Abstract
Northern Red Oak is a tree species native to North America. In Polish flora it has status of invasive plants. In the years 2008-2011 autoecological studies were conducted aiming at examination on what type of soils the species tends to regenerate ie appearance of seedlings in the vicinity of maternal trees. In total 250 phytosociological relevés and 100 soil samples (400 soil subsamples) were collected. It was observed that majority stands (almost 80%) of Northern Red Oak occupy sites very strongly acid and strongly acid. In reference to pH in KCl results are a little different, however, sites with soil very strongly acid (pH = 4.1-5.0) and stronly acid (pH < 4.1) also predominate. The investigated soils were typified by very low values of magnesium (< 10 mg/1000 g), phosphorus (< 3 mg/100 g) and potassium (< 7 mg/100 g). Total nitrogen in studied sites dominated in two the lowest classes (> 0.25%). The sites of Q. rubra are rich in organic carbon. Almost 50% of all sites covers two highest classes of concentration of this element ie 4.0-8.0% and > 8.0%. Soils where seedlings of Northern Red Oak were encountered, were characterized by humus medium for mezotrophic and eutrophic broad-leaved forests and mixed coniferous forests - more than 60% had ratio of carbon and nitrogen CN > 25. In several sites this ratio reached 50. The lower values in case of content of calcium and loss on ignition dominate. The studies showed that soils on which species grows and also spontaneously regenerates are typical for coniferous and mixed coniferous forests, however, in natural range Q. rubra is component of deciduous forests. It could be associated with the fact of more frequent introduction of Northern Red Oak into poorer sites than the consequence of its habitat requirements.