Index of Species Information

SPECIES:  Picea abies


Introductory

SPECIES: Picea abies
AUTHORSHIP AND CITATION : Sullivan, Janet. 1994. Picea abies. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].

ABBREVIATION : PICABI SYNONYMS : Picea excelsa Link [47,50] SCS PLANT CODE : PIAB COMMON NAMES : Norway spruce European spruce TAXONOMY : The currently accepted scientific name of Norway spruce is Picea abies (L.) Karst. [47]. There are no currently accepted infrataxa, although a number of cultivars exist [50]. LIFE FORM : Tree FEDERAL LEGAL STATUS : No special status OTHER STATUS : NO-ENTRY


DISTRIBUTION AND OCCURRENCE

SPECIES: Picea abies
GENERAL DISTRIBUTION : Norway spruce is native to the European Alps, the Balkan mountains, and the Carpathians, its range extending north to Scandinavia and merging with Siberian spruce (Picea obovata) in northern Russia [50]. It was introduced to the British Isles as early as 1500 AD, and is widely planted in North America, particularly in the northeastern United States, southeastern Canada, the Pacific Coast states, and the Rocky Mountain states [47,50]. Naturalized populations are known from Connecticut to Michigan and probably occur elsewhere [47]. ECOSYSTEMS : FRES11 Spruce - fir FRES15 Oak - hickory FRES18 Maple - beech - birch FRES19 Aspen - birch STATES : CT HI IL IN ME MA MI NY PA BLM PHYSIOGRAPHIC REGIONS : NO-ENTRY KUCHLER PLANT ASSOCIATIONS : K096 Northeastern spruce - fir forest K104 Appalachian oak forest K106 Northern hardwoods K107 Northern hardwoods - fir forest K108 Northern hardwoods - spruce forest K109 Transition between K104 and K106 SAF COVER TYPES : NO-ENTRY SRM (RANGELAND) COVER TYPES : NO-ENTRY HABITAT TYPES AND PLANT COMMUNITIES : In its native range, Norway spruce occurs in pure stands, transitional stands mixed with Scotch pine (Pinus sylvestris), or mixed stands with European beech (Fagus sylvatica) and European silver fir (Abies alba). Scattered Norway spruce occurs in seral stands of European aspen (Populus tremula) or hairy birch (Betula pubescens). Classification systems for Scandinavian forests where Norway spruce and/or Scotch pine are the major species are based on ground vegetation [11]. Common groundlayer species include bilberry (Vaccinium myrtillus), lingonberry (V. vitis-idaea), heather (Calluna vulgaris), and woodsorrel (Oxalis spp.) [5]. Good sites for Norway spruce occur on Oxalis-Myrtillus types and fair sites are indicated by Myrtillus. Vaccinium types are usually rather barren and not suited for good spruce growth [79]. Understory species most often associated with Norway spruce in Poland include raspberry (Rubus idaeus) and European mountain-ash (Sorbus aucuparia). Mature Norway spruce forests typically have very little groundlayer vegetation [5].

