Soils under beech forest in an experimental catchment area near Nelson, New Zealand

Abstract

Abstract Soils of four contiguous small forested experimental catchments, covering 40 ha in hill country formed in Moutere Gravel in NW South Island, New Zealand, were studied. The indigenous vegetation of the area was Nothofagus forest; the rainfall averages 1,550 mm per annum; the topography is a dissected pattern of narrow ridges and small valleys; and the parent materials are Late Pleistocene to Holocene slope deposits derived from reworking of underlying early Quaternary weathered gravels. One hundred and thirty-one profiles were described on cross-catchment traverses on a variety of sites in differing parts of the catchments. Additional profiles were described from tracks that were formed at the time of logging. The soils are characterised in terms of their physical properties by summarising all the profile data. Their particle size, chemical and clay mineralogical characteristics are also summarised from analyses of representative profiles. Variation in soil development, as expressed by horizon differentiation, was correlated with thickness of organic horizons and soil pH. The soils with the thickest 0 horizons and lowest pH values are podzols. Variation is attributed to differential biological decomposition which in turn is related to site differences. The three soil series identified are classified as podzols, podzolised yellow-brown earths and yellow-brown earths. Their distribution is complex, often passing from one to another in less than a metre. The yellow-brown earths occur widely over all landforms within the catchment, while the podzol and podzolised soils occur more commonly on ridges, spurs and upper slopes. Parent material variation and slope angle have no direct influence on the soil pattern. Soil disturbance by tree overturn is a major factor influencing soil development in the beech forest, and accounts for the high proportion of yellow-brown earths.