Module 3 — Stand level components
of biodiversity
British Columbia
Ministry of Forests
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Module 3, Part A — Stand structure — continued
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1. Horizontal structure — patchiness
 

  The horizontal structure is a mix of successional stages that creates a habitat mosaic of older forest, younger forest, openings or gaps in the canopy (containing early seral vegetation), and edges.

See Figure 7: Horizontal and vertical stand structure  

     
Name the locations of several good examples of horizontal stand structures

graphic

  Horizontal structure describes the patchiness in forest stands, as affected by factors such as:
  • Variations in soil depth, moisture, and productivity
  • Presence of natural opening (e.g., rock outcrops, bogs, rock talus, disease pockets, or minor windthrows)
  • Variations in microtopography, such as hummock/depression complexes

Habitat patchiness provides:

  • A mix of foraging, nesting, and resting habitat
  • Increased diversity of habitats that can support more species over time

Patchy habitats (with canopy openings or gaps) are created by disturbance factors such as windthrow, disease (e.g., root rot centres), insects, small-scale fires, and human activities.

These influence the horizontal variability within a stand.

For example, there is often a trend in tree species mix and performance as you progress further upslope, away from a wet depression or bog. There also is an associated understorey change from wet to drier microsites.

2. Vertical structure — multiple vegetation layers in the canopy

 
 

Vertical structure describes the top to bottom structure of a forest stand. A diverse stand would have multiple layers from tall to smaller trees, shrubs, forbs, grasses, mosses and coarse woody debris.

See Figure 7: Horizontal and vertical stand structure  

     

Name the locations of several good examples of vertical stand structures

graphic

 
 

The deep, multi-layered canopies are more likely to develop in low-density stands that allow light penetration through to the forest floor.

The multi-layered canopies:

  • Provide structural habitat for various birds that forage, nest and roost at intermediate heights
  • Intercept and retain snowfall, resulting in lesser accumulations of snow on the forest floor
  • Maintain moderate stand temperatures by reducing convective and radiative heat loss. These climatically buffered areas are often selected by ungulates as winter range
  • Provide an array of branches that are a substrate for invertebrates and arboreal lichen growth. These are an important food source for deer and caribou on their winter ranges
 
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