Constance A. Harrington and Warren D. Devine

A Practical Guide

to Oak Release

General Technical Report

PNW-GTR-666

February 2006

United States

Department of Agriculture

Forest

Service

Pacific Northwest

Research Station
Authors

Constance A. Harrington and Warren D. Devine are research foresters, 

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

Cover photograph by Constance Harrington.

Abstract

Harrington, Constance A.; Devine, Warren D. 2006. A practical guide to 

oak release. Gen. Tech. Rep. PNW-GTR-666. Portland, OR: U.S. Department 

of Agriculture, Forest Service, Pacific Northwest Research Station. 24 p.

Oregon white oak savannas and woodlands represent a biological and 

cultural legacy in the Pacific Northwest. Many Oregon white oak stands 

are deteriorating owing to invasion and eventual overtopping by Douglas-fir 

or other conifers. Releasing the shade-intolerant oak trees from overtopping 

conifers can often restore these oak stands. When planning a release operation, 

there are many factors to consider such as timing and intensity of release, 

which trees to select for release, and management of the understory. A carefully 

executed oak release can minimize damage to oak trees, and followup treatments may reduce the spread of invasive plants. This guide answers the most 

commonly asked questions related to oak release.

Keywords: Oregon white oak, Garry oak, Quercus garryana, release, restoration, 

competition, savanna.
A Practical Guide to Oak Release



Why manage for oak?

Our oak savannas and woodlands (and the associated prairies) represent a 

biological and cultural legacy. Most areas with oak trees were previously maintained 

in an open condition by frequent burning by Native Americans. Many plant and 

animal communities associated with oaks and prairies are unique, and most of the 

species in these communities are 

not found in conifer-dominated 

forests. More than 90 percent 

of the areas that had oak or 

were in prairies at the time of 

European settlement have been 

converted to agriculture, urban 

development, or conifer forests. 

If we allow the oak legacies 

we have to disappear, we will 

lose their associated species 

and communities. The primary 

reasons given for wanting to 

manage for oak are maintaining 

oak-related wildlife habitat, 

preserving ecological diversity, 

and desiring to have open areas 

in the landscape. Oaks also can 

be managed for timber production or specialty products.

To which oak species are you referring?

This guide is based on our experience with Oregon white oak, also known 

as Garry oak. This species is native in California, Oregon, Washington, and British 

Columbia. 

Few oak stands still contain native plant communities. The blue 

flowers in this photo are camas; its bulbs were an important food 

source for Native Americans.

Warren Devine
General Technical Report PNW-GTR-666

What does “oak release” mean?

In forestry terminology, release means to release a tree from competition, 

i.e., to reduce the competition for light, water, and nutrients associated with the 

presence of other trees. Here, oak release is a phrase used primarily to describe 

removing overtopping conifers from the vicinity of oak trees.

These oak trees once grew on an open savanna, but now they are surrounded by taller, faster 

growing Douglas-fir trees. Because the oak trees in this photo still have many living branches, 

they are good candidates for release.

Constance Harrington
A Practical Guide to Oak Release



Why do oak trees need to be released?

Oregon white oak is not shade tolerant, meaning its leaves do not 

photosynthesize at their maximum in the shade, and the shaded branches will 

die. If most of the crown becomes shaded, the tree may persist for several decades 

but will eventually die. In addition, the plant and animal communities associated 

with Oregon white oak need open areas or sunny conditions.

How do I know if an oak tree or 

oak stand needs to be released?

Oak trees with crowns that are partially or totally overtopped by the 

crowns of conifers will benefit from release. One of the best indications of whether 

an oak tree is being suppressed by conifers is the shape and condition of the oak’s 

crown. Tree crowns are influenced by the amount of crowding and shading they have 

experienced throughout their lives. Oak trees that initially developed with very little 

competition (i.e., open-grown) have wide-spreading crowns sometimes described as 

“mushroom shaped.” If one of these trees becomes overtopped, portions of the crown 

will die back slowly, and eventually the entire tree will die. Trees that initially grew 

in more crowded conditions will have narrower crowns, sometimes described as 

“columnar” or “vase-shaped,” with fewer large-diameter limbs. When these narrower 

crowned trees become overtopped, they may develop very irregular crown shapes, as 

the shading and dieback usually occur on one side first.

