No, not really. This is by far the most common misconception non-woodites have about wood when they browse the aisles at the Big Box. And you have to ask "Well, why do they call them that, anyway?"
The most likely reason has to do with logging back in the old days. Farmers clearing their land in the east back in the 18th and 19th centuries would have encountered a great range of deciduous trees, scientifically categorized as angiosperms, those that have broad leaves, true flowers, have their seeds enclosed in a fruit, and shed their leaves in the fall (they are deciduous). The soil of the northeastern part of North America was typically thick and rich in the valleys, because of the ancient age of the Appalachian mountains and the temperate climate that inhibited frequent and large wildfires. The result was a widely ranging deciduous forest, and the varied species that made them up consisted of a large percentage of oak, hickory, and maple. The oaks and hickories were spread far and wide by animals that loved the mast (nuts) produced by them, and recycled them periodically in their ramblings.
|Seed cases, or samaras, of Norway Maple (Acer platanoides).|
Now, the folks that were out there clearing all these oak, hickories, and maples with axes and two-man saws, and shaping them for utensils with draw knives, found them pretty tough customers. The oaks and hickories, in particular, are heavy woods, going from 60 to 70 pounds per cubic foot (960 to 1120 kilograms per cubic meter). And the folks down south, who were harvesting live oaks for ship timbers and bows, really had a chore...live oak is the heaviest hardwood in North America, running well over seventy pounds per cubic foot (1120 kg/m3) when green.
|Ahhhh...cottonwood cool. |
|Yes, white pines (Pinus strobus) get big.|
But as we spread out into the rest of the country, our common man's classification system started to break down. As we harvested the Lake States to build Chicago, Milwaukee, and Detroit, we found that aspen was a pretty "soft" hardwood. And early settlers out west found abundant red alder, a light-weight hardwood that has somewhat the look, weight, and feel of Western redcedar.
But the folks harvesting the southern U.S. were really confused, because not only did they find the super-light "hardwood" species basswood and cottonwood, but they found some of the continent's heaviest softwood, of which four species, longleaf, slash, shortleaf, and loblolly, are now marketed under the unifying moniker of Southern Yellow Pine. Southern pine not only has a relatively high density when dry (try driving a nail into a southern pine stud with ten or more growth rings per inch, and you'll bend a few nails) but it also has a resinous "pine tar" that served navies well in the wooden ship days (naval stores were buckets of pine tar and turpentine that were used to caulk seams and cracks in hulls, and seal wood from moisture), and this pine tar, or "pitch" retained moisture in the stem and added even more weight to the wood. Resultantly, old southern pine trees could yield pitch-filled logs that could weigh as much as the lighter oaks even though the specific gravity, the weight of a wood species relative to the weight of water, is quite a bit lower than those tough old oaks and hickories.
|Microscopic view of southern pine. Koch, P. 1972a. Utilization of the southern pines. I. The raw material. USDA Forest Service Agricultural Handbook No. 420. 733 pp.|
On the other hand, the moisture is transported in hardwoods through larger diameter pores, or vessels. These come in different shapes, sizes, and locations in the different hardwood species, and this variation contributes to the woodworker's sense that certain hardwoods are rough, or "hard" to machine.
|Microscopic view of white oak. http://classes.mst.edu/ide120/lessons/wood/cell_structure/index.html|
Nowadays, wood "hardness" is complicated (or, depending on your point of view, simplified) further by hardness standards developed and adopted for wood grading for different products. The most commonly used hardness metric used in the various wood industries is the "Janka-ball" hardness test, which is the amount of pounds-force (lbf) or newtons (N) required to imbed a .444″ (11.28 mm) diameter steel ball into the wood to half the ball’s diameter, as specifed in ASTM Standard D143. These standardized results are then used as a relative measure of the hardness of a wood, the results of which are fairly easy to find, such as at this Wikipedia page. If you browse the Janka hardness table, you'll see that the hardest woods are tropical hardwood species, but then below that, softwoods and hardwoods are relatively randomly mixed.
So, now you know the rest of the story...that hardwoods aren't necessarily hard, and softwoods aren't necessarily soft, and why. So next time, don't go wandering into Home Depot and start asking questions that make you look like a wood neophyte; do what I do, and pretend to actually know what you're talking about. :-)