Conversion of forest to rangelands suppress soil fauna and flora densities during long-term in mountain ecosystems

Abstract

The effect of vegetation types at mountainous sites on the relationships between soil biota and environmental variables applicable for the evaluation of soil quality and functions are barely studied and remain almost unknown. In the present study, the effect of forest degradation and vegetation types changes [i.e. natural forest with dominant species of Zelkova carpinifolia (Pall.) K. Koch. and three rangelands with dominant species of Festuca ovina L. Dactylis glomerata L. and Stachys byzantina K. Koch.] on the dynamics of soil properties and density of soil organisms in northern Iran has been considered. For each studied vegetation types, three different sites (at a distance of 4–6 km) with 1 ha area were selected. In summer (August), litter or O-horizon (i.e. L, F, and H) and soil (0–10 cm) layers were collected in an area of 30 × 30 cm. Also, in order to study the dynamics of soil properties, in addition to summer, soil samples were collected in the spring (May) and autumn (November) in each of the habitats. The study area is commonly covered with snow from late December to early April every year and therefore soil sampling was not considered in the winter season. A total of 48 litters (12 samples for each of those studied vegetation types), in the summer, and a total of 144 soil [(4 vegetation types × 3 seasons × 12 samples)] samples were collected and transferred to the laboratory. According to our findings, with higher values in the autumn season, the highest density of the soil earthworm (epigeic, anecic and endogeic), microarthropods (Acarina and collembola), nematode, and protozoa were detected in the Zelkova vegetation soils. Also, the highest density of bacterial and soil fungal communities were observed, especially in summer, under the tree cover of forest habitat. Based on our data, forest degradation and vegetation type changes suppressed the density of soil biota ranked in Zelkova > Festuca > Dactylis > Stachys due to low quality of litter, soil climate, and fertility condition. Although each vegetation type plays a prominent ecological role, forest covers are worthwhile because of their capacity to create hotspots identified by soil fauna and flora densities, which play a key role in the nutrient cycle and ecosystem services, in mountain habitats.