by Eric Flint
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In temperate climates, cut wood displays annual growth rings. The early (spring) wood is softer and lighter, while the late (summer) wood is harder and darker. (The late wood contains more wall material.) The difference is pronounced in some species, subtle in others. (Desch 16, 26; EB11/Timber) In the seventeenth century, it was already known that the age of a tree could be determined by counting the number of rings (Evelyn), and of course one could readily deduce that a tree with a low density of rings was growing rapidly. Strength is related to the growth rate; there is a rate at which strength is optimized. (Desch 56)
To a botanist, a tree is mature when it starts producing seed. The white cedar can drop cones when it is merely six years old, but it is most prolific when it is over seventy five years old. Likewise, a white pine can bear cones at five years old, but good production comes several decades later. The paper birch, a deciduous tree, starts seed production at age fifteen. (Error! Hyperlink reference not valid.) Oaks don't produce acorns until they are twenty years old.
To a logger, a mature tree is one which can be cut into merchantable timber, which usually means that it is over thirty centimeters diameter (the smallest base diameter for lumber) at "breast height" (1.3 meters). A "pole" has a diameter of at least seven centimeters, and can be used in paper production. A tree is considered "overmature" when decay becomes substantial. "Snag" is deadwood which is still standing (firewood in the eyes of neighborhood farmers, but an important wildlife microhabitat so far as environmentalists are concerned). (Wikipedia).
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It isn't surprising that wood is a useful structural material because the successful growth of forest trees is dependent on the physical properties of wood. From an engineering standpoint, wood is a bundle of cellulose fibers. If stretched along the grain, it does quite well (the tensile strength of spruce is about 17,000 p.s.i.). On the other hand, it is weak if compressed in the same direction, which causes the fibers to buckle (for spruce, the compressive strength is 4,000-5,000 p.s.i.). The lateral (across the grain) strength of wood is rather low, whether it is compressed or tensed (a few hundred p.s.i.).
Wood is also quite stiff (stiffness is the resistance to bending); it has a Young's modulus of about two million p.s.i. Both the tensile strength and stiffness of wood compare favorably, on a by weight basis, to that of steel.
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Generally speaking, the denser the wood of a particular tree, the greater its average strength (Desch 147). The specific gravity (density relative to that of water, which is 62.4 pounds per cubic foot) of the actual wood material is actually about 1.4 or 1.5. Timber floats because it contains a lot of air, and some timbers have more air space than others. The specific gravity of timber varies a great deal:
balsa 0.1
spruce 0.45
oak 0.7
lignum vitae 1.1
(Gordon, 157)
While an increased density has a favorable effect on strength, it has an unfavorable one on transportabity; the denser the timber, the less floatable it is.
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The principal dimension of lumber ideally runs parallel to the grain. Any slope reduces the bending strength, stiffness and impact resistance. A slope of only 1 in 25 reduces bending strength by 4%, stiffness by 3%, and impact resistance by 9%. (Desch 65).
Wood contains water and, the lower the moisture content, the greater the strength. Air-dry wood (moisture content about 12%) has about twice the strength in bending and endwise compression as it did prior to seasoning, and if kiln-dried (moisture content 5%) the factor is threefold. (Desch 168-9).
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A tough wood is flexible; it bends instead of breaking. The Encyclopedia Americana "Wood" article (EA/Wood) notes that hickory and ash are flexible while hemlock and pine are brittle. However, a tough wood must also be strong. EA/Wood says that elm and hickory are both tough. High moisture content increases toughness. (Desch 168-9)
Hardness is also different from strength, and it is something of a mixed blessing. The harder woods are less likely to be scratched or dented, but they are harder to saw across the grain. EA/Wood classifies twenty nine woods according to their hardness.
Wood is split by cleavage along the grain, and EA/Wood gives information on the relative splitting qualities of eighteen woods.
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The durability of a wood is its resistance to decay caused by fungi and bacteria. EA/Wood classifies forty seven woods according to their durability. Woods can be treated with preservatives; the tradeoff is between a cheap wood of low natural durability treated periodically with preservative, and an expensive wood of high natural durability.
