Softwoods II: European larch and Douglas fir

The heavier, coloured conifers

Larch and Douglas fir sit at the dense, resinous end of the softwoods profiled for Europe. Both have coloured heartwood and a very abrupt transition from earlywood to latewood, which helps identification. Their data need extra care with region: Douglas fir in Europe is a plantation tree, while most published reference data come from North America.

European larch (Larix decidua)

European larch is Europe's only deciduous conifer, growing in the mountains of central and eastern Europe. The heartwood is yellow to reddish brown and darkens in light; the sapwood is narrow, mostly under 2 cm (Germany) and nearly white.

Handling points from the profile:

• Drying: larch needs careful drying, with more checking and deformation than pine. No verified European schedule exists, so run trial charges.
• Resin and iron: resin gums up blades; iron contact discolours the wood (iron-tannin reaction). Test coatings, because earlywood/latewood contrast can cause adhesion problems.
• Specification: keep to DC 3-4 for heartwood; forum claims of higher durability are anecdotal. Exclude sapwood from exterior grades.

Douglas fir (Pseudotsuga menziesii)

Douglas fir is non-native in Europe, covers about 830,000 ha and is plantation-grown; many southern German stands are about 40 years old. European and North American (NA) Douglas fir are not the same product.

The two shrinkage rows have different bases and cannot be compared directly.

Juvenile wood

A Baden-Wuerttemberg review attributes about 20 rings around the pith to juvenile wood. In one Slovenian study of about 70-year-old trees (six trees, two sites), averages were:

Worked example 1 (juvenile versus mature). Juvenile density is 380 / 507 = 0.75, about 25 % lower. Taking the lower mature stiffness, 11.9 GPa, juvenile wood at 6.8 GPa is (11.9 - 6.8) / 11.9 = 0.43, about 43 % lower. Grade by ring width and pith position, not only knots. This is one small study with internal inconsistencies: use it for direction, not design values.

Durability

Mature heartwood resists decay better than sapwood or spruce. In the Slovenian brown-rot test (mass loss) spruce lost 35 %, Douglas fir sapwood 26-27 % and mature heartwood 14-16 %.

Worked example 2 (relative loss). Using the middle of the heartwood range, 15 %, heartwood lost 15 / 35 = 0.43, about 43 % of the spruce loss. Even so, European heartwood is DC 3-4: for ground contact specify treatment or protective design.

Drying and finishing

Kiln carefully to avoid resin outflow. US guidance (North America, softwoods generally) says stress reversal does not occur until 15 to 20 % MC, so do not drastically increase the wet-bulb depression before then. Teknos recommends knot sealer or an antistain primer.

Checklist: telling these conifers apart

• Larch: very abrupt ring transition, dark reddish-brown heartwood, narrow near-white sapwood.
• Douglas fir: very abrupt transition, orange-brown to yellowish-brown heartwood, a distinct resinous odour.
• When buying Douglas fir, ask whether it is European or North American.

Key points

• Larch is dense (0.60 g/cm3, Germany), resinous, DC 3-4, with non-durable narrow sapwood.
• Dry larch more gently than pine and test coatings; keep iron away from wet wood.
• Keep European plantation and North American Douglas fir data apart.
• A large juvenile core means lower density and stiffness (380 kg/m3, 6.8 GPa in one study).
• European Douglas fir heartwood is DC 3-4; do not rely on it alone in ground contact.