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In Mediterranean areas, fires are accelerators of soil degradation and the definition of the time extent to re-establish the soil community is a great challenge. The aims of the research were to evaluate, during two years after a fire: i) the potential recover of the soil abiotic properties; ii) the stability (resistance or resilience) of the soil microbial community; iii) the potential role of different plant covers on soil recover capability. To reach the aims, soil properties as organic matter content, C and N concentrations, microbial (MB) and fungal (FB) biomasses, respiration (Resp) and coefficient of endogenous mineralization (CEM) were measured twelve, fifteen, eighteen and twenty-four months after fire, and were compared to those in pre-fire soils. The results showed that the MB was less resistant in soils under herbs and black locust, and more resilient under pine and holm oak; FB showed low resistance till one year after fire regardless to the plant cover, and high resilience at two years after fire, especially under holm oak and pine; Resp greatly slowed down and did not recover the initial values regardless to the plant cover; CEM resisted to fire in soils under different plant covers. In conclusion, the soil abiotic properties were strongly affected by plant covers, whereas the biotic ones also by the time since fire. Finally, soils under holm oak were the most fire resistant.

Volcanic activity affects past and present landscapes. Here we present a case study related to the heat impact of the Xitle lava flow on the former soil cover. The eruption occurred 1670 years B.P., in south Mexico City. The evaluated properties include those related to the “soil memory”, used as tools of paleoenvironmental interpretation in volcanic paleosols: macro and micromorphology, color, grain size distribution, magnetic susceptibility, and carbon and nitrogen contents. Changes of these properties by the heat influence are relevant for an adequate paleoenvironmental reconstruction. Two sites and three soil profiles are selected to show soil modifications by the volcanic activity. The two sites represent the following: 1) slightly transformed paleosol buried by the lava flow, but separated from it by a 10 cm thick volcanic ash layer (site Cuicuilco-ENAH); 2) moderately and strongly transformed paleosols (two profiles inside the Copilco archeological zone). One of the Copilco profiles represents a buried paleosol with a very thin (3 cm) ash layer on top, at the contact with the lava; the second profile is the most affected by the lava flow, as it is directly beneath the lava. All studied paleosols are sandy, have a low amount of organic matter, narrow C/N ratios, and very high values of magnetic susceptibility. The strongest modifications are observed in the upper horizons, which are in contact with the lava. However, the presence of the ash layer minimizes the heat effect. Despite the observed modifications, it is possible to establish three cycles of soil formation in the paleolandscape. The first, and the oldest, related to the development of a Luvisol type soil, indicates a longer time of landscape stability. During the second cycle a pedosediment with a high concentration of artifacts was formed. The last and the youngest cycle includes the Ab and the AEb horizons (present only in Copilco). They form by an Andosol type pedogenesis, which reflects a shorter time of soil development. The presence of the AEb horizon is interpreted as the result of the degradation of the Ab horizon, either due to the heat effect of the lava, or to cultivation and irrigation practiced by the pre-Hispanic communities.

In this study the erubaz soil, a shallow soil influenced by volcanic parent rocks is examined with special emphasis on its clay content and clay-mineral-composition. Fifteen profiles at seven study areas and with four different parent material types are analysed. Bulk soil mineralogical and clay-mineralogical properties are examined by X-ray diffractometry (XRD). According to the mineralogical analysis the presence of the unstable mafic silicates indicates that the composition of the parent rock is still well reflected in the examined soil profiles. Illite is the most common clay mineral followed by kaolinite and smectite. Kaolinite and illite contain ca. 15–20% and 10% interlayered of smectite, respectively. Poor crystallisation and composition of secondary minerals suggest that these soils are in an early stage of their pedogenic evolution, but are more developed than the typical Andosols. Presence of opal-C and cristobalite in the andesitic samples is characteristic. Our study revealed that the erubaz soil type is not as homogeneous as it was suggested before. According to our analysis, mainly on the basis of their mineralogy, these soils can be divided into two well-defined groups. These two groups (erubaz soils formed on intermediate-acidic and on basic lithology) can be regarded as subtypes of the erubaz soil type. Moreover, two varieties (black and brown), mostly based on colour and SOM content, are distinguished. In these varieties the conditions of the decomposition of organic material are very different due to the moisture content, temperature and pH-conditions of the soil. The studied soil profiles were included into the WRB-system. On the basis of threshold-values of their diagnostic horizons, the studied profiles did not fulfil the criteria of the Andosol group and were inserted into the assemblage of Phaeozems.

