Douglas fir root system

Douglas-fir (Pseudotsuga menziesii)

  • Needles are yellowish-green, 1-inch-long and arranged in a spiral around the branchlets, like a bottlebrush.
  • Cones are oblong, 2 to 4 inches long with three-pointed bracts and are located primarily in the upper crown.
  • Bark on young trees is thin, smooth, and gray, with numerous resin blisters. On mature trees the bark is thick (4 to 12 inches) and corky.

Douglas-fir is not a true fir at all, nor a pine or spruce. It is a distinct species named after its discoverer Archibald Menzies and a botanist, David Douglas. A major characteristic that distinguishes it from true firs is its cone which falls from the tree intact.

Douglas-fir is one of the world’s most important and valuable timber trees. It grows across a larger portion of western North America, from 19 to 55 degrees North in latitude, than any other commercially used conifer.

Douglas-fir records

  • Diameter: > 11 1/2 feet (Coos County, Oregon)
  • Height: 330 feet (Little Rock, Washington)
  • Age: 1400 years (Mount Vernon, Washington)


RANGE: There are two varieties of Douglas-fir, the coast Douglas-fir and the Rocky Mountain Douglas-fir. Coast Douglas-fir grows from west-central British Columbia southward to central California. In California, it is found in the Klamath Mountains and Coast ranges as far south as the Santa Cruz Mountains, and in the Sierra Nevada as far south as Yosemite. The Rocky Mountain variety does not grow in California.

The tree grows under a wide variety of climatic conditions, including the mild maritime climate of the coast and the more severe weather of the Sierra Nevada.

Elevation range of the Douglas-fir in California:



Northern Sierra Nevada

2,000 to 6,000 feet

Southern Sierra Nevada

up to 7,500 feet

River valleys & canyon bottoms

800 to 900 feet

Climate in Douglas-fir’s natural range

Sierra Nevada


Average temp:


72• to 86•
68• to 81•


15• to 28•
28• to 37•

Frost free days


80 to 180
195 to 260



24 to 120
34 to 134



4 to 120
0 to 24 inches

Douglas-fir grows best on well-drained deep soils and will not thrive on poorly drained or compacted soils. Along the coast it is mostly found where marine sandstones and shales have weathered deeply to fine-textured, well drained soils. Douglas-fir is found on a wide variety of soils in the Sierra Nevada.

The principal limiting factors are temperature in the north and moisture in the south. Douglas-fir is found on south facing slopes in the northern part of its range (on warmer sites) and north facing slopes in the southern part (on moister sites).


Douglas-fir reproduces by seeds which form on cones. Trees start to bear seed at about age 20. Cones are fertilized in the spring and ripen in the fall, dropping seeds in fall, winter and spring. Seed crops occur at irregular intervals, with one heavy and one moderate crop every seven years. Even during heavy crop years, only about a quarter of trees produce many cones. Old growth trees produce the majority of cones.

Each cone produces up to 50 seeds. Seeds on California trees are light (23,000 of them in a single pound), and may be blown as far as a mile away, although most fall within 300 feet of the source. Seeds are eaten by the Douglas squirrel, chipmunks, mice, voles, and birds. Seeds germinate in the spring and grow relatively slowly in the first year.

Douglas-fir seedlings grow best on bare mineral soil but can tolerate a thin litter layer. First year seedlings, especially those on dry sites, actually survive and grow best in light shade, although older seedlings require full sun. Lack of summer moisture triggers young seedlings to go dormant until the following spring.

Full shade and moisture competition caused by competing vegetation such as understory hardwoods, woody shrubs, and grasses can kill Douglas-fir seedlings. Many of these plants grow much more quickly on disturbed sites than young Douglas-fir trees. This results in difficulties regenerating the species without weed control. Fire also will favor Douglas-fir by destroying other species that would compete with and outgrow young seedlings.

Seedling growth on productive sites along the coast

1st year

2.5 to 3.5 inches

Age 8 to 10

3 feet per year

Along the coast, height growth starts to accelerate after five years, and reaches its maximum at age 20 to 30, although the species can grow rapidly for up to 200 years.

In loose soils, Douglas-fir roots grow quickly, forming a taproot and reaching almost their entire length in the first ten years. The tree’s rooting habit is not particularly deep. The roots of young coast Douglas-fir tend to shallower than roots of the same aged ponderosa pine, sugar pine, or incense-cedar. Some roots are commonly found in organic soil layers or near the mineral soil surface. The spread of the roots generally conforms to the width of the tree’s crown.


In the Klamath and Coast ranges, Douglas-fir either grows in nearly pure stands, or in the mixed evergreen forest, while in the Sierra Nevada it is a component of the mixed conifer forest. Wherever Douglas-fir grows in mixture with other species, the amount of the species varies greatly and depends on aspect, elevation, soil and fire history of the areas.

Douglas-fir is a component of the redwood forest type, but as sites become drier farther inland, redwood gives way to mixed evergreen forests which are codominated by Douglas-fir, Pacific madrone, and tanoak. Canyon live oak, giant chinkapin, sugar pine, ponderosa pine, and incense-cedar are also found along with these dominant species.

Associates in the mixed-conifer zone include ponderosa pine, Jeffrey pine, sugar pine, incense-cedar, California black oak and white fir. Douglas-fir’s abundance in the mixed-conifer zone tends to decrease and that of ponderosa pine increase from north to south within this zone.

Shrubs associated with Douglas-fir in California

Vine maple

(Acer circinatum)


(Gaultheria shallon)

Pacific rhododendron

(Rhododendron macrophyllum)


(Arctostaphylos spp.)


(Ceanothus spp.)


