Geoecology of a granite dome: Spatial interactions between gnammas, rills, soils, and plant cover, Enchanted Rock (Texas, USA)
[Display omitted] •42 gnammas and 25 other microforms were studied on a large granite dome in Texas, USA.•Geoecological interactions between geomorphology, soils, and vegetation were analyzed.•Morphometric analyses revealed a close association between gnamma length and width.•Deep basin soils were H...
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Veröffentlicht in: | Catena (Giessen) 2023-04, Vol.223, p.106938, Article 106938 |
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•42 gnammas and 25 other microforms were studied on a large granite dome in Texas, USA.•Geoecological interactions between geomorphology, soils, and vegetation were analyzed.•Morphometric analyses revealed a close association between gnamma length and width.•Deep basin soils were Haplustolls or Dystrudepts; shallow pans had Lithic Ustorthents.•Plants on gnammas showed discrete concentric ring patterns correlated with soil depth.
This research examines geoecological connections between geomorphic, pedological,
hydrological, and vegetation components in gnammas—shallow pans and deeper basin pans—and in various microforms on Enchanted Rock (Texas), a large granite dome where an intricate rill drainage network connects microforms. Gnamma morphometric analysis (GMA) showed the association between mean basin length (418.8 cm) and width (258.2 cm) was more significant than in pans (150.9 × 84.0 cm); mean basin depth (44.0 cm) was correlated with length, but pan depth (7.8 cm) was independent. Debris depth was assessed by auger probing along transects on 8 basins and 20 pans; basin soils (11–98.5 cm) were deeper than those in pans (1–5 cm). Lens-shaped basins show Typic-Lithic Haplustolls or Typic-Lithic Dystrudepts with complex profiles; pans are shallow and flat-bottomed, and display simple Lithic Ustorthents with thin surficial gravel layers shielding finer subsoil horizons. Deeper basin profiles, along with greater SOM, nutrients, and fine-particle content, provided high water retention, facilitating dense plant growth. Rills showed discrete areas of debris deposition sequentially along channels; sediment patch size decreased downslope, while gravel content increased, and fine grains decreased, downhill.
Plants on gnammas and microforms included 48 vascular species, mostly annual or perennial herbs and nanoshrubs, followed by ferns and cacti. Vegetation on gnammas showed distinctive patterns of sequential, concentric, plant rings, with outer bands of Sedum nuttallianum and Allium drummondii on shallow (0–10-cm) soils, followed by narrow strips of annual plants growing on 8–40-cm-deep soils, and a sizable central area of tall perennial grasses, mainly Andropogon glomeratus, on ≤ 98.5-cm-deep profiles. A conceptual developmental model of geoecological interactions between gnammas, rills, and other microforms, suggests these are interconnected via channeled runoff and/or sheetwash, which transports debris and SOM downhill; in this view, gnammas |
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ISSN: | 0341-8162 1872-6887 |
DOI: | 10.1016/j.catena.2023.106938 |