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.