THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

The Design and Analysis of Experiments

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.

/pdf/effects-of-fire-on-properties-of-forest-soils-a-review-1ymllzm5e7.pdf

Effects of fire on properties of forest soils: a review

Natural organic biomass burning creates black carbon which forms a considerable proportion of the soil’s organic carbon. Due to black carbon’s aromatic structure it is recalcitrant and has the potential for long-term carbon sequestration in soil. Soils within the Amazon-basin contain numerous sites where the ‘dark earth of the Indians’ (Terra preta de Indio, or Amazonian Dark Earths (ADE)) exist and are composed of variable quantities of highly stable organic black carbon waste (‘biochar’). The apparent high agronomic fertility of these sites, relative to tropical soils in general, has attracted interest. Biochars can be produced by ‘baking’ organic matter under low oxygen (‘pyrolysis’). The quantities of key mineral elements within these biochars can be directly related to the levels of these components in the feedstock prior to burning. Their incorporation in soils influences soil structure, texture, porosity, particle size distribution and density. The molecular structure of biochars shows a high degree of chemical and microbial stability. A key physical feature of most biochars is their highly porous structure and large surface area. This structure can provide refugia for beneficial soil micro-organisms such as mycorrhizae and bacteria, and influences the binding of important nutritive cations and anions. This binding can enhance the availability of macro-nutrients such as N and P. Other biochar soil changes include alkalisation of soil pH and increases in electrical conductivity (EC) and cation exchange capacity (CEC). Ammonium leaching has been shown to be reduced, along with N2O soil emissions. There may also be reductions in soil mechanical impedance. Terra preta soils contain a higher number of ‘operational taxonomic units’ and have highly distinctive microbial communities relative to neighbouring soils. The potential importance of biochar soil incorporation on mycorrhizal fungi has also been noted with biochar providing a physical niche devoid of fungal grazers. Improvements in soil field capacity have been recorded upon biochar additions. Evidence shows that bioavailability and plant uptake of key nutrients increases in response to biochar application, particularly when in the presence of added nutrients. Depending on the quantity of biochar added to soil significant improvements in plant productivity have been achieved, but these reports derive predominantly from studies in the tropics. As yet there is limited critical analysis of possible agricultural impacts of biochar application in temperate regions, nor on the likelihood of utilising such soils as long-term sites for carbon sequestration. This review aims to determine the extent to which inferences of experience mostly from tropical regions could be extrapolated to temperate soils and to suggest areas requiring study.

Potential mechanisms for achieving agricultural benefits from biochar application to temperate soils: a review

Several recent papers have suggested replacing the terminology of fire intensity and fire severity. Part of the problem with fire intensity is that it is sometimes used incorrectly to describe fire effects, when in fact it is justifiably restricted to measures of energy output. Increasingly, the term has created confusion because some authors have restricted its usage to a single measure of energy output referred to as fireline intensity. This metric is most useful in understanding fire behavior in forests, but is too narrow to fully capture the multitude of ways fire energy affects ecosystems. Fire intensity represents the energy released during various phases of a fire, and different metrics such as reaction intensity, fireline intensity, temperature, heating duration and radiant energy are useful for different purposes. Fire severity, and the related term burn severity, have created considerable confusion because of recent changes in their usage. Some authors have justified this by contending that fire severity is defined broadly as ecosystem impacts from fire and thus is open to individual interpretation. However, empirical studies have defined fire severity operationally as the loss of or change in organic matter aboveground and belowground, although the precise metric varies with management needs. Confusion arises because fire or burn severity is sometimes defined so that it also includes ecosystem responses. Ecosystem responses include soil erosion, vegetation regeneration, restoration of community structure, faunal recolonization, and a plethora of related response variables. Although some ecosystem responses are correlated with measures of fire or burn severity, many important ecosystem processes have either not been demonstrated to be predicted by severity indices or have been shown in some vegetation types to be unrelated to severity. This is a critical issue because fire or burn severity are readily measurable parameters, both on the ground and with remote sensing, yet ecosystem responses are of most interest to resource managers.