(Berberis nervosa)


(Rubus spectabilis)

California hazel

(Corylus cornuta)


(Holodiscus discolor)

Red huckleberry

(Vaccinium parvifolium)


(Symphoricarpos mollis)

Poison oak

(Toxicodendron diversilobum)

Douglas-fir is classified as an intermediate shade intolerant after its first few years. It is, however, more tolerant than most associates including ponderosa pine, Jeffrey pine, sugar pine, western white pine, lodgepole pine, incense-cedar, noble fir, and red alder, but less than white fir. On drier sites, Douglas-fir tends to be more shade-tolerant.

Douglas-fir is more fire resistant than many of its associates because of it grows rapidly and is covered with a thick corklike bark along its stem and roots. In addition, the tall trees have their foliage concentrated on the upper bole, which makes it difficult for fire to reach the crown.

Regeneration of Douglas-fir is favored by fire. Since it is shade intolerant, new Douglas-fir trees are not established under current forests without fires to kill more shade tolerant competition. Forest fires therefore allow Douglas-fir to continue to be a dominant presence in the forest.

Douglas-fir is typically regenerated using even-aged management methods. Clear cutting with planting is most common. Shelterwood systems are also used since young seedlings can tolerate partial shade. Because young seedlings which grow from naturally falling seeds are so unevenly spaced, planting of new trees is often required. Young Douglas-fir respond well to release from brush or overstory trees if they have not been too suppressed.

Nitrogen is typically the limiting nutrient in forest soils that restricts growth of Douglas-fir. Application of nitrogen fertilizer has been used in combination with thinning to increase growth.

Productivity of managed stands of coastal Douglas-fir
(cubic feet/acre)

Growth per year
Total growth

Poor sites:


Best sites:


Trees 5 to 6 feet in diameter and 250 feet or more in height are common in old-growth stands. Self-pruning is generally slow and trees retain their lower limbs for a long period.

Douglas-fir is grown as a Christmas tree on harvest rotations ranging from 4 to 7 years. Attempts to grow Douglas-fir as a Christmas tree outside its native range have failed, due to frost and needle cast diseases. Coastal Douglas-fir will not tolerate frost below 14 degrees Fahrenheit for more than a week, even if the ground is well protected against freezing by snow cover.

Damaging Agents

Douglas-fir seedlings in nurseries may be killed by various species of fungi. Young trees in plantations are vulnerable to root rot which weakens them allowing them to blow over. Several heart rot species infect trees at their knots or scars after fire, lightning, or mechanical damage causing decay and reducing commercial value. Mistletoe occurs throughout its rare.

The Douglas-fir beetle is the most damaging insect and often attacks fire-killed or fire-weakened trees. Tussock moths and spruce budworm attack trees of all ages and often cause defoliation. Several species of insects are capable of reducing the seed crop but are not generally a problem for regeneration. Many small mammals depend upon the seeds for food and are capable of destroying virtually all unprotected seed. Browsing by deer, elk, and rodents can be a major problem in plantations.

Animals that Damage Douglas-fir

Deer mice

Eat seed


Eat seed


Eat seed


Browse seedlings and saplings

Brush rabbits

Browse seedlings and saplings

Mountain beaver

Browse seedlings and saplings

Pocket gophers

Girdle seedlings and saplings


Browse seedlings and saplings


Browse seedlings and saplings


Girdle pole timber

Insects That Damage Douglas-Fir

Douglas-fir beetles

(Dendroctonous pseudotsugae)

Kills older trees

Douglas-fir tussock moths

(Orgyia pseudotsugata)


Western spruce budworms

(Choristoneura fumferana)


Douglas-fir seed chalcids

(Megastigmus spermotrophus)

Matures in the seeds

Douglas-fir cone moths

(Barbara colfaxiana)

Retard growth in buds and shoots

Fir cone worms

(Diryctira abietivorella)

Damages cones

Douglas-fir cone gall midge

(Contarinia oregonensis)

Damages cones

Cone scale midge

(Contarinia washingtonensis)

Damages cones

Strawberry root weevils

(Otiorhynchus oratus)

Damages cones

Cranberry girdlers

(Chrysoteuchia topiaria)

Damage seedlings in nurseries

Rain beetles

(Pleocoma spp.)

Damage seedlings in nurseries


(Steremnius carinatus)

Damage seedlings in nurseries

Diseases of Douglas Fir


(Pythium, Rhizoctonia, Phytophthora, Fusarium, and Botrytis)

Kills seedlings in nurseries

Shoestring root rot

(Armillaria mellea)

Causes death in plantations

Laminated root rot

(Phellinus weirri)

Causes death in plantations

Red ring rot

(Phellinus pini)

Loss of sound wood in commercial stands

Heart rot

(Fomitopsis officinalis, F. canjanderi, F. pinicola)

Loss of sound wood in commercial stands

Heart rot

(Phaeolus schweinitzii)

Loss of sound wood in commercial stands

Indian paint fungus

(Echinodontium tinctorium)

Loss of sound wood in commercial stands

Dwarf mistletoe

(Arceuthobium douglasii)

Kills trees, stunts height growth,

Needle cast

(Rhabdocline pseudotsugae)

Damages needles on young trees

Needle cast

(Phaeocryptopus gaeumanni)

(Phaeocryptopus gaeumanni)


Coast Douglas-fir forest is one of the world’s best timber producers and yields more timber than any other forest type in North America. Coast Douglas-fir is used extensively in landscaping and as a Christmas tree.

