United States Department of Agriculture

DEPAR TMENT OF AGRICULT URE

Forest 

Service

Pacific Northwest 

Research Station

General Technical Report

PNW-GTR-956

November

2017

Historical Forest Structure, 

Composition, and Spatial Pattern 

in Dry Conifer Forests of the 

Western Blue Mountains, Oregon

Derek J. Churchill, Gunnar C. Carnwath, Andrew J. Larson, 

and Sean A. Jeronimo
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Authors

Derek J. Churchill is a research scientist and Sean A. Jeronimo is a Ph.D. candidate, School of Environmental and Forest Sciences, College of the Environment, 

University of Washington, Seattle, WA 98195; Gunnar C. Carnwath is a vegetation specialist, U.S. Department of Agriculture, Forest Service, Pacific Northwest 

Region, Custer Gallatin National Forest, Bozeman, MT, 59715 and Andrew J. 

Larson is an associate professor, Department of Forest Management, College of 

Forestry and Conservation, University of Montana, Missoula, MT 59812. 

Cover photo: Snag at Umatilla Breaks in Oregon on the Umatilla National Forest, 

USDA Forest Service.
Abstract

Churchill, Derek J.; Carnwath, Gunnar C.; Larson, Andrew J.; Jeronimo, 

Sean A. 2017. Historical forest structure, composition, and spatial pattern in dry 

conifer forests of the western Blue Mountains, Oregon. Gen. Tech. Rep. PNWGTR-956. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific 

Northwest Research Station. 93 p.

In frequent-fire forests of the interior Western United States, historical (prefire 

suppression) conditions are often used as a reference to set management objectives, 

guide prescriptions, and monitor treatment effectiveness. We quantified the historical size, density, composition, and spatial patterns of dry mixed-conifer forests in 

the Blue Mountains of Oregon to establish reference conditions that could be used 

for ongoing forest-restoration efforts. In total, 14 reconstruction plots ranging from 

2.3 to 5.0 ha were established, with plots located on ponderosa pine (Pinus ponderosa Lawson & C. Lawson), Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), 

and grand fir (Abies grandis (Douglas ex D. Don) Lindl.) potential vegetation sites. 

Within each plot, all historical structures—live trees, snags, and logs that were 

alive in 1890—were mapped, and 1890 diameters were reconstructed. Historical 

structure and composition on the 14 plots consisted of an open canopy, uneven-aged 

mosaic of widely spaced individual trees, tree clumps, and openings dominated 

by large trees. Mean values for historical tree density of trees greater than 15 cm 

diameter at breast height (d.b.h.) ranged from 53 to 197 trees per hectare, and basal 

area ranged from 11 to 24 m2

 ∙ ha-1. Basal area varied widely across each plot, and 

the mean value was not representative of the density in the majority of the plot 

in almost all cases. Mean tree diameter ranged from 35.2 to 57.8 cm, with over 

50 percent of the basal area composed of trees greater than 50 cm d.b.h. Species 

composition was dominated by ponderosa pine on plots within the ponderosa pine 

and Douglas-fir series. Grand fir was abundant on three of the four plots within the 

grand fir series, comprising 44 to 48 percent of the basal area on these three plots. 

The proportion of historical trees occurring as widely spaced individuals (no neighbors within 6 m) ranged from 0.53 to 0.10. Ten of 14 plots had large tree clumps 

(10 to 15 trees) or very large clumps (16 to 30 trees), with the proportion of trees 

in these clumps ranging from 0.05 to 0.43. The proportion of the plot area in large 

openings ranged from 0.15 to 0.72, with most openings being sinuous and linear 

in shape and ranging from 18 to 45 m across. The range of conditions presented in 

this reference dataset provides managers flexible targets that can be used to guide 

restoration of variable conditions within and across treatment units. When using the 

dataset to inform prescription development, we recommend first determining the 
target stem density appropriate for the site and then selecting a clumping level to 

help guide the spatial pattern to be created through restoration treatment. Management objectives, current conditions, biophysical conditions, and anticipated future 

disturbance and climate change can then be considered when setting targets for 

density and clumping. This reference information can also be used to monitor the 

extent to which treated stands are within the ranges of size, density, composition, 

and pattern quantified in this study. 

Keywords: Restoration, dry forests, spatial pattern, reference conditions.

Contents

1 Chapter 1: Introduction and Background

5 Chapter 2: Methods

5 Study Area Description

7 Site Selection

9 Field Methods

10 Stem Map Reconstruction

11 Current Conditions

12 Spatial Pattern Analysis

15 Assessing Relationships Among Pattern, Density, and Potential Vegetation Series

17 Chapter 3: Summary Results

17 Structure, Density, Composition, and Age

20 Spatial Pattern

25 Relationships Among Pattern, Density, and Plant Series 

27 Chapter 4: Individual Plot Results

27 Panels

28 Ponderosa Pine 1

30 Ponderosa Pine 2

32 Ponderosa Pine 3

36 Ponderosa Pine 5

38 Douglas-fir 1

40 Douglas-fir 2

42 Douglas-fir 3

44 Douglas-fir 4

46 Douglas-fir 5

48 Grand Fir 1

50 Grand Fir 2

52 Grand Fir 3

54 Grand Fir 4

57 Chapter 5: Ecological Implications

57 Structure, Density, Composition, and Age

58 Spatial Pattern 

60 Relationships Among Pattern, Density and Potential Vegetation Series 

61 Forest Development Pathways

63 Chapter 6: Management Implications

63 Key Functional Components of Reference Conditions

65 Using Reference Data to Set Targets for Density, Composition, and Pattern

67 Marking Guide Development and Implementation

69 Conclusion

69 English Equivalents

70 References

83 Appendix 1: Methods to Reconstruct Diameters in 1890

87 Appendix 2: Crown Radius Models

88 Appendix 3: Clump Size Proportions for All Trees >10 cm

89 Appendix 4: Distribution of Basal Area

90 Appendix 5: Pair Correlation Plots for 14 Reference Plots
1

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Three essential elements of forest ecosystems are structure, composition, and 

function. Structure includes the size, density, and spatial arrangement of live and 

dead vegetation. Structure and composition interact to regulate ecosystem function (Franklin et al. 2002), including feedbacks with disturbance processes such 

as fire (Noss et al. 2006). Presently, management objectives for dry, mixed-conifer 

forests on federal lands in the interior Western United States emphasize restoration of structure and composition consistent with the historical range of variability 

(HRV), promotion of resilience and adaptive capacity, and forest conditions that 

foster primarily low-severity fire effects (CFLRP 2012; USDA FS 2012, 2014). 

To meet these objectives, managers often use reference conditions, such as those 

provided by estimates of HRV, to develop understanding of system functioning 

and to guide development and evaluation of treatments (Hagmann et al. 2014, 

Moore et al. 1999, Reynolds et al. 2013, Stine et al. 2014) The HRV concept applies 

to contemporary management aimed not only at ecosystem restoration, but also at 

increasing resilience and climate change adaptation (Keane et al. 2009, Seidl et al. 

2015, Stephens et al. 2010). When used in the framework of climate analog conditions or the future range of variability (Gärnter et al. 2008, Stine et al. 2014)—reference sites with climate conditions similar to the projected future climate regime 

of the project area—historical reference conditions provide defensible, transparent 

data that can be used to inform treatment design and monitoring (Churchill et al. 

2013, Hessburg et al. 2013). 

The rationale for using reference conditions to guide management targets in dry 

forests is that historical forest conditions persisted through centuries of frequent 

disturbances and significant climatic fluctuation while sustaining native biodiversity 

and other ecosystem services (Fule 2008, Hessburg et al. 2015, Jackson and Hobbs 

2009, Keane et al. 2009, Swetnam et al. 1999). The mechanistic links between the 

structure and composition of historical forest conditions and their resilience have 

been the topic of much recent research (Agee 2005, Peterson et al. 2011, Reynolds 

et al. 2013, Stephens et al. 2010). The importance of structure dominated by large 

and old trees, and composition dominated by fire and drought-tolerant species has 

been well established (Agee and Skinner 2005, Franklin et al. 2013, Jain et al. 2012, 

Lutz et al. 2012, Powell 2014, Stine et al. 2014). Here we highlight a number of the 

mechanisms in which the spatial pattern of these forests engenders resilience:

Chapter 1: Introduction and Background
2

GENERAL TECHNICAL REPORT PNW-GTR-956

• The complex network of openings in frequent-fire forests is thought to 

inhibit the spread of crown fires by forcing crown fires back to the ground 

when flareups occur (Beaty and Taylor 2007, Parisien et al. 2010, Pimont et 

al. 2011, Stephens et al. 2010, Thaxton and Platt 2006). These openings also 

impede the buildup of epidemic insect outbreaks by disrupting pheromone 

plumes (Fettig et al. 2007). 

• Large openings and dense patches create variability in light, moisture, and 

soil nutrient environments that increases understory plant abundance and 

diversity (Dodson et al. 2008, Gundale et al. 2006, North et al. 2005). 

• The contrast of dense patches of tree clumps and openings provides the 

diversity of habitat conditions needed by many species of birds and small 

mammals (Buchanan et al. 2003, Dodd et al. 2006, Latif et al. 2015, Long 

and Smith 2000). 

• A variable spatial pattern facilitates frequent and patchy regeneration that 

creates a multiaged tree structure and a continuing flow of replacement 

trees. Frequent pulses of regeneration may contribute to high levels of 

within-stand genetic diversity of trees found in dry forests (Hamrick et al. 

1989, Linhart et al. 1981). 

• Variable overstory tree arrangements generate variation in litter accumulation that, in combination with a patchy understory of tree seedlings, 

saplings, herbs, forb, and shrubs, creates variability in surface fuel beds 

conditions (Fry et al. 2014, Fry and Stephens 2010, Gundale et al. 2006, 

Hiers et al. 2009, Thaxton and Platt 2006).

Reference information and guiding principles have been established for ecosystem restoration of many frequent-fire forest systems in the Western United 

States (Allen et al. 2002, Franklin et al. 2013, Hessburg et al. 2005, Jain et al. 2008, 

Kaufmann et al. 2007, Peterson et al. 2005, Powell 2014, Reynolds et al. 2013, Stine 

et al. 2014). However, the availability of reference information for spatial pattern was 

limited until relatively recently, and in some regions, still is. Larson and Churchill 

(2012) conducted a comprehensive literature review and found only 25 studies 

reporting reference spatial information, with most data coming from sites in southwestern ponderosa pine forests, Sierra Nevada mixed-conifer forests, and Cascadian 

mixed-conifer forests in central Oregon and Washington. Reference spatial information was conspicuously limited for dry mixed-conifer forests of the Rocky Mountain 

region and the Blue Mountains of eastern Oregon and southeastern Washington (Larson and Churchill 2012). Several new studies have begun to fill these gaps (Churchill 

2013, Fry et al. 2014, Hopkins et al. 2014, Lydersen et al. 2013, Schneider et al. 2015), 

but spatial reference information specific to the Blue Mountains is not available.
3

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

The purpose of this study is to quantify the historical structure and composition of dry mixed-conifer forests in the Blue Mountains of Oregon. Addressing the 

absence of historical spatial pattern information is a primary objective. The analyses and results reported here were designed to facilitate the use of reference information in guiding development of silvicultural prescriptions, marking guidelines, 

and treatment monitoring. We sought to define and report ranges of conditions in 

order to provide managers with flexible targets that can be used to guide restoration 

treatments within and across treatment units. 

The reference information can be incorporated into a variety of implementation 

approaches (e.g., Graham et al. 2007, Knapp et al. 2012, North and Sherlock 2012, 

Powell 2012). The results are especially suited to using the individuals, clumps, and 

openings (ICO) silvicultural and monitoring approach to quantifying spatial pattern 

developed by Churchill et al. (2013). Detailed implementation guidelines for using 

the ICO method are provided in Churchill et al. (2014), including examples of how 

to use the reference data presented in this report. 

We also wanted to improve understanding of the factors that shaped and 

maintained forest development and patterns on these sites. Specifically, we sought 

to determine if tree density and tree spatial patterns differed along a gradient of 

moisture and productivity as indicated by potential vegetation series (the ponderosa 

pine, Douglas-fir, and grand fir potential vegetation series) within the warm dry 

upland forest plant association group (sensu Powell et al. 2007). In earlier work and 

review of the literature, we noticed that historical tree density and spatial pattern 

seemed to vary systematically across environmental (e.g., moisture) gradients, with 

moister sites supporting higher tree densities, and a greater proportion of trees 

occurring as members of closely spaced tree clumps (Churchill 2013, Larson et al. 

2012). However, higher tree densities and greater clumping have not been found on 

more productive sites in other studies of historical conditions in dry mixed-conifer 

forests (Hagmann et al. 2014, Merschel et al. 2014, Reynolds et al. 2013, Schneider 

et al. 2015) We hypothesized that grand fir sites historically supported higher tree 

densities with more, larger tree clumps, and that ponderosa pine series sites historically had the lowest stem densities with fewer, smaller clumps. 

A secondary objective of this study was to compare current to historical density 

and composition. Although increases in density relative to historical conditions 

have been widely reported for dry forests (Covington and Moore 1994, Hagmann 

et al. 2013, Harrod et al. 1999, Hessburg et al. 1999, Lydersen et al. 2013, Reynolds 

et al. 2013, Sánchez Meador et al. 2009, Stine et al. 2014) some recent studies claim 

that forest density has not increased in the Blue Mountains and other portions of the 

West (Williams and Baker 2012).
4

GENERAL TECHNICAL REPORT PNW-GTR-956
5

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Study Area Description

This study was conducted on the southern Malheur National Forest within the Blue 

Mountains physiographic province of eastern Oregon. The climate is characterized 

by warm summers and cold winters. The majority of precipitation falls as snow 

with significant rain in the spring. Summers are generally very dry, though thunderstorms are common in July and August. The closest recording National Climate 

Data Center station in Seneca, Oregon, shows an average of 35 cm a year of precipitation between 1981 and 2010. Mean maximum temperature for July and August 

during this period was 27 °C, while mean minimum temperature during January 

and December was -11.5 °C. Because of its proximity to the Blue Mountains, 

climate conditions in Seneca should be a fair approximation for the study area. 

Sampling occurred in two primary areas: Dugout Creek Research Natural 

Area (RNA) and Canyon Creek RNA (fig. 2.1). These sites were chosen because 

they contain large, contiguous patches of the desired plant communities that have 

experienced little to no commercial logging or other management actions. Environmental information for RNA study sites is based on the Natural Area Establishment 

Reports (http://www.fsl.orst.edu/rna).

Chapter 2: Methods

! ! !

!

SENECA

JOHN DAY

PRAIRIE CITY

Dugout

Malhuer Ford

Canyon Creek

Legend

! Reference plots # Cities State highways National forest National parks

0 50 100

Miles

50 10

Miles

Figure 2.1—Reference plots in the Malheur National Forest.
6

GENERAL TECHNICAL REPORT PNW-GTR-956

The 350-ha Dugout Creek RNA was established to represent a ponderosa 

pine (Pinus ponderosa Lawson & C. Lawson) community with pinegrass (Calamagrostis rubescens Buckley) and elk sedge (Carex geyeri Boott), and a grand 

fir (Abies grandis (Douglas ex D. Don) Lindl.) community with pinegrass. The 

elevation of Dugout RNA ranges from about 1500 to 1750 m with moderately 

steep, west-facing slopes reaching down to the North Fork Malheur River. There 

are several small drainages within the RNA that flow in shallow ravines, including 

Dugout Creek and Stink Creek. The upper portion of the RNA consists of a large 

bench with generally open scablands. The undulating terrain of the lower slope is 

covered with deep soils and ponderosa pine/elk sedge, ponderosa pine/pinegrass, 

and grand fir/pinegrass communities. The area is broken by several ancillary ridges 

with generally shallow soils and stands of mountain mahogany (Cercocarpus spp.). 

The overstory of the forested area is generally dominated by large-diameter (up to 

1.5 m) ponderosa pines with a mixture of ponderosa pine, grand fir, and Douglas-fir 

(Pseudotsuga menziesii (Mirb.) Franco)) in the understory. Western larch (Larix 

occidentalis Nutt.) occurs as a minor overstory component, primarily in the grand 

fir communities. The herbaceous vegetation is usually dominated by either elk 

sedge or pinegrass, indicating different plant associations (sensu Johnson and 

Clausnitzer 1992). 

The 283-ha Canyon Creek RNA was established to represent unmanaged dry 

forest ecosystems in the Blue Mountains of central and northeastern Oregon. The 

Canyon Creek RNA is located within the southwestern corner of the Strawberry 

Wilderness Area. The RNA is generally south and east facing with a gentle 

slope rising from 1400 m at Canyon Creek to moderately steep ridges on the 

northern and western edges at approximately 1800 m. Ponderosa pine is the most 

common tree species throughout the RNA. Douglas-fir and grand fir become 

increasingly dominant with increasing elevation. Soils are variable but generally 

consist of residual andesitic soils with patches of colluvial and residual granitic 

soils. Strawberry (Fragaria spp.), heartleaf arnica (Arnica cordifolia Hook.), and 

grouseberry (Vaccinium scoparium Leiberg ex Coville) are common understory 

species at higher elevations with pinegrass and elk sedge dominating closer to 

Canyon Creek. On more open areas of the RNA, western juniper (Juniperus 

grandis R.P. Adams) and mountain mahogany are found along with bluebunch 

wheatgrass (Pseudoroegneria spicata (Pursh) Á. Löve ), and Sandberg bluegrass 

(Poa secunda J. Presl).
7

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Site Selection

This study focused on describing historical conditions within the warm-dry upland 

forest (UF) plant association group (PAG) as defined by Powell et al. (2007). The 

warm dry UF PAG represents a collection of finer scale potential vegetation types 

(PVTs) that are similar to each other within a temperature-moisture matrix. The 

biophysical environments delineated by the individual plant associations within the 

warm dry PAG are described in Johnson and Clausnitzer (1992). 

To capture the full range of environmental conditions that occur within the 

warm dry UF PAG, we stratified our sampling design based on the potential vegetation series. The series indicates the dominant climax plant species within a particular PVT (sensu Johnson and Claustnitzer 1992). For example, the grand fir series 

includes every PVT where grand fir is presumed to be the dominant tree species 

at climax. Within the warm dry UF PAG, there are three primary climax series: 

ponderosa pine, Douglas-fir, and grand fir. 

