white spruce

LC - Least Concern

N5 - Secure

SNR - Unranked

not listed

FACU - Facultative upland

FACU - Facultative upland

FACU - Facultative upland

White spruce is a large, moderately slow-growing, evergreen, coniferous tree. It rises on a single trunk from a taproot, shallow horizontal roots with sinker roots, and shallow fibrous roots. It is moderately long lived, often surviving 100 to 250 years, with older individuals reaching 300 years of age. In Minnesota mature trees are usually 40′ to 60′ tall and up to 24″ in diameter at breast height. The tallest trees may be more than 100′ tall and 33″ in diameter.

The crown is narrowly cone-shaped, relatively uniform, and dense. In open areas the crown extends well down the trunk. In crowded areas the lower branches are self-pruning and the crown is limited to the upper half of the tree. The trunk is straight and distinct to the top of the tree.

The bark on young trees is light gray or light grayish-brown and smooth or slightly rough at first. It soon breaks into small, flaky scales. On mature trees the bark is gray, darker, and broken into thin, irregular scales. The scales are closely appressed and do not curl outward at the top and bottom. On older trees the scales are thick. The inner bark on mature and older trees is salmon pink and silvery.

The branches are mostly horizontal and whorled, with each whorl representing one year of growth. The tree’s age can be determined by counting the number of whorls from the bottom up. Smaller branches develop between the whorls. Upper branches are ascending. Lower and middle branches are horizontal or slightly drooping.

First year twigs are slender, yellowish-brown, shiny, and hairless. They are sometimes covered with a whitish, waxy coating (glaucous). They do not hang downward (droop). Second year twigs are brown and may be tinged with orange, pink, or purple. The buds are egg-shaped, ⅛″ to ¼″ long, and rounded at the tip. They are covered with many overlapping, orangish-brown, scales.

The needle-like leaves are bluish-green and are arranged in a tight spiral pattern around the twig. They spread in all directions from the twig. They are evergreen and remain on the tree 7 to 10 years. When crushed they emit a pungent odor that has been compared to cat’s urine. Each needle is ⅝″ to ⅞″ long and 1 ⁄32″ to 1 ⁄16″ wide. It is borne singly on a peg-like base that persists after the needle is shed. It is stiff, sharply pointed, straight or slightly curved, 4-angled, and square in cross section. It rolls smoothly between the thumb and forefinger. There are two whitish lines of minute openings (stomata) on each surface. Each whitish dot (stomate) is a pore surrounded by two glaucous guard cells. The guard cells control the size of the opening, allowing the exchange of gasses and water vapor.

Male and female cones are borne on the same tree. New cones are produced every year. Pollen (male) cones appear in the lower half of the crown. They are borne in groups at the base of one year old (second-year) twigs or singly near but not at the tip of the twig. They are red and succulent when they first emerge. Mature cones are dry, yellow, oblong, and 5 ⁄16″ to ⅝″ long.

Seed (female) cones appear in the upper half of the crown. They are borne on leaf axils or at the tip of one year old (second-year) twigs. They are green at first. As the cone becomes receptive the scales turn red to green and the cone becomes erect. At the time of pollination the cones are ¾″ to 1″ long and the scales are widely spread. They reach full size in late June to early July, and maturity by August or September. Mature cones are brown, cylinder-shaped, 1″ to 2⅜″ long, and hang downward. The scales are fan-shaped, widest near the tip, light brown, thin, and flexible. The margins of the scale are untoothed. Most seeds are shed in September. Seed cones can remain on the tree one or two years after most of the seeds have been shed.

Pollination takes place from May to early June. Male cones shed pollen then soon turn brown and fall away. Female cones mature in August of the first year and disperse most of the seeds in September.

30′ to 60′

The champion white spruce in Minnesota is on public property near Littlefork, in Koochiching County. In 1974 it was measured at 133′ tall and 126″ in circumference (40″ in diameter), with a crown spread of 40′.

Balsam fir (Abies balsamea var. balsamea) has a narrowly pyramidal crown. The bark is not scaly but smooth except for raised resin blisters. The needles are longer and are attached flush with the twig. They are flattened in cross section, and do not roll easily between the thumb and forefinger. On lower branches they are often twisted at the base causing them to appear two ranked. The female cones are much longer, 1¼″ to 3⅛″ long.

Black spruce (Picea mariana) has a narrow, spire-like crown with short branches. The middle and lower branches are greatly drooping with upturned tips. The twigs are covered with short, stiff hairs. The needles are shorter and blunt tipped. Mature seed cones are shorter, no more than 1¼″ long.

Moist or dry. Moderately shade tolerant.

Early May to early June

eastern spruce budworm (Choristoneura fumiferana)

White spruce is the provincial tree of Manitoba.

Sources

2, 3, 4, 5, 7, 8, 28, 29, 30.

Native

Common

Four subspecies have been described, but these are not accepted my most taxonomists.