MANAGEMENT CONSIDERATIONS

SPECIES: Picea abies
WOOD PRODUCTS VALUE : Norway spruce wood is strong, soft, straight- and fine-grained, and easily worked [17,87]. It is not durable in contact with soil. It is widely used for construction, pulp, furniture, and musical instruments [17,80]. Norway spruce is one of the most common and economically important coniferous species in Europe and Scandinavia [46]. In Maine, thinned material and standing dead Norway spruce produced pulp of good strength as reported in a study of the pulp potential of seven softwoods [16]. IMPORTANCE TO LIVESTOCK AND WILDLIFE : Norway spruce seedlings are highly preferred winter browse for snowshoe hares in Quebec. Browsing of seedlings and saplings in plantations can be intense, as young plantations form ideal winter habitat for snowshoe hares [3]. Norway spruce is not a preferred browse for moose in Scandinavia; young and middle-aged stands of Scotch pine form habitat preferred by moose over mature Scotch pine-Norway spruce forests and bogs [14]. In Europe, red deer strip the bark of Norway spruce [60]. Other animals browse spruce foliage but it is not a highly preferred food source for either wildlife or domestic animals [87]. Norway spruce provides important winter cover for a number of species of wildlife [80]. Grouse eat spruce leaves and the seeds are consumed by a number of birds and small mammals [86,87]. PALATABILITY : Norway spruce nursery stock is of extremely low preference to white-tailed deer when compared with other ornamental species, including both conifers and hardwoods [18]. NUTRITIONAL VALUE : NO-ENTRY COVER VALUE : VALUE FOR REHABILITATION OF DISTURBED SITES : Norway spruce was planted on surface mine spoils in Indiana from 1928 to the 1960's [9]. It tolerates acidic soils but is not well suited for dry or nutrient deficient soils [80]. OTHER USES AND VALUES : Norway spruce has been planted for windbreaks and shelterbelts in western prairies, although it grows better in more humid environments [17]. It is recommended for shelterbelt plantings in humid, severe-winter regions [2]. Norway spruce is widely planted for Christmas trees and as an ornamental [17]. Norway spruce roots can be used as grafting stock for white spruce (Picea glauca) [52]. Norway spruce resin has been used to make Burgundy pitch, and the twigs used to make Swiss turpentine. The twigs and needles were used to make antiscorbutic and diuretic beverages [87]. OTHER MANAGEMENT CONSIDERATIONS : Norway spruce is the most intensively studied spruce in the world. A number of geographic races have been identified, and numerous genetic improvement programs are underway, mostly in Europe and Scandinavia [87]. In Europe, Norway spruce is the focus of increasing concern about forest decline. It is exhibiting a specific set of symptoms ("Waldsterben") which are also showing up in forest trees in the United States (including red spruce [Picea rubens] and Norway spruce) [40,46,55,66]. These symptoms include needle chlorosis combined with magnesium deficiency and thinning of the crown [46]. Explanations usually center on air pollution (ozone, acid deposition, or toxic metals contamination) coupled with acidified, depleted soils that cause, among other problems, foliar magnesium deficiency [12,46,55,58,66]. Soils under Norway spruce stands are often more acidic than soils under other species. Soil acidity appears to increase with stand age as soil buffering capacity decreases with age [4]. Norway spruce is not windfirm and is also subject to snowbreak [42]. Artificial Reforestation: Norway spruce has been widely planted in reforestation programs in the eastern United States [2]. In Ontario, expected rotation of Norway spruce ranges from 60 to 70 years. Sites are prepared by plowing, and Norway spruce seedlings are planted with 5 x 5 foot spacing (1.5 x 1.5 m) [19]. Silviculture: In Europe, Norway spruce is usually managed with selection systems in mixtures with European beech and European silver fir, particularly on private holdings. Such mixtures require frequent thinning to maintain European silver fir, which would otherwise be eliminated by the beech and Norway spruce [67]. Norway spruce is also managed with even-aged systems such as patch clearcutting and strip-cutting [49]. In Sweden, single-tree selection has been of limited use, but a recent report suggests that it is possible to obtain abundant regeneration and high ingrowth rates in selection stands with high levels of standing volume [48]. Scotch pine can be planted as a nurse tree for Norway spruce; such mixtures result in a net gain in production over monocultures of either species [10]. During dry summers, spruce litter buildup can create manganese concentrations that prevent regeneration of Norway spruce. As a consequence, land managers in France alternate rotations of Norway spruce and hardwoods, or destroy the toxic manganese in litter by scarification [20]. Norway spruce is resistant to mistblown glyphosate used to kill competing hardwoods [81]. Fertilization of Norway spruce can promote frost damage by prolonging the growing season, and delaying cuticularization of the epidermis [68]. Whole-tree harvesting in Sweden is deleterious to soil fertility and lowers soil pH [53]. In Belgium, Norway spruce was excluded from heathlands (Calluna vulgaris) created by burn-beating cultivation (cutting, piling and burning humus layers to fertilize fields), mowing, and sheep grazing. Norway spruce has been planted on these former heathlands, and burn-beating agriculture is no longer practiced. Since burn-beating removes the humus layer these Norway spruce plantations are growing on severely depleted soils. Depleted soils may be contributing to Waldsterben in these plantations, and may also present problems for future rotations [25]. In Finland, 15- to 20-year-old natural stands of Norway spruce were frost hardy (defined as the temperature at which 50 percent mortality of bud occurs) to 24.8 degrees Fahrenheit (-4 deg C) in mid-summer, and frost hardy to -54.4 degrees Fahrenheit (-48 deg C) in January. Hardening occurs over a short period in September, and is lost over a short period in early May [59]. Insect Pests: In North America, Norway spruce is host to western spruce budworm [13] and mountain pine beetle [32].