Douglas-fir is unique among all softwood species in that it is dimensionally stable without being dried, meaning that it does not shrink or twist significantly. Many builders prefer to cut, nail and fasten it in the “green” or unseasoned condition, allowing it to air dry during construction. For millwork, remanufacturing applications or glued products, Douglas-fir is dried in temperature and humidity-controlled kilns or stacked and air dried until its moisture content reaches the desired level for an intended purpose.

Douglas fir’s appearance and stability make it ideal for joinery, doors, millwork, window and door casings, mantels, stairs and baseboards, paneling, and flooring. Treated pilings and decking are used in marine structures. The wood is also made into railroad ties, mine timbers, house logs, posts and poles, flooring, veneer, pulp, and furniture.

This text was largely summarized from an article originally by Richard K. Hermann, Professor of Forest Ecology (retired), Oregon State University Corvallis and Denis P. Lavender Department Head. Faculty of Forestry, University of British Columbia, Vancouver. that appears in Burns, Russell M., and Barbara H. Honkala, tech. coords. 1990. Silvics of North America: 1. Conifers. Agriculture Handbook 654. U.S. Department of Agriculture, Forest Service, Washington, DC. vol. 1, 675 p.

Interested readers are referred to the original article for more detailed and technical information and references. Publication of this series was in part funded by California Department of Forestry and Fire Protection under Contract numbers 8CA96027 and 8CA96028

Tree hazards are more easily prevented than repaired. Your efforts at prevention will be much less expensive and more successful than attempting to cure a damaged tree that is on its way to becoming a hazard.

Choose Which Trees To Protect

For fruitful damage prevention, you need to correctly identify which trees are worth saving. Many well-intentioned protection efforts fail because large old trees nearing the end of their lifespans were protected and younger trees weren’t. Take time to look critically at your trees and decide what you want them to look like in 10-20 years. Some of your trees may be better off being removed; others may potentially become useful wildlife habitats. An ISA Certified Arborist can help you decide.

Trees don’t exist independently of their environment. Trees in a group, known as a stand, grove, or patch, should be evaluated together as well as individually.

Evaluating Forest Remnant Stands

Stands, groves, or patches of native Pacific Northwest trees, such as Oregon white oak, Western red cedar, red alder, bigleaf maple, and Douglas fir, are often found in urban or urbanizing areas. These are remnants of the larger forests that previously covered the area. They may range from less than a quarter acre to several acres in size. Conservation of existing groves of native trees often provides greater economic and environmental benefit than preserving individual trees in the developing landscape. However, you should still evaluate the quality of the forest stand to determine if it is worth preserving.

Excellent Stand Protection Zone

A stand to protect. Reproduced with
permission by the City of Chattanooga.

A high-quality forest remnant has high tree densities and an undisturbed understory. Look for the following characteristics:

  • Trees structurally support one another.
  • Soil remains undisturbed.
  • Wildlife uses are relatively unimpaired.
  • Shady microclimate encourages natural woodland plants.
  • Natural forest succession continues, and forest regeneration is ongoing.
  • The stand is visually attractive.
  • Ecological functions are relatively unimpaired.

Poor Stand Protection Zone

A stand that may not be
worth saving. Reproduced with permission by the City of Chattanooga.

Scattered trees with a highly disturbed or missing understory may not be worth saving. A poor stand protection zone has the following characteristics:

  • Trees blow over easily due to lack of support.
  • Soil dries out and soil erosion occurs due to disturbed soils and lack of understory.
  • Forest microclimate is disturbed.
  • Sunlight and temperature are increased.
  • Weeds and invasive species have taken over.
  • Forest succession is interrupted, and little regeneration occurs.
  • The stand is visually unattractive.
  • Ecological functions are severely interrupted.

Protecting Forest Stands

The best way to preserve a forest stand is to leave it alone. Fence the entire stand, grove, or patch to protect understory vegetation and soil as well as trees. Healthy soils require little if any fertilization, pesticides, or irrigation to support tree health.

When evaluating the members of a stand individually to see if they should be kept, consider whether or not the tree is on the edge of the group. These trees provide support and protection to the interior of the stand. If the tree in question is large and providing wind cover, do not remove it. Avoid removing vigorous, healthy trees and vegetation from the stand, and do not retain isolated single, tall, spindly trees; such trees are more likely to become structurally unstable, bend or blow over in storms, or become diseased and infested with insects.

Protecting Individual Trees

Tree protection involves activities designed to preserve and protect tree health by avoiding damage to a tree’s roots, trunk, or crown. The best way to do this is protect not only the tree itself but also the ground covering its most important roots, known as the critical root zone.

Critical Root Zone Protection

A critical step in retaining healthy trees is the protection of tree roots from disturbance. Each tree has a critical root zone (CRZ) that varies by species and site conditions. The International Society of Arboriculture defines CRZ as an area equal to a 1-foot radius from the base of the tree’s trunk for each 1 inch of the tree’s diameter at 4.5 feet above grade (referred to as diameter at breast height).

Critical root zone radius distances calculated by tree diameter at breast height

Tree diameter Critical root zone radius Total protection zone diameter, including trunk
2 inches 2 feet 4+ feet
6 inches 6 feet 13.5 feet
20 inches 20 feet 42 feet
46 inches 46 feet 96 feet

Using drip line to estimate critical root zone (CRZ). Adapted with permission by the City of Chattanooga.

Another common rule of thumb is to use a tree’s drip line to estimate the CRZ (see figure). Evaluate both of these and choose whichever provides the larger CRZ.

Under certain circumstances, disturbing or cutting roots in a CRZ may be unavoidable. In such cases, the work should be done only under the on-site supervision of an ISA Certified Arborist.