Within each potential vegetation series, we selected five plots to characterize 

historical conditions. Plot locations were determined by overlaying a modeled 

potential vegetation layer over the boundaries of Dugout and Canyon Creek RNAs 

using ArcGIS 10.1. The Create Random Points Tool was used to generate coordinates for 15 random points in each of the three potential vegetation series within the 

warm-dry UF PAG. Each point was numbered sequentially within each potential 

vegetation series (e.g., DF01-DF15, GF01-GF15, and PP01-PP15).

Random points were visited in the field in sequential order to determine their 

suitability for sampling. Criteria for site selection included (1) desired PAG and 

potential vegetation series (as determined in the field), (2) no or minimal evidence 

of previous management, (3) fairly homogenous slope and aspect with no major 

edaphic or topographic variation, and (4) no evidence of fire or other major disturbances since 1890. If a site was deemed suitable, it was accepted and subsequently 

sampled. If a site was deemed unsuitable because the potential vegetation series was 

incorrect but all other criteria were met (i.e., an error in the PVT map), it was designated as an alternate site for the series to which it actually belonged. For example, 

if “GF01” was a suitable sampling site but was actually a Douglas-fir climax area, 

it would become the first alternate site to sample in the event that a Douglas-fir site 

had to be rejected. 
8

GENERAL TECHNICAL REPORT PNW-GTR-956

Owing to a lack of suitable sites within the ponderosa pine series at Dugout 

and Canyon Creek RNAs, we added one additional sampling site in a nearby area 

known as the Malheur Ford. The Malheur Ford sampling area is located at the 

confluence of Black Canyon Creek and the Malheur River (fig. 2.1), and contains 

significant areas of unlogged, pure ponderosa pine forests. Two of the ponderosa 

pine series plots were located in this area using the protocol described above.

In total, 14 plots were established, with 8 in the Dugout Creek RNA, 4 in the 

Canyon Creek RNA, and 2 at Malheur Ford (table 2.1). Target plot size was 4 ha, as 

past reconstructions in dry forests have shown that 4 ha is a good threshold to 

capture gaps (Churchill 2013) in open canopy dry forests. Plots were square except 

where short slopes or complex topography required rectangular plots. Plot size was 

expanded where possible to capture additional area and to account for additional 

edge in rectangular plots. Actual plot size ranged from 3.8 to 5.0 ha for 13 of the 14 

plots. The size of the 14th plot was reduced to 2.3 ha owing to very high density and 

time constraints. In total, five plots totaling 21.6 ha were located on ponderosa pine 

series, five plots totaling 20.6 ha on Douglas-fir series, and four plots totaling 15.6 

ha on grand fir series. A fifth plot in the grand fir series was not installed owing to 

time constraints. Historical structures within a 10-m buffer around each plot were 

included in the mapping to reduce edge effects on spatial pattern analysis results. 

Table 2.1—Biophysical and location data for 14 plots 

Plot Locationa Plant associationb Plot size Elevation Aspect Avg. slope Plot type

Hectares Meters - Percent -

P1 Dugout RNA PIPO/CAGE 4.7 1699 SW 25 Stem map

P2 Dugout RNA PIPO/CARU 4.4 1760 SW 3 Stem map

P3 Canyon Creek RNA PIPO/CARU 4.1 1561 SW 30 Quick map

P4 Malheur Ford PIPO/CARU 4.4 1545 SW 4 Stem map

P5 Malheur Ford PIPO/CARU 4.0 1561 SW 15 Stem map

D1 Dugout RNA PSME/CARU 3.8 1649 W 30 Stem map

D2 Dugout RNA PSME/CAGE 4.2 1579 NW 30 Stem map

D3 Canyon Creek RNA PSME/CARU-VASC 4.1 1490 SE 15 Stem map

D4 Dugout RNA - North PSME/CARU 4.3 1615 W 25 Quick map

D5 Dugout RNA - North PSME/CAGE 4.1 1689 W 25 Stem map

G1 Dugout RNA ABGR/CARU 5.0 1740 N 20 Stem map

G2 Dugout RNA ABGR/CARU 4.0 1675 N 30 Stem map

G3 Canyon Creek RNA ABGR/CARU 2.3 1661 E 20 Stem map

G4 Canyon Creek RNA ABGR/CAGE-VASC 4.3 1704 E & S 15 Quick map

a

 RNA = research natural area.

b PIPO = Pinus ponderosa, CAGE = Carex geyeri, CARU = Calamagrostis rubescens, PSME = Pseudotsuga menziesii, VASC = Vaccinium scoparium, 

ABGR = Abies grandis.
9

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Tree clumps that extended past the buffer were also noted. The four corners of each 

plot were spatially referenced by global positioning system (GPS). One corner of 

each plot was monumented with rebar and referenced to a witness tree, except for 

plots in Canyon Creek on account of wilderness area regulations. 

Field Methods

All historical structures—live trees, snags, and logs that were believed to have been 

alive and greater than breast height in 1890—were mapped in the 14 plots. The reference year of 1890 was chosen based on the finding by Heyerdahl et al. (2001) size, 

season, and severity from fire scars and establishment dates of 1,426 trees sampled 

on grids in four watersheds (similar to 64 plots, over similar to 1620 ha each that this 

was the last fire year in the area before fire exclusion began. Bark and crown characteristics were used to determine if live trees were historical (>123 years, breast 

height age) using guidelines from Van Pelt (2008). Trees whose historical status was 

questionable were cored at breast height. Cores where age was not easily discernible 

in the field were analyzed in the lab using techniques described below. Decay class, 

combined with diameter at breast height (d.b.h.), was used to estimate whether snags 

and logs were live trees in 1890 using methods from Everett et al. (2007).

Tree locations were recorded in one of two ways: stem maps (11 plots) and 

“Quickmaps” (3 plots). For the 11 stem map plots, each tree was mapped using a 

total station survey instrument on a single closed-loop traverse (Nathanson et al. 

2006). In total, 10 to 20 survey stations were established on each plot from which the 

distance and angle to each tree, snag, or log was measured within the total station. 

On the remaining three plots—one plot in each potential vegetation series—a new 

method to map spatial pattern was used. This method, termed “Quickmapping,” 

was designed to reduce the time required to obtain sufficiently accurate spatial data 

needed to quantify stand-level spatial pattern. Mapping is done on the basis of tree 

clumps rather than discrete trees (Churchill et al. 2013). First, clumps of historical 

structures are identified in the field using a 6-m limiting distance from tree center 

to tree center (see section 2.6 for more information on clump delineation). Clumps 

are sequentially numbered and clump membership is recorded for each historical 

structure. Structures with no neighbors within 6 m are termed individuals. A GPS 

point is recorded at the center of each clump, or adjacent to the bole for individuals. 

For each clump the following characteristics are recorded: shape (circle, oval, or 

line), size (radius for circles, major and minor axes for ellipses, length for lines), and 

azimuth for lines and major axes. For large (more than five trees), irregularly shaped 

clumps, a boundary line is also recorded with a GPS in addition to the clump center. 
10

GENERAL TECHNICAL REPORT PNW-GTR-956

For this project, a minimum of 50 GPS locations were averaged for each point using 

a Trimble GEO XT1 with an external Hurricane antenna and differential correction.

For each live tree, we recorded species, d.b.h., age class, and vigor. Age class 

and vigor were determined using rating systems from Van Pelt (2008). A subset of 

live trees (15 percent, 60 to 100 live trees per plot) was sampled more intensively 

to determine age class distribution and develop growth regressions. One tree from 

each vigor class per species was randomly chosen at each survey station to ensure a 

random sample of live measure trees across species, diameters, and tree condition. 

Cores were taken at breast height and were saved in paper straws for laboratory 

analysis. For these live measure trees, we recorded three additional measurements 

in order to calibrate allometric equations and report height information: diameter at 

stump height (30 cm), height to live crown, and total tree height. 

For each snag and log with evidence of having been alive in 1890, we recorded 

species, diameter, and decay class (Cline et al. 1980). Height was also recorded for 

snags. Although species was generally evident, some logs with advanced decay 

could not be identified. Because diameter measurement outside bark at breast height 

was not always possible, we measured either at stump height or breast height and 

either inside or outside bark. A few cut stumps were found on several plots and 

were treated as snags. 

Stem Map Reconstruction

Increment cores from 940 live measure trees were air dried, mounted, and sanded. 

Blocks of processed cores were scanned using an Epson Expression 11000XL 

scanner at 3,000 dots per inch. Ring widths and total rings to pith at breast height 

were measured from the digital images of each core using CooRecorder software 

(Larsson 2003). Cores were not cross-dated as radial growth was the primary metric of interest. The loss of accuracy in growth measurements from not cross-dating 

was deemed to be minimal after inspection of a large sample of the cores showed 

minimal number of missing rings. For cores with a missing pith, curvature of rings 

was used to estimate distance and number of rings to pith where possible using a 

tool within the CooRecorder software (Larsson 2003). This was not possible for 

all cores with missing piths resulting from rot. These cores were eliminated from 

the sample. Automated ring detection was used, but ring locations were visually 

checked for each core and corrected when necessary. The sample of “live measure 

trees” was used to develop growth regressions for diameter reconstruction, and 

also to generate an age class distribution for each plot in 50-year age classes.

1 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.
11

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

We followed methods of North et al. (2007) and Bakker (2005) to reconstruct 

outside bark d.b.h. in 1890 for all live trees on the plot. A regression model was 

built using the live measure trees to predict total inside bark basal area increment 

from 1890 to 2013, which was then used to estimate 1890 d.b.h. for all live trees. 

For snags and logs that were believed to be alive in 1890, a similar approach was 

used, but year of death had to be estimated using equations from Everett et al. 

(1999). A full description of diameter reconstruction methods and model results is 

provided in appendix 1. 

Coordinates in local coordinate geometry were derived for each historical 

structure from survey data to generate stem maps for each plot. For the Quickmaps, 

a tool was built in ArcMap 10.1 to generate coordinates for each tree. The tool uses 

the recorded shape, size, and axies azimuth information for each clump to create 

a temporary shape (line, circle, oval). Trees within the clump are then randomly 

placed along the boundary of the shape, with minimum distance of 1.5 m apart. The 

line feature was used to outline large, irregular clumps. Geographic coordinates of 

trees were then converted and rotated to the same (0,0) grid as the stem maps. 

For all plots, stem density, composition, and size distribution information was 

calculated from species and reconstructed diameter. Trees within the 10-m buffer were not counted in summary inventory metrics, nor was the buffer included 

in the final plot size. All trees less than 15 cm d.b.h. in 1890 were removed from 

the dataset and were not counted in structure and pattern metrics. Accurately 

reconstructing tree populations less than 15 cm is challenging because of the faster 

decay of small trees (Barth et al. 2015). Historical canopy cover was also estimated 

for each plot by projecting the crowns of all trees onto a stem map, calculating the 

two-dimensional area covered by crowns, and dividing by the total area of the plot. 

This spatially explicit method thus accounted for crown overlap between neighboring trees. Crown projections were based on d.b.h. to crown radius models developed 

from U.S. Forest Service Current Vegetation Survey plots from the Blue Mountains 

and eastern Washington (see app. 2 for more information on these models). 

Current Conditions

To assess the change in density and species composition from 1890 to 2013, five 

0.04-ha fixed-area plots were installed in 6 of the 14 stem-mapped plots, all within 

the Dugout RNA. Two stem-mapped plots from each potential vegetation series 

were selected. All live trees and snags greater than 15 cm d.b.h. were measured and 

tallied within each fixed-area plot. The fixed-area plots were located on a systematic 

grid within each stem-mapped plot. 
12

GENERAL TECHNICAL REPORT PNW-GTR-956

Spatial Pattern Analysis

We quantified spatial patterns in terms of widely spaced individual trees, tree 

clumps, and openings using three metrics: (1) a clump identification algorithm from 

Plotkin et al. (2002), (2) the empty space distribution (Diggle 2003), and (3) opening sizes using a new delineation approach. The clump algorithm partitions a stem 

map of tree locations into clumps at a specified intertree distance (t), measured from 

tree center to tree center. Trees are members of the same clump if they are within 

distance t of at least one other tree in the clump. Trees with no neighbors within 

distance t are termed individuals. 

The clump algorithm can be used in two ways: a single intertree distance 

threshold, or crown radius modeled from allometric equations. For the singledistance method, trees are part of the same clump if they are within the threshold 

distance. This distance is based on the average distance at which mature trees of 

the dominant species in the study area display interlocking crowns. When using 

modeled crown radius, trees are members of the same clump if their projected 

crowns intersect. The crown radius method is a more accurate description of which 

trees have interlocking canopies (Fry et al. 2014, Lydersen et al. 2013). However, the 

single distance is faster and less subjective to use in the field and easier to translate 

into management guidelines (Churchill et al. 2013). 

As the primary purpose of this study was to generate reference conditions for 

management, we chose to use a single intertree distance to delineate clumps. We 

selected a threshold of 6 m based on the observed distance at which most mature 

and old ponderosa pine trees (>120 years) in our study have interlocking crowns. 

This method has been previously used to identify tree clumps in frequent-fire 

forests using the same or very similar distances (Abella and Denton 2009, Churchill 

et al. 2013, Sánchez Meador et al. 2011). 

The number of clumps of different sizes, measured in numbers of trees, was 

then tabulated and converted to a clump size distribution. This distribution summarizes the percentage of trees arranged as individuals and in clumps of different 

sizes. To facilitate translation to management guidelines, clump sizes were also 

reported in bins: individuals (1 tree), small clumps (2 to 4 trees), medium clumps 

(5 to 9 trees), large clumps (10 to 14 trees), and super clumps (15 to 30+ trees) 

based on functional differences (e.g., understory shading, number of interior trees) 

(Churchill et al. 2013). The proportion of basal area in each clump size bin and the 

quadratic mean diameter of trees in each clump size were derived. The proportion of trees and basal area in these five bin sizes was also generated for intertree 

distances of 3, 4, 5, and 7 m should managers want to select a different threshold 
13

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

distance to define clumps. A 10-m distance was also included to provide information on the proportion of widely spaced trees. We also generated clump size distributions at 6 m for all trees >10 cm (app. 3). 

Open space in low-canopy-cover forests is difficult to quantify as it typically does not occur in clearly definable canopy gaps. Instead, openings are the 

matrix or interspace component in which individual trees or clumps are distributed (Reynolds et al. 2013). Methods have been developed to delineate gaps in 

frequent-fire forests (see Lydersen et al. 2013), but require setting a distance on 

where gaps “close” or are pinched off. We found that a single distance does not 

work well for plots with varying tree densities and opening configurations; gap 

delineation ends up being quite arbitrary. Instead of focusing on gap delineation, 

we quantified openings based on the distance to the nearest tree. When standing 

in an open area (or anywhere in a plot), this is simply the distance to the nearest 

tree or gap edge. Many ecological processes such as regeneration and growth 

of shade-intolerant species (York et al. 2004), insect spread (Fettig et al. 2007), 

and crown fire spread can be related to distance from the nearest tree. A similar 

concept is used in variable-retention harvesting to quantify the amount of area 

beyond the “tree influence zone,” typically one tree height from a retention patch 

(Baker and Read 2011). 

We quantified distance to the nearest tree using the empty space function, F(t). 

This function quantifies what percentage of each plot is greater than a specified 

distance away from a tree (Diggle 2003). The function generates a grid of points 

across a plot, set to 0.5 m in our case, and then derives the distance from each point 

to its nearest tree. These distances are pooled to create a cumulative distribution 

that has no subjective settings and thus can be compared across plots. The function 

thereby quantifies the total amount of open area in a plot and distinguishes whether 

the total amount of opening is distributed in many small openings or fewer, larger 

ones. To facilitate use of F(t), we converted the cumulative distribution into 3-m 

bins. A graphical plot of this function was created to visually assess the spatial 

distribution of cells in the 3-m bins across each plot. 

We also choose a threshold distance to define what we consider to be open 

space in dry forests. We chose 9 m for several reasons: this distance is beyond 

where trees share resources across root and mycorrhizal networks (Simard et al. 

2012), adequate for ponderosa pine regeneration and growth (York et al. 2004), 

and wide enough to impede spread of active crown fire in all but very extreme fire 

weather (Peterson and Johnson 2007, Powell 2010). The percentage of plot area 

greater than 9 m away from a tree was then derived, which is the total open space 

that is at least 18 m across.
14

GENERAL TECHNICAL REPORT PNW-GTR-956

We then delineated large openings within each plot based on the 9-m threshold. 

First, polygons were created for all areas greater than 9 m away from a tree. Each 

polygon was then buffered by 5 m to expand the polygon to within 4 m of tree piths. 

The distance of 4 m was chosen as this was determined to be the average distance 

for which crowns of mature trees in these plots extend into openings. Intersecting 

and adjoining polygons were then dissolved (merged) to form contiguous polygons. 

The area for each polygon was derived in order to generate an opening size distribution and percentage of the plot in large openings. 

We used a similar edge correction method (Sanchez Meador et al. 2011) for all 

spatial analyses, but with some important differences. Here, the cluster algorithm 

was run using the plot and 10-m buffer. We then used a reduced sample edge correction in which all trees in the buffer are dropped from the tree list. However, the 

clump sizes of the trees within the plots still reflect the trees in the buffer that were 

dropped. Where clumps extended past the buffer, the total clump size noted in the 

field was used. For example, for a 12-tree clump with five trees inside the plot, five 

trees in the buffer, and two trees outside the buffer, the five trees in the plot would 

be tabulated as being part of a 12-tree clump. We used the same edge correction 

approach for the empty space function. F(t) was first run for the plot and buffer 

zone. We then removed the grid points in the buffer zone from the F(t) distribution. 

Large openings were cut off at the 10-m plot buffer. 

Two additional spatial pattern metrics were calculated. We measured the distribution of basal area and trees per hectare across each stem map using circular 

0.04- and 0.08-ha fixed-area plots, plus variable-radius plots with a 4.6-basal area 

factor (20 BAF). Plots were simulated on a square grid every 20 m on the computer. 

We derived the pair correlation function, g(t), for each plot to determine if they were 

statistically different from a random pattern, either clumped or uniformly spaced. 

