The ASTM testing standards are extremely important to the civil/structural engineer working on wood structures. But they are not very visible at the design level.
1) Offhand, I don't know the ASTM tests, but you can try asking someone over at the American Wood Council for specifics, awc.org, they have an email, a blog, and a phone number. They're a great source of information.
2) Massively significant, wood is a grown material, so testing is needed to establish confidence in what loads wood (lumber or timber) can safely support. The National Design Specification (Standard? I forget what S stands for), is released every four years or so, 2005, 2001, 1997, 1994, 1991, etc. It establishes safe stresses for wood design for most structural species (softwood, typically), including Southern Pine, Spruce Pine Fir, and Douglas Fir-Larch (the three most common structural grade species in the US). Since the forest folks are cutting the lumber faster and faster, growing them with chemicals or who knows what, the allowable stress values in lumber tend to decline every four years, meaning if you use old values, you are potentially unsafe. This has to do with the rate of production of the material and the quality of what is being cut down (old growth timber is now quite rare, and that stuff usually gets diverted to furniture or planking that people get to see anyway, not hidden inside a wall at the prices they want to charge for it).
3) As above, you need the testing (the NDS, not individual testing on the wood you're going to use on a project, it isn't like concrete where you take batches and test them every time you pour, wood typically doesn't have testing of material specific to the job), to design properly. The NDS is the critical reference for wood design in the US, the ASTM tests are behind the numbers in the NDS, no testing, no NDS, no wood structures stamped by a civil/structural engineer.
Bear in mind that the majority of wood structures for residential construction aren't quite engineered, they are designed under the International Residential Code, or similar, which has lists of material, species, and grade, and span limits, so you're required to use a 2x8 @ 16" o.c. to span say 14 feet, like that, but as long as your construction conforms to the tables, (called the prescriptive code) the structure is considered safe and doesn't need an engineer on it. If you have construction in places that does not meet the code, that is when you would want a structural engineer, (need a structural engineer) to tell you how to support the loads in that area. This is called "partial engineering" the engineer will look at the parts that don't meet the prescriptive code. You can also get some commercial structures to meet the prescriptive code as it is in the International Building Code as well, usually, this is pretty tough to do and they are designed with an engineer involved, and an architect making a mess of it, structurally. Wood isn't a hard material to work with or design with, but architects tend not to respect the 'conventional' spans and dimensions and appearance of a wood building, so you get long spans, tall walls, few shear walls, and other things that make it difficult to design quickly. Designing in wood takes time, attention, and skill. By contrast, a structure built according to the prescriptive code tends to have fewer openings, windows, doors, etc, interior walls that are closer together, and a structure that feels more like a house than a commercial building.
Answered By: dieyouevilfrustratingprogram - 10/13/2007