摘要:

Periodic inventory measurements of forest characteristics published by the U.S. Forest Service are used to assess trends in forest conditions in Idaho. Forest species composition, measured by growing stock volume, has changed since 1952. Western white pine and ponderosa pine have declined by 60% and 40%, respectively. True firs (mostly grand fir) increased by 60% lodgepole pine by almost 40%, and Douglas-fir, the predominant species throughout the state, increased by 15%. Measurements of tree mortality across the state and region from 1952 to 1987 establish a baseline regional range for judging current conditions. Recent mortality data from some Idaho national forests are much higher than the upper limit of the baseline regional range. On the Boise and Payette National Forests in southwestern Idaho, annual mortality exceeds annual growth. Recent inventories of national forests in northern Idaho show mature stands have mortality well above the baseline regional range, which projects into a negative net growth situation. Recent inventories of private and other public forests in northern Idaho do not show similarly elevated mortality in mature stands.

ISSN:1054-9811    

DOI:10.1300/J091v02n03_01

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Estimates of changes this century (1890-1990) in the total mortality from natural causes (wildfire, pests) and harvesting in the Rocky Mountain and Pacific Coastal regions of the United States (excluding Alaska) were based on yearly national forest statistics. Total accrual per year doubled this century as a result of fire suppression and accelerated tree growth. Total depletion per year did not change significantly from 1920 to 1985; after 1985, extensive pest and wildfire mortality sharply increased total losses. A model of accumulated fuel loads and shifts in forest density and species composition was used to account for this catastrophic jump in tree mortality concurrent with severe drought. The implications of a destabilized forest structure are discussed in terms of the needs to "defuel" many dominant forest types and to restore long-term sustainability.

ISSN:1054-9811    

DOI:10.1300/J091v02n03_02

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A landscape characterization procedure is described as a first step in ecosystem management. Five attributes were used to characterize patterns at different scales of ecological organization from the plot to the region: climatic regions, ecoregions, biophysical environments, floristics, and vegetation. Examples of the characterization of selected attributes are presented for three western U.S. study areas. Other aspects of the characterization process are illustrated with examples from the Northern Region of the Forest Service and from forested locations in the southwestern U.S. Location of a study area within a climatic region provided an understanding of broad-scale climatic constraints operating on the biota. Assessment at the ecoregion level was used to examine finer scale environmental constraints due to landform effects. The ecoregion also provided a context for further analysis of biotic and environment variability in a study area. Biophysical environments (combinations of environmental factors) were characterized within landscapes. The range of environmental variability in a landscape was compared to that of a larger region to determine the representation of regional environments in a landscape. Biotic variability was characterized at a relatively coarse spatial scale by examining plant species distributions among floristic types. Such an analysis provided information about the long-term ecological and evolutionary pressures exerted on species in an area. Variability in vegetation was characterized at a varietv of scales by examning the distribution of types within the levels of a hierarchical vegetation classification for the western U.S. In addition, biotic distributions along environmental gradients were described using canonical correspondence analysis to determine within-type variability. Temporal variability in vegetation was assessed within a hierarchical ecosystem-based framework. Characterization of biotic-abiotic relationships is important in determining biotic responses to historical and current landscape conditions. We constructed statistical models to predict biotic responses to environmental factors using a powerful class of regression models, generalized linear models. Models developed for a plant community in the Southwest, the ponderosa pine series, revealed complex biotic responses to environmental factors. This result suggests that biotic-abiotic relationships warrant careful characterization, and that some commonly used simple models may not accurately predict biotic responses to environmental change.

ISSN:1054-9811    

DOI:10.1300/J091v02n03_03

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Historically, buffer zones or reserved areas have been used to restrict the array of management actions within unique habitats or sensitive-species areas. This action, although necessary as an immediate protection measure, can create administrative fragmentation of the forest and associated problems over time. Rarely is the dynamic nature of the reserved or buffered area considered and the disturbance events that created and maintained these sites are not conserved. Sizes of buffer zones and reserved areas generally reflect concern for a single management action, such as local timber harvest activities, and do not reflect adequate concern for other disturbances such as fire, livestock grazing, insect hazard, or flooding that involve much larger landscape scales. Boundaries are usually hard in the sense that few management activities are allowed. However, management may be required to maintain the unique habitat and adjacent landscapes in dynamic forest ecosystems of eastern Oregon and Washington. We suggest a variable-source emphasis area that has multiple but softer boundaries that vary according to the spatial scale of the potential disturbance. Disturbances are evaluated at relative scales for their impact on the featured species or habitat and on sustainability of the associated landscape. Unique habitats or sensitive species are emphasized in management goals but required disturbance events are encouraged for long-term sustainability of the sensitive species, unique habitats, and associated landscapes.

ISSN:1054-9811    

DOI:10.1300/J091v02n03_04

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Vertebrate wildlife will probably continue to be a primary surrogate for assessing biological diversity in forested ecosystems. However, assessment tools such as wildlife-habitat models generally have proved to be poor predictors of wildlife population responses to landscape-scale changes in forest ecosystems. Forest ecosystem assessment therefore will require improved models. To improve modeling capabilities, scientists must clarify the primary determinants of wildlife habitat selection, which is a behavioral process that links wildlife populations with ecosystem processes. Wildlife populations respond to functional redundancies caused by multiple interactions among landforms, soils, and vegetation. Therefore, probing wildlife habitat selection responses to attributes of landforms, soils, and vegetation should result in improved wildlife-habitat models. In this paper, radiotelemetry data from a study on northern spotted owls (Strix occidentalis caurina) are used to illustrate how remote sensing and geographic information systems (GIs) analysis might clarify basic determinants of habitat selection.