This information permits inferences as to the nature of the processes that are creating 

the observed patterns. This analysis also allowed us to compare our results to other 

studies of reference spatial patterns (Larson and Churchill 2012). The pair correlation 

function is commonly used in analysis of tree patterns to investigate whether there is 

a nonrandom process creating patterns and to better understand the processes driving 

patterns (Fortin and Dale 2005, Larson and Churchill 2012, Perry et al. 2006). The 

g(t) function is a noncumulative form of Ripley’s K(t) (Ripley 1988). We first tested 

for overall departure from complete spatial randomness from 0.1 to 30 m using the 

Cramer–von Mises goodness-of-fit test from Loosmore and Ford (2006) with g(t) for 

each plot. The g(t) curves were then compared with 1,000 random patterns (complete 

spatial randomness) to assess distances at which patterns where clumped, random, or 

inhibited. We used an isotropic (Ripley 1988) edge correction for all g(t) tests.
15

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Assessing Relationships Among Pattern, Density, and Potential 

Vegetation Series

We assessed differences in pattern types among potential vegetation series in two 

ways. First, we sorted the plots by the proportion of trees occurring as individual 

trees and visually examined the results to see the extent to which the plots sorted by 

vegetation series. Next, we used PERMANOVA, which is a nonparametric permutation version of ANOVA (Anderson 2001), to test for overall statistical differences 

in clump size distributions among vegetation series. We ran PERMANOVA using 

a distance matrix of the proportions of trees in each plot in the five clump bins: 

individuals (1 tree), small clumps (2 to 4 trees), medium clumps (5 to 9 trees), large 

clumps (10 to 14 trees), and super clumps (15 to 30+ trees). Contrast Tests and 

PERMANOVA were then used to test for differences between each pair of potential 

vegetation series (see Churchill [2013] for a full description of this method). 

To facilitate translation of the pattern results into marking guidelines, we 

grouped patterns into “low,” “medium,” and “high” levels of clumping using 

hierarchical cluster analysis with the distance matrix of binned clump size proportions (McCune and Grace 2002). We reported the mean values for proportions of 

trees in each clump size bin for the three clumping levels. Finally, we examined the 

relationship between pattern and tree density by calculating the mean clump size for 

each plot (Plotkin et al. 2002) and the total plot area greater than 9 m away from the 

nearest tree (F > 9). Tree density was quantified as trees per hectare. 
16

GENERAL TECHNICAL REPORT PNW-GTR-956
17

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Chapter 3: Summary Results

Historical forest size, density, composition, and pattern information are summarized for 

all 14 plots in tables 3.1 through 3.4 and figs. 3.1 through 3.6. In addition, more detailed 

information and a stem map are provided for each plot in chapter 4. Model information 

and results for diameter reconstruction methods are provided in appendix 1. 

Structure, Density, Composition, and Age

Basic forest structure information was compiled for all 14 plots based on reconstructed diameters. A wide range of tree densities was found, ranging from 53 to 

197 trees per hectare (tph) (table 3.1). Basal area ranged from 11.1 to 24.2 m2 ∙ ha-1. 

Mean diameters ranged from 35.2 to 57.8 cm, and Stand Density Index ranged from 

183 to 415 (metric). In all plots except for G2, well over 50 percent of the basal area 

was composed of trees greater than 50 cm diameter at breast height (d.b.h.) (fig. 3.1). 

Most plots had somewhat normal or log-normal shaped diameter distributions with 

the majority of trees in the 30- to 50-cm range (fig. 4.1 panel A). Density of trees 

50 to 70 cm ranged from 20 to 40 tph. All plots had trees greater than 90 cm, but 

generally at a density level of less than five tph. 

Species composition was entirely or heavily dominated by ponderosa pine (Pinus 

ponderosa Lawson and C. Lawson) on plots within the ponderosa pine and Douglasfir series (fig. 3.1). Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) made up less 

than 10 percent of the basal area on plots within the Douglas-fir and grand fir series. 

Grand fir (Abies grandis (Douglas ex D. Don) Lindley), on the other hand, was abundant on three of the four plots within the grand fir series comprising 44 to 48 percent 

of the basal area on these three plots. Western larch (Larix occidentalis Nutt.) only 

was present on one of the plots within the Douglas-fir series and made up less than 10 

percent of the basal area on plots within the grand fir series. Rocky mountain juniper 

(Juniperus scopulorum Sarg.), lodgepole pine (Pinus contorta Douglas ex Loudon), 

and mountain mahogany (Cercocarpus Kunth) were present in very small amounts, 

primarily in the Douglas-fir and ponderosa pine series (fig. 3.1). All plots had a wide 

range in ages of trees that were alive in 1890 (fig. 4.1 panel B). In 12 of the 14 plots, 

the sample of live measure trees included 400- to 500-year-old trees. The other two 

plots had 300-year-old trees. Tree establishment occurred relatively continuously in 

most plots, although some pulses are apparent in the Canyon Creek plots. 

Current density (2013) was higher than historical density for all six plots that 

were sampled (fig. 3.2). Trees-per-hectare values increased by 41 to 460 percent, 

while basal area increased by 16 to 186 percent. This greater increase in tree 

density vs. basal area indicates that current mean diameters have decreased relative 

to historical conditions. The proportion of basal area in ponderosa pine decreased 

on the plots in the Douglas-fir and grand fir potential vegetation series (fig. 3.2). 
18

GENERAL TECHNICAL REPORT PNW-GTR-956Table 3.1—Summary information for 14 historical reference plots on the Malheur National Forest (forest structure was reconstructed to 1890) 

Plot

Plant 

series

Basal 

area Trees 

Average 

d.b.h. QMDa

Max 

height 

Canopy 

cover Openingsa

Basal 

area Trees 

Avg. 

d.b.h. QMDb SDIcc

Max 

height

m2/ ha-1 Ha-1 cm m Percent Ft2/ac-1 ac-1 - - - - inch - - - - ft

P1 PIPO 13 65 46.9 50.2 37 15 62 56 26 18.5 19.8 86 120

P2 PIPO 21 101 47.1 51 40 22 52 90 41 18.6 20.1 137 130

P3 PIPO 19 103 46.1 48.8 41 20 54 84 42 18.1 19.2 131 133

P4 PIPO 19 98 47 49.7 45 21 53 83 40 18.5 19.6 127 146

P5 PIPO 19 94 47.4 50.1 41 21 51 81 38 18.7 19.7 124 134

D1 PSME 14 59 51.1 54.6 41 16 72 61 24 20.1 21.5 91 134

D2 PSME 14 79 43.4 48 40 18 53 63 32 17.1 18.9 98 130D3 PSME 14 87 41.7 44.6 44 18 49 59 35 16.4 17.5 94 144

D4 PSME 13 64 47.2 50.6 37 15 67 56 26 18.6 19.9 86 120

D5 PSME 22 74 57.8 61.3 37 23 62 95 30 22.8 24.1 137 119

G1 ABGR 24 161 40.3 43.6 40 31 24 105 65 15.9 17.2 168 130

G2 ABGR 23 197 35.2 38.3 41 33 15 99 80 13.9 15.1 165 135

G3 ABGR 11 53 44.1 51.5 43 13 66 48 22 17.3 20.3 74 141

G4 ABGR 20 122 41.8 45.3 43 25 40 85 49 16.5 17.8 135 142

Note: Data are for all trees >14.9 cm diameter at breast height (d.b.h.). Canopy cover is based on modeled crown widths.a QMD = quadratic mean diameter.b Stand density index (SDI) in English units. An exponent of 1.7 was used to calculate SDI.c Percentage of plot in large openings. See section 2.6 for an explanation of how large openings were delineated.

PIPO = Pinus ponderosa.PSME = Pseudotsuga menziesii.ABGR = Abies grandis.
19

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

PlotPlot

Diameter class

10−30 cm

30−50 cm

50−70 cm

70−120+ cm

0 5 10 15 20 25 0 5 10 15 20 25

P1

P2

P3

P4

P5

D1

D2

D3

D4

D5

G1

G2

G3

G4

Species

PIPO

ABGR

PSME

LAOC

Other

P1

P2

P3

P4

P5

D1

D2

D3

D4

D5

G1

G2

G3

G4

Plot

Basal area (m2 ha−1) Basal area (m2 ha−1)

Figure 3.1—Left panel displays historical (1890) basal area in different size classes for 14 reference plots. Right panel displays breakdown of plot basal area by species. Other species include lodgepole pine, Rocky Mountain juniper, and mountain mahogany. PIPO = 

Pinus ponderosa, ABGR = Abies grandis, PSME = Pseudotsuga menziesii, LACO = Larix occidentalis.

Trees per hectare

0 100 200 300 400 500

2013

1890

2013

1890

2013

1890

2013

1890

2013

1890

2013

1890

2013

1890

2013

1890

2013

1890

2013

1890

2013

1890

2013

1890

P1

P2

D1

D2

G1

G2

0 10 20 30 40

2013

1890

2013

1890

2013

1890

2013

1890

2013

1890

2013

1890

2013

1890

2013

1890

2013

1890

2013

1890

2013

1890

2013

1890

P1

P2

D1

D2

G1

G2

Species

PIPO ABGR PSME LAOC Other

Basal area (m2

 ha−1)

Figure 3.2—Current (2013) vs. historical (1890) density (left panel) and basal area (right panel) for 14 reference plots. Current information 

is from five 0.04-ha fixed-area plots installed in each historical stem map. PIPO = Pinus ponderosa, ABGR = Abies grandis, PSME = Pseudotsuga menziesii, LACO = Larix occidentalis. Other species include lodgepole pine, Rocky Mountain juniper, and mountain mahogany.
20

GENERAL TECHNICAL REPORT PNW-GTR-956

Table 3.2—Clump size distributions for Malheur National Forest reference plots ordered by the proportion of 

trees that are individuals (clump size = 1) 

Proportion of trees Proportion of basal area

Clump size (number of trees)

Plot Series Clumping level 1 2-4 5-9 10-15 16-30+ 1 2-4 5-9 10-15 16-30+

G3 ABGR Low 0.53 0.34 0.04 0.08 0.00 0.68 0.26 0.02 0.03 0.00

P1 PIPO Low 0.38 0.49 0.13 0.00 0.00 0.46 0.47 0.07 0.00 0.00

D2 PSME Low 0.38 0.41 0.16 0.06 0.00 0.52 0.36 0.09 0.03 0.00

D1 PSME Low 0.36 0.42 0.11 0.11 0.00 0.50 0.39 0.06 0.06 0.00

D4 PSME Low 0.34 0.44 0.22 0.00 0.00 0.43 0.39 0.17 0.00 0.00

D3 PSME Low 0.34 0.42 0.24 0.00 0.00 0.36 0.45 0.19 0.00 0.00

D5 PSME Low 0.33 0.57 0.10 0.00 0.00 0.45 0.48 0.07 0.00 0.00

P5 PIPO Moderate 0.23 0.34 0.38 0.05 0.00 0.28 0.37 0.31 0.05 0.00

P4 PIPO Moderate 0.21 0.39 0.29 0.11 0.00 0.26 0.38 0.28 0.08 0.00

P2 PIPO Moderate 0.21 0.29 0.25 0.15 0.11 0.31 0.30 0.20 0.09 0.09

P3 PIPO Moderate 0.18 0.40 0.35 0.03 0.05 0.22 0.41 0.32 0.02 0.03

G4 ABGR High 0.17 0.33 0.22 0.11 0.18 0.25 0.33 0.19 0.10 0.14

G1 ABGR High 0.13 0.27 0.35 0.11 0.14 0.19 0.31 0.29 0.08 0.13

G2 ABGR High 0.10 0.20 0.27 0.16 0.27 0.14 0.23 0.27 0.15 0.22

a

 The clump size distribution is the proportion of trees or basal area by clump size. Clump size is the number of trees in a clump. Clumps are defined 

as trees within at least 6.1 m of another tree in the clump. Plots are grouped by plant series and clumping level. Clumping levels were derived using 

hierarchical cluster analysis. PIPO = Pinus ponderosa, PSME = Pseudotsuga menziesii, ABGR = Abies grandis

Spatial Pattern

Clump size distributions were generated using an intertree distance of 6 m with 

the Plotkin et al. (2002) clump detection algorithm. The cumulative form of 

these distributions are shown in figure 3.3, while the values grouped into five 

clump-size bins are displayed in table 3.2. The proportion of individual trees 

ranged from 0.53 to 0.10. Ten of the plots had large clumps (10 to 15 trees), with 

the proportion of trees in large clumps ranging from 0.03 to 0.16. Five plots had 

super clumps (16 to 30+ trees) with proportions ranging from 0.05 to 0.27. The 

largest clump identified was 32 trees in plot G2. The proportion of basal area 

in different clump sizes was consistently higher for individual trees and lower 

for large and super clumps (table 3.2), indicating that individual trees and small 

clumps had larger diameter trees. Individual trees had mean QMD values of 45 

to 70 cm (fig. 4.1 panel D), while the QMD of trees in large and super clumps 

was generally around 30 to 50 cm. However, large trees (>50 cm) did occur in 

large and super clumps. 
21

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Table 3.3—Clump size distributions from table 3.2 summarized by clumping level and plant 

association groupa

Proportion of trees Proportion of basal area

Clump size (No. of trees) Clump size (No. of trees) 

1 2-4 5-9 10-15 16-30+ 1 2-4 5-9 10-15 16-30+

Clumping level

Low 0.38 0.44 0.14 0.04 0.00 0.49 0.40 0.10 0.02 0.00

Moderate 0.21 0.35 0.32 0.09 0.04 0.27 0.37 0.28 0.06 0.03

High 0.13 0.27 0.28 0.13 0.19 0.19 0.29 0.25 0.11 0.17

Series:

PIPO 0.24 0.38 0.28 0.07 0.03 0.30 0.39 0.24 0.05 0.02

PSME 0.35 0.45 0.17 0.03 0.00 0.45 0.41 0.12 0.02 0.00

ABGR 0.23 0.29 0.22 0.12 0.15 0.31 0.28 0.19 0.09 0.12

a Values are averages for that group.

PIPO = Pinus ponderosa, PSME = Pseudotsuga menziesii, ABGR = Abies grandis.

0 5 10 15 20 25 30

0.0

0.2

0.4

0.6

0.8

1.0

Clump size (number of trees)

Proportion of trees

ABGR series

PSME series

PIPO series

Figure 3.3—Proportional clump size distributions of 14 references plots from the Malheur National 

Forest. Each line represents one plot. ABGR = Abies grandis, PSME = Pseudotsuga menziesii, 

PIPO = Pinus ponderosa.
22

GENERAL TECHNICAL REPORT PNW-GTR-956

Plots were grouped into three clumping levels (high, moderate, and low) using 

hierarchical cluster analysis (table 3.3). The high clumping group had a relatively 

even proportion of trees in all clump sizes with 13 percent of trees as individuals 

and 19 percent in super clumps (table 3.3). The moderate clumping group was 

dominated by small and moderate clumps, with 21 percent as individuals, and 13 

percent in large and super clumps combined. The low clumping group was dominated by small clumps and individuals, with 38 percent in individuals, 44 percent 

in small clumps, 14 percent in moderate clumps, 4 percent in large clumps, and 

no super clumps. We also generated binned clump-size distributions at 6 m for all 

trees >10 cm (app. 3). 

The cumulative distributions of the empty space function varied widely 

across the plots and were closely related to density (fig. 3.4). The proportion of 

the plot area greater than 9 m away from a tree ranged from 5 percent in G2 to 32 

percent in D1 and G3 (fig. 3.4). Total area in large openings varied from 15 to 72 

percent (table 3.1). Most large openings were less than 0.04 ha, however, and only 

13 openings greater than 0.4 ha were found across all 14 plots (fig. 3.5). Opening 

size distributions had a sharp negative exponential or “reverse J” shape (figs. 3.5). 

Openings were generally sinuous and irregular in shape, ranging from 18 to 45 

m across, and were often interconnected across a plot. Relatively few compact, 

circular gaps were found. 

ABGR series PSME series PIPO series

0 20 40 60 80 100

0 5 10 15

Density (tph)

Mean clump size

0 20 40 60 80 100

0.00 0.10 0.20 0.30

Density (tph)

F > 9

5 10 15 20 25

0.0 0.2 0.4 0.6 0.8 1.0

Distance to nearest tree (m)

Proportion of plot area

Figure 3.4—Left and center panels show scatterplots of density (trees per hectare [tph]), mean clump size, and F > 9 m (plot area greater 

than 9 m from the nearest tree or gap edge) for 14 reference plots. Right panel displays cumulative open space distribution, F(t), of 14 

plots. Vertical bar shows F > 9. ABGR = Abies grandis, PSME = Pseudotsuga menziesii, PIPO = Pinus ponderosa. 
23

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

The distribution of basal area (BA) from the 

fixed-area plots that were simulated across each 

stem map plot showed wide variations in all plots 

(figs. 3.6 and 4.1 panel G). All stem map plots had 

low density areas with few or no trees as well as 

areas of high basal area (60 to 80 m2 ha-1). Even the 

lowest density plot, G3, had areas with 40 to 50 m2 

ha-1 of basal area. Basal area distributions from the 

Douglas-fir and grand fir series were not normally 

distributed (fig. 3.6). Distributions were relatively 

flat up to the mean and then tapered off into a long 

right tail. Basal area distributions from the grand fir 

series were closer to a normal or bell-shaped distribution, but still had long right tails. For all plots, 

the mean BA value was not the majority condition 

on the plot (fig. 3.6). These results were the same 

for 0.08 ha fixed-area plots and 4.6 basal area factor 

variable radius plots (app. 4). 

The Cramer–von Mises goodness-of-fit test 

from Loosmore and Ford (2006) found that all plots 

were statistically different from a random pattern 

(p < 0.002) and clustered. The pair correlation 

function curves, g(t), showed that all plots were 

clustered at intertree distances from 1 to 6 m, with 8 out of 14 plots clustered up to 

10 to 12 m (app. 5). Four of the plots were clustered at even longer distances. This 

indicates nonstationary or inhomogeneous patterns where areas of higher density 

and higher clumping were not randomly or evenly spread out across these plots, 

but grouped into sections of the plot. 

