The recovery of soil physical and chemical indices in years after fire in Zagros oak woodlands in Kermanshah Province

Fire is the most important disturbance factor in forest ecosystems that can result in short and long term changes in soil physical and chemical properties. The changes of these properties in soil after fire may have negative effects on forest ecosystem even in long term. Since the fire frequency in Zagros forests have been increasing in the recent years, identifying the short term and long term effects of fire on soil properties in these forests is necessary to prevent soil degradation. Hence, in this study the short and long term responses of some physical and chemical properties of soil were investigated in order to identify the recovery time of these properties.
In order to investigate the recovery time of soil physical and chemical properties after fire, 3 places in one site (distance about 1km from each other) in Zagros forests were selected with different times of fire occurrence including: 1, 3 and 10 years after fire. To decrease the environmental effects, we considered a separate unburnt control plot for each place in their adjacent and each place was compared with its own control plot. The soil sampling was performed randomly from the depth of 0-20 cm with 4 replications. A total of 24 composite soil samples were collected. Several soil physical and chemical properties were measured including: pH, EC, CEC, organic carbon (OC), nitrogen (N), phosphorus (P), saturated water content, bulk density (BD), C/N ratio and soil texture. The statistical analysis of experiment data was performed using IBM SPSS software and mean comparison was done by t test method.
The results showed that soil pH, CEC, EC, and P were significantly increased 1 year after fire. Soil pH and CEC were recovered to the pre-fire level in treatments 3 and 10 years after fire, while, EC and P were significantly decreased compared to their control. Saturate water of soil was decreased 1 year after fire however, no significant difference was observed compared to the pre-fire level after 3 and 10 years. Results indicated that OC and N were significantly decreased in all the times after fire and they were not recovered to the pre-fire level even after 10 years. BD was decreased 1 and 3 years after fire however, after 10 years no significant difference was observed compared to the control. No significant difference was in soil C/N ratio, clay, sand, and silt compared to the control in any times after fire.
It was concluded that some physical and chemical properties of soil may recovered in short time however; some others may not have recovered even 10 years after fire. Soil OC, N and P are of those properties that need long time to be recovered.