Soil properties of thickets and adjacent land use types in coastal savanna landscape of Ghana

Abstract

Thicket vegetation may be of great importance in soil carbon (C) storage and in provision of other ecosystem services such as soil erosion control and biodiversity conservation. However, it is less studied in tropical ecosystems due to limited understanding of its ecological importance. This study reports soil C pools and nutrient concentrations [nitrogen (N), available phosphorus (P), exchangeable calcium (Ca), magnesium (Mg) and potassium (K)] of unique thicket formations on Vertisol in comparison with adjacent land use types viz. rangeland, dry forest, and farmland at Kpong in the coastal Accra plains of Ghana. We also examined soil particle and nutrient distributions of termitarium associated with the thicket clumps on the Vertisols. Soils were sampled from each land use at 0–30 cm depth in addition to deep coring up to 100 cm. In the rangeland, forest and farmland, we demarcated 1600 m2 area each and established 4 subplots measuring 20 × 20 m (400 m2) and selected for the thicket vegetation, 4 thicket clumps each of approximately 400 m2 for soil sampling. The thicket clumps had greater soil total N, available P, exchangeable Ca and Mg concentrations than the rangeland and farmland but the levels in the thicket were similar (p > 0.05) to that of the adjacent dry forest. Soil C stock varied from 59 Mg ha−1 in the rangeland to 111 Mg ha−1 in the thicket clumps. The C stored in the silt + clay (S + C) fraction did not differ significantly (p > 0.05) in both the thicket and the dry forest, indicating similar C sequestration abilities. The S + C fraction contributed 89.6, 82.8, 81.3, and 73.7% to total soil organic C content in the rangeland, farmland, dry forest, and thickets, respectively. Soils of the termite mounds in the thickets were more clayey (ca. 38–41% clay) than the surrounding thicket soils (ca. 32% clay). We conclude that Vertisols in thicket areas store soil C and nutrients comparably as tropical dry forest, underscoring their ecological importance and the need for their conservation to enhance soil quality in the Anthropocene.