Concepts of Forest Regeneration

Regeneration vs. Reproduction

• Regeneration: the act of renewing tree cover by establishing young trees naturally or artificially (verb)

• Reproduction: Seedlings or saplings existing in a stand (noun)

Artificial vs. natural regeneration

• Natural Regeneration - stand establishment is from natural sources: natural seeding, sprouting, suckering, layering

• Artificial Regeneration - stand establishment is from human intervention: planting seedlings or cuttings or by direct seeding.

Reforestation vs. afforestation

• Reforestation: reestablishment of forest cover on areas where it once occurred

• 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

• Key goals of a regeneration strategy:

– Make the results predictable• Control microenvironment

• Ensure prompt replacement of the stand

– Affect species composition• Match species to site and to objectives

• Arrest succession

– Many desirable species are early successional (oak and pine)

Concepts of Regeneration

• Key goals of a regeneration strategy:– Appropriately stock the site with desirable species

• Number and distribution

– Set the stage for future management• Minimize poor or excessive stocking• Minimize remedial treatments (problems that require fixing)

– Intermediate treatments should, where possible, be constructive

– Minimize the chance of failure• Ensure adequate seed supply• Ensure proper seed bed for good germination and establishment• Take prompt remedial action if necessary

Concepts of Regeneration

• Origin of reproduction– Seed vs. vegetative

– New individual vs. clonal

Categories of Reproduction

• New seedlings: originate following regeneration event

• Advance reproduction: in place prior to regeneration event and released by event

• Stump sprout: traditionally from stump >2” ground line diameter

• Root suckering: sprouts from shallow lateral roots– 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–Sprouting tends to decrease with size and age and varies by species

Tree Age

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Regeneration Process

• 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

• Flowering and seed production

– Influenced by species, genetics, climate

– Can be cyclical and have high year-to-year variation

• Example: masting species such as oaks

Regeneration Process

Seed dispersal• Reproductively mature trees within dissemination range required for

regeneration from seed – Vegetative or artificial regeneration required if seed is not available

• Factors influencing seed dissemination (i.e., dispersal)– Height of release

– Distance from source

– Abundance of seed

– Weight and aerodynamic structure

– Activity of dispersing agent

• 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

• Physical characteristics of forest floor affect germination

– Litter depth and type• 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 Seed Dissemination  Gravity Animals WindYellow-poplar     XWhite oak X X  Chestnut oak X X  Black oak X X  Northern red oak X X  Scarlet oak X X  Sugar maple     XRed maple     XPignut hickory X X  American beech X X  

Regeneration Process

Established Seedlings• Survival and growth of seedlings influenced by mitigating effects of

forest canopy on light, temperature, and moisture in the understory

• Species physiologic characteristics and shade tolerance affect their response to a given understory environment

• 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

Reverse J-shaped

Bell-shaped (normal distribution)

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 oak-dominated 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)