Rate of tree carbon accumulation increases continuously with tree size.

Forests are major components of the global carbon cycle, providing substantial feedback to atmospheric greenhouse gas concentrations. Our ability to understand and predict changes in the forest carbon cycle--particularly net primary productivity and carbon storage--increasingly relies on models that represent biological processes across several scales of biological organization, from tree leaves to forest stands. Yet, despite advances in our understanding of productivity at the scales of leaves and stands, no consensus exists about the nature of productivity at the scale of the individual tree, in part because we lack a broad empirical assessment of whether rates of absolute tree mass growth (and thus carbon accumulation) decrease, remain constant, or increase as trees increase in size and age. Here we present a global analysis of 403 tropical and temperate tree species, showing that for most species mass growth rate increases continuously with tree size. Thus, large, old trees do not act simply as senescent carbon reservoirs but actively fix large amounts of carbon compared to smaller trees; at the extreme, a single big tree can add the same amount of carbon to the forest within a year as is contained in an entire mid-sized tree. The apparent paradoxes of individual tree growth increasing with tree size despite declining leaf-level and stand-level productivity can be explained, respectively, by increases in a tree's total leaf area that outpace declines in productivity per unit of leaf area and, among other factors, age-related reductions in population density. Our results resolve conflicting assumptions about the nature of tree growth, inform efforts to undertand and model forest carbon dynamics, and have additional implications for theories of resource allocation and plant senescence.

New Forestry Principles from Ecosystem Analysis of Pacific Northwest Forests.

Forest management practices on Federal lands in the Pacific Northwest of the United States have been the center of intense controversy. Conflicting value systems, new information, and new perspectives have fueled the debate over the balance between timber production and preservation of natural ecosystems. In this paper we consider examples from three aspects of forest management: (1) management of forest stands, (2) management of the patchwork of forest stands at the landscape scale, and (3) management of streams and riparian networks. In each of these cases we examine: management practices and perspectives of the recent past, findings from ecosystem research that are leading to change in those practices, resulting changes in management practices, and future research directions. We also suggest a path for future change, including systems for managing in the face of uncertainty. Results of research in natural and managed forest and stream ecosystems have been pivotal in reassessment and redesign of management practices to provide a broader range of management options for society to consider. Results of studies of natural disturbance processes and their effects are used as reference points for management systems intending to sustain biological diversity and ecosystem productivity. Stand management practices, for example, are being modified to retain some live trees and greater amounts of dead woody debris, both standing and down, in areas that would instead be clear-cut under intensive plantation forestry practices. The motivations for these modified practices are to sustain biological diversity, including key wildlife species, and to maintain soil productivity. Models of alternative forest-cutting patterns at a landscape scale are being used to examine their effects on ecosystem structure and function. One result of this analysis has been to shift from the previous system of dispersing cutting units to a system involving greater aggregation of units using designs to provide for species preferring forest interior habitat as well as species favoring edge and early seral habitats. As a result of ecosystem research, the management of stream and riparian networks can now be based on understanding of forest-stream interactions and designed within a drainage-basin context. Overall, emphasis in research and management seems to be in early stages of shifting from featured species-e.g., Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and Northern Spotted Owl (Strix occidentalis caurina)-to ecosystems, and from the scale of forest stands to landscapes and the entire region. In addition to the contributions of ecosystem research to redesign of management techniques, ecosystem scientists also have roles in the social processes for determining the future course of management of natural resources. An important medium for scientist participation is establishment of adaptive management programs, in which management activities are conducted as experiments to test hypotheses and to develop information needed for future natural resource management.

Effects on carbon storage of conversion of old-growth forests to young forests.

Simulations of carbon storage suggest that conversion of old-growth forests to young fast-growing forests will not decrease atmospheric carbon dioxide (CO(2)) in general, as has been suggested recently. During simulated timber harvest, on-site carbon storage is reduced considerably and does not approach old-growth storage capacity for at least 200 years. Even when sequestration of carbon in wooden buildings is included in the models, timber harvest results in a net flux of CO(2) to the atmosphere. To offset this effect, the production of lumber and other long-term wood products, as well as the life-span of buildings, would have to increase markedly. Mass balance calculations indicate that the conversion of 5 x 10(9) to 1.8 x 10(9) megagrams of carbon to the atmosphere.

Percutaneous ureterolithotomy.

We describe a case of direct percutaneous ureterolithotomy in which the combination of antegrade control, a ureteral stent and precise fluoroscopic imaging resulted in a successful outcome. This technique may be helpful when other more traditional methods for percutaneous ureteral stone removal fail.

Foliage damage in coniferous trees following volcanic ashfall from Mt. St. Helens.

The foliage of coniferous plants in the area to the northeast of Mt. St. Helens, Washington State, was exposed to heavy ashfall during the May 18, 1980 eruption of the volcano. Significant damage to the pre-1980 foliage occurred after the eruption and continued through the summer. The amount of damage seen on the needles was significantly related to the amount of ash on the foliage.Elevated temperatures caused the foliage damage. The presence of ash on the foliage increased the dimensions of the shoot, thus increasing the boundary layer resistance. In turn this change in geometry elevated needle temperatures. Typical maximum needle temperatures for ash-laden foliage of Abies amabilis were in the range of 35° to 45° C and were 10° C above those of plants without ash. Damage occurred to needles at 40° C after a short growth-chamber exposure. Temperatures within the ash on the foliage also exceeded 40 degrees C.Neither chemical nor mechanical (abrasion) damage occurred. There was no melting of the cuticle. The plants with ash-covered foliage did not experience lower water potentials than those of control plants. The total radiation reflected from the needles was similar for foliage with and without ash.

Evergreen coniferous forests of the pacific northwest.

The massive, evergreen coniferous forests in the Pacific Northwest are unique among temperate forest regions of the world. The region's forests escaped decimation during Pleistocene glaciation; they are now dominated by a few broadly distributed and well-adapted conifers that grow to large size and great age. Large trees with evergreen needle- or scale-like leaves have distinct advantages under the current climatic regime. Photosynthesis and nutrient uptake and storage are possible during the relatively warm, wet fall and winter months. High evaporative demand during the warm, dry summer reduces photosynthesis. Deciduous hardwoods are repeatedly at a disadvantage in competing with conifers in the regional climate. Their photosynthesis is predominantly limited to the growing season when evaporative demand is high and water is often limiting. Most nutrients needed are also less available at this time. The large size attained by conifers provides a buffer against environmental stress (especially for nutrients and moisture). The long duration between destructive fires and storms permits conifers to outgrow hardwoods with more limited stature and life spans.

The biosphere reserve program in the United States.

The objective of the biosphere reserve program is to identify and protect representative and unique segments of the world's biotic provinces as major centers for biotic and genetic preservation, ecological and environmental research, education, and demonstration. It is intended to be more than simply another program of preservation layered onto existing parks and reserves. The success of the program will depend in large measure on the overall significance of the selected reserves and the degree to which they are active sites for scientific research and monitoring.