Number of openings

0

50

100

150

0− 0.04

0.041− 0.08

0.081− 0.20.21− 0.40.41− 0.8

0.81− 1.61.61− 2.4

Size class (ha)

ABGR series

PSME series

PIPO series

Figure 3.5—Number of large openings by size class and potential 

vegetation series for 14 reference plots. Openings are pooled together 

across all 14 plots. See “Spatial Pattern Analysis” on p.14 for an 

explanation of how large openings were delineated. PIPO = Pinus 

ponderosa, PSME = Pseudotsuga menziesii, ABGR = Abies grandis.
24

GENERAL TECHNICAL REPORT PNW-GTR-956

0.00

0.05

0.10

0.15

0.20

10

30

50

70

90

110130150170190210230250270280+

2.3

6.9

11.5 16.1 20.7 25.3 29.8 34.4 39

43.6 48.2 52.8 57.4 62

64.3+

PIPO series

Mean basal area

Proportion of plots

0.00

0.05

0.10

0.15

0.20

Proportion of plots

PSME series

Basal area (midpoint of 4.6 m

2

 ha−1class)

Proportion of plots

0.00

0.05

0.10

0.15

0.20

ABGR series

Basal area (midpoint of 20 ft

2

 ac−1 class)

Figure 3.6—Frequency distribution of historical basal area pooled by 

potential vegetation series. Basal area was calculated for 0.04-ha fixedarea plots on a 20-m grid across each of the 14 reference plots. Fixed-area 

plots were simulated. The top panel shows the pooled results for the five 

ponderosa pine plots, the middle panel shows results for the five Douglasfir plots, and the bottom panel shows results for the four grand-fir plots. 

Red lines are means for the respective series. 
25

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Relationships Among Pattern, Density, and Plant Series 

Some trends were evident in the relationships between clump size distributions, 

density, openings, and potential vegetation series (tables 3.1 and 3.2, figs. 3.3 

through 3.5). The Douglas-fir series plots had the lowest densities (mean tph: 73, sd: 

11.3), lowest levels of clumping, and more area in open space. The ponderosa pine 

series plots supported intermediate stem densities (mean tph: 92, sd: 15.6) and had 

moderate levels of clumping and openings. The grand fir series plots had the highest 

stem densities (mean tph: 133, sd: 61.6) and the highest levels of clumping and lowest levels of open space. Sorting the plots by the proportion of trees that occurred as 

individuals matches quite closely with potential vegetation series (table 3.2). 

There were two notable exceptions to these trends, however. Plots G3 and P1 had 

lower densities and levels of clumping than most Douglas-fir series plots and were 

both in the Low clumping group. The PERMANOVA test for a significant relationship between potential vegetation series and clumping levels was thus rejected (p 

= 0.065), but was very close to being statistically significant. Contrast tests showed 

that the Douglas-fir series plots had statistically different clumping levels from the 

ponderosa pine and grand fir series plots (p = 0.038 and p = 0.047, respectively), but 

the ponderosa pine and grand fir series plots were not different (p = 0.33). 

Overall, there is a clear increase in clumping and decrease in open space with 

increasing density (fig. 3.4). The relationship between density and mean clump size 

is roughly linear, while the density and open space (F > 9 m) have a reverse exponential distribution. 
26

GENERAL TECHNICAL REPORT PNW-GTR-956
27

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Chapter 4: Individual Plot Results

This section provides the range of conditions found in this study, including size, density, composition, and pattern results for each of the 14 plots. The same tables and figures are presented 

across two pages for each plot. All results are for live trees reconstructed to 1890, except 

for age class, which is age in 2013. Trees down to a lower diameter at breast height (d.b.h.) 

cutoff of 15 cm in 1890 are included in all figures. Species abbreviations are as follows: PIPO: 

ponderosa pine; ABGR: grand fir; PSME: Douglas-fir; LAOC: western larch; JUOC: rocky 

mountain juniper; PICO: lodgepole pine; and CELE3: mountain mahogany. CAGE = Carex 

geyeri Boott. CARU = Calamagroustis rubescens Buckley. VASC = Vaccinia scoporium 

Leiburg ex Colville. Below is a caption for the panels that are presented for each of the 14 plots. 

Panels

Panel A: Diameter distribution by species in 10-cm classes. Values on x-axis are diameterclass midpoints. The lower diameter cutoff is 15 cm; 20 equates to a 15- to 24.9-cm class. 

Diameters are reconstructed to 1890. 

Panel B: Age-class distribution for live measure trees where age could be determined. Age 

is from 2013, not 1890. 

Panel C: Stem map of reconstructed 1890 trees on plot. Tree boles are colored by species 

and proportional to size. A 3-m radius was used to project tree crowns on all trees to illustrate clump identification using a fixed distance of 6 m. Clump size is the number of trees 

in the clump. Large openings are shown with a dashed line (see chapter 2, “Spatial Pattern 

Analysis section,” for an explanation of how large openings were identified). Background 

yellow to red coloration is the graphical display of the empty space function; colors indicate 

distance to the nearest tree in meters. 

Panel D: Table showing clump size proportions for trees and basal area for various intertree 

distances. Quadratic mean diameter of different clump sizes is also shown. 

Panel E: Bar plot of empty space distribution. Each bar shows the proportion of the plot 

area that is within that range of distance from the nearest trees. Colors match background 

coloration from stem map on panel C. 

Panel F: Bar plot of opening size distribution for plot. Data are for large openings shown on 

stem map in panel C. See section 2.6 for an explanation of how large openings were identified. Note that size bins are not equal, but get proportionally larger. 

Panel G: Frequency distribution of historical basal area across plot. Basal area was calculated on 0.04-ha fixed-area plots laid out on a 20-m grid across the stem map plot. Fixedarea plots were run on the computer, not measured in the field. Values shown on x-axis are 

midpoints for each class or bin: 5 equates to the 0 to 9-m2

 ha-1 bin. To convert values to ft2

ac-1 multiply values by 4.36.
28

GENERAL TECHNICAL REPORT PNW-GTR-956

Ponderosa Pine 1

Location: Dugout Research Natural Area

Plant association: PIPO/CAGE

Topography: Slope: 15 to 40 percent, mean 25 

percent; aspect: SW; elevation: 5,480 to 5,695 ft, 

mean 5,575 ft.

Description: Historically low-density site 

with a preponderance of young pole-sized 

pine. Located at the upper reach of a southfacing slope above Stink Creek. The northern 

edge of the plot abuts the exposed rocks of 

the ridge top, among which grow juniper and 

mountain mahogany. 

Summary metrics

Hectares

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height 

Canopy 

cover Acres

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height SDI

m2

·ha-1 ha-1 m Percent ft2·ac-1 ac-1 ft

4.7 13 65 46.9 50.2 37 15 11.6 56 26 18.5 19.8 120 86

Avg. = average, d.b.h. = diameter at breast height, OMD = quadratic mean diameter, SDI = standard density index.

Proportion of basal area

PIPO ABGR PSME LAOC JUOC PICO CELE3 Unknown

0.992 0.002 0 0 0.002 0 0 0.005

D.b.h. class midpoint (10 cm)

Trees per hectare

0

5

10

15

20

25

2030405060708090100110120130

A

PIPO

ABGR

PSME

LAOC

Other

Tree age (years)

Number of trees

0

5

10

15

120−149150−199200−249250−299300−349350−399400−449450−499500+

B
29

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Species

PIPO

ABGR

PSME

LAOC

Other

Clump

size

1

2−4

5−9

10−15

16+

Openings

Distance to nearest tree (meters)

30

5

10

15

20

25

10 30 50 70 90 110 130 150 170 190 210 230

10

30

50

70

90

110

130

150

170

190

210

Meters

CProportion of area

0.0

0.1

0.2

0.3

0.4

0−33−66−99−1212−1515−1818−2121−2424+

Distance to nearest tree (m)

E

Number of openings

0

5

10

15

0− 0.040.041− 0.08

0.081− 0.2

0.21− 0.4

0.41− 0.8

0.81− 1.61.6− 2.4

Size class (ha)

F

Proportion of plots

0.0

0.1

0.2

0.3

0.4

5 101520253035404550

5560+

G

Basal area (midpoint m2·ha−1)

D Clump proportions 

(trees)

Clump proportions 

(basal area)

Clump quadratic mean diameter 

(cm)

Intertree 

dist. (m)

Clump size (No. of trees) Clump size (No. of trees) Clump size (No. of trees) 

1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+

2 0.83 0.17 0 0 0 0.86 0.14 0 0 0 51 45.7 0 0 0

3 0.7 0.3 0 0 0 0.74 0.26 0 0 0 51.4 47.2 0 0 0

4 0.6 0.39 0.02 0 0 0.66 0.33 0.01 0 0 52.6 46.7 39.5 0 0

5 0.46 0.51 0.03 0 0 0.53 0.45 0.02 0 0 54.3 46.9 39.3 0 0

6 0.38 0.49 0.13 0 0 0.46 0.47 0.07 0 0 55 49.2 37.7 0 0

7 0.31 0.44 0.2 0.04 0 0.38 0.42 0.14 0.05 0 55.7 49.1 41.7 56.2 0

10 0.12 0.3 0.29 0.13 0.16 0.16 0.31 0.29 0.1 0.14 57.8 51 50.4 44.1 46.5
30

GENERAL TECHNICAL REPORT PNW-GTR-956

Ponderosa Pine 2

Location: Dugout Research Natural Area

Plant association: PIPO/CARU

Topography: Slope: 1 to 10 percent, mean 3 percent; 

aspect: SW; elevation: 5,760 to 5,800 ft, mean 5,775 ft.

Description: Large flat table sitting above Dugout 

Creek. To the south, the stand grades into younger forest, which was apparently not forested until about 90 

years ago. To the north, there is a sharp transition into 

scablands. The plot boasts at least one ponderosa pine 

older than 500 years and multiple others greater than 400 

years. This plot encompasses one sample site from Emily 

Heyerdahl’s fire history reconstruction. 

Summary metrics

Hectares

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height 

Canopy 

cover Acres

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height SDI

m2

·ha-1 ha-1 m Percent ft2·ac-1 ac-1 ft

4.4 21 101 47.1 51 40 22 10.9 90 41 18.6 20.1 130 137

Avg. = average, d.b.h. = diameter at breast height, OMD = quadratic mean diameter, SDI = standard density index.

Proportion of basal area

PIPO ABGR PSME LAOC JUOC PICO CELE3 Unknown

0.983 0 0.001 0 0.002 0 0 0.016

D.b.h. class midpoint (10 cm)

Trees per hectare

0

5

10

15

20

A 25

Tree age (years)

Number of trees

0

5

10

15

120−149150−199200−249250−299300−349350−399400−449450−499500+

B

2030405060708090100110120130

PIPO

ABGR

PSME

LAOC

Other
31

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

D Clump proportions 

(trees)

Clump proportions 

(basal area)

Clump quadratic mean diameter 

(cm)

Intertree 

dist. (m)

Clump size (No. of trees) Clump size (No. of trees) Clump size (No. of trees) 

1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+

2 0.73 0.24 0.03 0 0 0.81 0.18 0.02 0 0 53.6 44.5 34 0 0

3 0.54 0.33 0.13 0 0 0.65 0.25 0.1 0 0 55.7 44.7 45.2 0 0

4 0.36 0.4 0.19 0.05 0 0.47 0.36 0.15 0.03 0 58.2 48.1 45.2 37.8 0

5 0.28 0.34 0.29 0.05 0.03 0.39 0.33 0.22 0.04 0.01 59.9 50.3 44.4 47.3 33.4

6 0.21 0.29 0.25 0.15 0.11 0.31 0.3 0.2 0.09 0.09 62.8 52.6 46.2 38.6 47.2

7 0.16 0.26 0.25 0.15 0.18 0.25 0.29 0.22 0.1 0.14 63.8 53.8 48 40.3 45.9

10 0.05 0.1 0.19 0.17 0.49 0.08 0.13 0.22 0.13 0.43 64.8 58 55.1 45.3 48

Species

PIPO

ABGR

PSME

LAOC

Other

Clump

size

1

2−4

5−9

10−15

16+

Openings

Distance to nearest tree (meters)

30

5

10

15

20

25

C

10 30 50 70 90 110 130 150 170 190 210 230

Meters

10

30

50

70

90

110

130

150

170

190

210

230

Proportion of area

0.0

0.1

0.2

0.3

0.4

0−33−66−99−1212−1515−1818−2121−2424+

Distance to nearest tree (m)

E

Number of openings

0

5

10

15

0− 0.040.041− 0.08

0.081− 0.20.21− 0.40.41− 0.8

0.81− 1.61.6− 2.4

Size class (ha)

F

Proportion of plots

0.0

0.1

0.2

0.3

0.4

5101520

2530354045505560+

G

Basal area (midpoint m2·ha−1)
32

GENERAL TECHNICAL REPORT PNW-GTR-956

Ponderosa Pine 3

Location: Canyon Creek Research Natural Area

Plant association: PIPO/CARU

Topography: Slope: 1 to 45 percent, mean 30 percent; aspect: SW; elevation: 4,975 to 5,210 ft, mean 

5,120 ft.

Description: This plot extends down the southfacing slope from the ridgetop northwest of 

Yokum Corrals Camp. The eastern edge of the 

plot includes some rocky outcrops featuring juniper and mountain mahogany. The site is noticeably 

dominated by old trees, many of which have large 

fire scars. 

Summary metrics

Hectares

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height 

Canopy 

cover Acres

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height SDI

m2

·ha-1 ha-1 m Percent ft2·ac-1 ac-1 ft

4.1 19 103 46.1 48.8 41 20 10.1 84 42 18.1 19.2 133 131

Avg. = average, d.b.h. = diameter at breast height, OMD = quadratic mean diameter, SDI = standard density index.

Proportion of basal area

PIPO ABGR PSME LAOC JUOC PICO CELE3 Unknown

0.979 0 0.008 0 0 0 0 0.013

D.b.h. class midpoint (10 cm)

Trees per hectare

0

5

10

15

20

A 25

Tree age (years)

Number of trees

0

5

10

15

120−149150−199200−249250−299300−349350−399400−449450−499500+

B

2030405060708090100110120130

PIPO

ABGR

PSME

LAOC

Other
33

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Species

PIPO

ABGR

PSME

LAOC

Other

Clump

size

1

2−4

5−9

10−15

16+

Openings

Distance to nearest tree (meters)

30

5

10

15

20

25

C

10 30 50 70 90 110 130 150 170 190 210

Meters

10

30

50

70

90

110

130

150

170

190

210

Proportion of area

0.0

0.1

0.2

0.3

0.4

0−33−66−99−1212−1515−1818−2121−2424+

Distance to nearest tree (m)

E

Number of openings

0

5

10

15

0− 0.040.041− 0.08

0.081− 0.20.21− 0.40.41− 0.8

0.81− 1.61.6− 2.4

Size class (ha)

F

Proportion of plots

0.0

0.1

0.2

0.3

0.4

5 1015202530354045505560+

G

Basal area (midpoint m2·ha−1)

D Clump proportions 

(trees)

Clump proportions 

(basal area)

Clump quadratic mean diameter 

(cm)

Intertree 

dist. (m)

Clump size (No. of trees) Clump size (No. of trees) Clump size (No. of trees) 

1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+

6 0.18 0.40 0.35 0.03 0.05 0.22 0.41 0.32 0.02 0.03 54.4 49.7 46.6 40.6 37.8
34

GENERAL TECHNICAL REPORT PNW-GTR-956

Ponderosa Pine 4

Location: Malheur Ford

Plant association: PIPO/CARU

Topography: Slope: 2 to 24 percent, mean 

4 percent; aspect: SW; elevation: 5,060 to 

5,130 ft, mean 5,070 ft.

Description: This plot is located on a flat 

table directly east of the Malheur Ford and 

north of Black Canyon. The northeastern portion of the plot sits on a small step 

above the rest. Many of the older pines 

are declining in vigor, possibly towing to 

defoliating insects. 

Summary metrics

Hectares

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height 

Canopy 

cover Acres

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height SDI

m2

·ha-1 ha-1 m Percent ft2·ac-1 ac-1 ft

4.4 19 98 47 49.7 45 21 10.8 83 40 18.5 19.6 146 127

Avg. = average, d.b.h. = diameter at breast height, OMD = quadratic mean diameter, SDI = standard density index.

Proportion of basal area

PIPO ABGR PSME LAOC JUOC PICO CELE3 Unknown

0.989 0 0 0 0 0 0 0.011

D.b.h. class midpoint (10 cm)

Trees per hectare

0

5

10

15

20

A 25

Tree age (years)

Number of trees

0

5

10

15

120−149150−199200−249250−299300−349350−399400−449450−499500+

B

2030405060708090100110120130

PIPO

ABGR

PSME

LAOC

Other
35

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

D Clump proportions 

(trees)

Clump proportions 

(basal area)

Clump quadratic mean diameter 

(cm)

Intertree 

dist. (m)

Clump size (No. of trees) Clump size (No. of trees) Clump size (No. of trees) 

1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+

2 0.73 0.27 0 0 0 0.78 0.22 0 0 0 51.5 44.7 0 0 0

3 0.52 0.43 0.04 0 0 0.58 0.38 0.03 0 0 52.6 46.6 45 0 0

4 0.4 0.52 0.08 0 0 0.46 0.47 0.07 0 0 53.4 47.3 45.9 0 0

5 0.28 0.48 0.21 0.03 0 0.33 0.46 0.2 0.01 0 53.7 48.8 48.4 31.6 0

6 0.21 0.39 0.29 0.11 0 0.26 0.38 0.28 0.08 0 55 49 49.1 42.6 0

7 0.12 0.29 0.38 0.13 0.08 0.15 0.31 0.37 0.11 0.05 56.4 51.2 49.6 45.2 41.1

10 0.04 0.14 0.11 0.15 0.56 0.06 0.16 0.1 0.13 0.55 60.8 53.6 46.7 47.4 49.1

Species

PIPO

ABGR

PSME

LAOC

Other

Clump

size

1

2−4

5−9

10−15

16+

Openings

Distance to nearest tree (meters)

30

5

10

15

20

25

C

10 30 50 70 90 110 130 150 170 190 210 230

Meters

10

30

50

70

90

110

130

150

170

190

210

Proportion of area

0.0

0.1

0.2

0.3

0.4

0−33−66−99−1212−1515−1818−2121−2424+

Distance to nearest tree (m)

E

Number of openings

0

5

10

15

0− 0.040.041− 0.08

0.081− 0.20.21− 0.40.41− 0.8

0.81− 1.61.6− 2.4

Size class (ha)

F

Proportion of plots

0.0

0.1

0.2

0.3

0.4

5101520

2530354045505560+

G

Basal area (midpoint m2·ha−1)
36

GENERAL TECHNICAL REPORT PNW-GTR-956

Ponderosa Pine 5

Location: Malheur Ford

Plant association: PIPO/CARU

Topography: Slope: 10 to 30 percent, 

mean 15 percent; aspect: SW; elevation: 

5,020 to 5,150 ft, mean 5,120 ft.

Description: This plot is located 3⁄4 

of a mi southeast of ponderosa pine 

4, also on a table east of the Malheur 

River. This plot appears to have burned 

at a very low severity sometime in the 

1980s; many small trees have recent 

bole char. 

