Spruce
A spruce is a tree of the genus Picea /paɪˈsiːə/, a genus of about 35 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal (taiga) regions of the Earth. Spruces are large trees, from about 20–60 m (about 60–200 ft) tall when mature, and can be distinguished by their whorled branches and conical form. The needles, or leaves, of spruces are attached singly to the branches in a spiral fashion, each needle on a small, peg-like structure. The needles are shed when 4–10 years old, leaving the branches rough with the retained pegs (an easy means of distinguishing them from other similar genera, where the branches are fairly smooth).
Spruces are used as food plants by the larvae of some Lepidoptera (moth and butterfly) species, such as the eastern spruce budworm. They are also used by the larvae of gall adelgids (Adelges species).
In the mountains of western Sweden, scientists have found a Norway spruce, nicknamed Old Tjikko, which by reproducing through layering, has reached an age of 9,550 years and is claimed to be the world's oldest known living tree.
| Spruce | |
| Kingdom: | Plantae |
| Division: | Pinophyta |
| Class: | Pinopsida |
| Order: | Pinales |
| Family: | Pinaceae |
| Subfamily: | Piceoideae |
| Genus: | Picea |
Etymology
The word "spruce" entered the English language from the Polish Prusy, Prussia (a historical region, today part of Poland and Kaliningrad Oblast). It became spruce because in Polish, z Prus ("from Prussia") sounded like "spruce" to English speakers and was a generic term for commodities brought to England by Hanseatic merchants and because the tree was believed to have come from Polish Ducal Prussia.
Classification
DNA analyses have shown that traditional classifications based on the morphology of needle and cone are artificial. A recent study found that P. breweriana had a basal position, followed by P. sitchensis, and the other species were further divided into three clades, suggesting that Picea originated in North America. Spruce has been found in the fossil record from the early Cretaceous, 136 million years ago.
Species
Thirty-five named species of spruce exist in the world. The Plant List has 59 accepted spruce names.[8]
Basal species:
- Picea breweriana – Brewer's spruce, Klamath Mountains, North America; local endemic
- Picea sitchensis – Sitka spruce, Pacific coast of North America; the largest species, to 95 m tall; important in forestry
- Clade I (Northern and western North America, in boreal forests or high mountains)
- Picea engelmannii – Engelmann spruce, western North American mountains; important in forestry
- Picea glauca – white spruce, northern North America; important in forestry
- Clade II (throughout Asia, a few isolated populations in mountainous areas of Mexico, mostly in mountainous areas)
- Picea brachytyla – Sargent's spruce, southwest China
- Picea chihuahuana – Chihuahua spruce, northwest Mexico (rare)
- Picea farreri – Burmese spruce, northeast Burma, southwest China (mountains)
- Picea likiangensis – Likiang spruce, southwest China
- Picea martinezii – Martinez spruce, northeast Mexico (very rare, endangered)
- Picea maximowiczii – Maximowicz spruce, Japan (rare, mountains)
- Picea morrisonicola – Taiwan spruce Taiwan (high mountains)
- Picea neoveitchii – Veitch's spruce, northwest China (rare, endangered)
- Picea orientalis – Caucasian spruce or Oriental spruce, Caucasus, northeast Turkey
- Picea purpurea – purple cone spruce, western China
- Picea schrenkiana – Schrenk's spruce, mountains of central Asia
- Picea smithiana – Morinda spruce, western Himalaya, eastern Afghanistan, northern and northwest India
- Picea spinulosa – Sikkim spruce, northeast India (Sikkim), eastern Himalaya
- Picea torano – Tiger-tail spruce, Japan
- Picea wilsonii – Wilson's spruce, western China
- Clade III (Europe, Asia, and North America, mostly in boreal forests or mountainous areas)
- Picea abies – Norway spruce, Europe; important in forestry, the original Christmas tree
- Picea alcoquiana – ("P. bicolor") Alcock's spruce, central Japan (mountains)
- Picea alpestris – Norway spruce, Alpine spruce, the Alps in Europe; rare, often treated as a variant of P. abies (and hybridises with it), but has distinct cones
- Picea asperata – Dragon spruce, western China; several varieties
- Picea crassifolia – Qinghai spruce, China
- Picea glehnii – Glehn's spruce, northern Japan, Sakhalin
- Picea jezoensis – Jezo spruce, northeast Asia, Kamchatka south to Japan
- Picea koraiensis – Korean spruce, Korea, northeast China
- Picea koyamae – Koyama's spruce, Japan (mountains)
- Picea mariana – Black spruce, northern North America
- Picea meyeri – Meyer's spruce, northern China (from Inner Mongolia to Gansu)
- Picea obovata – Siberian spruce, north Scandinavia, Siberia; often treated as a variant of P. abies (and hybridises with it), but has distinct cones
- Picea omorika – Serbian spruce, Serbia and Bosnia; local endemic; important in horticulture
- Picea pungens – blue spruce or Colorado spruce, Rocky Mountains, North America; important in horticulture
- Picea retroflexa – green dragon spruce, China
- Picea rubens – red spruce, northeastern North America; important in forestry, known as Adirondack in musical-instrument making
Morphology
