Stand composition affects soil quality in oak stands on reclaimed and natural sites

In many afforested reclamation sites as well as in commercial forests naturally settled shrubs or trees (“non-target species”; NTS) are cut down to improve the growth of the target trees (TT). In afforested oak plantations (Quercus robur) of the Rhineland (Germany) the NTS broom (Cytisus scoparius) and birch (Betula pendula) can occur in high densities during the first decades of succession. Hazel (Corylus avellana) is a common shrub in the understory of commercial oak forests (Quercus petraea). We studied the influence of these NTS on selected physical, chemical and biotic soil properties in cultures of oak (TT). Soil samples taken under single oak trees were compared with samples taken under broom and birch at afforested reclamation sites of different age (2, 9, 13 years) and with samples taken under hazel in an 80-year-old oak forest. At initial stages of succession (2 years) all of the investigated soil properties indicated a higher soil quality under broom than under oak. However, the advantage of broom was less evident in a later stage of succession (9 years). Birch (13 years) and hazel (80 years) only improved soil chemical properties. The soil pH and the content of Mg2+ were significantly higher under birch, the contents of Ca2+, Mg2+ and PO43− were significantly higher under hazel than under oak (p=0.05). The results demonstrate that the selected NTS improve soil quality in afforested and commercial oak forests. This effect is pronounced under the influence of broom at initial stages of soil development.