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Picea abies
GENERAL BOTANICAL CHARACTERISTICS : Norway spruce is an introduced evergreen tree. In central Europe, heights of up to 203 feet (61 m) have been reported [42]; the range is usually between 100 and 200 feet (30-61 m) [87]. The bole is usually straight and symmetrical, with no tendency to fork [42]. The bark of young trees has pale fine shreds [50]. The bark of older trees is usually heavy with algae and has shallow rounded scales that are easily shed [17,50]. The crown of young trees is narrowly conic, that of older trees becoming broadly columnar [50]. Secondary branchlets are characteristically drooping or pendulous [2]. Norway spruce cones are conspicuously large (4 to 7 inches [10-18 cm] long) [17]. The root system is typically shallow, with several lateral roots and no taproot. On rocky sites the roots spread widely, twining over the rocks. On bog soils, Norway spruce tends to form plate-like roots [42]. In Finland, a 140-year-old Norway spruce forest in a Vaccinium-Myrtillus vegetation type had a root zone extending only 12 inches (30 cm) into mineral soil [43]. Early growth of Norway spruce is slow, increasing to maximal rates from 20 to 60 years of age [42,50]. Within its native range, Norway spruce remains healthy up to 200 years, and lives up to 300 to 400 years at the northern limits of its range [42]. Senescence occurs at less than 200 years of age in the British Isles and North America [50]. RAUNKIAER LIFE FORM : Phanerophyte REGENERATION PROCESSES : Sexual reproduction: Norway spruce usually first reproduces at 30 to 40 years of age. Good seed crops are produced every 3 to 4 years in Britain, 8 to 10 years in Norway, and 12 to 13 years in Finland [42,87]. Most of the seeds are produced in the crowns of dominant stems; seed yield is lower in smaller stems in stands of the same age. Norway spruce seeds are wind dispersed, but do not usually travel much farther than the height of the parent tree [42]. Movement after dispersal, however, can be considerable when seeds are dispersed onto crusted snow and are pushed along on the surface by wind [34,74]. Seeds of Norway spruce germinate promptly and do not require pretreatment or exacting light regimes. Moist chilling of some spruce (Picea spp.) seeds removes the requirement for light [87]. Optimum germination temperature for Norway spruce seeds is around 73 degrees Fahrenheit (23 deg C) but germination will occur up to about 91 degrees Fahrenheit (33 deg C) [42]. Seedling growth is best at constant low temperature (48 degrees Fahrenheit [9 deg C]), rather than with fluctuating temperatures or steady high temperatures [36]. The seedlings are sensitive to drought and/or overheating, particularly when the soil surface is exposed to direct insolation [42]. In Utah, nursery-grown seedlings inclined to the south (to shade the soil directly under the seedling and keep the roots cooler and wetter) averaged 6 percent mortality from heat damage, whereas seedlings inclined to the north averaged 30 percent mortality from the same cause [41]. Other studies support the hypothesis that shading improves early seedling survival [33,77]. Thin humus (as opposed to thick humus) hinders Norway spruce establishment since it dries out more quickly and contributes to drought stress of the seedlings [70]. Vegetative reproduction: Under natural conditions, particularly in areas of high humidity and high soil moisture, Norway spruce reproduces by layering [42]. It does not sprout from stumps or roots [65]. Norway spruce can be propagated by cuttings and micropropagation techniques [30]. SITE CHARACTERISTICS : Norway spruce grows best in cool, humid climates on rich soils [2,17]. Preferred soils include well-drained sandy loams [2,17,42]. It also grows well on almost all other types of soils. Permanently waterlogged soils inhibit Norway spruce growth, but Norway spruce does occur on poorly drained soils and in bogs [42]. Growth rates increase with increased soil organic material and are positively correlated to the nitrogen content of the soil. In southern Finland, soil pH under 34- to 38-year-old plantations of Norway spruce ranged from 3.7 to 4.4. Norway spruce is also found on podzolized soils [45]. Norway spruce occurs at elevations up to 6,560 feet (2,000 m) in the Bavarian Alps, to 4,920 feet (1,500 m) in the Black Forest, and to 3,450 feet (1,051 m) in the Fichtel Mountains [42]. In Switzerland, the 'hilly zone' up to 1,800 feet (550 m) is occupied by mixed hardwoods with scattered conifers (European silver fir, Norway spruce and Scot's pine); the 'mountain zone' from 1,800 feet to 3,800 feet (550-1,160 m) is cooler and more humid and is dominated by European beech, European silver fir and increasing amounts of Norway spruce; the subalpine zone from 3,800 feet to 6,600 feet (1,160-2,000 m) is divided into two subzones: 'subalpine spruce' up to 5,500 feet (1,670 m) consisting of pure Norway spruce and mixed Norway spruce and European silver fir; and the 'Arolla pine (Swiss stone pine [Pinus cembra])- (European) larch (Larix decidua) zone' from 5,500 feet (1,670 m) to timberline [24]. This distribution is generally applicable to most of central Europe [42]. SUCCESSIONAL STATUS : Obligate Climax Species Norway spruce is tolerant of shade. Norway spruce stands form the climax forest of Scandinavia but stagnate with age [79]. Seeds of Norway spruce are probably not long lived in the soil, although under good storage conditions remain viable for up to 7 years [87]. The soil seedbank under a 100-year-old Norway spruce forest in Russia contained a large number of viable seeds of mostly early successional species. It was not representative of the aboveground flora and apparently did not contain many Norway spruce seeds [38]. Disturbance events such as windfalls, snow damage, disease and insect attack create small-scale gaps in the mature canopy. Norway spruce depends largely on advance regeneration (seedling banks) to capture such canopy gaps [56]. Norway spruce is the most common gapmaker and it is also the most common seedling in gaps. Seedlings survive in an extremely stunted condition for many years. This reservoir of seedlings functions in a way analogous to soil seedbanks [29]. Suppressed Norway spruce saplings can persist for several decades, retaining the ability to respond to canopy gaps with increased growth [35]. In Sweden, suppressed Norway spruce trees less than 8.2 feet (2.5 m) tall and 100 to 220 years old exhibited new growth during gap-phase replacement [70]. In Bavarian Norway spruce stands, storm-caused windfall disturbances were followed by new Norway spruce stands that were older than than the windfall event (indicating advance regeneration). Sites that had been cleaned (removal of dead trees and broken stems) had a birch-dominated regeneration layer that originated after the windfall event. Spruce seedlings were probably damaged by the cleaning operation [23]. In northern Sweden, Norway spruce-hairy birch forests consist of all-aged (up to 330 years) Norway spruce (largely as a result of gap-capture replacement) [35]. Norway spruce first occurred in Scandinavia approximately 2,500 years ago; its immigration from Europe is attributed to colder Scandinavian winters coupled with increased precipitation and storm events which allowed Norway spruce to colonize areas that were formerly too dry [7]. It survived in Scandinavia in low densities due to frequent disturbances until climatic changes coupled with a decrease in human-caused disturbances (mainly fire) allowed natural succession to proceed, resulting in the current widespread distribution of dense Norway spruce-dominated forests [8]. SEASONAL DEVELOPMENT : Norway spruce cones open from May to June. Seeds ripen in late autumn the same year. They are released on warm days in late autumn and winter, but are sometimes retained until spring [42].