When assessing the condition of oaks, it is often helpful to compare the crowns 

of overtopped oak trees to those of oak trees growing well away from any conifers. 

Compare the number of dead limbs on the overtopped oaks to the oaks growing 

apart from conifers. Also, compare the density of the crowns. If an oak is suffering 

from overtopping, its crown will be more sparse.
General Technical Report PNW-GTR-666



Can I use stand exam or forest inventory 

data to select stands for oak release?

Stand exam data often include detailed information on the tree species 

present and their size, as well as notes on site features or stand conditions of interest. If data from stand exams indicate that both Oregon white oak and conifers are 

present, those stands may be good candidates for release activities. If a stand is going 

to be inventoried or examined, it may be possible to request that notes be made 

on areas where release would be appropriate. A Landowner’s Guide for Restoring and 

Managing Oregon White Oak Habitats (see page 23) explains how a landowner can 

gather information on trees for use in developing a management plan.

Most forest inventory systems are designed to collect infomation on large areas to 

make summaries of timber volumes. They often only record information on trees of 

merchantable size and species, and thus, could provide only limited information on 

the location of stands that would be candidates for oak release. Sampling intensity 

is low in forest inventory systems, and so they can easily miss less common features 

that would be of interest. 

Should I release individual trees or 

do a stand-level release?

This depends on your management objectives. If you want to restore an oak 

woodland or oak savanna, then you should remove all (or most) of the conifers. You 

cannot manage for plant communities associated with prairies, oak savannas, and 

oak woodlands if you retain a conifer overstory. Keeping scattered conifers may, 

however, benefit wildlife species such as the western gray squirrel. On the other 

hand, if you are managing a predominantly coniferous forest for timber production 

and want to retain individual oak trees as legacies for the future, then removing 

conifers from the vicinity of individual oak trees might be appropriate. To make 
A Practical Guide to Oak Release



The top half of this diagram shows an overhead view 

of an individual oak (rounded orange crown) that 

is overtopped; the lower half shows an oak that has 

been released by removing all conifers (pointed green 

crowns) within a specified radius.

an effective individual-tree release, enough conifers must be removed to 

expose the whole oak crown to sunlight. Depending on the size of the trees, 

the slope, and the aspect, this usually means removing conifers within at 

least 30 to 40 feet (9 to 12 meters) of oaks (but often to a greater distance). 

An individual-tree release is not a permanent solution though, as the surrounding conifers will continue to grow at a faster rate than the oak and 

will eventually begin to shade it again requiring future release treatments.

Another option for release activities 

is to start with a core area that is in 

good condition and expand out from 

there. For example, many oak savannas and prairie areas had a fringe of 

oak trees around the outer edge, and 

these fringe trees have been overtopped. Expanding the boundary of 

the current oak woodland or savanna 

by removing conifers might result in 

areas that are easier to manage and 

have greater ecological value because 

the habitat would be more continuous.

If you do not have as many good 

trees to release as you want, consider 

releasing all of the trees that you do 

have. Although oak trees in poor 

health sometimes die back above 

ground, they may sprout from the 

base of the stem and regrow from the 

same root system. These sprouts will 

likely grow much faster than newly 

planted trees and thus will more 

quickly grow out of reach of animals 

that browse on young oaks.
General Technical Report PNW-GTR-666

In the top diagram, a conifer forest is encroaching, from left to 

right, upon an oak savanna. The lower diagram shows the result 

of releasing these oaks and thereby expanding the savanna.
A Practical Guide to Oak Release



Stand selection—Should I save the 

best first or save the best for last?

