U.S. Department of the Interior.

U.S. Geological Survey.

Open-file Report 2005-1385

Variability in Older Forest Structure in Western Oregon.
Cover credits:

Background image and cover design—Erik Ackerson, Earth Design, Ink.

Inset images—Tom Iraci, USDA Forest Service.
Variability in Older Forest Structure 

in Western Oregon

U.S. Department of the Interior

U.S. Geological Survey

By Nathan J. Poage

U.S. Geological Survey.

Open-file Report 2005–1385
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia: 2005

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1–888–ASK–USGS

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government.

Suggested citation:

Poage, Nathan, J. 2005, Variability in Older Forest Structure in Western Oregon. 

U.S. Geological Survey, Open-file Report 2005-1385, 28 p.

Key words:

1. old-growth. 2. late-successional. 3. forest structure. 4. Douglas-fir. 5. Pseudotsuga menziesii

6. Pacific Northwest. 7. Oregon
Acknowledgments iii

Acknowledgments.

This work was initially conducted as part of a two-year (2001-2002) postdoctoral contract between the author and the USGS Forest and Rangeland 

Ecosystem Science Center (FRESC), Corvallis, Oregon. Revisions to the initial 

report were made by the author while employed by the USDA Forest Service, 

Pacific Northwest Research Station (PNW). Support for revising the initial 

report was provided as part of an interagency agreement between FRESC 

and PNW. The support of the staff at FRESC has been greatly appreciated, 

particularly that of Ruth Jacobs and George Lienkaemper. The assistance of 

USDI Bureau of Land Management (BLM) personnel at the Coos Bay, Eugene, 

Medford, Portland, Roseburg, Salem, and Tillamook offices in completing 

the work presented here was likewise invaluable. Charley Thompson, Joyce 

Watson, and John Cissel of the BLM deserve special recognition for their 

efforts. Dr. John Tappeiner (Oregon State University) and Christopher Dowling 

(USDA Forest Service) contributed much in the way of discussion and fieldwork. Finally, thanks are due to Dr. Charles Peterson and Dr. Paul Anderson of 

the PNW’s Resource Management and Productivity Program for allowing the 

author the work time necessary to complete the report revisions.
iv Variability in Older Forest Structure in Western Oregon
Contents v

Contents

Acknowledgements ..................................................................................................................................... iii

Abstract .......................................................................................................................................................... 1

Introduction ................................................................................................................................................... 1

Methods ......................................................................................................................................................... 2

Objective 1 Create the BLM LSOG conifer database ................................................................. 2

Objective 2 Compare and contrast ecoregion-level variability in LSOG forest structure .... 3

Objective 3 Characterize the spatial variability of trees and snags in 14 LSOG forests ....... 5

Results and Discussion ................................................................................................................................ 7

Objective 1 Create the BLM LSOG conifer database ................................................................. 7

Objective 2 Compare and contrast ecoregion-level variability in LSOG forest structure .... 7

Objective 3 Characterize the spatial variability of trees and snags in 14 LSOG forests ..... 13

Management implications ......................................................................................................................... 13

Literature Cited ............................................................................................................................................ 17

Appendix 1 Mean number of trees/acre by species-diameter class and ecoregion .................. 19

Appendix 2 Pair-wise differences between ecoregions in terms of mean number 

 of trees/acre, by species-diameter class ............................................................... 20

Appendix 3 Mean basal area by species-diameter class and ecoregion ..................................... 24

Appendix 4 Pair-wise differences between ecoregions in terms of mean 

 basal area, by species-diameter class .................................................................... 25

List of Figures.

1. Locations of older forest study sites .................................................................................................. 9

2. Ecoregion-level differences in older forest structure, by species-diameter class ................. 10

List of Tables.

1. Descriptions of ecoregions containing older forest study sites ................................................... 4

2. Description of transects used to characterized older forest spatial variability ......................... 6

3. Ecoregion-level differences in older forest structure, by species presence ............................. 8

4. Ecoregion-level differences in older forest structure, by species-diameter class ................. 12

5. Within-SDC (species-diameter class) spatial patterns of older forests .................................... 14

6. Between-SDC (species-diameter class) spatial patterns of older forests ................................ 15
vi Variability in Older Forest Structure in Western Oregon
Abstract

The goal of this report is to assist Federal land managers 

in developing realistic structural targets for young forests for 

which the development of late-successional and old-growth 

(LSOG) characteristics is a long-term management objective (i.e., in Late-Successional Reserves established under the 

Northwest Forest Plan). A unique LSOG structural database 

was created using complete inventories, or censuses (i.e., 

100% timber cruise records), of all conifer trees > 1 ft diameter from 586 recently harvested older forests on five Bureau 

of Land Management (BLM) districts in western Oregon. The 

average area of each of the 586 inventoried older forests, 28.1 

ac, clearly reflected the spatial scales typical of forest management units on Federal lands covered by the Northwest Forest 

Plan. All told, the LSOG database contains conifer tree census 

data for over 16,400 ac of LSOG forests. Ecoregion-level variability in LSOG forest structure was compared and contrasted 

for sites contained in the LSOG database. The spatial variability of trees and snags at 14 LSOG sites was characterized 

using structural data collected along one or more long (396-

2178 ft) belt transects at each site.

Introduction

Late-successional forest habitat is considered critical for 

old-growth dependent species such as the northern spotted 

owl (Strix occidentalis var. caurina) and the marbled murrelet 

(Brachyramphus marmoratus). Regional concerns about 1) 

the loss of critical older forest habitat due to timber harvesting within the range of the northern spotted owl and 2) the 

need to produce timber and other forest products led to the 

formal adoption of the Northwest Forest Plan in 1994 by the 

USDI Bureau of Land Management (BLM) and USDA Forest 

Service (FS) (Record of Decision 1994, Regional Ecosystem 

Office 2005). The area covered by the Northwest Forest Plan, 

1Portland Forestry Science Laboratory, PNW Research Station, USDA 

Forest Service, 620 SW Main Street, Suite 400, Portland, Oregon 97205.

Variability in Older Forest Structure in Western Oregon

By Nathan J. Poage1

approximately 24.5 million acres in western Washington, 

western Oregon, and northwestern California, falls within the 

range of the northern spotted owl (Regional Ecosystem Office 

2005). Within the 7.4 million acre network of Late-Successional Reserves (one of seven Federal land-use allocations 

designated under the Northwest Forest Plan) forest managers 

may silviculturally treat young forests if the “purpose of these 

silvicultural treatments is to be beneficial to the creation and 

maintenance of late-successional forest conditions” (FSEIS 

1994).

Creating and maintaining late-successional and oldgrowth (LSOG) forest conditions requires an operational 

description of the forest structure desired in the future 

(i.e., the structural target). In theory, tree species and size 

distributions derived from actual old-growth forests can 

provide managers with realistic and easily communicated 

structural targets for young forests where accelerating the 

development of late-successional forest characteristics is a 

management objective. In practice, however, defining realistic 

old-growth forest structural targets is challenging for at least 

three reasons.

First, LSOG structural targets should reflect the local 

variability found within regionally defined forest types. 

For example, although Douglas-fir - western hemlock 

(Pseudotsuga menziesii [Mirb.] Franco - Tsuga heterophylla

[Raf.] Sarg.) forests occur in both the Oregon Coast Range 

and Cascades, these forests exhibit a great deal of structural 

variation between the two geographic areas (Poage and 

Tappeiner 2005). Might it not be realistic to establish different structural targets for older Douglas-fir - western hemlock 

forests in the Oregon Coast Range and Cascades? Characterizing the structure of LSOG forests by ecoregion is a straightforward means of reflecting local variation in LSOG structural 

targets. Ecoregions, or ecological regions, are areas identified 

by “the patterns and the composition of biotic and abiotic 

phenomena [e.g., geology, physiography, vegetation, climate, 

soils, land use, wildlife, and hydrology] that reflect differences in ecosystem quality and integrity...” (Pater et al. 1998). 
Ecoregions are hierarchical in nature. Lower-level, finer-scale 

ecoregions are nested within higher-level, coarser-scale ecoregions. In Oregon and Washington, for example, the level IV 

Coastal Uplands (1b) ecoregion is nested with eight other level 

IV ecoregions within the coarser-scale, level III Coast Range 

(1) ecoregion. Western Oregon and Washington are divided 

into 7 level III ecoregions, whereas North America is divided 

into 15 level I ecoregions (Pater et al. 1998).

Second, LSOG structural targets should reflect appropriate scales of management. Although forest management 

units on Federal lands covered by the Northwest Forest Plan 

are typically > 25 ac, almost all studies of old-growth forests 

in the Pacific Northwest have characterized tree species and 

size structure using a limited number of small (e.g., 0.25 ac) 

plots at multiple sites or somewhat larger plots (e.g., 1.25-8.25 

ac) at one or two sites (Juday 1977, Means 1982, Spies and 

Franklin 1991, Hershey 1995, Poage 1995, Tappeiner et al. 

1997, Poage and Tappeiner 2002, Goslin 1997, Winter et al. 

2002a,b). Scaling up research findings from finer plot-level 

scales (e.g., 0.25-8.25 ac) to the coarser scales (e.g., > 25 ac) 

typical of forest management activities in the Pacific Northwest may prove misleading if only the closed-canopy portions 

of old-growth forests have been sampled using small plots 

(Poage and Tappeiner 2005).

Third, and finally, LSOG structural targets should reflect 

the spatial variability in tree species and sizes present horizontally within older forests. With few exceptions (e.g., Kuiper 

1988, Spies et al. 1990, Bradshaw and Spies 1992, Poage 

1995, Goslin 1997, Franklin et al. 2002, Zenner 2004), most 

old-growth studies in the Pacific Northwest have not described 

horizontal spatial variability in older forests. Studies that 

have characterized spatial variability indicate that trees and 

snags are not uniformly distributed in LSOG forests. Lack 

of detailed information can make it difficult for managers 

to know, for example, how often large-diameter Douglas-fir 

and small-diameter non-Douglas-fir conifers (e.g., western 

hemlock) overlap spatially at fine scales when both are found 

in the same old-growth forest. As a result, managers may face 

difficulties establishing realistic spacing guidelines for young 

forests where the development of late-successional forest 

characteristics is a management objective.

The goal of this report is to assist Federal land managers 

in developing realistic structural targets for young forests for 

which the development of LSOG characteristics is a management objective (i.e., in Late-Successional Reserves). As such, 

this report has three specific objectives which collectively 

address the above-noted challenges associated with defining 

realistic old-growth forest structural targets. Objective 1 is to 

create a BLM LSOG conifer database of the conifer tree structure of 586 LSOG forests on the Coos Bay, Eugene, Medford, 

Roseburg, and Salem BLM districts in western Oregon. This 

was done using inventory data from harvest units of recent 

BLM old-growth timber sales. Objective 2 is to compare and 

contrast ecoregion-level variability in LSOG forest structure 

for BLM lands in western Oregon. Specifically, the conifer 

components of LSOG forest structure contained the BLM 

LSOG conifer database (Objective 1) were characterized and 

compared by level III and IV ecoregions (Pater et al. 1998). 

Objective 3 is to characterize the spatial variability of trees 

and snags at 14 different LSOG sites on BLM land in western 

Oregon. This was done using structural data collected along 

one or more long (> 330 ft) belt transects at each site.

Methods

Objective 1. Create the BLM LSOG 

conifer database

The BLM LSOG conifer database was created using 

complete inventories, or censuses (i.e., 100% timber cruise 

records), of all conifer trees > 1 ft diameter at breast height (or 

dbh, measured at 4.5 ft above the ground) from 586 recently 

harvested late-successional and old-growth (LSOG) forests on 

the Coos Bay, Eugene, Medford, Roseburg, and Salem BLM 

districts of the USDI Bureau of in western Oregon. All BLM 

timber sales terminated during the period 1990-1993 on these 

five BLM districts and stored at the National Archives and 

Records Administration in Seattle, Washington, were systematically examined to identify 100% timber cruise records of 

older forests. Timber sales terminated during the period 1990-

1993 through the Tillamook office of the Salem BLM were 

not archived in Seattle but were, instead, stored in Tillamook; 

these timber sales were similarly examined at the Tillamook 

office. Each timber sale comprised one or more separate 

harvest units. These harvest units are also referred to as sites 

throughout this report.

