Soil microbial activity in Aleppo pine stands naturally regenerated after fire: silvicultural management and induced drought

In post-fire restoration, early monitoring is mandatory to check impacts and ecosystem responses to apply proper management according to social standards and ecological conditions. In areas where the natural regeneration was successful, excessive tree density can be found which induces to high intraspecific competence and assisted restoration management could be adequate. In addition, climatic changes will have large impacts on vegetation productivity and resilience since the regional models for south-eastern Spain predicts a rainfall decrease of about 20% and temperature increase of 4.5 oC. The microbial biomass could be used as indicator of ecosystem recovery, since it is negatively affected by wildfires and depends on fire characteristics, vegetation and soil properties. Our aim is to determine how forest management may affect the ecosystem recovery in different climatic scenarios, included drought scenarios with and without forest management (thinning).We compared soil physicochemical properties and microbial activity in four scenarios: unmanaged and thinned stands in two rainfall scenarios (under induced drought). The study areas were set close to Yeste (Albacete) where Aleppo pine forest were burned in summer 1994 (nearly 14000 ha). We set sixteen rectangular plots (150 m2; 15 m ×10 m) implementing experimental silvicultural treatments: thinning eight plots in 2004, reducing the naturally recovered tree density from about 12000 to 1600 pine trees ha-1. In addition, in half the plots, we induced drought conditions from about 500 to 400 mm (20%) from March 2009. In every plot, we monitored temperature at ground level (Ts), 10 cm depth (T10d) and soil relative humidity (RH). Taking into account season of the year and canopy coverage, we collected soil samples in mid-winter (ending January 2011) and mid-spring (ending May 2011) under pine trees and in bare soil. The soil samples were used to evaluate soil physicochemical properties and soil microbial activity. The latter was indirectly analysed and was characterized by measuring a set of enzymatic activities (urease, phosphatase, b-glucosidase and dehydrogenase). Neither significant differences in the values of physicochemical properties (with exception of soil organic matter) nor in temperatures were found. Regarding the microbial activity, we found differences on the significance of factors depending on the enzymes.The results obtained indicate that ecosystem response can be modified by silvicultural treatments, at least in the short term. The soil microbial data can be evaluated using enzyme activi