Assessments of Wildlife

Viability, Old-Growth Timber

Volume Estimates, Forested

Wetlands, and Slope Stability

United States

Department of

Agriculture

Forest Service

Pacific Northwest

Research Station

General Technical

Report

PNW-GTR-392

March 1997
Conservation and Resource

Assessments for the Tongass Land

Management Plan Revision

Charles G. Shaw III

Technical Coordinator

Assessments of Wildlife Viability, Old-Growth Timber Volume

Estimates, Forested Wetlands, and Slope Stability

Kent R. Julin

Compiler

Published by:

U.S. Department of Agriculture

Forest Service

Pacific Northwest Research Station

Portland, Oregon

General Technical Report PNW-GTR-392

March 1997
Abstract Julin, Kent R., comp. 1997. Assessments of wildlife viability, old-growth timber

volume estimates, forested wetlands, and slope stability. Gen. Tech. Rep.

PNW-GTR-392. Portland, OR: U.S. Department of Agriculture, Forest Service,

Pacific Northwest Research Station. 58 p. (Shaw, Charles G., III, tech. coord.;

Conservation and resource assessments for the Tongass land management plan

revision).

Resource assessments on wildlife viability, old-growth timber volume estimates,

forested wetlands, and slope stability are presented. These assessments were used

in the formulation of alternatives in the revision of the Tongass land management

plan.

Keywords: Wildlife viability, timber volume, forested wetlands, slope stability,

Tongass, Alaska.

Preface This volume presents resource assessments used as part of the Tongass land

management planning process. Included here are assessments on (1) approaches to

maintaining well-distributed, viable wildlife populations; (2) options for estimating

old-growth timber volume; (3) suitability of forested wetlands for timber production;

and (4) slope stability factors with discussion of mass movement hazard indexing.

Our intent in providing this publication is to create a readily accessible and retrievable

record of the best available information on issues emphasized in the revision of the

Tongass land management plan.
Contents 1 Conceptual Approaches for Maintaining Well-Distributed,

Viable Wildlife Populations: A Resource Assessment

George C. Iverson and Bruce René

24 Options for Defining Old-Growth Timber Volume Strata:

A Resource Assessment

Kent R. Julin and John P. Caouette

38 Tentative Suitability of Forested Wetlands for

Timber Production: A Resource Assessment

Kent R. Julin and Chris T. Meade

44 Controlling Stability Characteristics of Steep

Terrain With Discussion of Needed Standardization

for Mass Movement Hazard Indexing:

A Resource Assessment

Douglas N. Swanston

58 Metric Equivalents
Contributors JOHN P. CAOUETTE is a statistician, U.S. Department of Agriculture, Forest Service,

Pacific Northwest Research Station, Forestry Sciences Laboratory, 2770 Sherwood

Lane, Suite 2A, Juneau, AK 99801-8545.

GEORGE C. IVERSON is the Regional Ecology Program leader, U.S. Department

of Agriculture, Forest Service, Alaska Region, P.O. Box 21628, Juneau, AK 99801.

KENT R. JULIN is a research forest ecologist, U.S. Department of Agriculture,

Forest Service, Pacific Northwest Research Station, Forestry Sciences Laboratory,

2770 Sherwood Lane, Suite 2A, Juneau, AK 99801-8545.

CHRIS T. MEADE is an environmental scientist, U.S. Environmental Protection

Agency, 410 Willoughby Avenue, Suite 100, Juneau, AK 99801.

BRUCE RENÉ is the document coordinator for the Tongass Land Management

Planning Team, U.S. Department of Agriculture, Forest Service, Tongass Land

Management Planning Team, 8465 Old Dairy Road, Juneau, AK 99801.

CHARLES G. SHAW III is research plant pathologist and science manager for

the Tongass Land Management Planning Team, U.S. Department of Agriculture,

Forest Service, Pacific Northwest Research Station, Forestry Sciences Laboratory,

2770 Sherwood Lane, Suite 2A, Juneau, AK 99801-8545.

DOUGLAS N. SWANSTON is a principal research geologist, U.S. Department

of Agriculture, Forest Service, Pacific Northwest Research Station, Forestry

Sciences Laboratory, 2770 Sherwood Lane, Suite 2A, Juneau, AK 99801-8545.

Conceptual Approaches for Maintaining

Well-Distributed, Viable Wildlife

Populations: A Resource Assessment

George C. Iverson and Bruce René

Background The National Forest Management Act of 1976 (NFMA; 16 USC §1604 [g] [3] [B])

requires that the USDA Forest Service provide for the diversity of plants and animals,

based on the suitability and capability of each National Forest. As part of meeting

overall multiple-use objectives, the implementing regulations (36 CFR §219.3) of

NFMA interpret the diversity requirement as maintaining habitat to support viable

and well-distributed populations of existing native and desired nonnative species in

the planning area. Maintaining the abundance and distribution of habitat necessary

to support well-distributed and viable populations of old-growth-associated wildlife

across the Tongass National Forest (Tongass) was one of five major issues considered in the Tongass land management plan (TLMP) revision. To address this

issue, several assessments were chartered to synthesize available information on

wildlife species with potential viability concerns at the Tongass. Individual assessments were conducted for the northern goshawk (Accipiter gentilis; Iverson and

others 1996), Alexander Archipelago wolf (Canis lupus ligoni; Person and others

1996), marbled murrelet (Brachyramphus marmoratus; DeGange 1996), and anadromous salmonids (Salmonidae; U.S. Department of Agriculture, Forest Service

1995). Broader, system-oriented assessments also were conducted for habitat

conservation areas: old-growth forest patch inventory (DeGayner and Iverson, in

prep.), karst and caves (Baichtal and Swanston 1996), and natural disturbance

with an emphasis on wind (Nowacki and Kramer, in prep.).

A workshop was held June 7-9, 1995, to synthesize information that related to fish

and wildlife viability and ecosystems within southeast Alaska and the Tongass.1 At

this workshop, several possible Forest-wide integrated strategies were developed

for maintaining habitat to support viable fish and wildlife populations and functional

old-growth ecosystems across the Tongass. These conceptual strategies, which

used key landscape parameters as building blocks, were made available to the

interdisciplinary team for use in drafting alternatives for the TLMP revision. This

paper summarizes the deliberations and findings of a viability synthesis workshop.

The workshop charter is given in appendix A; workshop participants are listed in

appendix B.

1 The workshop was held at the Tongass Land Management

Plan office, Juneau, AK.

1
A Working Definition of

Viability

The concept of viability and well-distributed populations initially was debated to establish a common understanding and a working foundation for addressing workshop

objectives. A consensus emerged that there is no generally accepted definition of

viability and that some commonly used terms within the definitions, such as “well

distributed,” also are not clearly defined. Based on definitions used in recent largescale viability analyses, such as that by the Forest Ecosystem Management Assessment Team (FEMAT) in the Pacific Northwest (FEMAT 1993), the following working

definition of viability was developed. For purposes of the workshop, the term “viability”

was defined as “the likelihood that habitat conditions will support persistent and well

distributed fish and wildlife populations over time.” The concept of “well distributed”

was based on the natural distribution and dispersal capabilities of individual species,

and it included the full range of their current or historically recent distribution within

southeast Alaska. “Dispersal” included the concepts of metapopulation dynamics

and gene flow.

The concepts of “minimum viable” populations and “productive” or “usable” populations also were debated. The fish and wildlife populations of southeast Alaska support many commonly accepted human uses (subsistence hunting, commercial fishing,

recreational activities, and tourism, for example) that are difficult to meaningfully

separate from some level of viability determined without considering these uses.

Many wildlife populations depend on others as prey, and the viable level for one

species (Sitka black-tailed deer [Odocoileus hemionus], for example) must consider

the needs for that species by other species (Alexander Archipelago wolf, for example)

along with human demands. These and other considerations also form parts of

“sustained yield” for fish and wildlife resources under NFMA (PL 86-517; 16 USC

§528) and the Multiple-Use Sustained-Yield Act of 1960 (PL 94-588; 16 USC §1600).

A consensus was reached among workshop participants that to provide information

to use in constructing TLMP revision alternatives, and to have a reasonable assurance of maintaining habitat sufficient to support populations of all fish and wildlife species of the Tongass, the term “viable” should include all these factors. An evaluation

of the TLMP revision alternatives themselves, in terms of maintaining viable populations pursuant to NFMA, was conducted later by independent scientific panels (Smith

and Shaw, in prep.; Swanston and others 1996).

Analysis of

Information

The first phase of the workshop consisted of summary presentations of the results

(often preliminary) of ongoing assessments, resource analyses, or other studies

concerning specific aspects of animals and ecosystems of the Tongass. These

included verbal presentations (presenters shown in parentheses) on the following

topics:

• Anadromous fish habitat assessment (USDA Forest Service 1995) and related

proposals (Fred Everest)

• Watershed reserve strategy and riparian prescriptions (Steven Kessler)

• Karst and cave resources (Douglas Swanston)

2
• Northern goshawk (George Iverson)

• Alexander Archipelago wolf (Matthew Kirchhoff)

• Marbled murrelet (Carol Hale)

• Inventory of existing old-growth forest blocks (Eugene DeGayner)

• Brown bear (Kimberly Titus)

• Principal disturbance processes in the temperate rain forest (Gregory Nowacki)

• Marten (Rod Flynn)

• Alternatives to clearcutting (Richard Zaborske)

• Reliability of timber inventory for differentiating timber volume classes

(John Caouette)

• Possible Forest plan scenarios (Steven Brink)

• Viability in relation to FEMAT (1993) (Martin Raphael)

• Interagency viable population committee conservation strategy (Suring and others

1993; Suring and others, in prep.), a review of this strategy (Kiester and Eckhardt

1994), and the response to the review of this strategy (Suring and others 1994)

(George Iverson; see appendix C)

Landscape Building

Blocks for Viability

Strategies

The first step in developing an array of Forest-wide, landscape-level management

options was to identify the key parameters relevant to viability by using information

presented about individual species and habitat components. This step was conducted

for five wildlife species of concern, fish in general, and the old-growth ecosystem

(table 1). For each species or issue, considerations for habitat management were

developed from the key parameters.

Elements common among parameters for the different species and issues were

then identified for specific habitats or management practices on which to focus.

These elements served as the components or building blocks of Forest-wide viability

approaches. Four components ultimately were identified: riparian areas, silvicultural

systems, old-growth reserves, and the beach fringe. Some of the important considerations for these components are discussed below. A fifth component, areas currently

in a withdrawn status (withdrawn from most forms of land-disturbing management

activities, including commercial timber harvesting), such as wilderness and research

natural areas, is an assumed land allocation applied equally to all approaches.

Riparian options—This subject includes consideration of fish viability and

productivity, as well as other aquatic organisms and riparian-associated wildlife.

To the extent that they contribute appropriate habitat, riparian areas may function

as wildlife travel corridors and provide important connectivity among habitats within

watersheds. From the anadromous fish habitat assessment (USDA Forest Service

1995) and subsequent work by the interdisciplinary team, three options for riparian

area habitat management are available; these options, together with current TLMP

direction (as amended after the Tongass Timber Reform Act), provided four conceptual choices for this viability component: proposed options 1 through 3 and the

current TLMP, as described below.

3
Table 1—Key parameters and range of recommendations used in the viability synthesis workshop to

develop management options for the Tongass land management plan

Species or issue Key parameters Range of recommendations

Marten

(Martes americana) High-productivity old growth (volume class 5+a) A habitat conservation area (HCA) network

2 square miles per female, 3 square consisting of HCAs of 34,000 acres, 25 miles

miles per male apart, to support 25 reproductive pairs; HCAs

16-mile mean dispersal range of 6,800 acres, 9 miles apart, to support

Roaded access-level of trapping 5 reproductive pairs or 13,600 acres,

Forest-wide application 16 miles apart, to support 10 pairs; and

HCAs of 2,100 acres, 1 for each 15 square

miles or larger watershed to support 1 pair

At a minimum, HCAs should be 50 percent

volume class 4+, and 25 percent volume

class 5+; they should be nonlinear in shape,

as much as possible

Forested riparian corridors and beach fringe

Consider road density and management

Reserves may be unnecessary if the stated

stand characteristics for HCAs could be

achieved through uneven-aged management,

longer rotations, or both

Could be applied within HCAs, or Forest-wide

if no HCA system is provided (the latter is

more risky)

If no HCAs, then spatial control of habitat juxtaposition required

Road management still required

Northern goshawk

(Accipiter gentilis) Volume class 4+ habitat No more than 33 percent of the productive

Home ranges (surveyed to date) contain forest land within a watershed, including

20 to 80 percent productive old-growth private land, should be in stands less than

forest 100 years old

Productive forest preferred (nonrandomly Representative nesting habitat (>600 acres)

selected) for nesting habitat available in each watershed (10,000 to

Most nests below 800 feet in elevation 30,000 acres)

Use areas range from 10,000 to 30,000 acres

Significant avoidance of clearcuts and nonforest

Need for continuous reserves not evident

Forest-wide application

Marbled murrelet

(Brachyramphus

marmoratus) Nest on large branches of the oldest and Maintain volume class 4+ in heads of bays,

largest diameter trees available within with emphasis on those near aquatic or

31 miles of the ocean terrestrial concentration areas

Nesting associated with low-elevation (300-foot

average; 800-foot maximum) forest in heads

of bays

Prefer trees with high epiphytic cover

Gill net mortality and other at-sea effects a concern

Forest-wide application

4
Table 1—Key parameters and range of recommendations used in the viability synthesis workshop to

develop management options for the Tongass land management plan (continued)

Species or issue Key parameters Range of recommendations

Wolf (Canis lupus) Road density and roaded access for trapping Manage mortality from trapping and illegal

Prey availability: primarily deer on the islands, kills

moose and goats on mainland Maintain habitat to maintain productive prey

Application: Yakutat Peninsula, mainland, and populations, especially deer (for deer,

the islands south of Frederick Sound emphasize volume class 5+ for winter habitat)

Consider a deer-density objective within wolf

range

Fish Fish viability Viability: Maintain multiple, well-distributed, unFish productivity disturbed watersheds within each evolutionary

Watershed integrity significant unit (ESU); the current proposal

Forest-wide application uses the State’s statistical troll units—other

options for identifying ESUs also could be

used, or the National Marine Fisheries Service

may define ESUs for the Tongass

Productivity: Also use one of the Riparian

Conservation Area options, which variously

allow some silviculture

Brown bear

(Ursus arctos) Availability of anadromous fish Reserves of 40,000 acres, with no roaded

Road density and roaded access concerns access, that include productive fisheries every

Availability of summer alpine habitat 20 miles

Camp and community waste disposal sites Maintain 300-foot buffers on low-gradient class I

Application: mainland, and Admiralty, Baranof, streams to provide visual barrier and foraging

and Chichagof Islands habitat

Provide for movement to alpine habitat

Manage human activity to minimize the chance

of encounters and illegal kills

Consider ways to concentrate human activity

within landscapes

If an HCA-type approach is used, then the above

reserves would not be an additional need if

each large HCA contains a class I stream

Old-growth ecosystem All other old-growth-associated wildlife Include a “full array” of habitats and environspecies mental conditions within an old-growth

Other riparian forest associates conservation network

All animal and plant ecosystem components This full array should include representation

Biological diversity by ecological province, elevation, plant

Old growth as an ecosystem association-cover type, island size, channel

How well these parameters are covered type, and old-growth patch sizes

(or not covered) by the individual species Maintain connectivity between the components

considered above of the network

Include unique and rare features (research

natural areas and special interest areas, for

example)

a See Julin and Caouette, this volume, for clarification of volume class.

5
Proposed option 1—This option has the widest stream buffers and the lowest level

of risk to fish compared to other options. It provides the greatest benefit to organisms

in addition to fish (USDA Forest Service 1994).

Proposed option 2—This option incorporates the basic recommendations of the

anadromous fish habitat assessment (USDA Forest Service 1995). Were this option

implemented, it would result in a moderate level of risk to fish compared to other

options. Organisms other than fish would experience a moderate level of benefit

under this option. Stream buffer widths are generally intermediate, between those

in options 1 and 3.

Proposed option 3—This option adopts the riparian direction of the 1991 TLMP

revision supplement (USDA Forest Service 1991), which goes beyond the Tongass

Timber Reform Act (TTRA) stream buffer requirements. This option has the highest

level of risk to fish compared to other options and is least beneficial to other

organisms.

