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Abstract "Heft 11"


Freiburger Bodenkundliche Abhandlungen

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


Heft 11


Wolfgang Raisch


Bioelementverteilung in Fichtenökosystemen der Bärhalde
(Südschwarzwald)


Freiburg im Breisgau 1983

ISSN 0344-2691


Summary:

The reserves and distribution of 18 bioelements were determined in five spruce ecosystems (trees and ground vegetation) and in a pasture ecosystem. The investigated sites are located on the north-eastern slope of the "Barhalde" near Neuglashutten (Municipality of Feldberg) at an altitude of 1160 to 1260 m a.s.l.. The climate is of atlantic regime, perhumid and cool (1800-2000 mm/5°C annual average precipitation/temperature.) Spruce stands predominate the actual vegetation.
The soil parent materials are periglacial solifluction deposits derived from the acidic "Barhalde"-granite. On the ridge and the upper part of the slope "Braunerde" (brown earth) and "Podsol" predominate whereas in the lower parts of the slope "Stagnogley" (surface water gley) and "Ockererde" (slope gley with oxide enrichment) are found. The investigated spruce stands cover these tour soils. All soils are strongly acid with low base saturation. The rooting depth of "Podsol" and "Stagnogley" is shallow and in "Braunerde" and "Ockererde" it is medium.
The spruce stands are 15, 25, 50, 75, and 130 years old. They cover almost a complete rotation cycle as practiced in this altitude. The mean annual increment per hectare varies from 6.6 to 8.3 solid cubic meters of standing crop. This is classified as low, whereas the degree of stocking is high.
The sample trees were divided into the following compartments:
-    needles from the current growing season
-    needles from all past growing seasons
-    twigs (diameter less than 1 cm) separated according age as the needles
-    branches.
Each of the compartments were separated into sun exposed and shade parts.
-    Dead (dry) branches and
-    cones if present were collected separately.
-    Trunks were divided into five sections of identical length; each was subdivided into bark, sapwood and if present heartwood.
In each of these 26 tree compartments and in the ground vegetation the contents of N, P, K, Ca, Mg, Mn, Cu, Zn, Fe, Al, Na, Pb, Cd, Co, Cr, Ni, V, and Be were analysed and the respective dry matter-weights per hectare were calculated.
The nutrient supply of the spruce stands was satisfactory for N, K, and Ca, very good for P, but critically short of Mg. Moreover, needle analysis revealed a nutrient deficiency for the micronutrients Zn and Cu.
Al levels were high in the spruce needles and correlated with the exchangeable Al of the soils thus reflecting soil conditions.
The heavy metals showed different distribution patterns within the ecosystems depending on their mobility in the soils as well as on the immitted far transported depositions into the Black Forest.
Especially the twigs and branches showed high contents of Pb, V, Cr, Ni, Cu, and Fe due to atmospheric pollution and dry deposition on the bark surfaces. This was confirmed by the fact, that the more exposed and older stands showed increased contents of these elements. The highest airborne accumulation of Zn was found on the bark of trunks of the oldest trees. The distribution pattern of Pb depended primarily on the input from the atmosphere and the dry and wet deposition on plant surfaces.
Thus the age and structure of the plant surface as well as the exposure and locality of the stand governed the distribution.
In contrast Cd, whose mobility under moist and acid conditions was high, was translocated reasonably within the plants. Thus the highest Cd contents were found in the stand growing on "Stagnogley". Mn, an element of similar mobility, was predomi-natly  enriched in the assimilation tissues of trees as well as in the ground vegetation. Very high contents were found in the spruce needles of the "Stagnogley" and "Ockererde" sites. In the ground vegetation, Vaccinium myrtillus - an acidophytic species -showed the highest content.
Of all elements investigated,  except Pb, an uptake by the roots can be presumed, depending upon soil pH, water regime, depth of rooting and occurance of the elements in the different soil components. The total reserves of the elements in the soil are much less related with the amounts in the different spruce stands.
In the ground vegetation, the average content of all elements, except Be, was higher than in spruce needles. Especially Pb, Cd, Cr, and V were enriched but also Cu and Fe. Oxalis aceto-sella, the fern species and Luzula silvatica had the best nutrient status. A high accumulation of non-nutrients in mosses and in the pasture vegetation was evident.
Calculations of element output by different methods of harvesting showed, that harvesting of whole trees resulted considerably higher losses of elements from the sites in comparison to a harvest limited to wood only. These additional losses ranged from 10 to 20 times in the case of N and P, whereas the export of heavy metals increases only 2 to 4 times.
By comparing the amounts of elements in the above ground plant biomass and those in the soils, it was shown that for each element the reserves in the soil exceeded considerably the quantities incorporated by the above ground plant parts. The above ground biomass contained as average values nearly 10 % (N) to less than 0,5 % (K, Na, Al, Fe, Be, Co, and V) of the reserves of the ecosystems with the older spruce stands.
Neglecting biomass output by harvesting the percentage of Pb and Cd accumulated in the vegetation may increase because of a positive input/output balance and the increment of biomass. In spite of the relative low atmospheric pollution, the balance of some heavy metals in the spruce ecosystems is clearly determined by immission (distinct  for Pb, Cd, and V; to a lesser degree Zn, Cu and Fe). As the supply of Zn and Cu of the investigated spruce stands are close to the level of deficiency, a small additional input may have a positive effect.



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