white pine

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White pine page 1

WHITE PINEBy Bill Pollock, Forest Engineer

Pinus strobus, commonly known as the eastern white pine, is the largest conifer of Eastern Canadian forests reaching50 meters in height and up to 100 cm in diameter. It occurs from Newfoundland west through the Great Lakes region toSoutheastern Manitoba. It is known to the Native American Haudenosaunee (Iroquois nation) as the Tree of Peace. It is also

revered by many people as being one of Eastern North Americas mostbeautiful trees.

In dense stands, trees produce tall, cylindrical stems with pyramidalshaped crowns, characterized by distinctive, plate like branching, espe-cially noticeable as the trees become older. The bark on young treesremains rather thin, smooth, and greenish-brown in color. On older treesthe bark becomes deeply ssured and dark grayish-brown in color. Itsevergreen needles are in clusters of 5, soft, exible, 6 to 12 cm long, andbluish-green in appearance. Its cones are about 10 to 20 cm long andabout 2 to 3 cm thick. These remain attached to the tree for 1 to severalmonths after ripening in the autumn of the second season.

It is believed by some that white pine cannot succeed itself. This ispartially true, for white pine usually does not replace white pine withoutthe application of management practices or re. White pine seedlingsgrow very slowly; few exceed a height of 25 cm in 5 years. By contrast,hardwood seedlings grow rapidly; this gives the broadleaf species animmediate advantage that results in complete dominance on most sites -

especially on the better ones - after a harvest. Balsam r is also found replacing white pine because of its tolerance to shadeand its prolic seed production.

It is well known that after the initial period of slow growth, white pine grows faster, sustains rapid growth over a longerperiod, and yields more volume per acre than stands of other species. But we are not capitalizing on this potential. Too manyof our pine stands are harvested with little regard for the particular needs of white pine reproduction. As a result, the veryexistence of white pine as an important component of our forests is threatened.

Growth and Development of White Pine

Seed production

The pollen-bearing owers are clustered in small cones at the base of the new growth. The bright red seed-producing owersoccur on other twigs. White pine begins to bear cones before it is 20 yearsold. Its optimum seed-bearing age is between 50 and 150 years. Abundantcone crops may occur only once every 3 to 5 years; The cones take twoyears to mature. Male strobili open and shed pollen in April through June,depending on latitude. Fertilization occurs 13 months after pollination. Bythe fall of the rst year, the cones are 2 to 5 cm long. The cones reach theirfull length - 12 to 28 cm early in the summer of the second year, if there is noinfestation by the white pine cone beetle, which can cause extensive damageto the second-year cone crop. Cones ripen and seeds are dispersed August

through September. Seeds germinate in the spring. Terminal shoot growthis usually completed by the end of June. By knowing a year in advancethat there will be a seed crop, the land manager gains valuable lead time inscheduling harvest cuts.

Seed dispersal is primarily by wind. Seeds travel 60 meters within a standand more than 200 meters in the open. Animals also disperse seeds. Miceand voles bury caches containing seed beneath the litter but on top of themineral soil. Caches that escape revisitation and decimation produce seed-lings. Seeds require cold stratication to break dormancy.

Favorable seedbeds include moist mineral soil, mosses such as (Polytrichum

Eastern range of white pine


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White pine page 2

spp.) and short grass cover of light to medium density. Dry mineral soil, pine litter, lichen, and very thin or very thick grasscovers are poor seedbeds in full light but adequate in some shade. There is very limited seed germination the second yearafter seed fall, and none after 3 years.

White pine regeneration colonizes disturbed sites, but a light nurse crop of aspen, birch, or other pioneer species promotesregeneration.

Seedlings require at least 20% full light for survival. Theyachieve maximum height growth in 45% of full light. Early

growth is slow, but between 10 and 20 years of age, theaverage annual height growth is about 40 cm per year undergood conditions.

Seedling development

Good seed germination and seedling growth do not requirefull sunlight. Although seedlings grow rapidly under fulllight, many may die because of high surface-soil tempera-tures. Seedlings under a full canopy of pine, the shade ofhardwood seedlings, or tall vegetation such as goldenrodor re weed, also have a high mortality rate because ofinsufcient light and an inability to compete for available

moisture.

A light intensity greater than 20 percent of full light - butless than full sunlight - will prevent seedling losses due to high surface-soil temperatures, yet support vigorous seedlinggrowth. A seed bed of exposed mineral soil is the best medium for the germination, growth, and survival of seedlingsbecause of the capacity of mineral soil for holding moisture. Seedlings that develop in a seed bed of mineral soil that isprotected from full sunlight rarely die because of high temperatures or insufcient moisture.