TLMP—The current TLMP follows the stream buffer requirements in TTRA and best

management practices (Forest Service Handbook [FSH] 2509.22—Soil and Water

Conservation Handbook). This option would have a higher risk to fish and riparianassociated wildlife (brown bear [Ursus arctos], for example) than any of the proposed

options. Risks were broadly categorized by participants into high, moderate, and low

groups, with the understanding that all such labels are intended only as relative comparisons among the approaches considered and do not relate to any outside standards per se. The evaluations also were predicated on our limited ability to predict

actual habitat conditions (changes) over time under each set of “building blocks.” This

effort thus was not a formal analysis of risks to viability—that will come later when

Forest plan alternatives have been developed—but it simply used the concept of risk

to combine elements of possible approaches and array those approaches

comparatively.

Wildlife corridors would experience reduced function as a result of this option.

Uneven-aged systems, long rotations, and an extensive reserve system could

compensate for the higher level of risk.

Silvicultural systems—Alternatives to clearcutting, including uneven-aged systems

and some even-aged systems, and the use of intermediate treatments (thinning and

pruning, for example), may reduce or mitigate the adverse effects of large, even-aged

clearcuts on forest fragmentation and help to maintain or promote the development of

certain stand characteristics found in old-growth forests. Using longer “rotations” or

cutting cycles (the number of years between final harvests for even-aged management, or the age of the oldest tree for uneven-aged management) also could help to

promote desired stand conditions by allowing timber stands more time to undergo

natural stand development processes.

The current rotation age of about 100 years was considered insufficient for development of forest stand attributes approximating the composition, structure, and function

of old-growth forests—attributes that generally do not develop until stands are at

least 150 to 250 years old.

6
Uneven-aged silvicultural systems that may closely approximate the natural disturbance patterns occurring in the temperate rain forest have been used rarely in

southeast Alaska. The long-term success of these alternative methods currently is

unknown. We are concerned about the long-term health and species composition

resulting from methods other than clearcutting. Extended rotations that help achieve

desired late-successional and old-growth conditions may be successful in promoting

forest health and biodiversity.

Longer rotations, uneven-aged management, and intermediate treatments also may

have potential for maintaining desired riparian and beach fringe characteristics and

could reduce size requirements for these areas. This approach has not been evaluated or tested, however, and was not considered in the anadromous fish habitat

assessment (USDA Forest Service 1995). In all cases, these methods may only

approximate certain old-growth forest attributes, and although they might meet needs

of certain wildlife species, they are not likely to provide the full range of structure and

composition characteristic of fully functioning, old-growth ecosystems. This incompleteness is partly because the periodic harvest of all areas suitable for timber production alters ecosystem dynamics, and partly because the removal of biomass alters

ecosystem function.

Conventional silvicultural systems provided four conceptual choices for this viability

component, which are described below.

Even-aged short rotation—This system prescribes the harvest of an entire timber

stand about every 100 years. An even-aged, short-rotation system was considered

to have the highest level of risk for old-growth-associated wildlife species.

Uneven-aged short cutting cycle—This system prescribes the periodic (<200

years) harvest of single trees or small groups of trees within a stand. This approach

was judged to have a moderate level of risk for old-growth-associated wildlife species.

Even-aged long rotation—This system prescribes the harvest of an entire timber

stand at intervals somewhat greater than 200 years. An even-aged, long-rotation

system has a moderate level of risk for old-growth-associated wildlife species.

Uneven-aged long cutting cycle—This system prescribes the periodic (>200 years)

harvest of single trees or small groups of trees within a stand. An uneven-aged, long

cutting-cycle system was considered to have the lowest level of risk for old-growthassociated wildlife species.

Old-growth reserves—One basic approach to wildlife conservation is to provide a

dispersed system of protected habitat areas or reserves of a specified size, forest

composition, and spatial distribution that are appropriately spaced throughout a

landscape and connected by suitable dispersal corridors. When based on the needs

of representative species, such a system can effectively contribute to maintaining

habitat to support viable populations of many old-growth-associated wildlife species.

The Interagency Viable Population Committee (Suring and others 1993) used the

habitat reserve approach in recommending a system of habitat conservation areas

(HCAs), well distributed across the Tongass, to provide habitat for viable populations

of old-growth-associated species.

7
We identified several limitations in the HCA strategy. The strategy was based on the

known requirements of only a few wildlife species. Although they all have a range of

needs related to old-growth forest, there is no assurance that all or even most other

old-growth-associated species have similar needs or are adequately represented.

Even our knowledge about the species used for the HCA system is limited. In addition, the HCA network is related more to the size and spacing requirements of certain

wildlife species rather than to the actual distribution of old-growth blocks found on the

Tongass; thus it may not accurately represent the extent or distribution of the oldgrowth forest ecosystem (DeGayner and Iverson, in prep.).

There is an even more fundamental concern: Our knowledge of the specific viability

requirements of most Tongass wildlife species is limited. The key species may

represent or be indicative of the requirements of other old-growth-associated species,

but these relations have not been described. The old-growth forest ecosystem is,

however, the dominant ecosystem in southeast Alaska that provides habitat for many

species. Therefore, a “systems” approach examining the old-growth ecosystem by

itself as a key component of a viability strategy is likely to address the requirements

of all old-growth-associated species. A recent inventory of the old-growth resource,

based on the size of the remaining contiguous old-growth areas, or “blocks,” provides

this old-growth ecosystem information (DeGayner and Iverson, in prep.).

The old-growth inventory (DeGayner and Iverson, in prep.) divided contiguous old

growth into four block sizes: category 1 (more than 10,000 acres), category 2 (1,000

to 10,000 acres), category 3 (less than 1,000 acres and with relatively high ecological

value), and category 4 (under 1,000 acres and with relatively low value). Blocks were

characterized by the proportion of interior forest, the range of elevations covered,

adjacency to diverse habitats, and distribution within a landscape or island. Two oldgrowth reserve options were considered. The first selects one category 1 old-growth

block for each of the 21 biogeographic provinces of the Tongass. The second selects

a proportional amount of the remaining old growth based on its current distribution—

in this case, 75 percent of the acreage of all category 1 and 2 blocks.

Four conceptual choices for the old-growth viability component were identified and

are described below. For all reserve options, we assumed that risk to viability decreases as the number and size of old-growth areas increase and as these areas

are more evenly distributed. It also was assumed that existing withdrawn areas will

remain in place. Reserves are designed to preserve old-growth ecosystems and

their inherent biodiversity, rather than for wildlife habitat conservation.

No old-growth reserves—This approach does not designate additional blocks or

areas of specifically protected old-growth forest beyond those already contained in

nontimber-harvest areas, such as wilderness. This option was considered to have

the highest risk of losing a representative amount and distribution of old-growthassociated organisms. This risk could be lowered by using long-rotation, unevenaged systems and maintaining large riparian buffers.

Habitat conservation areas—The HCA approach is a designed system of protected

old-growth reserves meeting specified size and spacing requirements. This option

was considered to have the lowest risk for many old-growth-associated species.

There is a moderate to high risk of losing representative amounts and distributions

of old-growth ecosystems Forest-wide. Use of long rotations or uneven-aged management within the matrix was thought to reduce viability risks.

8
One large block per ecological province—This approach provides old-growth

habitat blocks of 10,000 acres or more selected from the old-growth inventory and

maintained as habitat reserves. It was considered to have a moderate risk of losing

old-growth ecosystems distributed by their natural occurrence. The risk to many

old-growth-associated organisms was considered to be high, unless coupled with

HCAs, extended rotations, or uneven-aged management.

Proportional representation of Forest-wide distribution—This option selects a

proportional amount of the remaining old growth based on its current distribution—

in this case, 75 percent of the acreage of all large and medium blocks. A moderate

to low risk to old growth was thought to result from this option, depending on timber

practices within the matrix. This option may not meet size or distributional needs for

some species; connectivity needs to be considered.

Beach fringe—Beach fringe is the strip of vegetation adjacent to saltwater shorelines that serves as a wildlife travel corridor, a transition zone between interior forest

and saltwater influences, and an important habitat for many wildlife species (Suring

and others 1993). Beach fringes may provide important horizontal or low-elevation

connectivity between watersheds. In conjunction with riparian areas, which provide

elevation habitat connectivity within watersheds, beach fringes may function as an

important forested landscape link among watersheds, especially in the heavily

dissected landscape characterizing the Tongass.

It is not known if the beach fringe zone can be classified as its own ecosystem,

perhaps analogous to the riparian ecosystem that is defined in part by its riparian

soils, channel morphology, and forested component; however, the old-growth forest

portion of much of the beach fringe is the primary habitat component for numerous wildlife species including bald eagle (Haliaeetus leucocephalus), river otter

(Lutra canadensis), mink (Mustela vison), marten, and American crow (Corvus

brachyrhynchos). A concern is that a narrowly defined beach fringe corridor (average 500-foot width, for example) would not maintain “interior old-growth” characteristics of this forested component (Concannon 1995). Thus, one option considered

was to increase the beach fringe width to a 1,000-foot minimum to ensure that the

old-growth portion of this zone retains its interior old-growth function. This approach

also helps to eliminate the probably arbitrary distinction between beach fringe forest

and maritime-influenced forest. Thus, three beach fringe options were considered:

no beach fringe, 500-foot beach fringe, and 1,000-foot beach fringe. Each option is

described below.

No beach fringe—The current Forest plan prescribes no beach fringe. Use of this

option will reduce the beach forest ecosystem and interior old-growth functions. Loss

of wildlife travel corridors and important winter habitat also will result. This option was

considered to have the highest risk for wildlife viability associated with these habitat

functions.

500-foot beach fringe—This option provides a beach fringe of generally 500 feet

with a 1,000-foot corridor around estuaries. Use of this option will maintain a narrow

beach-forest ecosystem. It results in the loss of interior old-growth function and was

considered to present less risk to some species, but not to those requiring interior

old-growth habitat near the beach.

9
1,000-foot beach fringe—This option would maintain 1,000-foot “no harvest” buffers

along beaches. Use of this option will maintain the beach-forest ecosystem and the

quality of interior old-growth habitat. It was considered to present a low risk to associated wildlife and to maintain connectivity among intact blocks of old-growth forest.

Nine conceptual approaches—From the above considerations for these four

components, the various options within the components were variously combined

to portray several possible Forest-wide approaches to maintaining wildlife viability

(table 2).

For most of the conceptual approaches designed, the focus was on finding different

combinations of building block components that would result in different likelihoods

of ensuring viability. For example, the current TLMP has the following combination

of building block components: minimum 100-foot riparian buffers for the riparian

component, 85-percent even-aged short rotation and 15-percent even-aged long

rotation for the silvicultural system, and no reserves or beach fringe (table 2). We

consider these components to have a relatively high risk for wildlife viability. In

contrast, another conceptual design was developed with riparian option 1, unevenand even-aged long rotations, HCA reserves, and a 1,000-foot beach fringe with

additional species-specific management standards and guidelines. This conceptual

design was considered to have a relatively low risk of not maintaining viable wildlife

populations.

A few general comments on risks and tradeoffs among options:

• The existing system of reserves within the Tongass (areas withdrawn, such as

wilderness, legislated LUD II [LUD II lands are managed in a roadless state],

and research natural areas—regardless of the habitat they include) do not in

themselves provide sufficiently well-distributed or fully representative habitat

across the Tongass to ensure maintenance of viability for all species.

• A relatively high risk was assumed to exist for fish without application of the

proposed ecologically significant units (ESUs). This reserve system is designed

around fisheries concerns, however, and may contribute only minimally to a

wildlife or old-growth reserve system.

• The current Forest plan, due to its reliance on short-rotation clearcutting, lack of

a Forest-wide reserve strategy, and limited riparian protection, was considered to

have a high risk for all species of concern, for the old-growth ecosystem, and for

biodiversity. Generally, uneven-aged silvicultural methods, and (in particular) extended rotations (>200 years), were considered to either reduce the need for the

more extensive reserves or lower the risk category for an approach that otherwise

used even-aged management and short rotations. Some information suggests that

more than 300 years may be needed to achieve the structural characteristics of

old-growth forests. For the present effort, however, more than 200 years was

used to define extended or long rotations.

• The Interagency Viable Population Committee strategy (Suring and others 1993)

with its habitat conservation area system, as applied to the current Forest plan, may

be favorable for many species but is considered deficient in corridor design and

matrix management. It retains a high risk for fish, and possibly also for marbled

murrelet, northern goshawk, the old-growth ecosystem, and biodiversity.

10
Table 2—9 alternative conceptual approaches to a forest-wide viability strategy

Riparian optionsb Silvicultural systemsc Old-growth reservesd Beach fringe optionse

Viability VPOPapproachesa 1 2 3 TLMP ES US EL UL HCA 1/prov. % None 500 ft 1,000 ft S&GsfHigher risk:

TLMPg X 85% 15% X

High-risk approach 1 (H-1) X 75% 25% XHigh-risk approach 2 (H-2) X X XViable populations approach

(Suring and others 1993; VPOP) X X X X X

Moderate-risk approach 1 (M-1) X X X X XModerate-risk approach 2 (M-2) X X X X X XLow-risk approach 1 (L-1) X X X X X X XLow-risk approach 2 (L-2) X X X X XLow-risk approach 3 (L-3) X X X X X X X X

Lower riskh

a All approaches assume the same existing withdrawn areas (wilderness, research natural areas, legislated LUD II [lands managed in a roadless state]).b Riparian options: 1, 2, and 3 are from the anadromous fish habitat assessment-related proposals (USDA Forest Service 1995). TLMP includes the Tongass Timber Reform Act buffers.c Silvicultural options: ES = even-aged short rotation (<200 years); EL = even-aged long rotation (>200 years); US = uneven-aged short cutting cycle (<200 years); UL = uneven-aged long

cutting cycle (>200 years).

d Old-growth reserves: HCA = the Viable Populations Habitat Committee’s habitat conservation area guidelines (Suring and others 1993); 1/prov. = 1 large old-growth block per ecological

province. Where this and HCA are both checked, they are additive. % = the distribution of reserves based on the historical distribution of old-growth forest (1954 condition). As applied here,this means 75 percent of large- and medium-sized old-growth block acreage, including HCAs, in reserves.

e Beach fringe buffers: 500 ft = beach fringe as used in the TLMP revision supplement; 1,000 ft = beach fringe of a minimum of 1,000 feet, more if the beach fringe ecosystem extends further.f VPOP S&Gs: species-specific habitat management standards applied in addition to habitat conservation areas in Suring and others (1993).g TLMP: current Tongass Forest plan.h Conceptual approaches were ranked along a continuum from higher to lower potential risks to wildlife viability.

11
• Approaches lacking an old-growth reserve system, based on the old-growth

inventory and distributed proportionately, were considered less likely to ensure

a low level of risk for the old-growth ecosystem and for biodiversity (and also for

the northern goshawk, depending on management actions within the matrix).

Approaches that include the following components were considered to be in a lower

risk category:

• Species-specific standards and guidelines derived from the Viable Populations

Committee strategy (Suring and others 1993), particularly those for road access

management (i.e., wolf, brown bear, marten)

• Maintenance of the old-growth ecosystem across a full array of geographic and

environmental conditions (table 2)

• The 1,000-foot option for the beach fringe to help maintain interior forest conditions

in that zone

• One of the three riparian options, preferably option 1 or 2

Many possible tradeoffs exist between the type of silvicultural system(s) chosen and

the need for an extensive reserve system or wider riparian and beach fringe zones,

or both.

• One tradeoff of using extended rotations or uneven-aged systems is that, to

achieve the same harvest level as could have been achieved under even-aged,

short-rotation systems, more area would need to be harvested and more miles

of road built in a given time. Thus, the risk of not maintaining fully functioning

old-growth ecosystems may not decrease as a result of using these alternative

systems.

• When the use of any silvicultural system as an alternative to reserves is being

considered, the effects of roading and road use, which may in some cases equal

the effects of harvesting, also need to be considered, particularly for wolf, brown

bear, and marten.

• Many of these conceptual approaches assume a general tradeoff between areas

in short-rotation, even-aged systems and areas set aside in reserves (including

riparian and beach fringe). For instance, if the suitable timber base in an alternative

were managed under an even-aged, short-rotation system, then more areas within

reserves would be required for a comparable level of risk than if the suitable timber

base in the same alternative were managed for long rotations. As another example,

an alternative using only uneven-aged, longer cutting cycles and a less restrictive

riparian option than one using even-aged or short-rotation systems may achieve a

similar level of riparian risk.