A common opinion in ecological restoration discussions is that one should 

concentrate activities on the sites in the best condition first, and when those sites 

are in good shape, move on to sites in poorer conditions. The idea is that you can 

intervene in preventing a problem from developing in the better sites or bring them 

to the desired condition more quickly or less expensively, so they are the ones to 

target first. Does this concept apply to releasing oaks from overtopping conifers? 

Yes and no. If you have decided to concentrate your efforts on restoring an oak 

savanna or woodland on only one or a few sites and you have many to choose from, 

then certainly it would make sense to select the sites where the oak is currently 

in the best condition in terms of crown size and vigor. These sites will probably 

also have more of the plant species associated with oak savannas and prairies still 

present. If, however, you hope to treat all or many of the areas, but can only do a 

few at a time, there can be good reasons to treat at least some of the sites where the 

oak is in poor condition first. The oaks in poor condition will continue to decline 

in vigor and may die without treatment, so promptly releasing those trees is a 

“limited-time opportunity.” Even trees with a large amount of crown dieback and 

fairly low vigor can be rejuvenated by release. In addition, you can gain experience 

in treating some of the sites in poorer condition that can help in dealing with the 

more valuable sites where the oaks are in good condition. 
General Technical Report PNW-GTR-666



Oak trees near a large opening may still have very full crowns. Releasing these trees will allow the crowns to develop 

in a way similar to those of open-grown trees.

Constance Harrington
A Practical Guide to Oak Release



Should I gradually release the oaks 

or do it all at once?

Some people have advocated doing a gradual release to avoid 

“shocking” the released trees. There is no evidence, however, that a gradual 

release is necessary. As far as the tree’s vigor is concerned, the sooner it is 

completely released, the better. On the other hand, if you are managing the 

conifers in the stand for timber production, a gradual release will retain more 

of the stand in timber production for a longer period and allow flexibility in 

future timber management. Multiple harvest operations, however, could result 

in a stand with too few trees to interest a logger or in greater time and cost 

associated with setting up multiple timber sales.

The understory will likely require different levels of management depending 

on whether you release all at once or do a gradual release. Releasing all at once 

may accelerate growth of invasive species, but it may also facilitate understory 

management techniques such as burning and mowing.
General Technical Report PNW-GTR-666

10

This large Douglas-fir has been marked for removal because it is overtopping several oak trees. The large lower 

branches on the Douglas-fir indicate it developed in a low-density stand.

Joseph Kraft
A Practical Guide to Oak Release

11

Removing overtopping conifers along a section of road will create visual diversity for travelers. 

Because the road provides the opening on one side, fewer conifers need to be removed to release 

roadside oaks.

How long will it take an 

overtopped tree to respond?

Oak trees typically begin to benefit soon after release, and, 

depending on the condition they were in prior to release, you may be able to 

see some responses to release as early as the second year. For example, released 

trees often respond by increasing their acorn crops and building larger crowns. 

One way they do this is by sprouting epicormic branches (discussed below). 

However, a severely overtopped tree will take many years to expand its crown, 

and a tree with a very narrow crown will probably never achieve a wide-spreading, 

mushroom-shaped crown. Oaks can be long-lived, however, and the crowns should 

be able to expand for many years if future growing conditions are favorable.

Constance Harrington
General Technical Report PNW-GTR-666

12

What are epicormic branches and are 

they good or bad?

Epicormic branches sprout from suppressed buds (under the bark) 

on the trunk and limbs of trees. They may occur as a result of injury, such as 

crown dieback or logging damage. However, they also sprout in response to a 

sudden increase in sunlight, like that which results from release. In the past, 

many foresters considered epicormic branches to be undesirable as they could 

reduce the timber value of the tree. Because most oak trees that would be released 

are being managed for nontimber objectives, this concern is not relevant. Epicormic 

branches are important to released trees because this is the method the tree uses 

to rebuild its crown. Leaves on epicormic branches improve the tree’s capacity for 

photosynthesis; plus, epicormic branches can eventually bear acorns. Although 

they may look small and ineffective at first, some epicormic branches persist and 

develop into large-diameter, long-lived limbs. 

