Julia Krümmelbein

Grazing changes topography-controlled topsoil properties and their interaction on different spatial scales in a semi-arid grassland of Inner Mongolia, P.R. China

Semiarid steppe ecosystems account for large terrestrial areas and are considered as large carbon (C) sinks. However, fundamental information on topsoil sensitivity to grazing is lacking across different spatial scales including the effects of topography. Our interdisciplinary approach considering soil chemical, physical, and vegetation properties included investigations on pit scale (square-metre scale), plot scale (hectare scale), and the scale of a landscape section (several hectares). Five different sites, representing a grazing intensity gradient, ranging from a long-term grazing exclosure to a heavily grazed site were used. On the pit scale, data about aggregate size distribution, quantity of different soil organic carbon (SOC) pools, SOC mineralisation, hydraulic conductivity and shear strength was available for topsoil samples from representative soil profiles. Spatial variability of topographical parameters, topsoil texture, bulk density, SOC, water repellency, and vegetation cover was analysed on the basis of regular, orthogonal grids in differently grazed treatments by using two different grid sizes on the plot scale and landscape section. On the pit scale, intensive grazing clearly decreased soil aggregation and the amount of fresh, litter-like particulate organic matter (POM). The weak aggregation in combination with animal trampling led to an enhanced mineralisation of SOC, higher topsoil bulk densities, lower infiltration rates, and subsequently to a higher risk of soil erosion. On the plot scale, the effects of soil structure disruption due to grazing are enhanced by the degradation of vegetation patches and resulted in a texture-controlled wettability of the soil surface. In contrast, topsoils of grazing exclosures were characterised by advantageous mechanical topsoil characteristics and SOC-controlled wettability due to higher POM contents. A combined geostatistical and General Linear Model approach identified topography as the fundamental factor creating the spatial distribution of texture fractions and related soil parameters on the scale of a landscape section. Grazing strongly interfered with the topography-controlled particle relocation processes in the landscape and showed strongest effects on the aboveground biomass production and biomass-related soil properties like SOC stocks. We conclude that interdisciplinary multi-scale analyses are essential (i) to differentiate between topography- and grazing-controlled spatial patterns of topsoil and vegetation properties, and (ii) to identify the main grazing-sensitive processes on small scales that are interacting with the spatial distribution and relocation processes on larger scales.

Initial Ecosystem Processes as Key Factors of Landscape Development—A Review

The Earths surface is the dynamic interface of climatic, biotic, and geologic systems and is often described as the Earths critical zone. Structures and processes within this zone are highly complex and heterogeneous and therefore not yet completely understood, particularly with regard to their interactions. In contrast, parts of the critical zone still in their initial development stages are expected to be less complex and heterogeneous compared to mature systems. Therefore, research approaches concentrating on this crucial initial development period of ecosystems have been recently initiated. A central hypothesis is that the initial ecosystem development phase forms the later state of ecosystems. Similarly, the behavior of mature ecosystems can only be understood if knowledge about their evolution exists. The initial development stages of geo-ecosystems are characterized by highly dynamic abiotic and biotic processes. This results in the rapid formation and alteration of structures, which in turn constitute a new framework for new processes. To disentangle the structure-process interactions, interdisciplinary and integrative research approaches in the fields of geomorphology, ecology, biology, soil science, hydrology, and environmental modeling are required. We discuss ideas that emerged from the fourth Meeting of Young Researchers in Earth Sciences (MYRES IV) held at the Brandenburg University of Technology (BTU) Cottbus in 2010 (www.myres.org), which focused on the overarching question: what are the evolutionary constraints and pathways that govern development of spatiotemporal patterns in ecosystem process and structure? This paper presents a review of the most important aspects of initial ecosystem processes as key factors of landscape development.