Useable, 100% timber cruise records were identified for a 

total of 586 spatially distinct older forest sites. All 586 of these 

timber cruise records were used to construct the BLM LSOG 

conifer database. (No record was kept of the total number of 

timber cruise records examined, useable or otherwise.) To 

be considered useable, a 100% timber cruise record had to 

include:

1. a complete electronic inventory data file containing:

a. tree counts by four-inch dbh classes, sorted 

by sub-sale (each sub-sale in a timber sale 

corresponded to a unique harvest unit and 

species combination), and

b. the automated data processing (ADP) number 

used to link the electronic inventory data file 

with the archived hardcopy information (item 2), 

below;

2. archived hardcopy information, namely:

a. the list of sub-sales identifying the harvest units 

and species within each timber sale,

2 Variability in Older Forest Structure in Western Oregon
b. the timber sale contract map (i.e., the Exhibit A), 

used to identify the acreage and location (to the 

nearest quarter-quarter section) of each harvest 

unit; and

c. the timber sale summary, which contained the 

ADP number used to link the archived hardcopy 

information with the electronic inventory data file 

(item 1), above; and

3. the presence of at least one Douglas-fir tree with a dbh 

> 40 inches on each harvest unit.

The electronic inventory data files (item 1) were obtained 

from the BLM Oregon State Office in Portland, Oregon. The 

archived hardcopy information (item 2) was obtained from 

the National Archives and Records Administration in Seattle, 

Washington and the Tillamook office of the Salem BLM in 

Tillamook, Oregon.

Data extracted from the archived hardcopy information 

were entered into a Microsoft Access 2000 database. Custom 

software was developed and used to merge the Access database with the electronic inventory data files. The merged data 

were imported into SAS 9.1 (SAS Institute 2003). In SAS, the 

trees inventoried at each site were assigned to 1-foot diameter 

classes: 1-foot (1 ft < dbh < 2 ft), 2-foot (2 ft < dbh < 3 ft), 

and so forth to 9-foot and larger (dbh > 9 ft). Trees were then 

grouped by species and diameter class into species-diameter 

classes (SDCs). For example, western hemlock (WH) with 

diameters at breast height falling in the 2-foot diameter class 

(i.e., 2 ft < dbh < 3 ft) were assigned to the WH_2 speciesdiameter class (SDC). In addition to Douglas-fir and western 

hemlock, SDCs were created for the following 11 species of 

conifers: grand fir (Abies grandis (Dougl. ex D. Don) Lindl.), 

incense-cedar (Calocedrus decurrens Torr.), noble fir (Abies 

procera Rehd.), Port Orford cedar (Chamaecyparis lawsoniana (A. Murr.) Parl.), ponderosa pine (Pinus ponderosa

Laws.), Pacific silver fir (Abies amabilis (Dougl.) Forbes), 

sugar pine (Pinus lambertiana Dougl.), Sitka spruce (Picea 

sitchensis (Bong.) Carr.), white fir (Abies concolor (Gord. 

and Glendl.) Lindl. ex Hildebr.), western red cedar (Thuja 

plicata Donn), and western white pine (Pinus monticola

Dougl. ex D. Don).

Although all coniferous species present at each site 

were included in the electronic inventory data, the Coos 

Bay, Eugene, Medford, Roseburg and Salem BLM districts 

differed in terms of which (if any) of the hardwood species 

present at a given site were included in the electronic inventory data for that site. Inclusion in the electronic inventories 

of trees with dbh < 12 in and snags of all sizes was similarly 

variable among the five BLM districts in western Oregon. To 

ensure consistency across the five BLM districts, hardwood 

species, trees with dbh < 12 in, and snags were dropped from 

the merged dataset in SAS. For this reason, the BLM LSOG 

conifer database contains only data for live conifer trees with 

dbh > 12 in.

The final steps in constructing the BLM LSOG conifer 

database were:

1. calculate the number of trees/ac (TPA) and basal area 

(BA, ft2/ac) in each species-diameter class (SDC) at 

each site using SAS;

2. use the ArcView 3.3 (ESRI 2002) and ArcGIS 8.3 

(ESRI 2003) geographic information systems (GIS) to:

a. assign latitudes and longitudes in decimal degrees 

to each site based on the estimated center of each 

harvest unit,

b. create a point coverage of the sites using the 

assigned latitudes and longitudes, and 

c. assign level III and level IV ecoregions to each 

site using the point coverage of the sites and the 

ecoregion coverage (Pater et al. 1998) obtained 

from the Oregon Geospatial Data Clearinghouse 

(www.gis.state.or.us/data/alphalist.html);

4. merge the output from steps 1 and 2 with the archived 

hardcopy data for each site (previously imported from 

Access into SAS) and save the resulting data file as a 

permanent SAS dataset; and

5. export the permanent SAS dataset (step 4) to BLM_

LSOG_conifer_data.xls, the master Microsoft Excel 

2002 workbook.

Objective 2. Compare and contrast ecoregionlevel variability in LSOG forest structure

Comparisons of LSOG forest structure among ecoregions 

were made using two complimentary approaches. In the first 

approach, the species composition characteristic of each level 

IV ecoregion was determined and compared with the other 

level IV ecoregions. For each species, the proportion of sites 

containing the species was calculated for each of the level IV 

ecoregions containing 10 or more sites. A total of 10 level IV 

ecoregions met this criterion; 566 of 586 sites fell within these 

10 level IV ecoregions (Table 1). In all, 13 species proportions 

were calculated for each of these 10 level IV (i.e., a total of 

130 species proportions were calculated).

In the second approach, LSOG structural comparisons 

among ecoregions was made for each SDC combination of 

the 13 conifer species and 5 diameter classes (1 ft < dbh < 2 

ft, 2 ft < dbh < 3 ft, 3 ft < dbh < 4 ft, 4 ft < dbh < 5 ft, and dbh 

> 5 ft). The BAs were calculated for each SDC combination 

(65 total) and each level IV ecoregion containing 10 or more 

sites (10 total), for a total of 650 mean BAs. The 10 mean BAs 

(one for each level IV ecoregion) for each SDC were used to 

calculate a 99% confidence interval for the grand mean BA of 

the SDC. An SDC was considered to be significantly associated with a particular level IV ecoregion if the mean BA of the 

SDC for the level IV ecoregion was significantly larger than 

Methods 3
Level III

Ecoregion

Level IV

Ecoregion Physiography Potential Natural Vegetation

1. Coast Range 1b. Coastal Uplands

(n = 14)

Coastal headlands and upland terraces with medium to high gradient, black-water streams. Sitka spruce, western hemlock, western red cedar

1d. Volcanics

 (n = 64)

Steeply sloping mountains. High gradient, cascading streams and rivers occur and have stable summer flow. Western hemlock, western red cedar, Douglas-fir

1g. Mid-Coastal  Sedimentary

 (n = 197)

Moderately sloping, dissected mountains with medium to high gradient, sinuous streams. Western hemlock, western red cedar, Douglas-fir

1h. Southern Oregon  Coasal Mountains

 (n = 13)

Dissected mountains with high gradient, sinuous streams and rivers. This ecoregion is part of the Siskiyou Mountains.

Tanoak, Douglas-fir, western hemlock, Port Orford cedar

3. Willamette Valley 3d Valley Foothills

 (n = 30) Rolling foothills with medium gradient, sinuous streams. Oregon white oak and (drier sites), Douglas-fir (moister sites); some western red cedar

4. Cascades 4a. Western Cascades 

 Lowlands and Valleys

 (n = 53)

Westerly trending ridges and valleys with reservoirs and medium gradient rivers and streams. U-shaped, glaciated valleys in the east.

Western hemlock, western red cedar, Douglas-fir

4b. Western Cascades  Montane Highlands

 (n = 11)

Steep, glaciated, dissected mountains and ridges with high to medium gradient streams and glacial rock-basin lakes.

Pacific silver fir, western hemlock, mountain hemlock, Douglas-fir; some noble fir

4f. Umpqua Cascades

 (n = 49)

Highly dissected mountains with a few small lakes and high to medium gradient streams and rivers.

Grand fir, white fir, western hemlock, Pacific silver fir, Douglas-fir; some Shasta red fir, mountain hemlock

78. Klamath Mountains 78b. Siskiyou Foothills

 (n = 20)

Moderately sloping mountain foothills with reservoirs and perennial and intermittent streams and rivers.

Ponderosa pine, Douglas-fir, Oregon white oak, California black oak, madrone

78e. Inland Siskiyous

 (n = 115)

Highly dissected mountains with permanent and intermittent streams. A few small lakes at higher elevations.

Douglas-fir, ponderosa pine, Oregon white oak, incense cedar, grand fir

4 Variability in Older Forest Structure in Western Oregon

Table 1. Ecoregion descriptions of level IV ecoregions containing 10 or more of the late-successional and old-growth (LSOG) sites summarized in the Bureau of 

Land Management LSOG conifer database (described in the text of this report). Ecoregions, or ecological regions, are hierarchical in nature. Lower-level, finer-scale 

ecoregions are nested within higher-level, coarser-scale ecoregions. For example, North America is divided into 15 level I ecoregions; western Oregon and Washington are divided into 7 level III ecoregions. All data presented in Table 1 were quoted from the Ecoregions of Western Oregon and Washington (Pater et al. 1998).
the grand mean BA of the SDC for all 10 level IV ecoregions 

(i.e., the mean BA of the SDC for the level IV ecoregion fell 

outside of and above the 99% confidence interval for the grand 

mean BA of the SDC for all 10 level IV ecoregions).

To provide readers with a further level of detail, TPA and 

BA were summarized for each level IV ecoregion using two 

broad species groups of conifers (Douglas-fir and non-Douglas-fir) and the five diameter classes noted in the previous 

paragraph. For each combination of species group and diameter class, pair-wise comparisons of mean TPA and mean BA 

were made for all pairs of the 10 level IV ecoregions. Additional pair-wise comparisons of mean TPA and mean BA were 

made among level IV ecoregions for 1) the combination of all 

Douglas-fir diameter classes, 2) the combination of all other 

(i.e., non-Douglas-fir) conifer diameter classes, and 3) the 

combination all Douglas-fir and other conifer diameter classes. 

Whether the mean TPAs or mean BAs of two level IV ecoregions differed significantly from one another was assessed for 

each combination of species group and diameter class using 

Tukey’s Honest Significance Difference (HSD) method of 

multiple comparisons with an experiment-wise error rate of 

α = 0.05 (SAS Institute 2003, PROC GLM). Although not 

discussed further in detail, the TPA and BA summary tables 

and results of Tukey’s HSD multiple comparisons are included 

for readers as Appendices 1-4.

Objective 3. Characterize the spatial variability 

of trees and snags in 14 LSOG forests

Long belt transects were used to characterize the spatial 

variability of standing trees and snags at 14 different LSOG 

forest sites on BLM land in western Oregon. Both within- and 

between-SDC spatial patterns were described. Three sites 

were selected on each of the following BLM districts: Salem, 

Eugene, Roseburg, and Medford. Two sites were selected on 

the Coos Bay District. Sites were selected by consulting with 

BLM personnel and/or examining air photos of areas containing recent timber sales for which complete pre-sale inventories 

of trees existed. A range of species mixtures was selected, 

although all forests sampled were dominated by Douglas-fir.

One or more belt transects > 330 ft were established at 

each site (Table 2). At 13 of 14 sites with clearly sloping 

terrain, transects were oriented to run from ridge top to valley 

bottom (or vice-versa). The single transect at the one flat site 

was oriented to continuously sample the longest cross-section 

of forest possible. Although the general starting location of 

each transect was determined using air photos, the exact 

starting point of each transect was randomized.

