Beyond the Forest-Grassland Dichotomy: The Gradient-Like Organization of Habitats in Forest-Steppes.

László Erdős,György Kröel-Dulay,Zoltán Bátori,Csaba Tölgyesi,Péter János Kiss,Katalin Szitár,Ákos Bede-Fazekas,Péter Török

doi:10.3389/fpls.2020.00236

Abstract

Featuring a transitional zone between closed forests and treeless steppes, forest-steppes cover vast areas, and have outstanding conservation importance. The components of this mosaic ecosystem can conveniently be classified into two basic types, forests and grasslands. However, this dichotomic classification may not fit reality as habitat organization can be much more complex. In this study, our aim was to find out if the main habitat types can be grouped into two distinct habitat categories (which would support the dichotomic description), or a different paradigm better fits this complex ecosystem. We selected six main habitats of sandy forest-steppes, and, using 176 relevés, we compared their vegetation based on species composition (NMDS ordination, number of common species of the studied habitats), relative ecological indicator values (mean indicators for temperature, soil moisture, and light availability), and functional species groups (life-form categories, geoelement types, and phytosociological preference groups). According to the species composition, we found a well-defined gradient, with the following habitat order: large forest patches, medium forest patches, small forest patches, north-facing edges, south-facing edges, and grasslands. A considerable number of species were shared among all habitats, while the number of species restricted to certain habitat types was also numerous, especially for north-facing edges. The total (i.e., pooled) number of species peaked near the middle of the gradient, in north-facing edges. The relative ecological indicator values and functional species groups showed mostly gradual changes from the large forest patches to the grasslands. Our results indicate that the widely used dichotomic categorization of forest-steppe habitats into forest and grassland patches is too simplistic, potentially resulting in a considerable loss of information. We suggest that forest-steppe vegetation better fits the gradient-based paradigm of landscape structure, which is able to reflect continuous variations.

Highlights

Ecosystems where tree-dominated and grass-dominated patches form a mosaic cover a substantial proportion of Earth’s terrestrial surface (House et al, 2003), and their dynamics (e.g., Innes et al, 2013), biodiversity patterns (e.g., Erdos et al, 2018a,b), and conservation importance (e.g., Bergmeier et al, 2010; Prevedello et al, 2018) are in the focus of ecological studies
We evaluated six habitat types of sandy foreststeppes: large forest patches, medium forest patches, small forest patches, north-facing forest edges, south-facing forest edges, and grasslands
The Non-metric Multidimensional Scaling (NMDS) converged after 2267 tries and 90 iterations, achieving a stress value of 0.1784

Summary

Introduction

Ecosystems where tree-dominated and grass-dominated patches form a mosaic (e.g., savannas, wood pastures, and forest-steppes) cover a substantial proportion of Earth’s terrestrial surface (House et al, 2003), and their dynamics (e.g., Innes et al, 2013), biodiversity patterns (e.g., Erdos et al, 2018a,b), and conservation importance (e.g., Bergmeier et al, 2010; Prevedello et al, 2018) are in the focus of ecological studies The components of such systems can conveniently be classified into two basic types, forests and grasslands, which differ substantially in several biotic (e.g., species composition and leaf area) and abiotic (e.g., solar radiation and soil moisture) parameters (Breshears, 2006). Some animal species need both components for their full life cycles, while some plant species may switch preferences between the components in years with different weather patterns (Bartha et al, 2008; Luza et al, 2014)

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