Some plant relationships in the bauxitic soils of Kauai

Abstract

Interest in bauxitic soils has increased in recent years in Hawaii since Sherman (1953) pointed out that some Hawaiian soils could be considered ferruginous bauxites. Research in bauxitic soils was stimulated with the appropriation of funds by the 1957 Territorial Legislature for research in problems in reclaiming land used for mining. A study of vegetation of bauxitic soils was included in this research. Moomaw et al. (1959) studied the aluminum concentrations of plants growing on bauxitic soils of Hawaii. Of 23 plant species sampled, 13 were aluminum accumulators (>1000 parts per million in dry plant material). Ecologic and floristic studies of bauxitic soils of Kauai were conducted by Moomaw and Takahashi (1960) .who concluded most species present showed no definite affinity for soils of high aluminum content but rather were those plants adapted to warm and moist environments, acid and infertile soils, and to a shallow root zone. An important factor in present distribution of these species was the original site of introduction. Revegetation of stripmined bauxite soils of Kauai was studied by Younge and Moomaw (1961) who conducted fertility and vegetation experiments on the stripped surface and on topsoil returned to the stripped surface after mining. Forage on stripsoil was slow to establish but by the end of the first year the stripsoil outyielded the topsoil. Other' major studies of plants on aluminous soils have been conducted by Webb (1954) in Australia and New Guinea, and by Howard and Proctor (1957) in Jamaica. Webb analyzed 1324 plant species and found 80 accumulator species. Obligate accumulators were restricted to leached acid soils in areas of comparatively high rainfall. Howard and Proctor (1957) concluded that Jamaican bauxite soils contained no characteristic plant species and few accumulator species. No species were found on adjacent soils which would not grow on the bauxitic soils. Few quantitative comparisons of soil aluminum and plant aluminum concentrations have beep made. Usually plants sampled from areas thought to be high in aluminum have been analyzed for aluminum with no attempt to measure soil aluminum. Although shallow root systems are reported in bauxitic soils (Moomaw and Takahashi, 1960), no detailed studies of root development and distribution in these soils have been conducted. An interesting plant in the bauxitic soils of Kauai is Rhodomyrtus tomentosa (Ait.) Hassk., a shrub introduced on Kauai about 50 years ago which now infests thousands of acres of land on that island. R. tomentosa poses a real threat to pasture and virgin areas on and around K110hana Crater, the original site of introduction, where it forms dense impenetrable thickets. Closely associated with R. tomentosa is Melastoma malabathricum L., another shrub introduced on Kilohana Crater which is also a frequently reported aluminum accumulator. Moomaw et ale (1959) reported 110 ppm aluminum in leaves of R. tomentosa and 10300 ppm aluminum in leaves of M. malabathricum from the Wailua Game Refuge area on Kauai. A detailed study of some plant relationships of bauxitic soils of Kauai was undertaken using R. tomentosa as the main test plant. M. malabathricum, Leucaena glauca (L.) Benth. and Araucaria excelsa (Lamb.) R. Br. were also used in some of the studies. The objectives of the study were: 1. To compare plant growth in soils of varying aluminum content. 2. To measure extractable aluminum from soils and to relate it to aluminum concentration in plant tissues. 3. To study the distribution of R. tomentosa and M. malabathricum on different soil series. 4. To study root distribution of R. tomentosa and M. malabathricum in profiles of several soil series.