Trees and snags > 36 in dbh were tallied along each transect using pairs of 0.10 ac, square (66 ft × 66 ft) plots located 

contiguously on the left and right sides of the transect center 

line. Data from each pair of 0.10 ac, square plots were pooled 

into a single 0.20 ac, rectangular (66 ft × 132 ft) plot extending 

66 ft along the transect line and 66 ft on either side of the transect line. (Recall that 66 ft = 1 chain and that the area defined 

by 1 chain × 1 chain = 0.10 ac.) Trees and snags < 36 in dbh 

(but with heights > 4.5 ft) were sampled using circular, 0.05 

ac plots centered at 66 ft intervals along the transect line. The 

centers of the circular, 0.05 ac plots were located at 0 ft, 66 ft, 

132 ft, and so on along each transect; the 0.20 ac, rectangular 

plots were centered at 33 ft, 99 ft, 165 ft, and so on along each 

transect. Consequently, with the exception of the circular, 0.05 

ac plots located at the start and end point of each transect, the 

two halves of each circular, 0.05 ac plot fell within two 

different (but contiguous) 0.20 ac, rectangular plots.

Trees and snags with one-half or more of their basal 

area falling within the appropriately sized plot were tallied by 

diameter class: 0 in < dbh < 3 in, 3 in < dbh < 6 in, 6 in < dbh 

< 12 in, 12 in < dbh < 24 in, 24 in < dbh < 36 in, and so forth 

by 12-inch diameter class to dbh > 96 in. The species of each 

tree and the decay class of each snag was recorded. Decay 

classes ranged from 1 (least decayed) to 5 (most decayed). 

A complete description of the characteristics associated with 

each decay class is found in Maser et al. (1988).

Prior to analysis, the tree and snags data were summarized in five general diameter classes: 0 in < dbh < 3 in, 3 in 

< dbh < 12 in, 12 in < dbh < 36 in, 36 in < dbh < 60 in, and 

dbh > 60 in. Trees were separated into three species groups: 

Douglas-fir, other conifer species, and hardwood species. 

Snags were separated into two species groups based on 

decay classes: decay classes 1-2 and decay classes 3-5. Taken 

together, the 5 tree and snag species groups and 5 diameter 

classes formed 25 species-diameter classes, or SDCs. (Note 

that SDC is defined somewhat differently for Objective 3 than 

for Objectives 1 and 2.) The number of trees/ac or snags/ac 

was calculated for each SDC for each 0.20 ac, rectangular plot 

(trees and snags > 36 in dbh) or 0.05 ac, circular plot (trees 

and snags < 36 in dbh). Because the centers of the circular, 

0.05 ac plots and 0.20 ac, rectangular plots were offset from 

each other by 33 ft along each transect, an average number 

of trees/ac or snags/ac was calculated for each SDC < 36 in 

dbh for each successive pair of 0.05 ac, circular plots. These 

average values were used for all subsequent spatial analyses 

involving SDCs originally sampled using 0.05 ac, circular 

plots.

The spatial variability of the 25 SDCs was characterized 

in terms of both within-SDC spatial patterns and betweenSDC spatial patterns. Within-SDC spatial patterns were 

described in terms of mean patch length and patch density 

(i.e., number of trees or snags/ac) of a single SDC along 

transect, as well as the mean gap length between patches of 

the same SDC. For example, casual field observations in 

LSOG forests suggest that Douglas-fir 36-60 in dbh might be 

expected to occur in patches with average lengths of 132-

264 ft and average densities of 7-13 trees/ac. Similarly, prior 

observations suggest that the average gap lengths between 

patches of Douglas-fir 36-60 in dbh might fall between 66 

and 198 ft. Patch and gap lengths along each transect were 

measured in multiples of 66 ft. Means, standard deviations, 

minima, and maxima of patch length, patch density, and gap 

Methods 5
District Site Name Transect Length (ft) Azimuth (deg) Elevation Range (ft) Township-Range-Section (1⁄4, 1⁄41⁄4)

Salem North Prairie 1 660 224 2700-2825 T15S-R07W-07 (NW, SE)

2 528 360 2650-2800 T15S-R07W-07 (NW, SE)3 594 354 2600-2800 T15S-R07W-07 (NW, SE)

Lobster South Fork 1 660 45 1200-1650 T15S-R08W-36 (NW, SE)

2 594 45 1175-1600 T15S-R08W-36 (NW, SE)

South Fork Skyline II 1 924 240 2200-2625 T11S-R03E-14 (SW, SW)

2 990 240 2250-2625 T11S-R03E-14 (SW, SW)

Eugene Johnson Creek 1 924 360 875-1200 T19S-R07W-33 (NE, SW)

2 462 90 790-900 T19S-R07W-33 (NE, SW)3 990 180 925-1335 T19S-R07W-33 (NE, SW)

Penn Again 1 1980 360 775-825 T18S-R07W-01 (SE, SW)Mill Pond 1 924 110 1550-1725 T15S-R07W-25 (NW, SE)

Roseburg Pebble Creek 1 1254 260 2625-3475 T25S-R02W-01 (NE, SE)

2 792 290 2725-3260 T25S-R02W-01 (NE, SE)

Indian Crest 1 726 240 2950-3360 T31S-R04W-29 (SW, SW)

2 594 60 3010-3300 T31S-R04W-29 (SW, SW)

Wolf Bate 1 528 165 675-725 T25S-R08W-09 (NE, NE)

2 396 345 660-675 T25S-R08W-09 (NE, NE)

Medford Hoxie 1 2178 290 4860-4880 T38S-R04E-29 (SE, SW)

Tin Cup 1 1782 210 5425-5450 T38S-R03E-33 (SE, NW)

2 396 30 5425-5500 T38S-R03E-33 (SE, NW)

Whiskey Creek 1 1320 190 2925-3285 T33S-R08W-20 (SE, SE)

Coos Bay Morgan Ridge 1 1782 120 825-925 T26S-R12W-01 (NE, SW)

Faerial Aerial 2 1914 90 980-1585 T26S-R10W-04 (NW, SE)

6 Variability in Older Forest Structure in Western Oregon

Table 2. Description of the transects used to characterize the spatial variability of trees and snags at 14 late-successional and old-growth sites located in 

five Bureau of Land Management districts in western Oregon. Township-Range-Section (1⁄4, 1⁄41⁄4) contains the legal description of the quarter-quarter (1⁄41⁄4) 

section within which the majority of each transect was located.
length were calculated for each SDC using data pooled from 

all sites where the SDC occurred.

Between-SDC spatial patterns were characterized in 

terms of the degree of spatial overlap occurring between 

two SDCs along each 66 ft of transect length. Specifically, 

the proportion of times SDC 1 overlapped with SDC 2 was 

calculated using data pooled from all sites where both SDC 1 

and SDC 2 were present. For example, when both Douglas-fir 

36-60 in dbh (SDC 1) and other (non-Douglas-fir) conifers 

12-36 in dbh (SDC 2) occur in the same LSOG forest, it might 

be expected that the larger Douglas-fir (SDC 1) will overlap 

spatially one-half of the time with the smaller, other conifers 

(SDC 2). A total of 25 × 24 = 600 between-SDC spatial patterns were characterized for the 25 SDCs.

Results and Discussion

Objective 1. Create the BLM LSOG 

conifer database

The BLM LSOG conifer database created contains 

estimates of the number of trees/ac (TPA) and basal area 

(BA, ft2/ac) for 13 tree species and 9 diameter classes at 

586 late-successional and old-growth (LSOG) sites on BLM 

lands in western Oregon. The combination of 13 species and 

9 diameter classes represents 117 species-diameter classes 

(SDCs). The following are also included in the database for 

each of the 586 sites: BLM district, timber sale and unit, sale 

year, unit acreage, legal coordinates (i.e., nearest township, 

range, section, quarter section, and quarter-quarter section) 

and geographic coordinates (i.e., longitude and latitude in 

decimal degrees) of the estimated unit center, and the level 

III and IV ecoregions within which the majority of the unit 

fell. As of the date of publication of this report, the BLM 

LSOG conifer database may be downloaded from the USGS 

Forest and Rangeland Ecosystem Science Center website 

(http://fresc.usgs.gov/ArcIMS/Website/lsog).

The BLM LSOG conifer database is absolutely unique 

for three reasons. First, the database contains structural data 

for a particularly large number—586—of LSOG forests 

inventoried over a wide geographic area (Figure 1). Second, 

the structural data—the number of trees/ac and basal area in 

different species and diameter classes—are based on complete 

censuses of all conifer trees > 1 ft diameter at breast height 

found at each of the 586 inventoried older forests. Third, the 

average area of each of the 586 inventoried older forests, 28.1 

ac, clearly reflects the spatial scales typical of forest management units on Federal lands covered by the Northwest Forest 

Plan. All told, the BLM LSOG conifer database contains conifer tree census data for a staggering 16,470 ac, or 25.7 mi2

, of 

late-successional and old-growth forests on five BLM districts 

in western Oregon. As such, the BLM LSOG conifer database 

represents one of the largest collections of detailed data ever 

assembled on older forest structure.

Objective 2. Compare and contrast ecoregionlevel variability in LSOG forest structure

The presence and absence of species identified coarse 

ecoregion-level differences in LSOG forest structure. Certain 

species were relatively consistent among the level III and 

level IV ecoregions, whereas other species exhibited a high 

degree of variability among ecoregions. For example, western 

hemlock (WH) was present at > 0.50 of all sites in the level 

III Coast Range (1), Willamette Valley (3), and Cascades 

(4) ecoregions (Table 3). Similarly, six out of eight level IV 

ecoregions in these three level III ecoregions had western red 

cedar (WRC) present at > 0.50 of sites. In contrast, WH and 

WRC were far less common at sites in the level III Klamath Mountains (78) ecoregion. Indeed, WH and WRC were 

entirely absent at sites in the level IV Siskiyou Foothills (78b) 

ecoregion.

Viewing species differences by diameter class (i.e., by 

SDC) and density (e.g., BA) in each SDC highlighted more 

subtle structural differences among ecoregions. For example, 

WH and WRC occurred in both the Coastal Uplands (1b) and 

Western Cascades Montane Highlands (4b) level IV ecoregions (Table 3). Clear differences in the densities of WH and 

WRC existed between the two ecoregions in terms of diameter 

classes, however. The highest mean density of WRC observed 

in each of the five diameter classes occurred in the Coastal 

Uplands (1b), whereas the highest mean densities of WH all 

occurred in the Western Cascades Montane Highlands (4b) 

(Figure 2, Table 4).

The following narrative descriptions of LSOG forest 

structure by level IV ecoregion were drawn from the data 

summaries in Table 3, Figure 2, and Table 4. The Coastal 

Uplands (1b) were characterized by WRC in all diameter 

classes (as noted above), the largest Douglas-fir (DF), and 

mid-sized Sitka spruce (SS). DF and SS were also characteristic of the Coastal Volcanics (1d) ecoregion, but for different 

diameter classes (DF 1-3 ft, SS 1-3 ft, and SS > 5 ft) than for 

the Coastal Uplands (1b). The densities of WH and WRC were 

considerably lower in the Coastal Volcanics (1d) ecoregion 

than in the Coastal Uplands (1b).

In contrast to the Coastal Uplands (1b) and Coastal 

Volcanics (1d), SS was almost entirely absent from the 

Mid-Coastal Sedimentary (1g) and Southern Oregon Coastal 

Mountains (1h). The Mid-Coastal Sedimentary (1g) and 

Southern Oregon Coastal Mountains (1h) were the only level 

IV ecoregions with sites containing Port Orford Cedar (POC). 