The andosols of south-central Chile (36–42°S) are developed on yellow-brown loams that cover the region with a thickness of several meters. In the literature, several hypotheses concerning the nature, origin, mode of transport and deposition of the andosol parent material have been advanced but no general agreement has been found. In this paper, we test these hypotheses by analyzing new representative outcrops located around Icalma (38°50′S) and Puyehue (40°40′S) lakes by a pluri-methodological approach. Our data demonstrate that the andosol parent material has the typical mineralogical and geochemical signature of the regional volcanism and that these deposits are post-glacial in age. The grain size of the deposits and the morphology of the coarse grains evidence that most of these particles haven't been re-transported by wind but are direct volcanic ash falls deposited throughout the Late Glacial and Holocene. Because of the prevailing westerly winds, most of these volcanic ashes have been transported to the East. Following the deposition of the volcanic particles, weathering and pedogenetic processes have transformed part of the volcanic glasses and plagioclases into allophane and have wiped out the original layering. This work demonstrates that most of the andosols that occur in the Andes and in the eastern part of the Intermediate Depression of south-central Chile are developed on volcanic ashes directly deposited by successive volcanic eruptions throughout the Late Glacial and Holocene.

The Azores Islands are of recent volcanic origin and their soils, classified as Andosols, have characteristics peculiar to their formation and constituents. Several other areas in the world, including parts of Europe, have Andosols, but their hydraulic properties are not well known. To improve understanding of the hydrologic behaviour of these soils, two experimental sites were selected for in situ hydrological observations and sampling for laboratory analysis. The two studied soils are classified as Ferric Andosol and Haplic Andosol. Soil use at one site is permanent grassland and at the second there is a rotation of 5-year grass and 1-year silage maize. Water retention curves were measured using a sand box, a sand and kaolin box and a pressure membrane apparatus. Hydraulic conductivity curves were measured by the crust, hot air and two-step methods. Measurements in in situ soil monoliths were by the internal drainage and zero flux plane methods. The hot air and two-step methods overestimated the hydraulic conductivity compared with the field methods. These results suggest that soil physical properties of Andosols containing allophanes change when they are dried. Results for the crust method generally agreed with field data. Water retention values near saturation measured with the sand box tended to be greater than those observed in the field. Those estimated with the sand and kaolin box and with the pressure membrane apparatus agreed well with field observations. The water retention and the hydraulic conductivity curves fit the Mualem–van Genuchten model well (coefficient of determination 0.96).

Volcanic ash soils are usually associated within the weathering sequence glass --> allophane --> 4 halloysite. On the eastern slopes of the volcano La Soufriere, Guadeloupe, this sequence occurs in a toposequence Molli-silicic Andosol-Humic Andosol-Haplic Andosol-Haplic Nitisol, where the average annual rainfall decreases from 4000 mm at 420 m a.s.l. to 2500 mrn at 30 m a.s.l. Of this sequence, we selected four profiles and examined the relationships between weathering stage, clay mineralogy and exchangeable K+-Ca2+ selectivity. With increasing weathering, the total content of alkaline and alkaline-earth cations of the B horizon steadily decreased from 185 cmol(c) kg(-1) soil in the Molli-silicic Andosol to 24 cmol(c), kg(-1) soil in the Nitisol. K+ selectivity was small in the Molli-silicie Andosol, but significantly increased with increasing weathering stage and increasing content of halloysite. In the Haplic Andosol and Nitisol, the very strong selectivity for K+ ions may be linked with the presence of a 2:1 clay mineral, but could not be attributed unequivocally to this mineral or to halloysite. The 2:1 mineral occurred as a discrete phase mixed with halloysite and exhibited X-ray diffraction features, suggesting its vermiculitic nature. (C) 2003 Elsevier B.V. All rights reserved.

In France, andic soils mainly occur in the Massif Central (andic and other volcanic soils >5000 km 2 ), and on the Vosges and the Morvan Hercynian massifs. In the Massif Central, Silandosols on recent pyroclastics are distinguished from Aluandosols on older Mio-Pliocene lavas. After a brief introduction to the parent materials, soil characterisation, survey, genesis, properties and land use are reviewed in two periods: from 1960 to 1979, and from 1980 to 2000. Soil distribution is related schematically to topo-climatic sequences, comparing recent pyroclastics to older volcanic lavas. An udic or perudic soil moisture regime is the primary factor in Andosol genesis in France. Silandosols occur only on recent pyroclastics and Aluandosols on old lavas after reworking by glacial erosion from a mantle of loose and pre-weathered materials. The anthropic impacts include accelerated erosion and changes in carbon content.

