Land characteristics and plant resources in relation to agricultural land-use planning in a humid tropical strand plain, southeastern Thailand

Abstract

Recently in humid tropical Asia, human activities have begun to extend toward the coastal lowland areas where widespread peat swamps are distributed. Draining peat swamp areas for agricultural uses creates a high risk of sulfuric acidification. The research site in this paper was a strand plain comprising beach ridges, swales on inter-ridges, and peaty backswamps in southeast Thailand. Thus, the actual and potential acid sulfate soil in the peaty backswamps is a major problem there, but sandy podzols on older beach ridges are also considered an agricultural problem soil. To establish an agricultural landscape plan encompassing the whole of the strand plain, we studied the land characteristics associated with the landforms and soils, their spatial variability related to landscape evolution, and the status of present plant resources in terms of biomass and species diversity for local farmers on peaty backswamps and beach ridges. We found that all spatial attributes of the two soils, such as the locations, profiles, and chemical and physical properties, were closely related to the geomorphic formation process or chronosequence: the landward or older backswamp has ripe clay and the seaward or younger one partly has unripe clay; the degree of spodic horizon development with ortstein is highest in the most landward beach-ridge system and decreases seaward; and the profile positions of the spodic horizons were related to the fluctuations of marine sand sediments, as revealed in a fine-scale survey. Finding these spatial regularities is useful for predicting land characteristics in areas outside of detailed research sites, reducing time and cost as well as forming the basis of landscape planning. Plant resources presently utilized by local farmers on the strand plain are Melaleuca cajuputi forests on both the peaty backswamps and the beach ridges, and home gardens of tropical fruit trees around settlements. Ecological carrying capacity in terms of biomass of M. cajuputi was not significantly different among soil types in the strand plain, but the growth rate and potential biomass of the species appears to be highest in thick, water-saturated peaty backswamps with acid sulfate soils. By comparing the species composition of home gardens in different areas, we found that on the beach ridges, although the ecological carrying capacity in terms of biomass for several types of fruit trees appears lower, a great number of species particular to the shrub layer are maintained. Based on the spatial variability of land characteristics and the ecological carrying capacity in terms of biomass, we identified separate land units and suggested future land-management and land-use systems appropriate to each unit.