POC was present at a higher proportion of the Southern 

Oregon Coastal Mountains (1h) sites than of the Mid-Coastal 

Sedimentary (1g) sites. Grand fir (GF) was present in both the 

Mid-Coastal Sedimentary (1g) and Southern Oregon Coastal 

Mountains (1h) ecoregions, but occurred more frequently and 

with higher mean densities at sites in the Southern Oregon 

Results and Discussion 7
Level III

Ecoregion

Level IV

Ecoregion DF GF IC NF POC PP PSF SP SS WF WH WRC WWP

1. Coast Range 1b. Coastal Uplands

(n = 14) 1.00 . . . . . . . 0.36 . 1.00 1.00 .

1d. Volcanics

 (n = 64) 1.00 0.03 . . . . . . 0.20 . 0.90 0.48 .

1g. Mid-Coastal  Sedimentary

 (n = 197)

1.00 0.35 0.07 . 0.29 . . 0.01 0.01 0.01 0.90 0.73 .

1h. Southern Oregon  Coasal Mountains

 (n = 13)

1.00 0.85 . . 0.77 . . . . . 0.69 0.39 .

3. Willamette

Valley

3d Valley Foothills

 (n = 30) 1.00 0.67 0.70 . . . . . . . 0.50 0.53 .

4. Cascades 4a. Western Cascades 

 Lowlands and Valleys

 (n = 53)

1.00 0.26 0.15 0.08 . . 0.02 0.04 . . 0.96 0.72 0.08

4b. Western Cascades  Montane Highlands

 (n = 11)

1.00 . . 0.46 . . 0.46 . . . 1.00 0.27 0.09

4f. Umpqua Cascades

 (n = 49) 1.00 0.41 0.86 . . . . 0.90 . . 0.94 0.76 0.22

78. Klamath

Mountains

78b. Siskiyou Foothills

 (n = 20) 1.00 . 0.65 . . 0.65 . 0.60 . 0.35 . . .

78e. Inland Siskiyous

 (n = 115) 1.00 0.05 0.62 . . 0.37 . 0.70 . 0.39 0.30 0.02 .

8 Variability in Older Forest Structure in Western Oregon

Table 3. Ecoregion-level differences in late-successional and old-growth (LSOG) forest structure in terms of species presence. The degree to which 

a species is characteristic of a level IV ecoregion is indicated by the proportion of LSOG sites containing the species within the level IV ecoregion. For example, the proportion of sites in the level IV Coastal Uplands (1b) ecoregion containing Sitka spruce (column SS) was 0.36. Proportions > 0.50 appear in 

bold; proportions < 0.25 are italicized. The coded column headings indicate the common names for the following species: DF = Douglas-fir, GF = grand fir, IC = incense-cedar, NF = noble fir, POC = Port Orford cedar, PP = ponderosa pine, PSF = Pacific silver fir, SP = sugar pine, SS = Sitka spruce, WH = white fir, WH = western hemlock, WRC = western red cedar, and WWP = western white pine (see text for scientific names). See Table 1 for descriptions of the level IV ecoregions.
1b. Coastal Uplands 

(n = 14)

1d. Volcanics

(n = 64)

1g. Mid-Coastal 

(n = 197)

Locations of All Sites within Oregon

 (n = 586)

1h. Southern Oregon 

(n = 13)

3d. Valley Foothills

(n = 30)

4a. Western Cascades 

(n = 53)

4b. Western Cascades 

(n = 11)

4f. Umpqua Cascades 

(n = 49)

78b. Siskiyou Foothills

(n = 20) 

78e. Inland Siskiyous

(n = 115)

Sedimentary Coastal Mountains

Lowlands and Valleys Montane Highlands

Results and Discussion 9 Figure 1. Locations of late-successional and old-growth (LSOG) sites summarized in the Bureau of Land Management LSOG conifer database (described in the text of this report). Sites are shown by level IV ecoregion. The level IV ecoregions shown contain ≥ 10 LSOG sites. The numbers in parentheses below each level IV ecoregion name indicate the number of LSOG sites within that level IV ecoregion.
Diameter 1-2 ft Diameter 2-3 ft Diameter 3-4 ft Diameter 4-5 ft Diameter ≥5 ft

Douglas-Fir (DF)

Grand-Fir (GF)

Incense-Cedar (IC)

Port Orford-Cedar (POC)

Noble Fir (NF)

Ponderosa Pine (PP)

Pacific Silver Fir (PSF)

Douglas-Fir (DF)

Grand-Fir (GF)

Incense-Cedar (IC)

Port Orford-Cedar (POC)

Noble Fir (NF)

Ponderosa Pine (PP)

1d

1d 3d

1h 3d

1h 4f

3d 4f 4f 4f

4f 4f

4f

4b

4b

4b

4b

4b

4b

4b

1g

1g

1h 1h

1h

1h

1h

1h

78b

78e

78b

78e 78b

78e 78b

78b

78b 4f 3d

1b

3d

Pacific Silver Fir (PSF)

1b 1d 1g 1h 3d 4a 4b 4f 78b 78e 1b 1d 1g 1h 3d 4a 4b 4f 78b 78e 1b 1d 1g 1h 3d 4a 4b 4f 78b 78e 1b 1d 1g 1h 3d 4a 4b 4f 78b 78e 1b 1d 1g 1h 3d 4a 4b 4f 78b 78e

100

0

5

0

5

0

10

0

2

0

10

0

Level IV Ecoregion

Basal Area (ft2 /ac)

5

0

10 Variability in Older Forest Structure in Western Oregon

Figure 2. Species-diameter classes (SDCs) characteristic of level IV ecoregions. (Figure 2 should be viewed with Table 4.) Mean basal areas (BA, ft2/ac) are shown 

for all combinations of level IV ecoregion and SDC. For each SDC, the dashed lines indicate the 99% confidence interval for the grand mean BA of the SDC for all 10 level IV ecoregions. An SDC was considered to be significantly associated with a particular level IV ecoregion if the mean BA of the SDC for the level IV ecoregion fell 

outside of and above the 99% confidence interval for the grand mean BA of the SDC for all 10 level IV ecoregions. For example, Douglas-fir in the 2-3 ft diameter class 

was characteristic of both the Volcanics (1d) and Valley Foothills (3d) level IV ecoregions. See Table 1 for descriptions of the level IV ecoregions.
Diameter 1-2 ft Diameter 2-3 ft Diameter 3-4 ft Diameter 4-5 ft

Sugar Pine (SP)

Sitka Spruce (SS)

White Fir (WF)

Western Red Cedar (WRC)

Western Helmlock (WH)

Western White Pine (WWP)

10

0

2

0

5

0

100

0

1

0

Level IV Ecoregion

Basal Area (ft

2 /ac)

1b 1d 1g 1h 3d 4a 4b 4f 78b 78e 1b 1d 1g 1h 3d 4a 4b 4f 78b 78e 1b 1d 1g 1h 3d 4a 4b 4f 78b 78e 1b 1d 1g 1h 3d 4a 4b 4f 78b 78e 1b 1d 1g 1h 3d 4a 4b 4f 78b 78e

10

0

Sugar Pine (SP)

Sitka Spruce (SS)

White Fir (WF)

Western Red Cedar (WRC)

Western Helmlock (WH)

Western White Pine (WWP)

Coast Range Cascades

Willamette

Valley

Kalamath

Mountains

Level III Ecoregion

4f 78b

1d

78b 78e

4b

4a

1b

4f

4f

78b78e

1b 1d

78e

4b

1b

4f

4f

1b

78b78e

4b

1b

4f

4f

1b

78b

4b

1b

4f

1d

4b

1b

Diameter ≥5 ft

Results and Discussion 11 Figure 2.—continued
Level III

Ecoregion

Level IV

Ecoregion DF GF IC NF POC PP PSF SP SS WF WH WRC WWP

1. Coast Range 11b. Coastal Uplands

(n = 14) ____5 . . . . . . . _234_ . . 12345 .

1d. Volcanics

 (n = 64) 12___ . . . . . . . 12__5 . . . .

1g. Mid-Coastal  Sedimentary

 (n = 197)

. . . . 1___5 . . . . . . . .

1h. Southern Oregon  Coasal Mountains

 (n = 13)

. 123__ . . 12345 . . . . . . . .

3. Willamette

Valley

3d Valley Foothills

 (n = 30) _2___ 1____ 1__45 . . . . . . . . . .

4. Cascades

4a. Western Cascades  Lowlands and Valleys

 (n = 53)

. . . . . . . . . . . 1____ .

4b. Western Cascades  Montane Highlands

 (n = 11)

___4_ . . 1234_ . . 12___ . . . 12345 . .

4f. Umpqua Cascades

 (n = 49) . _2_45 12345 . . . . 12345 . . . . 123__

78. Klamath

Mountains

78b. Siskiyou Foothills

 (n = 20) . . __3__ . . 12345 . 12___ . 1234_ . . .

78e. Inland Siskiyous

 (n = 115) . . . . . 123__ . _2___ . 123__ . . .

12 Variability in Older Forest Structure in Western Oregon

Table 4. Species-diameter classes (SDCs) characteristic of level IV ecoregions. (Table 4 should be viewed with Figure 2.) SDCs characteristic of a level IV ecoregion are 

indicated by species (columns DF-WWP) and diameter class (1 = 1-2 ft dbh, 2 = 2-3 ft dbh, 3 = 3-4 ft dbh, 4 = 4-5 ft dbh, 5 = > 5 ft dbh; dbh = diameter at breast height, measured 

at 4.5 ft above the ground). For example, the level IV Coastal Uplands (1b) ecoregion was characterized by Douglas-fir (column DF) in the 5 ft diameter class (____5), Sitka spruce (column SS) in the 2-4 ft diameter classes (_234_), and western red cedar (column WRC) in all diameter classes (12345). An SDC was considered to be significantly associated with a particular level IV ecoregion if the mean basal area (BA, ft2/ac) of the SDC for the level IV ecoregion fell outside of and above the 99% confidence interval for 

the grand mean BA of the SDC for all 10 level IV ecoregions. The coded column headings indicate the common names for the following species: DF = Douglas-fir, GF = grand 

fir, IC = incense-cedar, NF = noble fir, POC = Port Orford cedar, PP = ponderosa pine, PSF = Pacific silver fir, SP = sugar pine, SS = Sitka spruce, WH = white fir, WH = western hemlock, WRC = western red cedar, and WWP = western white pine (see text for scientific names). See Table 1 for descriptions of the level IV ecoregions.
Coastal Mountains (1h). GF was also characteristic of sites in 

the Willamette Valley Foothills (3d). The Willamette Valley 

Foothills (3d) ecoregion was additionally characterized by DF 

(2-3 ft) and incense-cedar (IC, 1-2 ft and > 4 ft).

The three level IV Cascade (4) ecoregions were more 

different from one another than the level IV ecoregions of the 

Coast Range (1) or Klamath Mountains (78). Although 9 of 

the 13 conifer species represented in the BLM LSOG conifer 

database occurred at sites in the Western Cascades Lowlands 

and Valleys (4a), 5 of these 9 species occurred at 0.15 or fewer 

of the Western Cascades Lowlands and Valleys (4a) sites. (A 

similar pattern of high species diversity within an ecoregion 

and low species consistency across sites was observed for 

the Mid-Coastal Sedimentary (1g) ecoregion, above.) Consequently, only small WRC was characteristic of the Western 

Cascades Lowlands and Valleys (4a) ecoregion. The Western 

Cascades Montane Highlands (4b), in contrast, were characterized by WH in all diameter classes (as noted above), noble 

fir (NF, 1-4 ft), and Pacific silver fir (PSF, 1-2 ft). The SDCs 

characterizing the Umpqua Cascades (4f) were GF (2 ft and 

> 4 ft), IC (all diameter classes), sugar pine (SP, all diameter 

classes), and western white pine (WWP, 1-3 ft).

The species characteristic of the Umpqua Cascades (4f) 

were more similar to the species characteristic of the two level 

IV ecoregions of the Klamath Mountains (78) than the species 

characteristic of the other two level IV Cascades (4) ecoregions. SP was characteristic of the Umpqua Cascades (4f), 

the Siskiyou Foothills (78b), and the Inland Siskiyous (78e), 

and IC characterized both the Umpqua Cascades (4f) and the 

Siskiyou Foothills (78b). Two other species—ponderosa pine 

(PP) and white fir (WF)—were almost entirely confined to 

sites in the Klamath Mountains (78).

