Two forest soils rich in organic matter but differing in texture (sandy loam and silty loam) were heated under controlled laboratory conditions in order to examine the consequences of the heating effect that accompanies the passage of a fire on the physical properties of soil. Three samples of both soils were heated for 30 min in a muffle furnace at temperatures of 25, 170, 220, 380 and 460°C. At each temperature, the following parameters were determined: dry aggregate size distribution, water aggregate stability, total porosity, pore size distribution, water repellency and hydraulic conductivity. Heating the soils at 170 and 220°C caused no significant changes in aggregate size distribution or total porosity but increased water aggregate stability and the volume of pores 0.2–30 μm. Also, increased water repellency and strongly decreased the hydraulic conductivity. All parameters underwent much more dramatic changes at 380 and 460°C that can be ascribed to the combustion of organic matter. At such temperatures, water repellency was destroyed and the low hydraulic conductivity can be attributed to the aggregate breakdown observed under dry and wet conditions.

SUMMARY: Three Spanish Antarctic research cruises were carried out in the South Shetland Archipelago (Antarctic Peninsula) and Scotia Arc (South Orkney, South Sandwich and South Georgia archipelagos) on the continental shelf and upper slope (10-600 m depth). They have contributed to our knowledge about ascidian distribution and the zoogeographical relationships with the neighbouring areas and the other Subantarctic islands. The distribution of ascidian species suggests that the Scotia Arc is divided into two sectors, the South Orkney Archipelago, related to the Antarctic Province, and the South Georgia Archipelago (probably including the South Sandwich Archipelago), which is intermediate between the Antarctic Province and the Magellan region.Keywords: ascidians, Antarctic, Scotia Arc, Magellan, biogeography. RESUMEN: RELACIONES ZOOGEOGRÁFICAS DE LA ASCIDIOFAUNA LITORAL EN LA PENÍNSULA ANTÁRTICA, ARCO DE SCOTIA Y REGIÓN MAGALLÁNICA. -Tres campañas antárticas españolas (Ant-86, Bentart-94 y Bentart-95) en el Archipiélago de las Shetland del Sur (Península Antártica) y Arco de Scotia (Archipiélagos de las Órcadas del Sur, Sandwich del Sur y Georgia del Sur), sobre fondos de la plataforma continental y parte superior del talud (profundidades entre 10 y 600 m), han contribuido a ampliar el conocimiento de la distribución de las ascidias en estas zonas, y sus relaciones biogeográficas con las áreas vecinas y otras islas subantárticas. Desde el punto de vista de la ascidiofauna, el Arco de Scotia se divide en dos sectores, por un lado las Órcadas del Sur más relacionadas con la Provincia Antártica; y por otro el Archipiélago de las Georgias del Sur (y probablemente las islas Sandwich del Sur) que ocupa una posición intermedia entre la Provincia Antártica y la región magallánica.

Abstract:The purpose of this study was to assess how terracing affected overland flow and associated sediment losses, at the micro-plot scale (0.25 m 2 ), in recently burnt stands of the two principal forest types in north-central Portugal, i.e. mono-specific stands of Maritime Pine and Eucalypt. Terracing is an increasingly common practice of slope engineering in the study region but its impacts on runoff and erosion are poorly studied. Non-terraced plots at the Eucalypt and the Pine site revealed similar median runoff coefficients (rc: 20-30%) as well as comparable median sediment losses (15-25 g m -2 ) during the first seven months following wildfire. During the ensuing, slightly wetter 18-month period, however, non-terraced plots at the Pine site lost noticeably more sediments (in median, 90 vs. 18 g m -2 ), in spite the runoff response had remained basically the same (median rc: 33 vs. 28%). By contrast, terraced plots at the same Pine site lost hugely more sediments (in median, 1,200 g m -2 ) during this 18-month period. Terraced plots at the Eucalypt site even lost three times more sediments (in median, 3,600 g m -2 ). Ground cover and resistance to shear stress seemed to be key factors in the observed/inferred impacts of terracing.

At three adjacent sites in steeply sloping woodland in Galicia (NW Spain), surface runoff and associated erosion under simulated rainfall (64 mm h 1 ) were measured on five occasions between June 1998 and July 1999. Two of the three sites had recently been deforested and topsoil added, and one of these two had been sown with grass, which was germinating at the onset of the study. Deforestation greatly increased runoff and erosion rates, and the recovery of plant cover reduced erosion. All three soils were very hydrophobic due to high levels of poorly humified organic matter, which led to higher runoff rates than expected, especially during dry periods. However, great structural stability prevented there being a significant correlation between runoff rate and soil erosion.

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