Timber and lumber are basically wood and they mean the same thing.
Timber/lumber is wood used as building material, or a tree considered as a source of wood instead of as a plant. It can also mean a beam or a person who is a timber, thought the person meaning I've not heard of much.
Answer
Timber is usually the wood as it grows or is felled. Lumber is the wood after it is milled and ready for use.
how is lumber and timber the same thing
Timber is to lumber as quarry is to stone because timber is where cut lumber comes from and a quarry is where cut stone comes from.
People buy "timber" as an investment. Timber is uncut lumber. People buy lumber because it is an excellent building material and is renewable.
Lumber
The harvesting and sale of raw lumber\wood (a.k.a. Timber)
Lumber jacks.
Pressure treated timber is timber impregnated with chromated copper arsenate under pressure and vacuum cycles. These preserve the timber from various fungicides that would normally eat the timber reducing its life-span.
A lumber is that person who falls timber. The activity is called lumbering.
Lumber or timber.
lumber
Laminated veneer lumber
iron and lumber [timber]