Fig. 2. Rates (area basis, +1 SE) of gross production and immobilization of NH₄⁺–N and NO₃^––N as measured in spring (April) and fall (October) 1999 by the ¹⁵N pool dilution method in disturbed surface soils (0–15 cm), by vegetation type and topographic position. Data for April are based on one sample per combination of vegetation and topographic position, hence no error bars are shown. Fill patterns denoting vegetation type are the same as shown in Fig. 1.