By modifying the soil structure, flora and fauna play a major role in controlling water infiltration and erosion. Little is known, however, about local feedback effects during the initial stage of soil development. Initial soil formation was studied in an artificial catchment where coarse-textured, sandy sediments were left to undirected succession. In a patchy moss-covered area, the surface was colonized by larvae of the ground-dwelling beetle Cylindera arenaria viennensis [Schrank, 1781], as indicated by millimeter-sized cylindrical burrows. Our objective was to study the effects of both moss vegetation and beetle larvae on pore structure and infiltration. The pore structure of sparsely and densely moss-vegetated and unvegetated samples containing a single burrow was characterized by x-ray computed tomography (CT). Flow patterns of infiltration experiments were visualized using neutron radiography (NR). The micro-CT scans revealed a variety of more unstable pore systems in the bare soil, locally compacted regions in the moss-covered samples, and isolated vesicular pores similar to those reported for desert soils. The NR series showed water flow around the cylindrical burrow under initially moist conditions and pronounced preferential flow within the burrow under initially dry soil conditions. Water-repellent regions in the initially dry sample explained pressure buildup before gravity-driven flow in the burrow started. The moss cover seemed to stabilize the surface soil, visible in the absence of a depositional sediment layer. The results suggest that moss vegetation and ground beetle burrowing activity control initial soil development by modifying pore structure and water infiltration.

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