In general, these decay organisms require warmth and moisture (wood moisture content over 20%) to do their work. That is one reason for seasoning (drying) wood. Good ventilation also helps to inhibit fungal growth (Desch 248).
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Color is of course relevant to the marketability of ornamental woods used in furniture. However, dark woods tend to be more durable, because the same chemicals which provide the coloration may also be part of the tree's defenses against microbial attack. Resins, gums and latexes seal the attackers off from oxygen, while tannins counterattack them.
Contemporary European Trees
Trees have preferences as to soil and climate, and what thrives in one place may languish somewhere else. Oak, for example, didn't grow particularly well in the Norwegian forests, whereas Norway was an excellent source of fir. (Tossavainen 1.1)
The woods used in Western Europe during the Middle Ages and the Renaissance included alder (German erle), apple (apfel), ash (esche), beech (buche), birch (birke), boxwood (buchsbaum), cedar (zeder), cherry (kirsche), chestnut (katainien), cornel cherry (kornelkirsche), cranberry schneeball), cypress, ebony (ebenholz), elder (holunder), elm (ulme), fir (tanne), hawthorn (weissdorn), hazel (haselnuss), holly (stechpalme), hornbeam (weissbuche or hainbuche), juniper, larch (larche), laurel (lorbeer), linden (linde), maple (ahorn), oak (eiche), pear (birne), pine (kiefer), plum (pflaume), poplar (pappel), roeswood, rowan (eberesche), service (speierling), spindle (pfaffenhuten), spruce (fichte), sycamore (bergahorn), thorn (schedorn or schawrzdorn), tartary dowood (hartriegel), wanut (walnuss), whitebam, willow (weide), and yew (eibe)(Halstead/Wood). The above list probably omits a few imported luxury woods.
I don't have a chronology of the introduction of forest trees to Germany. However, Nesbet's British forest tree list may be of interest:
Pre-Roman: oak, beech, Scots pine, birch, ash, mountain ash, Scots elm, sallow, aspen, alder, yew, hawthorn.
Introduced by the Romans: plane, chestnut, walnut, English elm, lime (linden), alder, poplar, box, and many ornamental and fruit trees (mulberry, service, hazel, medlar, apple, pear, prune, cherry, peach, apricot, quince and rose) which didn't fully develop .
Before end of fifteenth century (15C): hornbean, sycamore, willow, poplars (white and grey).
16C: spruce, walnut (re-introduced), laburnum, juniper, holly, holm oak, stone or cluster pine, alderberry, viburnum, mulberry.
17C: silver fir, maple, plane (re-introduced), horse-chestnut, larch (1629), robinia, buckthorn.
The trees brought to Britain only in the eighteenth or nineteenth centuries include Weymouth, maritime, cembran and pitch pines, service, cedar, Austrian, yellow and Jeffrey pines, Normann's and Douglas firs, deodar, and eucalyptus.
European Exploitation of Exotic Trees
Down-time Europeans are well aware that there are many new tree species to be found in Africa, Asia and the Americas. However, it was only economical to ship timber by water. Hence, the only tree species likely to make major contributions to the timber trade are those found near the coast, or the banks of navigable rivers.
For the woods of other trees to be exploited, either they must be harvested locally, and their products exported, or the seeds must be transplanted to Europe. Orange trees were brought from India to Europe (protected, if need be, by growing them in orangeries)
and re-exported to the Americas. The American Robinia (black locust) was brought to Germany in 1638 (Fernow 62).
Successful transplantation, of course, requires suitable soil and climate conditions, and, even then, it may be many years before the newcomer is mature enough to be commercially exploited. These transfers tend to be either latitudinal (e.g., South America/Africa, or North America/Europe), or between equivalent north/south regions, because the climate has to be the same. New World trees which found homes in the Old World include the Para rubber and cinchona trees. Likewise, the New World was enriched with Old World trees, including coffee, apple and coconut (Robinson).