ISSN:1054-9811    

DOI:10.1300/J091v02n03_05

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Concerns for maintaining biodiversity have led to the adoption of ecosystem management as the paradigm for federal land management. This approach will identify desired future conditions as the goal for management, based on ecological objectives for a given landscape. Some management efforts attempt to identify desired future conditions based on existing successional stages as defined by a classification of overstory vegetation types. Such an approach ignores most of the underlying ecological parameters of the landscape, and is inadequate for identifying past disturbance regimes and future successional pathways. An assessment of desired future conditions based on an ecological classification system is essential to overcome these inadequacies. The strategy proposed in this paper uses an appropriate ecological land classification, based on either ecological land types or habitat types, included in a broader hierarchical classification system. It also uses a vegetation map of existing overstory vegetation. These two maps are overlaid to generate polygons of ecological units that can then be used to create an ecosystem diversity matrix. Each polygon (stand) can be evaluated as to its composition and structure relative to its possible placement within the ecosystem diversity matrix through comparisons with historical ranges of variability. The overall ecosystem diversity matrix can then be examined in terms of the distribution of successional stages within each habitat type or ecological land type. The goal should be to maintain at least adequate ecological representation of all successional stages within each habitat type that occurred historically, based on past disturbance regimes. Adequate ecological representation is defined as sufficient size and distribution of inherent ecosystems to maintain viable populations of all endemic species dependent on these ecosystems. This approach can maintain and enhance regional biodiversity, but also maintain flexibility in land management options.

ISSN:1054-9811    

DOI:10.1300/J091v02n03_06

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The two national forests in southwestern Idaho-the Boise and Payette National Forests-have both recently experienced five years of "catastrophic" timber mortality. That is, annual mortality exceeded annual growth on lands suitable for timber production. Boise Cascade Corporation lands lie between and, in some cases, are interspersed with these two national forests, and did not experience such high levels of mortality. The major difference in management strategies is that the company practices stand density control on all its lands; the national forests have not historically placed the same emphasis on stocking control. The Payette and Boise National Forests developed different strategies for approaching their tree mortality problems. The Payette placed a priority on developing a comprehensive treatment plan for the affected acres in the roaded portions of the suitable base. The Boise opted for a three phase approach, which stressed rapid salvage efforts, followed by cultural treatments designed to improve the vigor of remaining stands, and a comprehensive public education program. In each case, the U.S. Forest Service was confronted with appeals or litigation due to the public mistrust of such efforts.

ISSN:1054-9811    

DOI:10.1300/J091v02n03_07

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Fire and timber harvesting are two major factors affecting the development of forests in the Inland West. Prior to 1900, wildfires burned at various intervals and intensities, regenerating and tending forests creating a mosaic of conditions. After 1900, fire exclusion and timber harvesting created forests that are overstocked with trees and prone to epidemics of insects and diseases and forest replacing fires. The tools and methods developed by silviculturists for producing high value timber products can be used to manage forests for sustainability. If forests of the Inland West are going to be sustained, some type of active management other than fire exclusion is going to be needed. These management activities can best be determined by analyzing large tracts of forests in both temporal and spatial scales. These ecosystem analyses can guide the development of silvicultural systems for the long-term maintenance of ecosystems.

ISSN:1054-9811    

DOI:10.1300/J091v02n03_08

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Changes in old growth structural features as well as susceptibilities to disturbances were projected in stands typical of the eastern Washington Cascades. Projected changes with and without silvicultural operations were made. Doing no silvicultural activities in these stands will not rapidly increase old growth structural features and will allow the stands to become very susceptible to insects and wind breakage, followed by fires. Specifically designed silvicultural operations can maintain or rapidly increase old growth structural features and reduce susceptibilities to most disturbances. Unless some trees killed in the silvicultural operations are removed, the treated stands will become very susceptible to fires. Removing some of the thinned trees can also offset the costs of doing the operations. A landscape approach of treating various stands with different silvicultural regimes will probably best maintain a dynamic balance of structural features, a reduced susceptibility to various disturbances, and a steady flow of wood for manufacturing.

ISSN:1054-9811    

DOI:10.1300/J091v02n03_09

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The National Forest Management Act (NFMA) requires the Forest Service to provide for diversity of plant and animal communities and maintain viable wildlife populations. Changes in forest stand structure, species composition and disturbance patterns within ponderosa pine (Pinus ponderosa)-Douglas-fir (Pseudotsuga menziesii) habitat types on the Boise National Forest make it difficult to meet NFMA direction. Three management strategies, including "no action," were evaluated in terms of the risk of wildfire's effects on plant community diversity and distrbution, dispersal, and local population viability for the pileated woodpecker (Dryocopus pileatus) and flammulated owl (Otus flammeolus). The no action alternative appeared to have the greatest long-term risk to plant community diversity and wildlife species distribution and dispersal. Landscape analysis that considers the capabilities and risks associated with different-management strategies is recommended to meet NFMA direction while responding to diverse public expectations of the Forest.

ISSN:1054-9811    

DOI:10.1300/J091v02n03_10

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor