The Trees Species List contains 2 sheets -- one of scientific and common names, and the other includes "T", "T/N", or "T/C" designations for each region. An explanation of the codes are as follows: T = tally species with a cover option These tree species must be tallied on plots where even one plant of this species is tree form, or evidence shows that there were plants of tree form (cutting, fire, etc). Tree form is defined as: a woody plant, having one or more perennial stems at least 3 inches in diameter and at least 16 feet tall at maturity (Resource Glossary). Where a species was designated T, but does not occur in tree form on a plot, a cover estimate will be made for that species instead of the tally measures. Examples: subalpine fir growing at timberline as krummholz, or shrub form peach leaf willow, both of which are typically tree form. C = cover species Although these species are often tree form, volume, growth, or mortality estimates in the traditional sense are not needed, or the need for volume estimates has never been demonstrated. However, the accounting of the area of these species is important ecologically. Example: Palo Verde, Tamarisk, and canyon oak are very tree-like, yet have never been quantified with traditional tally. N = not a tree for FIA These species should not be considered a tree for the national list because, although it may occur throughout a region, it is not commonly tree form. Serviceberry and jumping cholla. These types of species are showing up on a tree list because of some designation somewhere, e.g. PLANTS. They occasionally occur in tree form, but usually do not, and field visits over their entire range will be cost-prohibitive. Some of these species could even be hazardous to measure. N/A = not applicable No knowledge or experience with these species in a particular region. The Cover Species List is a short list of species that had a summary of "C" or "T/C." A species with some "C" designations, but no "T" designations were NOT added to the national list, which at this time is a list only of tree species tallied somewhere in the U.S. An option is allowed to not tally a species that is on the list if it only or usually occurs in shrub form in a particular region. At this point, the "C" designation is an academic exercise -- there is no methodology or intent to inventory "C" species at this time, but the information may be useful for further discussion in the future.