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Effects of Soil Properties on Restoring Indigenous Plants in Coral Reef Landscapes
土壤性質對珊瑚礁地形上原生海岸林復舊之影響
摘要
亞熱帶或熱帶地區珊瑚礁地形上之海岸林受銀合歡（Leucaena leucocephala）入侵嚴重，於是原生林之復舊顯得急迫且重要。土壤性質的空間變異與復舊樹種的選擇為決定原生林復舊效率的重要因子。本研究在臺灣墾丁國家公園海岸珊瑚礁地形上，於伐除入侵之銀合歡後，種植17種臺灣海岸原生樹種，並於22個月後調查樣區內樹種存活情形、樹高與地徑；同時，以網格方式採集表土（0~15 cm），且分析土壤基本性質（包含土壤深度、總體密度、水分含量、土壤有機質及土壤質地），並繪製空間分布狀態。本研究之目的在於評估土壤性質與復舊樹種存活率間之關係，以及確認復舊樹種之合適性。研究主成分分析結果顯示，樹種存活率乃取決於土壤深度、質地和乾季（10月至隔年4月）時水分含量。土壤水分特性曲線結果顯示樣區土壤，於乾季時之水分含量皆低於永久凋萎點（permanent wilting coefficient），尤其是樣區中黏粒含量高於30%之土壤，顯示植物種植於黏質地土壤中相當不易生長。此外，研究結果顯示，樹種生長情形乃取決於土壤性質之空間變異。林投、紅柴、海檬果、雀榕、繖楊與瓊崖海棠為不受樣區內土壤性質空間變異影響之樹種；存活率皆超過50%，屬於相當適合選作復舊之原生樹種。水黃皮、臺灣海桐、臭娘子、黃槿與樹青為較不耐水分逆境之樹種，需種植於樣區較砂質地之土壤中以利水分之獲取。稜果榕與蓮葉桐受土壤深度影響顯著，較適合種植於深度超過30cm之處。血桐與草海桐較適合種植於土壤pH ≥ 7.2的區域，而白榕和欖仁為不適合於珊瑚礁地形上生長之樹種。
並列摘要
Restoring indigenous plants is an urgent concern in coral reef landscapes severely invaded by white leadtrees (Leucaena leucocephala). The efficiency of restoration is largely influenced by the spatial heterogeneity of soils and selecting suitable species. In this study, we evaluated the relationships of soil properties with the mortality and growth performance of restored seedlings, and clarify suitable species on the basis of some specific soil properties. Seventeen species of indigenous plant seedlings were randomly planted in the study area after clearcutting white leadtrees in southern Taiwan. At the beginning of seedling planting, 142 surface soil samples were collected in a grid for analysis, including the soil depth, bulk density, water content, organic matter contents, and soil texture. Mortality and physiological characteristics of the planted seedlings, including the plant height and root collar diameter, were also investigated at 22 mo after seedling planting. Based on analytical results of a principal components analysis (PCA) and correlations, the survival rate of seedlings was determined by the soil depth, soil texture, and soil water contents in the dry season (October to April of the following year). There were significant correlation of the survival rate of seedlings with soil depth (r = 0.58, p ＜ 0.05), sand fraction (r = 0.63, p ＜ 0.05), and clay fraction (r = -0.63, p ＜ 0.05). During the dry seasons, soil water contents were always below the permanent wilting coefficient, especially in clayey soils (≥ 30% clay fraction contents) in the study area. Additionally, the investigation results indicated that the growth of plants responding to soils was species specific. Pandanus odoratissimus, Aglaia formosana, Cerbera manghas, Ficus superba var. japonica, Thespesia populnea, and Calophyllum inophyllum were independent of soil properties and were most suitable for restoration in coastal coral reef landscapes. Pongamia pinnata, Pittosporum pentandrum, Premna serratifolia, Hibiscus tiliaceus, and Planchonella obovata were sensitive to soil texture and moisture stress, and should be planted in the areas with sandy soils. Ficus septica and Hernanadia nymphaeifolia were susceptible to soil depth, and these 2 species should be planted in areas with thick soil depths (≥ 30 cm). Macaranga tanarius and Scaevola taccada were species favored to grow in high-pH (≥ 7.2) areas. Furthermore, F. benjamina. and Terminalia catappa are unsuitable species for restoration of coral reef landscapes.