How it is judged
The measurement runs from the top of the tree to the lowest live branch that is part of the crown, not to a stray sprout. It gives a quick read on vigour, since the crown is the tree's food factory. A tree with a small crown has fewer leaves to feed the trunk and roots, and it often has a slender trunk that moves more in the wind.
Low ratios have different causes. Trees grown close together lose lower branches to shade, which is normal in a forest stand. A tree can also have a low ratio from heavy pruning, disease, or years of drought dieback.
Why it matters in Northern Nevada
Pines in the Sierra foothills and around Tahoe grow in stands, and a tree left alone after neighbours are removed has a tall trunk with a small top and a lot of wind. In town, a tree that has been limbed up too far, topped, or stripped by storms carries a small crown too. A related warning sign is dieback; see drought stress and dieback.
Keep this in mind for fire work. Limbing up to remove ladder fuels means raising the crown, and the live crown ratio is part of how much can come off.
What an arborist does about it
The arborist includes the ratio when judging a tree, along with trunk taper, wounds and lean. A low ratio does not mean a tree must go; it means pruning has to be gentle, because a tree with little crown has little to spare. Lifting the lowest limbs for clearance or fire safety is planned so the tree keeps enough crown to stay vigorous.
Sources
- International Society of Arboriculture, Trees Are Good: Pruning Mature Trees (brochure) (read October 17, 2026)