All reserve options considered herein should be understood to exclude timber harvest

within the reserve. It may be possible, however, to include a form of reserve that

allows some types of light-intensity timber harvest closely emulating the size, scale,

and intensity of natural disturbance processes (Nowacki and Kramer, in prep.).

Although there was not consensus among workshop participants concerning exact

rankings, there was agreement on general levels of risk (i.e., low, moderate, high).

Table 3 includes the rationale (based on the subjective judgment of meeting participants) used for these relative rankings, which is divided into riparian, terrestrial

vertebrate, and old-growth ecosystem concerns. Much of this rationale is drawn from

12
Table 3—Rationale for the relative risks associated with each conceptual approach to viability (refer to

table 2 for conceptual approaches)

Approaches and

relative risk Riparian Terrestrial vertebrates Old-growth ecosystem

Current TLMP

and high-risk Concern for fish and Excess amount of landscape in Lack of adequate reserve system,

approach 1 aquatic organisms early seral conditions extensive use of short rotations,

(H-1) Reduced connectivity Inadequate control on size and and lack of connectivity

within watersheds distribution of reserves Reduction in available interior oldConcern for riparian- Reduced connectivity between growth conditions

associated wildlife patches, complicated by lack of Will not provide full representation of

(such as brown bear) beach fringe habitat old-growth ecological conditions

Potential impact of roads

High-risk Similar to above, but Similar to above, except more Potential high risk with more acreage

approach 2 risk is reduced with connectivity provided within under timber management

(H-2) higher percentage of and between watersheds owing

landscape in late seral to extended rotations

condition at any one time Road impacts could be higher

Viable Beach fringe and reserve Moderate connectivity provided Representation of old-growth

populations system mitigate current within beach fringe and riparian conditions not ensured and not

approach (Suring riparian policy; may not areas extensive

and others 1993; meet long-term productivity Percentage of landscape in late Connectivity between many blocks

VPOP) goals seral condition may be insufficient remains low

Concern for riparian- for some species (e.g., goshawk,

associated wildlife and deer, wolf)

aquatic organisms

Moderate-risk Reserve system con- Greater contribution of riparian More extensive reserves and riparian

approach 1 tributes to riparian Percentage of landscape in late areas

(M-1) ecosystem seral condition may be insufficient Connectivity between many blocks

for some species (e.g., goshawk, remains low

deer, wolf)

Moderate-risk Beach fringe and Tradeoff between lower amount Tradeoff between lower amount in

approach 2 reserves contribute in reserves and longer rotations reserves and longer rotations

(M-2) to riparian ecosystem Moderate connectivity provided

Low-risk Intermediate coverage More productive riparian area Adequate size and distribution of

approach 1 of riparian ecosystem Extended beach fringe connectivity habitats and patches; less in late

(L-1) High percentage of landscape in successional forest than L-2 or L-3

late seral stages Connectivity provided by extensive

riparian and beach fringe systems

and well-distributed reserves

Low-risk Intermediate coverage Same as L-1, except tradeoff Same as L-1, except better

approach 2 of riparian ecosystem between more reserves and representation of late successional

(L-2) short-rotation, even-aged forest conditions

management

Low-risk Extensive riparian Essentially the same as L-1 Greatest representation of late

approach 3 area in combination with but a greater percentage of successional forest conditions

(L-3) reserves and long rotations landscape in late seral stages

13
the species- and issue-specific information provided during workshop presentations

(table 1) and consideration of landscape building block key components. This information provides in detail the criteria, rationale, and thought processes used to develop

an array of conceptual approaches to manage for viability and to develop other approaches from the same components. This information was developed to provide the

TLMP Revision Interdisciplinary Team with necessary input to incorporate reasonable

strategies for maintaining the habitat necessary to ensure viable, well-distributed

populations of fish and wildlife species across the Tongass.

References Baichtal, J.F.; Swanston, D.N. 1996. Karst landscapes and associated resources:

a resource assessment. Gen. Tech. Rep. PNW-GTR-383. Portland, OR: U.S.

Department of Agriculture, Forest Service, Pacific Northwest Research Station.

(Shaw, Charles G., III, and Julin, Kent R., tech. coords.; Conservation and

resource assessments for the Tongass land management plan revision).

Concannon, J.A. 1995. Characterizing structure, microclimate and decomposition

of peatland, beachfront, and newly-logged forest edges in southeastern Alaska.

Seattle: University of Washington. 325 p. Ph.D. dissertation.

DeGange, A.R. 1996. The marbled murrelet: a conservation assessment. Gen. Tech.

Rep. PNW-GTR-388. Portland, OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Research Station. 72 p. (Shaw, Charles G., III, tech.

coord.; Conservation and resource assessments for the Tongass land management

plan revision).

DeGayner, E.; Iverson, G.C. [In prep.]. Productive old-growth block inventory. In:

Shaw, Charles G., III, tech. coord. Conservation and resource assessments for the

Tongass land management plan revision. Gen. Tech. Rep. Portland, OR: U.S.

Department of Agriculture, Forest Service, Pacific Northwest Research Station.

Forest Ecosystem Management Assessment Team [FEMAT]. 1993. Forest

ecosystem management: an ecological, economic, and social assessment.

Portland, OR: U.S. Department of Agriculture; U.S. Department of the Interior

[and others]. [Irregular pagination].

Iverson, G.C.; Hayward, G.D.; Titus, K. [and others]. 1996. Conservation

assessment for the northern goshawk in southeast Alaska. Gen. Tech. Rep.

PNW-GTR-387. Portland, OR: U.S. Department of Agriculture, Forest Service,

Pacific Northwest Research Station. 101 p. (Shaw, Charles G., III tech. coord.;

Conservation and resource assessments for the Tongass land management plan

revision).

Kiester, A.R.; Eckhardt, C. 1994. Review of wildlife management and conservation biology on the Tongass National Forest: a synthesis with recommendations.

Corvallis, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Research Station. 282 p. Administrative report. On file with: A. Ross Kiester,

Forestry Sciences Laboratory, 3200 SW Jefferson Way, Corvallis, OR 97331.

Nowacki, G.J.; Kramer, M.G. [In prep.]. The natural disturbance regime with

emphasis on wind disturbance. In: Shaw, Charles G., III, tech. coord. Conservation and resource assessments for the Tongass land management plan revision.

Gen. Tech. Rep. Portland, OR: U.S. Department of Agriculture, Forest Service,

Pacific Northwest Research Station.

14
Person, D.K.; Kirchhoff, M.; Van Ballenberghe, V. [and others]. 1996. The

Alexander Archipelago wolf: a conservation assessment. Gen. Tech. Rep.

PNW-GTR-384. Portland, OR U.S. Department of Agriculture, Forest Service,

Pacific Northwest Research Station. 42 p. (Shaw, Charles G., III, tech coord.;

Conservation and resource assessments for the Tongass land management plan

revision).

Smith, W.P.; Shaw, C.G., III. [In prep.]. The risk assessment panel process. In:

Shaw., Charles G., III, tech. coord. Conservation and resource assessments for

the Tongass land management plan revision. Gen Tech. Rep. Portland, OR: U.S.

Department of Agriculture, Forest Service, Pacific Northwest Research Station.

Suring, L.H., Crocker-Bedford, C.D.; Flynn, R.W. [and others]. 1993. A proposed

strategy for maintaining well-distributed, viable populations of wildlife associated

with old-growth forests in southeast Alaska. Draft. On file with: USDA Forest

Service, Alaska Region, P.O. Box 21628, Juneau, AK 99801.

Suring, L.H.; Crocker-Bedford, C.D.; Flynn, R.W. [and others]. 1994. Response

to the peer review of: a proposed strategy for maintaining well-distributed, viable

populations of wildlife associated with old-growth forests of southeast Alaska.

Juneau, AK: U.S. Department of Agriculture; Alaska Department of Fish and

Game [and others]. 11 p.

Suring, L.H., Crocker-Bedford, C.D.; Flynn, R.W. [and others]. [In prep.]. A

process for conserving wildlife species associated with old-growth forests in

southeast Alaska.

Swanston, D.N.; Shaw, C.G.,III; Smith, W.P. [and others]. 1996. Scientific information and the Tongass land management plan: key findings derived from the

scientific literature, species assessments, resource analyses, workshops, and risk

assessment panels. Gen. Tech. Rep. PNW-GTR-386. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 30 p.

(Shaw, Charles G., III tech. coord.; Conservation and resource assessments for

the Tongass land management plan revision).

U.S. Department of Agriculture, Forest Service. 1991. Tongass land management

plan revision: supplement to the draft environmental impact statement. R10-MB149. Juneau, AK: Alaska Region. [Irregular pagination].

U.S. Department of Agriculture, Forest Service. 1994. Pacific fisheries assessment: draft environmental assessment for the implementation of interim strategies

for managing anadromous fish-producing watersheds in eastern Oregon and

Washington, Idaho, and portions of California. Washington, DC: U.S. Department

of Agriculture, Forest Service; U.S. Department of the Interior, Bureau of Land

Management. 68 p.

U.S. Department of Agriculture, Forest Service. 1995. Report to Congress: anadromous fish habitat assessment. R10-MB-279. [Place of publication unknown]:

Pacific Northwest Research Station; Alaska Region. 265 p.

15
Appendix A The Viability Synthesis Workshop Charter.

Introduction As part of the revision process for the Tongass land management plan (TLMP),

five assessments designed to synthesize available information on wildlife species

of particular concern to management of the Tongass National Forest (Tongass) have

been conducted. In addition to these species-specific assessments, which include

the northern goshawk (Accipiter gentilis), Alexander Archipelago wolf (Canis lupus

ligoni), marbled murrelet (Brachyramphus marmoratus), and anadromous salmonids

(Salmonidae), ecosystem-oriented assessments were conducted (i.e., habitat conservation areas, old-growth patch analysis, and karst terrain and caves). These

assessments augment other information available on an array of species of management interest in the Tongass (e.g., Sitka black-tail deer [Odocoileus hemionus],

brown bear [Ursus arctos], mountain goat [Oreamnos americanus], bald eagle

[Haliaeetus leucocephalus], and marten [Martes americana]). Brief presentations

on each assessment and on the other major species of interest will be provided

at the workshop.

At present, the information contained within each individual assessment has not

been evaluated in context with the other assessments. No attempt has yet been made

to synthesize this array of assessments and other information sources to clarify

habitat factors in common versus those that may be species specific. There is a

strong need to accomplish this evaluation and synthesis and then package the

combined information such that it provides direct input for development of alternatives for TLMP.

Objective The objective of the workshop is to evaluate and synthesize available information

obtained from recently conducted, Tongass-specific assessments and various other

sources (Suring and others 1993). The process needs to identify habitat factors and

other needs that may be in common across the various species of interest (e.g.,

old-growth association or dependence), as well as those factors that may still be

highly important but more species specific (e.g., road density).

Product Ideally, we would like to leave the workshop with an array of landscape-level management options for use in development of Forest plan alternatives that adequately

address the issues associated with species and ecosystem viability. Specifically, the

workshop needs to provide various combinations of the above-mentioned landscape

designs, guidelines, and other “building blocks” that will maintain or restore:

• Terrestrial habitat conditions for the northern goshawk, Alexander Archipelago wolf,

and marbled murrelet so that viable populations will persist in a well-distributed

manner across their current ranges.

• Terrestrial habitat conditions to support viable populations, well distributed across

their ranges, of terrestrial species associated with all Tongass ecosystems.

• Aquatic habitats to support viable populations of resident and anadromous fish

species and stocks of other aquatic organisms.

• Functional and interactive ecosystems, including old-growth forests and aquatic

systems.

16
The actual “risk” assessment that any particular Forest plan alternative will meet

the species-specific viability needs will be independently evaluated through a panel

review process.

We will develop sets of alternative landscape designs and management guidelines

that incorporate (separately or in various combinations) reserves, matrix management,

or other “building blocks” to provide various levels of assurance that any subsequent

Forest plan alternative developed from these sets will maintain viable populations of

all species as well as sustain overall ecosystem structure, composition, and function.

In developing these sets, we need to ensure that land stewardship is not compromised and appreciate that some level of long-term, sustainable output of various

resources (e.g., timber, recreational experiences) is desired.

Possible Approach We should consider a landscape approach that builds on other spatially explicit

components of the Forest plan (e.g., designated wilderness, anadromous fisheries

habitat assessment [USDA Forest Service 1995], directed riparian management

standards). To build this foundation, we append additional standards or landscape

features as building blocks considered necessary to provide well-distributed habitat

for the above-mentioned species and environments. These components can then

be used to construct Forest plan alternatives. Four landscape-level themes serve

as possible approaches:

1. Dynamic landscape management predicated on disturbance regimes and no

reserves.

2. Some combination of small, medium, and large reserves connected by a matrix

of lands experiencing various management actions (e.g., patch cuts of various sizes

and distributions, partial cuts of various sizes and distributions, partial cuttings that

remove various levels and components of stocking).

3. Fewer but very large reserves within each landscape stratum (e.g., biogeographic

province or island) coupled with the matrix management approach indicated in

number 2 above.

4. Combinations across the forest of numbers 1, 2, and 3 specifically applied to

landscapes and predicated on the existing and desired condition.

17
Appendix B Viability Synthesis Workshop participants, June 7-9, 1995.

Participants Affiliation

Mike Brown USDA Forest Service, Alaska Region

Steve Brink USDA Forest Service, Alaska Region

Jack Capp USDA Forest Service, Alaska Region

John Caouette USDA Forest Service, Pacific Northwest Research Station

Eugene DeGayner USDA Forest Service, Alaska Region

Richard Enriquez U.S. Fish and Wildlife Service

Rod Flynn Alaska Department of Fish and Game

Rick Griffen USDA Forest Service, Alaska Region

Carol Hale U.S. Fish and Wildlife Service

Dick Holthausen USDA Forest Service, Alaska Region

George Iverson USDA Forest Service, Alaska Region

Steve Kessler USDA Forest Service, Alaska Region

Matthew Kirchhoff Alaska Department of Fish and Game

Jerry McIlwain USDA Forest Service, Pacific Northwest Research Station

Chris Meade U.S. Environmental Protection Agency

Gregory Nowacki USDA Forest Service, Alaska Region

Martin Raphael USDA Forest Service, Pacific Northwest Research Station

Bruce René USDA Forest Service, Alaska Region

Ted Schenk USDA Forest Service, Alaska Region

Terry Shaw USDA Forest Service, Pacific Northwest Research Station

Winston Smith USDA Forest Service, Pacific Northwest Research Station

Douglas Swanston USDA Forest Service, Pacific Northwest Research Station

Kimberly Titus Alaska Department of Fish and Game

Richard Zaborske USDA Forest Service, Alaska Region

18
Appendix C Materials presented by George Iverson during the workshop.

Table 4—Criteria for habitat conservation areas proposed to maintain viable and well-distributed

populations of wildlife associated with old-growth forests in southeast Alaska

Species Large HCAsa Medium HCAsa Small HCAsa

Brown bear 40,000 acres — —

20 miles apart

1 class-I stream

5 females

Marten 40,000 acres 8,000 acres 1,600 acres per watershed

25 miles apart 9 miles apart 50 percent volume class 4+

25 percent volume class 4b 25 percent volume class 4 1 reproductive unit

25 percent volume class 5+ 25 percent volume class 5+

25 reproductive units 5 reproductive units

Flying squirrel — — 1,000 acres per watershed

volume class 4+

10-20 pairs

Northern goshawk 40,000 acres 10,000 acres —

20 miles apart 20 miles apart

25 percent volume class 4 25 percent volume class 4

25 percent volume class 5+ 25 percent volume class 5+

8 pairs 2 pairs

Combined standard 40,000 acres 10,000 acres 1,600 acres per watershed

20 miles apart 20 miles apart 50 percent volume class 4+

25 percent volume class 4 25 percent volume class 4

25 percent volume class 5+ 25 percent volume class 5+

1 class-I stream

a HCA = Habitat conservation area.

b See Julin and Caouette, this volume, for clarification of volume class.

Source: Suring and others 1993.

19
Table 5—Wildlife species associated with

old-growth forest habitats that are recognized

as having potential viability or distribution

concerns in southeast Alaska

Common name Scientific name

Bald eagle Haliaeetus leucocephalus

Marbled murrelet Brachyramphus brevirostris

Vaux’s swift Chaetura vauxi

Black bear Ursus americanus

Least weasel Mustela nivalis

Mink Mustela vison

River otter Lutra canadensis

Mountain goat Oreamnos americanus

Sitka mouse Peromyscus sitkensis

Coronation Island vole Microtus coronarius

Source: Suring and others, in prep.

