Effects of Soil Properties on Restoring Indigenous Plants in Coral Reef Landscapes

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.