Douglas Fir has the edge when it comes to structural stability. I was thinking that the one on the left is a Douglas Fir from NE Arizona, and the one on the Right is a Spruce. There are so many different conifers it can be difficult. If you need to span a long distance or hold up a substantial amount of weight, Douglas Fir may be the lumber … I found that an 8X12X24ft #1 grade douglas fir beam would handle the same load at 1/3 less cost to the lam. It has a consistent density that allows for measurable span tables. The beam has been in place for 13 years now with no perceptable deflection. In short, the doug fir handles loads well-can't tell you about spruce. SPF – Douglas fir, spruce, or white pine SYP – Southern yellow pine SYF – Pine and fir. However, there are some clear indicators to determine a spruce from a fir. … If you do not see these markers, it is still possible that you are not purchasing whitewood that comes from the tulip tree. How do you tell the difference between spruce and fir trees. user-7009029 01/12/2018 Douglas-fir are not true firs. However, it is somewhat more difficult to find out which species of spruce or fir. There was some twisting, but that's the way trees are.