Cutting or disturbing a large percentage of a tree’s roots increases the likelihood of the tree’s failure or death. Never cut tree roots that are more than four inches wide; roots that large are usually structural. Cutting them can destroy the stability of the tree, causing it to fall over!

If you must cut tree roots, do so cleanly with sharp tools. Never tear with a backhoe or other dull instrument. A clean cut encourages good wound closure and confines the spread of decay. If damage is severe, consider removing the tree because its stability may have been compromised.

Activities to Avoid in the Critical Root Zone

The CRZ that should be protected from negative interactions. Avoid the following activities:

  • Stockpiling construction materials or demolition debris
  • Parking vehicles or equipment
  • Piling soil and/or mulch
  • Trenching for utilities installation or repair, or for irrigation system installation
  • Changing soil grade by cutting or filling
  • Damaging roots by grading, tearing, or grubbing
  • Compacting soil with equipment, vehicles, material storage, and/or foot traffic
  • Contaminating soil from washing out equipment (especially concrete) and vehicle maintenance
  • Installing impervious parking lots, driveways, and walkways
  • Attaching anything to trees using nails, screws, or spikes
  • Wounding or breaking tree trunks or branches through contact with vehicles and heavy equipment
  • Wounding trunks with string weed trimmers and lawn mowers
  • Causing injury by fire or excessive heat

Some tree species are more tolerant of damage and disturbance in the CRZ than others. A tree’s tolerance depends not only upon the species but also upon conditions present prior to and at the time of the damage. Tree health, age of the tree, soil aeration and moisture, the time of year the damage occurs, its severity, and the weather conditions prior to, during, and after the damage all contribute to the tree’s response. An ISA Certified Arborist can analyze these variables and make specific recommendations to retain or recover a tree’s health and safety during and after the construction process.

Protecting Trees From Construction

Tree protection during construction may be passive or active. Passive tree protection, most commonly used during the planning or post-development stages, simply means avoiding any disturbance or harmful activity near the tree. Active tree protection, by contrast, involves physical protective barriers and is generally required during any site disturbance that may impact your trees, such as grading, building or surface construction and maintenance, infrastructure and utility installation and maintenance, lawn renovation, and other landscape changes that may affect the structural integrity and stability of your trees.

While these practices are presented here as voluntary guidelines, some local jurisdictions have tree protection regulations that must be followed. Contact your local planning department for specific regulations for your area.

Before Construction

The goal of tree protection is to help trees remain as healthy after you work around them as they were before you began. Plan and budget for tree conservation and protection as part of the development process, before construction begins. Optimally, tree protection should begin at least one growing season prior to the beginning of construction activities.

Start by making an inventory of the trees you will be working around. Include not just your trees but also your neighbor’s trees, if working close to the edge of your property. Evaluate soil health and past site damage; you will need to incorporate that information into tree protection measures. If you are just working around one or two trees, you can do that by making a simple map listing the size, species, and health of each tree. If you have a lot of trees that need to be protected, it may make sense to hire an ISA Certified Arborist to develop the plan for you.

Take your tree information and overlay it with your construction plans to determine how much the planned activity will impact the tree. If the planned construction will have such an impact on the tree that it won’t survive, either make the decision to remove the tree or change the construction project to avoid the tree. Consider the tree’s location, species, quality, health, and benefits such as energy savings by shade or wind protection in order to make your decision. Remove trees that:

  • Are within ten feet of the proposed building or structure
  • Cannot be adequately protected
  • Have less than a quarter of their total height composed of tree crown (tall and spindly)
  • Have trunks that are more than a third wounded

Once you have identified which trees are in the path of your planned construction activities, put that information down on paper and communicate it to anyone you hire to work on the project. Reinforce your tree protection intentions by writing tree damage and noncompliance with tree protection clauses into any service contract. This should provide financial penalties to any contractor who damages your trees. If your property is large, engage maintenance staff in early decision-making and education about care of retained trees.

Fencing for tree protection. Reproduced with permission by the City of Arlington, Virginia.

Install strong fencing around the CRZ and require the fence to remain in place for the life of the development project. This barrier can be a chain link or other type of fencing. Fencing protects both the root system and the trunk from being damaged.

Clearly identify the perimeter of the protection zone with highly visible signs.

Protect high-value trees with stem, branch, and root padding or wraps in addition to CRZ barriers.

To minimize soil compression across the property, establish one access route into the site and one exit route out of the site.

Complete preconstruction tree maintenance, including mulch, fertilization, supplemental irrigation as necessary, and pruning to remove dead, structurally weak, and low-hanging branches.

During Construction

Monitor compliance with tree protection requirements and the impacts of construction activities on tree health regularly during construction. If there are incursions into the root zone, ensure roots have been severed cleanly, enforce penalties, and reestablish the protection zone. Confer with your contractors to make sure that construction offices, vehicular parking, worker break sites, concrete washout areas or other pollutants, and material storage will remain outside of protected areas. Diligence in maintaining barriers and in enforcing your protection plan will pay great dividends at the end of the project when the tree is still healthy.

Following the guidelines laid out above will serve in most situations, but occasionally construction plans will require impingement on the CRZ.


Proposed trench through a critical root zone. Adapted with permission by the City of Chattanooga.

Trenching is a standard way to install utilities. It is best to entirely avoid trenching through the CRZ (see figure); such practice could severely destabilize a tree, as well as adversely affect its health through loss of roots. Workers performing such operations should understand that 85% of the mass of a tree’s root system is located within the CRZ and that most of a tree’s roots are within the top 18 inches of soil. Alter routes of underground infrastructure or use alternate methods such as pipe boring. Tunneling at least 18 inches beneath the root zone will prevent loss of critical root mass if underground utilities must unavoidably be placed within the CRZ.

