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Abstract "Heft 9"


Freiburger Bodenkundliche Abhandlungen

Schriftenreihe des
Institut für Bodenkunde und Waldernährungslehre
der Albert-Ludwigs-Universität Freiburg i.Br.
Schriftleitung: F. Hädrich


Heft 9


Karl Stahr


Die Bedeutung periglazialer Deckschichten für Bodenbildung
und Standorteigenschaften im Südschwarzwald


Freiburg im Breisgau 1979

ISSN 0344-2691


Summary:

The effects of Pleistocene periglacial cover Sediments on soil development and Site properties in Southern Black Forest.
Three selected areas in the crystalline mountain region in Southern Black Forest were investigated. Each area is charakterized by a relatively uniform rock type: polymetamorphous Sediment gneisses = Gneissarea; "Münstertäler" ignimbrite = Ignimbritearea; Malsburggranite or Bärhaldegranite = Gra-nitearea. Following a preliminary investigation of the distribution of periglacial Sediments and estimation of forest Site quality,   34 (12-9-13) profiles were selected in such a way that they form Catenas from the west edge of the Black Forest through the summit area extending into the high plateau. Through the discription of the stratified profiles,  nine different parent materials (substrate) were recognized on the bases of their petrological properties.  "Deckfolge" (surface series) = Df,  "Decksediment" (surface layer) = Ds,  "Hauptfolge" (main series) = H,   "Basisfolge" (basic series) = B,   "Zersatzzone" (saprolitic zone) "= Zs,  "Zerfallzone" (regolithic zone) = Zf,  "Anstehendes" (solid rock)  =A,   "Löß" and "Lößlehm" (Loess and lime-free Loess) = L,  "Geschiebelehm" and "fluvioglaziale Ablagerungen" (till and fluvioglacial deposits) = G.  These parent materials occur in sequences of destinctly different stratified profiles (stratiotypes),   however only few stratiotypes have a widespread areal distribution.
At  elevations below 600 m   the     stratiotype Ds-H-B-Zs/Zf-A predominates, but between 600 and 900 m the stratiotype H-B-Zf/Zs-A is the most common. Above 900 m elevation the three stratiotypes H-B-Zf/Zs-A,   H-G-A and Df-H-B-A are the most widespread.  At all elevations incomplete stratiogra-phic profiles exist in which individual layers are absent.  The stratiograph.e boundaries between and within the series were qualitatively and quantitatively investigated using sedimentological methods. Thereby mechanical and mineralogical analyzis confirmed over 80 % of the stratiographic boundaries identified by morphological features in the field.  Through identification of foreign admixtures in the individual solifluction layers (far transported - and local loess) and observation of the disintegration of rock fragments,  it was possible to obtain information about the properties of the solifluction deposits at the beginning of the Holocene soil formation.
In the stratiotype Ds-H-B-Zs/Zf-A zone at the lower elevations,  "Pseudo-gley-Parabraunerde" and integrades between "Braunerden" and "Parabraun-erden" have developed.  In these soils there is an obvious clay illuviation encouraged by the presence of far transported loess.  The boundaries of the main horizons coincide as a rule with stratiographic boundaries.
Above 600 m "Braunerden" showing a Al-deposition in a B horizon develope from the stratiotype H-B-Zs/Zf-A. "Braunerden" also develope on the high plateaus when the "Hauptfolge" are of moderate (60-90 cm) thickness. Where very thick "Hauptfolge" occur    locally,  "Humusbraunerden" develope, which have "Mull humus" up to 40 cm thick and with at least 4 % organic matter.  Due to the high base absorption capacity of the organic matter the loss of bases pro mass unit is lowest in these soils.  Where only traces of the "Hauptfolge" occur in this region,   podsols or "Sauerbraunerden" are found.  The "Sauerbraunerden" are characterized by raw-humus at the surface,  acidification (pHKCl in the surface layers 3, 0),  intensive weathering of the silicates, Al-deposition in the B horizon,  and shallow profiles.   Morphological and analytical investigations show that podsolization (Fe-eluviation and -deposition) does not occur.
The stratiotype (as parent material) has pronounced influences on the soil development as demonstrated by different soil genesis in profiles that are close to each other,  but developed on different stratiotypes.  In particular the soil forming processes of humue accumulation,  clay and iron oxide formation are highly influenced by the thickness and prominence of the "Hauptfolge". Stratiographic boundaries have larger influences on horizon development when characterized by transport processes (eluviation and deposition) than horizons characterized by weathering processes.
The site factors determined by the soil are also directly or indirectly through the soil formation dependent on the stratiotype.  The physical barrier to rooting is still the upper boundary of the "Basisfolge" or the saprolitic zone.  Physiological rooting barriers due to moisture characteristics or poor aeration are also associated with stratiographic boundaries.  The root penetration,  moisture characteristics and aeration are determined by the secondary properties (texture and structure) of the profiles.  These are, however,   strongly influenced by the primary properties (stone content, frost shattering,  and compaction of the layers).  Nutrient reserves in the rooting zone are related to the soil mass and the earlier periglacial frost cracking.  The availability of these reserves is,  however,  dependent on fluctuating properties such as base saturation etc..
Considering the site factors limited by the soil,  the site quality generally increases in the following order of soil type: Podsols and "Sauerbraunerden" < "Parabraunerden-Braunerden" < "Braunerden" < "Humusbraun-erden".
As far as development and site properties are concerned in the three study areas only small quantitative differences occur. In the Ignimbritarea the weathering phenomena of oxide and clay formation have proceeded furthest, however without extreme acidification.  In contrast acidification,   podsoliza-tion and the development of unfavourable raw-humus is clearest on the high plateau of the Gneiss- and Barhaldegranite-areas.  The site properties are most favourable in the Ignimbritarea again in contrast to the Gneiss- and Barhaldegranite-areas where the site properties are least favourable.


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