Height growth

An inherent weakness that places white pine at a disadvantage in competing with other species - particularly hardwoods - isthe slow height growth of seedlings during the rst 5 years. The average height of white pine seedlings for the rst 10 yearsis: 1 year: 2.5 cm; 2 years: 3.75 cm; 3 years; 8.75 cm; 4 years: 17.5 cm; 5 years: 27.5 cm; 6 years: 42.5 cm; 7 years: 60 cm;

8 years: 80 cm; 9 years: 112,5 cm; 10 years: 152.5 cm..

After the initial 5-year period of slow growth, white pine that is free to grow begins to grow rapidly, but it is still at a disad-vantage compared to hardwood species. On medium and better sites, and for an initial period of 10 to 25 years, the heightgrowth of hardwoods far exceeds that of pines; so hardwoods can easily dominate these sites during this period.

Management Implications

Regenerating white pine

We know that to regenerate white pine naturally there needs to be a mature white pine in the vicinity to provide the seed Itis essential that pine seedlings become established before or almost immediately afterany thinning or harvesting. This means that any thinning or harvesting should be doneduring, or immediately after, a seed year. To provide ideal conditions for seed beds(and seedling development), it is necessary to break up the accumulation of litter on theforest oor, loosen the top soil and expose the underlying mineral soil. These condi -tions usually are created by scarication that results from logging during the snowlessmonths.

To ensure that seedlings do not receive too much light and to protect them againstdrying winds during the rst critical years after a harvesting or partial cutting opera -tion, the tops of harvested trees should be lopped so that branches lie close to theground.

Advance vegetative growth of broadleaf species, and a rank growth of grass and weeds,Seed bearing white pine cone


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will seriously interfere with the development of white pine seedlings and, in most cases, guarantee failure in the naturalregeneration of white pine.

Nature, other than providing abundant seed, usually cannot be depended upon to meet all of the requirements of youngpine seedlings. Re-establishing white pine is possible, but it requires the application of forest management practices atcrucial times during the development of the stand.

Rogeneration cuttings

Clear cutting, strip cutting, seed-tree cutting (where the best white pine trees are left unharvested as a source of seedfor regeneration of the harvested area), and shelterwood (where the stand is harvested in two or more cuts at intervalsof about ve to ten years) are the best methods available for regenerating white pine. Although each method has advan-tages and disadvantages, experience has taught us that a two or three-cut shelterwood system is the most successful.Selection cutting is not recommended because there is too much shade from the unharvested trees to promote white pineregeneration.

In the shelterwood method the rst cut is made during or immediately after an abundant seed year (a cardinal rule), andconsists of removing 40 to 60 percent of the over-story. It is essential that the rst cut results in the disturbance of accu-mulated litter and the exposure of mineral soil (scarication) so that white pine seed can germinate and grow.

The second cut, to remove the shelter trees, can take place after the seedlings have entered the period of rapid growth,usually after the rst 5 to 10 years.

If the choice is to perpetuate pine, the following corrective measures must accompany the harvest to ensure the successof the shelterwood system and the ultimate dominance of pine.

1. Before the rst cut, remove advance regeneration of hardwoods and balsam r from the areas near the white pineseed producing tree.

2. Before the second cut, examine the area to determine whether white pine has become adequately established. Ifbroadleaf species have become established to the extent that they would interfere with the rapid growth of, or threaten thesurvival of pine, they should be removed before or immediately after the second cut. If sufcient numbers of seedlingshave not become established, delay the overwood removal. In some instances, another preparatory cut or site-preparationmeasure (scarication) might be necessary to improve conditions for seed beds (expose mineral soil).

In the past, these measures were applied in-advertently by light to moderate grazing by live-stock; this resulted in theremoval of grasses, weeds, and hardwoods, which would have hindered the development of white pine. In fact, animalgrazing accounts for many of the pure stands of pine we have today.

Soil considerations

White pine can be grown on nearly every soil within its range; but heavy clayey soils are exceptions. Because competi-tion from hardwoods and balsam r is an important factor in establishing pine, the choice to manage for pine must bemade with this consideration in mind. Hardwoods offer the least competition on excessively drained and well-drainedsandy soils, and on droughty, loamy sands. On stony loams, silty loams, and glacial tills with good or impeded drainage,

balsam r and some hardwoods may be more aggressive and usually will predominate unless special measures are taken.

