In conifers with pre-formed shoots (buds that form at end of growing season in preparation for next year's branch development), one can count "whorls" of branches. These are the strongly developed clusters of branches at regular intervals up the stem, forming what foresters call "nodes" (the clusters of branches, usually 3-4 radiating outward) and "internodes" (the branch-free sections of stem). Douglas-fir and most of the pines fall into this category. Since Douglas-fir is so common on both sides of the Cascades, it is a good one to become familiar with.
Simply count the nodes from the ground up, as each represents 1 year of growth. This works well until the trees have reached about 20-30 years of age, when most plantations will be in a "stem exclusion" or "dark understory" stage. At this point, no new trees are really establishing. Deer and elk have minimal nutritious understory forage at this point, as it has been "shaded out". They will, however, use this stage for hiding and resting cover, so keep a mental map of these areas as well.
What I personally look for are wetland openings and clearcuts in the 5-10 year age class. The 5-10 year old clearcut will have had time for lots of shrub and herb development, but the crop trees have not "closed crowns" yet to shade out these valuable plants. Look for ample space between trees, and lots of grasses, herbs, and shrubs. These are good feeding areas, and tree age is really only a surrogate measure for the abundance of these forage variables.
If you really, really want to go the extra step, pick up a copy of Pojar and MacKinnon's "Plants of the Pacific Northwest Coast", and combine it with a reference on preferred forage plants for deer or elk. If you are an east side hunter, then Parish, Lloyd, and Coupe's "Plants of Southern Interior British Columbia" is a functional reference. It is worth knowing what your critters are eating!
Best of luck this fall!