Summary metrics

Hectares

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height 

Canopy 

cover Acres

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height SDI

m2

·ha-1 ha-1 m Percent ft2·ac-1 ac-1 ft

4 19 94 47.4 50.1 41 21 10 81 38 18.7 19.7 134 124

Avg. = average, d.b.h. = diameter at breast height, OMD = quadratic mean diameter, SDI = standard density index.

Proportion of basal area

PIPO ABGR PSME LAOC JUOC PICO CELE3 Unknown

0.99 0 0.006 0 0 0 0 0.004

D.b.h. class midpoint (10 cm)

Trees per hectare

0

5

10

15

20

A 25

Tree age (years)

Number of trees

0

5

10

15

120−149150−199200−249250−299300−349350−399400−449450−499500+

B

2030405060708090100110120130

PIPO

ABGR

PSME

LAOC

Other
37

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Species

PIPO

ABGR

PSME

LAOC

Other

Clump

size

1

2−4

5−9

10−15

16+

Openings

Distance to nearest tree (meters)

30

5

10

15

20

25

C

10 30 50 70 90 110 130 150 170 190 210

Meters

10

30

50

70

90

110

130

150

170

190

210

Proportion of area

0.0

0.1

0.2

0.3

0.4

0−33−66−99−1212−1515−1818−2121−2424+

Distance to nearest tree (m)

E

Number of openings

0

5

10

15

0− 0.040.041− 0.08

0.081− 0.20.21− 0.40.41− 0.8

0.81− 1.61.6− 2.4

Size class (ha)

F

Proportion of plots

0.0

0.1

0.2

0.3

0.4

5101520

2530354045505560+

G

Basal area (midpoint m2·ha−1)

D Clump proportions 

(trees)

Clump proportions 

(basal area)

Clump quadratic mean diameter 

(cm)

Intertree 

dist. (m)

Clump size (No. of trees) Clump size (No. of trees) Clump size (No. of trees) 

1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+

2 0.76 0.23 0.01 0 0 0.81 0.18 0.01 0 0 51.8 44.3 49 0 0

3 0.56 0.4 0.04 0 0 0.64 0.33 0.03 0 0 53.5 45.5 45.4 0 0

4 0.45 0.45 0.1 0 0 0.53 0.39 0.08 0 0 54.6 46.4 45.3 0 0

5 0.33 0.42 0.25 0 0 0.39 0.42 0.19 0 0 54.9 50 43.4 0 0

6 0.23 0.34 0.38 0.05 0 0.28 0.37 0.31 0.05 0 55.3 51.7 45.3 49 0

7 0.16 0.3 0.41 0.05 0.08 0.21 0.32 0.35 0.05 0.07 57.5 51.8 46.5 49 46.9

10 0.07 0.11 0.29 0.25 0.28 0.09 0.12 0.27 0.22 0.3 56.9 51.8 48.2 47.8 51.6
38

GENERAL TECHNICAL REPORT PNW-GTR-956

Douglas-fir 1

Location: Dugout Creek Research Natural Area

Plant association: PSME/CARU

Topography: Slope: 25 to 40 percent, mean 30 

percent; aspect: W; elevation: 5,300 to 5,545 ft, 

mean 5,410 ft.

Description: This plot sits on a side slope at the 

head of a dry gulch between Stink Creek and 

Dugout Creek. The plot is quite open in places, 

but scattered patches of denser Douglas-fir and 

grand fir regeneration do exist. Vegetation uphill 

from the plot grades into an orchard-like stand 

of mountain mahogany. 

Summary metrics

Hectares

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height 

Canopy 

cover Acres

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height SDI

m2

·ha-1 ha-1 m Percent ft2·ac-1 ac-1 ft

3.9 14 59 51.1 54.6 41 16 9.5 61 24 20.1 21.5 134 91

Avg. = average, d.b.h. = diameter at breast height, OMD = quadratic mean diameter, SDI = standard density index.

Proportion of basal area

PIPO ABGR PSME LAOC JUOC PICO CELE3 Unknown

0.975 0.008 0.017 0 0 0 0 0

D.b.h. class midpoint (10 cm)

Trees per hectare

0

5

10

15

20

A 25

Tree age (years)

Number of trees

0

5

10

15

120−149150−199200−249250−299300−349350−399400−449450−499500+

B

2030405060708090100110120130

PIPO

ABGR

PSME

LAOC

Other
39

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Species

PIPO

ABGR

PSME

LAOC

Other

Clump

size

1

2−4

5−9

10−15

16+

Openings

Distance to nearest tree (meters)

30

5

10

15

20

25

C

10 30 50 70 90 110 130 150 170 190

Meters

10

30

50

70

90

110

130

150

170

190

210

230

Proportion of area

0.0

0.1

0.2

0.3

0.4

0−33−66−99−1212−1515−1818−2121−2424+

Distance to nearest tree (m)

E

Number of openings

0

5

10

15

0− 0.040.041− 0.08

0.081− 0.20.21− 0.40.41− 0.8

0.81− 1.61.6− 2.4

Size class (ha)

F

Proportion of plots

0.0

0.1

0.2

0.3

0.4

510152025303540455055

60+

G

Basal area (midpoint m2·ha−1)

D Clump proportions 

(trees)

Clump proportions 

(basal area)

Clump quadratic mean diameter 

(cm)

Intertree 

dist. (m)

Clump size (No. of trees) Clump size (No. of trees) Clump size (No. of trees) 

1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+

2 0.76 0.23 0.01 0 0 0.81 0.18 0.01 0 0 51.8 44.3 49 0 0

3 0.56 0.4 0.04 0 0 0.64 0.33 0.03 0 0 53.5 45.5 45.4 0 0

4 0.45 0.45 0.1 0 0 0.53 0.39 0.08 0 0 54.6 46.4 45.3 0 0

5 0.33 0.42 0.25 0 0 0.39 0.42 0.19 0 0 54.9 50 43.4 0 0

6 0.23 0.34 0.38 0.05 0 0.28 0.37 0.31 0.05 0 55.3 51.7 45.3 49 0

7 0.16 0.3 0.41 0.05 0.08 0.21 0.32 0.35 0.05 0.07 57.5 51.8 46.5 49 46.9

10 0.07 0.11 0.29 0.25 0.28 0.09 0.12 0.27 0.22 0.3 56.9 51.8 48.2 47.8 51.6
40

GENERAL TECHNICAL REPORT PNW-GTR-956

Douglas-fir 2

Location: Dugout Creek Research Natural Area

Plant association: PSME/CAGE

Topography: Slope: 20 to 40 percent, mean 30 

percent; aspect: NW; elevation: 5,040 to 5,310 

ft, mean 5,180 ft.

Description: This plot spans the slope south of 

Dugout Creek from the creek bottom to the ridge 

top. The lower areas of the plot are relatively 

dense with young Douglas-fir and ponderosa 

pine. Close to the ridge top, composition shifts 

more toward pine and becomes sparser. 

Summary metrics

Hectares

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height 

Canopy 

cover Acres

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height SDI

m2

·ha-1 ha-1 m Percent ft2·ac-1 ac-1 ft

4.2 14 79 43.4 48 40 18 10.4 63 32 17.1 18.9 130 98

Avg. = average, d.b.h. = diameter at breast height, OMD = quadratic mean diameter, SDI = standard density index.

Proportion of basal area

PIPO ABGR PSME LAOC JUOC PICO CELE3 Unknown

0.824 0 0.162 0 0 0 0 0.014

D.b.h. class midpoint (10 cm)

Trees per hectare

0

5

10

15

20

A 25

Tree age (years)

Number of trees

0

5

10

15

120−149150−199200−249250−299300−349350−399400−449450−499500+

B

2030405060708090100110120130

PIPO

ABGR

PSME

LAOC

Other
41

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Species

PIPO

ABGR

PSME

LAOC

Other

Clump

size

1

2−4

5−9

10−15

16+

Openings

Distance to nearest tree (meters)

30

5

10

15

20

25

C

10 30 50 70 90 110 130 150 170 190

Meters

10

30

50

70

90

110

130

150

170

190

210

250

230

Proportion of area

0.0

0.1

0.2

0.3

0.4

0−33−66−99−1212−1515−1818−2121−2424+

Distance to nearest tree (m)

E

Number of openings

0

5

10

15

0− 0.040.041− 0.08

0.081− 0.20.21− 0.40.41− 0.8

0.81− 1.61.6− 2.4

Size class (ha)

F

Proportion of plots

0.0

0.1

0.2

0.3

0.4

5101520

2530354045505560+

G

Basal area (midpoint m2·ha−1)

D Clump proportions 

(trees)

Clump proportions 

(basal area)

Clump quadratic mean diameter 

(cm)

Intertree 

dist. (m)

Clump size (No. of trees) Clump size (No. of trees) Clump size (No. of trees) 

1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+

2 0.83 0.17 0 0 0 0.9 0.1 0 0 0 49.9 37.5 0 0 0

3 0.71 0.29 0 0 0 0.81 0.19 0 0 0 51.5 38.6 0 0 0

4 0.61 0.37 0.02 0 0 0.74 0.26 0.01 0 0 52.8 39.8 33.1 0 0

5 0.5 0.37 0.13 0 0 0.66 0.28 0.06 0 0 55 41.8 33.2 0 0

6 0.38 0.41 0.16 0.06 0 0.52 0.36 0.09 0.03 0 56.6 45.2 36.6 32.6 0

7 0.26 0.43 0.2 0.11 0 0.41 0.4 0.14 0.05 0 59.9 46.3 40.2 33.8 0

0 0.08 0.28 0.2 0.04 0.41 0.14 0.39 0.18 0.02 0.27 64.9 56.9 45.7 38.2 38.7
42

GENERAL TECHNICAL REPORT PNW-GTR-956

Douglas-fir 3

Location: Canyon Creek Research Natural Area

Plant association: PSME/CARU-VASC

Topography: Slope: 10 to 25 percent, mean 15 

percent; aspect: SE; elevation: 4,825 to 4,960 ft, 

mean 4,890 ft.

Description: This plot is on a southeast-facing 

slope above the East Fork of Canyon Creek. The 

northern portion of the plot is fairly dry and 

rocky, mostly composed of ponderosa pine. In 

contrast, the southern portion of the plot is more 

mesic, with an understory of grouseberry and a 

greater proportion of Douglas-fir. 

Summary metrics

Hectares

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height 

Canopy 

cover Acres

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height SDI

m2

·ha-1 ha-1 m Percent ft2·ac-1 ac-1 ft

4.1 14 87 41.7 44.6 44 18 10.2 59 35 16.4 17.5 144 94

Avg. = average, d.b.h. = diameter at breast height, OMD = quadratic mean diameter, SDI = standard density index.

Proportion of basal area

PIPO ABGR PSME LAOC JUOC PICO CELE3 Unknown

0.847 0 0.035 0.041 0 0 0 0.078

D.b.h. class midpoint (10 cm)

Trees per hectare

0

5

10

15

20

A 25

Tree age (years)

Number of trees

0

5

10

15

120−149150−199200−249250−299300−349350−399400−449450−499500+

B

2030405060708090100110120130

PIPO

ABGR

PSME

LAOC

Other
43

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Species

PIPO

ABGR

PSME

LAOC

Other

Clump

size

1

2−4

5−9

10−15

16+

Openings

Distance to nearest tree (meters)

30

5

10

15

20

25

C

10 30 50 70 90 110 130 150 170

Meters

10

30

50

70

90

110

130

150

170

190

210

230

Proportion of area

0.0

0.1

0.2

0.3

0.4

0−33−66−99−1212−1515−1818−2121−2424+

Distance to nearest tree (m)

E

Number of openings

0

5

10

15

0− 0.040.041− 0.08

0.081− 0.20.21− 0.40.41− 0.8

0.81− 1.61.6− 2.4

Size class (ha)

F

Proportion of plots

0.0

0.1

0.2

0.3

0.4

5101520

2530354045505560+

G

Basal area (midpoint m2·ha−1)

D Clump proportions 

(trees)

Clump proportions 

(basal area)

Clump quadratic mean diameter 

(cm)

Intertree 

dist. (m)

Clump size (No. of trees) Clump size (No. of trees) Clump size (No. of trees) 

1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+

2 0.86 0.14 0 0 0 0.87 0.13 0 0 0 44.9 42.2 0 0 0

3 0.68 0.29 0.03 0 0 0.72 0.25 0.03 0 0 45.8 41.5 43.8 0 0

4 0.61 0.34 0.06 0 0 0.66 0.29 0.05 0 0 46.5 41.5 41 0 0

5 0.47 0.39 0.13 0 0 0.5 0.4 0.1 0 0 45.9 44.9 38.3 0 0

6 0.34 0.42 0.24 0 0 0.36 0.45 0.19 0 0 46.2 46 39.4 0 0

7 0.25 0.32 0.24 0.1 0.1 0.28 0.36 0.2 0.08 0.08 47.4 47.5 40.6 39.7 41

10 0.09 0.18 0.16 0.13 0.45 0.1 0.22 0.13 0.11 0.44 47.8 49.8 39.8 41.9 44.1
44

GENERAL TECHNICAL REPORT PNW-GTR-956

Douglas-fir 4

Location: North of Dugout Creek Research 

Natural Area

Plant association: PSME/CARU

Topography: Slope: 20 to 40 percent, mean 25 

percent; aspect: W; elevation: 5,200 to 5,380 ft, 

mean 5,300 ft.

Description: The plot is divided roughly in half 

by a large gulch. The southern portion, which 

faces to the northwest, is composed of smaller, 

denser Douglas-fir. The northern portion has a 

more prominent population of older pines. The 

south-facing downslope areas are occupied by 

small open patches of mountain mahogany. 

Summary metrics

Hectares

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height 

Canopy 

cover Acres

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height SDI

m2

·ha-1 ha-1 m Percent ft2·ac-1 ac-1 ft

4.3 13 64 47.2 50.6 37 15 10.7 56 26 18.6 19.9 120 86

Avg. = average, d.b.h. = diameter at breast height, OMD = quadratic mean diameter, SDI = standard density index.

Proportion of basal area

PIPO ABGR PSME LAOC JUOC PICO CELE3 Unknown

0.908 0 0.087 0.041 0 0 0 0.005

D.b.h. class midpoint (10 cm)

Trees per hectare

0

5

10

15

20

A 25

Tree age (years)

Number of trees

0

5

10

15

120−149150−199200−249250−299300−349350−399400−449450−499500+

B

2030405060708090100110120130

PIPO

ABGR

PSME

LAOC

Other
45

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Species

PIPO

ABGR

PSME

LAOC

Other

Clump

size

1

2−4

5−9

10−15

16+

Openings

Distance to nearest tree (meters)

30

5

10

15

20

25

C

10 30 50 70 90 110 130 150 170 190 210

Meters

10

30

50

70

90

110

130

150

170

190

210

Proportion of area

0.0

0.1

0.2

0.3

0.4

0−33−66−99−1212−1515−1818−2121−2424+

Distance to nearest tree (m)

E

Number of openings

0

5

10

15

0− 0.040.041− 0.08

0.081− 0.20.21− 0.40.41− 0.8

0.81− 1.61.6− 2.4

Size class (ha)

F

Proportion of plots

0.0

0.1

0.2

0.3

0.4

5 1015202530354045505560+

G

Basal area (midpoint m2·ha−1)

D Clump proportions 

(trees)

Clump proportions 

(basal area)

Clump quadratic mean diameter 

(cm)

Intertree 

dist. (m)

Clump size (No. of trees) Clump size (No. of trees) Clump size (No. of trees) 

1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+

6 0.34 0.44 0.22 0 0 0.43 0.39 0.17 0 0 57.0 48.1 44.5 0 0
46

GENERAL TECHNICAL REPORT PNW-GTR-956

Douglas-fir 5

Location: North of Dugout Creek Research 

Natural Area

Plant association: PSME/CAGE

Topography: Slope: 15 to 30 percent, mean 25 

percent; aspect: W; elevation: 5,440 to 5,640 ft, 

mean 5,540 ft.

Description: This plot sits between Telephone Creek 

to the north and an unnamed perennial stream to the 

south. The plot’s northeastern and southeastern corners feature large rocky outcrops. The remainder of 

the plot is an interspersed mixture of widely spaced 

old ponderosa pine and denser pole-sized Douglas-fir patches. The southwestern portion of the plot, which is lower on 

the slope, contains most of the old pines.

Summary metrics

Hectares

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height 

Canopy 

cover Acres

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height SDI

m2

·ha-1 ha-1 m Percent ft2·ac-1 ac-1 ft

4.1 22 74 57.8 61.3 37 23 10.1 95 30 22.8 24.1 119 137

Avg. = average, d.b.h. = diameter at breast height, OMD = quadratic mean diameter, SDI = standard density index.

Proportion of basal area

PIPO ABGR PSME LAOC JUOC PICO CELE3 Unknown

0.87 0 0.13 0 0 0 0 0

D.b.h. class midpoint (10 cm)

Trees per hectare

0

5

10

15

20

A 25

Tree age (years)

Number of trees

0

5

10

15

120−149150−199200−249250−299300−349350−399400−449450−499500+

B

2030405060708090100110120130

PIPO

ABGR

PSME

LAOC

Other
47

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Proportion of area

0.0

0.1

0.2

0.3

0.4

0−33−66−99−1212−1515−1818−2121−2424+

Distance to nearest tree (m)

E

Number of openings

0

5

10

15

0− 0.040.041− 0.08

0.081− 0.20.21− 0.40.41− 0.8

0.81− 1.61.6− 2.4

Size class (ha)

F

Proportion of plots

0.0

0.1

0.2

0.3

0.4

5101520

2530354045505560+

G

Basal area (midpoint m2·ha−1)

Species

PIPO

ABGR

PSME

LAOC

Other

Clump

size

1

2−4

5−9

10−15

16+

Openings

Distance to nearest tree (meters)

30

5

10

15

20

25

C

10 30 50 70 90 110 130 150 170 190 210

Meters

10

30

50

70

90

110

130

150

170

190

210

D Clump proportions 

(trees)

Clump proportions 

(basal area)

Clump quadratic mean diameter 

(cm)

Intertree 

dist. (m)

Clump size (No. of trees) Clump size (No. of trees) Clump size (No. of trees) 

1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+

2 0.86 0.14 0 0 0 0.87 0.13 0 0 0 44.9 42.2 0 0 0

3 0.68 0.29 0.03 0 0 0.72 0.25 0.03 0 0 45.8 41.5 43.8 0 0

4 0.61 0.34 0.06 0 0 0.66 0.29 0.05 0 0 46.5 41.5 41 0 0

5 0.47 0.39 0.13 0 0 0.5 0.4 0.1 0 0 45.9 44.9 38.3 0 0

6 0.34 0.42 0.24 0 0 0.36 0.45 0.19 0 0 46.2 46 39.4 0 0

7 0.25 0.32 0.24 0.1 0.1 0.28 0.36 0.2 0.08 0.08 47.4 47.5 40.6 39.7 41

10 0.09 0.18 0.16 0.13 0.45 0.1 0.22 0.13 0.11 0.44 47.8 49.8 39.8 41.9 44.1
48

GENERAL TECHNICAL REPORT PNW-GTR-956

Grand Fir 1

Location: Dugout Creek Research Natural 

Area

Plant association: ABGR/CARU

Topography: Slope: 15 to 25 percent, mean 

20 percent; aspect: N; elevation: 5,650 to 

5,790 ft, mean 5,710 ft. 

