Transcript Lecture: Concepts of Regeneration

Concepts of Forest Regeneration
Regeneration vs. Reproduction
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Regeneration: the act of renewing tree cover by establishing
young trees naturally or artificially (verb)
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Reproduction: Seedlings or saplings existing in a stand
(noun)
Artificial vs. natural regeneration
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Natural Regeneration - stand establishment is from natural
sources: natural seeding, sprouting, suckering, layering
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Artificial Regeneration - stand establishment is from human
intervention: planting seedlings or cuttings or by direct
seeding.
Reforestation vs. afforestation
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Reforestation: reestablishment of forest cover on areas
where it once occurred
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Afforestation: introduction of trees to sites that did not
support forests or had no forest cover for a long period of
time.
Concepts of Regeneration
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Key goals of a regeneration strategy:
– Make the results predictable
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Control microenvironment
Ensure prompt replacement of the stand
Affect species composition
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Match species to site and to objectives
Arrest succession
– Many desirable species are early successional (oak and pine)
Concepts of Regeneration
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Key goals of a regeneration strategy:
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Appropriately stock the site with desirable species
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Number and distribution
Set the stage for future management
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Minimize poor or excessive stocking
Minimize remedial treatments (problems that require fixing)
– Intermediate treatments should, where possible, be
constructive
Minimize the chance of failure
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Ensure adequate seed supply
Ensure proper seed bed for good germination and establishment
Take prompt remedial action if necessary
Concepts of Regeneration
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Origin of reproduction
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Seed vs. vegetative
New individual vs. clonal
Categories of Reproduction
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New seedlings: originate following regeneration event
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Advance reproduction: in place prior to regeneration event
and released by event
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Stump sprout: traditionally from stump >2” ground line
diameter
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Root suckering: sprouts from shallow lateral roots
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Typically follows the severing of the parent stem and with direct
sunlight to the forest floor
Examples: black locust, sweetgum, aspen
Stump Sprouting
Stump Sprouting Probability by Age and Species
Probability
Stump Sprout
–Sprouting tends to decrease with size and age and varies by species
Tree Age
Regeneration Process
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New forest communities establish whenever three
conditions develop:
1. Presence of abundant viable seed or vegetative
propagules
2. Soil and seedbed conditions enable germination of seed
or help induce shoot development off parent trees
3. Environmental conditions foster the survival and growth
of established trees
Regeneration Process
Seed Supply
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Flowering and seed production
– Influenced by species, genetics, climate
– Can be cyclical and have high year-to-year variation
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Example: masting species such as oaks
Regeneration Process
Seed dispersal
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Reproductively mature trees within dissemination range required for
regeneration from seed
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Vegetative or artificial regeneration required if seed is not available
Factors influencing seed dissemination (i.e., dispersal)
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Height of release
Distance from source
Abundance of seed
Weight and aerodynamic structure
Activity of dispersing agent
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Wind speed and direction, topography, numbers and movement of
animals
• Seed dispersal distance is species dependent
Regeneration Process
Seed bank
• Viability and germination stimuli various among species
Regeneration Process
Seed Bed and Germination
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Physical characteristics of forest floor affect germination
– Litter depth and type
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Some species (for example, many pines) require a mineral
seedbed
– Mineral seed beds can created by natural disturbances (i.e.
fire) or site preparation treatments
Position of seed within the seedbed affect predation and
germination rates
Light, temperature, and moisture affect seed viability and
germination
Concepts of Regeneration
Generally,
• Light wind-disseminated seeds require mineral seedbed
• Large seeded species like oaks are aided by being buried under
a litter layer as long is it is not too thick (5 cm)
– Litter layer helps protect against predation, desiccation, and extreme
temperatures
Species of the Central Hardwood Region
Species
Yellow-poplar
White oak
Chestnut oak
Black oak
Northern red oak
Scarlet oak
Sugar maple
Red maple
Pignut hickory
American beech
Seed Dissemination
Gravity Animals Wind
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Regeneration Process
Established Seedlings
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Survival and growth of seedlings influenced by mitigating effects of
forest canopy on light, temperature, and moisture in the understory
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Species physiologic characteristics and shade tolerance affect their
response to a given understory environment
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Silvical characteristics of desired species must be considered in
conjunction with those of competitor species to assess competitive
dynamics of newly established seedlings.
Regeneration Process
Established Seedlings and Shade Tolerance
• Shade tolerant: Not only are they able to establish in the understory, but
they are able to persist.
– This doesn't necessarily mean they are putting on a lot of growth, but they are
staying alive
• Intermediate tolerance: Able to establish in the understory but they cannot
survive for extended periods
• Shade intolerant: May establish in the understory, but normally die out in
dense shade
– When released following extended periods of low light they respond with
sluggish growth
Overview of Silvicultural Systems
Even-aged vs. Uneven-aged
Common characteristics of even-aged stands
• Crown canopy is generally limited to a single layer elevated above the
ground
• Diameters vary widely only if shade-tolerant species are present
• Only old stands have sawtimber sized trees
• Small trees have short live crown length when compared to total height
• Largest trees often have 25-40 percent live crown, depending on stand
density
Common characteristics of uneven-aged stands
• Crown canopy is generally comprised of multiple layers and commonly
extends close to the ground
• Diameters range from seedling-sapling to sawtimber sizes, regardless of
species present
• Trees of all diameters have a large live-crown ratio, often as high as 40 to
60 percent in managed stands
• Tree heights vary with tree diameter, with short ones having small
diameters and tall trees having larger diameters
Even-aged vs. Uneven-aged Diameter Distributions
Bell-shaped (normal
distribution)
Reverse J-shaped
Reverse J-shaped does not always indicate a true uneven-aged
stand (3+ age classes)
Example from the Central Hardwood Region: Two-storied stand with oakdominated overstory and midstory/understory canopy dominated by shade
tolerants like beech and maple.
Silvicultural Systems
• Even-aged and Uneven-aged systems
– One age class vs. at least three age classes in a stand (an age class is
defined at 20% of the rotation length)
– Mature trees are removed:
• Short window of time in even-aged
• Periodically in uneven-aged
– Maintains continuous canopy cover
Timeline of practices in an even-aged silvicultural system
• During the rotation age r, treatments are applied across the entire stand
to meet silvicultural objectives that are related to tree age
• Concurrent application of individual practices of an uneven-aged
silvicultural system during a cutting cycle harvest in a balanced
uneven-aged stand
• Treatments are applied to subunits of the stand depending on conditions
within each subunit
• Each cutting cycle harvest will support similar treatments
Silvicultural Systems
• Two-aged systems
– Hybrid of even- and uneven-aged
– Uses even-aged methodology while maintaining some continual
canopy cover
– Regeneration is accomplished two times over a standard rotation
– Referred to as: irregular shelterwoods, reserve shelterwoods, two-aged,
or leave tree systems
Regeneration Methods
• Regeneration methods are classified as follows:
– Even-aged
• Clearcut
• Seed-tree
• Shelterwood
– Uneven-aged
• Selection
– Two-aged (Hybrid)