，彌補演替中後期樹種苗木數量不足之現況，可加速此崩塌地植群的演替。

關鍵字

崩塌地演替；淨光合作用率；黎明前葉部水勢；樹苗建立

並列摘要

Duona forest road 8.7 kmin Kaohsiung, had formed landslides after typhoon Morakot in 2009. It has undergonenatural succession for 10 years, some areas have been restored to secondary forests, and the dominant vegetation are pioneer trees, but shade-tolerant seedlings have also established.The mountainous areas of Taiwan are fragile and often have heavy rains in summer, so landslidesin Taiwan are likely to continue to collapse without proper management. Therefore, it is needed to artificially accelerate the restoration of vegetation in landslides.Thus, the purpose of this study is to understand the current status of vegetationsuccession of Duona landslide, especiallythe regenerationdynamics and growth performanceof shade-tolerantseedlings, and to explore whether the physiological activities of shade-tolerant seedlings are significantly inhibited during the dry season. These basic ecological information can provide a scientific basis for speedingthe vegetation succession of this landslide through ecological restorationin the future. In July 2017, four 0.25 ha large plots were established in the Duona landslide. The number and height of all the shade-tolerant seedlings in the large plots were investigated every 2 to 6 months. In February 2019, there were 851 seedlings in the 4large plots, including 18species and 481stems of shade-intolerant seedlings, and 34species and 370stems of shade-tolerant seedlings.The proportion of shade-tolerant seedlings (43%) has gradually approached to thatof shade-intolerant seedlings (57%), indicating Duona landslide has gradually been advanced from the initial stage of succession. In the 1.5 year study time, there were 178 shade-tolerant seedlings established, and 127 died, hence 51 net increase of shade-tolerant seedlings.The seedlings ofArdisia virens,Litsea hypophaea,Eurya septata,and Acer albopurpurascenshave higher relatively high growth ratethan other species, so can be preferentially used as restoration treespecies forsecondaryforestof landslide.This study also determined the pre-dawn leaf water potential and net photosynthesis rate of the shade-tolerant seedlings in the study area in the rainy and dry season. It was found that the secondary forest tree in the late dry season compete for water severely, which may make the available water resources of the underground seedlings lack. Therefore, most of the shade-tolerant seedlings in the area with very dense trees, have lower pre-dawn leaf water potential in the late dry season.In the late dry season,the light resources available to the shade-tolerant seedlings increased due to the deciduous trees defoliated. Neolitsea parvigemma, Litsea hypophaea, Machilus philippinensis, and Acer albopurpurascensdid not suffer from obvious water shortage in the late dry season. Therefore, these seedlings of the above 4 species could maintain similar net photosynthesis rate in the late dry season as in the rainy season, indicating that they can survive through severe drought and live for a long time, finally becomecanopy trees in the future, and replacethe existing shade-intolerant trees. The shade-tolerant seedlings in this study grow well and have good physiological performance in the landslide which succession for 10 years. However, the amount of the seedlings is still lower than other landslides in Taiwan. Thus, this study suggest that it is feasible to introduce shade-tolerant seedlings by artificial way, to supply the seedlings of middle or later successional species that the landslide lacking, and to build suitable place for establishment, leading the effect of speeding vegetation succession of the landslide.