A decision must be made as to where best to locate utility trenches. Planners and designers must be made aware that trenches may not cross a CRZ and design alternate alignments accordingly; such realignments are not the responsibility of the construction crew.

Best practices for trenching include the following:

  • Protect the trunks of high-value trees from scraping and gouging to a height of at least eight feet.
  • Keep equipment and excavated backfill on the side furthest from the tree, not against the trunk.
  • Place excavated backfill on a plastic or canvas tarp outside the CRZ.
  • Prune away jagged roots back to the trench wall closest to the tree. Use a handheld pruner or pruning saw to make sharp, clean cuts.
  • Replace the backfill on the same day if at all possible. Cover exposed roots with wet burlap to prevent them from drying out; in hot dry conditions, small roots may be injured in as little as 30 minutes.
  • Do not allow chemicals, trash, or other foreign debris to become mixed with the backfill.
  • If earthwork specifications allow it, firm the backfill to the same compaction as the surrounding soil and no more.
  • Water the backfill to prevent excessive root drying.

Grade or Ground Level Changes

Grade changes should be avoided in order to prevent serious damage or death to a tree. Fill that is added over existing soils can smother and kill roots, or invite disease if piled around the trunk. Even temporary fills such as stockpiling mulch or soil in the CRZ of a tree for as little as several days during the construction process can have severe, long-term negative effects, though symptoms may not appear for several years.

The extent of injury from adding soil around a tree varies with the kind, age, and condition of the tree; the depth and type of fill; drainage; and several other factors. Maple, oak and evergreens are most susceptible, while elm, ash, willow, sycamore, and locust are least affected.

Little can be done to save trees that have been suffering from soil added over an extended period of time. It is prudent to consider possible damage that may occur to a tree and take alternative action before the fill is made; prevention is less expensive and more effective than attempting to correct the situation after damage has been done.

Best practices for fill operations include the following:

  • Never place any fill or organic materials directly against the tree.
  • Never compact the soil within the CRZ.
  • If using no more than two to four inches of fill around existing trees, significant damage may be avoided if the fill has a coarser texture than the existing soil.

Less damage to a tree’s roots is likely with a lowered grade than when it is raised, unless exposing or removing a great deal of the root mass. A general rule-of-thumb used by landscape architects is to remove no more than six inches of soil from the existing grade in the CRZ; however, this is dependent on the soils in which the tree is growing. A tree’s roots may all exist in the top foot of a shallow soil; removing the top six inches would have tremendous negative impact in that case.

Best practices for removing soil include the following:

  • Consider removal and replacement if the tree is young, in poor condition, an undesirable species, or very susceptible to insects and disease.
  • Plan grade changes well in advance of construction using the appropriate method to prevent injury to desirable trees.
  • Use retaining walls or terraces to avoid excessive soil loss in the area of greatest root growth.
  • Spread mulch over the exposed root area when possible to help prevent soil erosion, reduce moisture loss, and keep soil temperatures lower.
  • Provide supplementary water when rainfall is less than one inch per week.
  • Prune roots to prepare the tree for root loss due to grade lowering. Root pruning is best left to an ISA Certified Arborist, who can take into account the variables necessary to reduce the stress of the pruning to the tree.

Two decades ago, while researching her doctoral thesis, ecologist Suzanne Simard discovered that trees communicate their needs and send each other nutrients via a network of latticed fungi buried in the soil — in other words, she found, they “talk” to each other. Since then, Simard, now at the University of British Columbia, has pioneered further research into how trees converse, including how these fungal filigrees help trees send warning signals about environmental change, search for kin, and transfer their nutrients to neighboring plants before they die.

Suzanne Simard

By using phrases like “forest wisdom” and “mother trees” when she speaks about this elaborate system, which she compares to neural networks in human brains, Simard’s work has helped change how scientists define interactions between plants. “A forest is a cooperative system,” she said in an interview with Yale Environment 360. “To me, using the language of ‘communication’ made more sense because we were looking at not just resource transfers, but things like defense signaling and kin recognition signaling. We as human beings can relate to this better. If we can relate to it, then we’re going to care about it more. If we care about it more, then we’re going to do a better job of stewarding our landscapes.”

Simard is now focused on understanding how these vital communication networks could be disrupted by environmental threats, such as climate change, pine beetle infestations, and logging. “These networks will go on,” she said. “Whether they’re beneficial to native plant species, or exotics, or invader weeds and so on, that remains to be seen.”

Yale Environment 360: Not all PhD theses are published in the journal Nature. But back in 1997, part of yours was. You used radioactive isotopes of carbon to determine that paper birch and Douglas fir trees were using an underground network to interact with each other. Tell me about these interactions.

Suzanne Simard: All trees all over the world, including paper birch and Douglas fir, form a symbiotic association with below-ground fungi. These are fungi that are beneficial to the plants and through this association, the fungus, which can’t photosynthesize of course, explores the soil. Basically, it sends mycelium, or threads, all through the soil, picks up nutrients and water, especially phosphorous and nitrogen, brings it back to the plant, and exchanges those nutrients and water for photosynthate from the plant. The plant is fixing carbon and then trading it for the nutrients that it needs for its metabolism. It works out for both of them.

It’s this network, sort of like a below-ground pipeline, that connects one tree root system to another tree root system, so that nutrients and carbon and water can exchange between the trees. In a natural forest of British Columbia, paper birch and Douglas fir grow together in early successional forest communities. They compete with each other, but our work shows that they also cooperate with each other by sending nutrients and carbon back and forth through their mycorrhizal networks.

e360: And they can tell when one needs some extra help versus the other, is that correct?