Table 6—Wildlife species associated with

old-growth habitats that are recognized as

having viability or distribution concerns in

southeast Alaska

Common name Scientific name

Osprey Pandion haliaetus

Queen Charlotte goshawk Accipiter gentilis laingi

Spruce grouse Dendragapus canadensis

Alexander Archipelago wolf Canis lupus ligoni

Brown bear Ursus arctos horribilis

Wolverine Gulo gulo

Marten Martes americana

Lynx Lynx canadensis

Northern flying squirrel Glaucomys sabrinus

Source: Suring and others, in prep.

20
Table 7—Levels of concerna associated with viability or distribution, or both, for the 9 highest

ranked wildlife species in southeast Alaskab

Evaluation criteriac

Species 1 2 3 4 5 6 7 8 9 10 11 12 Totald

Brown bear 3 0 0 2 3 2 1 3 1 3 3 1 22 (61)

Marten 3 0 0 1 3 2 3 3 2 1 0 2 20 (56)

Queen Charlotte goshawk 3 0 2 2 2 2 3 2 0 1 1 2 20 (56)

Osprey 2 3 0 3 1 1 2 2 0 2 2 2 20 (56)

Spruce grouse 3 2 0 2 1 2 2 3 2 0 0 3 20 (56)

Wolverine 3 1 0 3 2 2 1 1 0 2 1 3 19 (53)

Northern flying squirrel 3 0 0 — 2 — 3 0 2 2 0 3 19 (53)

Alexander Archipelago wolf 3 0 2 2 1 0 1 3 2 1 1 2 18 (50)

Lynx 3 2 0 — 1 1 0 3 1 1 1 3 18 (50)

a Level of concern:

— = information is inadequate (assigned 2 points)

0 = no concern

1 = low

2 = moderate

3 = high b Ranked 50 percent or greater.

c Evaluation criteria:

Criteria Assigned

1. Seasonal occurrence in southeast Alaska points

a. Transient 0

b. Resident during winter or breeding season 1

c. Resident during breeding season 2

d. Permanent resident 3

2. Geographic distribution within southeast Alaska

a. Species occurs in 7+ ecological provinces 0

b. Species occurs in 4-6 ecological provinces 1

c. Species occurs in 2-3 ecological provinces 2

d. Species occurs in 1 ecological province 3

3. Geographical distribution outside southeast Alaska

a. Species distribution more than 200 percent of the size of southeast Alaska 0

b. Species distribution 100 to 200 percent of the size of southeast Alaska 1

c. Species distribution 50 to 100 percent of the size of southeast Alaska 2

d. Species distribution 0 to 50 percent of the size of southeast Alaska 3

4. Estimated size of the population in southeast Alaska

a. More than 10,000 individual throughout its range 0

b. 2,500 to 10,000 individuals throughout its range 1

c. 250 to 2,500 individuals throughout its range 2

d. Less than 250 individuals throughout its range 3

5. Population trend throughout the species’ range

a. Population known or suspected to be stable or increasing 0

b. Population formerly experienced a downward trend but presently is stable or increasing 1

c. Population suspected to be decreasing over a 10-year period 2

d. Population known to be decreasing over a 10-year period 3

21
Table 7—Levels of concerna associated with viability or distribution, or both, for the 9 highest

ranked wildlife species in southeast Alaskab (continued)

c Evaluation criteria: (continued)

Criteria Assigned

6. Population trend of the species in southeast Alaska points

a. Population known or suspected to be stable or increasing 0

b. Population formerly experienced a downward trend but presently is stable or increasing 1

c. Population suspected to be decreasing over a 10-year period 2

d. Population known to be decreasing over a 10-year period 3

7. Vulnerability of habitats in southeast Alaska

a. Species’ habitat is unlikely to be affected by land management activities, species is not negatively

affected by habitat fragmentation, and species is an ecological generalist 0

b. Species’ habitat is likely to be affected by land management activities, species is not negatively

affected by habitat fragmentation, and species is an ecological generalist 1

c. Species’ habitat is likely to be affected by land management activities, species is negatively

affected by habitat fragmentation, or species is an ecological specialist 2

d. Species’ habitat is likely to be affected by land management activities, species is negatively

affected by habitat fragmentation, and species is an ecological specialist 3

8. Vulnerability to road construction and increased access

a. Species unlikely to be affected by increased access 0

b. Species harvest likely to increase but will not affect population levels; species not susceptible

to increased disturbance 1

c. Species not harvested but susceptible to increased disturbance 2

d. Species vulnerable to over harvest or other increased mortality as a result of increased access 3

9. Capability of a species to disperse

a. Species are mobile and dispersal is not limited 0

b. Dispersal is limited 3

10. Demographic characteristics of the species. Average number of eggs or live young produced

per adult female per year

a. Less than 1 egg 3

b. 1 to 2 eggs 2

c. 3 to 5 eggs 1

d. More than 5 eggs 0

11. Demographic characteristics of the species. Minimum age of first reproduction.

a. More than 5 years 3

b. 3 to 4 years 2

c. 2 years 1

d. Less than 2 years 0

12. Knowledge about the species in southeast Alaska

a. Limited knowledge concerning a species beyond documentation of their occurrence in

southeast Alaska 3

b. Species are monitored locally without statistical validity, and habitat associations are extrapolates

from other areas 2

c. Species are monitored throughout southeast Alaska with statistical validity, and habitat associations

are established in southeast Alaska 1

d. Species whose distribution and habitat relations are well documented in southeast Alaska and

throughout their range 0

d Percent is shown in parentheses.

Source: Suring and others, in prep.

22
Appendix D

Immediate Actions

Needed

The following is a summary of suggested actions that respond to comments made

by the peer reviewers (Kiester and Eckhardt 1994). In particular, the peer reviewers’

recommendations to keep landscape options open (i.e., avoid logging low-elevation,

high-volume old-growth forests; maintain connectivity between habitat conservation

areas; consider larger habitat conservation areas; pay attention to the matrix) until

the revision of the Tongass land management plan has been completed are briefly

addressed here. Pertinent suggestions from the review are given.

1. Restrict logging and road building to areas other than volume classes 6 and 7 in

old-growth forests (as determined by field reconnaissance) below 800 feet in

elevation.

2. Restrict logging, road building, and salvage sales to areas other than large- and

medium-sized habitat conservation areas.

3. Restrict logging and road building to areas other than the three largest old-growth

forest patches within each ecological province.

4. Establish a 0.5- to 1-mile buffer around all large- and medium-sized habitat conservation areas (as mapped in Suring 1993) as a “special management zone” in

which road building and clearcutting are prohibited. Selection harvest may be permitted so long as no more than 25 percent of the volume in any 5-acre block is

harvested and original species and size class distributions are maintained.

5. Connect large- and medium-sized habitat conservation areas (as mapped in Suring

and others 1993) with corridors in which logging is not allowed (1,600 feet wide

between large habitat conservation areas, which are further apart; 1,000 feet wide

between medium habitat conservation areas, which are closer together). Keep

corridors below 800 feet in elevation. Place a 3,300-foot-wide “special management

zone” along the coastline.

6. Maintain old-growth forests that have been identified through local knowledge or

field experience as important wildlife habitat (e.g., wildlife habitat retention areas

mapped in records of decision before 1992).

7. The number of old-growth forest, volume class 5 acres scheduled for harvest in

any sale should not exceed the number of acres scheduled for harvest in old-growth

forest, volume class 4.

23
Options for Defining Old-Growth Timber

Volume Strata: A Resource Assessment

Kent R. Julin and John P. Caouette

Issue Definition The Alaska Region had to decide whether and how the interpreted timber type data

layer (TIMTYP) database could be used in the revision of the Tongass land management plan (TLMP revision) for defining the old-growth forest resource. This database,

in conjunction with other resource inventories, was used historically by planners at the

Tongass National Forest (Tongass) for estimating the allowable sale quantity (ASQ),

determining volume proportionality,1 analyzing timber economics, and calculating wildlife habitat capability. The decision from the Wildlife Society and others vs. Barton

(U.S. District Court for the District of Alaska 1994) raised questions about the suitability of the TIMTYP database for determining proportionality under the Tongass

Timber Reform Act (TTRA § 301 [c] [2]). In this paper, we discuss five options for

estimating old-growth volume and implications of their use on modeling wildlife habitat

capability. We also present an approach for reducing the likelihood of overestimating

timber volume on the Tongass.

Background The key components used to define the old-growth volume strata options developed

in this paper include the TIMTYP database, the common land unit (CLU) database,

and the Tongass timber inventory. Each of these components is described below.

TIMTYP Database A land type map was created in 1978 by ESCA-Tech2 for the Tongass. The primary

objective of this work was to delineate major land types and their attributes from aerial

photographs of the Forest. These land types were mapped at a polygon level—areas

generally homogenous in character and greater than 10 acres in size. Polygons in

forested areas were assigned a single, representative set of attributes: species composition, age, stocking, volume class, and decadence rating. For example, if a 100-

acre area was generally a Sitka spruce (Picea sitchensis (Bong.) Carr) forest type in

an old-growth condition with uniform crown sizes, it could be classified as S4=5H.

This classification means that for average conditions, this polygon was predominantly

Sitka spruce (S) identified as old growth (4), was moderately stocked (=), had an

estimated volume of 20-30 thousand board feet per acre (5), and had relatively high

decadence (H). Within such a 100-acre polygon, however, openings, small stands of

different species, and lower and higher volume strata often exist. Forest-wide, there

are about 300,000 forested polygons with a mean size of about 60 acres. These land

type map data were entered into the Tongass Geographic Information System (GIS)

as the TIMTYP database in 1988-89.

1 The Tongass Timber Reform Act (Sec. 301 [c] [3]) requires

that the harvest of high-volume old growth (volume classes 6

and 7) will not be at an accelerated rate. The act requires

that the proportion of harvest in volume classes 6 and 7

will not exceed the proportion of volume of these classes

currently represented in a contiguous management area.

2 The use of trade or firm names in this publication is for

reader information and does not imply endorsement by

the U.S. Department of Agriculture of any product or service.

24
Common Land Unit

Database

The CLU database was created independently by Administrative Area (Chatham,

Ketchikan, and Stikine) and has been subject to a fairly rigorous field review. This

database contains numerous features including but not limited to landform, plant

association, and soil series. These features were mapped at a soil management

unit (SMU) scale. About 825 separate SMU types were assigned to nearly 114,000

polygons across the Forest. The SMU polygons range from less than 1 acre to nearly

900,000 acres for the Brabazon Range near Yakutat; the Forest-wide average size

of these polygons is 115 acres. In this analysis, we used slope class, soil type (hydric

or nonhydric), and average site index in the development of options D and E for estimating old-growth timber volumes.

Tongass Timber

Inventory

The most recent timber inventory of the Tongass, completed in the early 1980s,

estimated net timber volume for each Administrative Area of the Forest plus or

minus 10 percent per billion net cubic feet at a 68-percent confidence level. The

original objective of the timber inventory was not to sample stands or polygons,

but to sample the stratum to which the polygons belonged. The design provides a

reasonable estimate of the true average net volume of a particular stratum within

an Administrative Area. Because only a relatively small proportion of each polygon

was sampled, however, the level of confidence in our estimates of net volume for

a particular polygon within any stratum is poor.

The sampling design used in the Ketchikan and Stikine Administrative Areas was

different from that used in the Chatham Area. Sampling units for the Ketchikan and

Stikine Administrative Areas were 5-acre cluster plots consisting of five systematically

placed points each (USDA Forest Service 1984). Whenever plot cluster points fell

within two adjacent TIMTYP polygons, points were relocated into the polygon where

the first randomly located point was established. In the Ketchikan Area, 201 polygons

were sampled, and 139 in the Stikine Area. In the Chatham Area, the sampling unit

was a 250-acre cluster plot consisting of about 55 subplots. Point locations were

systematically established within polygons (USDA Forest Service 1982). A total of

176 polygons was sampled in the Chatham Administrative Area.

Of the 516 polygons sampled Forest-wide, 457 were within forested volume class

(VC) 4-7 polygons. Wilderness areas were excluded from this timber inventory.

The Forest inventory estimated volume for each Administrative Area by using the

plots described above and areal coverage from the volume item of the TIMTYP

database in a poststratified fashion. Using this approach, Rogers and van Hees

(1992a, 1992b, 1992c) developed timber resource statistics for each Administrative

Area of the Tongass.

Accuracy of Volume

Strata Estimates

The spatial accuracy of the volume item of the TIMTYP database was tested by Jim

Brickell (former USDA Forest Service, Northern Region, biometrician) with Stikine

and Ketchikan data from the Tongass timber inventory (Brickell 1989). Brickell found

that the inventory provides a Forest-wide and Administrative Area-wide assessment

of the TIMTYP database for each volume stratum, but it cannot be used to assess

the TIMTYP database on a polygon level. This inability arises from too few observation points within any given polygon. Brickell also found no statistical basis for

25
maintaining separate strata for VC5, VC6, and VC7, based on the timber inventory.

Volume strata means were not analyzed by Brickell for the Chatham Area because

unit volumes were not readily available. From his experience with timber inventories

of similar design in the Northern Region, Brickell opined that “results would not have

been substantially different” for the means for the Ketchikan and Stikine Administrative

Areas. Our review of these data supports his conclusions (appendix).

Options for

Estimating Timber

Volume

Five options for estimating net timber volume were identified by TLMP revision team

members in 1995. These five options are summarized in figure 1 and are described

below. We used the volume class item (volume classes 4, 5, 6, and 7) from the

TIMTYP database alone and in combination with the forest type item from the

TIMTYP database and several items from the CLU database (slope, hydric and

nonhydric soils, and site index) to redefine volume strata. Mean strata volumes and

95-percent confidence intervals are reported for all options for each Administrative

Area and the entire Tongass (i.e., all areas combined). Differences in strata means

for each option were tested by using analysis of variance (ANOVA) and the Scheffé

multiple comparison tests (α = 0.05; SAS Institute 1990). Statistics for individual

polygon volume estimates within strata are not reported. These statistics are known

to include a significant amount of added variation, primarily the result of the limited

number of inventory sample points in each polygon.

Figure 1—Descriptions and relations among options for estimating old-growth volume.

26
Option A: Volume

Classes 4, 5, 6, and 7

Option A retains the four strata used in the current draft plan revision (USDA Forest

Service 1991; fig. 1, table 1). Although there is a statistical basis for segregating VC4

from the higher strata (Brickell 1989), there is none for dividing the higher volume

strata. Adopting this option would invite the same type of criticism as received on the

draft and supplement to the draft for the TLMP revision (USDA Forest Service 1990,

1991). Although option A appears to offer an opportunity to model habitat capability

with the greatest resolution and widest range of conditions, it does not provide confidence because of a lack of statistical differences among the higher volume strata

(see appendix).

Table 1—TIMTYP option A net volume estimates, sample sizes, and

95-percent confidence intervals

Volume strata 95-percent

and area Mean volume confidence interval Sample size

Mbf/acrea Mbf/acrea Numberb

Volume class 4:

Chatham Area 19.3 ± 2.8 58

Ketchikan Area 20.4 ± 2.3 72

Stikine Area 23.9 ± 3.5 56

Forest wide 21.1 ± 1.6 186

Volume class 5:

Chatham Area 29.4 ± 5.2 29

Ketchikan Area 33.1 ± 2.8 71

Stikine Area 32.2 ± 3.5 55

Forest-wide 32.1 ± 2.0 155

Volume class 6:

Chatham Area 38.3 ± 9.5 6

Ketchikan Area 32.5 ± 6.4 23

Stikine Area 35.4 ± 13.5 8

Forest-wide 34.1 ± 4.7 37

Volume class 7:

Chatham Area 43.7 ± 25.0 2

Ketchikan Area 37.1 ± 15.5 8

Stikine Area 51.9 ± 130.9 2

Forest-wide 40.7 ± 10.5 12

a Mbf = thousand board feet, Scribner decimal C, 16-foot logs.

b 67 samples were excluded from our analysis because they had 3 or fewer

subplots (Chatham Administrative Area), had a history of partial cutting, or were

on private land.