Determining that a tree is a member of a spruce species is not difficult; evergreen needles that are more or less quadrangled, and especially the pulvinus, give it away. Beyond that, determination can become more difficult. Intensive sampling in the Smithers/Hazelton/Houston area of British Columbia showed Douglas (1975), according to Coates et al. (1994), that cone scale morphology was the feature most useful in differentiating species of spruce; the length, width, length: width ratio, the length of free scale (the distance from the imprint of the seed wing to the tip of the scale), and the percentage free scale (length of free scale as a percentage of the total length of the scale) were most useful in this regard. Daubenmire (1974), after range-wide sampling, had already recognized the importance of the 2 latter characters. Taylor (1959) had noted that the most obvious morphological difference between typical Picea glauca and typical P. engelmannii was the cone scale, and Horton (1956,1959) found that the most useful diagnostic features of the 2 spruces are in the cone; differences occur in the flower, shoot and needle, "but those in the cone are most easily assessed" (Horton 1959). Coupé et al. (1982) recommended that cone scale characters be based on samples taken from the midsection of each of 10 cones from each of 5 trees in the population of interest.
Without cones, morphological differentiation among spruce species and their hybrids is more difficult. Species classification for seeds collected from spruce stands in which introgressive hybridization between white and Sitka spruces (P. sitchensis) may have occurred is important for determining appropriate cultural regimens in the nursery. If, for instance, white spruce grown at container nurseries in southwestern British Columbia are not given an extended photoperiod, leader growth ceases early in the first growing season, and seedlings do not reach the minimum height specifications. But, if an extended photoperiod is provided for Sitka spruce, seedlings become unacceptably tall by the end of the first growing season. Species classification of seedlots collected in areas where hybridization of white and Sitka spruces has been reported has depended on (i) easily measured cone scale characters of seed trees, especially free scale length, (ii) visual judgements of morphological characters, e.g., growth rhythm, shoot and root weight, and needle serration, or (iii) some combination of (i) and (ii) (Yeh and Arnott 1986). Useful to a degree, these classification procedures have important limitations; genetic composition of the seeds produced by a stand is determined by both the seed trees and the pollen parents, and species classification of hybrid seedlots and estimates of their level of introgression on the basis of seed-tree characteristics can be unreliable when hybrid seedlots vary in their introgressiveness in consequence of spatial and temporal variations in contributions from the pollen parent (Yeh and Arnott 1986). Secondly, morphological characters are markedly influenced by ontogenetic and environmental influences, so that to discern spruce hybrid seedlot composition with accuracy, hybrid seedlots must differ substantially in morphology from both parent species. Yeh and Arnott (1986) pointed out the difficulties of estimating accurately the degree of introgression between white and Sitka spruces; introgression may have occurred at low levels, and/or hybrid seed lots may vary in their degree of introgression in consequence of repeated backcrossing with parental species.
Growth
Spruce seedlings are most susceptible immediately following germination, and remain highly susceptible through to the following spring. More than half of spruce seedling mortality probably occurs during the first growing season and is also very high during the first winter, when seedlings are subjected to freezing damage, frost heaving and erosion, as well as smothering by litter and snow-pressed vegetation. Seedlings that germinate late in the growing season are particularly vulnerable because they are tiny and have not had time to harden off fully.
Mortality rates generally decrease sharply thereafter, but losses often remain high for some years. "Establishment" is a subjective concept based on the idea that once a seedling has successfully reached a certain size, not much is likely to prevent its further development. Criteria vary, of course, but Noble and Ronco (1978), for instance, considered that seedlings 4 to 5 years old, or 8 cm to 10 cm tall, warranted the designation "established", since only unusual factors such as snow mold, fire, trampling, or predation would then impair regeneration success. Eis (1967) suggested that in dry habitats on either mineral soil or litter seedbeds a 3-year-old seedling may be considered established; in moist habitats, seedlings may need 4 or 5 years to become established on mineral soil, possibly longer on litter seedbeds.
Growth remains very slow for several to many years. Three years after shelterwood felling in subalpine Alberta, dominant regeneration averaged 5.5 cm in height in scarified blocks, and 7.3 cm in non-scarified blocks (Day 1970), possibly reflecting diminished fertility with the removal of the A horizon.
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