Softwoods I: Norway spruce, Scots pine and silver fir

Why start with the conifers

Norway spruce is the workhorse softwood of European sawmilling; EUFORGEN calls it the most economically important conifer in Europe. In this course every figure carries its region and basis (moisture content, clear specimens or graded timber), because a number means little without that label. Values are European unless stated.

Norway spruce (Picea abies)

Spruce is pale, with heartwood and sapwood of the same colour once dry. Typical European figures:

Swedish Wood puts the scatter within one wood type at about +/-20 % for density and +/-40 % for strength. Most European values come from small clear specimens, not graded lumber.

Worked example 1 (scatter). Mean density 440 kg/m3 with +/-20 % gives 440 x 0.8 = 352 to 440 x 1.2 = 528 kg/m3. Bending strength 75 N/mm2 with +/-40 % gives 45 to 105 N/mm2. Sort by origin and ring width.

Storage. A 2023 Silva Fennica study of 24 spruce logs at two Austrian sites found first sap stain after 14 days in summer storage at the higher site (864 m), but 82 to 97 days for spring-stored logs. Process summer-felled logs quickly (a small study: a warning, not a rule).

Drying. Teknos and LWF Bayern say spruce dries easily; CIRAD warns of a high checking risk. CIRAD's schedule ("for information only", thickness up to 38 mm):

Worked example 2 (wet-bulb depression). The wet-bulb depression is dry bulb minus wet bulb: 60 - 56 = 4 K at green, 80 - 61 = 19 K at 15 % MC, so it grows by 15 K. Validate any schedule on your own kiln.

Scots pine (Pinus sylvestris)

Pine is easy to recognise: light reddish-brown heartwood against pale sapwood, a resinous smell and resin canals. Pine rarely has pitch pockets; spruce usually does (Swedish Wood).

• Density 470 kg/m3 (12 % MC, Sweden, small clear); NIBIO's general European range is 330-510-890 kg/m3.
• Heartwood DC 3-4; sapwood is highly susceptible to fungi and blue stain, so dry soon after sawing.
• Clear versus structural: bending strength is 87 MPa for small clear Swedish pine but 40.5 N/mm2 for Norwegian structural planks. Never mix the two scales.

Swedish Wood gives green moisture content for conifers: heartwood 30-50 %, sapwood 120-160 %. Moisture content here is water mass divided by oven-dry mass.

Worked example 3 (water to remove). Take 100 kg of oven-dry wood and the midpoints, 140 % (sapwood) and 40 % (heartwood). Drying to 12 % MC leaves 12 kg of water. Sapwood must lose 140 - 12 = 128 kg, heartwood 40 - 12 = 28 kg. Sapwood-rich pine therefore needs 100 kg more water removed per 100 kg of dry wood.

Silver fir (Abies alba)

Silver fir looks like spruce, but the Wood Database reports no resin canals (only occasional traumatic ones). Its density is in the same broad range as spruce (Teknos 0.43-0.48 g/cm3, 12-15 % MC), but sources disagree on stiffness (8.3 to 14.3 GPa) and on drying (Teknos easy, CIRAD high checking risk). Durability is DC 4 at best: dry or protected use only. Do not assume fir is stiffer or weaker than spruce.

Checklist: receiving a conifer lot

• Record origin and ring width, not just the species name.
• Dry sapwood-rich pine promptly.
• Confirm spruce versus fir with a lens before mixing them in a kiln charge.

Key points

• Spruce: 0.46 g/cm3 (Bavaria, 12-15 % MC), DC 4, strength scatter +/-40 %.
• Pine: sharp heartwood/sapwood contrast; sapwood holds far more water and blue-stains quickly.
• Fir has no resin canals; its data differ by source, so test your own material.
• Never mix clear-wood with structural figures, or shrinkage bases.