America's potential as a source of wood and wood products was recognized by Thomas Harriot (1587)(Cox 11). European exploitation of American forests began prior to the RoF. The James River colony began shipping clapboards to England in 1607, and the first American sawmill was built near Richmond in 1611. The Dutch had three sawmills in operation in New Amsterdam as of 1623. New England followed suit soon thereafter; its first sawmills appeared in the early 1630s, one on the Neponset River (Massachusetts) and the other on the Picataqua (New Hampshire). However, lumbering for export was on a small scale until the Dutch War of 1654, which blocked British access to the Baltic. (Cox, 14-15, Cronon, 109-10)
Certain Asian (sappanwood, Caesalpinia sappan, native to India, Malaya and Sri Lanka), Brazilian (brazilwood, Caesalpinia echinata), and Yucatan (logwood, Haemotoxylum campechianum) trees were valued because their heartwoods contained brilliant red dyes. In the 1600s, fifty tons of logwood was worth in excess of 1000 pounds sterling. (Armstrong)
Lignum vitae (gaiac) is highly durable, and has been used in "sheaves for blocks" ((Baker, 226). It was exported by Martinique (settled in 1635) to France in the seventeenth century; 35,000 metric tons were shipped in 1672 (Richards, 433).
Other woods exported to Europe, albeit in small quantities for high-end furniture, included mahogany (used in the Armada ships), rosewood, ebony, teak and sandalwood. (Elliot, 12; Edlin, 218) There was limited trade in ebony beginning in the fourteenth century, rosewood in the fifteenth, and Caribbean mahogany in the sixteenth (Halstead/Trade).
Exotic (or once exotic) trees valued for plant parts other than the wood (e.g., fruit, seed, flowers, leaves, roots) include coffee, cacao (source of chocolate), nutmeg, clove, and various citrus trees.
Grantville Trees
West Virginia trees include red spruce, hemlock, white oak, yellow poplar, laurel, chestnut oak, walnut, cherry, white pine, persimmon, sassafras, sycamore, hickory, chestnut, locust, maple, beech, basswood, dogwood, and pawpaw. It is uncertain how many of these passed through the Ring of Fire. Of course, those that didn't are still available (if indigenous to America) in the down-time West Virginia!
There are also likely to be some ornamental and fruit trees, of more exotic origin, in Grantville yards and farm plots.
It is interesting to note that both Marion County, West Virginia and modern Thuringia, Germany are in USDA hardiness zone 6 (Plant Hardiness). However, because seventeenth century Thuringia is experiencing the Little Ice Age (albeit not the worst of it), some trees which throve outdoors before the RoF might need to be moved indoors during the winter.
Exotic Trees Known in Grantville
The encyclopedias of Grantville may provide motivation to seek out economically interesting trees in other parts of the world. A few examples follow.
Balsa ( Ochroma pyramidale) is found, scattered, in rainforests in much of Latin America. The tree is ready for cutting at 6-10 years. Balsa is the lightest commercial wood. In the seventeenth century, it was used in native rafts. Centuries later, it was one of the component woods of World War II's "Wooden Wonder." It is the premiere material nowadays for model airplanes.
Redwood ( Sequoia sempervirens) is lightweight and resistant to both fire and decay. It is found on the Pacific Coast of California and Oregon. Seeds of the sequoia were planted in England in 1854. A century later, some of the trees had reached a height of 150 feet. (Baker, 48).
Greenheart ( Chlorocardium rodiei) is noted for its strength (density 61 pounds per cubic foot), and its resistance to marine organisms. It is found in British Guiana. (EB11, "Greenheart").
Teak, because of its strength and durability, is a favored wood for the planking of ships. Indeed, it can be laid as decking over iron plates, since oils in the wood help preserve the iron. Some may question its inclusion in this section, since teak has been used in Asia for over 2,000 years. While there was trade between Europe and the teak-producing areas of Asia (India, Burma, northern Thailand) in the seventeenth century, "the first reference to teak was in the second half of the eighteenth century" (Teak). Kew Gardens didn't obtain its first specimen of Tectona grandis until 1777 (Aiton 57).
Numerous rubber-producing trees are discussed in my article "Bouncing Back" (Grantville Gazette, Volume 6).