Objective 3. Characterize the spatial variability 

of trees and snags in 14 LSOG forests

The spatial distribution of trees and snags was not uniform at the 14 older forest transect sites in western Oregon. 

Both within-SDC spatial patterns and between-SDC spatial 

patterns were highly variable. The mean within-SDC patch 

length and mean within-SDC patch density (TPA) of individual species groups generally decreased with increasing 

diameter class (Table 5). For example, the mean patch length 

of Douglas-fir decreased from 377 ft for the 0-3 in diameter 

class to 126 ft for the > 60 in diameter class. Similarly, the 

mean density of Douglas-fir decreased from 43 TPA for the 

0-3 in diameter class to 7 TPA for the > 60 in diameter class.

The general trends observed for within-SDC spatial 

patterns are most likely reflections of the normal processes of 

tree mortality and snag production and decay within stands. 

As the trees in a patch increase in size, self-thinning reduces 

patch density and—by creating gaps within a patch—can 

divide the original patch into two smaller ones. Similarly, 

tree growth and mortality lead to fewer but larger snags in a 

patch. Decay also decreases the patch density of snags and 

can lead to the formation of gaps within patches of snags. The 

formation of gaps within patches appears somewhat random, 

however. Clear patterns for mean gap length between adjacent 

patches of the same SDC were not as apparent for within-SDC 

patch length and density (Table 5). For example, the mean gap 

length between adjacent patches of Douglas-fir > 60 in (273 

ft) was larger than that for Douglas-fir 36-60 in (133 ft), but 

was smaller than that for Douglas-fir 12-36 in (335 ft).

Between-SDC spatial patterns were varied at the scale 

examined (i.e., 66 ft of transect length). Not surprisingly, 

more common SDCs occurred less frequently with less 

common SDCs than vice versa (Table 6). For example, other 

(i.e., non-Douglas-fir) conifers 0-3 in were far more common 

than Douglas-fir > 60 in. The more common other conifers 

0-3 in overlapped spatially with the less common Douglas-fir 

> 60 in only 0.29 of the time. In contrast, the probability of 

Douglas-fir > 60 in co-occurring spatially with other conifers 

0-3 in was 0.75. Decay class 3-5 snags 0-3 in always occurred 

with Douglas-fir and other conifers 3-36 in, but never with 

hardwoods.

Management implications

An estimated $600,000-$1,200,000 worth of late-successional and old-growth (LSOG) structural data are summarized in the BLM LSOG conifer database (assuming a cost of 

$1,000-$2,000 to inventory each of the 586 sites). Although 

these data were collected as part of the BLM’s timber sale 

program, they can prove extremely useful in setting long-term 

structural goals for young stand where accelerating the development of LSOG structural characteristics is a management 

objective. Managers can, for example, use the BLM LSOG 

conifer database to identify LSOG sites that are (were) located 

close to a young stand they intend to manipulate silviculturally and then use the SDC data from these LSOG sites to help 

define an LSOG structural target for the young stand. The 

BLM LSOG conifer database also can be used to establish 

more regional LSOG structural goals for young forests 

(e.g., by ecoregion, as described above under Objective 2).

The average area inventoried at each of the 586 sites in 

the BLM LSOG conifer database was 28.1 ac. Consequently, 

LSOG structural targets derived from the BLM LSOG conifer 

database will accurately reflect the scales typical of forest 

management units on Federal lands in the Pacific Northwest 

(e.g., > 25 ac). Combining the data in the BLM LSOG conifer 

database with the within-SDC and between-SDC spatial data 

(Objective 3) will enable managers to define more realistic 

LSOG structural targets. This is particularly true if managers 

are permitted to define LSOG structural goals at the 10- to 

25-acre scale rather than establishing structural targets that 

must be met on each and every acre. Consider, for example, 

young stands in the level IV Coastal Uplands (1b) ecoregion 

for which long-term LSOG structural goals are being defined 

(e.g., Figure 2). For these stands, an LSOG basal area target 

Management implications 13
Patch Length (feet) Patch Density (number / acre) Gap Length (feet)

Species-Diameter Class Mean S.D. n Min Max Mean S.D. n Min Max Mean S.D. n Min Max

Douglas-fir 0-3 in 377 332 17 66 1320 43 37 17 10 128 358 364 19 66 1518

3-12 in 340 335 26 66 1320 35 47 26 10 243 401 429 28 66 1650

12-36 in 266 306 36 66 1320 25 23 36 10 118 335 313 37 66 151836-60 in 194 193 76 66 792 11 6 76 5 30 133 93 69 66 462

≥ 60 in 126 79 51 66 330 7 3 51 5 15 273 261 64 66 1188

Other Conifers 0-3 in 416 340 40 66 1584 93 193 40 10 1170 207 176 35 66 660

3-12 in 514 532 34 66 2178 47 38 34 10 156 256 257 25 66 858

12-36 in 468 469 36 66 2178 40 29 36 10 110 221 238 26 66 85836-60 in 145 107 57 66 594 8 4 57 5 25 215 241 58 66 990

≥ 60 in 66 0 9 66 66 6 2 9 5 10 424 341 12 66 1254

Hardwoods 0-3 in 206 196 24 66 924 35 50 24 10 250 416 334 26 66 1386

3-12 in 222 188 33 66 990 27 29 33 10 153 303 177 34 66 594

12-36 in 210 137 34 66 594 20 15 34 10 87 300 243 35 66 125436-60 in 74 23 8 66 132 6 2 8 5 10 310 194 10 66 594

≥ 60 in 99 47 2 66 132 5 0 2 5 5 875 359 4 396 1254

Snags, decay 1-2 0-3 in 222 270 22 66 1320 33 31 22 10 111 387 415 31 66 1584

3-12 in 244 239 37 66 1320 20 16 37 10 90 304 320 41 66 1584

12-36 in 177 114 40 66 660 14 7 40 10 40 353 291 45 66 132036-60 in 100 55 47 66 264 6 2 47 5 13 263 240 62 66 1122

≥ 60 in 66 0 9 66 66 6 2 9 5 10 579 464 13 66 1782

Snags, decay 3-5 0-3 in 132 0 1 132 132 10 0 1 10 10 638 550 3 198 1254

3-12 in 143 38 12 132 264 13 9 12 10 40 452 318 27 66 1518

12-36 in 155 49 20 66 264 16 8 20 10 40 387 357 35 66 158436-60 in 95 69 50 66 396 6 2 50 5 13 304 267 63 66 1056

≥ 60 in 66 0 4 66 66 5 0 4 5 5 469 205 9 132 726

14 Variability in Older Forest Structure in Western Oregon

Table 5. Within-SDC (species-diameter class) spatial patterns of trees and snags at 14 late-successional and old-growth (LSOG) sites in western Oregon. A complete 

description of the characteristics associated with each snag decay class is found in Maser et al. (1988).
Douglas-fir Other Conifers Hardwoods

Species-Diameter Class 0-3 in 3-12 in 12-36 in 36-60 in ≥ 60 in 0-3 in 3-12 in 12-36 in 36-60 in ≥ 60 in 0-3 in 3-12 in 12-36 in 36-60 in ≥ 60 in

Douglas-fir 0-3 in - 0.92 0.86 0.65 0.10 0.56 0.45 0.46 0.24 . 0.62 0.74 0.63 . .

3-12 in 0.76 - 0.87 0.63 0.16 0.58 0.57 0.61 0.28 0 0.57 0.64 0.57 0.33 0

12-36 in 0.72 0.83 - 0.66 0.17 0.61 0.58 0.60 0.28 0.17 0.52 0.61 0.54 0.17 0.1736-60 in 0.47 0.45 0.45 - 0.28 0.67 0.74 0.76 0.32 0.06 0.32 0.42 0.39 0.17 0.04

≥ 60 in 0.25 0.26 0.31 0.64 - 0.75 0.80 0.81 0.31 0.05 0.24 0.33 0.31 0.20 0.04

Other Conifers 0-3 in 0.43 0.38 0.38 0.60 0.29 - 0.88 0.85 0.41 0.11 0.29 0.39 0.38 0.14 0

3-12 in 0.34 0.35 0.34 0.62 0.29 0.84 - 0.95 0.44 0.08 0.23 0.32 0.34 0.12 0.03

12-36 in 0.31 0.34 0.33 0.62 0.31 0.83 0.98 - 0.44 0.05 0.22 0.31 0.34 0.13 0.0336-60 in 0.38 0.36 0.30 0.46 0.22 0.75 0.82 0.80 - 0.18 0.20 0.24 0.27 0.15 0.04

≥ 60 in . 0 0.40 0.22 0.22 0.78 0.56 0.33 0.78 - 0 0.22 0.22 0.25 0.13

Hardwoods 0-3 in 0.79 0.77 0.76 0.64 0.20 0.63 0.47 0.45 0.24 0 - 0.75 0.63 0.50 0

3-12 in 0.77 0.65 0.68 0.64 0.25 0.62 0.49 0.49 0.19 0.08 0.56 - 0.85 0.14 0.14

12-36 in 0.72 0.58 0.61 0.61 0.25 0.61 0.54 0.55 0.22 0.07 0.49 0.87 - 0.10 0.2036-60 in . 0.25 0.25 0.44 0.56 0.56 0.44 0.44 0.44 0.22 0.25 0.22 0.11 - 0.22

≥ 60 in . 0 0.50 0.33 0.33 0 0.33 0.33 0.33 0.33 0 0.67 0.67 0.67 -

Snags, decay 1-2 0-3 in 0.73 0.67 0.63 0.65 0.28 0.77 0.77 0.74 0.36 0 0.55 0.47 0.36 0 0

3-12 in 0.53 0.56 0.59 0.64 0.24 0.66 0.72 0.76 0.36 0 0.34 0.43 0.41 0 0

12-36 in 0.46 0.45 0.50 0.64 0.23 0.68 0.74 0.81 0.34 0.05 0.27 0.41 0.44 0.08 036-60 in 0.33 0.31 0.30 0.61 0.27 0.79 0.85 0.84 0.42 0.09 0.27 0.39 0.28 0.09 0

≥ 60 in 0.33 0.22 0.44 0.44 0.22 0.89 1.00 0.89 0.33 0 0.17 0.33 0.33 0 0

Snags, decay 3-5 0-3 in 0.50 1.00 1.00 1.00 0 1.00 1.00 1.00 0 . 0 0 0 . .

