Showing papers by "W. Wallace Covington published in 1994"

Postsettlement Changes in Natural Fire Regimes and Forest Structure: Ecological Restoration of Old-Growth Ponderosa Pine Forests

Abstract: Heavy livestock grazing, logging, and fire exclusion associated with Euro-American settlement has brought about substantial changes in forest conditions in western forests. Thus, old-growth definitions based on current forest conditions may not be compatible with the natural conditions prevalent throughout the evolutionary history of western forest types. Detailed analysis of data from two study areas in the southwestern ponderosa pine type suggests that average tree densities have increased from as few as 23 trees per acre in presettlement times to as many as 851 trees per acre today. Associated with these increases in tree density are increases in canopy closure, vertical fuel continuity, and surface fuel loadings resulting in fire hazards over large areas never reached before settlement. In addition, fire exclusion and increased tree density has likely decreased tree vigor (increasing mortality from disease, insect, drought, etc.), herbaceous and shrub production, aesthetic values, water availability a...

Historical and Anticipated Changes in Forest Ecosystems of the Inland West of the United States

Abstract: Euro-American settlement of the Inland West has altered forest and woodland landscapes, species composition, disturbance regimes, and resource conditions. Public concern over the loss of selected species and unique habitats (e.g., old-growth) has caused us to neglect the more pervasive problem of declining ecosystem health. Population explosions of trees, exotic weed species, insects, diseases, and humans are stressing natural systems. In particular, fire exclusion, grazing, and timber harvest have created anomalous ecosystem structures, landscape patterns, and disturbance regimes that are not consistent with the evolutionary history of the indigenous biota. Continuation of historical trends of climate change, modified atmospheric chemistry, tree density increases, and catastrophic disturbances seems certain. However, ecosystem management strategies including the initiation of management experiments can facilitate the adaptation of both social and ecological systems to these anticipated changes. A fairly ...

Sustainable ecological systems: Implementing an ecological approach to land management

Abstract: This conference brought together scientiests and managers from federal, state, and local agencies, along with private-sector interests, to examine key concepts involving sustainable ecological systems, and ways in which to apply these concepts to ecosystem management. Session topics were: ecological consequenses of land and water use changes, biology of rare and declining species and habitats, conservation biology and restoration ecology, developing and applying ecological theory to management of ecological systems, sustainable ecosystems and forest health, and sustainable ecosystems to respond to human needs. A plenary session established the philosophical and historial contexts for ecosystem management.

Fire‐Regime Disruption and Pine‐Oak Forest Structure in the Sierra Madre Occidental, Durango, Mexico

Abstract: Fire is a common but poorly understood disturbance in the forested ecosystems of the Sierra Madre Occidental of Mexico. In this study, fire history, forest structure (density, species composition, regeneration, forest floor fuels, herbaceous cover, and age of pines), and the dendrochronological tree-ring record were measured at two unharvested 70-ha pine-oak sites near Ojito de Camellones, Durango, Mexico. Study sites were matched in slope, aspect, elevation, slope position, and plant composition, but they differed in fire history since 1945 and in forest structure. The long-term mean fire intervals (MFI) for all fires at both sites up to 1945 were similar—4.0 years at Site 1 (1744–1945) and 4.1 years at Site 2 (1815–1945)—but Site 1 burned only three times at the site margins since 1945 while Site 2 had 9 fires that scarred two or more sample trees and 15 total fires since 1945. Density measurements and age and diameter distributions showed that Site 1 was dominated by numerous, younger, smaller trees (mean total basal area of 23.4 m2/ha and 2730 trees/ha), while Site 2 had fewer, older, larger trees (basal area of 37.2 m2/ha, 647 trees/ha). Large, rotten fuel loading and duff depth were also greater at Site 1. Because regeneration averaged 6200 stems/ha at Site 1 and 8730 stems/ha at Site 2 (no significant difference), forest density at Site 2 was not limited by regeneration capability. The distributions of overstory diameter and pine age at both sites indicate that tree establishment occurred in pulses, with the largest cohort of trees establishing at Site 1 following the 1945 fire. The dense regeneration and heavy fuel accumulation at Site 1 are likely to support a switch from the former low-intensity fire regime to a high-intensity, stand-replacing fire across the site when the next suitable combination of ignition and weather occurs. Baseline quantitative information on fire frequency and ecological effects is essential to guide conservation or restoration of Madrean forests and may prove valuable for restoration of related fire-dependent ecosystems that have experienced extended fire exclusion elsewhere in North America.

Double Sampling Increases the Efficiency of Forest Floor Inventories for Arizona Ponderosa Pine Forests

Abstract: Stand and natural fuel conditions were sampled in ponderosa pine forests in northern and central Arizona to develop predictive fuel depth and loading equations. Litter and duff depths can be estimated from measure- ments of stand density (basal area, stand density index). Although woody fuel loading did not correlate well with stand variables, correlations were found among loadings of different woody fuel size classes, so that results from a planar intersect tally of certain single woody fuel size classes may be used to predict the loadings in certain other size classes. The relatively low precision of esti- mates from these predictive equations can be substan- tially increased by applying them in a double sampling scheme. Making use of these predictive relationships, managers can devise simple, rapid, and cost-effective fuel inventories that focus on the fuel category of interest. Fuel loads can be estimated at a desired precision with reduced investment of time and funds compared to a more comprehensive direct fuel inventory.