Diffuse-porous hardwoods I: beech, birch and sycamore maple

What "diffuse-porous" means

In diffuse-porous woods the pores are roughly the same size across the growth ring, so no pore ring is visible. Beech, birch, maple, poplar, alder, linden and hornbeam all belong here. They are mostly pale, fine-textured and hard to tell apart. Their shared weakness is low natural durability (class 5 or equivalent), so they are interior woods.

European beech (Fagus sylvatica)

Beech is the dominant broadleaf of central and western Europe, pale straw to pinkish brown with no sharp heartwood/sapwood boundary. Its rays are well visible on all surfaces.

Beech has a tangential/radial ratio near 2.0 (11.8 / 5.8 = 2.03) and large volumetric shrinkage, so it moves with humidity and tends to distort. The commercial problem is red heart, a brown-red core that forms where oxygen reaches the stem centre in older trees. It does not weaken the wood but is a colour defect, so sort logs for it at the yard. No source gave a frequency or price discount. No open European beech drying schedule was found; one small, inconsistent Slovak high-temperature study showed noticeable colour change and cup. Dust extraction matters: beech is a reported sensitiser.

Birch (Betula pendula and B. pubescens)

Birch is pale with little contrast between sapwood and heartwood. The numbers come from a Finnish thesis (261 trees):

• Basic density: 512 kg/m3 silver birch, 478 kg/m3 white (downy) birch.
• Density at 12-15 % MC: about 0.65 g/cm3 (0.51-0.83), Germany and Europe.
• Silver birch bending strength 114 MPa, white birch 104 MPa; heartwood class 5.

Worked example 1. Silver birch is denser than white birch by (512 - 478) / 478 = 0.071, about 7 %.

Context (Finland, 2000, not Europe-wide): plywood mills took about 84 % of mechanically processed birch, so sawn birch competes with plywood for the best logs.

Storage is the main risk. In a Latvian study of silver birch, logs at +18 C showed first discolouration after 6 days and all were discoloured after 23 days; at +6 C the first signs came after 17-18 days and all logs after 68-69 days. Sprinkling reduced discolouration in a Swedish trial. Dry birch gently where colour matters: high temperatures darken it.

Sycamore maple (Acer pseudoplatanus)

Maple is a high-value, small-volume line sold on its pale colour. Heartwood is mostly white to yellowish; the wood darkens and yellows in light. Rays are visible only on the radial surface (this is how it is separated from beech).

The datasets disagree on volumetric shrinkage, so quote a range. The Croatian study found maple more dimensionally stable than beech but softer (beech density about 10 % higher).

Prices (Croatia, 2019, one country and year): high-quality sycamore maple logs 140-320 EUR/m3 against 95-125 EUR/m3 for comparable beech. In a Slovenian auction analysis, figure alone did not guarantee a high price, but large figured logs did best.

Protecting colour. North American evidence on hard maple (a different species) showed that low-temperature schedules kept boards white and that stain rose with sticker moisture. Use dry, clean stickers, load promptly and test a schedule on a pilot charge.

Checklist: pale hardwood stack

• Beech or maple? Look at rays on the end grain and tangential face.
• Sort beech for red heart before sawing.
• Keep birch and maple logs cool, wet or processed fast in warm weather.
• Label all three as interior (class 5).

Key points

• Beech: about 0.72 g/cm3, tangential shrinkage near 12 %, T/R about 2.0, class 5.
• Birch: silver birch is about 7 % denser than white birch; warm-weather log storage discolours it within days.
• Maple's value is whiteness: protect it from log yard to kiln.
• Quote density and shrinkage as ranges and name the source and region.