United States Department of Agriculture

DEPAR TMENT OF AGRICULT URE

Seeing the Forest Below the Trees: 

Occurrences of Shrubs in the 

Pacific Northwest

Jacob L. Strunk, Constance A. Harrington, Leslie C. Brodie, 

and Janet S. Prevéy

Forest 

Service

Pacific Northwest 

Research Station

General Technical Report

PNW-GTR-980

January

2020
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Authors

Jacob L. Strunk is a statistician, Constance A. Harrington is a research forester, 

and Leslie C. Brodie is a forester, Pacific Northwest Research Station, Forestry 

Sciences Laboratory, 3625 93rd Avenue SW, Olympia, WA 98512-9193; Janet S. 

Prevéy is a research ecologist, U.S. Geological Survey, 2150 Centre Avenue # C, 

Fort Collins, CO 80526 (formerly, Pacific Northwest Research Station, Forestry 

Sciences Laboratory, 3625 93rd Avenue SW, Olympia, WA 98512-9193).

Cover: Pacific rhododendron (Rhododendron macrophyllum) growing in a canopy gap 

on the Olympic Pennisula. Photo by Leslie Brodie, USDA Forest Service.
Abstract

Strunk, Jacob L.; Harrington, Constance A., Brodie, Leslie C.; Prevéy, Janet 

S. 2020. Seeing the forest below the trees: occurrences of shrubs in the Pacific 

Northwest. Gen. Tech. Rep. PNW-GTR-980. Portland, OR: U.S. Department of 

Agriculture, Forest Service, Pacific Northwest Research Station. 87 p.

Shrubs are an important component of terrestrial plant communities in both forested and nonforested ecosystems, but relatively little information is available on 

their distributions. This project provides mapped occurrences for 78 native shrub 

species found in the Pacific Northwest (Oregon, Washington, Idaho, and western 

Montana) as derived from two large regional databases: the U.S. Department of 

Agriculture, Forest Service Forest Inventory and Analysis database of vegetation 

collected as part of a nationwide forest inventory and the Consortium of Pacific 

Northwest Herbaria online database (http://www.pnwherbaria.org) of species 

locations from forested and nonforested habitats. Background information on the 

project and maps of locations by species and data source are included. 

Keywords: Shrubs, location, map, Pacific Northwest, western Montana, Idaho, 

Oregon, Washington.
Contents

1 Introduction

2 Datasets

3 Assumptions and Limitations

4 Information Provided in This Project

4 Acknowledgments

5 U.S. Equivalents

5 Literature Cited

7 Appendix
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Seeing the Forest Below the Trees: Occurrences of Shrubs in the Pacific Northwest

Introduction

Shrubs are an important component of terrestrial plant communities in both 

forested and nonforested ecosystems. They may be the dominant species in nonforested landscapes or an integrated member of very diverse plant communities 

(Francis 2004). Generally defined as perennial plants with woody stems (usually 

multiple stems), shrubs vary in stature from tree-like shrubs up to 10 m tall to 

subshrubs or viney shrubs with a maximum height of less than 0.5 m (Pojar and 

MacKinnon 1994). Shrubs provide structure for nesting and foraging habitat for 

many animals (Martin et al. 1961) and substrate for insect and disease organisms 

as well as lichens and bryophytes (Tappeiner et al. 2015). In addition, because their 

short stature increases foraging opportunities for people and nonflying animals 

and because many shrubs have fleshy berries or nuts, shrubs contribute to food 

resources far beyond what might be expected based on their biomass in the ecosystem. For example, more than 50 percent of the shrubs in the Pacific Northwest 

coast area of Oregon, Washington, British Columbia, and Alaska have fleshy fruits, 

often, in the form of edible berries (Pojar and MacKinnon 1994). Furthermore, 

several species of shrubs are traditionally used by American Indian tribal members 

as a food resource and for teas, dyes, medicines, implements, and other cultural 

purposes (Gunther 1945; Turner 1995, 1997; Turner et al. 1990).

Despite the importance of shrubs, detailed range maps are not available for 

many northwest shrub species. Most plant identification books (e.g., Hitchcock and 

Cronquist 1973, Pojar and McKinnon 1994) or plant association guides (e.g., Brockway et al. 1983, Hemstrom et al. 1982) describe the types of habitats in which a species is found, e.g., “marshy lowland habitats,” or indicate a very general geographic 

range such as “west of the Cascade Crest from British Columbia to central Oregon.” 

Elbert Little published a series of atlases for many U.S. tree species, including one 

on “minor western hardwoods” (Little 1976) with general range maps for several of 

the larger shrubs such as vine maple, serviceberry, hazelnut, and cherry; however, 

it did not include smaller plants such as those in the Rubus or Vaccinium genera. 