Description: This plot is in the middle of 

a long slope running down to Stink Creek. 

The plot is contemporarily quite dense, and 

large openings are scarce. Almost all underand mid-story trees are grand fir, with occasional western larch. 

Summary metrics

Hectares

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height 

Canopy 

cover Acres

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height SDI

m2

·ha-1 ha-1 m Percent ft2·ac-1 ac-1 ft

5 24 161 40.3 43.6 40 31 12.3 105 65 15.9 17.2 130 168

Avg. = average, d.b.h. = diameter at breast height, OMD = quadratic mean diameter, SDI = standard density index.

Proportion of basal area

PIPO ABGR PSME LAOC JUOC PICO CELE3 Unknown

0.501 0.438 0.039 0.013 0 0 0 0.008

D.b.h. class midpoint (10 cm)

Trees per hectare

0

5

10

15

20

A 25

Tree age (years)

Number of trees

0

5

10

15

120−149150−199200−249250−299300−349350−399400−449450−499500+

B

2030405060708090100110120130

PIPO

ABGR

PSME

LAOC

Other
49

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Proportion of area

0.0

0.1

0.2

0.3

0.4

0−33−66−99−1212−1515−1818−2121−2424+

Distance to nearest tree (m)

E

Number of openings

0

5

10

15

0− 0.040.041− 0.08

0.081− 0.20.21− 0.40.41− 0.8

0.81− 1.61.6− 2.4

Size class (ha)

F

Proportion of plots

0.0

0.1

0.2

0.3

0.4

5101520

2530354045505560+

G

Basal area (midpoint m2·ha−1)

Species

PIPO

ABGR

PSME

LAOC

Other

Clump

size

1

2−4

5−9

10−15

16+

Openings

Distance to nearest tree (meters)

30

5

10

15

20

25

C

10 30 50 70 90 110 130 150 170 190 210 230

Meters

10

30

50

70

90

110

130

150

170

190

230

210

D Clump proportions 

(trees)

Clump proportions 

(basal area)

Clump quadratic mean diameter 

(cm)

Intertree 

dist. (m)

Clump size (No. of trees) Clump size (No. of trees) Clump size (No. of trees) 

1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+

2 0.71 0.27 0.02 0 0 0.77 0.22 0.01 0 0 45.5 39 29.7 0 0

3 0.49 0.46 0.05 0 0 0.58 0.39 0.03 0 0 47.5 40.2 31.8 0 0

4 0.35 0.47 0.15 0.03 0 0.43 0.44 0.1 0.03 0 48.6 42 35.6 42.3 0

5 0.22 0.36 0.31 0.09 0.02 0.28 0.38 0.24 0.09 0.01 49.5 44.3 38.5 43.3 36.1

6 0.13 0.27 0.35 0.11 0.14 0.19 0.31 0.29 0.08 0.13 52.7 46 39.9 37.2 42.9

7 0.08 0.19 0.24 0.15 0.34 0.11 0.22 0.2 0.13 0.33 52.3 46.2 40.2 41.3 43.1

10 0.01 0.02 0.04 0.08 0.84 0.03 0.03 0.04 0.08 0.82 61.6 47.9 42.9 43.1 43.2
50

GENERAL TECHNICAL REPORT PNW-GTR-956

Grand Fir 2

Location: Dugout Creek Research Natural Area

Plant association: ABGR/CARU

Topography: Slope: 20 to 40 percent, mean 30 

percent; aspect: N; elevation: 5,400 to 5,600 ft, 

mean 5,495 ft.

Description: This plot sits below Grand fir 

1 and immediately south of Stink Creek. It is 

somewhat steep, and vegetation is quite dense. 

Most of the plot is a combination of small patches of dense grand fir regeneration and larger 

patches of mid- and overstory trees. Some large, 

very old grand fir are present. 

Summary metrics

Hectares

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height 

Canopy 

cover Acres

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height SDI

m2

·ha-1 ha-1 m Percent ft2·ac-1 ac-1 ft

4 23 197 35.2 38.3 41 33 9.8 99 80 13.9 15.1 135 165

Avg. = average, d.b.h. = diameter at breast height, OMD = quadratic mean diameter, SDI = standard density index.

Proportion of basal area

PIPO ABGR PSME LAOC JUOC PICO CELE3 Unknown

0.364 0.473 0.055 0.06 0 0.001 0 0.046

D.b.h. class midpoint (10 cm)

Trees per hectare

0

5

10

15

20

A 25

Tree age (years)

Number of trees

0

5

10

15

120−149150−199200−249250−299300−349350−399400−449450−499500+

B

2030405060708090100110120130

PIPO

ABGR

PSME

LAOC

Other
51

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Proportion of area

0.0

0.1

0.2

0.3

0.4

0−33−66−99−1212−1515−1818−2121−2424+

Distance to nearest tree (m)

E

Number of openings

0

5

10

15

0− 0.040.041− 0.08

0.081− 0.20.21− 0.40.41− 0.8

0.81− 1.61.6− 2.4

Size class (ha)

F

Proportion of plots

0.0

0.1

0.2

0.3

0.4

5101520

2530354045505560+

G

Basal area (midpoint m2·ha−1)

Species

PIPO

ABGR

PSME

LAOC

Other

Clump

size

1

2−4

5−9

10−15

16+

Openings

Distance to nearest tree (meters)

30

5

10

15

20

25

C

10 30 50 70 90 110 130 150 170 190 210

Meters

10

30

50

70

90

110

130

150

170

190

D Clump proportions 

(trees)

Clump proportions 

(basal area)

Clump quadratic mean diameter 

(cm)

Intertree 

dist. (m)

Clump size (No. of trees) Clump size (No. of trees) Clump size (No. of trees) 

1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+

2 0.71 0.29 0 0 0 0.74 0.26 0 0 0 39 36.4 0 0 0

3 0.49 0.46 0.06 0 0 0.53 0.43 0.04 0 0 40.1 36.9 32.2 0 0

4 0.33 0.44 0.16 0.05 0.02 0.39 0.42 0.13 0.04 0.02 41.4 37.6 34.7 35.1 33.8

5 0.2 0.34 0.27 0.08 0.11 0.24 0.34 0.26 0.06 0.09 42.3 38 37.8 35.3 34.4

6 0.1 0.2 0.27 0.16 0.27 0.14 0.23 0.27 0.15 0.22 44.4 40.4 38.5 36.2 34.9

7 0.05 0.11 0.18 0.12 0.53 0.09 0.14 0.21 0.12 0.45 49.7 42.1 41.5 37.7 34.9

10 0.01 0.03 0.03 0.03 0.91 0.01 0.04 0.04 0.03 0.89 41.2 45.2 42.8 40.3 37.8
52

GENERAL TECHNICAL REPORT PNW-GTR-956

Grand Fir 3

Location: Canyon Creek Research Natural Area

Plant association: ABGR/CARU

Topography: Slope: 15 to 30 percent, mean 20 percent; 

aspect: E; elevation: 5,390 to 5,520 ft, mean 5,450 ft.

Description: This plot lies on a narrow flat above an 

unnamed tributary of East Fork Canyon Creek. The 

flatter portions of the plot consist of young grand fir 

and old ponderosa pine. The upslope portions are 

mainly composed of 150-year-old western larch, many 

of which have died or are declining in vigor. A highseverity fire appears to have occurred in portions of 

this plot around 150 years ago, which initiated the 

larch cohort. 

Summary metrics

Hectares

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height 

Canopy 

cover Acres

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height SDI

m2

·ha-1 ha-1 m Percent ft2·ac-1 ac-1 ft

2.3 11 53 44.1 51.5 43 13 5.6 48 22 17.3 20.3 141 74

Avg. = average, d.b.h. = diameter at breast height, OMD = quadratic mean diameter, SDI = standard density index.

Proportion of basal area

PIPO ABGR PSME LAOC JUOC PICO CELE3 Unknown

0.773 0.137 0 0.09 0 0 0 0

D.b.h. class midpoint (10 cm)

Trees per hectare

0

5

10

15

20

A 25

Tree age (years)

Number of trees

0

5

10

15

120−149150−199200−249250−299300−349350−399400−449450−499500+

B

2030405060708090100110120130

PIPO

ABGR

PSME

LAOC

Other
53

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Proportion of area

0.0

0.1

0.2

0.3

0.4

0−33−66−99−1212−1515−1818−2121−2424+

Distance to nearest tree (m)

E

Number of openings

0

5

10

15

0− 0.040.041− 0.08

0.081− 0.20.21− 0.40.41− 0.8

0.81− 1.61.6− 2.4

Size class (ha)

F

Proportion of plots

0.0

0.1

0.2

0.3

0.4

5101520

2530354045505560+

G

Basal area (midpoint m2·ha−1)

Species

PIPO

ABGR

PSME

LAOC

Other

Clump

size

1

2−4

5−9

10−15

16+

Openings

Distance to nearest tree (meters)

30

5

10

15

20

25

C

10 30 50 70 90 110 130 150

Meters

10

30

50

70

90

110

130

150

D Clump proportions 

(trees)

Clump proportions 

(basal area)

Clump quadratic mean diameter 

(cm)

Intertree 

dist. (m)

Clump size (No. of trees) Clump size (No. of trees) Clump size (No. of trees) 

1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+

2 0.9 0.1 0 0 0 0.94 0.06 0 0 0 52.7 39.5 0 0 0

3 0.85 0.15 0 0 0 0.88 0.12 0 0 0 52.6 45.2 0 0 0

4 0.77 0.15 0.08 0 0 0.82 0.15 0.03 0 0 53.3 51.8 30.7 0 0

5 0.62 0.3 0 0.08 0 0.71 0.26 0 0.03 0 55.4 47.7 0 30.7 0

6 0.53 0.34 0.04 0.08 0 0.68 0.26 0.02 0.03 0 58.3 45.2 39.1 30.7 0

7 0.42 0.39 0.11 0.08 0 0.55 0.34 0.08 0.03 0 59 48 45.7 30.7 0

10 0.17 0.32 0.2 0 0.32 0.21 0.28 0.25 0 0.26 57.6 48.7 58 0 46.3
54

GENERAL TECHNICAL REPORT PNW-GTR-956

Grand Fir 4

Location: Canyon Creek Research Natural Area

Plant association: ABGR/CAGE-VASC

Topography: Slope: 5 to 50 percent, mean 15 

pecent; aspect: split, E and S; elevation: 5,540-

5,685 ft, mean 5,590 ft.

Description: This plot straddles a draw running from northwest to southeast. The southern 

aspect portions contain very large old ponderosa pine with some old grand fir, while the 

areas across the draw have more medium-size 

Douglas-fir and grand fir with some lodgepole 

pine and larch. The understory is covered with grouseberry in shady spots, but grades into elk sedge and pinegrass in drier openings. 

Summary metrics

Hectares

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height 

Canopy 

cover Acres

Basal 

area Trees 

Avg. 

d.b.h. QMD 

Max 

height SDI

m2

·ha-1 ha-1 m Percent ft2·ac-1 ac-1 ft

4.3 20 122 41.8 45.3 43 25 10.7 85 49 16.5 17.8 142 135

Avg. = average, d.b.h. = diameter at breast height, OMD = quadratic mean diameter, SDI = standard density index.

Proportion of basal area

PIPO ABGR PSME LAOC JUOC PICO CELE3 Unknown

0.409 0.479 0.094 0.012 0 0.002 0 0.003

D.b.h. class midpoint (10 cm)

Trees per hectare

0

5

10

15

20

A 25

Tree age (years)

Number of trees

0

5

10

15

120−149150−199200−249250−299300−349350−399400−449450−499500+

B

2030405060708090100110120130

PIPO

ABGR

PSME

LAOC

Other
55

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Proportion of area

0.0

0.1

0.2

0.3

0.4

0−33−66−99−1212−1515−1818−2121−2424+

Distance to nearest tree (m)

E

Number of openings

0

5

10

15

0− 0.040.041− 0.08

0.081− 0.20.21− 0.40.41− 0.8

0.81− 1.61.6− 2.4

Size class (ha)

F

Proportion of plots

0.0

0.1

0.2

0.3

0.4

5 1015202530354045505560+

G

Basal area (midpoint m2·ha−1)

Species

PIPO

ABGR

PSME

LAOC

Other

Clump

size

1

2−4

5−9

10−15

16+

Openings

Distance to nearest tree (meters)

30

5

10

15

20

25

C

10 30 50 70 90 110 130 150 170 190 210

Meters

10

30

50

70

90

110

150

190

130

170

210

D Clump proportions 

(trees)

Clump proportions 

(basal area)

Clump quadratic mean diameter 

(cm)

Intertree 

dist. (m)

Clump size (No. of trees) Clump size (No. of trees) Clump size (No. of trees) 

1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+ 1 2-4 5-9 10-15 16+

6 0.17 0.33 0.22 0.11 0.18 0.25 0.33 0.19 0.10 0.14 54.8 44.9 42.4 42.7 40.6
56

GENERAL TECHNICAL REPORT PNW-GTR-956
57

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Chapter 5: Ecological Implications

Structure, Density, Composition, and Age

The historical stem densities and basal areas found in this reconstruction study 

are consistent with other reference condition studies in pine and mixed-conifer, 

frequent-fire forests in the Western United States (Abella and Denton 2009, Clyatt 

et al. 2016, Fry et al. 2014, Harrod et al. 1999, Larson et al. 2012, Lydersen et 

al. 2013, Reynolds et al. 2013, Schneider et al. 2015, Taylor 2004, Youngblood 

et al. 2004). The historical basal areas in this study are generally in the upper 

50th percentile of those found on ponderosa pine (Pinus ponderosa Lawson & C. 

Lawson) and mixed-conifer forest types on the Klamath and Warm Springs Indian 

Reservations in 1920s timber inventories (Hagmann et al. 2013, 2014). While 

direct comparisons among studies are complicated by differences in reconstruction methods (especially lower diameter cutoffs); frequent-fire forests with active 

fire regimes historically had densities well below maximum carrying capacities 

(Kaufmann et al. 2007). The dramatic increase in density after fire exclusion is 

clear evidence of this (Agee 1993). The basal areas and equivalent stand density 

index (SDI) levels found in this study are in line with this conclusion. Even the 

higher density grand fir (Abies grandis (Douglas ex D. Don) Lindl.) plots were 

relatively open-canopy forests with reconstructed canopy cover just over 30 

percent (table 3.1). 

The dominance of ponderosa pine on the pine and Douglas-fir (Pseudotsuga 

menziesii (Mirb.) Franco) series plots is also consistent with other reference 

condition studies in these forest types in Oregon and Washington (Churchill 

2013; Hagmann et al. 2013, 2014; Harrod et al. 1999). The high percentage of 

grand fir (Abies grandis (Douglas ex D. Don) Lindl.) in terms of tree density and 

basal area on three of the four grand fir plots was surprising, as these sites are on 

dry grand fir plant associations within a dry forest landscape that had a frequentfire-regime (Heyerdahl et al. 2001). Data from other sites in central and eastern 

Oregon indicate that grand and white fir (Abies concolor (Gord. & Glend.) Lindl. 

ex Hildebr, plant associations were historically dominated by ponderosa pine 

(Hagmann et al. 2014, Merschel et al. 2014). However, the proportion of grand 

fir is consistent with results from Johnston et al. (2016) who examined historical 

structure and composition in similar forest types in the same region. Potential 

reasons for high levels of grand fir are deep, ash-capped soils and longer firereturn intervals than on adjacent plots. An analysis of the relationship between 

fire-return intervals and density on the plots is underway using fire history data 

from Heyerdahl et al. (2001). The fact that we found high proportions of grand 

fir on three of four grand fir plots does not suggest that all grand fir sites in the 

Blue Mountains were historically similar. The low density and low proportion 
58

GENERAL TECHNICAL REPORT PNW-GTR-956

of grand fir on G3 is evidence of this. We can infer, however, that not all dry 

grand fir sites were pine-dominated forest similar in structure and density to dry 

Douglas-fir and ponderosa pine plant associations. 

The higher current densities relative to historical conditions is consistent with 

many other studies that have shown increases in density (Covington and Moore 

1994, Hagmann et al. 2013, Harrod et al. 1999, Lydersen et al. 2013, Reynolds et 

al. 2013, Sánchez Meador et al. 2009, Schneider et al. 2015) The decrease in mean 

diameter indicates that structure has changed owing to infill of small-diameter 

trees. While our reconstruction methods likely underestimate small trees and 

thus overall density, we observed during our sampling an obvious postfire suppression cohort on these sites that was dense in many places. Our sites have never 

been logged and retain a robust old-tree population; thus density increases can be 

attributed to a combination of fire exclusion, grazing, and favorable climate for tree 

establishment in the early part of the 20th century (Merschel et al. 2014, Naficy et al. 

2010, Rummel 1951).

Spatial Pattern 

Spatial pattern was also similar to the patterns of individual trees, clumps, and 

openings found at other dry-forest reference sites (Larson and Churchill 2012). 

Clump size proportions span the range found at other sites (Churchill 2013, Clyatt et 

al. 2016, Fry et al. 2014, Larson and Churchill 2012, Lydersen et al. 2013, Schneider 

et al. 2015). In general, the proportion of individual trees in dry forest reference 

sites appears to range from around 10 percent in highly clumped plots to around 50 

percent in the least clumped plots (at an intertree distance of 6 m). Plots with low 

clumping often have no large clumps (10+ trees), while highly clumped plots can 

have 20 to 30+ percent of trees in large clumps (Larson and Churchill 2012). The 

largest clumps found in most studies are generally 30 to 40 trees (also at an intertree distance of 6 m). The similarity of the range of clump size distributions found 

in this study to others suggests that these reference sites are a reasonable representation of the envelope of historical patterns in the study domain. Areas with higher 

and lower levels of clumping were likely present but do not appear to have been 

very common based on the available data. Our data are from a relatively narrow 

geographic area, however, and further reconstruction studies would be necessary to 

have higher confidence that the historical range and distribution of pattern is indeed 

represented by this dataset. 
59

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

The shape and amount of open space found on the plots illustrates the discontinuous nature of forest canopy in frequent-fire forests. Even the higher density 

plots had 5 to 10 percent of their area in open space (F > 9 m) and openings of up to 

0.1 ha that are large enough for regeneration and growth of shade-intolerant species. 

