BCI soil mapping units

The soil classes are distributed in intricate spatial patterns and cannot be mapped as pure units.  However, we have sufficient data to map consociations, in which there is a single dominant soil class, with soils of other named classes as minor constituents.  At one stage the intricate intermixture of Standley and Fairchild suggested that they would have to be mapped as a complex, with several classes codominant.  However consociations are preferred, because they are more specific and informative than complexes.  As more data accrued, we were able to separate the area into two consociations, with Fairchild predominant on the northern penisulae and Standley on the steep terrain of the northern scarp.

There are 14 mapping units (Table 6.1) but some are minor and the ten most extensive cover 98% of the island.  Because of the lithological emphasis in the definition of the soil classes and mapping units, the soil map accords closely with the geological map.

The brown fine loams predominate on the steeper topography in the north of the island, along the Lutz-Drayton fault system, and on the fringes of the andesite plateau.  The shallow red light clays are mainly on the northern penisulae.  The deep red light clays predominate on the andesite plateau, western Poacher peninsula and in patches on the Harvard peninsula.  The pale swelling clays are concentrated in the west and southwest of the island, with patches elsewhere. The mottled heavy clays are rare outside the catchment of Lutz Creek. The gleys are mapped only in the swamp at the centre of the andesite plateau.

Table – Soil mapping units for BCI