Pedodiversity in the Caspian forests of Iran

Abstract

Abstract We propose that three primary causes of pedodiversity within old-growth northern hardwood forests of Iran are (i) pit and mound topography from past tree fall events, (ii) current canopy gaps from tree falls, and (iii) the influence of individual tree species on soil properties and processes. This research was conducted in a 20 ha area in the Experimental Forest Station of Tarbiat Modares University that is located in a temperate forest of Mazandaran province in the north of Iran. Soil organic matter (SOM) and carbon (SOC), total nitrogen (N), moisture, N mineralization, microbial respiration, earthworm abundance and biomass were significantly greater in pits compared with mounds and level areas. Mounds had higher pH, C/N ratios, sand contents, and bulk density, whereas available phosphorus (P), potassium (K), calcium (Ca) contents, silt, clay and CEC tended to be than in level areas. Soil pH, SOM and SOC, N, P, K, Ca, content of sand, bulk density, N mineralization and microbial respiration were significantly greater in gaps compared to level areas. Level areas had greater silt content and lower bulk densities, sand contents, and soil K compared to gaps and gap-edges. Soil clay, moisture, C/N ratio, earthworm abundance and biomass decreased from the closed canopy to the gap-edge, and gap-center. Soil organic matter, SOC, N, P, Ca, N mineralization, and microbial respiration increased from the undisturbed forest, to the gap-edge, to the gap-center. The degree of increase for these nutrients and processes was positively related to the size the gap. Soil organic matter, SOC, C/N ratio, sand, bulk density and moisture tended to be greater under beech compared with hornbeam, whereas higher pH, N, P, K, Ca, silt, clay, N mineralization, microbial respiration, earthworm abundance and biomass were found under hornbeam. We quantified pedodiversity using principal component analyses (PCA) and biodiversity indices. Our rank abundance model approximated the lognormal distribution. Values for our diversity analyses were S (richness) = 5, H′ (Shannon index) = 0.94, H (maximum) = 1.61, and E (evenness) = 0.58. Our results show that top–down trophic interactions are linked to forest pedodiversity; thus, forest management practices that mimic tree windthrow and facilitate mixed species composition may promote pedodiversity and ultimately forest biodiversity.