27
Option B: Productive

Forest

Under this option, all volume strata designations (VC4-7) from TIMTYP are collapsed

into a single stratum and designated “productive forest” for each Administrative Area

(fig. 1, table 2). This option uses Area-wide mean volumes from the timber inventory

and volume class from TIMTYP. Option B does not distinguish between forest types

(VC4 and a grouping of VCs 5, 6, and 7 as depicted on TIMTYP) that the timber inventory shows have statistically significant volume differences at the Forest or Administrative Area scales (see appendix).

The single designation of productive forest provided by this option includes sites

representing an extremely broad range of conditions. Using this approach would

essentially reduce the stand-level wildlife habitat coefficient to a single value for all

sites, though the physical characteristics of each may differ considerably. For wildlife

species that are most productive in a relatively narrow range of habitat conditions,

this option does not permit a habitat capability analysis that discriminates among

suitability of stands differing widely in habitat conditions. Use of a single value to

represent stand condition, moreover, excludes specialist species requiring dense

high-volume stands or open-canopied low-volume stands. Estimates of wildlife species

that occupy a broad range of habitats will be poor because the single volume stratum

value will reflect only a small portion of the spectrum of habitat capability that exists

and changes across the Forest. For species that do best under disparate volume

conditions, but especially those that do best in lower volume conditions, this option

will result in underestimating habitat capability. Conversely, it will grossly overestimate

habitat capability for species that do best under conditions represented by the mean

volume value applied across the Forest. Significantly underestimating or overestimating capability may have implications for subsistence and viability effects analyses.

Table 2—Option B net volume estimates, sample sizes, and

95-percent confidence intervals

95-percent

Area Mean volume confidence interval Sample size

Mbf/acrea Mbf/acrea Numberb

Chatham Area 24.1 ± 2.7 95

Ketchikan Area 28.0 ± 2.0 174

Stikine Area 28.9 ± 2.5 121

Tongass-wide 27.3 ± 1.4 390

a Mbf = thousand board feet, Scribner decimal C, 16-foot logs.

b 67 samples were excluded from our analysis because they had 3 or fewer

subplots (Chatham Administrative Area), had a history of partial cutting,

or were on private land.

28
Option C: Low- and

High-Volume Strata

The low- and high-volume option segregates VC4 from a grouping of VCs 5-6-7

for each Administrative Area (fig 1., table 3). This option follows recommendations

offered by Brickell (1989) and allows us to recognize statistical distinctions among

TIMTYP volume strata shown by the timber inventory. For the Ketchikan and Stikine

Administrative Areas, Brickell found that even though there was a statistical difference between VC4 and VCs 5-6-7, there generally were no differences among VCs

5, 6, and 7. Brickell did find one significant difference at the 0.05 probability level for

VC5 and VC7 in the Stikine Area but cautioned that it would be unwise to base any

inference on only two samples for VC7 (Brickell 1989). He concluded that we could

combine VCs 5, 6, and 7 with little sacrifice to the precision of timber estimates.

Option C is an improvement over option B relative to wildlife modeling, because

it provides for two stand-level habitat conditions that allow some discrimination of

habitat suitability among stands with widely differing conditions. Option C still suffers,

however, from some of the problems identified under option B, notably excluding

evaluation of specialist species that need habitat conditions at the upper or lower

portions of the range of volumes. Although not as often or as great as under option

B, option C could result in appreciable underestimates and overestimates of habitat

capabilities for some wildlife species across portions of the Forest.

Option D: Low-,

Medium-, and

High-Volume Strata

Option D uses soils and slope information from the CLU database to explain the

variation in the low-and high-volume strata developed in option C (Brickell’s [1989]

recommendation). This option takes two basic, statistically defensible predictors of

volume from the CLU database (i.e., hydric soils and slope) and combines them with

Table 3—Option C net volume estimates, sample sizes, and 95-percent

confidence intervals

Volume strata 95-percent

and area Mean volume confidence interval Sample size

Mbf/acrea Mbf/acrea Numberb

Low-volume stratum:

Chatham Area 19.3 ± 2.8 58

Ketchikan Area 20.4 ± 2.3 72

Stikine Area 23.9 ± 3.5 56

Forest-wide 21.1 ± 1.6 186

High-volume stratum:

Chatham Area 31.6 ± 4.4 37

Ketchikan Area 33.3 ± 2.5 102

Stikine Area 33.2 ± 3.4 65

Forest-wide 33.0 ± 1.8 204

a Mbf = thousand board feet, Scribner decimal C, 16-foot logs.

b 67 samples were excluded from our analysis because they had three or fewer

subplots (Chatham Administrative Area), had a history of partial cutting, or were

on private land.

29
the two most basic, statistically defensible predictors from the TIMTYP database (fig.

1, table 4). The result is a statistically significant delineation of the forest into three

strata (i.e., low, medium, and high) for each Administrative Area (except for low vs.

medium for the Stikine Area 0.05<p<0.10). This option is the product of a study of

the applicable “regression variables” suggested by Brickell (e.g., elevation, aspect,

slope percentage, site index, landform-plant association, soil type, and forest type).

The inventory plots established within a CLU polygon having hydric (≥50-percent

areal coverage of hydric soils) and poorly drained soils (as inferred by having less

than a 55-percent slope) had a statistically significant lower mean net volume than

those that did not for both the “low” VC4 and “high” VC 5-6-7 strata in option C.

Polygons in hydric, poorly drained soils often are mixed with or surrounded by

nonforested peatlands and often are ecologically different from those polygons

surrounded by upland forested areas.

Option D provides a wider range of volume conditions to evaluate habitat capability,

which could improve the resolution of effects analysis for more wildlife species. One

limitation of option D is that soils and slope information is not available for most

wilderness areas within the Tongass, which has important implications for modeling

wildlife populations.

Table 4—Option D net volume estimates, sample sizes, and 95-percent

confidence intervals

Volume strata 95-percent

and area Mean volume confidence interval Sample size

Mbf/acrea Mbf/acrea Number

b

Low-volume stratum:

Chatham Area 13.2 ± 3.2 22

Ketchikan Area 16.1 ± 2.5 39

Stikine Area 18.3 ± 5.3 16

Forest-wide 15.7 ± 1.9 77

Medium-volume stratum:

Chatham Area 23.0 ± 3.0 43

Ketchikan Area 26.2 ± 2.7 55

Stikine Area 26.0 ± 4.2 42

Forest-wide 25.1 ± 1.9 140

High-volume stratum:

Chatham Area 34.6 ± 5.6 25

Ketchikan Area 35.0 ± 2.9 80

Stikine Area 34.0 ± 3.5 61

Forest-wide 34.6 ± 2.0 166

a Mbf = thousand board feet, Scribner decimal C, 16-foot logs.

b 74 samples were excluded from our analysis: 67 samples because they had 3 or

fewer subplots (Chatham Administrative Area), had a history of partial cutting, or were

on private land; 7 samples were excluded because they did not have common land unit data.

30
Option E: Low-,

Medium-, High-, and

Very High-Volume Strata

This option uses site index from the CLU database, and volume class and forest type

information from the TIMTYP database, to subdivide the three strata in option D into

four strata: low, medium, high, and very high (fig. 1, table 5). This option is our best

effort to statistically delineate the very high volume with available Tongass GIS data.

Option E provides a statistically defensible four-strata coverage for the entire Tongass

(i.e., all Areas combined) but not for each Administrative Area. This option is less statistically defensible than option D but still has sufficient statistical merit to be considered for quantifying the very high-volume stratum at the Forest scale.

Table 5—Option E net volume estimates, sample sizes, and 95-percent

confidence intervals

Volume strata 95-percent

and area Mean volume confidence interval Sample size

Mbf/acrea Mbf/acrea Numberb

Low-volume stratum:

Chatham Area 13.2 ±3.2 22

Ketchikan Area 16.1 ±2.5 39

Stikine Area 18.3 ±5.3 16

Forest-wide 15.7 ±1.9 77

Medium-volume stratum:

Chatham Area 23.0 ±3.0 43

Ketchikan Area 26.2 ±2.7 55

Stikine Area 26.0 ±4.2 42

Forest-wide 25.1 ±1.9 140

High-volume stratum:

Chatham Area 29.0 ±9.2 8

Ketchikan Area 32.4 ±3.4 47

Stikine Area 30.6 ±4.4 38

Forest-wide 31.4 ±2.5 93

Very high-volume stratum:

Chatham Area 37.2 ±7.3 17

Ketchikan Area 39.6 ±5.3 29

Stikine Area 39.6 ±5.3 23

Forest-wide 39.0 ±3.2 69

a Mbf = thousand board feet, Scribner decimal C, 16-foot logs.

b 78 samples were excluded from our analysis: 67 samples because they had 3

or fewer subplots (Chatham Administrative Area), had a history of partial cutting,

or were on private land; 7 samples because they did not have common land unit

data; and 4 samples because they did not have site index data.

31
An Approach for

Reducing the

Likelihood of

Overestimating

Timber Volume

A basic tenet of the forest planning process is that resources are to be managed

sustainably (16 U.S.C. § 531, Multiple-Use Sustained-Yield Act of 1960). In estimating resource abundance, one usually overestimates or underestimates the

availability of a given resource. If resources were uniformly distributed spatially,

an across-the-area mean probably would not result in the continued underuse or

overuse of a resource. In southeast Alaska, though, where the forest is clearly

distributed in a spatially heterogeneous fashion, an Area-wide averaging approach

will not prevent the possibility of resource overuse in certain segments of the

landscape.

It seems prudent that if one wishes to manage resources sustainably, then one

needs to prevent overestimating the abundance of resources under management.

This approach is especially critical when one recognizes that the management of

a keystone resource (fundamental component of an ecosystem, for example) has

significant implications for numerous resources across the Forest (wildlife, for

example).

Using the mean of a normal sampling distribution of the sample means for a population will, by definition, overestimate the true mean 50 percent of the time. Alternatively, one can reduce the probability of overestimating the true mean by using an

estimate of the mean that is less than the mean of the sampling distribution. A conventional approach to characterizing the availability of a resource is to define the

population with a mean and a range of values that are inclusive within a specified

probability of occurrence within that population for a given sample size. This range of

values is typically referred to as a “confidence interval.” The confidence interval

represents a range of values between which there is a given probability (95 percent,

for example) of correctly estimating the true population mean. For example, the lower

limit of a confidence interval provides a 5-percent chance of overestimating the true

population mean and a 95-percent chance of underestimating the true population

mean. Using a lower confidence interval value is one refinement that reduces the

likelihood of overestimating the timber resource.

Key Results Use of the timber volume item of the TIMTYP database in the TLMP revision is limited

by the resolution and quality of information available from the timber inventory. The

timber inventory used 457 plots distributed across the Forest to estimate volume

within the Forest-wide strata identified on a land type map. Even though these data

provided a statistical basis for discerning volume strata at the Administrative Area or

Forest scale, they did not sample enough points per polygon to estimate the volume

of individual polygons. We cannot currently use the timber inventory in a statistically

reliable fashion to evaluate the accuracy of the TIMTYP database at scales finer than

the Administrative Area (options B, C, and D) and at scales finer than the Forest

(option E). None of the options is statistically reliable at the management area, value

comparison unit (VCU), or project level. Table 6 presents several advantages and

disadvantages of using each option presented above.

32
Table 6—Advantages and disadvantages of the TIMTYP options

Options Advantages Disadvantages

Option A, forest volume

classes 4-7 Provides Forest-wide coverage Is not statistically reliable at the Forest,

Offers spatially explicit volume information Administrative Area, or finer levels

May be useful in identifying stand attributes

other than net volume (density, tree size,

for example) that are useful in describing

wildlife habitat quality

Option B, productive forest Provides a single, Area-wide volume Does not distinguish between forest types

stratum for productive forest that the timber inventory suggests are

Simplifies modeling statistically different

Statistically reliable at the Area- and Does not distinguish the less economical

Forest-wide levels land base from the rest

Excludes ability to evaluate some volumespecific species

Poorly estimates habitat capabilities for

species that do best under extremely lowor high-volume conditions

Option C, low- and highvolume strata Distinguishes among forest types that the Allows some discrimination of habitat

timber inventory indicates are statistically suitability among stands with widely

different differing conditions

Offers spatially explicit volume information Excludes our ability to evaluate some

Provides Forest-wide coverage volume-specific species

Is statistically reliable at the Area- and Could result in appreciable underestimates

Forest-wide scales and overestimates for some wildlife

species (less than option A)

Option D, low-, medium-,

and high-volume strata Provides differences among volume strata Cannot be applied in most wilderness areas

that are statistically significant at the Areaand Forest-wide levels

Offers spatially explicit volume information

Provides a wide range of volume conditions

that could improve the resolution of effects

analyses

Option E, low-, medium-,

high-, and very highvolume strata Provides differences among volume strata Cannot be applied in most wilderness areas

that are statistically significant at the Forestwide level

Offers spatially explicit volume information

Provides the widest range of volume

conditions that could improve the resolution

of effects analyses

33
References Brickell, J.E. 1989. Review of forest inventory methodology and results, Tongass

National Forest. [Place of preparation unknown]: U.S. Department of Agriculture,

Forest Service, Northern Region. Unpublished report. 28 p. On file with: Alaska

Region, 709 W. 9th Street, Juneau, AK 99801.

Rogers, G.; van Hees, W.W.S. 1992a. Timber resource statistics for the Chatham

Area of the Tongass National Forest, Alaska, 1982. Resour. Bull. PNW-RB-186.

Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Research Station. 20 p.

Rogers, G.; van Hees, W.W.S. 1992b. Timber resource statistics for the Ketchikan

Area of the Tongass National Forest, Alaska, 1985. Resour. Bull. PNW-RB-184.

Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Research Station. 18 p.

Rogers, G.; van Hees, W.W.S. 1992c. Timber resource statistics for the Stikine

Area of the Tongass National Forest, Alaska, 1984. Resour. Bull. PNW-RB-185.

Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Research Station. 19 p.

SAS Institute. 1990. SAS/STAT user’s guide. Cary, NC. 1686 p.

U.S. Department of Agriculture, Forest Service. 1982. Timber management plan

inventory handbook. Forest Service Handb. 2409.21b R10. May 7, 1982. 137 p.

U.S. Department of Agriculture, Forest Service. 1984. Timber management plan

inventory handbook. Forest Service Handb. 2409.21b R10. March 1984. 162 p.

U.S. Department of Agriculture, Forest Service. 1990. Tongass land management

plan, draft environmental impact statement. Juneau, AK: Alaska Region.

U.S. Department of Agriculture, Forest Service. 1991. Tongass land management

plan revision: supplement to the draft environmental impact statement. R-10-MB149. Juneau, AK: Alaska Region. [Irregular pagination].

U.S. District Court for the District of Alaska. 1994. The Wildlife Society, Alaska

Chapter, and others; Plaintiff, vs. Michael A. Barton, Regional Forester, Alaska

Region, United States Forest Service, and others, Defendants, and The Alaska

Forest Association, Defendant-Intervenor. Order dated April 11, 1994. No.

J93-0001-CIV (HRH).

34
Appendix

Summary of Statistical

Tests

A summary of results from statistical tests is provided below, by option, that compares polygon sample means within Administrative Areas (Chatham, Ketchikan, and

Stikine) and Tongass-wide (ANOVA, Scheffé multiple comparison, α = 0.05; SAS

Institute 1990). All tests used square root-transformed data to meet assumptions

of ANOVA.

1. Option A—Tests for differences among VC 4-5-6-7 Forest-wide

H0: μ (i) = μ (j) Ha: μ (i) μ (j)

i,j = VC4, VC5, VC6, VC7

Results: The results of the tests are mixed and are tabulated below. Significant

values are in bold type.

Area (Scheffé Scheffé test statistic, by volume strata

critical value)

and volume strata VC4 VC5 VC6

Chatham Area (2.849):

VC5 3.978

VC6 3.861 1.675

VC7 2.843 1.560 0.477

Ketchikan Area (2.824):

VC5 6.911

VC6 4.503 0.322

VC7 3.779 0.677 0.804

Stikine Area (2.837):

VC5 3.608

VC6 2.358 0.545

VC7 2.788 1.836 1.410

Tongass-wide (2.808):

VC5 8.840

VC6 6.137 0.783

VC7 5.262 2.021 1.392

2. Option B—No test was made because there is only one volume stratum

3. Option C—Test for difference between low- (VC4) and high- (VC5-6-7) volume

strata

H0: μ Low = μ High Ha: μ Low μ High

Results: Rejected the null hypothesis. There is a difference between low- and

high-volume strata for each Administrative Area and Tongass-wide. Significant

values are in bold type.