Site considerations

There are no hard and fast rules for selecting a forested site for hardwood or white pine. Over a rotation, white pine willoutgrow the hardwoods on the poor and the good sites. But, because of the difculties of trying to grow pine on goodhardwood sites, the wisest decision might be to grow or manage for pine on the poorer or lighter soils (sands, gravelsand sandy loams) and for hardwoods on the heavier soils (loams and clays). This practice not only will provide goodrepresentation of hardwood and white pine, but also will ease the task of developing a greater proportion of white pine.

Stocking

The term stocking refers to the relative density of a stand, or the degree of crowding or competition among the trees thatcomprise a stand. Control of stocking is the most common and feasible way of controlling the development of a stand.

The number of trees in various size or height classes may be too high or too low as compared to the ideal for best results.A forester can analyze a stand and provide information on stocking and stand density of seedlings, saplings (regeneration)



and trees larger than 10 cm. in diameter at breastheight necessary for the management of the stand.

Plantation Culture

Open elds should not be planted with white pinedue to the fact that the white pine weevil (See page9) prefers open grown trees such as those plantedwith no overhead cover.

Under planting of white pine in natural stands ofmixed species which have been thinned or partiallyharvested is highly recommended as the white pineweevil is less likely to attack white pine undercover. However, the cover should provide no morethan 50% shading otherwise the seedlings willgrow more slowly or die for lack of sunlight. Thespacing of the planted trees should not be less than3 meters and sporadic planting at greater spacing isquite acceptable. Trees attacked by the weevil can

be pruned to remove the damaged leaders, (tops)but severely affected trees from weevil or blisterrust should be removed and burned. Thus growing

white pine in mixed uneven aged stands is a good idea to avoid this pest as well as white pine blister rust described below.

The management of an under planted stand involves the gradual removal of overstory trees to maintain the 50% shadinguntil the trees are at least 10 meters tall which is when the weevil becomes less interested in attacking the white pine.

Pollen bearing fowers

Stand of white pine


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Rodents, particularly porcupines, frequently feed on rust-infected bark because of its high sugarcontent. Bark injured by rodents yields copious amounts of resin, which may ow down the tree,often obscuring the typical symptoms of rust infection.

On Ribes, the symptoms develop throughout the growing season and are comparatively lessobvious. The lower leaf surface, when infected,

becomes pale. This is followed within afew days by the development of tiny orange

pimple-like fruiting bodies (uredinia) in which

yellow-orange rust spores are produced. Thesespores cause repeated new infections on Ribesleaves from May through late summer, when

another spore-bearing structure of the rustfungus appears. This structure, called a telium,

is a short, yellow-brown, hair-like lament (See photo on right). Largenumbers of these laments give the lower leaf surface a fuzzy brownappearance.

Environment

The disease is often most severe in areas, and following years, with

extended, cool, moist conditions during late summer and early fall.Such conditions facilitate basidiospore production, dispersal and infec-tion in pine needles. Hazard rating systems may be based in part on suchweather patterns. High hazard areas tend to be low-lying areas wherecool air settles found in frost pockets, small canopy gaps, north aspects,west aspects and slope bases. In contrast, the tops of hills, slope shoul-ders, south and east aspects, and under an existing canopy are low hazard sites where many young pine are likely to escapeinfection. Because of the delicacy of the spores (basidiospores) and their need for good conditions, successful dispersaldistances are generally about 300 meters and at most 3-4 kilometers. Infections of pine are not consistent from year toyear, but occur in wave years, when weather is ideal. In some areas, the moisture that facilitates basidiospore produc-

tion, survival and infection is often fromdew.

Disease Cycle

During moist weather in August and earlySeptember, after seasonally cool weatherhas prevailed for about 2 weeks, telia onleaves of Ribes plants produce basidio-spores that travel by wind to cause newinfections on pine needles. The rust fungusgrows slowly within the pine needle andtwig and ruptures the bark in April-May ofthe second or third growing season after the

pine needle becomes infected. The spores

from these blisters (aeciospores) travel backto theRibescausing new infections (uredi-

biaspores) on the leaves of Ribes plantsbut are not capable of causing infectionson pine. This alternation of host plants isessential for the perpetuation of the fungus;it cannot complete its life cycle on the pineorRibesalone. See diagram at left.

The urediniospores cause new infections onRibesleaves throughout the growing season.These spores, however, are not capable ofcausing infections on pines. The telia thatdevelop on infected Ribes leaves from the

Cronartium ribicola on underside of Ribesleaf. Note the fuzzyness

Damage caused byrodent feeding



urediniaspores in late summer produce basidiospores that do cause infections on pines. The infected pines provide a placewhere the rust fungus safely overwinters; it cannot survive in the Ribesleaves or outside a living host plant. Nothingoverwinters onRibes. The rust is perennial on pine only but there can be no pine-to-pine spread.