3-12 in 0.40 0.35 0.50 0.62 0.15 0.69 0.88 0.88 0.44 0 0.14 0.31 0.25 0 0

12-36 in 0.45 0.37 0.34 0.74 0.21 0.70 0.83 0.88 0.42 0 0.14 0.34 0.22 0 036-60 in 0.65 0.34 0.37 0.60 0.32 0.72 0.85 0.82 0.54 0.11 0.31 0.39 0.39 0.21 0

≥ 60 in 0 0.25 0.25 0.50 0.25 1.00 1.00 1.00 0.67 0 0.33 0.50 0.50 0 0

Management implications 15 Table 6. Between-SDC (species-diameter class) spatial patterns of trees and snags at 14 late-successional and old-growth (LSOG) sites in western Oregon. The proportion of times SDC 1 (column 1) overlapped spatially with SDC 2 (columns 2-4 and 6-7) was calculated using data pooled from all sites where both SDC 1 and SDC 2 were present. For example, the proportion of times Douglas-fir in the 0-3 in diameter class (SDC 1) overlapped spatially with hardwoods in the 3-12 in diameter class (SDC 2) was 0.74. Proportions > 0.50 appear in bold; proportions < 0.25 are italicized. A complete description of the characteristics associated with each snag decay class is found in Maser et al. (1988). -
Snags, decay 1-2 Snags, decay 3-5

Species-Diameter Class 0-3 in 3-12 in 12-36 in 36-60 in > 60 in 0-3 in 3-12 in 12-36 in 36-60 in > 60 in

Douglas-fir 0-3 in 0.54 0.70 0.33 0.15 0.05 0.08 0.08 0.14 0.15 0

3-12 in 0.48 0.70 0.34 0.14 0.06 0.09 0.09 0.16 0.13 0.11

12-36 in 0.42 0.66 0.36 0.15 0.11 0.07 0.15 0.17 0.16 0.0636-60 in 0.30 0.44 0.32 0.21 0.07 0.07 0.12 0.22 0.19 0.05

> 60 in 0.27 0.36 0.27 0.25 0.06 0 0.09 0.19 0.24 0.04

Other Conifers 0-3 in 0.31 0.39 0.30 0.26 0.08 0.11 0.12 0.19 0.21 0.07

3-12 in 0.28 0.39 0.31 0.27 0.08 0.11 0.15 0.20 0.23 0.07

12-36 in 0.28 0.39 0.33 0.28 0.07 0.13 0.15 0.20 0.23 0.0836-60 in 0.28 0.33 0.26 0.25 0.06 0 0.12 0.15 0.28 0.09

> 60 in 0 0 0.11 0.13 0 . 0 0 0.33 0

Hardwoods 0-3 in 0.58 0.65 0.23 0.17 0.13 0 0.05 0.10 0.20 0.17

3-12 in 0.36 0.56 0.27 0.19 0.10 0 0.07 0.18 0.19 0.13

12-36 in 0.27 0.54 0.29 0.16 0.08 0 0.06 0.12 0.19 0.1336-60 in 0 0 0.11 0.11 0 . 0 0 0.33 0

> 60 in 0 0 0 0 0 . 0 0 0 0

Snags, decay 1-2 0-3 in - 0.73 0.46 0.18 0.04 0.33 0 0.13 0.14 0

3-12 in 0.44 - 0.65 0.21 0.11 0.04 0.22 0.28 0.16 0.05

12-36 in 0.37 0.85 - 0.23 0.09 0 0.27 0.28 0.13 036-60 in 0.23 0.37 0.31 - 0.04 0 0.12 0.18 0.21 0

> 60 in 0.14 0.56 0.44 0.20 - . 0 0 0.22 0.50

Snags, decay 3-5 0-3 in 1.00 0.50 0 0 . - 0 . 0 .

3-12 in 0 0.54 0.65 0.25 0 0 - 0.92 0.38 0

12-36 in 0.21 0.56 0.48 0.25 0 . 0.58 - 0.26 0.0736-60 in 0.20 0.33 0.20 0.27 0.08 0 0.26 0.26 - 0.07

> 60 in 0 0.25 0 0 0.50 . 0 0.25 0.25 -

16 Variability in Older Forest Structure in Western Oregon

Table 6.

—continued
of 80 ft2

 per 10 acres for western red cedar 2-3 ft dbh would 

allow managers to define LSOG structures at scales that are 

more realistic ecologically and operationally than would a 

basal area target of 8 ft2 per 1 acre. Although 80 ft2 per 10

acres is mathematically equivalent to 8 ft2 per 1 acre, the former target affords managers more opportunities when working 

with young forests where accelerating the development of 

realistic LSOG forest structures is a management goal.

Literature Cited

Bradshaw, G.A. and T.A. Spies. 1992. Characterizing canopy 

gap structure in forests using wavelet analysis. Journal of 

Ecology 80:205-215.

ESRI 2002. ArcView, Version 3.3. Environmental Systems 

Research Institute, Inc., Redlands, California.

ESRI 2003. ArcGIS, Version 8.3. Environmental Systems 

Research Institute, Inc., Redlands, California.

Franklin, J.F., T.A. Spies, R. Van Pelt, A.B. Carey, D.A. 

Thornburgh, D.R. Berg, D.B. Lindenmayer, M.E. Harmon, 

W.S. Keeton, D.C. Shaw, K. Bible, and J. Chen. 2002. 

Disturbances and structural development of natural forest 

ecosystems with silvicultural implications, using Douglasfir forests as an example. Forest Ecology and Management 

155:399-423.

FSEIS. 1994. Final supplemental environmental impact statement on management of habitat for late-successional and 

old-growth forest related species within the range of the 

northern spotted owl, volume 1. USDA Forest Service and 

USDI Bureau of Land Management, Portland, Oregon.

Goslin, M.N. 1997. Development of two coniferous stands 

impacted by multiple, partial fires in the Oregon Cascades: 

establishment history and the spatial pattern of colonizing tree species relative to old-growth remnant trees. M.S. 

thesis. Oregon State University, Corvallis, Oregon.

Hershey, K., 1995. Characteristics of forests at spotted owl 

nest sites in the Pacific Northwest. M.S. thesis. Oregon 

State University, Corvallis, Oregon.

Juday, G.P. 1977. The location, composition, and structure of 

old-growth forests of the Oregon Coast Range. Ph.D. thesis. 

Oregon State University, Corvallis, Oregon.

Kuiper, L.C. 1988. The structure of natural Douglas-fir forests 

in western Washington and western Oregon. Agricultural 

University Wageningen Papers 88-5(1988). Agricultural 

University Wageningen, Wageningen, The Netherlands.

Maser, C., R.F. Tarrant, J.M. Trappe, and J.F. Franklin. 1988. 

From the forest to the sea: a story of fallen trees. General 

Technical Report PNW-GTR-229, USDA Forest Service, 

Pacific Northwest Region, Portland, Oregon. 153 p.

Means, J.E. 1982. Developmental history of dry coniferous 

forests in the central western Cascade Range of Oregon. 

In: Means, J. E. (Ed.), Forest Succession and Stand 

Development Research in the Northwest: Proceedings of 

a Symposium, March 26, 1981, Oregon State University. 

Forest Research Laboratory, Oregon State University, 

Corvallis, Oregon. pp. 142–158.

Pater, D.E., S.A. Bryce, T.D. Thorson, J. Kagan, C. Chappell, 

J. M. Omernik, S.H. Azevedo, A.J. Woods. 1998. Ecoregions of Western Washington and Oregon. 1:1,350,000 map. 

USDI Geologic Survey, Denver, Colorado.

Poage, N.J. 1995. Comparison of stand development of a 

deciduous-dominated riparian forest and a coniferousdominated riparian forest in the Oregon Coast Range. M.S. 

thesis, Oregon State University, Corvallis, Oregon.

Poage, N.J. and J.C. Tappeiner. 2002. Long-term patterns of 

diameter and basal area growth of old-growth Douglasfir trees in western Oregon. Canadian Journal of Forest 

Research 32:1232-1243.

Poage, N.J. and J.C. Tappeiner. 2005. Tree species and size 

structure of old-growth Douglas-fir forests in central 

western Oregon, USA. Forest Ecology and Management 

204:329-343.

Record of Decision. 1994. Record of decision for amendments 

to Forest Service and Bureau of Land Management planning 

documents within the range of the northern spotted owl. 

USDA Forest Service and USDI Bureau of Land Management, Portland, Oregon.

Regional Ecosystem Office. 2005. About the Northwest Forest 

Plan (NWFP). www.reo.gov/general/aboutNWFP.htm.

SAS Institute. 2003. SAS System for Windows, Version 9.1. 

SAS Institute, Inc., Cary, North Carolina.

Spies, T.A. and J.F. Franklin. 1991. The structure of natural young, mature, and old-growth Douglas-fir forests in 

Oregon and Washington. In: L.F. Ruggerio, K.B. Aubry, 

A.B. Carey, and M.H. Huff, editors. Wildlife and Vegetation 

of Unmanaged Douglas-fir Forests. USDA Forest Service 

General Technical Report PNW-GTR-285. Pacific Northwest Research Station, Portland, Oregon. pp. 90–109.

Spies, T.A., J.F. Franklin, and M. Klopsch. 1990. Canopy gaps 

in Douglas-fir forests of the Cascade Mountains. Canadian 

Journal of Forest Research 20:649-658.

Literature Cited 17
Tappeiner, J.C., D. Huffman, D. Marshall, T.A. Spies, and J.D. 

Bailey. 1997. Density, ages, and growth rates in old-growth 

and young-growth forests in coastal Oregon. Canadian Journal of Forest Research 27:638–648.

Winter, L.E., L.B. Brubaker, J.F. Franklin, E.A. Miller, D.Q. 

DeWitt. 2002a. Initiation of an old-growth Douglas-fir stand 

in the Pacific Northwest: a reconstruction from tree-ring 

records. Canadian Journal of Forest Research 32:1039-1056.

Winter, L.E., L.B. Brubaker, J.F. Franklin, E.A. Miller, D.Q. 

DeWitt. 2002b. Canopy disturbances over the five-century 

lifetime of an old-growth Douglas-fir stand in the Pacific 

Northwest. Canadian Journal of Forest Research 32:1057-

1070.

Zenner, E.K. 2004. Development of tree size distributions in 

Douglas-fir forests under differing disturbance regimes. 

Ecological Applications 15:701-714.

18 Variability in Older Forest Structure in Western Oregon
Level III Level IV Douglas-fir Other Conifers Grand

Ecoregion Ecoregion 1-2 ft 2-3 ft 3-4 ft 4-5 ft ≥ 5 ft Total 1-2 ft 2-3 ft 3-4 ft 4-5 ft ≥ 5 ft Total Total

1. Coast Range

1b. Coastal Uplands

(n = 14)

11.13 10.59 4.85 1.02 0.75 28.34 9.67 4.34 1.66 0.35 0.17 16.20 44.54

(7.03) (7.24) (2.84) (0.56) (1.13) (15.23) (6.84) (3.88) (1.84) (0.45) (0.29) (11.78) (16.04)

1d. Volcanics

(n = 64)

21.27 18.65 3.79 0.56 0.17 44.43 8.19 2.95 0.38 0.05 0.02 11.59 56.02

(14.45) (8.61) (3.06) (1.00) (0.41) (20.02) (11.48) (4.47) (0.72) (0.15) (0.13) (16.28) (21.01)

1g. Mid-Coastal Sedimentary

(n = 197)

14.77 11.10 5.84 2.05 0.81 34.58 9.02 2.18 0.77 0.18 0.05 12.20 46.78

(13.94) (7.95) (3.44) (1.80) (1.00) (17.66) (9.01) (2.50) (1.28) (0.44) (0.25) (11.34) (16.98)

1h. Southern Oregon Coastal Mountains

(n = 13)

10.42 8.89 4.04 1.21 0.82 25.37 6.94 1.12 0.33 0.08 0.01 8.48 33.85

(8.98) (8.42) (2.83) (1.04) (1.04) (16.75) (7.20) (1.44) (0.46) (0.10) (0.02) (8.34) (19.40)

3. Willamette Valley

3d. Valley Foothills

(n = 30)

19.67 15.39 5.77 2.00 0.67 43.50 6.18 1.57 0.35 0.11 0.03 8.25 51.74

(13.04) (8.30) (2.78) (1.15) (0.58) (19.55) (5.81) (2.07) (0.55) (0.18) (0.07) (8.17) (18.20)

4. Cascades 4a. Western Cascades Lowlands and Valleys

(n = 53)

18.66 11.35 5.54 2.10 0.79 38.44 13.94 4.17 1.16 0.14 0.01 19.43 57.86

(17.78) (8.91) (4.30) (1.70) (0.99) (23.08) (12.49) (4.61) (1.69) (0.23) (0.04) (16.48) (23.36)

4b. Western Cascades Montane Highlands

(n = 11)

6.84 6.53 5.79 2.24 0.65 22.05 20.91 13.14 5.28 0.58 0.02 39.93 61.98

(19.37) (7.56) (3.20) (1.48) (0.57) (21.38) (13.90) (4.33) (2.18) (0.43) (0.02) (11.69) (30.50)

4f. Umpqua Cascades

(n = 49)