≠

≠

35
Area (Scheffé Scheffé test statistic, by volume strata

critical value)

and volume strata VC4

Chatham Area (1.986):

VC5-6-7 5.098

Ketchikan Area (1.974):

VC5-6-7 7.555

Stikine Area (1.980):

VC5-6-7 4.092

Tongass-wide (1.966):

VC5-6-7 10.060

4. Option D—Tests for differences between low- and medium-, and medium-, and

high-volume strata

H0: μ (i) = μ (j) Ha: μ (i) μ (j)

i,j = low, medium, high

Results: Rejected the null hypothesis for each Administrative Area and Tongasswide. There is a significant difference for each Administrative Area except for low

vs. medium in the Stikine Area (0.05<p<0.10). Significant values are in bold type.

Scheffé test statistic,

Area (Scheffé by volume strata

critical value)

and volume strata Low Medium

Chatham Area (2.491):

Medium 3.524

High 6.940 4.398

Ketchikan Area (2.469):

Medium 4.342

High 8.731 4.546

Stikine Area (2.480):

Medium 1.984

High 4.263 3.064

Tongass-wide (2.457):

Medium 5.701

High 11.779 7.104

≠

36
5. Option E—Tests for differences between low-, medium-, high-, and very

high-volume strata

H0: μ (i) = μ (j) Ha: μ (i) μ (j)

i,j = low, medium, high, very high

Results: Results were mixed. There is a significant difference between the high and

very high strata at the Tongass-wide scale only. Significant values are in bold type.

Scheffé test statistic,

Area (Scheffé by volume strata

critical value)

and volume strata Low Medium High

Chatham Area (2.852):

Medium 4.378

High 4.180 1.501

Very high 7.509 4.458 1.631

Ketchikan Area (2.824):

Medium 5.348

High 7.939 3.022

Very high 9.421 5.188 2.500

Stikine Area (2.837)

Medium 2.269

High 3.603 1.818

Very high 5.423 4.237 2.619

Tongass-wide (2.808):

Medium 6.974

High 10.164 4.310

Very high 13.179 8.126 3.894

≠

37
Tentative Suitability of Forested

Wetlands for Timber Production:

A Resource Assessment

Kent R. Julin and Chris T. Meade

Issue Definition The Alaska Region had to decide whether forested wetlands on Kaikli, Karheen,

Kitkun, and Maybeso soil series would be retained in the tentatively suitable land

base in the revision of the Tongass land management plan. The issue of retaining

forested wetlands on organic soils within the tentatively suitable land base at the

Tongass National Forest was raised by Forest Service soil scientists (Brock and

Kissinger 1995). They recommend that forested wetlands be reclassified as unsuitable forest land owing to a lack of adequate response information (Forest

Service Handbook [FSH] 2409.13). This paper examines the issue of tentative

suitability as it relates to forested wetlands on the four soil series listed above.

Background Forest Service regulations include criteria for identifying lands “not suitable” for

timber production (36 Code of Federal Regulations [CFR] §219.14[a]) and lands

“not appropriate” for timber production (36 CFR §219.14[c]). The Forest Service

Handbook provides additional guidance on how to determine which lands are

“tentatively suitable” fortimber production (FSH 2409.13-21) and which lands are

“not appropriate” for timber production (FSH 2409.13-23).

Forest Service regulations also require that “forest planning shall provide for

adoption of measures, as directed in applicable Executive orders, to minimize

risk of flood loss, to restore and preserve flood plain values, and to protect

wetlands” (36 CFR §219.23[f]). Executive Order 11990: Protection of Wetlands

(1977) requires that:

each agency shall provide leadership and shall take action to minimize

the destruction, loss or degradation of wetlands, and to preserve and

enhance the natural and beneficial values of wetlands in carrying out

the agency’s responsibilities for...managing...Federal lands....

Analysis of

Information

In our analysis, we reviewed background information on forested wetlands in

southeast Alaska and discussed the issue with Forest Service Regional and

Area silviculturists and soil scientists. Our analysis emphasized the questions

posed in the tentatively suitable forest land classification process (i.e., 36 CFR

§219.14[a] and FSH 2409.13-21). The six questions used in this decision

process for determining tentative suitability are addressed below relative to

forested wetlands.

38
Is the Land Forested?1 Forested land is defined in 36 CFR §219.3 as “land at least 10 percent occupied by

trees of any size or formerly having had such tree cover and not currently developed

for non-forest use. Lands developed for non-forest use include areas for crops, improved pasture, residential, or administrative areas, improved roads of any width, and

adjoining road clearing and powerline clearing of any width.” Because all soil series

in question can support forested plant associations (DeMeo and Loggy 1989), they

could be carried forward to the next step in the tentatively suitable process.

Is the Land Withdrawn

From Timber

Production?2

Forested wetlands as a whole are not withdrawn from timber production under the

current Tongass land management plan. However, forested wetlands within wilderness areas, national monuments, or other areas where timber harvest is prohibited

by law (e.g., Tongass Timber Reform Act [1990] riparian buffers and land use designation II [LUD II] areas) are by definition unsuitable for timber production. The

remaining forested wetlands within the Tongass National Forest are not withdrawn

from timber production, and thus could be carried forward to the next step in the

tentatively suitable process.

Is the Land Capable of

Producing Crops of

Industrial Wood?3

Lands capable of producing crops of industrial wood are those that support tree

species currently used or likely to be used by the timber industry within the next

10 years. The soil series under consideration support commercial tree species

including western hemlock (Tsuga heterophylla (Raf.) Sarg.), Sitka spruce (Picea

sitchensis (Bong.) Carr.), western redcedar (Thuja plicata Donn ex D. Don), and

Alaska-cedar (Chamaecyparis nootkatensis (D. Don) Spach). Because these lands

are capable of producing industrial wood crops, they could be carried forward to the

next step in the tentatively suitable process.

Is Irreversible Damage

Likely to Occur?4 Forest land is considered physically suitable if technology is available to ensure

that timber production will not result in irreversible resource damage to soils,

productivity, or watershed conditions. Research concerning damage to forested

wetlands in southeast Alaska resulting from timber harvest is limited. Kissinger

and others (1979) report severely stunted young-growth stands on Kaikli, Karheen,

and Maybeso soils in the south Kupreanof area. Seven to nine years after stand initiation, they observed reduced height and diameter growth rates, which they attributed

to nitrogen deficiency. It was not established whether this pattern of decline was a

result of timber harvest or whether it represented the normal growth patterns of

young-growth stands on wetland soils.

1 36 CFR 219.14[a][1] and FSH 2409.13-21.1.

2 36 CFR §219.14[a][4] and FSH 2409.13-21.2.

3 FSH 2409.12-21.3.

4 36 CFR 219.14[a][2] and FSH 2409.13-21.41.

39
Weetman and others (1989) describe young-growth plantations of Sitka spruce that

occurred after clearcutting and burning5 on deep humic podzols on Vancouver

Island, British Columbia. They attributed the sharp decline in height growth and

needle chlorosis observed in 8- to 14-year-old plantations to nitrogen and phosphorus deficiencies and a suspected allelopathic effect from salal (Gaultheria

shallon Pursh) colonizing the site after harvest.

Silviculturists at the Tongass National Forest have observed no short-term

damage to forested wetlands harvested during the past 20 years. They have

observed adequate restocking of forested wetland sites, which indicates that

short-term damage has not occurred (Zaborske 1995).

There is no compelling scientific basis for concluding that harvest from forested

wetlands will or will not result in irreversible damage to soil productivity or watershed conditions. Fertilization could be used to restore soil productivity, should it be

demonstrated that timber harvest on forested wetlands negatively affects soil fertility.

More information clearly is needed on the impacts to the functions and values of

forested wetlands following timber management activities (i.e., road building,

harvesting, thinning) to adequately address the question of irreversible damange.

Can the Area Be

Restocked Within 5

Years?6

The purpose of this step in the tentatively suitable process is to “determine whether

or not there is a reasonable assurance that it is possible to restock the remaining

forest lands adequately within five years of final harvest, based on existing technology and knowledge” (FSH 2409.13-21.42). “Adequate restocking means that the

cut area will contain the minimum number, size, distribution, and species composition

of regeneration as specified in Regional silvicultural guides for each forest type”

(36 CFR §219.27[c][3]).

The Alaska Regional silvicultural guide (FSH 2409.17-2.4) specifies the density

(300 trees per acre), height (4 inches), and distribution goals (60 percent stocked in

natural stands; 80 percent stocked in planted stands) in its restocking assessment.

We believe that the Regional silvicultural guide could be improved by adding species

composition to its assessment.

In the Alaska Region, natural regeneration accounts for over 93 percent of the

reforestation program and is almost always successful. Many of these areas are

certified as restocked in the third year. Those areas not certified as restocked after

3 years are closely monitored and, if necessary, planted to bring stocking levels to

standards. Planting accounts for the remaining portion of the reforestation program

and almost always is successful. For areas receiving final harvest in 1988 or 1989,

almost 96 percent have been certified as restocked through either natural regeneration or planting. The remaining areas were planted within the past 2 to 3 years and

will not be eligible for certification until 5 years after planting occurs (Zaborske 1995).

5 Burning of slash after clearcutting is an uncommon practice

in the Tongass National Forest (Zaborske 1995).

6 36 CFR 219.14[a][3] and FSH 2409.13-21.42.

40
Evidence suggests that regeneration on the soils in question technically meets

the criteria for adequate restocking as specified in the Regional silvicultural guide.

Therefore, forest land on these wetland soils could be carried forward in the tentatively suitable process.

Is Adequate Response

Information Available?7 The tentatively suitable determination process also evaluates whether adequate

growth response information is available. Response information can include existing

research and professional experience necessary to project responses to timber management practices.

Information concerning the productivity of forested wetlands in southeast Alaska is

extremely limited for defining forested wetland yield. These data (table 1), collected

primarily from stands growing on Maybeso soils, were used to construct site index

curves for Sitka spruce. There is no information concerning growth on the Kitkun

soils or for growth of western redcedar or Alaska-cedar at these sites. Current

research, as summarized in table 1, although not statistically conclusive, suggests

that Maybeso, Kaikli, and Karheen soils are capable of producing Sitka spruce and

western hemlock within a moderate growth range.

Stephens and others (1968a) obtained site index values of 38 and 41 for Sitka spruce

on Maybeso soils. In a subsequent study, Stephens and others (1968b) found that

Maybeso and Kaikli soils had an average 100-year site index of 73 for Sitka spruce

(estimated 50-year site index of 45) and that the Karheen soils studied had an average 100-year site index of 100 (estimated 50-year site index of 65).

Babik (1983) described soil profiles, measured tree heights, and estimated tree ages

in a mixed western hemlock-Sitka spruce stand on Brownson Island in the Stikine

Area. From this information, 50-year site indexes of 43 for western hemlock and 57

for Sitka spruce were estimated.

7 FSH 2409.13-21.5.

Table 1—Site indices for several forested wetland soil series in

southeast Alaskaa

50-year

Soil series site index Species Reference

Feet

Maybeso 38 Sitka spruce Stephens and others 1968a

Maybeso 41 Sitka spruce Stephens and others 1968a

Maybeso 57 Sitka spruce Babik 1983

Maybeso 43 Western hemlock Babik 1983

Maybeso/Kaikli 45 Sitka spruce Stephens and others 1968b

Kaikli 48 Sitka spruce Farr 1984

Karheen 65 Sitka spruce Stephens and others 1968b

a Yield tables for young-growth western hemlock-Sitka spruce stands provide a basis for relating

site index and yield. Stands with a site index of 43 (50-year index age) produce 53 cubic feet per

acre per year at the culmination of mean annual increment (Taylor 1934).

41
A site index and height growth curve study by Farr (1984) includes one plot with

wetland soils. The Young Bay plot was on Kaikli soils and showed a 50-year site

index of 48 for Sitka spruce.

The cooperative stand density study8 included two plots with organic wetland soils.

One plot was at Falls Creek (no. 2830) on Maybeso Series and showed 50-year site

indexes of 81 and 88 for Sitka spruce and western hemlock, respectively. This plot

produced 840 cubic feet in the 19 years after stand initiation (44 cubic feet per year).

Another plot was at Saks Cove (no. 1700) on Karheen Series and exhibited 50-year

site indexes of 101 and 87 for Sitka spruce and western hemlock, respectively. This

plot produced 10,624 cubic feet in the 58 years after stand initiation (183 cubic feet/

year). These volumes may not be representative for the Karheen series owing to the

presence of other soil series on the plot.

Stunted young-growth stands on Kaikli, Karheen, and Maybeso soils in the south

Kupreanof area were investigated by Kissinger and others (1979) as described previously. Data presented in this report were insufficient to calculate site index values

or yield. Kissinger and others (1979) noted, however, that height and diameter growth

patterns for trees on these soils were comparatively lower than those for adjacent

upland stands.

Because of a paucity of research and documented experience, we conclude that

there is inadequate information for responses to timber management practices on

the soils in question.

Key Findings The Forest Service Handbook provides six criteria for determining whether land

is tentatively suitable for timber production. We reviewed these criteria with consideration of forested wetlands on Kaikli, Karheen, Kitkun, and Maybeso soil series

in the Tongass National Forest. Forested wetlands on the soil series in question

satisfy four of these criteria: this land (1) is forested, (2) is not withdrawn from timber production, (3) is capable of producing crops of industrial wood, and (4) can be

restocked within 5 years of final harvest. Two criteria clearly are not satisfied: (1) it

is unknown whether irreversible damage is likely to occur to soils, productivity, or

watershed conditions; and (2) there is inadequate response information to project

the effects of timber management practices on this land. A current study on growth

and yield of forested wetlands will address the response question. Additional work

may be necessary to address fully the question of irreversible damage. Documenting

the impacts to the functions and values of forested wetlands resulting from timber

harvest could be accomplished as part of the monitoring program of the Forest.

8 Data on file with: Pacific Northwest Research Station,

2770 Sherwood Lane, Suite 2A, Juneau, AK 99801.

42
References Babik, N. 1983. Soil-woodland correlation field data sheet, small island south of

Brownson Island. On file with: Tongass Land Management Plan Office, 8465

Old Dairy Road, Juneau, AK 99801.

Brock, T.; Kissinger, E. 1995. Questioning the suitability of volume class 4 forests

that occur on organic soils. Position paper. Juneau, AK: U.S. Department of

Agriculture. On file with: Tongass Land Management Plan Office, 8465 Old

Dairy Road, Juneau, AK 99801.

DeMeo, T.E.; Loggy, W.D. 1989. Identification, classification, and delineation of

wetlands using soils and vegetation data. Ketchikan, AK: U.S. Department of

Agriculture, Forest Service. On file with: Tongass Land Management Plan Office,

8465 Old Dairy Road, Juneau, AK 99801.

Farr, W.A. 1984. Site index and height growth curves for unmanaged even-aged

stands of western hemlock and Sitka spruce in southeast Alaska. Res. Pap.

PNW-326. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific

Northwest Forest and Range Experiment Station. 26 p.

Kissinger, E.; Kaija, K.; Skrine, G. 1979. Preliminary report, investigation of stunted

second growth stands, south Kupreanof area. Juneau, AK: U.S. Department of

Agriculture, Forest Service, Alaska Region. 11 p.

Stephens, F.R.; Gass, C.R.; Billings, R.F.F. 1968a. Provisional site index curves

based on tallest Sitka spruce and bh age. Rep. 1, R-10 Soil-Site Index Administrative Study. Juneau, AK: U.S. Department of Agriculture, Forest Service,

Alaska Region. 11 p.

Stephens, F.R.; Gass, C.R.; Billings, R.F.F. 1968b. Soils and site index in

southeast Alaska. Rep. 2, Soil-Site Index, Administrative Study. Juneau, AK:

U.S. Department of Agriculture, Forest Service, Alaska Region. 17 p.

Taylor, R.F. 1934. Yield of second-growth western hemlock-Sitka spruce stands

in southeastern Alaska. Tech. Bull. 412. Juneau, AK: U.S. Department of

Agriculture, Forest Service, Alaska Region. 29 p.

Weetman, G.F.; Fournier, R.; Baker, J.; Schnorbus-Panozzo, E.; Germain, A.

1989. Foliar analysis and response of fertilized chlorotic Sitka spruce plantations

on salal-dominated cedar-hemlock cutovers on Vancouver Island. Canadian

Journal of Forest Research. 19: 1501-1511.

Zaborske, Richard. 1995. Personal communication. Regional silviculturist, Alaska

Region, Box 21628, Juneau, AK 99802-1628.