Contemporary (Down-Time) Wood Products and Their Uses
Firewood. Regardless of the species of tree, logs which are equal in weight and moisture content have about the same energy content, ranging from 10 megajoules/kilogram for "green" wood to 20 for kiln-dried wood. However, since tree species vary in the density of their wood, they also vary in their heating potential per unit volume.
As populations increased, firewood demand rose, and wood had to be brought in from greater distances. In London, the price of wood in 1600-1650 was in the range of 6-9 grams of silver per million BTUs, up from 4-6 in 1400-1550. Coal, in 1500-1650, sold for 2-4. (Allen 8) Outside London, the price differential was less acute (Unger, 7).
This price differential ultimately encouraged the use of mined coal as a residential heat source, in place of firewood or charcoal. Anthracite coal has a heat content of 26-33 MJ/kg, while that of bituminous coal is 21-30.
Firewood wasn't needed just for residential use. Wood-burners included smiths, bakers, barber-surgeons (who kept bathhouses), brickmakers, glassworkers, saltmakers, cutlers, dyers, potters, founders, and innkeepers (Warde 272, 300-1).
Charcoal. An alternative to burning firewood is to use charcoal. Charcoal may be derived by pyrolyzing wood (heating it in the absence of oxygen, so it chars but doesn't burn). One metric ton of wood yields 150-300 kg charcoal, depending the moisture content of the wood and on kiln efficiency (Keita).
Charcoal's advantage as a fuel is that it "burns hotter and cleaner than wood." (Wikipedia). It has almost three times the energy content of an equal mass of wood. (Logan 127) Consequently, charcoal was the fuel of choice in the iron industry. (Cox, 15) A charcoal fire could achieve the temperature needed to smelt iron (1500 deg. C.). Charcoal is also the "fuel" element of gunpowder (because charcoal burns rapidly).
In 1603, Sir Henry Platt urged that coal could be charred to produce a product ("coke") analogous to wood charcoal. Coke was first used commercially in 1642, for roasting malt. The first use of coke in iron making was in 1709.
Still, even in modern times, some wood is used to make charcoal. Small branches and stems, which might otherwise be wasted, can be used for this purpose. (Edlin, 80)
Fencing. Logan (95) says that in the Middle Ages, fencing was the second most common use of wood (after firemaking). Palisades, used for temporary or outer defenses, were constructed by driving tree trunks vertically into the ground, without gaps, and then binding them together. One could also make anti-cavalry protection by diagonally emplacing stakes, sharpened at both ends, into an earthwork.
Other fences were used merely to restrict the movement of livestock or to establish property lines. The simplest such fence to build was the "zigzag" rail fence ("worm," "snake"). While economical of labor, it was wasteful of wood (Williams 69), and therefore was most popular in North America and perhaps in far northern Europe. The post-and-rail fence was more labor-intensive.
Lumber. Lumber is wood sawn into boards. The lumber, in turn, can be used to construct buildings, ships, furniture and other articles.
Machinery parts—gears, screws, bearings,
and so forth—can be made from stout woods such as dogwood (Tree Safari). In the nineteenth century, Peter Mitterdorfer constructed a typewriter almost entirely out of wood! However, the parts will wear out more rapidly than metal ones.
Barrels. Barrels are not just a medium of storage, but also one of transport. A barrel can be rolled.
Log cabins. While the standard English and Dutch construction was sparing in its use of wood, that wasn't true in the more forested parts of Europe, including southern Germany, Sweden and Finland. Immigrants from those regions were the first to construct log cabins in America, from 1638 on. (Lillard, 15).
Saps. Saps are plant fluids. In the seventeenth century, the Europeans collected a type of sap (pine resin) from pine trees. The raw resin was separated by distillation into volatile liquid (turpentine) and non-volatile solid (rosin, pine tar, pitch) components. Turpentine was used medically, or as a solvent in paint, while pine tar was used as a waterproofing agent, especially on ships. Resins were also used directly as coatings and adhesives. Tar and turpentine were considered strategic materials, "naval stores."
