Giacomo Certini

Effects of fire on properties of forest soils: a review

Many physical, chemical, mineralogical, and biological soil properties can be affected by forest fires. The effects are chiefly a result of burn severity, which consists of peak temperatures and duration of the fire. Climate, vegetation, and topography of the burnt area control the resilience of the soil system; some fire-induced changes can even be permanent. Low to moderate severity fires, such as most of those prescribed in forest management, promote renovation of the dominant vegetation through elimination of undesired species and transient increase of pH and available nutrients. No irreversible ecosystem change occurs, but the enhancement of hydrophobicity can render the soil less able to soak up water and more prone to erosion. Severe fires, such as wildfires, generally have several negative effects on soil. They cause significant removal of organic matter, deterioration of both structure and porosity, considerable loss of nutrients through volatilisation, ash entrapment in smoke columns, leaching and erosion, and marked alteration of both quantity and specific composition of microbial and soil-dwelling invertebrate communities. However, despite common perceptions, if plants succeed in promptly recolonising the burnt area, the pre-fire level of most properties can be recovered and even enhanced. This work is a review of the up-to-date literature dealing with changes imposed by fires on properties of forest soils. Ecological implications of these changes are described.

Anthropogenic soils are the golden spikes for the Anthropocene

We propose that the Anthropocene be defined as the last c. 2000 years of the late Holocene and characterized on the basis of anthropogenic soils. This contrasts with the original definition of the Anthropocene as the last c. 250 years (since the Industrial Revolution) and more recent proposals that the Anthropocene began some 5000 to 8000 years ago in the early to mid Holocene (the early-Anthropocene hypothesis). Anthropogenic soil horizons, of which several types are recognized, provide extensive terrestrial stratigraphic markers for defining the start of the Anthropocene. The pedosphere is regarded as the best indicator of the rise to dominance of human impacts on the total environment because it reflects strongly the growing impact of early civilisations over much of the Earth’s surface. Hence, the composition of anthropogenic soils is deemed more appropriate than atmospheric composition in providing ‘golden spikes’ for the Anthropocene.

Carbon dioxide efflux and concentrations in two soils under temperate forests

The carbon dioxide efflux to the atmosphere and the concentrations at various depths in two soils were measured, for more than a year, under pure stands of silver fir ( Abies alba Mill.) and European beech ( Fagus sylvatica L.) in central Italy. Microbial biomass and activity at the monitored depths were determined in the laboratory and the CO2 evolved from incubated samples was submitted to radiocarbon analysis to assess the mean residence time of the organic matter degraded by microorganisms. The CO2 efflux showed similar trends in the two soils, with highest values in October and lowest in January. The efflux depended more on air and soil temperatures than soil moisture, and was related to these variables better under fir than under beech. In both soils, the CO2 concentration increased with depth: in the top horizon it was low and similar to that of the atmosphere, while in the deeper horizons it often amounted to considerable values (up to more than 1% by volume in the BC horizon under fir). The subsoil of the fir stand generally showed much higher CO2 concentrations than that of the beech. The basal respiration as determined in the laboratory was at a maximum in the topsoil and decreased sharply downwards. Therefore, the high CO2 concentrations measured in the field at the bottom of the profiles—where roots were few, and microbial biomass and available C pool were at a minimum—appeared to be due more to slow diffusivity of the soil matrix rather than to heavy release of the gas by the biota. The organic matter respired by microorganisms in incubated soil samples showed positive values of Δ14C that revealed a recent synthesis. The estimated mean residence time increased with depth, suggesting a generally higher degree of stabilisation of the organic pool in the subsoil.

Direct Determination of Organic Carbon by Dry Combustion in Soils with Carbonates

Abstract In acid soils, where organic carbon (C) corresponds to total C, direct determination of organic C by dry combustion is possible, whereas in soils with carbonates also a separate measurement of inorganic C is required. In this case, direct quantification of organic C can be accomplished by the Walkley‐Black method, which is time‐consuming and involves greatly polluting by‐products. Hence, a method able to determine directly organic C by dry combustion is strongly needed for soils with carbonates. This study proposes such a method, after it was found to be highly reliable in calcareous soils of a Mediterranean island. The correction factor to use in the Walkley‐Black method to account for nonrecoverable C was calculated. It does not show any overall relationship with the contents of either organic C or inorganic C, and for all land uses examined in the island, it is not significantly different from the commonly suggested value 1.30.

Exchangeable Ca, Mg, and K of rock fragments and fine earth from sandstone and siltstone derived soils and their availability to grass

Rock fragments (particles >2 mm, are usually considered chemically inert for plant growth. In this paper, the potential fertility in terms of exchangeable Ca, Mg, and K of rock fragments from sandstone and siltstone derived soils from northern Apennines (Italy) is reported and contrasted with that of the fine earth (particles <2 mm). The results show that rock fragments are a source of Ca, Mg, and K. When expressed on a volume basis, the abundance of these exchangeable nutrients sometimes may equal or surpass that of the fine earth. The plant uptake of Mg and K has been demonstrated in growth experiments with Agrostis under controlled conditions.

Soils: basic concepts and future challenges.

This book was born as an international tribute to Fiorenzo C. Ugolini, an outstanding soil scientist who recently retired from university teaching and research. It is a fully up-to-date synthesis of the present knowledge of soils, their genesis, functions and management. It includes contributions from leading soil scientists and the result is a book that provides the basic concepts as well as the latest data and practical examples from across the discipline, including many issues that are overlooked in other treatments. The book also discusses the increasingly important role of soils in enabling the preservation of life.