Simard: That’s right. We’ve done a bunch of experiments trying to figure out what drives the exchange. Keep in mind that it’s a back and forth exchange, so sometimes the birch will get more and sometimes the fir will get more. It depends on the ecological factors that are going on at the time.

One of the important things that we tested in that particular experiment was shading. The more Douglas fir became shaded in the summertime, the more excess carbon the birch had went to the fir. Then later in the fall, when the birch was losing its leaves and the fir had excess carbon because it was still photosynthesizing, the net transfer of this exchange went back to the birch.

There are also probably fungal factors involved. For example, fungus that is linking the network is going to be looking to secure its carbon sources. Even though we don’t understand a whole lot about that, it makes sense from an evolutionary point of view. The fungus is in it for its own livelihood, to make sure that it’s got a secure food base in the future, so it will help direct that carbon transfer to the different plants.

I don’t think there’s ever going to be a shortage of an ability to form a network, but the network might be different.

e360: Do you think this exchange system holds true in other ecosystems as well, like grasslands, for instance? Has there been any work done on that?

Simard: Yes, not just in my lab, but also in other labs well before me”¦ Grasslands, and even some of the tree species we’re familiar with like maple and cedar, form a different type of mycorrhiza. In British Columbia, we have big grasslands that come up through the interior of the province and interface with the forest. We’re looking at how those grasslands, which are primarily arbuscular mycorrhizal, interact with our ectomycorrhizal forest, because as climate changes, the grasslands are predicted to move up into the forests.

e360: Will these exchanges continue under climate change, or will communication be blocked?

Simard: I don’t think it will be blocked. I don’t think there’s ever going to be a shortage of an ability to form a network, but the network might be different. For example, there will probably be different fungi involved in it, but I think these networks will go on. Whether they’re beneficial to native plant species, or exotics, or invader weeds and so on, that remains to be seen.

e360: Through molecular tools, you and one of your graduate students discovered what you call hub, or mother, trees. What are they, and what’s their role in the forest?

Simard: Kevin Beiler, who was a PhD student, did really elegant work where he used DNA analysis to look at the short sequences of DNA in trees and fungal individuals in patches of Douglas fir forest. He was able to map the network of two related sister specials of mycorrhizal fungi and how they link Douglas fir trees in that forest.

Just by creating that map, he was able to show that all of the trees essentially, with a few isolated , were linked together. He found that the biggest, oldest trees in the network were the most highly linked, whereas smaller trees were not linked to as many other trees. Big old trees have got bigger root systems and associate with bigger mycorrhizal networks. They’ve got more carbon that’s flowing into the network, they’ve got more root tips. So it makes sense that they would have more connections to other trees all around them.

In later experiments, we’ve been pursuing whether these older trees can recognize kin, whether the seedling that are regenerating around them are of the same kin, whether they’re offspring or not, and whether they can favor those seedlings — and we found that they can. That’s how we came up with the term “mother tree,” because they’re the biggest, oldest trees, and we know that they can nurture their own kin.

A diagram of a fungal network that links a group of trees, showing the presence of highly connected “mother trees.” BEILER ET AL 2010

e360: You also discovered that when these trees are dying there’s a surprising ecological value to them that isn’t realized if they’re harvested too soon.

Simard: We did this experiment actually in the greenhouse. We grew seedlings of with neighbors , and we injured the one that would have been acting as the mother tree, the older fir seedling. We used ponderosa pine because it’s a lower elevation species that’s expected to start replacing Douglas fir as climate changes. I wanted to know whether or not there was any kind of transfer of the legacy of the old forest to the new forest that is going to be migrating upward and northward as climate changes.

When we injured these Douglas fir trees, we found that a couple things happened. One is that the Douglas fir dumped its carbon into the network and it was taken up by the ponderosa pine. Secondly, the defense enzymes of the Douglas fir and the ponderosa pine were “up-regulated” in response to this injury. We interpreted that to be defense signaling going on through the networks of trees. Those two responses — the carbon transfer and the defense signal — only happened where there was a mycorrhizal network intact. Where we severed the network, it didn’t happen.

The interpretation was that the native species being replaced by a new species as climate changes is sending carbon and warning signals to the neighboring seedlings to give them a head start as they assume the more dominant role in the ecosystem.

e360: You’ve talked about the fact that when you first published your work on tree interaction back in 1997 you weren’t supposed to use the word “communication” when it came to plants. Now you unabashedly use phrases like forest wisdom and mother trees. Have you gotten flack for that?

Simard: There’s probably a lot more flack out there than I even hear about. I first started doing forest research in my early 20s and now I’m in my mid-50s, so it has been 35 years. I have always been very aware of following the scientific method and of being very careful not to go beyond what the data says. But there comes a point when you realize that that sort of traditional scientific method only goes so far and there’s so much more going on in forests than we’re able to actually understand using the traditional scientific techniques.

So I opened my mind up and said we need to bring in human aspects to this so that we understand deeper, more viscerally, what’s going on in these living creatures, species that are not just these inanimate objects. We also started to understand that it’s not just resources moving between plants. It’s way more than that. A forest is a cooperative system, and if it were all about competition, then it would be a much simpler place. Why would a forest be so diverse? Why would it be so dynamic?

To me, using the language of communication made more sense because we were looking at not just resource transfers, but things like defense signaling and kin recognition signaling. The behavior of plants, the senders and the receivers, those behaviors are modified according to this communication or this movement of stuff between them.

Also, we as human beings can relate to this better. If we can relate to it, then we’re going to care about it more. If we care about it more, then we’re going to do a better job of stewarding our landscapes.