The online USDA PLANTS database (USDA NRCS 2006) includes range maps for 

many species, but their finest level of resolution indicates only whether a species 

is present within a county. Our preliminary evaluation of several northwest shrubs 

revealed that some counties with multiple occurrences of a species, as determined 

from other sources, are not shown by the PLANTS database to be part of the range 

of that species. Conversely, some very large counties are displayed as part of the 

species range when the plant may be found only in a small portion of the county. 

Thus, we concluded that better species occurrence maps were needed of shrubs in 

this region.
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GENERAL TECHNICAL REPORT PNW-GTR-980

Datasets

We were interested in determining where shrub species are currently found in 

Washington, Oregon, Idaho, and western Montana as the first step in developing 

habitat suitability or range models that can be used to predict where a species might 

grow now and, as climates alter, in the future. For example, current range breadth 

could be an indicator of sensitivity to changing climate or habitat specificity 

(Emery et al. 2018). We used publicly available data sources to document current 

plant occurrences of common and culturally important shrub species across the 

Pacific Northwest region. To select which species to evaluate, we first started with 

the plot data collected by the U.S. Department of Agriculture, Forest Service Forest 

Inventory and Analysis (FIA) program, which inventories resources on forested 

lands in the United States, as this grid of plots would cover the entire geographic 

area we were interested in studying. The FIA database (https://apps.fs.usda.gov/

fia/datamart/CSV/datamart_csv.html) indicated that potentially hundreds of shrub 

species (species recorded by field personnel as having a structure of tree-shrub, 

shrub, subshrub, dwarf shrub, or viney shrub with cover of greater than 3 percent) 

were present in the Pacific Northwest area. We decided to focus on native shrub 

species that were present in 75 or more unique FIA plot locations. This resulted in 

78 species for our geographic area. Note that FIA primarily inventories forested 

lands (see additional discussion below), so our 78 species were either forestassociated species, found in woodlands or ecotones, or were in a few plots found 

in nonforested areas on national forests. This inventory source does not generally 

cover shrub-steppe or other open areas. Downloaded data included plots measured 

in 2016 or earlier.

Our second information source was the Consortium of Pacific Northwest 

Herbaria, an association of 60 regional herbaria with an online database (CPNH 

2017). We downloaded the records for the 78 shrub species selected from the FIA 

database (USDA FS 2015). The consortium database includes data from multiple 

herbaria sources across the Pacific Northwest, with individual herbarium specimens 

collected in different locations for diverse purposes over a period of more than 200 

years, in some cases (although most specimens were collected after 1920). These 

data were not restricted to forested locations.

We are aware of other datasets that include locations of specific shrubs (e.g., 

Oregon Flora, Forest Service and U.S. Department of the Interior Bureau of Land 

Management ecology plots, National Phenology Network, and iNaturalist). We 

chose not to include them as part of this project because of geographic constraints 

for some datasets or lack of documentation. However, these datasets may be 

very useful for other types of projects that document plant locations and in the 
3

Seeing the Forest Below the Trees: Occurrences of Shrubs in the Pacific Northwest

future are likely to grow dramatically both in geographic extent and number 

of observations. This may apply particularly to datasets associated with citizen 

science contributions.

The two datasets we used are very large databases that cover our area of 

interest. They differ in several important ways (see table 1), including the type of 

sampling and the type of habitats that were sampled. We see these data sources as 

complementary, but users need to be aware of the differences in the way the data 

were collected.

Assumptions and Limitations

Although the FIA observations are valuable for making inferences about 

species ranges on forest lands, the data are primarily limited to lands designated 

as “forest” (areas ≥0.4 ha with tree cover ≥10 percent, including recently disturbed 

forests without trees), large riparian strips, and some nonforested areas on national 

forests. In addition, the requirement that plant cover be ≥3 percent for the species 

to be recorded means that small plants would generally be underrepresented in the 

data. Thus, the FIA data cannot be interpreted as range maps. Herbaria data, in 

contrast, can be observed on forest or nonforest land, but the locations of herbaria 

Table 1—Datasets used to map occurrences for 78 native shrub species found in the Pacific 

Northwest (Oregon, Washington, Idaho, and western Montana)

Attribute Pacific Northwest FIA vegetation plots

Consortium of Pacific 

Northwest Herbaria

Type of sampling Grid Varies based on individual 

project, some projects 

follow roads or trails

Years of data Started in 2003 Some samples are from 

the 1800s

Detection of uncommon species Not recorded if <3 percent cover Can record if only one 

plant found

Type of observer and plant 

knowledge

Trained crew but not experts in plant 

identification (vouchers not collected)