43
Controlling Stability Characteristics

of Steep Terrain With Discussion

of Needed Standardization for Mass

Movement Hazard Indexing:

A Resource Assessment

Douglas N. Swanston

Issue Definition This paper presents an overview of factors controlling soil stability on steep terrain in

southeast Alaska. A Forest-wide standardized approach for stability hazard assessment in the Tongass National Forest (Tongass) also is presented.

Background

Failure Type

A debris avalanche, defined as the failure of a finite mass of water-charged

overburden material along a more-or-less planar or flat surface (Swanston 1974b), is

the dominant failure type on steep forested slopes in southeast Alaska. Once failure

occurs, the initial mass rapidly breaks apart owing to internal stresses; because

of the high water content, it is transformed into a mixture of water, soil, rock, and

organic debris that rapidly moves downslope. This type of secondary failure is

called a debris flow.

Failure Mode These landslides primarily occur at a shallow depth (1 to 3 feet) and develop entirely

in the soil overburden. Few involve bedrock failure or deep rotational failures in silts

and clays. Failure generally occurs along a well-defined plane marking the boundary

between soil overburden and either bedrock or compact glacial till (fig. 1).

Once failure occurs, movement is predominantly translational (all particles of the

soil mass move with the same velocity along parallel paths) with displacement

along and parallel to the failure surface. Because of the shallow nature of the soil

overburden, the gradient of the potential failure surface is approximately equal to

the slope gradient.

Soil Overburden

Characteristics

The soil overburden texture is characteristically gravely sandy silt or gravely silty sand

(MH-ML; SM-GM according to the Unified Classification System [U.S. Army Corps

of Engineers 1953]); less commonly the texture may be sandy gravel (Schroeder

and Swanston 1987). Soil overburden with these textural characteristics generally

has low liquid limits and low plasticity, indicating little or no cohesion. The dominant

steep-slope soil types in southeast Alaska are no exception (Schroeder and Swanston

1987). For the most part, these index properties (called Atterberg Limits) are of little

value for judging strength characteristics. Plasticity is so low (except for marine silts)

as to have little influence on cohesion. Organic content has no significant effect on

cohesive strength. The organic content is highly variable, however, and may exceed

30 percent locally owing to downward migration of organic particles into the mineral

soil zone. This occurrence could substantially increase plasticity and apparent

cohesion at some sites.

44
These soil overburden materials compress readily during shear, thereby reflecting

low densities (80 to 100 pounds per square foot) and high void ratios (Wu and

others 1979, Wu and Swanston 1980). The materials are commonly assumed to

be cohesionless for general analysis purposes, although some cohesion usually is

present. This becomes significant in determining the resistance to failure on very

steep sites where the angle of internal friction of the material exceeds the slope

gradient.

Potentially unstable slope gradients range from 60 to 72 percent. Engineering

analyses of soils in southeast Alaska (Schroeder and Swanston 1987) indicate

that slopes must be considered highly unstable when they exceed 72 percent.

Based on statistical analysis of grouped samples of dominant soil types on steep

terrain in southeast Alaska, the mean effective angle of internal friction for till and

colluvial soils is 72 percent (Schroeder and Swanston 1987). This mean drops to

70 percent for residual soils. The mean values may be used for general assessment of soil behavior (i.e., for Forest planning purposes). The fifth percentile values

for these soil groups is 51 percent for colluvium and till soils and 65 percent for

residual soils. The fifth percentile is the value such that only 5 percent of the values

of a normally distributed sample population are less than this. The fifth percentile

values are comparative and should be used in sensitive situations where the consequences of occasional failures are undesirable.

Figure 1—Debris avalanche-debris flow in Marten Arm, northern shore of Bradfield Canal,

southeast Alaska.

45
Typical of coarse-grained materials in general, these soils have a high hydraulic conductivity or permeability (Terzaghi and Peck 1960). Unsaturated flow rate is about

1.3 inches per hour, and saturated flow rate is about 0.25 inch per hour (Vandre and

Swanston 1977). Infiltration rates are rapid and capable of transmitting low-intensity

precipitation virtually without surface runoff occurring. During high-intensity storms,

input of rainfall may reach or exceed the infiltration rate, and a steady state of transmission of infiltrating water downward to an impermeable surface occurs. Because

of the lower saturated flow rate for these materials, water ponds above this impermeable surface and a temporary water table develop. If precipitation intensities are

great enough and rainfall duration is long enough, the water table will reach the

surface and runoff will occur.

Slope microtopography is an important factor in determining where and how often

landslides occur (Swanston 1974b, Swanston and Howes 1991). Linear depressions

or “hollows” (also called zero-order basins) initially produced by differential weathering

and erosion along fractures and joints in bedrock, and by prehistoric landslide activity,

are widespread on steep slopes of southeast Alaska (Swanston 1974b, Sidle and

others 1985). Over geologic time periods, these hollows fail cyclically. Once failure

occurs, they refill with soil and debris from local slumping and with sliding from the

sides of the hollows. Soils in these areas commonly display well-developed horizons

and support mature forest growth, suggesting a minimum of 300- to 500-year land

slide intervals in individual hollows. Such sites are natural foci of convergent ground

water flows, where the accumulated soil and debris become locally saturated and

form temporary water tables that initiate landslides. These features are the points of

origin of most of the landslides in southeast Alaska (Swanston 1967). The degree of

soil development (indicating relative age) within the hollows, the thickness of soil and

debris infill, and the spacing of the hollows on steep slopes are strong indicators of

landslide hazard. In general, land slide hazard increases with increases in deposit

thickness and age and landslide spacing (number per unit area). Water table depth in

these overburden materials depends on factors such as, but not limited to:

• Antecedent moisture conditions—how much rain has fallen and how much water

is present in the overburden at the time of a high-intensity storm.

• Hydraulic conductivity along the soil-rock interface.

• Storm intensity—for overburden materials characteristic of southeast Alaska,

a rainfall intensity of 6 inches per 24 hours is usually adequate to completely

saturate the overburden and thus develop a temporary water table with a

piezometric surface at or near the ground surface (Schroeder and Swanston

1987, Sidle and Swanston 1982, Swanston 1967).

Failure Mechanics Because of the coarse soil textures, shallow overburden, and planar nature of the

underlying bedrock or till surfaces on which sliding occurs, these debris avalanches

and debris flows can be analyzed from a practical engineering standpoint by using

the infinite slope model (Hough 1957, Swanston 1970, Terzaghi 1950, Terzaghi and

Peck 1960, Wu 1966). The infinite slope model considers forces acting on a block of

material of unit thickness and width situated on a slope of infinite length. The forces

developed in the overburden material upslope of the block and tending to push the

block downslope are countered by equal and opposite forces tending to maintain the

block in situ. The same is true for lateral forces acting against the block.

46
The only forces that need to be considered in the analysis are illustrated in figure 2:

• Weight of the soil block (W).

• Component of the weight directed upslope as frictional resistance along the failure

surface ( ).

• Component of the weight directed downslope as gravitational stress ( ).

• Cohesion (C), or the ability of individual soil particles to stick together because of

weak electrical bonding of clay components or capillary tension during dry periods.

• Root stabilization (R) developed in the overburden by (a) anchoring of roots

through the shallow overburden and into the underlying till, and (b) reinforcing

and binding of the overburden materials laterally.

The relative stability of a site can be approximated by considering the factor of safety

against failure (FS) developed along the potential failure surface (Swanston 1970).

This factor is expressed as the ratio of the strength (S) or forces tending to resist

failure and the shear stress (T) or forces tending to cause failure. Weight of the soil

block is the product of the unit weight of the soil (γ), and soil depth (D). Cohesion (C),

root strength effects (R), and the frictional resistance developed along the sliding

surface (Wcosβtanφ) are forces within the overburden that help constitute its strength

(S) or resistance to failure. Gravitational stress (Wsinβ) and any external dynamic

stresses developed due to cyclical loading caused by machinery, earthquakes, or

blasting (W/gα) constitute forces tending to cause failure:

Wcos tan β φ

Wsinβ

Figure 2—Infinite slope model.

47
(1)

where:

= gradient of the failure surface,

= angle of internal friction,

g = acceleration of gravity (32 feet per second per second), and

= peak particle acceleration generated by vibrations of materials.

The stability of materials on steep forested slopes is strongly influenced by the development of a temporary water table and by slope gradient. Saturation of materials and

development of a water table produce a vertical force called pore-water pressure (μ)

that reduces the effective weight (and thus frictional resistance) of the material acting

along the failure surface by creating a buoyancy effect. If slope gradient approaches

or exceeds the angle of internal friction of the material, then stability of a site is decreased to a critical level. In the absence of any water table, gradient alone controls

slope stability. This situation is illustrated by reformulation of the factor of safety equation and consideration of conditions typical of steep, unstable slopes in southeast

Alaska:

(2)

Cohesion and root strength effects are small in these coarse granular materials but

significant on extremely steep, unstable sites; cohesion is generally less than 206

pounds per square foot (Schroeder and Swanston 1987). Root strength is generally

less than 144 pounds per square foot (Wu and others 1979). If these forces are

ignored, then the factor of safety equation can be rewritten as:

(3)

Under natural undisturbed conditions, the factor of safety and therefore the stability

of a site, is controlled by the angle of internal friction, gradient of the slope, and the

presence or absence of a temporary water table (Swanston 1970).

General Stability

Situation of Forested

Slopes in Southeast

Alaska

Slopes with gradients at or near the angle of internal friction of the overburden

materials are in a delicately balanced state relative to stability. They are highly

susceptible to any activity that might upset the balance of forces acting to maintain

the overburden materials in place. Factors affecting their stability include:

• Destruction or reduction of stabilizing root system effects through a windthrow, fire,

or management activity.

• Destruction or reduction of cohesion by collapse of soil structure or saturation of

overburden materials.

• Removal of the weight of trees. Although rare, this removal may be a stabilizing

factor on steep slopes underlain by deep, fine-grained residual soils and elevated

glaciomarine silts and glacial lake clays. This stability factor is generally not

significant in southeast Alaska, but may be important on individual sites.

FS = S

T

C+R+ Wcos tan

Wsin W / g = +

β φ

β α

β

φ

α

FS = C+R+ WW W/g

μ βφ

β α

b gcos tan

sin . +

FS = W -

Wtan

μ φ

β

b gtan

48
• Reduction in frictional resistance along the potential failure surface by:

—development of a temporary water table.

—reduction in weight of overburden.

• Increasing downslope stresses by:

—removing downslope support of the soil block.

—increasing overburden weight by saturation or surcharging.

—dynamic loading of the soil mass by earthquake or other external stresses.

Management directly influences stability condition through timber harvesting, road

construction, and quarry development. Clearcut harvesting results in degradation

of anchoring and reinforcing root systems (Sidle 1991, 1992; Sidle and Swanston

1982; Swanston 1969, 1970; Wu and others 1979; Wu and Swanston 1980; Ziemer

and Swanston 1987). It also changes the hydrologic regime through decreases in

evapotranspiration and increased water levels in the soil during the fall rainy season.

Road construction may (1) undercut slopes; (2) surcharge or load the surface by

sidecast, rock overlayment, and stockpiling waste; (3) concentrate surface and subsurface water in ditches and culverts that may discharge into unstable sites; and from

(4) cause dynamic loading of the soil mass by machinery vibration and right-of-way

blasting (Swanston 1971a, 1971b, 1974a, 1975). Quarry development may increase

surcharging from dumping of stripped materials onto unstable waste sites and from

dynamic loading of steep-slope soil surfaces from ground vibration and rock-throw

during blasting. Dynamic loading during periods of temporary water table development is important. The temporary water table couples soil and bedrock together and

transmits lateral stresses to the soil from blasting vibration (Vandre and Swanston

1977).

A Revised

Methodology for

Mass Failure

Hazard Indexing

Current Indexing

Methodology

Hazard indexing for mass failure is a qualitative measure of the expected increase

in frequency of mass failures when vegetation is cleared or the land is disturbed.

Although sufficient baseline data are not available to develop a quantitative index

of mass failure hazard, a qualitative system was developed to rate soils of the

Tongass as part of the land management plan revision process (Alexander 1987).

This mass movement index methodology is based on characteristics of identified

and mapped soil units across the Tongass and on the inherent slope, drainage,

and landform characteristics that control stability of the overburden on the slope. The

methodology, with modifications by the Chatham, Ketchikan, and Stikine Administrative Areas of the Tongass, has been applied since 1989 and is used extensively in

Forest- and project-level planning to assess risks related to the amount and method

of timber harvest. The index values also are used in the Tongass FORPLAN model

to construct soil management unit tables that identify lands with a high hazard of

landslide initiation following management activity.1

In this indexing procedure, five mass movement classes were recognized across

the Forest. These classes are listed with expected effects of disturbance in table 1.

As initially used, the susceptibility for mass failure identified by these indices was

a function of slope gradient, expressed in 15-percent increments, and by parent

material type (related to soil series) as mapped on Administrative Area soil resource

inventories and displayed in the Alaska Region Geographic Information System (GIS).

1 Information available from the Tongass land management

planning record, U.S. Department of Agriculture, Forest

Service, 8465 Old Dairy Road, Juneau, AK 99801.

49
The locations are identified by surface characteristics related to slope gradient,

vegetation cover, drainage, and soil properties measured in sample sections. These

surface characteristics and properties are also soil resource inventory (SRI) and GIS

mapping criteria.

Proposed Indexing

Methodology

With new information and analyses, a more quantitative approach to hazard indexing

was developed from identified critical slope gradients, soil (regolith) depth estimates,

soil strength criteria as defined by measured engineering properties, simple soil drainage estimates, and limiting landform characteristics (Schroeder and Swanston 1987;

Swanston 1969, 1974b; Swanston and Howes 1991; Wu and Swanston 1980). The

direct effects of soil depth are greatest in very deep cohesive soils, such as unconsolidated marine silts and glacial lake deposits of silts and clays. In such materials,

slope and failure surface gradients are low and thus mass of the potential sliding

material becomes more important. In the soil overburden typically underlying forested

slopes in southeast Alaska, depths are shallow, averaging about 3 feet or less, and

mass plays a much less important role. Such materials are coarse textured, highly

permeable, and underlain by relatively impervious substrata that inhibit or stop vertical

water movement and promote saturation and lateral drainage through the shallow

overburden. Soil strength is a function of particle size, shape, composition, and structure (Alexander and Poff 1985, Mitchell 1976, Terzaghi 1950, Terzaghi and Peck

1960). Together, these variables control porosity, permeability, intragranular friction,

and friction along various planes within the soil mass. Strength is largely determined

by intragranular friction and frictional resistance developed along the potential failure

surface that is controlled by engineering properties inherent to the soil material. The

mean and fifth percentile values of engineering properties of a limited sample of

dominant surface geologic materials in southeast Alaska (Schroeder and Swanston

1987) are displayed in table 2.

These materials also have been mapped as soil series at the broad, Forest-wide,

landscape level as part of the Tongass integrated resource inventory; as such they

are part of the Tongass GIS database. Series corresponding to dominant steep-slope

geologic material types are shown in table 3.

Table 1—Definitions of mass movement indices

developed as part of the 1987 Tongass land

management plan revision

Expected effect of disturbance on

Movement index the frequency of mass failures

Extreme Highly probable increase

High Likely increase

Moderate Moderately probable increase

Low Unlikely increase

Nil Improbable increase

50
Table 2—Estimated range of engineering properties (angle of internal friction

[ ] and unit weight [γ] for surface geologic materials in southeast Alaska

Meana 5th percentileb Meana 5th percentileb Meana

Geologic origin (γ)

––– Percent ––– ––––––– lb/ft2 – – –– – – –

Colluvium and till soils 72 51 206 0 116

Marine sediments 65 36 312 0 131

Alluvium 78 60 182 0 109

Volcanic ash 62 21 240 210 82

Residual soils 70 65 115 85 102

a Mean values should be used for general assessment of soil behavior.

b 5th percentile values should be used for conservative analysis of sensitive areas.

