Uneven-aged

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Uneven-aged beech stand, Germany
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Uneven-aged mixed-hardwood stand, Michigan
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Uneven-aged mixed spruce/fir stand, Germany
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Density and structure in uneven-aged stands are
defined by

• Overall density (basal area after cutting)
• Maximum diameter
• Relative proportions of large and small trees),
  diameter distribution or Q-value

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Marking guide

• lt 11 no cutting
• 12 16 or small sawtimber cut 1/5 of trees
• 16-23 or large sawtimber cut 1/6
• gt 24 inches or mature remove all

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Density management

• Area (e.g., 4 size classes, each covering the
  same area)
• Leaf area allocation (after K. OHara)
• Represents occupied 3-D growing space
• Is related to rates of energy and material
  exchange
• Calculating growing space efficiency by relating
  tree increment to leaf area
• Growing space efficiency of trees is determined
  by crown class, age, or species
• Optimize structures for growth

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Selection criteria in uneven-aged stands

• Maturity
• Risk
• Vigor
• Soundness
• Stem form, crown size and branching habit
• Species
• Crown position
• Release effect (of seedlings/saplings)

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Single Tree Selection

• Means cutting single tree and growing single
  trees
• Only limited reduction of below-ground
  competition
• More diffuse light, but only limited direct light
  (sunflecs)
• Moderate increase in soil temperature and
  nutrient release
• Overall, environmental conditions are fairly
  stable

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Single-tree selection

• Density management is a combination/compromise
  between good growing conditions for overstory
  trees and establishment of regeneration
• Continuous forest cover
• Usually not limiting to germination
• Limiting to growth and survival of shade
  intolerant species

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To ensure regeneration of shade intolerant
species

• On stable sites
• Reduce overall density
• Tradeoffs in growth
• Longer cutting cycles
• Sort out species in pre-commercial thinning
  entries
• Pruning to reduce LAI

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Single tree selection

• High vertical structure
• Wildlife habitat
• Fire ladder
• Disease potential
• Mistletoe

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Uneven-aged mixed spruce/fir forests, single tree
selection Switzerland
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Group selection

• Homogenous groups created by patchy cutting
  patterns
• Provides more resources (light) for regeneration
  cohorts
• Regeneration of intermediate shade tolerant trees
• More efficient harvesting and management of
  regeneration

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Uneven-aged mixed spruce/fir forests, group
selection, Germany
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Uneven-aged mixed spruce/fir forests, group
selection, Germany
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Group selection

• Resource availability driven by
• Group size
• Spatial layout
• Size and density of neighboring trees
• Slope
• Aspect
• Not homogenous within group (and stand edge)

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Group selection

• Resource (light, moisture, nutrients) increase
  within opening
• Edge effect due to surrounding trees
• Higher light/temperature conditions in group
  improve decomposition/nutrient release within
  opening
• Range of conditions within group and edge (in
  matrix) may lead to recruitment of multiple
  species

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Uneven-aged mixed (oak) hardwood forest, group
selection, Germany
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Group selection

• Trees are not necessarily naturally grouped
• Cutting of immature trees
• Edge effect may reduce ecological size of group
• Especially with irregular shapes
• Difficult to map and document
• Inventory methods may have to be modified
• On ground work is complicated
• May require different access system
• Changes over time

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Guide to implementation of group cutting

• Determine desired number of age classes and gap
  sizes
• Calculate number of gaps per acre
• Based on
• density of mature trees
• area in gaps
• calculate number of trees to be cut

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Conversion

• Irregular stands are easier to convert
• During Conversion
• Lower residual densities
• Longer cutting cycles
• Lower maximum diameter
• Keeping healthy trees regardless of form or
  species

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Ex - Uneven-aged mixed spruce/fir forests,
managed with single tree selection until 20 years
ago, no management since, Germany
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Traffic patterns on a harvesting unit
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