Control

Blister rust control in eastern white pine largely depends on escape owing to regional climate or landscape site factorsthat determine the development and dispersal of blister rust at various life-cycle stages. Temperature, moisture and airow are critical environmental conditions that affect pathogen growth, spore dispersal, germination and infection. The

stages most inuenced by the environment are the telial stage onRibeswhich is favoured by cool summers and the basid-ial stage which requires a long, cool, wet period (48 h,



Pine can only be infected by basidiosporesproduced on Ribes plants. These spores aresomewhat delicate and short-lived, so sporestypically are not dispersed fromRibesto pinemore than about 300 meters. Because the infec-tion moves from currant plants, to pines, and

back again, it cannot continue to exist withoutits alternate host. Although effective in theory,removal of Ribes is rarely a total success in

practice, as they readily re-grow from smallpieces of root left in the soil, and the seeds arewidely spread in birds droppings.

The most common species of Ribes in theLaurentians is Ribes glandulosum (Skunkcurrant). However Ribes hudsonianum(Northern black currant) is also found. Bothare major hosts of blister rust fungi. Some

Ribes species such as Alpine currant (Ribesalpinum) and its varieties have been plantedornamentally in low hedges in residentialareas. Some states and municipalities have

banned it because it hosts white pine blis-ter rust. Skunk currant and Northern blackcurrant have no prickly thorns. The leavesof all species are up to 10 centimeters long,

divided into three, or rarely ve, sharp-toothed lobes, having long hairs on the undersides, studded with yellow glands.The leaves are shaped quite similar to a mountain maple (Acer spicatum) leaf but are smaller and brighter.

Skunk currant is found in cool, moist woods and clearings. It prefers moisture retentive but well-drained loamy soil of atleast moderate quality. It is often found in drier spots in and around swamps, in recent clearcut patches, in places in thewoods where grasses are found and under young hardwoods such as white birch, pin cherry, aspen and red maple. It doesnot like heavy shade or very dry areas. It is not found in dense forest stands, but will tolerate some shade. Skunk currantspreads along the ground with most of its roots close to the soil surface which makes it easy to extract from the soil. It

seldom exceeds a height of 50 cm and is commonly no taller than 30 cm above the ground.

Northern black currant is found on stream banks, in moist woods, thickets at edges of mountain meadows, treed bogs,swamps, shaded rock outcrops, deciduous, mixed, and coniferous forests on moist to wet organic and mineral soils atelevations from 300-3300 m. It requires less sunlight than skunk currant. It has a strong, sweetish, unpleasant tom

White pine killed by blister rust

Ribesleaf



cat odor, and bears its leaves on long shoots.Contrary to skunk currant it grows erect from0.5 to 2 meters tall.

Both species prolically invade areas alongstreams that were once ooded by beaverdams.Both species are among the earliestshrubs to produce leaves in the spring andthe leaves are generally a brighter green than

other plants. Usually the best time for iden-tication is from mid May to early June andthis is the best time for eradication.

Eradication is accomplished by getting agood grip on the stems of the plant and pull-ing gently and steadily to remove the plantfrom the soil without breaking any roots. Itis difcult to remove all the roots without

breaking some and when a root is broken itmay resprout. This means that the area must be inspected annually in order to remove the sprouts. If eradication is donein the spring the plants can be hung on the branches of surrounding trees and shrubs in order for the roots to dry killingthe plant. If eradication is done past midsummer the plants should be burnt to destroy the basidiospores that may haveformed.

Since there is a liklihood of resprouting, it is necessary to return to areas where the plant was found on an annual basis,preferably in early spring when the leaves are more visible, to complete the eradication process. All landowners shouldbe encouraged to carry out an eradication program in order to protect their own and nearby white pines.

Other forestry controls

Many forest management approaches are available to combat white pine blister rust, but none is completely satisfactory.In some areas, a recommendation is to avoid regenerating or planting white pines in small openings. Dew that formson seedlings under open conditions is likely to persist in smaller openings, creating better conditions for basidiosporeinfection. Maintaining a partial overstory over developing seedlings reduces dew formation and infection levels. It also

reduces the likelihood of infection by the white pine weevil insect as well.

Active programs are underway to select and/or breed trees for resistance to white pine blister rust but no resistant seed-lings are yet available from any nurseries.

