Influence of Fire On Soil Respiration Rates in Forest Stands Adjacent to Madrid, Spain.

Mediterranean forest ecosystems have unique features and provide multiple goods and services crucial for the welfare of urban populations of the Mediterranean region.  Mediterranean forest are vulnerable to numerous threats such as forest fires. Over the last decades the number of wildfires has doubled in the area around Madrid, and increasing temperatures and lower precipitation will enhance fire frequency.  This may have important consequences for the C dynamics in these ecosystems.  Soil respiration is one of the main pathways of C loss but the effects of fire on soil respiration in Mediterranean ecosystems are still largely unknown.

The purpose of this study was to evaluate the effects of fire on the soil properties and soil respiration in Pinus sylvestris, Quercus ilex and Quercus pyrenaica forest stands in the surrounding area of Madrid (Spain). Soil respiration was measured monthly since July 2007 on burned and undisturbed plots in each forest stand.  Physico-chemical and biological soil properties were also measured throughout the year. Fire produced similar effects in all forest stands: a reduction in soil respiration, soil moisture, hot water-soluble C, soil microbial biomass C, C/N ratio, soil organic matter, pH,  and exchangeable cations (Ca²⁺, Mg²⁺, K⁺ and Na⁺); and an increase in soil temperature, CEC, and exchangeable acidity . Phospholipid fatty acid (PLFA) analysis indicated a change in microbial community structure between burned and undisturbed plots.