Early stages of podzolization under Corsican pine (Pinus nigra Arn. ssp. laricio)

Abstract To assess the effects of the plants on pedogenesis, two arboreal species, Corsican pine ( Pinus nigra Arn. ssp. laricio ) and silver fir ( Abies alba Mill.) were compared. We observed that at the base of the largest Corsican pines, patches of bleached soil occur on top of the A horizon. These eluviated areas lie at the outlet of wide bark channels through which the stemflow reaches the ground. In addition, an apparently less bleached material, in the shape of collars, is present around the big roots that collect and conduct the stemflow into the soil. On the contrary, patches and collars are absent in the soil under firs. To understand the role of the two species in the formation of the bleached material, throughfall, stemflow and forest floor solutions were collected for pine and fir. For pine, the stemflow moving along a wide bark channel was collected separately. All these solutions plus the rainfall were obtained and analysed seasonally for 1 year. Also, a number of profiles were excavated in the vicinity of the trunk base of pines and firs. Two profiles were selected for sampling and for the attendant analyses. The results indicate that under silver fir, the processes induce in the formation of an A horizon. The Corsican pine, on the other hand, in 50 years, has been able to produce, even if in small areas, a separate pedogenic process responsible for the bleaching of an existing A horizon. Because the bleaching process is at an initial stage, the chemical differences between the E material and the surrounding A horizon are small. Nevertheless, the E material is poorer in organic matter and in the most mobile inorganic elements than the A horizon. The presence of E material exclusively at the trunk base of the pines is due to the strong acidity of the stemflow — about 30-times higher than that of the fir. The most evident differences between the soils under pine and fir concern the features more directly related to the dynamics of the soil organic matter. Mineral assemblage, which needs longer time for its evolution, is very similar in the two soils; nonetheless a small amount of pedogenic smectite has been recognized in the E material.

Pedogenesis induced by Genista aetnensis (Biv.) DC. on basaltic pyroclastic deposits at different altitudes, Mt. Etna, Italy

The paper deals with the role of Etnean broom [Genista aetnensis (Biv.) DC.] on the early stages of pedogenesis on basaltic pyroclastic deposits (Mt. Etna, Italy) of different age and altitude previously not vegetated. After a few decades, this plant has been capable to arrest erosion and produce some soil features in both Entisols. The soil of Mts. Rossi, at a lower altitude, formed from a centenary parent material and hosted a broom plantation of about 50 years old. Here, the regimes of soil moisture (ustic) and temperature (mesic) limited the diffusion of the grass to the projection of the broom crowns, but favoured the diffusion of microorganisms and pedofauna. These conditions favoured a generalised alteration of the parent material and induced a certain horizon organisation. The soil of Mt. Vetore, at higher altitude, formed from a millenary parent material, and hosted a broom plantation of about 35 years old. At this site, the soil moisture (udic) and temperature (frigid) regimes favoured the formation of a thick and continuous carpet of gramineae. Yet, these conditions limited the activity of microorganisms and pedofauna, thus inducing a poorer horizon organisation. In this soil, because of the higher mean annual precipitation and root activity, most of the chemical modifications of the parent material occurred at the level of the rhizosphere, which acquired a thickness of 2–3 cm. From a chemical and mineralogical point of view, horizontal variations between rhizosphere and matrix were more evident than those among horizons. The most striking change occurring in the rhizosphere was the accumulation of secondary minerals such as oxalates and easily reducible Fe-oxyhydroxides. We also inferred that, in the environment of Mt. Etna, the excretion of oxalic acid from the roots of the broom could represent a strategy of nutrient uptake, in particular P, Mg and K.

Fire as a Soil-Forming Factor

In the span of a human generation, fire can, in theory, impact all the land covered by vegetation. Its occurrence has many important direct and indirect effects on soil, some of which are long-lasting or even permanent. As a consequence, fire must be considered a soil-forming factor, on par with the others traditionally recognized, namely: parent material, topography, time, climate, living beings not endowed with the power of reason, and humans.

The contrasting effect of broom and pine on pedogenic processes in volcanic soils (Mt. Etna, Italy)

Abstract Effects of Etnean broom ( Genista aetnensis (Biv.) DC.) and Corsican pine ( Pinus nigra Arn. ssp. laricio Maire) on the morphological, mineralogical and chemical properties of volcanic soils from Mt. Etna (Italy) were compared and contrasted. For this purpose, we studied the rhizosphere and the bulk soils under adjacent 30 years old pure plantations of both species. Morphology of the soil under broom differs from that under pine for (i) a higher accumulation of organic matter in the topsoil, (ii) an incipient formation of E material around the base of the stem, and (iii) the presence of yellowish collars around the primary roots. Mineral horizons of the two soils are made of plagioclases, pyroxenes, magnetite and glass. The yellowish colour of the collars is attributed to a root effect that results in a confined alteration of primary volcanic glass and also iron-bearing minerals, leading to the precipitation of amorphous Fe-oxides. Under pine, we observed a more widespread weathering of primary minerals throughout the profile, and a depletion of base cations and a release of Al in the topsoil. On the whole, therefore, Corsican pine—commonly planted in the last decades on the pyroclastic deposits and lava flows of the Etna volcano—seems to play a detrimental role on these soils.