W. Wallace Covington

Bio: W. Wallace Covington is an academic researcher from Northern Arizona University. The author has contributed to research in topics: Restoration ecology & Understory. The author has an hindex of 51, co-authored 113 publications receiving 9191 citations. Previous affiliations of W. Wallace Covington include University of Nevada, Las Vegas & United States Forest Service.

Determining reference conditions for ecosystem management of southwestern ponderosa pine forests

Abstract: The fire disturbance regime and forest structure prior to Euro-American settlement (AD 1883) of a southwestern ponderosa pine (Pinus ponderosa) landscape were quantified in order to establish reference conditions as a baseline for ecosystem management. The mean presettlement fire interval between 1637 and 1883 was 3.7 yr for all fires and 6.5 yr for widespread fires, but fire has been excluded from the study area since 1883. Forest density increased under fire exclusion from an average of 148 trees/ha in 1883 (65 pines, 80 oaks, three other species), an open forest dominated by relatively large ponderosa pines, to 1265 trees/ha in 1994/1995 (720 pines, 471 oaks, 74 others), a dense forest characterized by relatively small and young trees. Species composition has shifted toward greater dominance by Gambel oak (Quercus gambelii) and conifers less adapted to frequent fires: white fir (Abies concolor) and Douglas-fir (Pseudotsuga menziesii). The reference presettlement conditions can be applied to management of this ecosystem in two ways. First, reference conditions are a benchmark against which to evaluate contemporary conditions and future alternatives. The comparison shows that the contemporary forest is well above the range of presettlement variability in forest density, and both live and dead fuel structures have developed that can support high-intensity wildfire. Second, reference conditions can serve as a goal for ecological restoration treatments.

Changes in Forest Floor Organic Matter and Nutrient Content Following Clear Cutting in Northern Hardwoods

Abstract: A secondary succession sequence of 14 northern hardwoods stands was sampled for forest floor organic matter and nutrient content. During the first 15 yr following clear cutting, the forest floor decreased by 30.7 Mg/ha, a decline of over 50%. The decrease in the forest floor and slahs (logging residue) may be greater than the increase in the living biomass. During the next 50 yr the forest floor increased by 28.0 Mh/ha and by year 64 was within 5% of an asymptote of 56.0 Mg/ha. Nutrients were analyzed in 6 of the 14 stands. Magnesium, potassium, and nitrogen concentrations showed no successional pattern. However, calcium concentrations were significantly higher in the stands in which forest floor mass was low. The initial decrease in forst floor mass is attributed to lower leaf and wood litter fall and to mroe rapid decay resulting from higher temperature, moisture content, and nutrient levels and to early successional litter being more easily decomposed. The recovery of the forest floor is explained primarily as resulting from the rapid increase in the quantity and diameter of wood litter fall. JABOWA, the northern hardwood forest growth stimulator, predicts a maximum rate of increase in woody litter by years 10-20 with a lveling off by years 30-50. An apparent asynchrony in function of the forest floor and slash as nutrient sources may be important to the recovery process. During the first 15 yr the forest floor is a major source of nutrients, releasing a net amount of approximately 800 kg/ha of nitrogen. During this period nitrogen immobilization in the decay of slash may account for as much as one-half of the nitrogen released from the forest floor. After year 15 the forest floor is no longer a source but a sink for nutrients as nutrients and organic matter accumulate. By year 15 the slash probably shifts in function from a sink to a source, providing nitrogen for the continuing rapid nitrogen accumulation in vegetation beyond year 15.

Reference conditions and ecological restoration: a southwestern ponderosa pine perspective

Abstract: Ecological restoration is the process of reestablishing the structure and func- tion of native ecosystems and developing mutually beneficial human-wildland interactions that are compatible with the evolutionary history of those systems Restoration is based on an ecosystem's reference conditions (or natural range of variability); the difference between reference conditions and contemporary conditions is used to assess the need for restorative treatments and to evaluate their success Since ecosystems are highly complex and dynamic, it is not possible to describe comprehensively all possible attributes of ref- erence conditions Instead, ecosystem characteristics with essential roles in the evolutionary environment are chosen for detailed study Key characteristics of structure, function, and disturbance—especially fire regimes in ponderosa pine ecosystems—are quantified as far as possible through dendroecological and paleoecological studies, historical evidence, and comparison to undisrupted sites Ecological restoration treatments are designed to reverse recent, human-caused ecological degradation Testing of restoration treatments at four sites in northern Arizona, USA, has shown promise, but the diverse context of management goals and constraints for Southwestern forest ecosystems means that appropriate applica- tions of restoration techniques will probably differ in various settings

Warming and Earlier Spring Increase Western U.S. Forest Wildfire Activity

Abstract: Western United States forest wildfire activity is widely thought to have increased in recent decades, yet neither the extent of recent changes nor the degree to which climate may be driving regional changes in wildfire has been systematically documented. Much of the public and scientific discussion of changes in western United States wildfire has focused instead on the effects of 19th- and 20th-century land-use history. We compiled a comprehensive database of large wildfires in western United States forests since 1970 and compared it with hydroclimatic and land-surface data. Here, we show that large wildfire activity increased suddenly and markedly in the mid-1980s, with higher large-wildfire frequency, longer wildfire durations, and longer wildfire seasons. The greatest increases occurred in mid-elevation, Northern Rockies forests, where land-use histories have relatively little effect on fire risks and are strongly associated with increased spring and summer temperatures and an earlier spring snowmelt.

Handbook of Chemistry and Physics

Abstract: There is a special reason for reviewing this book at this time: it is the 50th edition of a compendium that is known and used frequently in most chemical and physical laboratories in many parts of the world. Surely, a publication that has been published for 56 years, withstanding the vagaries of science in this century, must have had something to offer. There is another reason: while the book is a standard fixture in most chemical and physical laboratories, including those in medical centers, it is not as frequently seen in the laboratories of physician's offices (those either in solo or group practice). I believe that the Handbook can be useful in those laboratories. One of the reasons, among others, is that the various basic items of information it offers may be helpful in new tests, either physical or chemical, which are continuously being published. The basic information may relate

Fire in the Earth System

Abstract: Fire is a worldwide phenomenon that appears in the geological record soon after the appearance of terrestrial plants. Fire influences global ecosystem patterns and processes, including vegetation distribution and structure, the carbon cycle, and climate. Although humans and fire have always coexisted, our capacity to manage fire remains imperfect and may become more difficult in the future as climate change alters fire regimes. This risk is difficult to assess, however, because fires are still poorly represented in global models. Here, we discuss some of the most important issues involved in developing a better understanding of the role of fire in the Earth system.

Effects of fire on properties of forest soils: a review

Abstract: 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.