Epicormic branches often 

form on the stem and 

limbs of released oaks.

Warren Devine
A Practical Guide to Oak Release

13

Although these oaks have been released, decades of suppression have already caused severe crown 

dieback and mortality.

Constance Harrington
General Technical Report PNW-GTR-666

14

Should I concentrate on removing 

conifers on all sides of the oak 

or is just removing them on the 

south side good enough?

If you decide to remove only a few trees because of other resource 

objectives, then the conifers on the south and southwest sides of the oak 

are blocking the most direct sunlight and should be targeted for removal. 

However, if trees on the other sides of the oak are not also removed, the 

oak crown will develop in a very lopsided way. Additionally, the overtopped 

oaks also are competing with surrounding trees for water and nutrients, so 

only removing the overtopping conifers on one side will not provide the 

whole benefit that removing conifers on all sides would.

What time of year is best for 

releasing oaks?

Releasing suppressed oak trees in summer can potentially 

damage their leaves because oak trees, like other deciduous trees, form leaves 

that are adapted to the amount of sunlight they receive. A shaded oak tree 

typically has thinner leaves, and sudden exposure of these leaves to direct 

sunlight may damage or kill the leaves. Leaf damage can be avoided by 

releasing trees during the dormant season when leaves have turned brown 

or fallen. During the dormant season, soils can be wet and thus may be susceptible to rutting or compaction from logging equipment. You may want 

to restrict or monitor heavy equipment on the site during the wettest times 

but still schedule the release in the fall, winter, or spring prior to leaf-out.
A Practical Guide to Oak Release

15

Oaks that have an opening on only one side usually form an unbalanced crown and often lean 

toward the sunlight. 

Joseph Kraft
General Technical Report PNW-GTR-666

16

Do I only need to worry about the 

larger conifers, or should I treat 

smaller ones also?

Removing (cutting or

girdling) the large overtopping 

conifers is the first priority 

as these trees are having the 

greatest negative impact on the 

oaks. However, conifers that 

are not currently overtopping 

oaks probably will do so in 

the future and it may be much 

easier to cut them when they 

are still small. 

Which sites should not be released?

You should be cautious in removing conifers from a site with major 

amounts of invasive species in the understory. Plan ahead how you will deal with 

the aggressive growth of scotsbroom, Himalayan blackberry, English ivy, false 

brome, and other species that are likely to greatly increase their growth under more 

sunlight. Treating some of these undesirable species prior to release is often advantageous because control activities may be more effective on plants in an understory. 

Specific treatments will depend on the site and the species that you are working 

to control. But even if the understory requires extensive work following the release 

operation, the oaks in the overstory will already be benefiting from the release.

These oak trees have been released, but the next generation of 

conifers will soon overtop them again. Constance Harrington

Constance Harrington
A Practical Guide to Oak Release

17

Which trees should not be released?

If you have more oak trees than you need for your final objectives, 

then you should concentrate on trees with large spreading crowns and no sign 

of major decay in the stem (evidenced by large scars or mushroom fruiting 

bodies). Priority for release should then be placed on the largest trees because 

they would take the longest to replace. If you have noticed that certain trees 

are good acorn producers, you may want to favor these trees for their ability 

to produce wildlife food and for regeneration. 

Large scars or visible fungi are signs of internal decay. These trees are important as wildlife 

habitat, but they may not be structurally sound. 

Joseph Kraft
General Technical Report PNW-GTR-666

18

Do I need to obtain any permits 

before I start?