16.52 9.81 5.21 1.96 0.41 33.91 16.37 3.85 1.66 0.57 0.09 22.55 56.45

(10.47) (5.32) (2.90) (1.50) (0.51) (15.15) (10.40) (2.31) (3.13) (1.22) (0.20) (12.48) (14.31)

78. Klamath Mountains

78b. Siskiyou Foothills

(n = 20)

13.83 6.82 1.68 0.51 0.09 22.93 3.78 1.33 0.39 0.08 0.01 5.58 28.51

(20.11) (3.65) (1.13) (0.76) (0.16) (23.32) (3.86) (1.52) (0.60) (0.10) (0.02) (4.55) (24.96)

78e. Inland Siskiyous

(n = 115)

16.61 9.63 3.61 0.79 0.10 30.74 5.14 1.33 0.48 0.10 0.01 7.06 37.80

(12.33) (6.02) (2.86) (1.01) (0.20) (16.79) (6.68) (1.63) (0.58) (0.17) (0.03) (8.06) (19.56)

All Units Combined

(n = 586)

16.28 11.34 4.80 1.50 0.50 34.42 9.14 2.63 0.84 0.18 0.04 12.82 47.24

(14.32) (7.95) (3.45) (1.59) (0.80) (19.27) (9.88) (3.40) (1.57) (0.48) (0.17) (13.20) (20.71)

Appendix 1 19

Appendix 1Mean number of trees/ac by species-diameter class (SDC) and level IV ecoregion. Standard deviations are shown in parentheses below each mean.
Douglas-fir Other Conifers Grand

Comparison 1-2 ft 2-3 ft 3-4 ft 4-5 ft ≥ 5 ft Total 1-2 ft 2-3 ft 3-4 ft 4-5 ft ≥ 5 ft Total Total

1b - 1d . -8.06 . . . . . . . . . . .1b - 1g . . . . . . . . . . . . .1b - 1h . . . . . . . . . . . . .1b - 3d . . . . . . . . . . . . .1b - 4a . . . . . . . . . . . . .1b - 4b . . . . . . . -8.81 -3.62 . . -23.74 .1b - 4f . . . . . . . . . . . . .1b - 78b . . . . . . . . . . . . .1b - 78e . . . . . . . 3.01 . . 0.16 . .1d - 1b . 8.06 . . . . . . . . . . .1d - 1g 6.49 7.54 -2.05 -1.49 -0.64 9.85 . . . . . . 9.241d - 1h . 9.75 . . . 19.05 . . . . . . 22.161d - 3d . . . -1.44 . . . . . . . . .1d - 4a . 7.30 . -1.54 -0.62 . -5.75 . . . . -7.84 .1d - 4b . 12.12 . -1.69 . 22.38 -12.72 -10.19 -4.91 -0.53 . -28.34 .1d - 4f . 8.84 . -1.40 . . -8.18 . -1.29 -0.52 . -10.96 .1d - 78b . 11.83 . . . 21.49 . . . . . . 27.501d - 78e . 9.02 . . . 13.68 . 1.62 . . . . 18.211g - 1b . . . . . . . . . . . . .1g - 1d -6.49 -7.54 2.05 1.49 0.64 -9.85 . . . . . . -9.241g - 1h . . . . . . . . . . . . .1g - 3d . . . . . . . . . . . . .1g - 4a . . . . . . -4.92 -2.00 . . . -7.23 -11.081g - 4b . . . . . . -11.89 -10.96 -4.51 . . -27.73 .1g - 4f . . . . 0.39 . -7.35 -1.67 -0.89 -0.39 . -10.34 .

Appendix 2Pair-wise differences between level IV ecoregions in terms of mean number of trees/ac (TPA), by species-diameter class (SDC). The values shown, the pair-wise differences between level IV ecoregion mean TPAs, are all significantly different than 0. For example, the Volcanics (1d) level IV ecoregion had an average of 6.49 TPA more Douglas-fir in 

the 1-2 ft diameter class than did the Mid-Coastal Sedimentary (1g) ecoregion. Empty cells indicate that the difference between means was not significantly different than 0. Significance was assessed for each combination of species group and diameter class using Tukey’s Honest Significance Difference (HSD) method of multiple comparisons with 

an experiment-wise error rate of α = 0.05. See Appendix 1 for the mean TPAs by species-diameter class (SDC) and level IV ecoregion.

20 Variability in Older Forest Structure in Western Oregon
1h - 4a . . . . . . . -3.06 . . . . -24.01

1h - 4b . . . . . . -13.97 -12.02 -4.95 . . -31.45 -28.121h - 4f . . . . . . -9.44 . . -0.49 . -14.06 -22.601h - 78b . . . . . . . . . . . . .1h - 78e . . . . 0.71 . . . . . . . .3d - 1b . . . . . . . . . . . . .3d - 1d . . . 1.44 . . . . . . . . .3d - 1g . . . . . . . . . . . . .3d - 1h . . . . . . . . . . . . .3d - 4a . . . . . . -7.76 -2.61 . . . -11.18 .3d - 4b . 8.86 . . . 21.45 -14.73 -11.57 -4.93 . . -31.68 .3d - 4f . 5.58 . . . . -10.19 -2.28 -1.31 -0.46 . -14.30 .3d - 78b . 8.57 4.09 1.49 . 20.56 . . . . . . 23.233d - 78e . 5.76 2.16 1.20 0.57 12.75 . . . . . . 13.941g - 78b . . 4.16 1.54 0.72 . . . . . . . 18.271g - 78e . . 2.23 1.25 0.71 . 3.88 . . . . 5.14 8.971h - 1b . . . . . . . . . . . . .1h - 1d . -9.75 . . . -19.05 . . . . . . -22.161h - 1g . . . . . . . . . . . . .1h - 3d . . . . . . . . . . . . .

Douglas-fir Other Conifers Grand

Comparison 1-2 ft 2-3 ft 3-4 ft 4-5 ft ≥ 5 ft Total 1-2 ft 2-3 ft 3-4 ft 4-5 ft ≥ 5 ft Total Total

4a - 1b . . . . . . . . . . . . .4a - 1d . -7.30 . 1.54 0.62 . 5.75 . . . . 7.84 .4a - 1g . . . . . . 4.92 2.00 . . . 7.23 11.084a - 1h . . . . . . . 3.06 . . . . 24.014a - 3d . . . . . . 7.76 2.61 . . . 11.18 .4a - 4b . . . . . . . -8.97 -4.12 . . -20.50 .4a - 4f . . . . . . . . . -0.43 . . .4a - 78b . . 3.86 1.59 0.69 15.50 10.16 2.84 . . . 13.85 29.35

Appendix 2—continued

Appendix 2 21
4a - 78e . . 1.93 1.31 0.68 . 8.80 2.85 . . . 12.37 20.06

4b - 1b . . . . . . . 8.81 3.62 . . 23.74 .4b - 1d . -12.12 . 1.69 . -22.38 12.72 10.19 4.91 0.53 . 28.34 .4b - 1g . . . . . . 11.89 10.96 4.51 . . 27.73 .4b - 1h . . . . . . 13.97 12.02 4.95 . . 31.45 28.124b - 3d . -8.86 . . . -21.45 14.73 11.57 4.93 . . 31.68 .4b - 4a . . . . . . . 8.97 4.12 . . 20.50 .4b - 4f . . . . . . . 9.30 3.62 . . 17.39 .

4b - 78b . . 4.11 1.73 . . 17.13 11.81 4.90 . . 34.35 33.474b - 78e . . . . . . 15.77 11.81 4.80 0.48 . 32.87 24.18

4f - 1b . . . . . . . . . . . . .4f - 1d . -8.84 . 1.40 . . 8.18 . 1.29 0.52 . 10.96 .4f - 1g . . . . -0.39 . 7.35 1.67 0.89 0.39 . 10.34 .4f - 1h . . . . . . 9.44 . . 0.49 . 14.06 22.604f - 3d . -5.58 . . . . 10.19 2.28 1.31 0.46 . 14.30 .4f - 4a . . . . . . . . . 0.43 . . .4f - 4b . . . . . . . -9.30 -3.62 . . -17.39 .

4f - 78b . . 3.53 1.45 . . 12.59 2.52 1.28 0.49 . 16.97 27.944f - 78e . . . 1.16 . . 11.24 2.52 1.18 0.47 . 15.49 18.65

Douglas-fir Other Conifers Grand

Comparison 1-2 ft 2-3 ft 3-4 ft 4-5 ft

≥ 5 ft Total 1-2 ft 2-3 ft 3-4 ft 4-5 ft

≥ 5 ft Total Total

78b - 1b . . . . . . . . . . . . .78b - 1d . -11.83 . . . -21.49 . . . . . . -27.5078b - 1g . . -4.16 -1.54 -0.72 . . . . . . . -18.2778b - 1h . . . . . . . . . . . . .78b - 3d . -8.57 -4.09 -1.49 . -20.56 . . . . . . -23.2378b - 4a . . -3.86 -1.59 -0.69 -15.50 -10.16 -2.84 . . . -13.85 -29.3578b - 4b . . -4.11 -1.73 . . -17.13 -11.81 -4.90 . . -34.35 -33.4778b - 4f . . -3.53 -1.45 . . -12.59 -2.52 -1.28 -0.49 . -16.97 -27.94

Appendix 2—continued

22 Variability in Older Forest Structure in Western Oregon
78b - 78e . . . . . . . . . . . . .

78e - 1b . . . . . . . -3.01 . . -0.16 . .78e - 1d . -9.02 . . . -13.68 . -1.62 . . . . -18.2178e - 1g . . -2.23 -1.25 -0.71 . -3.88 . . . . -5.14 -8.9778e - 1h . . . . -0.71 . . . . . . . .78e - 3d . -5.76 -2.16 -1.20 -0.57 -12.75 . . . . . . -13.9478e - 4a . . -1.93 -1.31 -0.68 . -8.80 -2.85 . . . -12.37 -20.0678e - 4b . . . . . . -15.77 -11.81 -4.80 -0.48 . -32.87 -24.1878e - 4f . . . -1.16 . . -11.24 -2.52 -1.18 -0.47 . -15.49 -18.6578e - 78b . . . . . . . . . . . . .

