Forest Regeneration

Chapters 7 & 10 Smith, et al. Forest Regeneration

Trees live long, but not forever so the time comes when they naturally are, or, must be, replaced by new ones. Regeneration plays such a prominent role in silviculture that most silvicultural systems are named for their method of regeneration

2 Regeneration or Reproduction Method

“ a process or procedure by which a stand is established or renewed ”

Two main objectives Free up growing space (either partially or totally); translates into removing some of mature trees Create environment for establishment of new Other included considerations Treatments of vegetation, slash, or soil to create and maintain conditions favorable to the establishment and early growth of regeneration

3 Two types of regeneration or reproduction Natural Establishing and releasing seed or vegetative sprouts (propagules) originating from sources within or adjacent to the stand being regenerated Artificial Regeneration is artificially seeded or planted, and planted trees can be either from natural origin dug from elsewhere in the forest or grown in seedling nurseries or greenhouses 4 Artificial Regeneration

Crucial decision and investment

Site preparation and species match

Planting / Direct seeding

5 Artificial Regeneration

Planting stock bare-root seedlings ↑ light, easy transportation and cheaper ↓ planting can be done only in short periods of time containerized seedlings ↑ quick root-soil contact, can be grown faster, greater uniformity makes planting cheaper, less seed is used ↓ more costly to transport vegetative propagation ↑ genetic qualities are perpetuated, easier and faster establishment if species forms roots readily, reproduce several individuals from a single one ↓ no root system (some planting limitations), few species

6 Artificial Regeneration

Size of plants “bigger is not necessarily better!” large planting stock vs. small planting stock Season of planting Breaking of dormancy - Active root elongation period Temperature and moisture Site preparation for improvement of site Reduction of competing vegetation Drainage of water Placement of seedlings

7 Methods of planting

Manual or hand planting compression methods: bar-slit (sandy soils) , grub-hoe-slit (stony or clay soils) dug-hole methods (when previous methods fail): side-hole, center-hole, wedge uniform holes can be made using special devices for containerized seedlings (uniform size & shape) Mechanized planting (mostly compression method) flat or gently sloping sites, stump free (abandoned agricultural fields) Usually more effective and cheaper Afforestation 8 Density of plantations

Important decision Good control of initial density and spatial arrangement Best to envision the kinds of trees wanted in the stand late in the rotation and work backward from this goal - tendency to think how many trees will be needed to achieve early occupancy of the growing space High density vs. low density → site and objective of production Spatial arrangement: square, hexagonal, staggered, “random,” clumped

9 Plantation protection

Plantations require a large investment → losses represent a much larger waste of money compared to natural regeneration Part of the cost of artificial regeneration goes towards protection Damaging agents: wild animals (rodents, browsing, ants, etc) and competing vegetation (woody plants)

10 Direct seeding

Requires Adequate seed supply Seed treatment (often for germination) Control of seed-eating animals Favorable site and seedbed conditions Moisture during germination (rain) Site factors and site preparation define the feasibility of the method Types: broadcast or strip and spot seeding 11 Natural regeneration and disturbance

Natural succession and development of new stands proceeds in one of two ways Advance regeneration (already established survivors) Germination of seeds Once established, woody perennials usually command growing space so tenaciously that only the death of some of them can make vacancies large enough for the establishment of new ones Disturbance, particularly lethal, figures prominently in the ecology of natural regenerative processes

12 Natural regenerative disturbance

Fire is most common natural disturbance Ignited by lightning, volcanoes, spontaneous Kills small trees most efficiently, so old stands are killed from the bottom upwards Favors the return of two major categories of species Those that sprout from roots or bases of fire girdled stems Species germinating from small, wind-blown seeds adapted to germinate on mineral soil surfaces bared by fires

13 Adaptations to fire (more examples)

Species w/hard-coated seeds that survive long periods in the forest floor, springing up after fires, such as Cherries and Ribes shrubs

Sprouting species, mainly angiosperms (broad- leaved trees) and some conifers such as pitch pine and coast redwood

Light-seeded species that thrive on seedbeds of bare mineral soil exposed by fire but not outstandingly resistant to fire (e.g., alder, cottonwood, poplar) 14 Adaptations to fire (some examples)

Closed-cone pines, such as jack pine in the Lake States, lodgepole pine and Monterey in the west – regeneration occurs after a crown fire has killed the old crop, exposed mineral soil, and opened the cones

15 Adaptations to fire (ya example)

Species with sufficiently fire-resistant bark to withstand burning at intervals throughout an entire single generation, like the hard pines of the South, such as longleaf, loblolly, and shortleaf, and ponderosa pine in the northwest and west