Many states in the USA have quarantines to prevent cultivation of suchRibesspecies. For instance, Maine law prohibitsthe planting and cultivation of currants and gooseberries in most of Southern Maine, and prohibits the planting and culti-vation of European black currants and their hybrids anywhere within the state. However, enforcement of such regulationsis sometimes lax and there are increasing initiatives from growers to repeal or relax such regulation.

2. White pine weevil (Pissodis strobi)

The white pine weevil is considered the most destructive insect pest of eastern white pine in North America. It kills theterminal leader primarily of eastern white pine. Colorado

blue and Norway spruces, Scots, red, jack, and Austrianpines are also attacked. Trees become susceptible to injurywhen they reach a height of about three feet. The white pineweevil prefers to attack trees exposed to direct sunlight.

The adult insect is a small rust-colored weevil that is about4-6 mm long. It has irregularly shaped patches of brownand white scales on the front wings. Near the apex of thefront wings is a large white patch. Like most weevils, theadult has a long snout-like beak from which small anten-nae arise. The larval stage, which lives beneath the bark, is

white with a distinct brown head. When mature, the larva isapproximately 7 mm long, legless, and slightly C-shaped.

Severlydamagedwhite pine

showing resinfow.

Tree will notsurvive

Adult weevil



Weevil damage

Adults spend the winter in the leaf litter under or near host trees. On warm spring days they y or crawl to the leadersof suitable hosts usually during the period from mid-March through April. Most feeding by adults is done within 25 cmof the terminal buds. From mid-April through early May, females mate and each deposits one to ve eggs in feedingwounds. Hundreds of eggs may be deposited in one terminal leader. The eggs hatch in about seven days. When the termi-

nal shoot is heavily infested larvae feed side by side in a ringencircling the stem. They feed downward on the inner bark of theleader. Larvae reach maturity in mid to late July and pupate in theinfested terminal. The pupal chambers called chip cocoons arelled with shredded wood and can be found inside the terminal at

this time. Adults emerge in 10 to 15 days through small holes atthe base of the dead terminal of the host plant usually in late Julyand August. During this time feeding by adults is not consideredimportant since little is done before they enter the leaf litter tooverwinter. The white pine weevil has one generation per year.

Site and stand conditions strongly inuence the severity ofdamage by white pine weevils. Trees growing in full sun arevulnerable to weevil attack; whereas shade-grown trees with

slow shoot growth and reduced bark thickness are rarely attacked. White pine weevils prefer laying eggs in leaders witha bark thickness of 1.82.2 mm and select fast growing, vigorous trees with thick succulent bark. Growing white pineunder shade, however, involves a tradeoff as strong shade reduces tree growth. Trees with 5075% of full sunlight canachieve good growth at tolerable levels of weevil damage.

Damage

The rst symptom evident from successful attack by this pest is glistening droplets ofresin on terminal leaders of the host plant in late March and April. This is the result of

punctures made by adults in the process of feeding and cutting egg-laying sites. Injury toeastern white pine and some species of spruce is usually conned to the previous yearsterminal leader. Damage on Scots pine and Colorado blue and Serbian spruces oftenextends downward through two or three years growth. The good news is infested treesare seldom killed.

Most damage is done by the larval stage. Larvae are found just under the bark of infested

terminals from May through July. Larvae chew and burrow completely around the stemcausing the current years growth to wilt, droop, and eventually die. One or more side

branches (laterals) may then bend and grow upward to take over as theterminal leader. At this point the tree is now permanently crooked. Forseveral years after successful attack by this pest, a few more laterals maygrow as leaders. This condition may result in a forked tree.

Management

Eastern white pine is most attractive to this pest when trees are less than 20 feet in height. In July look forcurled, dead, or dying terminal leaders that may have the appearance of a shepherds crook. The infested

leaders should be pruned and burned beforemid-July to destroy life stages of this pest.Prune all but one live lateral shoot just belowthe damaged terminal. This should promotesingle stem dominance on the affected host

plant.

Observations of resin droplets on the leaderin early spring may be an indication thatadults are feeding. Application of a registeredformulation of an insecticide should be madefrom late March through April when dropletsof resin are rst detected. Only the terminal leader needsto be sprayed. Insect parasitoids and predators as well as

birds feed on this pest. However, the effect of these naturalenemies is not signicant enough to prevent damage.

Earlyspringresin

dropletsand

weevilholes

Larvae feeding onleader

A cabbage tree with multipleleaders from multiple attacks

white pine

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