This document discusses key concepts for designing effective density management regimes for thinning stands of trees, including: 1) Site index - a measure of site quality based on average dominant tree height that can be used to estimate future stand age. 2) Stand dynamics - the different stages of stand development with varying levels of relative density, competition, and site occupancy. 3) Size-density relationships and relative density - ways to quantify current density and desired future condition (DFC) to inform thinning plans. Relative density compares current stand density to the density at full site occupancy.

1. 1
Key Concepts
James N. Long
Department of Wildland Resources & Ecology
Center
Utah State University
Objectives
• Review several key concepts and tools;
• These are useful in designing reasonable
and effective density management regimes
(thinning);
• Design a density management regime for a
particular set of objectives.
Concepts and tools
• Site index
• Stand dynamics
• Size-density relationships and relative
density
• Designing a density management regime
Site index
From Vacchiano et al. (2008), after Wiedemann (1949)
Site index
• Average height of dominant trees is:
– A function of potential productivity
– Little influenced by stand history
• Used as a species-specific index of site
quality
• SI = ave. dominant height at the base age
(e.g., 50, 100, etc.)
• Used to estimate age in future
Site index
From Vacchiano et al. (2008), after Wiedemann (1949)

2. 2
Stand dynamics
Stages of stand development, with different levels
of:
relative density
competition
site occupancy
Stand dynamics
Pinus contorta var. latifolia
Stand dynamics
Pseudotsuga menziesii
Stand dynamics
Picea engelmannii
Stand dynamics
Pinus ponderosa
Size-density relations
• A way to quantify relative density
• A way to characterize DFC
• Basis for designing density management
regimes
DFC = Desired future condition

3. 3
Relative density
• Absolute density and relative density
• The predictable relationship between mean
size and density in crowded, self-thinning
populations
Powell
Relative density
Insectanddiseasesusceptibility
Crowningindex
Relative density
Stand dynamics
Picea engelmannii

4. 4
D
A
B
C
60%
25%
35%
A C D EB
Density management
• Relative density is basic tool for translating
qualitative objectives into a quantitative
density management regime
• We use an index of relative density to:
– assess current condition;
– characterize desired future condition; and
– develop a tactical plan for achieving DFC
Some key relative densities
• Crown closure/on-set of competition
25% SDImax
• Lower limit of full site occupancy
35% SDImax
• Lower limit of self-thinning
60% SDImax
Density management
• Deciding on appropriate upper and lower
limits of relative density
• Choices depend on management objectives
Examples of (situational)
appropriate limits
• Maintain vigor, avoid self-thinning < 60%
• Delay self-pruning < 25%
• Promote self-pruning > 25%
• Full site occupancy > 35%
D
A
B
C
60%
25%
35%

5. 5