The impact of mound-building termites on surface soil properties in a secondary forest of Central Amazonia

Abstract

Termites are important components of biologically mediated feedback to land-use change in the tropics. In Central Amazonia, termite mounds are prevalent in post-clearing landscapes and appear to constrain re-colonization of the landscape by vegetation. To determine the most important constraints imposed by termite mounds on plant establishment, we investigated chemical, physical, and hydraulic properties of termite mounds at an 8-year-old secondary forest site, and their effects on the development of native plant species. Mounds contained only half of the root biomass found in neighboring soil in the surface 0.05 m. Carbon, nitrogen, and potassium levels in the termite mounds were significantly elevated, by 33, 28, and 38%, respectively (44 g kg −1, 2.5 g kg −1, and 33 mg kg −1), while no significant difference in phosphorus, magnesium, iron, zinc, or copper concentrations was observed. Calcium was depleted by 27% in the termite mounds at 0.026 g kg −1. Aluminum concentrations and acidity were significantly higher in the termite mound material (0.23 g kg −1, pH 4.3) than surrounding soils (0.15 g kg −1, pH 4.4). Resistance to penetration was significantly higher in termite mounds, at 13.5 MPa. Termite mounds were on average 5 mm drier than the control soil in the surface 0.05 m, with a significantly higher median water infiltration rate through the termite mound than the adjacent soil (16 mm s −1 vs. 3 mm s −1). Although drainage through the mounds in situ was faster, termite mound samples absorbed water significantly more slowly than control soil. Termite mound material retained significantly less water than control soil under the same suction. Plant assays ruled out an effect of aluminum toxicity on seed germination and seedling development in termite mounds over control soil. Water availability and mechanical impedance were the most important constraints for seed germination and seedling development. The abundance of termite mounds was 760 ha −1 in the study site, but covered only 3% of the area. Complementing the results from this study with investigations of termite mounds and nutrient cycling, carbon storage, and biodiversity will further our understanding of the effects of mound-building termites in the pastures and secondary forests of Amazonia.