In Europe, non-allophanic Andosols are linked with Hercynian basic and metabasic rocks in smoothed highlands with a cool and humid climate. We describe an Andosol-Cambisol toposequence derived from Variscan coarse-grained granite in Northern Austria (Bohemian Massif), where Andosols have formed on plateaus and Cambisols on steep slopes. The climate is continental, cool and humid (mean annual temperature and rainfall: 5.4 degreesC and 914 mm), with a 100-day mean annual period of snow cover. The forest is dominated by beech and spruce trees. Both soils are rich in organic matter and strongly acidic, but the Andosol is more strongly weathered than the Cambisol. Below the 15-cm-thick litter in the Andosol, the 38-cm-thick AB-Bw solum is dark reddish brown to strong brown, has a large C content (9.0-4.4%), and meets all the requirements of an andic horizon. In these horizons, oxalate extractable iron content (1.62.8% Fe-o) represents 76-84% of free iron, and is much larger than Al-o (0.8-1.5%). Both biotite and plagioclase are sources of Fe and Al. The fort-nation of non-allophanic Andosol from granite was likely due to the combination of the following factors: cool and humid climate, large accumulation of organic matter, high infiltration rate, intense water percolation during spring thawing and significant content of weatherable minerals. As such conditions are not rare in European highlands, andic soils are probably more widespread in Europe than is currently thought. (C) 2003 Elsevier B.V All rights reserved.

Soils conforming to Andosols in the World Reference Base (WRB) of Soil Resources have not yet been recognised in Germany. The aims of this study were to (i) show whether some German soils developed in volcanic parent materials are Andosols, (ii) investigate their pedogenetic development and (iii) determine their local distribution. We selected a soil on Quaternary basalt in the Eifel region (the “Windsborn” profile), and a soil from the summit of the Tertiary basaltic stratovolcano Vogelsberg (the “Kohlerwald” profile) northwest of Frankfurt am Main. The Windsborn soil is classified as a Silic Andosol. Allophane contents are near 10%, and allophane globules were identified by transmission electron microscopy (TEM). By progressively constraining field parameters in GIS-generated maps, we found that Andosols in the Mosenberg chain are confined to a few isolated occurrences. The Kohlerwald profile in the Tertiary Vogelsberg is an acid, base-poor and strongly weathered Aluandic Luvisol. Metal–humus complexes are the dominant colloidal phase. In the topsoil, both Fep and Alp are in excess of Feo and Alo values. Our data suggest the presence of phases like hydroxy-Al (e.g. from Al-interlayers or poorly ordered gibbsite) and opaline silica that are easily attacked by the alkaline (pH 9.5–10.5) pyrophosphate extractant, but may be resistant to the acid (pH 3) oxalate procedure. We conclude that there are limited occurrences of silandic Andosols in the Eifel area, Germany. The Windsborn soil is in an early pedogenetic development stage, but pedogenesis in the Kohlerwald soil has advanced beyond the Andosol phase to the stage of clay translocation. Therefore the existence of aluandic Andosols in Germany seems possible, but remains to be proven.

Surface and buried Andosols and buried Luvisols of the Nevado de Toluca Late Quaternary tephra-paleosol sequence (Central Mexico) were studied to show whether these soils present an evolutionary sequence and to determine the pedogenic mechanisms and environmental factors involved in the evolutionary process. Micromorphological observations and mineralogical composition of fine sand and clay fractions were used to detect type and succession of soil-forming process. Some of the buried Andosols, defined as “intergrade” Andosols, have a predominantly blocky structure, humus-depleted areas, redoximorphic features and thin clay coatings in Ah horizons. Clay fractions of buried Andosols contain halloysite besides amorphous components, whereas in modern Andosols, allophane is dominant. Luvisols have micro-areas with granular structure and abundant phytoliths in the groundmass of Bt horizons assumed to be the relict Andosol features. Luvisol clay fractions are dominated by halloysite and kaolinite. Primary minerals show micromorphological weathering features in all studied soils being stronger in Luvisols; however, even in Luvisols, sand fractions consist mostly of unstable volcanic silicates. We hypothesise that the studied profiles form an evolutionary sequence: Andosols–“intergrade” Andosols–Luvisols; the soil transformation is supposed to be linked to progressive crystallisation of 1:1 clay minerals. Comparing the Nevado de Toluca paleosol properties with the existing data on volcanic soil climo- and chronesequences and assessing the regional paleopedological and lacustrine records of Quaternary paleoclimates, we concluded that wet/dry climatic oscillations took place during the formation of the studied paleosols. Rapid crystallisation of 1:1 minerals occurred during dry phases, which speeded up the Andosol to Luvisol transformation and made it independent from the primary mineral weathering status. The Andosol to Luvisol transformation accelerated by climatic fluctuations is thought to be a common soil evolutionary pathway in the subtropical and tropical regions of recent volcanism, which suffered contrasting precipitation oscillations in the Quaternary.

Summary Soils developed from volcanic ash in the drier parts of the Colombian Andes are sensitive to erosion. From a comparative study of the clay composition, grain-size distribution, soil fabric and various physical parameters of two soil profiles in dry areas, and of an andosol profile in a humid area, it appears that the erosion in the drier areas is induced by the combination of thin A and B horizons, very sandy and very clayey respectively, and a clayey subsoil of low resistance.