Openings often extended throughout much of the plot in a linear, sinuous fashion. 

In the lower density plots, openings tended to join together into large interconnected, sinuous openings (e.g., D4). In very few cases were the larger openings 

(>0.4 ha) circular or compact in shape. Instead, these sinuous openings created 

multiple breaks in the canopy across each plot that were wide enough to force active 

crown fire onto the ground in all but the most extreme conditions (Peterson et al. 

2005). By reducing canopy bulk density, openings allow for greater release of heat 

from surface fires, which reduces potential for passive or active crown fire (Graham 

et al. 2004). We hypothesize that the amount and shape of openings in frequent-fire 

forests is a major driver of their resistance and resilience to disturbance. Treatments 

that sought to mimic historical clumped-stand structure with such openings were 

effective at reducing fire severity and crown scorch in the Wallow fire in Arizona 

compared to untreated conditions (Kennedy and Johnson 2014). 

We found that density, clumping, and openings were unevenly distributed 

across some of our plots (i.e., nonstationary or inhomogeneous patterns), similar 

to Fry et al. (2014). Large clumps were often grouped together in areas of a plot 

and not evenly spread out (e.g., plot D1). Likewise, portions of some plots were 

much more open than the rest of the plot (e.g., plot G3). This was likely caused 

by a significant change in the processes creating pattern such as a change in soil 

conditions (e.g., area of shallow soil) or past disturbance severity (e.g., a large root 

rot pocket or past torching of a patch of trees) (Fry et al. 2014, Getzin et al. 2008, 

Perry et al. 2006). The presence of inhomogeneous patterns suggests that spatial 

pattern of these plots was likely driven by a mix of fine-scale gap-phase processes 

(<0.2 ha) that maintained the basic pattern of individuals, clumps, and openings and 

somewhat larger scale variation in soils, solar radiation, topographic position, and 

disturbance intensities (1~10+ha) that caused higher variation in densities, levels of 

clumping, and amount of open space.

The variation in density and pattern among the 14 plots also suggests that larger 

scale variation in topography, climate, and disturbance behavior created varying 

patterns of structure and composition at larger spatial extents (100s to 1000s of ha) 

(Cansler 2011, Hessburg et al. 1999, Heyerdahl et al. 2001, Kane et al. 2015, Perry et 

al. 2011, Taylor and Skinner 2003)
60

GENERAL TECHNICAL REPORT PNW-GTR-956

Relationships Among Pattern, Density and Potential 

Vegetation Series 

The strong relationship between higher stem densities and higher proportions of 

clumping found in this study has also been found on other dry forest sites (Abella 

and Denton 2009, Churchill 2013, Clyatt et al. 2016, Fry et al. 2014). As tree density 

increases, the proportion of trees in individuals and small clumps declines, while 

the proportion in medium and large clumps increases. Part of this relationship is 

simply a matter of more trees connecting into larger clumps as the available space 

is filled with additional trees. However, higher density stands with low levels of 

clumping have not been found in reference studies even though there is more than 

enough physical space for trees to be individuals or in small clumps. This suggests 

that higher densities in dry forests are primarily the result of higher numbers of 

trees in clumps vs. individual trees. Plot P1, for example, has 65 trees per hectare 

(tph) and 25 tph as individuals while G1 has 161 tph but only 21 tph as individuals. 

Under strict uniform spacing, all 161 tph in G1 would be individuals. Also, the 

denser plots still have open space (F >9 m), which is directly related to high levels 

of clumping in these plots. 

The relationships we found between potential vegetation series and pattern 

are difficult to disentangle from the underlying relationship of density to pattern. 

The ponderosa pine, Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), and 

grand fir plots have similar pair correlation curves and appear to follow the same 

basic relationships between density, mean clump size, and openings (fig. 3.5). The 

Douglas-fir plots are not more uniform or less clumped than the pine or grand fir, 

given that they are lower in density. Furthermore, the two outlier plots suggest 

that adding more plots from more areas would further weaken the relationship 

between potential vegetation series and pattern. The Douglas-fir plots are in the 

middle in terms of productivity, but were statistically less clumped than the other 

two series. 

Given the lack of a clear trend between more productive plant associations and 

pattern, we thus rejected our hypothesis that density and average clump size would 

increase with productivity. Plant association classification offers a useful approach 

to characterize gradients in the biophysical environment (Powell et al. 2007), but 

there are clearly many other factors that influence structure and composition. 

Hagmann et al. (2013, 2014) and Merschel et al. (2014) also found that potential 

vegetation was not a significant predictor of structure in mixed-conifer forests in 

central and eastern Oregon. Our hypothesis that the historical range, or envelope, 

of density and spatial pattern in dry forests was partitioned by potential vegetation 

series was clearly too simplistic. 
61

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

A more likely hypothesis is that higher productivity plant associations, especially those that had more variable fire regimes (Everett et al. 2000, Heyerdahl et 

al. 2001), had a wider envelope of structure and composition. More productive sites 

can support higher tree densities, and thus higher clumping levels, owing to lower 

levels of moisture stress, presence of shade-tolerant species, and higher overall 

carrying capacity (Powell 1999). As found in this study, higher productivity sites 

likely occupied the higher density and higher clumping end of the overall dry forest 

envelope. However, fire and other disturbances created low density and low clumping patterns on all sites, including the Grand fir series. In contrast, low productivity 

sites can support fewer trees and so have a narrower potential range of conditions. 

Other important mechanisms such as seed caching by birds and small mammals, 

interspecies competition within clumps, soil conditions, and understory composition likely also created variability in clumping and density across different potential 

vegetation series. 

Forest Development Pathways

The historical forest conditions we reconstructed on these plots have all of the characteristics of frequent-fire, open-canopy, old-growth, pine and mixed-conifer forests 

described by many researchers (Agee 1993, Cooper 1961, Fry and Stephens 2010, 

Kaufmann et al. 2007, Keen 1940, Larson and Churchill 2012, Sánchez Meador 

et al. 2009, Weaver 1961). The strongly clumped spatial patterns, openings, wide 

distribution of age classes, presence of old trees, and dominance of large-diameter 

trees are clear evidence of a fine-scale, multicohort, gap-phase replacement system 

that has persisted through multiple centuries of frequent disturbance and climatic 

fluctuation (Kaufmann et al. 2007). Relatively few trees appear to have lived past 

300 years, however, indicating a dynamic tree population. 

Tree recruitment appears to have occurred somewhat continuously over time 

with some discreet pulses. However, further investigation is needed to explain temporal patterns of tree establishment and potential mechanisms. Also, we did not collect a sufficient number of tree cores to fully determine whether tree establishment 

occurred primarily in spatially segregated, even-aged clumps or within multiage 

clumps. Our limited data suggest that many clumps have multi-age cohorts, similar 

to findings from northern Arizona (White 1985). 
62

GENERAL TECHNICAL REPORT PNW-GTR-956
63

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Key Functional Components of Reference Conditions

The structure and composition of the historical forests found in this study offer 

information that can be used to guide restoration efforts. However, managers 

must first understand the key components of historical patterns from a functional 

perspective. Quantifying historical structure and composition is only the first step 

in understanding how these systems function and provide the ecosystem functions 

and services that humans want. Ultimately, targets for variability should consider 

the desired functions, current structure, biophysical conditions, and anticipated 

future disturbances. Determining which components of historical patterns drive key 

ecosystem functions and services and which components are just natural variations 

is necessary. Density, composition, and pattern targets from reference forests offer 

useful guideposts but should not become ends in themselves. 

Much progress has been made in understanding how size, density, and 

composition interact with forest development and disturbance processes in dry 

forests to drive resilience and ecological function at the stand level (see chapter 

1). How some components of pattern affect particular functions is also known. 

Examples include the effects of gap size on tree regeneration and growth (Bigelow and North 2012, York et al. 2004), and the use of dense patches for nesting 

or denning by many wildlife species (Lehmkuhl et al. 2006, Long and Smith 

2000, Roberts et al. 2008). However, relatively little experimental work has 

been done to empirically test how different stand-level patterns affect specific 

processes such as fire behavior or ecosystem functions and services such as snow 

retention or provision of wildlife habitat. Managing for resilient forests in the 

face of changing climate will require such knowledge in order to critically evaluate and modify historical reference targets (Joyce et al. 2009, Spies et al. 2010, 

Stephens et al. 2010). Studies on such topics have been initiated and results are 

beginning to emerge (e.g., Latif et al. 2015), but it will be some time before we 

have a robust understanding of the relationships between structure, composition, 

process, and function. 

Below, we describe the key functional components of pattern, based on 

current scientific understanding, to consider when setting pattern targets. Keep 

in mind, however, that restoration of the fine-scale, multicohort, gap-phase stand 

development processes associated with dry forests is as important as restoring 

historical structure and composition. Frequent fire is of course the key driver of 

these processes. 

Chapter 6: Management Implications
64

GENERAL TECHNICAL REPORT PNW-GTR-956

• Openings: They provide an array of ecological functions and are as important in terms of function as the trees (see Chapter 1). The number and size 

of openings will depend on overall tree density, but linear, sinuous openings with a wide range of widths have been found in almost all reference 

studies (Larson and Churchill 2012). In this study, all plots had some openings that were at least 18 m across. The largest openings found were up to 

50 m across. Large, circular gaps (>0.4 ha) are not consistent with the shape 

and size of openings found in this study. 

• Medium and large clumps: These provide patches of continuous canopy 

that are large enough to create a shady understory light environment and 

differences in subcanopy temperatures and soil moisture levels. This creates niches for different understory species and can alter fire behavior. It 

also provides cover and nesting locations for wildlife species and snag 

creation through competitive mortality. The largest clumps appear to be 

around 30 to 40 trees in this dataset (for trees greater than 15 cm diameter 

at breast height [d.b.h].), but multiple large clumps are sometimes adjacent 

and form larger patches (e.g., 0.2 to 0.5 ha). Large clumps (10+ trees) were 

not present on every acre, however, and four of our 4-ha plots did not contain any large clumps. 

• Widely spaced individuals: Large trees with deep and wide crowns are a 

defining component of frequent-fire forests. They are fire resistant, provide habitat elements, and eventually become large snags and downed logs. 

While we define individuals here as trees with no neighbors within 6 m, 

many individuals in our plots had wider spacing (e.g., 8 to 12 m). 

• Variation in density and clumping within and across treatment units:

The multiscale variation found in this study and others is thought to be an 

important aspect of resilience, akin to having a diversified investment portfolio. Multiscale variation is thought to impede the spread of high-severity 

disturbances, perpetuate variable postdisturbance patterns, and facilitate 

species diversity (Beaty and Taylor 2007, Hessburg et al. 2015, Pimont et al. 

2011, Stephens et al. 2008, Virah-Sawmy et al. 2009). Creating the same 

clump and opening size distribution across a whole treatment unit (10+ ha) 

or set of units (hundreds of hectares) is not consistent with the multiscale 

variation found in this study and others. There is no “average” or target 

level of variability that should be replicated across a whole unit. Although 

unit-level targets and averages are a necessity for management, the range 

and distribution of density and clumps are more important. 
65

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Using Reference Data to Set Targets for Density, 

Composition, and Pattern

As a whole, the 14 plots provide an estimate of the historical range of variation 

(or envelope) for stand-level density, size, composition, and pattern in dry forests. 

The pattern envelope found in this study has boundaries that are consistent with 

other dry-forest reference sites (see citations above). The least variable plots have 

a maximum of around 50 percent of trees as individuals and have no large clumps 

(10+ trees greater than 15 cm d.b.h.). The most clumped plots have around 10 

percent as individuals and 10 to 30 percent in large clumps. These data suggest 

minimum and maximum values for treatments that seek to restore patterns that 

are consistent with the patterns found in historical reference studies. For example, 

spacing-based thinning and fuel reduction treatments can result in 80 percent or 

more individual trees, no medium or large clumps, few or no openings, and create 

different patterns than found in this and other reference studies. (Churchill et al. 

2013). However, it is unlikely that this study, along with others, captured the full 

range of historical variation. 

A wide range of pattern and density configurations exists within the historical 

envelope found in this study that offers flexibility to managers. To determine a 

target level of variability for a particular treatment unit, managers may wish to first 

consider the target stem density and species composition appropriate for the site. 

Many factors will go into this decision, including management objectives, biophysical conditions, carrying capacity, current conditions, future management entries, 

operational considerations, anticipated future disturbances, and climate change 

projections. Density management guidelines based on plant associations (Cochran 

1994, Powell 1999) are a useful starting point, as are density and composition data 

from reference sites (Franklin et al. 2013). These may need to be modified, however, 

based on anticipated climate change. Conditions and planned treatments in surrounding units should also be considered. A landscape prescription can provide 

guidance for setting unit-level targets based on achieving landscape-level objectives 

(Hessburg et al. 2015). The overall goal of density and composition targets is to 

better align the vegetation with the current and future biophysical conditions and 

disturbance regime of the site. 

Once the target stem density and composition have been determined, spatial 

pattern targets that are appropriate for the site can be selected. Pattern targets based 

on clumping levels offer a simplified approach (e.g., Low, Mod, or High; table 3.3). 

Basal area distributions from reference plots can also be used. As our results show 

considerable variation in the relationship between potential vegetation series and 
66

GENERAL TECHNICAL REPORT PNW-GTR-956

pattern, directly using potential vegetation series to select a clumping level can 

be challenging. Instead, potential vegetation series or plant association group can 

be one of the factors considered when selecting target density, which will in turn 

influence the clumping target. We suggest the following considerations in selecting 

a clumping level for a particular unit. 

• Align clumping levels with target density. Historically, low-density 

stands (50 to around 100 trees per hectare [tph]) typically had low or 

moderate clump level, while higher density stands have moderate to high 

clumping levels. 

• Assess the number and clumping levels of live old trees in the stand. If 

retaining old trees is part of the prescription, the clump percentage targets 

should accommodate retaining existing old trees to avoid conflicts for the 

marking crew. 

• Assess the extent to which leave trees of the desired species and condition 

are clumped in the stand. (e.g., healthy foliage, crown ratio greater than 40 

percent, wildlife habitat features). If there are not a sufficient number of 

suitable leave trees in clumps, prescribing higher clumping levels can result 

in excessive numbers of trees with poor vigor. Some inferior trees can be 

retained to make up larger clumps and will provide for snag recruitment 

over time. 

• Factor in wildlife habitat requirements and visual considerations. Larger 

clumps can provide cover for different species and break up siting distances 

(Franklin et al. 2013). 

• Factor in the potential effects of prescribed fire. Some clumps can be intentionally killed or thinned out with prescribed fire to create snag patches 

and openings. 

• Factor in no-cut buffers or larger skips (~0.2+ ha) that will be retained 

within the unit or on unit edges (Franklin et al. 2013). These dense leave 

areas will provide many of the functions of large or very large clumps. 

However, keep in mind that the clumping levels found in this study are 

from 2.4- to 6-ha reference plots, indicating that clumps were distributed 

across stands and not packed into riparian areas or other microsites. 

• Vary pattern among units. Varying clumping levels for units across a larger 

project area will avoid creating a similar fine-scale pattern across large 

areas. Treatments that only achieve one end of the historical envelope (e.g., 

the more uniform end) will not create the larger scale variability associated 

with historical forests. 
67

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Targets for openings should also be considered. However, because density, 

clumping level, and openings are closely related, we have found through monitoring that small- to medium-sized openings are created in the course of achieving a 

particular density and clumping level, and that the resulting openings are within the 

range of reference conditions. As long as some areas are left without leave trees for 

20 to 50 m apart, specific targets for openings may not be necessary. Additionally, 

most openings found in this study were small (<0.04 ha), and opening size distributions exponentially decreased (fig. 3.5). Also, opening shape was generally linear 

and sinuous vs large, circular gaps (>0.4 ha). Monitoring or real-time tracking can 

be done to assess where openings are indeed being created. Guidance as to where to 

locate openings can also be helpful as soil conditions or disturbance pockets often 

drive opening locations. 

For openings larger than about 0.4 ha, we have found that specific marking 

guidelines may be needed. Instead of prescribing openings in terms of area, we 

have found width and linear distance to be easier to implement. Linear, sinuous 

openings can be laid out prior to general marking with a flag line. Marking crews 

can then be instructed to space off of the flag line for a certain width (e.g., remove 

most trees within 9 to 30 m of the flag line). 

Marking Guide Development and Implementation

Translating density, compositional, and clumping targets into an operationally 

practical marking guide can be done in a number of ways. The Individuals, clumps, 

and openings (ICO) method (Churchill et al. 2014) is one option. The ICO method 

was designed to explicitly combine typical dry-forest prescriptions with targets 

for clumping. Instead of marking for an average or range of basal area, crews are 

given a target number of individuals, and small, medium, and large clumps to retain 

across a unit. The use of unit-wide targets instead of per-acre targets provides more 

flexibility to work with stand conditions. 

Basal area or other marking guide approaches can also be used to achieve the 

target range of variability (e.g., Franklin et al. 2013, Jain et al. 2012, Powell 2014). 

We have found that individual trees and small clumps are relatively easy to retain 

with a basal-area marking guide that emphasizes tree selection over strict spacing. Medium and larger clumps, however, generally are more difficult to achieve 

without specific direction (Churchill et al. 2013). Thus, adding targets for medium 

and large clumps to a basal area marking guide can provide clear guidance to 

marking crews and can be easily tracked during marking. A challenge with basal 
68

GENERAL TECHNICAL REPORT PNW-GTR-956

area marking, however, is the tendency to leave the target basal area in the majority of the stand with some variation around the mean (a normal distribution or 

bell-shaped curve). However, basal area was not normally distributed in most of 

the reference plots (fig. 3.6), and the mean basal area value was not the dominant 

condition. Restoring the multiscale variability similar to that of the reference plots 

may require marking for a wide range of basal area where the mean is not the 

dominant condition. 

