Ecology of serpentinized areas of north-east Portugal

Abstract

After a brief description of the geology, climate and main soil types derived from serpentinized ultramafic rocks in north-east Portugal, detailed information is given regarding the behavior of some elements in relation to the weathering and soil forming processes.

The flora and vegetation and aspects of the autecology of some serpentinophytes are discussed regarding the most important ecological factors in the area: summer drought, nickel toxicity, and unbalanced Mg/Ca quotient. The serpentinomorphoses suggest an adaptation to drought, and to other soil toxicity characteristics.

The main adverse factors are probably the high Mg/Ca quotient, the high Ni and the low N, P, K and Ca concentrations. These may eliminate strongly competitive serpentinofuges and allow the establishment of peculiar serpentine flora and vegetation. When no erosion occurs, deeper and more fertile soils are developed (with higher water holding capacity, increased organic matter, and nutrient levels), tolerant shrubs and trees may grow, the serpentine character of the flora and vegetation decreases, but the Mediterranean character remains, not only because of summer drought, but especially because the toxic effects are not eliminated. A high concentration of nickel remains during the soil forming process — a dissolution — in spite of evolution diminishing its toxic effects.

In deep soils, nickel behavior and toxicity are probably also controlled by the relative stability of Cu and Ni organic complexes.