This study examined the effect of wildfire on the physical degradation of two forest soils in NW Spain and
compared this against changes produced by controlled laboratory heating experiments in which unburned
soils from neighbouring sites were exposed to five different heating regimes. The physical soil degradation was
considered with respect to organic carbon content, dry aggregate size distribution, water aggregate stability,
water repellency, and hydraulic conductivity. The results of this analysis show that the changes in the physical
properties of the wildfire-affected soils were similar to the changes observed in the heating experiments.
However, the wildfire had contrasting effects in terms of soil physical degradation at the two study sites,
which can be attributed to differences in soil heating regimes and fire severity. At one study site, the wildfire
did not produce marked changes in organic carbon content or in aggregation, except for a slight fragmentation
of macro-aggregates into micro-aggregates. Also, soil water repellency remained very strong after the wildfire,
resulting in lowhydraulic conductivity. Based on the laboratory experiments, the soil at this sitewas not exposed
to temperatures above 220 °C. The wildfire at the other study site resulted in more pronounced degradation of
the soil, as shown in the reduction of organic carbon content by almost 50%, resulting in reduced stability of
the aggregates. The wildfire also reduced soil water repellency considerably, but hydraulic conductivity did not
increase noticeably. In this case the soil could be exposed to temperatures between 220 and 380 °C.
This study examined the effect of wildfire on the physical degradation of two forest soils in NW Spain andcompared this against changes produced by controlled laboratory heating experiments in which unburnedsoils from neighbouring sites were exposed to five different heating regimes. The physical soil degradation wasconsidered with respect to organic carbon content, dry aggregate size distribution, water aggregate stability,water repellency, and hydraulic conductivity. The results of this analysis show that the changes in the physicalproperties of the wildfire-affected soils were similar to the changes observed in the heating experiments.However, the wildfire had contrasting effects in terms of soil physical degradation at the two study sites,which can be attributed to differences in soil heating regimes and fire severity. At one study site, the wildfiredid not produce marked changes in organic carbon content or in aggregation, except for a slight fragmentationof macro-aggregates into micro-aggregates. Also, soil water repellency remained very strong after the wildfire,resulting in lowhydraulic conductivity. Based on the laboratory experiments, the soil at this sitewas not exposedto temperatures above 220 °C. The wildfire at the other study site resulted in more pronounced degradation ofthe soil, as shown in the reduction of organic carbon content by almost 50%, resulting in reduced stability ofthe aggregates. The wildfire also reduced soil water repellency considerably, but hydraulic conductivity did notincrease noticeably. In this case the soil could be exposed to temperatures between 220 and 380 °C.
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