Soil humus changes with elevation in Scots pine stands of the Moncayo Massif (NE Spain)

Because of its rapid temporal variation, humus characterization is one of the most useful approaches when studying the influence of multiple variables on soil. The aim of this study is to describe the elevation effect on terrestrial humus formed under Scots pine stands that developed on homogeneous parent material in the Moncayo Massif (NE Spain). The humus forms evolved from Dysmull to Hemimoder and Humimor with elevation. These morphological and analytical changes are considered a consequence of the increasing soil constraints (acidity, podzolization) and decreasing temperatures with elevation, which reduce soil biological activity and lead to an accumulation of soil organic matter. About 10 Mg organic C/ha in the low altitudinal pinewood stand and 54 Mg C/ha in the top stand were stored in the O horizons. The total organic C also increased significantly with elevation in the Ah horizon. However, the pH and the size of aggregates decreased with increasing elevation in the Ah horizon.