φ′

b g φ′ b g φ′ b g φ′ b g φ′

Table 3—Important soil resource inventory (SRI) series

by geologic origin

Soil series Geologic origin

Karta Compact glacial till (basal till)

Tokeen Residual soil derived from igneous rocks

Ulloa Residual soil derived from carbonate rocks

Wadleigh Compact glacial till (basal till)

Mitkof Colluvium and ablation glacial till

Traitors (Vixen) Residual soil high in micacious materials

derived from phyllite and schist

Tolstoi Residual soil derived from noncalcareous rocks

51
By using the existing soil series boundaries from individual maps, the Tongass GIS

database, the mean engineering properties, and measured slope gradients (table 2),

a revised and more accurate mass movement indexing methodology can be developed. At the Forest plan level, ratings made with this revised index are based on

SRI soil series criteria and mapped boundaries, mean engineering properties of soil

series obtained from the literature, and slope gradients estimated from the Tongass

GIS database. At the Area and project levels, accuracy and reliability of the indexing

system can be improved by considering several factors. These include direct sampling

and analysis of soil engineering properties, using indirect indicators of instability—

such as dissection frequency, soil drainage condition, and parent material characteristics—using more accurate mapping of soil series boundaries, and measuring slope

gradients directly. Thus, the system can be used for any Administrative Area of the

Tongass, regardless of variations in detailed soil map unit differentia, where the soil

taxonomic units, or series, are the same. Detailed soil unit differentia including variations in soil properties, and topographic conditions can be used in the rating system

to improve class definitions and hazard assessments, particularly at Administrative

Area and project levels. These include (1) variations in parent material type and

origin, which provide useful additional information on density, texture, porosity, permeability, and degree of weathering; (2) depth, local variations of which may alter estimated driving and resisting forces; (3) drainage class, which provides an indication of

local groundwater conditions; and (4) landform type, which identifies specific terrain

conditions, such as slope configuration and dissection, conducive to landslide initiation and increased frequency.

The soil material groups of the rating system are essentially those already in use,

with little modification. The soil depth classes are based on the thickness of nonorganic material (mineral soil) over an impermeable boundary such as bedrock,

compact glacial till, or fine sediments. Depths are divided into the following categories: micro—less than 7 inches; shallow—8 to 20 inches; moderately deep—21

to 40 inches; and deep—greater than 40 inches. Only the qualitative values of well,

poorly, and very poorly drained classes are used to assess soil drainage. Poorly

and very poorly drained soils on steep, unstable sites are strong indicators of rapid

temporary water table development during storm periods and increased potential

for failure.

This methodology provides a standardized base for Forest-wide stability hazard

assessment at the Administrative Area and project levels. It can be expanded and

adjusted to fit local needs, conditions, and knowledge. The primary purpose of the

protocol is to assure that the same basic data and information are collected and

used across the Forest so that effective comparisons and cross-correlations can be

done on the Tongass. The framework for this suggested methodology was developed

as part of the Alaska Region’s watershed analysis procedures to address the 1994

Amendment by Senator Ted Stevens to the Appropriations Act (Loggy and Swanston

1994) and is based on current Chatham and Ketchikan Area field procedures. The

Chatham and Ketchikan Areas have agreed to this Region-wide standardization;

the Stikine Area has tentative agreed to accept the methodology for limited field use.

The protocol has been further modified by the information presented in this paper.

52
A combination of eight quantitative and qualitative variables considered to be controlling factors in determining the stability of a soil map unit are grouped into four

mass failure hazard classes to estimate a map unit’s natural mass movement (fig. 3).

A mass failure hazard class of 1 is for a factor having a lower potential for contributing

to a mass failure; a rating of 4 indicates a factor having the highest potential for contributing to a mass failure. Each variable is weighted based on a qualitative estimate

of its degree of importance in contributing to a mass failure. Numerical ratings, multiplied by the weighting factor, yield a total rating or index for each variable. Ratings

are summed, divided by the total points possible (260) and then multiplied by 100 to

obtain the mass unit failure hazard rating. The range in ratings by class or index and

the GIS equivalents appear in table 4. The original five classes from table 1 are

reduced to four by combining high and extreme categories.

Figure 3—Form used to calculate the mass failure hazard of a map unit.

Mass failure hazard classes (MFHC) Rating

Weighting (MFHC

Criteria 1 2 3 4 factor (WF) ∋ WF)

Landform:

Slope shape Vertical Broken Convex Concave-straight 5 —

Slope length (ft) 0-300 301-700 701-1,500 >1,500 5 —

Slope gradient (percent) 5-35 36-55 56-72 >72 20 —

Drainage feature:

Drainage density

(percentage of area) 1-9 10-19 20-39 >40 10 —

Soils:

Soil drainage classa WD, MW b SPD VP, PD 10 —

Soil depth (in) >40 b 20-40 <20 5 —

Geology:

Parent material Carbonate, Noncarbonate, Compact till, Volcanic

colluvium, granitics, marine ash 5 —

alluvium glacial till sediments

Textural class Sand, gravel, Loam Silt Silty clay 5 —

fragmental

loam

Total of ratings —

Map unit mass failure hazard rating (100 ∋ total of ratings / 260) —

—

a Soil drainage classes: MW = moderately well drained; PD = poorly drained; SPD = somewhat poorly drained; VP = very poorly drained;

WD = well drained.

b No soil drainage class or depth information is available for broken slopes.

53
The reasons for and identification of factors used to assess each variable in determining mass failure hazard are documented by Swanston and Rosgen (1980),

Swanston and Howes (1991), Howes and Swanston (1991), and Schroeder and

Swanston (1987). The methodology is designed primarily for planning-level analyses

but may be modified for use at the project level if sufficient field information is available for factor assessment. The basic procedure has been well documented and

used with modifications throughout the Tongass.

The rating is based on how the soils will react at soil saturation but without water

table development and without application of major destabilizing events, such as

high-intensity storms, rockfall, windthrow, earthquakes, and human-caused disturbance. It thus reflects the natural stability (or instability) of a slope under normal or

average conditions. Other factors, such as anchoring by roots, bedrock structure,

and hollows, are important to maintaining soil and forest cover at an otherwise

unstable site. These modifying factors can and should be used to adjust index

values at the Area and project level to reflect local experience and knowledge.

For example, rating limits have been adjusted in all Areas to allow for limited

management activities on MMI4 soils that are found on historically stable land

forms or have locally variable gradients verified in the field to be below critical

levels (72 percent).

The stability hazard class ratings for mass movement listed in table 4 represent

general guidelines only. At the project level, each soil map unit should be rated

individually because various combinations (fig. 3) of landform, drainage, dissection

frequency, soils, and geology may yield ratings either above or below individual

class limits.

Table 4—Distributions of mass unit failure hazard ratings

in relation to current mass movement indices and Tongass

GIS equivalents

Mass unit Mass

failure hazard movement

rating Class index GIS equivalent

63+ High to extreme MMI4 High to extreme

50-62 Moderate MMI3 Moderate

28-49 Low MMI2 Low

0-27 None MMI1 Low

54
Descriptions of

Mass Failure

Rating Classes

Descriptions of the rating classes with their controlling and contributing variables are

provided below.

High to Extreme Map units in this class have a high to extreme risk of failure and fall into the 63+

value range of the high to extreme hazard class (table 4). Natural mass failures

in this class are often frequent and large, and there is a high risk of managementinduced failure. Standard management practices can be expected to have only

limited success, and on-the-ground assessment is necessary to determine the need

for mitigating measures. There is a moderate risk of failure even with the use of

mitigation. Some portions of the units may have a significantly lower risk of failure

due to local benching or higher risk due to cliffs and very steep slope breaks. Soils

with gradients in the 72- to 85-percent range with low levels of dissection, welldrained soils, and stable parent materials may be operable with adequate

on-the-ground verification and site-specific investigation before any management

activity is undertaken.

Characteristics of this class include:

• Moderately steep slopes (36 to 55 percent) with high levels of dissection and either

unstable parent materials or reduced soil drainage (i.e., somewhat poorly drained

or poorly drained).

• Steep slopes (55 to 72 percent) with moderate to high levels of dissection and

well-drained soils.

• Steep slopes (55 to 72 percent) with high to extreme levels of dissection,

somewhat poorly to poorly drained soils, and unstable parent materials.

• Very steep slopes (>72 percent) with moderate to high levels of dissection and

well to poorly drained soils.

• Very steep slopes (>72 percent) with evidence of prior mass wasting or snow

avalanching.

Moderate Map units in this class have a moderate risk of failure and fall into the 50-to-62 value

range of the moderate hazard class (table 4). In this class, natural mass failures are

usually small and infrequent, but there is a moderate risk of management-induced

failure. Standard and best management practices are usually successful but on-theground investigation is still recommended. Mitigating measures occasionally may be

needed. Characteristics of this class include:

• Gentle slopes (5 to 35 percent) with moderate to high dissection, poor to very

poor drainage, and unstable parent materials.

• Moderately steep (36 to 55 percent) frequently dissected slopes with stable parent

materials and somewhat poorly drained soils.

• Steep slopes (56 to 72 percent) with low levels of dissection, well-drained soils,

and stable parent materials.

55
Low Map units in this class have a very low risk of failure and fall into the 28-to-49 value

range of the low hazard class. Natural mass failures in this class usually are rare or

small. There is a low risk of management-induced failure except on unstable microsites, such as scarps, V-notches, and streambanks. Standard best management

practices that control surface disturbance and stream flows can be expected to be

highly successful without special mitigating measures. Characteristics of this class

include:

• Gentle slope gradients (5 to 35 percent), with unstable parent materials or reduced

soil drainage (somewhat poorly or poorly drained).

• Moderately steep slope gradients (36 to 55 percent) with low to moderate

dissection, well-drained soils, and stable parent materials.

References Alexander, E.B. 1987. Mass failure hazard rating, Tongass National Forest. Document dated June 23. 5 p. On file with: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Research Station, Forestry Sciences Laboratory,

2770 Sherwood Lane, Suite 2A, Juneau, AK 99801-8545.

Alexander, E.B.; Poff, R. 1985. Soil disturbance and compaction in wildland management. Earth Resour. Monog. 8. San Francisco, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. 169 p.

Hough, B.K. 1957. Basic soils engineering. New York: The Ronald Press Co. 513 p.

Howes, D.E.; Swanston, D.N. 1991. A technique for stability hazard assessment.

In: Chatwin, S.C.; Howes, D.E.; Schwab, J.W.; Swanston, D.N., eds. A guide for

management of landslide-prone terrain in the Pacific Northwest. Land Manage.

Handb. 18. Victoria, BC: British Columbia Ministry of Forests; Portland, OR: U.S.

Department of Agriculture, Forest Service, Pacific Northwest Research Station:

19-83.

Loggy, W.D.; Swanston, D.N. 1994. Mass movement hazard protocol. In: Kuehn,

M.; Aho, D.; Day, J. [and others]. Alaska Region watershed analysis team report.

Juneau, AK: U.S. Department of Agriculture, Forest Service, Alaska Region: app.

4.1.

Mitchell, J.R. 1976. Fundamentals of soil behavior. New York: Wiley. 422 p.

Schroeder, W.L.; Swanston, D.N. 1987. Application of geotechnical data to

resource planning in southeast Alaska. Gen. Tech. Rep. PNW-198. Portland,

OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research

Station. 22 p.

Sidle, R.C. 1991. A conceptual model of changes in root cohesion in response to

vegetation management. Journal of Environmental Quality. 20(1): 43-52.

Sidle, R.C. 1992. Theoretical model of the effects of timber harvesting on slope

stability. Water Resources Research 28(7): 1872-1910.

Sidle, R.C.; Pearce, A.J.; O’Loughlin, C.L. 1985. Hillslope stability and land use.

Spec. Monog. Washington, DC: American Geophysical Union. 140 p.

Sidle, R.C.; Swanston, D.N. 1982. Analysis of small debris slide in coastal Alaska.

Canadian Geotechnical Journal. 19(2): 167-174.

56
Swanston, D.N. 1967. Soil-water piezometry in a southeast Alaska landslide area.

Res. Note PNW-68. Portland, OR: U.S. Department of Agriculture, Forest Service,

Pacific Northwest Forest and Range Experiment Station. 17 p.

Swanston, D.N. 1969. Mass wasting in coastal Alaska. Res. Pap. PNW-103.

Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station. 17 p.

Swanston, D.N. 1970. Mechanics of debris avalanching in shallow till soils of

southeast Alaska. Res. Pap. PNW-103. Juneau, AK: U.S. Department of

Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment

Station. 17 p.

Swanston, D.N. 1971a. Judging impact and damage of timber harvesting to forest

soils in mountainous regions of western North America. In: Maintaining productivity

of soils. Proceedings of the 62d western forestry conference; 1971 November 30;

Portland, OR. Portland, OR: Western Forestry and Conservation Association:

14-20.

Swanston, D.N. 1971b. Principal mass movement processes influenced by logging,

road building, and fire. In: Krieger, J. ed. Proceedings of a symposium on forest

land uses and stream environment; 1970; Corvallis, OR. [Place of publication

unknown]: [publisher unknown]. 29-40.

Swanston, D.N. 1974a. Slope stability problems associated with timber harvesting

in mountainous regions of the Western United States. Gen. Tech. Rep. PNW-21.

Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Forest and Range Experiment Station. 14 p.

Swanston, D.N. 1974b. The forest ecosystem of southeast Alaska. 5: Soil mass

movement. Gen. Tech. Rep. PNW-17. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station.

22 p.

Swanston, D.N. 1975. Interpreting stability problems for the land manager. In:

Proceedings of a symposium on new requirements in forest road construction;

1974 December 9-12; [location of meeting unknown]. Vancouver, BC: University

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147-176.

Swanston, D.N.; Howes, D.E. 1991. Slope movement and processes and characteristics. In: Chatwin, S.C.; Howes, D.E.; Schwab, J.W.; Swanston, D.N., eds.

A guide for management of landslide-prone terrain in the Pacific Northwest. Land

Manage. Handb. 18. Victoria, BC: British Columbia Ministry of Forests; Portland,

OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research

Station: 1-15.

Swanston, D.N.; Rosgen, D. 1980. Chapter V: Soil mass movement. In: Lulkey,

L.A., ed. An approach to water resources evaluation of non-point silvicultural

sources (a procedural handbook). Washington, DC: U.S. Department of

Agriculture, Forest Service. [Irregular pagination].

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engineering geology. Berkeley, CA: [Geological Society of America]: 83-123.

57
Terzaghi, K.; Peck, R.B. 1960. Soil mechanics in engineering practice. New York:

John Wiley & Sons. 566 p.

U.S. Army Corps of Engineers. 1953. The unified soil classification system.

Tech. Memo. 3-357(1). Vicksburg, MS: U.S. Department of the Army, Corps

of Engineers, Waterways Experiment Station.

Vandre, B.; Swanston, D.N. 1977. A stability evaluation of debris avalanches

caused by blasting. Effects of blasting on landslides on the Tongass National

Forest. Bulletin of the Association of Engineering Geologists. 14(4): 205-223.

Wu, T.H. 1966. Soil mechanics. Boston: Allyn and Bacon. 431 p.

Wu, T.H.; McKinnell, W.P., III; Swanston, D.N. 1979. Landslides on Prince of

Wales Island, Alaska. Canadian Geotechnical Journal. 16(1): 19-33.

Wu, T.H.; Swanston, D.N. 1980. Risk of landslides in shallow soils and its relation

to clearcutting in southeastern Alaska. Forest Science. 26(3): 495-510.

Ziemer, R.R.; Swanston, D.N. 1977. Root strength changes after logging in southeast Alaska. Res. Note PNW-306. Portland, OR: U.S. Department of Agriculture,

Forest Service, Pacific Northwest Forest and Range and Experiment Station. 10 p.

Metric Equivalents When you know: Multiply by: To find:

Inches 2.54 Centimeters

Feet 0.305 Meters

Miles 1.609 Kilometers

Square miles 2.59 Square kilometers

Acres 0.405 Hectares

Cubic feet 0.028 Cubic meters

Board feet 0.007 Cubic meters

Board feet per acre 0.017 Cubic meters per hectare

Pounds 0.45 Kilograms

Pounds per square foot 47.9 Newtons per square meter

58
Julin, Kent R., comp. 1997. Assessments of wildlife viability, old-growth timber

volume estimates, forested wetlands, and slope stability. Gen. Tech. Rep.

PNW-GTR-392. Portland, OR: U.S. Department of Agriculture, Forest Service,

Pacific Northwest Research Station. 58 p. (Shaw, Charles G., III, tech. coord.;

Conservation and resource assessments for the Tongass land management

plan revision).

Resource assessments on wildlife viability, old-growth timber volume estimates,

forested wetlands, and slope stability are presented. These assessments were used in

the formulation of alternatives in the revision of the Tongass land management plan.

Keywords: Wildlife viability, timber volume, forested wetlands, slope stability, Tongass,

Alaska.

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