SOIL AGGREGATE STABILITY UNDER DIFFERENT MEDITERRANEAN VEGETATION TYPES

The influence of vegetation type on soil erodibility was studied by me ans of aggregate stability measurements using the Modified Emerson Wat er Dispersion Test (MEWDT), water-drop impacts (CND and TDI) and Ultra sonic Disruption (UD) methods on soils from north-facing slopes of the mountain range of La Serra Grossa in the eastern Iberian Peninsula. S oils with similar characteristics but covered by the main plant specie s at the study area were selected, Quercus ilex woodland showed the mo st resistant soil aggregates followed by e. coccifera and Pistacea len tiscus scrubland, Brachypodium retusum grassland and Pinus halepensis woodland. Aggregates developed beneath dwarf shrubs like Rosmarinus of ficinalis, Thymus vulgaris, Ulex parviflorus and Anthyllis cystisoides were least resistant. The different methods and tests applied are use ful to study the soil aggregate stability. The MEWDT and TDI tests sho wed only minor differences between samples due to the high aggregate r esistance and the low energy applied by these tests. CND and UD tests are considered to be more suitable for resistant Mediterranean soil de veloped on limestone due to the greater energy applied. Aggregates tes ted from an initially moist (pF1) condition were always more stable th an air dried aggregates. Rangeland management after disturbances by fi re, agriculture or grazing, etc. should try to establish natural woodl and (e. ilex) in order to get the most stable soil. Alternative vegeta tion cover to the climax vegetation that give high aggregate stability are e. coccifera and P. lentiscus scrublands. immediately after distu rbance, B. retusum grassland seems to be the best option for soil prot ection. (C) 1998 Elsevier Science B.V. All rights reserved.