FIRE ECOLOGY

SPECIES: Picea abies
FIRE ECOLOGY OR ADAPTATIONS : Norway spruce is not well adapted to survive fire. Fire in mature stands of Norway spruce is usually of high intensity and destroys all standing trees [15]. Fire severity usually depends on a number of factors, primarily soil moisture [74]. In taiga forests over permafrost, low-severity fires leaving standing live trees may eventually result in complete stand destruction since windfall of the remaining trees may occur when increased insolation on blackened soil thaws the permafrost. There is little regeneration in stagnant stands of Norway spruce; the next generation of trees is only produced after a fire [15]. Norway spruce is easily killed by fire and is not an early colonizer in postfire succession; stand-destroying fires usually result in replacement by Scot's pine. Norway spruce develops as the understory in Scot's pine stands on suitable sites, and will eventually replace Scot's pine to complete the successional cycle [7,15,70]. Fire history in Norway: Fire was used extensively for agricultural clearing in southeastern Norway 300 to 400 years ago. After a short period of cultivation, depleted soils were left to natural reforestation, forming mixtures of conifers and broadleaf trees, mostly birch (Betula pubescens or B. verrucosa) [6]. In the pollen record, Norway spruce pollen increased during periods of lower disturbance and fewer fires. In the last 200 years, since agricultural burning has virtually ceased, Norway spruce stands have formed closed canopies with very little groundlayer vegetation [7]. Fire history in Finland: Fire frequencies have been estimated to range from 31 to 81 years for different historical periods. Human activity has played a large role in fire history; a large amount of burning occurred during the Iron Age and medieval periods, mostly due to slash and burn agriculture, from about 1 AD to 1750 AD [72]. Prior to the appearance of cereal pollens, charcoal analysis of bog soils indicates that, an average of one fire every 84 years occurred between 3000 and 2000 BP. There is an inverse relationship between the amount of Picea pollen and the amount and frequency of charcoal particles; when fire frequency is high, Norway spruce densities are low [73]. Fire history in Sweden: In northern Sweden, the mean fire rotation (the amount of time equivalent to the area studied divided by the area of sample plot burned annually) was approximately 100 years for mixed stands of Norway spruce and Scotch pine from the end of the medieval period up to the end of the nineteenth century. Since fire suppression, the estimated fire rotation is on the order of 3,500 years. The presuppression fire rotation created a mosaic of even-aged stands at different successional stages. Norway spruce often forms the undergrowth in Scotch pine stands that survive or are regenerated after fire; Scotch pine often survives as an overstory tree and can reach very old ages. In Norway spruce forests on wet sites fires have been rare; fire-free intervals of up to 500 years have been reported for such sites [21,84,85]. The mean number of years between fires and the amount of time since the last fire were positively correlated to basal area of Norway spruce; Norway spruce density increases when fires occur at long intervals and shorter intervals favor Scotch pine [21]. Fire history in northern European Russia: Estimates from fire scar data indicate fire frequencies on the order of 130 to 200 years in spruce forests (including Siberian spruce and Norway spruce) [76]. POSTFIRE REGENERATION STRATEGY : Tree without adventitious-bud root crown

FIRE EFFECTS

SPECIES: Picea abies
IMMEDIATE FIRE EFFECT ON PLANT : Norway spruce is easily damaged or killed by fire [74]. The crown canopy of Norway spruce is often totally destroyed by even minor surface fires [64,76]. However, there are almost always scattered survivors even following crown fires; in most cases survival is due to local topography which prevents fire spread [82]. In Finland, forest fire damage is greatest in Norway spruce forests (compared with mixed or pure Scotch pine stands) [61]. In the United States, grass fires are reported to cause severe damage to Norway spruce plantations [17]. Norway spruce seeds buried in humus at 1.2 inch (3 cm), 1.9 inch (5 cm), and 3.9 inch (10 cm) depths were undamaged by the heat of a prescribed fire that measured 820 degrees Fahrenheit (438 deg C) at the soil surface. The humus provided excellent insulation; the temperature at 1.2 inches (3 cm) was only 80 degrees Fahrenheit (26.5 deg C) [74]. In a laboratory study in which heated air was applied to stem sections and to whole tops of dormant 3- and 4-year-old Norway spruce seedlings, Norway spruce was found to be more tolerant of heat than European larch or Japanese larch (Larix leptolepis). Active Norway spruce seedlings were more heat tolerant than European and Japanese larch, eastern white pine (Pinus strobus), Scotch pine, or American beech (Fagus grandifolia), but none were very tolerant. In this experiment, no seedlings were killed by the heat treatment, but dormant Norway spruce seedlings were almost completely defoliated [39]. DISCUSSION AND QUALIFICATION OF FIRE EFFECT : NO-ENTRY PLANT RESPONSE TO FIRE : Norway spruce seedlings are not usually present on burned areas; the soils are usually too dry and hot to support good seedling establishment [74]. DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : NO-ENTRY FIRE MANAGEMENT CONSIDERATIONS : Prescribed fire has been used as a tool for forest regeneration in Norway, primarily to prepare the ground for natural regeneration from seed trees, usually Scotch pine. Management of Norway spruce in Norway is often based on information from other countries where Norway spruce and Scot's pine are the dominant conifers. After World War II, prescribed fires were used to prepare sites for artificial regeneration, either for sowing Scot's pine seeds or for planting Norway spruce nursery stock. It is often difficult to conduct prescribed fires in Norway; the weather is changeable and conditions are often too moist for burning. These facts, coupled with increasing costs of burning, have led to a preference for site scarification by mechanical means instead of fire [6]. Prescribed fires are not used much in Finland today either, due to high costs and variable weather [78]. The average size of individual wildfires is usually greatest in mixed stands of Scot's pine and Norway spruce [61]. Norway spruce is known as a nutrient-demanding species; this has led to concern that prescribed fire for site preparation burns too much of the humus and results in soils that are not favorable for good Norway spruce growth. In Norway, Norway spruce seedlings showed good 12-year survival on both burned (83 percent survival) and unburned (78 percent survival) sites. Overall height growth on unburned sites was slightly better at 12 years than on burned sites, although early growth on burned sites was better [6]. In Sweden, sites that were clearcut and burned, then seeded with Norway spruce were compared with similar sites that had not been burned. The unburned sites had thicker humus layers after 43 years of growth. The authors estimate that it takes 70 to 80 years from the time of the fire for burned humus layers to be rebuilt to prefire levels [37]. Prescribing fire for site preparation in Scandinavia depends on the vegetation type. Types that are characterized by thick, raw humus layers benefit from fire, which releases nutrients and activates the humus [6,74]. After fire passes over humus, ashes and carbonized plants form a thin cover over the otherwise undamaged humus layers [74]. Prescribed fires used for site preparation must be conducted with care to prevent destruction of humus and excessive heating of upper mineral soil. Fires temperatures of 662 degrees Fahrenheit (350 deg C) or less at the soil surface will release nutrients stored in litter and allow them to condense in the humus and upper mineral soils [28]. Fires that burn quickly enough to leave humus may be acceptable. Decomposition rates in northern Norway spruce forests are very slow. In Finland, 56 years after logging, even very thin branches are left intact in slash and litter [54]. Prescribed fires can release some of this organic matter, and increase the pH of the soil. Some nutrients are lost to the atmosphere [78]. Types with thin humus layers are better unburned, since the humus would be destroyed by fire [66,79]. Norway spruce is unsuited for such sites, since its shallow roots render it less able to exploit the mineral soil for nutrients than Scotch pine [37]. Prescribed burning is usually not necessary on most fertile soils, but may be useful on sites that have experienced swale cultivation [79]. Fire suppression in Sweden since the nineteenth century has resulted in an over-representation of aging Norway spruce forests, and it has been recommended that prescribed fires for stand rejuvenation are necessary in Swedish National Parks and nature reserves to improve stand health by reestablishing a mosaic of seral stands [84].

