The erodibility of soils beneath wildfire prone grasslands in the humid tropics, Hong Kong

The paper analyses factors influencing soil erodibility in a grassland area of the humid tropics subject to frequent wildfires. The interrelationships between aggregate stability, soil physicochemical properties and pore size characteristics are examined. At the multifire scale aggregate stability w as significantly (P > 0.01) correlated with cation exchange capacity (CEC) (R = 0.76) and, in order of explained variance, exchangeable magnesium, alu minium, potassium, calcium and hydrogen concentration. At the individual fi re scale only CEC and exchangeable magnesium had a significant ameliorating influence in the more recently burnt areas, whilst both exchangeable magne sium and calcium were significant in the area of longest post-fire recovery . At the multifire scale aggregate, stability was also significantly correl ated with soil texture and organic matter partly through their influence on CEC. These interactions between aggregate stability and soil physicochemic al properties influence soil drainage, and low but significant correlations were recorded between aggregate stability and total porosity (R = 0.55 P > 0.05) and the relative proportion of transmission pores to storage pores ( R = 0.44 P greater than or equal to 0.05). Water release curves showed that areas with the longest post-fire recovery times held higher amounts of wat er at most suctions and hence contained a greater volume of pores of differ ent sizes, than more recently burnt areas. Soil erodibility in wildfire pro ne areas therefore reflects complex interactions and feedbacks between soil physicochemical properties, aggregate stability and pore size characterist ics which vary spatially and with time as soil and vegetation recovery prog resses. (C) 1999 Elsevier Science B.V. All rights reserved.