The Effect of Land-Use Change on Urban Grassland Soil Quality (Southern Poland)

We aimed to evaluate the changes in grassland soils resulting from forest tree planting using two soil quality indices—a soil evaluation factor (SEF) and a soil quality index (SQI). We studied the impact of introducing forest trees (conifers, broadleaves or mixed) on natural meadows. We examined how the soil properties were affected by the tree species and their ages (25, 35 and 65 years old). Soil samples were collected from meadows and their adjacent forests, all situated within the boundaries of Krakow (Poland). Before the trees were planted, all areas were grassland, used for agricultural and recreational purposes. The soil samples taken from surface and subsurface horizons were analysed for pH, nutrients (C, N, P, K, Mg), humus compounds and dehydrogenase activity (DHA), and basic cations (Ca2+, Mg2+, K+, Na+). The introduction of trees on the grasslands lowered the pH and DHA activity, and impoverished the soils in nutrients. The impact on the soil properties of the tree species was more important than their age. The biggest negative changes were found in the soils covered by coniferous trees, in which the lowest values of SEF and SQI (respectively, 9 and 0.24) were recorded. The highest values of both soil quality indices (SEF—147, SQI—0.66) were observed in the meadow soils. The soils of a 35-year-old deciduous forest and a 65-year-old forest with deciduous and coniferous tree species had similar SEF and SQI values. The deciduous trees adapted better to the meadow soils than the conifers and, over time, an improvement in the soil properties occurred as a result of the accumulation of tree residues.