Wildfire as a hydrological and geomorphological agent

mented, if not .particularly new. Chapter 15, on the boron hydrides, has been almost entirely rewritten by the translators, with curious results. Historically, Syrkin and Dyatkina were among the first authors to revive the bridged structure for diborane and related molecules, and their views on the electronic structure of the bridge are clearly not entirely acceptable to the translators, who give prominence to Pitzer's subsequent ideas, and ignore altogether the extension of the bridge theory to beryllium and aluminium borohydrides. The effect is confusing, and the altered chapter has lost in clarity what it may have gained in modernity. The more theoretical chapters are not quite so good. I t is, of course, wellnigh impossible to do justice to the wave mechanics of atoms and molecules in 140 pages without oversimplifying or passing over the mathematical and physical difficulties. One must admire the ambitious a t tempt of the authors to do this, and much of the fundamental theory--for instance, the exclusion principle and the variation method--is well explained. But surely some mention should have been made of the fixed-nucleus approximation, and the fact tha t the Aufbauprinzip is only an approximation, even for atoms ? Chapters 5 and 6 show up the resonance theory at its worst, though this does not seem to have been the intention of the authors. We now know that the 'unexcited structures' of large aromatic molecules make scarcely any contribution to the ground state; and counting resonance structures is a theoretically unjustifiable procedure. Also, t h e theory of ionic-covalent resonance, in its simple form, has not stood up to recent critical examination, and can no longer be taken very seriously. These last two criticisms, however, are mainly based on work which has been done since the book was written, and can hardly be laid at the door of the authors. Chapter 7 has been added in translation, and is a good chapter in its own right, t-hough, as one might have expected, it is not particularly well integrated into the rest of the book. The printing is good, and the translation intelligent, though it is regrettable t h a t Mulliken's name should have been misspelt every time it is mentioned--more than twenty times. Taken as a whole, the book is an important contribution to the literature, and is to be recommended to everyone interested in molecular structure. H. C. LONGUET-HIGGINS Department of Chemistry University of Manchester England

X‐Ray Identification and Crystal Structures of Clay Minerals

Influence of heating on various properties of six Mediterranean soils. A laboratory study

Post-fire evolution of soil properties and vegetation cover in a Mediterranean heathland after experimental burning: A 3-year study

Wildfires may produce several changes in the short- and longterm in the landscape and in the soil system. The magnitude of these changes induced by fire in the components of ecosystems (water, soil, vegetation and fauna) depends on fire properties (fire intensity and severity) and environmental factors (vegetation, soil, geomorphology, etc.). The most important impacts on soils in the short-term are the reduction of vegetation cover (which increases soil erosion risk), the deposition of ash after combustion of biomass, the induction of enhancement of water repellency and changes in the structure and soil components. Combustion of biomass and soil organic matter also results in the release of gases and other pollutants into the atmosphere. Similarly, the changes induced by fire on the biological soil components (vegetation, animals and soil microorganisms) may occur rapidly and produce a large-scale response. The long-term effects of fire on soils and water may well persist for relatively short periods (hours, days or months), long (years or tens of years), or be permanent depending on the severity of fire and fire regime. Some of these effects are a consequence of the relationship between fire, soil, hydrology and nutrient cycling

/pdf/how-wildfires-affect-soil-properties-a-brief-review-4frguqkpc8.pdf

How wildfires affect soil properties. A brief review

Changes in color parameters with increasing temperatures over the range of 20 to 700 °C were studied in samples from the uppermost surface layer of the A horizon of various typical Mediterranean soils. Because changes in soil color during heating relate to the formation of Fe hydrous oxides species (such as maghemite and hematite) that increase the red color, and the close relationship between the redness rating index (RR) (a color index that is easily measurable) and hematite content, we studied the potential relationship between such an index and the temperature reached by soil samples over the range of 20 to 700 °C. The variation of the RR index with temperature was found to be similar in large soil groups. This allows the estimation of the temperature reached by a soil sample from the increase in redness rating index, provided the variation of RR with temperature for the soil group concerned has previously been determined. This study provides a first approximation to the estimation of the temperature level reached by the soil during a fire and the soil damage by effect of vegetation burning, which depends on the temperature reached. The soil temperature increase by fire is short-lived, but the changes induced in the color and other soil properties by fire are more or less permanent.

Relationship between soil color and temperature in the surface horizon of mediterranean soils: a laboratory study

Laboratory simulations were used to study the potential influence of bases (K + , Mg ++ , Ca ++ ) reaching soil via the burning of natural vegation-a common practice of shifting agriculture-on the genesis of argillic horizons and the evolution of Oxisols to Ultisols on the plateaus of Cabo Delgado (NE Mozambique). The effect of such a practice on the gradual enrichment with sand of the soils on slopes and in the bottom of valleys and dambos imbedded in the plateaus was also examined. The results suggested that the burning of natural vegetation before the establishment of shifting agriculture on plateaus in the province of Cabo Delgado causes the pH of the topmost soil layer to rise and facilitates its disaggregation. This, in turn, results in clay illuviation to subsurface horizons, as well as the erosion of fine sand by runoff water and its accumulation on slopes and in valley bottoms, all of which will have major implications on soil morphology and evolution.

T. Terefe Wondafrash

Papers

Relationship between soil color and temperature in the surface horizon of mediterranean soils: a laboratory study

Estimating the impact of vegetation burning on soil morphology in the plateaus of northeastern mozambique via a laboratory test