Forest practices regulations in individual states (or in British 

Columbia) will specifiy certain practices that need to be followed. Most regulations 

were written with the assumption that managing for conifers was most desirable 

and there are still features in some of these regulations that make management for 

hardwoods more difficult. There is an appreciation by many involved in overseeing 

these regulations that changes or exemptions are sometimes needed to ensure 

that desirable activities are not discouraged. Contact your state or provincial forest 

practices forester to see which regulations you need to be concerned with.

How much will it cost to release oaks?

Often, removal of conifers does not result in a cost to the landowner, 

as the trees can be sold. However, if you only want a few trees removed, it may be 

difficult to get a contractor to bid on them. In addition, some of the conifers growing among oaks may have developed when the stand was more open and therefore 

have many large-diameter branches, and thus, a lower timber value. Low-value 

trees can be girdled to create snags for wildlife or cut for firewood. Information 

from a forestry consultant or an extension service specialist can help you determine 

if there would be costs to you. Cost-share programs, through agencies such as the 

USDA Natural Resources Conservation Service, may be available.
A Practical Guide to Oak Release

19

Will the oaks be 

damaged during 

logging?

It is important that before 

taking bids from logging contractors on 

the release, the contractors understand 

that the main objective is to preserve the 

oak trees. If possible, you should choose 

a logging contractor who has experience 

thinning stands and therefore knows 

how to minimize damage to the trees you 

are keeping. Prior to the operation, meet 

with the contractors and anyone else 

involved to discuss the specifics of the 

release. In some situations, even the most 

skilled loggers will not be able to save all 

of the oak trees when they are removing 

many large conifers from the immediate 

vicinity. Sometimes a good compromise 

is to girdle a conifer if it is not easily 

accessible to loggers or if felling it would 

cause certain damage to oaks. You should 

be prepared to accept that some oak 

trees will be damaged during the logging 

operation. Unless damaged or dead oak 

trees present a safety issue for humans, 

they should be left standing as they are 

important as wildlife habitat. For example, where a limb is broken off during 

logging, a nesting cavity may form. Some conifers cannot be removed 

without seriously damaging oak trees. 

It may be best to girdle the conifer in 

such situations. 

Hugh Snook

Constance Harrington
General Technical Report PNW-GTR-666

20

If I cut the conifers, would it be better 

to just leave them on the ground to 

provide coarse woody debris than 

to remove them?

The plant and animal communities associated with oaks and 

prairies are not associated with conifer woody debris so, no, there is not an 

ecological reason to leave the conifer wood on the site. Also, if you want to use 

prescribed burning to maintain the understory after releasing oaks, it would 

be better not to leave the woody debris on the site as it could make the fires 

much hotter than desired. 

Large amounts of logging slash may be created during the release operation. 

You should plan ahead of time how this slash is to be managed. Possible options 

include chipping slash or burning the slash in piles, although you may be able to 

remove larger pieces of wood for firewood before piling. Always check with local 

authorities on burning restrictions and regulations.
A Practical Guide to Oak Release

21

Logging slash is inevitable; it may be piled and then burned when wildfire risk is low.

Constance Harrington Warren Devine
General Technical Report PNW-GTR-666

22

Once I release my oaks, will I need to 

do any followup treatments?

The need for future treatments will depend on your management 

objectives and the current stand conditions. Most areas with overtopping conifers 

will have smaller conifers present and a seed source to regenerate future conifers. 

Followup treatments are often desirable to prevent these conifers from competing 

with the oaks. If you choose to release individual oak trees rather than the entire 

stand, future release treatments will be necessary as the conifers fill in the gaps 

created to release the oaks.

Followup treatments will typically be necessary if you want the understory to 

be relatively free of invasive species. Treatments to control invasives may include 

removing them by hand, mowing, herbicide application, or prescribed fire. Fire 

is the most natural method because it is a part of these oak ecosystems; however, 

it requires significant planning, proper permissions, and experienced personnel. 

Once invasive species are under control, you may want to purchase native plants 

and seed to reestablish particular species. 

