Selected Biological Properties of the Soil in a Burnt-Out Area under Old Pine Trees Three Years after an Fire

Fires, on account of their emotional, economic and cognitive aspects, are of interest to numerous researchers, and their impact is often unpredictable and difficult to investigate. They are among some of the most dynamic factors shaping terrestrial ecosystems. They destroy vegetation and alter the physicochemical and biological properties of the soil. Fires significantly influence the abundance and biodiversity of soil microorganisms and soil mesofauna, which are important elements of soils of every ecosystem, especially forest soils. Restoration of communities of soil organisms takes place at different rates and depends on, among other things, the intensity of the fire. The aim of the research was to determine the degree of restoration of the abundance of microorganisms and mesofauna in areas burnt out by anthropogenic fires of different intensity in an old pine forest. The research was conducted in a two-hundred-year-old pine stand (Peucedano-Pinetum), in the Kampinos National Park (near Warsaw, central Poland). In August 2018, three years after the fires, 3 test areas (10x10 m) were designated on each burnt-out site: after a weak fire (W) and after a strong fire (S), and also in adjacent unburnt (control, C) areas. In each test area, 6 samples were taken both from the organic layer (0-5 cm) and the mineral layer (5-25 cm - for microorganisms, and 5-10 cm for mesofauna) of the soil using standard methods for microorganisms and mesofauna. It was found that three years after the fires, the restoration of communities of soil organisms in terms of numbers was at an advanced stage (this was especially true for soil mesofauna). Based on the PCA analysis, it was found that the restoration of microbial communities and of the communities of mesofauna were interrelated, which was also influenced by the environmental conditions of the soils after the fires, in particular the physicochemical soil properties resulting from the intensity of the fire.