Bodenreaktion und basensättigung in den buchenwaldgesellschaften Kroatiens

Summary

Soil Reaction and Exchangeable Base of the Beech Forest Soils in Crotia.

According to I. Horvat (1938, 1950, 1954) the beech (Fagus silvatica L.) forms in Croatia two forest associations: Fagetum silvaticae croaticum Horv. and Blechno-Fagetum Horv. Both are developed in the mountainous parts of Croatia. The first one belongs to the alliance Fagionillyricum Horv. and includes three subassociations being dependent on height: Fagetum silvaticae croaticum montanum Horv., F. s. cr. abietetosum Horv. and F. s. cr. subalpinum Horv.) and one being conditioned by vicinity of the Adriatic sea (F. s. cr. seslerietosum Horv.).

Although the predominating forest tree in both associations is the beech, which was repeatedly designed as a tree-species which creates his own environment and improves the soil, there are only a few plant species which are common for both associations. Especially there is no natural tendency for the basophilic, neutrophilic and slightly acidophilic species of the Fagetum silvaticae croaticum to invade into the Blechno-Fagetum; if this occurs it is always due to secondary base enrichment (for instance along the roads built from limestone material). It could be on the contrary sometimes established the invading of acidophilic species of the Blechno-Fagetum into the Fagetum silvaticae croaticum and a tendency of the Fagetum silvaticae croaticum to pass into the Blechno-Fagetum or — in the zone of F. s. cr. abietetosum — into the Blechno-Abietum.

Fagetum silvaticae croaticum is extended mainly on the soils developed from calcareous and dolomitic parent materials such as mull-rendzina, degraded rendzina, brown carbonatic soil, bleached brown carbonatic soil, bleached and humus-rich forms of relictic terra rossa, but it too occurs on some soils developed from non-calcareous parent materials.

Blechno-Fagetum is chiefly to be found on the podzolic soils similar to those which are covered by Blechno-Abietum. Soils of both of these associations are mainly developed on non-calcareous parent materials such as sandstone, but sometimes limestone or dolomite is their paren material too.

Detailed soil research was made in South West Croatia to establish soil properties marking the boundary line between Fagetum silvaticae croaticum and the too acidophil associations. Soil reaction and properties of base exchange complex seem to be the most important factors for the distribution of these forest associations.

The critical soil reaction at which the basophil-neutrophil species of the Fagetum silvaticae croaticum disappear and the highly acidophil characteristic species of the Blechno-Fagetum and the Blechno-Abietum begin to occur is pH(H₂O) 5.5–5.0. There were no highly acidophil species at pH (H₂O) above 5.5, and no characteristic species of the Fagetum silvaticae croaticum occured, if pH(H₂O) was below 5.0.

Nevertheless the saturation degree of the base exchanging complex of A₀″ and A₁ horizons seems to be the most proper to mark the boundary line of the Fagetum s. cr. to the acidophilic associations. The saturation degree of A₀″ and A₁ horizons of soils under the Fagetum croaticum is high (V>60%) or moderate (V35–60%) in the sense of classification of M. Gračanin (1950, 1951). In soils of the Blechno-Fagetum and the Blechno-Abietum the saturation degree is always low (less than 35%). In the transitional stages where A₀″ and A₁ belong to different grades of saturation degree, the most important for the occurring of the first acidophil species is the saturation degree of A₀″.

The distribution of soil reaction and S, T and V-values in single soil profiles shows:

• I) In all studied profiles there are much more adsorbed bases (S) in A₀″, than in the underlying mineral horizons.

• 2) the increase of S-values from mineral horizons to A₀″ takes place not only in soils under beech forest, but also under Abies alba and even under spruce (Picea excelsa):

• 3) The accumulation of exchangeable bases in A₀″ under the Blechno-Fagetum as well as under the Blechno-Abietum is not great enough to diminish the acidity of this horizon in comparison to the mineral soil and parent material. On the contrary — because of the forming of acid humus —the A₀″ horizon in these soils generally is the most acid part of the whole profile; consequently neither beech nor Abies alba are able to make possible the evolution of the Fagetum silvaticae croaticum on soils poor in bases.

• 4) In soils of the Fagetum silvaticae croaticum, which have horizons rich in bases in the depth which can be attained by a great part of roots, more bases come with the litter to the soil surface and the conditions for decomposition are more favourable, consequently smaller amounts of acid humus are formed and to a great part with bases saturated. The degree of base saturation is high. The pH in A₀″ is therefore often higher than in A₁. In this case beech retards the acidification of soil, although it does not prevent it.