Several important factors should be considered for all prescription approaches. 

The first is to emphasize to marking crews that the goal of these treatments is to 

create or maintain an overall pattern of individuals, clumps, and openings. The 

targets should not be applied in a rigid manner, but instead used as “guard rails” 

to help marking crews know if they are creating too little or too much variability. 

Second, marking crews can work with existing tree and biophysical conditions 

to create variable patterns within and across treatment units and avoid trying to 

force the same density and variability on every acre. For example, medium and 

large clumps can be concentrated in areas where good leave tree candidates exist. 

Individuals and openings can be more dominant in other areas. Underlying variation in soils, topography, and disturbance processes can also be used to adjust 

target density and clumping levels across a stand (e.g., leave more clumps on 

north-facing slopes and more individuals and openings on patches with shallow 

soils) (North et al. 2009). 

Finally, we have found that real-time tracking of leave tree density, clumps, 

and openings greatly helps marking crews implement these kinds of prescriptions. 

Tracking gives crews flexibility to adjust their marking to work with existing tree 

and biophysical conditions as they move through a unit while knowing where they 

are relative to the “guard rails.” An android app has been developed to facilitate 

such tracking. Contact the lead author for more information. 
69

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Conclusion

Restoration and sustainable long-term management of dry-forest ecosystems in 

eastern Oregon requires looking to the past to understand how these forests developed and persisted under intact natural disturbance regimes, as well as anticipating 

future climate change and disturbance regimes. The historical data for forest 

ecosystem composition, structure, and spatial pattern we report here can be used to 

inform the development of prescriptions, and monitoring using the ICO (Churchill 

et al. 2014) or other methods. These are “historical estimates,” but their value lies 

in showing the range of variability that was present within and across a sample 

of historical stands. Restoring such variability is a reasonable approach to restoring the functions that historical forests provided and that society desires today. 

Current conditions, future stand development and disturbance, and anticipated 

climate change can necessitate deviating from these historical estimates, however. 

Ultimately, these historical data provide a quantitative baseline for managers and 

stakeholders to draw upon when developing marking guidelines and interpreting 

monitoring results in dry forests of the Blue Mountains. Combined with results 

from similar studies from across the interior West, they can be used to inform restoration of dry forests in similar forest types in other areas as well. 

English Equivalents

When you know: Multiply by: To get:

Centimeters (cm) 0.394 Inches

Meters (m) 3.28 Feet

Hectares (ha) 2.47 Acres
70

GENERAL TECHNICAL REPORT PNW-GTR-956

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Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

We followed methods used by North et al. (2007) and Bakker (2005) to reconstruct 

outside bark diameter at breast height (d.b.h.) in 1890 for all live trees on each plot. 

A regression model was built using the live measure trees to predict total inside 

bark basal area increment from 1890 to 2013, which was then used to estimate 

1890 d.b.h. for all live trees. Predictor variables that were tested to develop the 

best model included 2013 inside bark d.b.h., species, potential vegetation series, 

location, vigor class, age class, and a neighborhood competition index using 2013 

diameters from Contreras et al. (2011). Numeric values for Van Pelt rating and vigor 

rating were used vs. categorical values. This model was then used to derive 1890 

inside bark d.b.h. for the rest of the live trees by subtracting the predicted basal area 

increment from 1890 to 2013 from the 2013 inside bark basal area (derived from 

field-measured outside bark d.b.h.). Inside bark d.b.h. in 1890 was then converted to 

outside bark d.b.h. All conversions between inside and outside bark diameters were 

done using bark thickness equations from Spada (1960).

For snags and downed logs that were believed to be alive in 1890, diameter in 

1890 was established using the following approach. First, diameters taken at stump 

height were converted to breast height diameters using regression equations developed from the live measure trees and from Bones (1960). Year of death was then 

estimated from species and decay class using equations from Everett et al. (1999) 

and rounded to the nearest 5th year. Regression models from the live measure trees 

were then developed to predict basal area increment from 1890 to year of death. 

These models were then used to “grow” all structures back to 1890. 

Model form, predictors, and parameters are provided below for regression 

models used to reconstruct 1890 d.b.h. for live trees that were not cored. Models 

were based on 940 cores from live trees: Pinus ponderosa (PIPO) 667 trees, 

Abies grandis (ABGR) 176 trees, Pseudotsuga menziesii (PSME) 71 trees, Larix 

occidentalis (LAOC) 26 trees. Separate models for snags and downed logs were 

created owing to the fact that ratings for vigor and Van Pelt age could not be made 

for dead structures. 

Appendix 1: Methods to Reconstruct Diameters in 1890
84

GENERAL TECHNICAL REPORT PNW-GTR-956

Live Tree Model 

Model form:

BAE = ea + b × ln(DIA) + c × NI + d × VPR + h × VIG

Parameters and R2 (all parameters were significant: p < 0.05): 

a b c d h r2

2.2122 1.4801 -0.0068 -0.2913 -0.1289 0.7953

Predictor variables:

• BAI: Basal area increment in cubic centimeters from 2013 to 1890. 

• DIA is inside bark d.b.h. in 2013. 

• VPR is the Van Pelt (2008) age rating as a continuous variable: 

- 1: young (<80 years); 2: mature (80 to 150); 3: old (15 to 250); 4: very old 

(>250). 

• VIG: is Van Pelt (2008) vigor rating as a continuous variable: 

- 1: A (very high vigor); 2: B (high vigor); 3: C (moderate vigor); 

4: D (low vigor). 

• NI is a neighborhood index from Contreras et al. (2011) that measures the 

competitive environment of the tree using an 11-m radius. Values were calculated using 2013 diameters of neighboring trees. Values for dead neighbors were weighted by the number of years they were alive from 1890 to 

2013 (e.g., the index value for a neighbor that died in 1980 was weighted by 

a value of (1980 to 1890)/123 = 0.73. The index is calculated using the following formula:

Where

d is the diameter of the subject tree. 

n is the number of trees within a 8-m radius of the subject tree. 

di

 is the diameters of ith neighbor. 

disti is the distance from the ith neighbor to the subject tree. 

Diameter in 2013 (DIA) was the most important predictor, followed by NI, 

VPR, and VIG. Potential vegetation series, tree species, and plot location (e.g., 

Dugout Research Natural Area [RNA] vs. Canyon Creek RNA), were not significant predictors. 

∑n

i=1(di /d) × arctan (di /disti

)
85

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Dead Structure Model 

Model form:

BAE = ea + b × ln(DIA) + c × NI + d × PVGF + h × PVPP

Parameters (all parameters were significant: p < 0.05): 

a b c d h r2

Year of 

death

2.7065 1.1161 -0.0153 0.1676 -0.0776 0.7182 2010

2.7711 1.0950 -0.0160 0.1611 -0.0825 0.7160 2005

2.8311 1.0749 -0.0167 0.1570 -0.0880 0.7145 2000

2.8995 1.0507 -0.0175 0.1570 -0.0907 0.7118 1995

2.9456 1.0334 -0.0181 0.1577 -0.0940 0.7090 1990

3.0133 1.0092 -0.0190 0.1604 -0.0971 0.7053 1985

3.0817 0.9824 -0.0200 0.1587 -0.1038 0.7039 1980

3.1276 0.9618 -0.0208 0.1548 -0.1088 0.7029 1975

3.1592 0.9439 -0.0216 0.1515 -0.1107 0.7020 1970

3.1819 0.9263 -0.0223 0.1476 -0.1151 0.7001 1965

3.2024 0.9077 -0.0230 0.1432 -0.1183 0.6971 1960

3.2225 0.8866 -0.0239 0.1366 -0.1208 0.6942 1955

3.2354 0.8645 -0.0247 0.1275 -0.1213 0.6917 1950

3.2270 0.8450 -0.0255 0.1160 -0.1270 0.6914 1945

3.1580 0.8386 -0.0256 0.0977 -0.1298 0.6926 1940

3.0893 0.8365 -0.0256 0.0796 -0.1315 0.6946 1935

3.0248 0.8304 -0.0255 0.0683 -0.1277 0.6931 1930

2.9792 0.8147 -0.0258 0.0629 -0.1207 0.6893 1925

2.8774 0.8081 -0.0263 0.0654 -0.1177 0.6871 1920

2.2218 0.9334 -0.0219 0.0948 -0.1168 0.6947 1915

2.2466 0.8705 -0.0228 0.0355 -0.1387 0.6906 1910

1.7821 0.9157 -0.0191 0.0151 -0.1332 0.6824 1905

2.1247 0.7193 -0.0254 -0.0358 -0.1407 0.6642 1900

1.5301 0.6982 -0.0256 -0.0428 -0.1667 0.6593 1895

Variables:

• BAI: Basal area increment in cubic centimeters from year of death to 1890. 

• DIA is inside bark diameter as derived from field measurement

▪ NI is a neighborhood index (see explanation above)

▪ PV: Potential vegetation series as a categorical variable:

- PVGF: 1 value for plots in grand fir series. 0 values for other series.

- PVPP: 1 value for plots in ponderosa pine series. 0 values for other 

series.
86

GENERAL TECHNICAL REPORT PNW-GTR-956

Bark thickness equation to derive diameter outside bark 

(DOB) from diameter inside bark (DIB) at breast height:

Equation form:

DOB = a = b × DIB

Parameters: 

Species a b

PSME 0.079782 1.133273

PIPO 0.616246 1.108156

ABGR 0 1.10673

Other 0.079782 1.133273

This equation is used in reverse to derive diameter inside bark from diameter 

outside bark. Equations are from Spada (1960)
87

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

The following models were used to derive crown radii from diameter at breast 

height (d.b.h.) to project crowns and estimate canopy cover. Data are from U.S. Forest Service Current Vegetation Survey plots from the Blue Mountains and eastern 

Washington. 

Model form:

CR = ea+b×ln(DBH)

Model information and parameters: 

Species a b r2

No. of 

trees

ABGR -0.8822 0.5261 0.79 11,732 

PIPO -1.4210 0.6462 0.82 9,900 

PSME -0.9025 0.5420 0.83 43,113 

LAOC -1.3965 0.6322 0.77 8,991 

Variables

• CR: Crown radius in meters

• DBH: diameter at breast height in cubic centimeters. 

Appendix 2: Crown Radius Models
88

GENERAL TECHNICAL REPORT PNW-GTR-956

Table 3A.1—Clump size distributions for Malheur National Forest reference plots ordered by the proportion of 

trees that are individuals (clump size = 1)

Proportion of trees Proportion of basal area

Clump size (No. of trees) Clump size (No. of trees) 

Plot Seriesb

Clumping 

level 1 2-4 5-9 10-15 16-30+ 1 2-4 5-9 10-15 16-30+

G3 ABGR Low 0.41 0.45 0.08 0.07 0.00 0.66 0.28 0.03 0.03 0.00

P1 PIPO Low 0.38 0.48 0.11 0.04 0.00 0.45 0.47 0.06 0.01 0.00

D2 PSME Low 0.35 0.36 0.19 0.09 0.00 0.52 0.32 0.12 0.04 0.00

D1 PSME Low 0.36 0.43 0.11 0.11 0.00 0.49 0.39 0.06 0.06 0.00

D4 PSME Low 0.31 0.42 0.20 0.07 0.00 0.42 0.39 0.17 0.02 0.00

D3 PSME Low 0.32 0.37 0.31 0.00 0.00 0.35 0.40 0.25 0.00 0.00

D5 PSME Low 0.33 0.56 0.08 0.03 0.00 0.45 0.48 0.07 0.00 0.00

P5 PIPO Mod 0.20 0.38 0.38 0.05 0.00 0.27 0.37 0.31 0.05 0.00

P4 PIPO Mod 0.21 0.39 0.28 0.11 0.00 0.26 0.38 0.28 0.08 0.00

P2 PIPO Mod 0.20 0.27 0.23 0.20 0.11 0.31 0.30 0.19 0.11 0.09

P3 PIPO Mod 0.16 0.37 0.34 0.07 0.05 0.21 0.40 0.32 0.04 0.03

G4 ABGR High 0.15 0.33 0.24 0.10 0.17 0.24 0.32 0.20 0.09 0.14

G1 ABGR High 0.11 0.27 0.26 0.10 0.24 0.17 0.31 0.23 0.07 0.22

G2 ABGR High 0.07 0.16 0.18 0.18 0.41 0.11 0.19 0.19 0.18 0.33

a

 The clump size distribution is the proportion of trees or basal area by clump size. Clump size is the number of trees in a clump. Clumps are defined as 

trees within at least 6.1 ha of another tree in the clump. Plots are grouped by plant series and clumping level.

b

ABGR = Abies grandis, PIPO = Pinus ponderosa, PSME = Pseudotsuga menziesii.

Table 3A.2—Clump size distributions from table 3A.1 summarized by clumping level 

and plant association groupa

Proportion of trees Proportion of basal area

Clump size (No. of trees) Clump size (No. of trees) 

Clumping 

level 1 2-4 5-9 10-15 16-30+ 1 2-4 5-9 10-15 16-30+

Low 0.35 0.44 0.15 0.06 0.00 0.48 0.39 0.11 0.02 0.00

Mod 0.19 0.35 0.31 0.11 0.04 0.26 0.36 0.28 0.07 0.03

High 0.11 0.25 0.23 0.13 0.28 0.17 0.27 0.21 0.12 0.23

Series

PIPO 0.23 0.38 0.27 0.09 0.03 0.30 0.38 0.23 0.06 0.02

PSME 0.33 0.43 0.18 0.06 0.00 0.45 0.40 0.13 0.02 0.00

ABGR 0.19 0.30 0.19 0.11 0.21 0.30 0.27 0.16 0.09 0.17

a

 Values are averages for that group. 

b

 ABGR = Abies grandis, PIPO = Pinus ponderosa, PSME = Pseudotsuga menziesii.

Appendix 3: Clump Size Proportions for 

All Trees >10 cm
89

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Appendix 4: Distribution of Basal Area

Figure 4A.1—Frequency distribution of historical basal area pooled by potential vegetation series. Left panel displays basal area calculated using variable radius plots with a 4.6-basal area factor (20 English basal area factor) on a 20-m grid across each of the 14 stem map 

reference plots. The right panel displays results from 0.08-ha fixed area plots. See figure 3.5 for results from 0.04-ha fixed area plots. 

Orange bars show the pooled results for the five ponderosa pine plots, green bars show results for the five Douglas-fir plots, and the dark 

green bars show results for the four grand-fir plots. Red lines are means for the respective series. All plots were simulated. 

0.00

0.05

0.10

0.15

0.20

PIPO series

Mean basal area

0.00

0.05

0.10

0.15

0.20

Proportion of plots

PSME series

0.00

0.05

0.10

0.15

0.20

ABGR series

0.00

0.05

0.10

0.15

0.20

PIPO series

Mean basal area

0.00

0.05

0.10

0.15

0.20

Proportion of plots

PSME series

0.00

0.05

0.10

0.15

0.20

ABGR series

10

30

50

70

90

110

130

150

170

190

210

230

250

270

280+

2.3

6.9

11.5

16.1

20.7

25.3

29.8

34.4

39

43.6

48.2

52.8

57.4

62

64.3+

Basal area (midpoint of 4.6 m2 ha−1class)

Basal area (midpoint of 20 ft2

 ac−1 class)

10

30

50

70

90

110

130

150

170

190

210

230

250

270

280+

2.3

6.9

11.5

16.1

20.7

25.3

29.8

34.4

39

43.6

48.2

52.8

57.4

62

64.3+

Basal area (midpoint of 4.6 m2 ha−1class)

Basal area (midpoint of 20 ft2

 ac−1 class)
90

GENERAL TECHNICAL REPORT PNW-GTR-956

Plot

95% CI

0 10 20 30 40 50

0.5

1.0

1.5

2.0

2.5

Intertree distance (m)

g(t)

0 10 20 30 40 50

0.5

1.0

1.5

2.0

2.5

Intertree distance (m)

g(t)

Plot

95% CI

0 10 20 30 40 50

0.5

1.0

1.5

2.0

2.5

Intertree distance (m)

g(t)

Plot

95% CI

P1 P2 P3

0 10 20 30 40 50

0.5

1.0

1.5

2.0

2.5

Intertree distance (m)

g(t)

Plot

95% CI

0 10 20 30 40 50

0.5

1.0

1.5

2.0

2.5

Intertree distance (m)

g(t)

Plot

95% CI

0 10 20 30 40 50

0.5

1.0

1.5

2.0

2.5

Intertree distance (m)

g(t)

Plot

95% CI

P4 P5 D1

0 10 20 30 40 50

0.5

1.0

1.5

2.0

2.5

Intertree distance (m)

g(t)

Plot

95% CI

0 10 20 30 40 50

0.5

1.0

1.5

2.0

2.5

Intertree distance (m)

g(t)

Plot

95% CI

0 10 20 30 40 50

0.5

1.0

1.5

2.0

2.5

Intertree distance (m)

g(t)

Plot

95% CI

D2 D3 D4

Appendix 5: Pair Correlation Plots for 14 Reference Plots
91

Historical Forest Structure, Composition, and Spatial Pattern in Dry Conifer Forests of the Western Blue Mountains, Oregon

Figure A5.1—Plots of pair correlation function, g(t), for 14 reference plots. Red lines display the g(t) values from 0.1 to 30 m intertree 

distance for each plot. The hatched envelopes are the 95 percent confidence intervals (CI) from 1,000 simulated random patterns 

(complete spatial randomness [CSR]). Tree patterns are clustered when the red lines are above the 95 percent CSR confidence interval, 

random when inside the envelope, and uniform when below the envelope.

0 10 20 30 40 50

0.5

1.0

1.5

2.0

Intertree distance (m)

g(t)

Plot

95% CI

0 10 20 30 40 50

0.5

1.0

1.5

2.0

Intertree distance (m)

g(t)

Plot

95% CI

0 10 20 30 40 50

0.5

1.0

1.5

2.0

Intertree distance (m)

g(t)

Plot

95% CI

0 10 20 30 40 50

0.5

1.0

1.5

2.0

Intertree distance (m)

g(t)

Plot

95% CI

0 10 20 30 40 50

0.5

1.0

1.5

2.0

Intertree distance (m)

g(t)

Plot

95% CI

D5 G1 G2

G3 G4

Pacific Northwest Research Station

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P.O. Box 3890

Portland, OR 97208–3890
U.S. Department of Agriculture

Pacific Northwest Research Station

1220 SW 3rd Ave., Suite 1400

P.O. Box 3890

Portland, OR 97208–3890

Official Business

Penalty for Private Use, $300