If we leave trees that support not just mycorrhizal networks, but other networks of creatures, then the forest will regenerate.

e360: The mountain pine beetle is devastating western landscapes, killing pine and spruce trees. You coauthored research on what pine beetle attacks do to mycorrhizal networks. What did you find, and what are the implications for regeneration of those forests?

Simard: That work was led by Greg Pec, a graduate student at the University of Alberta. The first stage (of the attack) is called green attack. They go from green attack to red attack to gray attack. So basically, by the third or fourth year, the stands are dead.

We took soil from those different stands and grew log pole pine seedlings in them. We found that as time went on with mortality, that mycorrhizal network became less diverse and it also changed the defense enzyme in the seedlings that were grown in those soils. The diversity of those molecules declined. The longer the trees had been dead, the lower the mycorrhizal diversity and the lower the defense molecule diversity was in those seedlings.

Greg, in looking at the fungal diversity in those stands, found that even though the fungal diversity changed, the mycorrhizal network was still important in helping regenerate the new seedlings that were coming up in the understory.

Even though the composition of that mycorrhizal network is shifting, it’s still a functional network that is able to facilitate regeneration of the new stand.

e360: What does your work tell you about how to maintain resilience in the forest when it comes to logging and climate change?

Simard: Resilience is really about the ability of ecosystems to recover their structures and functions within a range of possibilities. For forests in particular, trees are the foundation. They provide habitat for the other creatures, but also make the forest work. Resilience in a forest means the ability to regenerate trees. There’s a lot that can be done to facilitate that because of these mycorrhizal networks, which we know are important in allowing trees to regenerate. It’s what we leave behind that’s so important. If we leave trees that support not just mycorrhizal networks, but other networks of creatures, then the forest will regenerate. I think that’s the crucial step is maintaining that ability to regenerate trees.

e360: You’ve spoken about your hope that your findings would influence logging practices in British Columbia and beyond. Has that happened?

Simard: Not my work specifically. Beginning in the 1980s and 90s, that idea of retaining older trees and legacies in forests retook hold. Through the 1990s in Western Canada, we adopted a lot of those methodologies, not based on mycorrhizal networks. It was more for wildlife and retaining down wood for habitat for other creatures.

But for the most part, especially in the last decade and a half, a lot of defaults to clear-cutting with not that much retention. Part of that was driven by the mountain pine beetle outbreak that is still going on. The good forestry practices that were developing got swept away in the salvage logging of those dying trees.

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Today, people are still trying retention forestry, but it’s just not enough. Too often it’s just the token trees that are left behind. We’re starting on a new research project to test different kinds of retention that protect mother trees and networks.

e360: That’s the grant that you just received from the Canadian government to reassess current forest renewal practices?

Simard: Yes, we’re really excited about this. We’re testing the idea of retaining mother trees in different configurations — so leaving them as singles, as groups, as shelter woods, and then regenerating the forest using a mix of natural regeneration and traditional regeneration practices. We’re testing these across a range of climates in Douglas fir forest, from very dry and hot all the way up to cool and wet. There’s going to be about 75 sites in total that cross this climate gradient. We’re going to be measuring things like carbon cycling and productivity and bird and insect diversity. And we’ve got a lot of interest from First Nations groups in British Columbia because this idea of mother trees and the nurturing of new generations very much fits with First Nations’ world view.

Douglas Fir Tree

For a robust accent in your landscape, try the excellent evergreen tree Douglas Fir (Pseudotsuga menziesii). It features a very symmetrical, upright pyramidal shape and looks great in every season. It even smells wonderful!

You might see the name sometimes written as Douglas-Fir or Douglasfir, because it’s actually not a Fir. This beautiful tree is actually a member of the genus Pseudotsuga, which means “False Hemlock”.

Any way you want to call it, we bet you’ll love running your hand over the soft, blue-green needles. They aren’t stiff and pokey like other evergreens. Kids like to pet them, too.

This is also one of the fastest growing evergreen trees available. It will grow about 3 feet a year to quickly provide a wonderful focal point or privacy screen for you and your family.

It’s lovely in its natural form, so no need to prune. Older trees can develop those romantic, pendulous lower branches that sway in the slightest breeze.

Create fun memories by decorating it for Christmas every year! Cute pine cones grow 3 – 4 inches long and can be used for fall and winter decorations, too.

Local birds love to nest in the shelter of a Douglas Fir. But deer seem to leave this tree alone.

Native Douglas Fir trees are found in the wild; from the slopes of the Rocky Mountains to the Pacific Northwest. The oldest specimen is nearly 1500 years old. As it ages, the fissured, reddish-brown bark brings a tremendous amount of visual interest.

It’s a particularly hardy tree and grows in a variety of soils. For a fast-growing, hardy evergreen tree that is versatile and care free, you can’t go wrong with a Douglas Fir. Order yours today!

How to Use Douglas Fir in the Landscape

This is a terrific specimen plant or focal point for larger landscapes. If you have the space, try an informal group of 3, 5 or 7 in an oversized lawn planting.

Imagine you are recreating the look of the Mountain West, and let your creativity run wild.

For Douglas Firs to touch and make a solid screen, plant them 12 to 15 feet apart. For the trees to stand alone as individual trees, give them at least 18 feet apart.

For the most natural look, try to vary the distances between them, and don’t plant them in a straight line. Rather, stagger the trees off-center, keeping the design loose.

Keep your new trees in their nursery containers and play around with the spacing. Far easier to move potted plants around to make sure you love the design, before you plant your trees in your soil. It’s a good idea to check from various vantage points.

