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Equations to convert compacted crown ratio to uncompacted crown ratio for trees in the Interior West

Author(s): Chris Toney, Matthew C. Reeves
Year Published: 2009

Crown ratio is the proportion of total tree length supporting live foliage. Inventory programs of the US Forest Service generally define crown ratio in terms of compacted or uncompacted measurements. Measurement of compacted crown ratio (CCR) involves envisioning the transfer of lower branches of trees with asymmetric crowns to fill holes in the upper portion of the crown. Uncompacted crown ratio (UNCR) is measured without adjustment for holes in the crown and may be a more appropriate measurement when interest is on height to the first live branches in the crown. CCR is more commonly available because it is a standard measurement of the Forest Inventory and Analysis (FIA) program of US Forest Service, and UNCR is an optional measurement at the discretion of regional FIA units. The mean difference between UNCR and CCR of trees in the western United States (0.17 live crown) could be large enough to introduce biologically significant bias in applications that use crown ratio to derive height to crown base. Equations were developed to convert CCR to UNCR for 35 tree species in Idaho, Montana, Wyoming, Nevada, Utah, Colorado, Arizona, and New Mexico using data from the Interior West FIA unit. UNCR was modeled as a logistic function of CCR and tree diameter, and species-specific equations were fit by nonlinear regression. Root mean squared error for the regression equations ranged from 0.06 to 0.15 UNCR (mean absolute error, 0.04-0.12 UNCR). Equations for most species performed well when applied to test data that were not available at the time of model fitting.

Citation: Toney, Chris; Reeves, Matthew C. 2009. Equations to convert compacted crown ratio to uncompacted crown ratio for trees in the Interior West. Western Journal of Applied Forestry. 24(2): 76-82.
Topic(s): Fuels, Fuel Descriptions
Ecosystem(s): Alpine forest/krummholz, Subalpine wet spruce-fir forest, Subalpine dry spruce-fir forest, Montane wet mixed-conifer forest, Montane dry mixed-conifer forest, Aspen woodland, Riparian woodland/shrubland, Ponderosa pine woodland/savanna, Juniper woodland, Mountain shrubland/wooded draw
Document Type: Book or Chapter or Journal Article
NRFSN number: 8368
FRAMES RCS number: 8334
Record updated: Jun 21, 2018