/pdf/fire-intensity-fire-severity-and-burn-severity-a-brief-3f34ow4qed.pdf

Fire intensity, fire severity and burn severity: a brief review and suggested usage

https://www.fs.fed.us/rm/pubs_other/rmrs_1999_neary_d001.pdf

Fire effects on belowground sustainability: a review and synthesis

/pdf/restoring-ecosystem-health-in-ponderosa-pine-forests-of-the-3i078e73qf.pdf

Restoring Ecosystem Health in Ponderosa Pine Forests of the Southwest

https://www7.nau.edu/mpcer/direnet/publications/publications_c/files/Covington_WW_Sackett_SS_Soil_mineral_nitrogen_changes_following.pdf

Soil mineral nitrogen changes following prescribed burning in ponderosa pine

After 100 years of fire exclusion, controlled burning in the fall was used as a first step in the reintroduction of periodic burning in a southwestern ponderosa pine ecosystem near Flagstaff, Arizona, U.S.A. Organic matter storage in woody debris was decreased 63 percent from 2,325 g/m 2 to 869 g/m 2 , with a disproportionate (99 percent) decline in the large, rotten wood. Nutrient storage in the woody debris decreased by 80 percent for N, 62 percent for P, 70 percent for Ca, 71 percent for Mg, and 74 percent for K. Forest floor storages were less drastically affected, with organic matter content declining 37 percent from 3,170 g/m 2 to 1,990 g/m 2 immediately after burning. Nutrient content of the forest floor was not significantly affected by burning due, in part, to the transfer of nutrients from woody debris to the forest floor. By 7 months after burning, the forest floor had declined by an additional 440 g/m 2 of organic matter, most likely from microbial mineralization. Also during this period forest floor storages for all nutrients declined significantly, except K which was unchanged. Mg exhibited the greatest proportional decline (40 percent), followed by N, P, and Ca, all of which decreased by approximately 25 percent. Numerous potential benefits to productivity may be associated with this prescribed bum-reduced fire hazard, accelerated nutrient mobilization, and reduced forest floor interception of precipitation. FOREST SCI. 30:183-192.

https://www.fs.fed.us/psw/publications/sackett/psw_1984_sackett001_covington.pdf

The Effect of a Prescribed Burn in Southwestern Ponderosa Pine on Organic Matter and Nutrients in Woody Debris and Forest Floor

https://www.fs.fed.us/psw/publications/sackett/psw_1996_sackett002.pdf

Lessons learned from fire use for restoring southwestern ponderosa pine ecosystems

The effect of repeated prescribed burning on long term growth of Pinus ponderosa in northern Arizona was examined. Fire treatments for hazard reduction were initiated in 1976, acid growth was evaluated in 1988 for fire rotations of 1, 2, 4, 6, 8, and 10 years. Dendroecological analysis shows that there were only small changes in tree growth (compared to controls) in the first few years after the initial fire treatment despite large fuel reductions and thinning, and that annual precipitation was positively correlated with growth. Moderate changes in growth relative to that of control trees were apparent after 1984. The 1-, 2-, 8-, and 10-year treatments had lower growth than controls after this date, while 4- and 6-year treatments had slightly higher growth. Although additional data are needed to determine long term growth effects in the longer fire rotations, a fire treatment interval of 4 to 6 years appears to provide adequate fuel reduction without reducing long term growth in Southwestern P. ponderosa forests.

/pdf/the-effects-of-repeated-prescribed-burning-on-pinus-3bix57m2wu.pdf

Stephen S. Sackett

Papers

Restoring Ecosystem Health in Ponderosa Pine Forests of the Southwest

Soil mineral nitrogen changes following prescribed burning in ponderosa pine

The Effect of a Prescribed Burn in Southwestern Ponderosa Pine on Organic Matter and Nutrients in Woody Debris and Forest Floor

Lessons learned from fire use for restoring southwestern ponderosa pine ecosystems

The effects of repeated prescribed burning on Pinus ponderosa growth