This study showed that forest harvesting causes a decrease in imogolite-type material (ITM) content in podzols. This has considerable implications in terms of soil properties and for the understanding of watershed response to environmental disturbance. Imogolite-type material refers to poorly ordered aluminosilicates with an Al:Si ratio of 2:1. It is comprised of (1) imogolite, a mineral of stoichiometr(O₃Al₂O₃SiOH, and (2) proto-imogolite allophane, a less ordered material with similar composition. Imogolite forms nanotubes of approximately 2 nm in diameter while proto-imogolite allophane has been shown to form nanospheres with diameters ranging from 3 to 3.5 nm. Imogolite-type material is a naturally occurring pedogenic mineral. It was first identified in volcanic soils and is also a common phase in illuvial horizons of podzols. Because of its poorly crystalline nature, ITM is among the most reactive components of soil and can be readily impacted by environmental disturbance. The objectives of this research are to: (1) document the nature and amount of poorly ordered aluminosilicates, including ITM, at the study sites, (2) determine the impact of forest harvesting on ITM and discover which geochemical processes are responsible for the observed changes, and (3) describe the effects of ITM content variations on soil properties and assess ITM role in watershed response to forest harvesting. The study area is located in the Roberts Creek Study Forest (Sunshine Coast, Southwest British Columbia, Canada). The area is characterised by low elevation (ranging from 350 to 500m above sea level), gentle slopes (average gradient of 15%), and a south-westerly aspect. It lies within the Pacific Range Drier Maritime variant of the Coastal Western Mountain Hemlock Zone. Douglas fir is the dominant vegetation species. The climate is characterised by warm, relatively dry summers and moist, mild winters with little snowfall.Soils are Humo Ferric Podzols in the Canadian system of soil classification. A general description of the soil profile consists in: (1) forest floor LFH (3 to 15 cm in thickness), (2) eluvial horizon Ae (2 to 10 cm thickness), (3) illuvial horizon Bf (25 to 35 cm thickness), (4) BC horizon (20 to 40 cm thickness) showing mottling, and (5) C horizon consisting of basal till. We collected soil samples from undisturbed forested plots (control), and compared them to samples from plots that were clear-cut harvested 1 to 8 years ago. All soil horizons from H to C were sampled. Samples were analysed for poorly ordered aluminosilicates using selective dissolution analysis and transmission electron microscopy. Other analyses conducted for site characterisation included soil pH, soil organic matter and organic C content, dissolved organic matter concentration, exchangeable cations and anions, plant-available and total phosphorus and nitrogen, soil solution composition, and texture. Selective dissolution of poorly ordered aluminosilicates revealed that the atomic Al:Si ratio equals 2, indicating the presence of ITM. Transmission electron micrographs showed no sign of imogolite morphology (tubes or threads) but instead showed aggregates of spherical nanoparticles consistent with the presence of proto-imogolite allophane. Proto-imogolite allophane is believed to be the main form of poorly ordered aluminosilicates in the Roberts Creek podzols. Control sites are very high in ITM, containing up to 40g/kg of ITM in the Bf, BC, and upper C horizons. This value is among the highest reported in the literature for podzols. Imogolite-type material content decreases significantly after logging to a low of 5g/kg occurring in the 8 years old harvested plot. There is no sign of recovery of the ITM pool after 8 years following logging. Additional sampling was conducted in August 2005 to include plots that were logged up to 15 years ago. Results show that soil pH in the B and C horizons averages 5.4 and is constant in logged and control plots. pH variation is not believed to be the cause of ITM dissolution.These findings show that ITM content in the pedon declines following clear-cut logging. This attests to a decrease in intensity of the podzolization processes and may be an early sign of human-induced regressive pedogenesis. Imogolite-type material dissolution also has a strong impact on soil properties. This mineral exhibits a large specific surface area and bears a weak permanent positive surface charge. It is an important mineral for the anion retention capacity of many volcanic soils and podzols, and its depletion is likely to promote nutrient leaching. Imogolite-type material also releases significant amounts of Al ions upon dissolution and may be involved in the occurrence of Al toxicity in drainage waters often reported after logging on acidic forest soils. Finally, ITM is a powerful organic matter stabiliser and its depletion leads to increased decomposition and reduces carbon sequestration potential of soil. This presentation briefly discusses these environmental implications and outlines new research possibilities.