Editing Spruce (section)

== Description ==

===Morphology===
[[File:Picea abies Nadelkissen.jpg|thumb|The peg-like base of the needles, or pulvinus, in [[Norway spruce]] (''Picea abies'')]]
[[File:Picea glauca twig Denali NP AK.jpg|thumb|Pulvini remain after the needles fall (white spruce, ''[[Picea glauca]]'')]]
Determining that a tree is a spruce 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),<ref name="doug">Douglas, G.W. (1975). Spruce (''Picea'') hybridization in west-central British Columbia. B.C. Min. For., Forest Science, Smithers BC, unpublished report, cited by Coates et al. 1994. (Cited by Coates et al. 1994, orig. not seen)</ref> according to Coates et al. (1994),<ref name="coat">Coates, K.D.; Haeussler, S.; Lindeburgh, S.; Pojar, R.; Stock, A.J. (1994). Ecology and silviculture of interior spruce in British Columbia. Canada/British Columbia Partnership Agreement For. Resour. Devel., Victoria BC, FRDA Rep. 220. 182 p.</ref> that cone scale [[Morphology (biology)|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),<ref name="daub">{{cite journal|author=Daubenmire, R. |year=1974|title=Taxonomic and ecologic relationships between ''Picea glauca'' and ''Picea engelmannii''|journal= Can. J. Bot. |volume=52|issue=7|pages=1545–1560|doi=10.1139/b74-203|bibcode=1974CaJB...52.1545D }}</ref> after range-wide sampling, had already recognized the importance of the two latter characters. Taylor (1959)<ref name="taylor">{{cite journal|author=Taylor, T.M.C. |year=1959|title= The taxonomic relationship between ''Picea glauca'' (Moench) Voss and ''P. engelmannii'' Parry|journal= Madroño |jstor=41422994|volume=15|issue=4|pages=111–115}} (Cited in Coates et al. 1994).</ref> had noted that the most obvious morphological difference between typical ''Picea glauca'' and typical ''P. engelmannii'' was the cone scale, and Horton (1956,1959)<ref name="horton1">Horton, K.W. (1956). A taxonomic and ecological study of ''Picea glauca'' and ''Picea engelmannii'' in North America. Diploma thesis, Oxford Univ., U.K. 103 p.</ref><ref name="horton2">Horton, K.W. (1959). Characteristics of subalpine spruce in Alberta. Can. Dep. Northern Affairs National Resour., For. Branch, For. Res. Div., Ottawa ON, Tech. Note 76. 20 p.</ref> found that the most useful diagnostic features of the two spruces are in the cone; differences occur in the flower, shoot and needle, "but those in the cone are most easily assessed" (Horton 1959).<ref name="horton2" /> Coupé et al. (1982)<ref name="coup">Coupé, R.; Ray, C.A.; Comeau, A.; Ketcheson, M.V.; Annas, R.M. (1982). A guide to some common plants of the Skeena area, British Columbia. B.C. Min. For., Res. Branch, Victoria BC.</ref> recommended that cone scale characters be based on samples taken from the midsection of each of ten cones from each of five 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.<ref name="arn1">Arnott, J.T. (1974). "Germination and seedling establishment". pp. 55–66 in Cayford, J.H. (Ed.). ''Direct Seeding Symposium'', Timmins ON, Sept. 1973, Can. Dep. Environ., Can. For. Serv., Ottawa ON, Proc., Publ. 1339.</ref><ref name="arn2">{{cite journal | last1 = Arnott | first1 = J.T. | year = 1979 | title = Effect of light intensity during extended photoperiod on growth of amabalis fir, mountain hemlock, and white and Engelmann spruce seedlings | journal = Can. J. For. Res. | volume = 9 | issue = 1 | pages = 82–89 | doi=10.1139/x79-014| bibcode = 1979CaJFR...9...82A }}</ref> But, if an extended photoperiod is provided for Sitka spruce, seedlings become unacceptably tall by the end of the first growing season<!-- (Arnott, unpublished data, cited by Yeh and Arnott 1986) -->.<ref name="yeh" /> 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).<ref name="yeh">{{cite journal | last1 = Yeh | first1 = F.C. | last2 = Arnott | first2 = J.T. | year = 1986 | title = Electrophoretic and morphological differentiation of ''Picea sitchensis, Picea glauca,'' and their hybrids | journal = Can. J. For. Res. | volume = 16 | issue = 4| pages = 791–798 | doi = 10.1139/x86-140| bibcode = 1986CaJFR..16..791Y }}</ref> 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).<ref name="yeh" /> 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)<ref name="yeh" /> 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,<ref name="alex">Alexander, R.R. (1987). Ecology, silviculture, and management of the Engelmann spruce–subalpine fir type in the central and southern Rocky Mountains. USDA, For. Serv., Washington DC, Agric. Handb. 659. 144 p.</ref> 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 [[Hardiness (plants)|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),<ref name="nob">Noble, D.L.; Ronco, F. (1978). Seedfall and establishment of Engelmann spruce and subalpine fir in clearcut openings in Colorado. USDA, For. Serv., Rocky Mountain For. Range Exp. Sta., Res. Pap. RM-200. 12 p.</ref> for instance, considered that seedlings four to five years old, or 8&nbsp;cm to 10&nbsp;cm tall, warranted the designation "established", since only unusual factors such as [[Phacidiaceae|snow mold]], [[Wildfire|fire]], [[Disturbance (ecology)|trampling]], or predation would then impair regeneration success. Eis (1967)<ref name="eis">{{cite journal|author=Eis, S. |year=1967|title= Establishment and early development of white spruce in the interior of British Columbia|journal= For. Chron.|volume= 43|issue=2|pages=174–177|doi=10.5558/tfc43174-2|doi-access=free}}</ref> 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 cutting|shelterwood felling]] in subalpine Alberta, dominant [[Regeneration (biology)|regeneration]] averaged 5.5&nbsp;cm in height in [[Scarification|scarified]] blocks, and 7.3&nbsp;cm in non-scarified blocks (Day 1970),<ref name="day2">Day, M.W.; Rudolph, V.J. (1970). Development of a white spruce plantation. Michigan State Univ., Agric. Exp. Sta., East Lansing MI, Res. Pap. 111. 4 p.</ref> possibly reflecting diminished fertility with the removal of the A horizon.