Soil functional indicators in different development stages of an oak (Quercus castaneifolia C.A. Mey.) stand

Abstract

As the remaining widespread Tertiary forests, the Hyrcanian forest of northern Iran, together with the south-eastern forests of Azerbaijan, are the last habitat ecosystems for chestnut-leaved oak species (Quercus castaneifolia C.A. Mey.) in the world. The present study aimed to investigate the influence of oak forest stands with different development stages (i.e. initial, optimal and decay) on soil functional indicators, i.e. fertility and biological activities, in Loveh forest, northern Iran. During the summer season, a total of 18 forest floor and topsoil samples (30 × 30 × 10 cm) from each development stage were transferred to the laboratory. In order to obtain a temporal pattern of soil climate, biota and microbial characteristics, samples were also collected during the autumn season. Concerning the independent individual factors, including development stage, season, and development stage × season, two-way ANOVA and general linear models as well as a PCA were applied. The first factor explained the observed variations in the total earthworm density (36.3 %) and biomass (33.5 %), acarina (47.3 %), nematodes (52.3 %), protozoa (54.6 %), bacteria (60.9 %), fungi (53.4 %), basal respiration (35.9 %), substrate-induced respiration (37.2 %), microbial biomass C (25.7 %), microbial biomass N (35.4 %), and the ratio of microbial biomass C to microbial biomass N (18.8 %). In contrast, the season factor explained changes in soil water content (31.2 %), temperature (22.6 %) and collembola density (59.7 %). Based on heat plots (as a part of the principal component analysis output) of studied properties, the decay stage of the oak stand created hot spots of soil functional indicators in the study area. Although all forest stand stages of the oak have an important ecological role, and place value in the evolutionary process, the old-growth (i.e. decay) stage is crucial for the soil functions exhibiting the highest fertility and biological relevance. As a management strategy, forest decision-makers may be advised to introduce diverse tree species into the stands, especially in areas with patchy canopy, and thus enhance forest soil microbial activity, nutrient cycles and, finally, variation of soil properties within the area (pedodiversity).