REFERENCES

SPECIES: Picea abies
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Browse supply in lowland forests of eastern Poland. Holarctic Ecology. 3: 202-213. [19884] 6. Braathe, Peder. 1974. Prescribed burning in Norway--effects on soil and regeneration. In: Proceedings, annual Tall Timbers fire ecology conference; 1973 March 22-23; Tallahassee, FL. No. 13. Tallahassee, FL: 211-222. [18976] 7. Bradshaw, Richard; Hannon, Gina. 1992. Climatic change, human influence and disturbance regime in the control of vegetation dynamics within Fiby Forest, Sweden. Journal of Ecology. 80: 625-632. [21222] 8. Bradshaw, Richard H. W.: Zackrisson, Olle. 1990. A two thousand year history of a northern Swedish boreal forest stand. Journal of Vegetation Science. 1(4): 519-528. [12762] 9. Brothers, Timothy S. 1988. Indiana surface-mine forests: historical development and composition of a human-created vegetation complex. Southeastern Geographer. 28(1): 19-33. [8787] 10. Brown, H. H. F. 1992. Functioning of mixed-species stands at Gisburn, N.W. England. 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Development of crop plans for hardwood and conifer stands on boreal mixedwood sites. In: Samoil, J. K., ed. Management and utilization of northern mixedwoods: Proceedings of a symposium; 1988 April 11-14; Edmonton, AB. Inf. Rep. NOR-X-296. Edmonton, AB: Canadian Forestry Service, Northern Forestrty Centre: 87-98. [13050] 20. Duchaufour, Ph.; Rousseau, L.-Z. 1959. Phenomena of poisoning of conifer seedlings by manganese in forest humus. Revue Forestiere Franciose. 11(4): 835-847. [French]. [23674] 21. Engelmark, Ola. 1987. Fire history correlations to forest type and topography in northern Sweden. Annales Botanici Fennici. 24(4): 317-324. [6688] 22. Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Washington, DC: Society of American Foresters. 148 p. [905] 23. Fischer, Anton. 1992. Long term vegetation development in Bavarian Mountain forest ecosystems following natural destruction. Vegetatui. 103: 93-104. [21272] 24. Fischer, F. 1960. 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