Crown Classification of Trees: 

Crown classification is a framework to understand and describe the vertical position of tree crowns within a forest canopy. It plays a vital role in assessing forest health, competition among trees, and the impact of light availability on tree growth. This classification is particularly valuable in even-aged forest stands but can also be applied to uneven-aged stands by comparing trees within similar canopy layers.

Definitions and Characteristics of Crown Classes

Dominant Trees

• • Description:
    Dominant trees are those whose crowns rise above the general canopy level. These trees have access to the most light, receiving full sunlight from above and partial sunlight from the sides.
  • Characteristics:
    • Largest and fullest crowns.
    • Exhibit high vigor and strong growth.
    • Play a key role in seed production and canopy composition.
  • Role in the Ecosystem:
    Dominant trees significantly influence the forest microclimate, shading lower layers and affecting the growth of subordinate trees.
  • Example Species Behavior:
    In mixed stands, shade-intolerant species like Douglas-fir often occupy the dominant class.

Codominant Trees

• • Description:
    Codominant trees make up the general canopy layer, receiving full sunlight from above but minimal or no light from the sides. They share space and compete with other codominant trees.
  • Characteristics:
    • Slightly smaller crowns than dominant trees.
    • Contribute to the bulk of the canopy structure in even-aged stands.
  • Role in the Ecosystem:
    These trees maintain the primary canopy level, contributing to forest stability and ecosystem function.
  • Example Species Behavior:
    Both shade-tolerant and intolerant species can be codominant, depending on site conditions and competition.

Intermediate Trees

• • Description:
    Intermediate trees occupy a subordinate position in the canopy. Their crowns are narrower and typically receive limited sunlight from above, with no sunlight from the sides.
  • Characteristics:
    • Crowns may be one-sided or restricted in growth due to shading from dominant and codominant trees.
    • Exhibit slower growth and lower vigor than trees in higher classes.
  • Role in the Ecosystem:
    Intermediate trees act as a middle layer in the forest, providing structural complexity and habitat for certain wildlife species.
  • Example Species Behavior:
    Shade-tolerant species like western hemlock often survive in the intermediate class.

Suppressed Trees (Overtopped Trees)

• • Description:
    Suppressed trees are located beneath the canopy and receive no direct sunlight. Their growth is often stunted, and crowns are sparse and poorly developed.
  • Characteristics:
    • Weak and narrow crowns.
    • Low vigor and high susceptibility to stress or mortality.
  • Role in the Ecosystem:
    Suppressed trees contribute to biodiversity by providing habitat and ground-level shade. They may also act as a reserve for future growth if gaps in the canopy appear.
  • Example Species Behavior:
    Shade-tolerant species like western hemlock can persist in the suppressed class, whereas shade-intolerant species like Douglas-fir often perish.

Factors Influencing Crown Classes

1. Tree Vigor:
   Healthier, faster-growing trees are more likely to occupy dominant or codominant positions.
2. Stand Density:
   High-density stands lead to competition for light and nutrients, often crowding trees into intermediate or suppressed classes.
3. Shade Tolerance:
   • Shade-Tolerant Species: These species, such as western hemlock, can persist in suppressed or intermediate classes.
   • Shade-Intolerant Species: These species, like Douglas-fir, require more sunlight and are less likely to thrive in lower crown classes.

Crown Class Distribution and Forest Health

The distribution of crown classes within a stand provides insights into stand vigor and management needs:

1. Overcrowded Stands:
   • A high proportion of intermediate and suppressed trees.
   • Indicative of stagnation and competition for light.
   • May require thinning to enhance growth and health.
2. Understocked Stands:
   • Dominated by trees in the dominant and codominant classes.
   • Sparse or young stands with ample sunlight for all trees.
3. Healthy Stands:
   • Balanced distribution, with most trees in the codominant class and fewer in the suppressed category.

Example Data: Even-Aged Stand Analysis

The following example illustrates crown class distribution in a 60-year-old stand of Douglas-fir and western hemlock near Larch Mountain, Oregon:

Crown Class Distribution by Species

Observations:

1. Dominant and Codominant Classes:
   • Predominantly Douglas-fir, a shade-intolerant species requiring direct sunlight.
2. Intermediate and Suppressed Classes:
   • Predominantly western hemlock, a shade-tolerant species that can persist under the canopy.