Soils, relief, surface dynamics, and their interrelations were investigated in the scarps of the itamambuca basin (Ubatuba, SP). The study area lies within a state park and the forest cover -the vanishing Atlantic Forest- is mostly primary.
The region has an af - cfa climate type with a marked maritime influence and high atmospheric humidity and rainfall rates. precambrian basement is composed of partially migmatized charnockites; quaternary sediments are continental (e.g. talus slopes, alluvial fans) and/or marine.
We have recognized four distinct units:
- superior slopes. erosive and straight steep slopes (>30°). main surface processes are creep, landslides, subsurface runoff, and infiltration due to the high density of the forest. despite the steepness, soils are deep and highly weathered, mainly typic hapludox (lva), clayey, allic, kaolinitic, with low silt:clay ratios (<0.2) and ki indices (<0,6).
- intermediate slopes. straight slopes (20°-30°), where detrital material may occasionally accumulate. creep and the other processes mentioned are also the determinants of surface dynamics. similarly, the main soil type is the typic hapludox;
- colluvial deposits. accumulative slopes (5°-20°) convex in profile, reworked at the base by river action and also affected by creep, landslides, and subsurface runoff. soils are mainly oxic dystropepts (ca latossólico). the low ki index (0.33) indicates a pre-weathered parent material;
- alluvial-colluvial deposits (alveoli) and alluvial fans (<5°). fluvial erosion and deposition, and runoff are the main surface processes. soil may be fairly developed in the alveoli, where lithic oxic dystropepts (ca) predominate. Tropofluvents (aa) occur in restricted portions of the alluvial fans; on most of these deposits there is no soil cover.
The presence of deep and highly weathered soils on the scarps of the serra do mar confirm that the only appropriate "use" for these unstable area is the effective preservation of the primary forest.