Transcript Selection criteria in uneven

Uneven-aged
beech stand,
Germany
Uneven-aged
mixed-hardwood
stand, Michigan
Uneven-aged mixed
spruce/fir stand,
Germany
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
Marking guide:
•< 11” – no cutting
•12 – 16 or small
sawtimber – cut
1/5 of trees
•16-23 or large
sawtimber – cut
1/6
•> 24 inches or
mature – remove
all
Density management
• Area (e.g., 4 size classes, each covering the same
area)
• Leaf area allocation (after K. O’Hara)
– 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
Selection criteria in unevenaged stands
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Maturity
Risk
Vigor
Soundness
Stem form, crown size and branching habit
Species
Crown position
Release effect (of seedlings/saplings)
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
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
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
Single tree selection:
High vertical structure
– Wildlife habitat
– Fire ladder
Disease potential
– Mistletoe
Uneven-aged
mixed spruce/fir
forests, single
tree selection
Switzerland
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
Uneven-aged
mixed
spruce/fir
forests,
group
selection,
Germany
Uneven-aged
mixed
spruce/fir
forests,
group
selection,
Germany
Group selection:
• Resource availability driven by
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Group size
Spatial layout
Size and density of neighboring trees
Slope
Aspect
• Not homogenous within group (and stand
edge)
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
Uneven-aged
mixed (oak)
hardwood
forest, group
selection,
Germany
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
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
Conversion:
• Irregular stands are easier to
convert
• During Conversion
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Lower residual densities
Longer cutting cycles
Lower maximum diameter
Keeping healthy trees regardless of
form or species
Ex - Uneven-aged
mixed spruce/fir
forests, managed
with single tree
selection until 20
years ago, no
management since,
Germany
Traffic patterns on a harvesting unit
Feller buncher
traffic
Skidder- traffic -
Area in skid trails following a single
harvest operation
16
% Stand Area
14
13.7
13.2
12.5
12
9.6
10
8.2
8
6
4
2
0
Clearcutting Shelterwood Seed-Tree
Group
Selection
Single Tree
Selection