From novice to expert 

(vouchered specimens 

available for all plants in 

this database)

Plant communities sampled Primarily forested areas Can sample all vegetation 

types

Location accuracy “Fuzzed” slightly to protect landowner 

privacy concernsa

Range from precise 

estimates to very general 

locations, especially for 

older observations

FIA = Forest Inventory and Analysis.

a Fuzzed locations are generally within 1.6 km and ± 30.5 m in elevation of the actual location (USDA FS 2015).
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GENERAL TECHNICAL REPORT PNW-GTR-980

observations are purposive, or nonrandom. Absence of herbaria observations in an 

area may be due to species absence or to lack of sampling. Thus, neither data source 

can represent the full range or habitat breadth of a species, but both are informative 

with respect to areas in which the species were observed. It would be desirable if 

habitat suitability or fine-scale range models could be developed for many of these 

species in the future, but currently doing so is beyond the scope of this project. We 

hope these current maps will be useful in the near term until more detailed analyses 

can be completed.

We have included all observations regardless of the year that the data were collected (e.g., 1900 vs. 2000), although we recognize that environmental conditions at 

a particular site may no longer support a particular species as a result of, for example, erosion, urbanization, agriculture, forest management, or changes in climate.

Information Provided in This Project

These maps include data for 78 shrub species in our geographic area from the 

2016 FIA database and from data contributed to the Consortium of Pacific Northwest Herbaria, as of June 1, 2018.

The maps are organized alphabetically by scientific name. If you wish to search 

for a common name, use the search feature (on a PC, hit Ctrl+F, then enter the common name). In the appendix is a table of scientific and common names with links to 

the USDA PLANTS database (USDA NRCS 2006) for additional information.

Notes on maps—

The maps include a forested layer to illustrate the areas in which FIA sampling 

could occur. The points from FIA plots were plotted with closed symbols that are 

partially transparent. Thus, if there were multiple points in a general area, the plotting symbols will appear to be darker in color than points in areas with few observations. The plotting symbols from the Consortium of Pacific Northwest Herbaria 

were plotted with open diamonds to minimize occluding the underlying FIA points. 

The plotting points were made large enough to reduce concerns about landowner 

privacy (each symbol covers approximately 160 ha; moreover, the locations from 

the FIA plots were slightly “fuzzed”).

Acknowledgments

We downloaded plant location data by species from the database of the Consortium of Pacific Northwest Herbaria, an association of more than 60 regional herbaria; we thank the contributors to these datasets. Funding from the U.S. Geological 

Survey Northwest Climate Science Center partially supported this project.
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Seeing the Forest Below the Trees: Occurrences of Shrubs in the Pacific Northwest

Literature Cited

Brockway, D.G.; Topik, C.; Hemstrom, M.A.; Emmingham, W.H. 1983. Plant 

association and management guide for the Pacific silver fir zone: Gifford Pinchot 

National Forest. Rep. R6-Ecol-130a-1983. Portland, OR: U.S. Department of 

Agriculture, Forest Service, Pacific Northwest Region. 122 p.

Consortium of Pacific Northwest Herbaria [CPNH]. 2017. Herbarium specimens 

from the Pacific Northwest. http://www.pnwherbaria.org. (5 June 2018).

Emery, M.R.; Patel-Weynand, T.; Patel, A.R.; Chamberlain, J.L. 2018.

Conclusions: nontimber forest products in an era of changing climate. In: 

Chamberlain, J.L.; Emery, M.R.; Patel-Weynand, T., eds. Assessment of 

nontimber forest products in the United States under changing conditions. Gen. 

Tech. Rep. SRS-GTR-232. Asheville, NC: U.S. Department of Agriculture, 

Forest Service, Southern Research Station: 193–200. Chapter 8.

Francis, J.K., ed. 2004. Wildland shrubs of the United States and its territories: 

thamnic descriptions: vol. 1. Gen. Tech. Rep. IITF-GTR-26. San Juan, PR: U.S. 

Department of Agriculture, Forest Service, International Institute of Tropical 

Forestry; and Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station. 830 p.

Gunther, E. 1945. Ethnobotany of western Washington: the knowledge and use of 

indigenous plants and Native Americans. Seattle, WA: University of Washington 

Press. 71 p.

Hemstrom, M.A.; Emmingham, W.H.; Halverson, N.M.; Logan, S.E.; Topik, 

C. 1982. Plant association and management guide for the Pacific silver fir zone: 

Mt. Hood and Willamette National Forests. R6-Ecol-100-1982a. Portland, OR: 

U.S. Department of Agriculture, Forest Service, Pacific Northwest Region. 104 p.

Hitchcock, C.L.; Cronquist, A. 1973. Flora of the Pacific Northwest. Seattle, WA: 

University of Washington Press. 730 p.

U.S. Equivalents

When you know: Multiply by: To get:

Kilometer (km) 0.621 Miles

Meters (m) 3.28 Feet

Hectares (ha) 2.47 Acres
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GENERAL TECHNICAL REPORT PNW-GTR-980

Little, E.L. 1976. Atlas of United States trees: vol. 3. Minor western hardwoods. 

Misc. Publ. 1314. Washington, DC: U.S. Department of Agriculture, Forest 

Service. 13 p., 290 maps.

Martin, A.C.; Zim, H.S.; Nelson A.L. 1961. American wildlife and plants: a guide 

to wildlife food habits. Toronto, ON: General Publishing Company, Ltd. 500 p.

Pojar, J.; MacKinnon, A., eds. 1994. Plants of the Pacific Northwest Coast: 

Washington, Oregon, British Columbia & Alaska. Vancouver, BC: Lone Pine 

Publishing. 528 p.

Tappeiner, J.C.; Maguire, D.A.; Harrington, T.B.; Bailey, J.D. 2015.

Silviculture and ecology of western U.S. forests. 2nd ed. Corvallis, OR: Oregon 

State University Press. 446 p.

Turner, N.J. 1995. Food plants of coastal First Peoples. Vancouver, BC: Royal 

British Columbia Museum and UBC Press. 164 p.

Turner, N.J. 1997. Food plants of interior First Peoples. Vancouver, BC: Royal British 

Columbia Museum, and Seattle, WA: University of Washington Press. 224 p. 

Turner, N.J.; Thompson, L.C.; Thompson, M.T.; York, A.Z. 1990. Thompson 

ethnobotany: knowledge and usage of plants by the Thompson Indians of British 

Columbia. Memoir No. 3. Victoria, BC: Royal British Columbia Museum. 335 p.

U.S. Department of Agriculture, Forest Service [USDA FS]. 2015. Forest 

Inventory and Analysis national program: tools and data. Washington, DC. 

https://www.fia.fs.fed.us/tools-data/spatial/Policy/index.php. (31 May 2018).

U.S. Department of Agriculture, Natural Resources Conservation Service 

[USDA NRCS]. 2006. The PLANTS database. Baton Rouge, LA: National Plant 

Data Center. http://plants.usda.gov. (1 July 2019).
7

Appendix

Common, scientific, and stanardized symbol names of Pacific Northwest shrubs are given here, as well as 

links to additional information in the USDA PLANTS online database (USDA NRCS 2016).

Scientific name Common names Symbol and link

Acer circinatum Pursh vine maple ACCI

Acer glabrum Torr. Rocky Mountain maple, Douglas maple ACGL

Alnus incana (L.) Moench gray alder ALIN2

Alnus viridis (Chaix) DC. green alder ALVI5

Amelanchier alnifolia (Nutt.) Nutt. ex M. Roem. Saskatoon serviceberry AMAL2

Arctostaphylos nevadensis A. Gray pinemat manzanita ARNE

Arctostaphylos patula Greene greenleaf manzanita ARPA6

Arctostaphylos uva-ursi (L.) Spreng. kinnikinnick, common bearberry ARUV

Artemisia arbuscula Nutt. little sagebrush ARAR8

Artemisia tridentata Nutt. big sagebrush ARTR2

Ceanothus prostratus Benth. prostrate ceanothus CEPR

Ceanothus sanguineus Pursh redstem ceanothus CESA

Ceanothus velutinus Douglas ex Hook. snowbrush ceanothus CEVE

Cercocarpus ledifolius Nutt. curl-leaf mountain mahogany CELE3

Chrysothamnus viscidiflorus (Hook.) Nutt. yellow rabbitbrush CHVI8

Cornus sericea L. redosier dogwood COSE16

Corylus cornuta Marshall beaked hazelnut, California hazelnut COCO6

Crataegus douglasii Lindl. black hawthorn CRDO2

Ericameria nauseosa (Pall. ex Pursh) G.L. Nesom 

& Baird

rubber rabbitbrush ERNA10

Frangula purshiana (DC.) A. Gray Cascara buckthorn FRPU7

Gaultheria ovatifolia A. Gray western teaberry GAOV2

Gaultheria shallon Pursh salal GASH

Holodiscus discolor (Pursh) Maxim. oceanspray HODI

Juniperus communis L. common juniper, ground juniper JUCO6

Juniperus scopulorum Sarg. Rocky Mountain juniper JUSC2

Ledum glandulosum Nutt. western Labrador tea LEGL

Ledum groenlandicum Oeder bog Labrador tea LEGR

Linnaea borealis L. twinflower LIBO3

Lonicera utahensis S. Watson Utah honeysuckle LOUT2

Mahonia aquifolium (Pursh) Nutt. hollyleaved barberry, tall Oregon grape MAAQ2

Mahonia nervosa (Pursh) Nutt. Cascade barberry, dull Oregon grape MANE2

Mahonia repens (Lindl.) G. Don creeping barberry, creeping Oregon-grape MARE11

Malus fusca (Raf.) C.K. Schneid. Oregon crab apple, Pacific crab apple MAFU

Menziesia ferruginea Sm. rusty menziesia, false azalea MEFE

Oemleria cerasiformis (Torr. & A. Gray ex Hook. 

& Arn.) Landon

Indian plum OECE

Oplopanax horridus (Sm.) Miq. devilsclub OPHO

Paxistima myrsinites (Pursh) Raf. Oregon boxleaf, mountain boxwood PAMY

Philadelphus lewisii Pursh Lewis’ mock orange, mock orange PHLE4
8

Scientific name Common names Symbol and link

Phyllodoce empetriformis (Sm.) D. Don pink mountainheath, pink mountain heather PHEM

Physocarpus malvaceus (Greene) Kuntze mallow ninebark, Pacific ninebark PHMA5

Prunus emarginata (Douglas ex Hook.) D. Dietr. bitter cherry PREM

Prunus virginiana L. chokecherry PRVI

Purshia tridentata (Pursh) DC. antelope bitterbrush PUTR2

Quercus chrysolepis Liebm canyon live oak QUCH2

Rhododendron albiflorum Hook. Cascade azalea, white-flowered rhododendron RHAL2

Rhododendron macrophyllum D. Don ex G. Don Pacific rhododendron RHMA3

Ribes bracteosum Douglas ex Hook. stink currant RIBR

Ribes cereum Douglas wax currant RICE

Ribes lacustre (Pers.) Poir. prickly currant, black gooseberry RILA

Ribes montigenum McClatchie gooseberry currant RIMO2

Ribes viscosissimum Pursh sticky currant RIVI3

Rosa gymnocarpa Nutt. dwarf rose, baldhip rose ROGY

Rosa nutkana C. Presl Nootka rose RONU

Rosa woodsii Lindl. Woods’ rose ROWO

Rubus lasiococcus A. Gray roughfruit berry, dwarf bramble RULA2

Rubus leucodermis Douglas ex Torr. & A. Gray whitebark raspberry, blackcap RULE

Rubus parviflorus Nutt. thimbleberry RUPA

Rubus pedatus Sm. strawberryleaf raspberry RUPE

Rubus spectabilis Pursh salmonberry RUSP

Rubus ursinus Cham. & Schltdl. California blackberry, trailing blackberry RUUR

Salix scouleriana Barratt ex Hook. Scouler’s willow SASC

Sambucus nigra L. black elderberry, black elder SANI4

Sambucus racemosa L. red elderberry, red elder SARA2

Shepherdia canadensis (L.) Nutt. russet buffaloberry, soapberry SHCA

Sorbus scopulina Greene Greene’s mountain ash SOSC2

Sorbus sitchensis M. Roem. western mountain ash SOSI2

Spiraea betulifolia Pall. white spirea SPBE2

Symphoricarpos albus (L.) S.F. Blake common snowberry, waxberry SYAL

Symphoricarpos hesperius G.N. Jones trailing snowberry SYHE

Symphoricarpos oreophilus A. Gray mountain snowberry SYOR2

Toxicodendron diversilobum (Torr. & A. Gray) 

Greene

Pacific poison oak TODI

Umbellularia californica (Hook. & Arn.) Nutt. California laurel UMCA

Vaccinium cespitosum Michx. dwarf bilberry, dwarf blueberry VACE

Vaccinium membranaceum Douglas ex Torr. thinleaf huckleberry, black huckleberry VAME

Vaccinium myrtillus L. whortleberry VAMY2

Vaccinium ovalifolium Sm. oval-leaf blueberry VAOV

Vaccinium ovatum Pursh California huckleberry, evergreen huckleberry VAOV2

Vaccinium parvifolium Sm. red huckleberry VAPA

Vaccinium scoparium Leiberg ex Coville grouse whortleberry, littleleaf huckleberry VASC
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