Concepts of Forest Regeneration

1. Concepts of Forest Regeneration

2. 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)

3. 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.

4. 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.

5. 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)

6. 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

7. Concepts of Regeneration • Origin of reproduction • Seed vs. vegetative • New individual vs. clonal

8. 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

9. Stump Sprouting

10. Stump Sprouting Probability by Age and Species • Sprouting tends to decrease with size and age and varies by species Stump Sprout Probability Tree Age

11. Regeneration Process • New forest communities establish whenever three conditions develop: • Presence of abundant viable seed or vegetative propagules • Soil and seedbed conditions enable germination of seed or help induce shoot development off parent trees • Environmental conditions foster the survival and growth of established trees

12. 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

13. 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

14. Seed dispersal distance is species dependent

15. Regeneration Process Seed bank • Viability and germination stimuli various among species

16. 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

17. 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

18. Species of the Central Hardwood Region

19. 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.

20. 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

21. Overview of Silvicultural Systems Even-aged vs. Uneven-aged

22. 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

23. 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

24. Even-aged vs. Uneven-aged Diameter Distributions Bell-shaped (normal distribution) Reverse J-shaped

25. 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.

26. 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

27. 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

28. 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

29. 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

30. Regeneration Methods Regeneration methods are classified as follows: Even-aged Clearcut Seed-tree Shelterwood Uneven-aged Selection Two-aged (Hybrid)

31. Common Even-Aged Systems Clearcut Seed Tree Shelterwood

32. Clearcutting • Clearcutting: A method of regenerating an even aged stand in which a new age class develops in a fully exposed microclimate after removal, in a single cutting, of all trees in the previous stand. • Regeneration is from natural seeding, direct seeding, planted seedlings, and/or advance reproduction. • Silvicultural clearcuts differ from ‘commercial clearcuts’ • The first removes all trees, the second only merchantable trees

33. How Clearcutting Changes the Microenvironment • Full sunlight conditions • Air and soil temperature near the surface increases • Humidity decreases and surface evaporation increases • Soil moisture increases because transpiration decreases • Precipitation interception decreases, more water reaches the surface • Water infiltration and percolation increases; subsurface flow increases • Decomposition increases (warmer and wetter), releasing more nutrients • Nutrients not taken up or bound to soil leach out of system

34. Clearcutting • Edge effect • Moisture increases on a gradient for 30-40 feet into a clearing and then levels off • Shade (in the northern hemisphere) is more pronounced on the south edge of the clearing. East to west shade depends on time of day.

35. Clearcutting • Alternate clearcutting arrangements • Strip clearcut • Block clearcut • Patch clearcut • Use of alternative methods: • Ensure good seed rain • Manage shade patterns • Protect against wind or ice/snow • Improve aesthetics or meet policy-based constraints

36. Alternative Clearcutting Approaches Block clearcutting • All trees are removed in a single operation • Size limitations are based on policy and site conditions, not on regeneration constraints

37. Alternative Clearcutting Approaches Progressive strip clearcut Alternate strip clearcut Strip clearcuts, alternate or otherwise, are best oriented at right angles to prevailing winds. The width of the strips will depend on seedfall distances for the preferred species, wind hazard, and other factors

38. Alternative Clearcutting Approaches Patch clearcutting • Stand is regenerated in a series of clearcuttings made in patches • Patch size influences light availability within the patch and should be chosen to match species silvics

39. Other considerations when using even-aged methods • Stream Side Management Zones (SMZ’s) • Typically leave an unharvested or partially harvest buffer • Legacy trees • Travel corridors for wildlife • Management of viewscapes • Orientation on landscape • Aesthetic buffers • Alter shapes, adjacencies • Avoid straight edges and square corners • Limit harvest size

40. Clearcutting and Site Preparation • Site preparation considerations for natural regeneration • Some important questions • Is it needed or would it be detrimental? • Do you need it for a desired species? • Does species need a mineral seedbed

41. Site preparation and clearcutting: Considerations for natural regeneration • Scarification → mineral seedbed • Control slash residues • Partial shade or browse protection afforded by slash • Control slash cover to manage seed eating mammals • Mechanical or chemical vegetation control • Competing vegetation that may inhibit or delay regeneration and effect subsequent growth rates

42. Advantages Clearcutting with Natural Regeneration • Good method for most shade intolerant species • Commercially attractive • Ease of administration and implementation of regulated forest • Clean site eases site preparation • Easy machine access eases harvesting • Total overstory removal reduces some pests (e.g. dwarf mistletoe) • Facilitates regeneration of species with serrotinous cones • Precludes blow down • Increases herbaceous cover (browse and cover for many wildlife species)

43. Shortcomings of Clearcutting with Natural Regeneration • Problems with dependable seed sources and seedling establishment • Seed shortage limits regeneration to light seeded species • Poor seed years may lead to regeneration failure or irregular stocking • Overstory removal limits within stand seed production following harvest • Density and uniformity of a species is difficult to control • Issues associated with no high forest cover and high light environment • Lack of cover may adversely impact some tree species and may increase competition by herbaceous and shrubs • Dense competition may require costly site preparation • Cold air drainage may damage reproduction • Dry sites may not have sufficient surface moisture to support germination • Reduced chance for genetic improvement

44. Shortcomings of Clearcutting with Natural Regeneration • Impacts on soils and hydrology • Wet sites may become wetter • Wet soils may become unstable on steep slopes • Mineral soil exposure may increase soil erosion • Increased decomposition rates and potential nutrient leaching • Decreased visual aesthetics • Increased fuel loading and fire danger • Decreased wildlife habitat for some species

45. Coppice Silviculture

46. Coppice • The term "coppice" is commonly applied to any regeneration arising from sprouts or suckers—typically hardwoods of young to moderate age • As a method, it is where regeneration is solely from sprouts or root-suckers • Associated with short rotation production of pulpwood or fuelwood • Historically associated with charcoal iron production

48. Coppice • Some coppice principles: • Low stumps produce better quality sprouts • Best sprouts originate from the root collar • Sprouting vigor tends to decline with age and size of stems • smaller stems, better sprouting • Sprouting is most vigorous from dormant season cutting • Least vigorous from late spring cutting

49. Coppice • Coppice for energy, bioremediation, environmental cleanup • Repeated crops without replanting • Vegetative propagation maintains genetic integrity of plantation • Increased growth rates allow large volume production on limited land base • Short cycle provides quick return on investment • Second and third rotation often produces greater biomass in shorter time frame due to multiple stems from sprouts