The effect of the bulk density and the decomposition index of organic matter on the water storage capacity of the surface layers of forest soils

- The species composition of a stand affects the physical properties of organic horizons.
- Capillary capacity is related to the bulk density of single soil horizons.
- There is a relationship between capillary capacity and the index of decomposition.
- A correlation has been shown between the degree of saturation and the index of decomposition.

Forests play an extremely important role in the formation of water circulation in a catchment. Despite numerous studies concerning the relations between forest and water, many problems still remain unexplained. Among them is the influence of the species composition in a stand on the water storage capacity of forest soils, especially of their surface horizons, whose physico-chemical properties are directly affected by the stand. The knowledge of those interactions is significant not only in the aspect of modelling of hydrological phenomena occurring in forest ecosystems but may also be helpful in indicating the directions of stand rebuilding aimed at extending the water-protective functions of forest.The aim of the present research is to analyse the influence of the bulk density and the index of decomposition of organic matter on the water storage capacity of the surface layers of forest soils formed under beech (Fagus sylvatica L.) and fir (Abies alba Mill.) stands in southern Poland. The water storage capacity of individual forest soil horizons shows a distinct relationship with their bulk density. In beech and fir stands there is a critical value of bulk density, amounting to 0.48 and 0.51 g·cm− 3, which corresponds to culmination of the water storage capacity. A strong correlation has been shown between water storage capacity and the index of decomposition of beech and fir organic matter. It has also been found that the index of decomposition of organic matter and the degree of saturation, an indicator of water-filled voids in the soil, can constitute useful measures for describing and comparing the water storage capacity of the surface layers of forest soils formed under stands with a different species composition.