Publications with more information:

Devine, W.D.; Harrington, C.A. 2004. Garry oak woodland restoration in the Puget 

Sound Region: releasing oaks from overtopping conifers and establishing oak 

seedlings. In: Proceedings of the 16th international conference of the Society for 

Ecological Restoration. Victoria, BC, Canada. http://www.fs.fed.us/pnw/olympia/

silv/publications/no_497_2004_devinew_garryoakwoodland.pdf. (15 November 

2005).

Harrington, C.A.; Kallas, M.A., comps. 2002. A bibliography for Quercus garryana

and other geographically associated and botanically related oaks. Gen. Tech. Rep. 

PNW-GTR-554. Portland, OR: U.S. Department of Agriculture, Forest Service, 

Pacific Northwest Research Station. 115 p. http://www.fs.fed.us/pnw/pubs/gtr554.

pdf. (15 November 2005). Search bibliography at: http://www.ncrs.fs.fed.us/RIS/

RISWEB.isa. (15 November 2005).
A Practical Guide to Oak Release

23

Vesely, D.; Tucker, G. 2004. A landowner’s guide for restoring and managing Oregon 

white oak habitats. Salem, OR: U.S. Department of the Interior, Bureau of Land 

Management. 65 p. Available at many Bureau of Land Management, state extension 

service, and Natural Resources Conservation Service offices. Request a copy by 

emailing your name and address to: or080mb@or.blm.gov.

Other resources:

Garry Oak Ecosystems Recovery Team. 301-1205 Broad Street, Victoria, BC 

V8W 2A4. http://www.goert.ca/.

Oregon Oak Communities Working Group. http://www.oregonoaks.org/. 

Email: oregonoaks@comcast.net.

Scientific names

Common name Scientific name

Plants:

Douglas-fir Pseudotsuga menziesii (Mirb.) Franco

English ivy Hedera helix L.

Himalayan blackberry Rubus armeniacus Focke

Oregon white oak (also called Garry oak) Quercus garryana Dougl. ex Hook.

scotsbroom Cytisus scoparius (L.) Link

slender false brome Brachypodium sylvaticum (Huds.) Beauv.

Mammals:

Western gray squirrel Sciurus griseus

Acknowledgments

We thank the Forestry Program, U.S. Army, Fort Lewis, for financial support.
General Technical Report PNW-GTR-666

24

Christel Kern

Several oak trees have been released by cutting conifers in a portion of this stand.
Pacific Northwest Research Station 

Web site http://www.fs.fed.us/pnw/

Telephone (503) 808-2592

Publication requests (503) 808-2138

FAX (503) 808-2130

E-mail pnw_pnwpubs@fs.fed.us

Mailing address Publications Distribution

	 	 Pacific Northwest Research Station

 P.O. Box 3890

	 	 Portland, OR 97208-3890

The Forest Service of the U.S. Department of Agriculture is dedicated to the principle of 

multiple use management of the Nation’s forest resources for sustained yields of wood,

water, forage, wildlife, and recreation. Through forestry research, cooperation with the

States and private forest owners, and management of the National Forests and National

Grasslands, it strives—as directed by Congress—to provide increasingly greater service to a

growing Nation.

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and 

activities on the basis of race, color, national origin, age, disability, and where applicable,

sex, marital status, familial status, parental status, religion, sexual orientation, genetic 

information, political beliefs, reprisal, or because all or part of an individual’s income is

derived from any public assistance program. (Not all prohibited bases apply to all programs.)

Persons with disabilities who require alternative means for communication of program 

information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at

(202) 720-2600 (voice and TDD). To file a complaint of discrimination, write USDA, Director,

Office of Civil Rights, 1400 Independence Avenue, SW, Washington, DC 20250-9410 or call

(800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider

and employer.
U.S. Department of Agriculture

Pacific Northwest Research Station

333 SW First Avenue

P.O. Box 3890

Portland, OR 97208-3890