Topographic patterns of soil traits and macro fauna in oriental beech forests in Iran

Hyrcanian forests are recognized by UNESCO World Heritage for their ecological importance related to their relic and rich endemic species. The goal of this study was to provide a baseline understanding of earthworm, nematode, and millipede abundance with regard to soil physicochemical properties and topography. Samples were collected from three soil depths, in five slope positions (summit, shoulder, backslope, foot slope, and toe slope) in each of three concave and three convex catenas. Organic matter (OM), organic C and N, pH, bulk density, particle size distribution, available P, K, Ca, the number and biomass of earthworms, nematodes, and millipedes were measured. Most soil properties (clay ( P value = 3.61*), Ca ( P value = 9.81*), K ( P value = 10.07**), P ( P value = 4.23*), and OM ( P value = 3.76*)) were greater in downslope positions, however, pH ( P value = 7.38**), C/N ( P value = 9.81**), and bulk density ( P value = 2.83*) showed the opposite pattern. Earthworm, nematode, millipede numbers and biomass were greater in concave catenas, toe slopes, and in shallow rather than deep soil samples. A regression tree analysis of soil OM successfully classified 85% of samples with variable importance decreasing from soil sample depth to slope position to catena shape. Results provide important baseline data, a simple model of soil traits, and a suggested approach for continued surveying of soils in this ecosystem which is susceptible to rapid changes due to climate change and human management. • Landscape patterns of soil Ca, K, P, OM and earthworm for Hyrcanian beech forests • OM correlated with many soil traits • Regression tree model used to summarize OM across the landscape • Strong correlation between earthworm, millipede and nematode abundance and soil fertility • Soil macrofauna sampling may provide rapid assessment of soil fertility.