Douglas-fir Other Conifers Grand

Comparison 1-2 ft 2-3 ft 3-4 ft 4-5 ft ≥ 5 ft Total 1-2 ft 2-3 ft 3-4 ft 4-5 ft ≥ 5 ft Total Total

Appendix 2—continued

Appendix 2 23
Level III Level IV Douglas-fir Other Conifers Grand

Ecoregion Ecoregion 1-2 ft 2-3 ft 3-4 ft 4-5 ft

≥ 5 ft Total 1-2 ft 2-3 ft 3-4 ft 4-5 ft

≥ 5 ft Total Total

1. Coast Range

1b. Coastal Uplands

(n = 14)

19.7 52.0 46.6 16.3 23.6 158.2 17.1 21.3 16.0 5.6 4.9 64.9 223.1

(12.4) (35.6) (27.3) (8.9) (38.9) (72.4) (12.1) (19.1) (17.7) (7.2) (9.1) (56.8) (84.8)

1d. Volcanics

(n = 64)

37.6 91.5 36.5 8.8 4.4 178.8 14.5 14.5 3.6 0.8 0.7 34.1 212.9

(25.5) (42.3) (29.4) (15.8) (10.7) (67.9) (20.3) (22.0) (6.9) (2.3) (4.3) (50.1) (63.2)

1g. Mid-Coastal Sedimentary

(n = 197)

26.1 54.5 56.2 32.6 21.3 190.7 15.9 10.7 7.5 2.9 1.3 38.2 229.0

(24.6) (39.0) (33.1) (28.7) (26.9) (63.4) (15.9) (12.3) (12.3) (7.0) (6.5) (40.1) (67.2)

1h. Southern Oregon Coastal Mountains

(n = 13)

18.4 43.7 38.9 19.2 22.2 142.3 12.3 5.5 3.2 1.3 0.3 22.5 164.8

(15.9) (41.3) (27.2) (16.6) (28.5) (66.5) (12.7) (7.1) (4.4) (1.6) (0.4) (21.4) (70.0)

3. Willamette Valley

3d. Valley Foothills

(n = 30)

34.8 75.5 55.5 31.7 17.2 214.8 10.9 7.7 3.4 1.8 0.8 24.6 239.4

(23.0) (40.7) (26.7) (18.3) (15.3) (65.9) (10.3) (10.1) (5.3) (2.8) (1.8) (26.5) (56.8)

4. Cascades 4a. Western CascadesLowlands and Valleys

(n = 53)

33.0 55.7 53.3 33.4 20.7 196.1 24.6 20.5 11.2 2.2 0.3 58.8 254.9

(31.4) (43.7) (41.3) (27.1) (26.5) (76.0) (22.1) (22.6) (16.2) (3.7) (1.0) (53.8) (55.3)

4b. Western Cascades Montane Highlands

(n = 11)

12.1 32.0 55.7 35.7 16.5 152.0 36.9 64.5 50.8 9.3 0.4 161.9 313.9

(34.2) (37.1) (30.8) (23.5) (14.6) (41.8) (24.6) (21.3) (20.9) (6.9) (0.5) (30.4) (40.2)

4f. Umpqua Cascades

(n = 49)

29.2 48.1 50.1 31.1 10.0 168.6 28.9 18.9 16.0 9.1 2.3 75.2 243.8

(18.5) (26.1) (27.9) (23.9) (12.5) (66.2) (18.4) (11.4) (30.1) (19.4) (4.9) (55.7) (60.7)

78. Klamath Mountains

78b. Siskiyou Foothills

(n = 20)

24.4 33.5 16.2 8.1 2.2 84.4 6.7 6.5 3.7 1.2 0.2 18.3 102.7

(35.5) (17.9) (10.9) (12.1) (3.8) (59.1) (6.8) (7.4) (5.8) (1.6) (0.6) (15.7) (62.2)

78e. Inland Siskiyous

(n = 115)

29.4 47.3 34.7 12.6 2.5 126.5 9.1 6.5 4.6 1.7 0.2 22.1 148.6

(21.8) (29.5) (27.5) (16.0) (4.9) (64.7) (11.8) (8.0) (5.6) (2.7) (0.7) (22.5) (70.2)

All Units Combined

(n = 586)

28.8 55.7 46.2 23.8 13.2 167.7 16.1 12.9 8.0 2.8 1.0 40.9 208.6

(25.3) (39.0) (33.2) (25.3) (21.8) (74.1) (17.5) (16.7) (15.1) (7.7) (4.6) (46.2) (79.0)

Appendix 

3

Mean basal area (ft 2/ac) by species-diameter class and level IV ecoregion. Standard deviations are shown in parentheses below each mean.

24 Variability in Older Forest Structure in Western Oregon
Douglas-fir Other Conifers Grand

Comparison 1-2 ft 2-3 ft 3-4 ft 4-5 ft ≥ 5 ft Total 1-2 ft 2-3 ft 3-4 ft 4-5 ft ≥ 5 ft Total Total

1b - 1d . -39.6 . . . . . . . . . . .1b - 1g . . . . . . . . . . . . .1b - 1h . . . . . . . . . . . . .1b - 3d . . . . . . . . . . . . .1b - 4a . . . . . . . . . . 4.7 . .1b - 4b . . . . . . . -43.2 -34.8 . . -97.0 -90.81b - 4f . . . . . . . . . . . . .1b - 78b . . . . . 73.7 . . . . . 46.6 120.31b - 78e . . . . 21.1 . . 14.8 . . 4.7 42.8 74.51d - 1b . 39.6 . . . . . . . . . . .1d - 1g 11.5 37.0 -19.7 -23.7 -16.9 . . . . . . . .1d - 1h . 47.9 . . . . . . . . . . .1d - 3d . . . -22.9 . . . . . . . . .1d - 4a . 35.8 . -24.6 -16.3 . -10.2 . . . . -24.7 -42.01d - 4b . 59.5 . -26.8 . . -22.5 -50.0 -47.2 -8.5 . -127.8 -101.01d - 4f . 43.4 . -22.3 . . -14.5 . -12.4 -8.3 . -41.1 .1d - 78b . 58.1 . . . 94.4 . . . . . . 110.21d - 78e . 44.3 . . . 52.4 . 8.0 . . . . 64.31g - 1b . . . . . . . . . . . . .1g - 1d -11.5 -37.0 19.7 23.7 16.9 . . . . . . . .

1g - 1h . . . . . . . . . . . . 64.11g - 3d . . . . . . . . . . . . .1g - 4a . . . . . . -8.7 -9.8 . . . -20.6 .1g - 4b . . . . . . -21.0 -53.8 -43.4 . . -123.7 -84.9

Appendix 4Pair-wise differences between level IV ecoregions in terms of mean basal area (BA, ft 2/ac), by species-diameter class (SDC). The values shown, the pair-wise differences 

between level IV ecoregion mean BAs, are all significantly different than 0. For example, the Volcanics (1d) level IV ecoregion had an average of 11.5 more BA in the Douglasfir 1-2 ft diameter class than did the Mid-Coastal Sedimentary (1g) ecoregion. Empty cells indicate that the difference between means was not significantly different than 0. Significance was assessed for each combination of species group and diameter class using Tukey’s Honest Significance Difference method of multiple comparisons with an 

experiment-wise error rate of α = 0.05. See Appendix 3 for the mean BAs by SDC and level IV ecoregion.

Appendix 4 25
Douglas-fir Other Conifers Grand

Comparison 1-2 ft 2-3 ft 3-4 ft 4-5 ft

≥ 5 ft Total 1-2 ft 2-3 ft 3-4 ft 4-5 ft

≥ 5 ft Total Total

1g - 4f . . . . 11.3 . -13.0 -8.2 -8.6 -6.2 . -36.9 .1g - 78b . . 40.0 24.5 19.1 106.3 . . . . . . 126.21g - 78e . . 21.5 19.9 18.8 64.3 6.9 . . . . 16.1 80.41h - 1b . . . . . . . . . . . . .1h - 1d . -47.9 . . . . . . . . . . .1h - 1g . . . . . . . . . . . . -64.11h - 3d . . . . . -72.5 . . . . . . -74.61h - 4a . . . . . . . -15.0 . . . . -90.11h - 4b . . . . . . -24.7 -59.0 -47.6 . . -139.4 -149.11h - 4f . . . . . . -16.7 . . -7.8 . -52.6 -79.01h - 78b . . . . . . . . . . . . .1h - 78e . . . . 19.7 . . . . . . . .3d - 1b . . . . . . . . . . . . .3d - 1d . . . 22.9 . . . . . . . . .3d - 1g . . . . . . . . . . . . .3d - 1h . . . . . 72.5 . . . . . . 74.63d - 4a . . . . . . -13.7 -12.8 . . . -34.2 .3d - 4b . 43.5 . . . . -26.0 -56.8 -47.4 . . -137.3 -74.53d - 4f . 27.4 . . . . -18.0 -11.2 -12.6 -7.3 . -50.5 .3d - 78b . 42.1 39.3 23.6 . 130.3 . . . . . . 136.63d - 78e . 28.3 20.8 19.1 14.7 88.3 . . . . . . 90.8

4a - 1b . . . . . . . . . . -4.7 . .4a - 1d . -35.8 . 24.6 16.3 . 10.2 . . . . 24.7 42.04a - 1g . . . . . . 8.7 9.8 . . . 20.6 .4a - 1h . . . . . . . 15.0 . . . . 90.14a - 3d . . . . . . 13.7 12.8 . . . 34.2 .4a - 4b . . . . . . . -44.0 -39.6 . . -103.1 .4a - 4f . . . . . . . . . -6.9 . . .

Appendix 4—continued

26 Variability in Older Forest Structure in Western Oregon
4a - 78b . . 37.1 25.3 18.5 111.6 18.0 14.0 . . . 40.5 152.2

4a - 78e . . 18.6 20.8 18.2 69.6 15.6 14.0 . . . 36.7 106.34b - 1b . . . . . . . 43.2 34.8 . . 97.0 90.84b - 1d . -59.5 . 26.8 . . 22.5 50.0 47.2 8.5 . 127.8 101.04b - 1g . . . . . . 21.0 53.8 43.4 . . 123.7 84.94b - 1h . . . . . . 24.7 59.0 47.6 . . 139.4 149.14b - 3d . -43.5 . . . . 26.0 56.8 47.4 . . 137.3 74.54b - 4a . . . . . . . 44.0 39.6 . . 103.1 .4b - 4f . . . . . . . 45.6 34.8 . . 86.8 70.14b - 78b . . 39.5 27.6 . . 30.3 58.0 47.1 . . 143.6 211.24b - 78e . . . . . . 27.9 58.0 46.2 7.6 . 139.8 165.34f - 1b . . . . . . . . . . . . .4f - 1d . -43.4 . 22.3 . . 14.5 . 12.4 8.3 . 41.1 .4f - 1g . . . . -11.3 . 13.0 8.2 8.6 6.2 . 36.9 .4f - 1h . . . . . . 16.7 . . 7.8 . 52.6 79.04f - 3d . -27.4 . . . . 18.0 11.2 12.6 7.3 . 50.5 .4f - 4a . . . . . . . . . 6.9 . . .4f - 4b . . . . . . . -45.6 -34.8 . . -86.8 -70.14f - 78b . . 33.9 23.0 . 84.2 22.3 12.4 12.3 7.9 . 56.9 141.14f - 78e . . . 18.5 . 42.2 19.9 12.4 11.4 7.4 . 53.1 95.278b - 1b . . . . . -73.7 . . . . . -46.6 -120.378b - 1d . -58.1 . . . -94.4 . . . . . . -110.278b - 1g . . -40.0 -24.5 -19.1 -106.3 . . . . . . -126.278b - 1h . . . . . . . . . . . . .78b - 3d . -42.1 -39.3 -23.6 . -130.3 . . . . . . -136.678b - 4a . . -37.1 -25.3 -18.5 -111.6 -18.0 -14.0 . . . -40.5 -152.278b - 4b . . -39.5 -27.6 . . -30.3 -58.0 -47.1 . . -143.6 -211.278b - 4f . . -33.9 -23.0 . -84.2 -22.3 -12.4 -12.3 -7.9 . -56.9 -141.1

Douglas-fir Other Conifers Grand

Comparison 1-2 ft 2-3 ft 3-4 ft 4-5 ft ≥ 5 ft Total 1-2 ft 2-3 ft 3-4 ft 4-5 ft ≥ 5 ft Total Total

Appendix 4—continued

Appendix 4 27
Douglas-fir Other Conifers Grand

Comparison 1-2 ft 2-3 ft 3-4 ft 4-5 ft

≥ 5 ft Total 1-2 ft 2-3 ft 3-4 ft 4-5 ft

≥ 5 ft Total Total

78b - 78e . . . . . . . . . . . . .78e - 1b . . . . -21.1 . . -14.8 . . -4.7 -42.8 -74.578e - 1d . -44.3 . . . -52.4 . -8.0 . . . . -64.378e - 1g . . -21.5 -19.9 -18.8 -64.3 -6.9 . . . . -16.1 -80.478e - 1h . . . . -19.7 . . . . . . . .78e - 3d . -28.3 -20.8 -19.1 -14.7 -88.3 . . . . . . -90.878e - 4a . . -18.6 -20.8 -18.2 -69.6 -15.6 -14.0 . . . -36.7 -106.378e - 4b . . . . . . -27.9 -58.0 -46.2 -7.6 . -139.8 -165.378e - 4f . . . -18.5 . -42.2 -19.9 -12.4 -11.4 -7.4 . -53.1 -95.278e - 78b . . . . . . . . . . . . .

Appendix 4—continued

28 Variability in Older Forest Structure in Western Oregon