Site this planting where you’ll enjoy it from your deck. You want to be able to see it from inside your home. Leave room for a rustic fire pit, hammock or picnic table in the shade of your trees.

Douglas Fir has a big personality and can carry a “lot of look.” Try mixing it with other evergreens, including smaller upright Junipers and Pine trees. Don’t forget about the rounded evergreen shrubs, like Mugo Pine to soften the foreground.

They make a magnificent backdrop for smaller accent trees, like Eastern Redbud, Pink Flowering Dogwood or Japanese Maple. They stand up to exterior sculpture without stealing the show.

Partner with rugged Ornamental Grasses and the bright stems of Red Twigged Dogwood. Or, use a complementary color – like the chartreuse green of First Editions® Tiger Eyes® Sumac.

Another classic use for these trees is as windbreaks and in shelterbelts. Plant them in staggered, zig-zagging rows to create an interesting living fence to cut down on wind and blowing snow in big, open areas. Keep them tightly planted about 12 feet apart for the fastest screen.

It’s best practice to mix other plants in these windbreaks, and we’ve got a huge variety of trees and large shrubs that will work together beautifully. Be sure to add Lilacs for fragrance and flowers.

Many like to use soft and natural looking Douglas Fir to screen out ugly views and buildings along an existing fence. No matter how you install your planting design, you’ll easily create a beautiful backdrop for your property.

#ProPlantTips for Care

Plant Douglas Fir where it will receive at least 4 hours of sunlight a day. They love cooler climates.

They do demand a very well-drained soil, or they will not perform well for you. Moist, well-drained soils are best.

They won’t tolerate standing water. If you see puddles that remain on your planting site, you’ll need to improve the drainage. Bring in additional soil and mound it up 24 inches above the soil line. Plant directly in that mound.

Careful, regular watering is needed for the entire first season to keep your plants stress free. Once established, they can be very drought tolerant. After all, you will see them growing right out of the rocks in the Rocky Mountains.

It’s usually best to allow the plants to grow naturally, but you can shorten up the new growth by simply breaking or snipping part of that new expanding growth, if needed. You could also prune back excessive long growth from the previous season in early spring, if necessary.

You’ll love having your own living Christmas Tree in your landscape. Enjoy this magnificent native evergreen. Order today!

Douglas Fir Tree

Popular Fir to Enjoy for a Lifetime

Why Douglas Fir Trees?

Grow the most popular fir variety in your own yard. The Douglas Fir Tree is one of America’s top sources of lumber and stands the test of time – it’s hardy, sturdy and it’s easy to grow.

Get ready for a tree that lives for centuries to come. Planting a Douglas Fir means you’re contributing to an important part of the ecosystem that will live for centuries. And the Fir is cold hardy, all the way down to -20 degrees, with soft, flexible foliage that adapts to a variety of climates.

Why is Better

For starters, there’s nothing to taking care of our Douglas Fir. They’re drought tolerant, and there’s no pruning, fertilizing or disease maintenance to be done. Just sit back and watch this gorgeous evergreen grow.

But best of all, because we’ve planted and grown your Douglas Fir with care, long before it arrives to your door, you get tried-and-true performance. And you’ll get a tree that’s strong and sturdy to acclimate well to your landscape.

It’s hard to resist the charm, sturdiness and easygoing nature of the Douglas Fir. It’s one of the most popular trees for a reason; so, don’t let your chance to grow your own slip by. Order your Douglas Fir Tree today!

Planting & Care

1. Planting: Plant your Douglas Fir in a spot in your yard that gets at least 6 hours of sun each day. Well-drained soil is also ideal. To plant, dig a hole in the ground that is two times as large as the root ball. Place the tree in the loose soil and press the soil down until the tree’s roots are completely covered.

2. Watering: Water the ground immediately after you plant your tree, but don’t oversoak. To establish your young tree, you may need water 1 to 4 times each month during the summer. Your tree will need around 20 inches of water each year, so rainfall should work well unless there is a period of extreme drought.

3. Pruning: If you do see infested or diseased branches, you can prune them down to the trunk in the fall.

Fast Growing Trees evergreen trees evergreens for cold climates Planting Kit privacy trees Tree Spikes // // // 13940924448820 1-2 ft. 34.95 34.95 // InStock 1-2 ft. 13940924481588 1 Gallon 24.95 24.95 // InStock 1 Gallon

Douglas Fir (Pseudotsuga menziesii)


Sorry, we can not ship to Canada.

Latin: Pseudotsuga menziesii

Zones: 4-6

Other Common Names: Douglas Fir, Douglas Tree, Oregon Pine, Douglas Pine

Mature Height/spread: Douglas fir commonly grow 100-250 ft high and have a 12-20 ft. spread in ideal conditions

Soil / Climate: Douglas Fir do well in a variety of soils and climates. Is native to western North America both in Rocky Mountains and coastal regions. Full sun is best.

Notes: Not a true fir. Very popular Christmas tree variety. Soft needles 1-2” long. Medium growth rate. Good as a large shade or lawn tree, a Christmas tree. Used as a accent or specimen in groups or clustered decoration. Douglas firs were used by American Indians for medicinal purposes: stomach aches, headaches, and the common cold. Very valuable as a timber resource. The Douglas Fir’s thick bark protects it from forest fires. Even though the bark may be black, the tree can still survive.
Wildlife: Birds such as Siskins and Crossbills will eat the seeds. Deer, porcupine and beavers will also eat the needles.

Cold Stream Farm supplies Douglas Fir trees which are grown as bare root seedlings and transplants and sold both wholesale and retail with no minimum order.

Additional information on Pseudotsuga menziesii can be found on the link: USDA / NRCS plants database.

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