It has to do with the rate of growth. This wood is from trees that grew slowly and evenly.
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The private limited company Hasslacher Drauland Holzindustrie GmbH is a family-owned enterprise founded in 1901. For generations, we have been processing high-quality, slow-grown wood from the Alpine mountain forests in the Austrian province of Carinthia, near the Italian border. With a staff of 250 people and more than 600,000 cubic metres in annual conversion, we are one of the largest players in the Austrian timber industry.

http://www.hasslacher.at/index.php?Sel=94&Lang=en

Fein gewachsen = wood of good growth, close-grained wood, narrow-ringed wood

grobjährig: schnell gewachsenes Holz mit breiten Jahresringen. Meist weiches Holz (Beispiel Pappel oder Weide).

Feinjährigkeit: Wenn die Jahresringe eng und gleichmäßig beieinander liegen, spricht man von "feinjährigem Holz". Dieses ist qualitativ besonders hochwertig.

http://www.fertighaus.de/f_haus/info/holzabc.htm

feinjährig = narrow-ringed, slow-grown, close-grained
Feinjährigkeit = closeness of the annual rings, close grain

Wörterbuch der Holzwirtschaft

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In the case of the ring-porous hardwoods there seems to exist a pretty definite relation between the rate of growth of timber and its properties. This may be briefly summed up in the general statement that the more rapid the growth or the wider the rings of growth, the heavier, harder, stronger, and stiffer the wood. This, it must be remembered, applies only to ring-porous woods such as oak, ash, hickory, and others of the same group, and is, of course, subject to some exceptions and limitations.

In ring-porous woods of good growth it is usually the middle portion of the ring in which the thick-walled, strength-giving fibres are most abundant. As the breadth of ring diminishes, this middle portion is reduced so that very slow growth produces comparatively light, porous wood composed of thin-walled vessels and wood parenchyma.

Wide-ringed wood is often called "second-growth," because the growth of the young timber in open stands after the old trees have been removed is more rapid than in trees in the forest, and in the manufacture of articles where strength is an important consideration such "second-growth" hardwood material is preferred.

The effect of rate of growth is, therefore, not the same as in the ring-porous woods, approaching more nearly the conditions in the conifers. In general it may be stated that such woods of medium growth afford stronger material than when very rapidly or very slowly grown. In many uses of wood, strength is not the main consideration. If ease of working is prized, wood should be chosen with regard to its uniformity of texture and straightness of grain, which will in most cases occur when there is little contrast between the late wood of one season's growth and the early wood of the next.

http://www.answers.com/topic/wood


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Note added at 1 hr 10 mins (2005-02-26 15:48:38 GMT)
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Q-Deck products are machined from slow grown (Predominantly Northern Scandinavian) and carefully selected softwood (European Redwood) to give a better looking and smoother finish.

http://www.qualitydecking.co.uk/why/page4/qpages2.htm

Selected slow grown wood has excellent tonal qualities, and is used for piano soundboards and violin and guitar bellies.

http://website.lineone.net/~rod_elliott/norwayspruce.htm


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Note added at 1 hr 12 mins (2005-02-26 15:50:43 GMT)
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Slow-grown timber might be better than slow-grown wood.