16 Kinds and severity of disturbances

Geologic, erosional events are the most severe kind of natural disturbance

17 Kinds and severity of disturbances

Geologic, erosional events are the most severe kind of natural disturbance E.g., landslides, melting of glaciers, formation of new land by water, wind, volcanism Ecologically, true primary succession occurs after these events Ordinarily, herbaceous vegetation colonizes these areas, though some tree species can also, such as true poplars, alders, some others SELDOM wise to imitate this with silviculture, but foresters are often called upon to re-vegetate these areas as well as strip mines, or such areas caused by other events

18 Kinds and severity of disturbances

Next most severe is a hot fire that burns large amounts of dead fuel created by blow-downs or pest outbreaks

19 Kinds and severity of disturbances

Next most severe is a hot fire that burns large amounts of dead fuel created by blow-downs or pest outbreaks Some fires can burn so hot as to be almost as lethal as landslides, but after fire organic matter usually remains in the soil A few silvicultural techniques artificially create similar disturbances, leaving mostly bare soil with organic matter intact, freeing all the growing space for establishment of new vegetation from seed or other methods

20 Kinds and severity of disturbances

Next most severe are “releasing disturbances” caused by wind or pests of large trees that kill forests from the top down, sparing most plants in lower strata Species adapted to such disturbances have foliage constructed and displayed in ways that make them tolerant to shade These species may exist as seedlings or saplings for many years beneath old stands, retaining the capacity for rapid height growth whenever some lethal event releases them Tend to be limited to sites and regions that are continuously moist enough to reduce exposure to fire or drought stress

21 Kinds and severity of disturbances

Natural disturbances are not uniform in severity, type, or extent

22 Kinds and severity of disturbances

Natural disturbances are not uniform in severity, type, or extent Differences are degree of exposure of mineral soil, extent of freedom from root competition, intensity of solar radiation Pioneer communities are the result of catastrophic disturbances Late-successional communities result from a long series of frequent, light, “releasing” disturbances

23 Environment of the microsite

The first few weeks in the life of a seedling are the most dangerous for its survival Seedlings respond to light, water, carbon dioxide, chemical nutrients, and biotic influences (regardless of the name of any silvicultural treatments)

24 Environment of the microsite - Water loss

Water is lost to the atmosphere by direct evaporation from the uppermost layers of soil and organic material Loose materials lose water so fast they are seldom hospitable for plants Direct evaporation explains the loss of water from the top layers of soil when there are no roots (capillary action) Shade and mulching can greatly slow down direct evaporation losses

25 Environment of the microsite - Surface Temperature Survival of new unshaded seedlings depends heavily on physical processes dissipating solar energy load Reflection, convection, conduction, evaporation, and outgoing re-radiation are the processes that take heat energy away from absorbing surfaces of plants Shading is the most important physical process that is subject to silvicultural manipulation Chlorophyll reflects heat energy (longwave infrared radiation) to some extent, but opaque objects like rocks and trees are most effective in reflecting harmful radiation away from seedlings

26 Environment of the microsite - Light

Light regimes beneath forest canopies can be dramatically altered by changes in quality, intensity, and proportion of direct versus diffuse light For deciduous canopies, moisture and temperature affect the times when leaves are present that reduce solar radiation to the forest floor Seedlings of many species thrive by being out of synchrony Some by early emergence before older trees leaf out in spring or before wet season Others by delaying leaf shedding in fall or at beginning of dry season The greatest difference in light radiation quality beneath a forest canopy occurs across forest openings – under direct or indirect manipulation of the silviculturist Slope and aspect also will influence groundstory radiation 27 Regeneration Process

Initiation of natural regeneration from certain kinds of disturbances can be mimicked to a degree with silviculture Goal is providing right amount of growing space for establishment and growth of the desired species Selection Systems (single-tree, group) Shelterwood Systems Seed-tree Systems Single-cohort Systems (coppice, clearcut) Success of regeneration can be regulated through manipulation of overhead cover and the characteristics of surface materials 28 Essential stages of natural regeneration

Overview Flowering Seed supply Seed dispersal Storage Germination Succulent stage Growth and establishment

29 Essential stages of natural regeneration

Flowering All tree species can reproduce sexually from seed Monoecious species have both functional sexes on the same plant, but in separate flowers, e.g. Red alder

30 Essential stages of natural regeneration

Flowering All tree species can reproduce sexually from seed Dioecious species have trees with flowers of only one functional sex, e.g. Black cottonwood

These strategies can contribute to creation of a viable propagule that will advance the genetic vigor of the future

population 31 Essential stages of natural regeneration

Flowering Some species occurring in some environments rely heavily on vegetative (asexual) regeneration e.g. Quaking aspen

32 Essential stages of natural regeneration

Seed supply First prerequisite! – no tree or group of trees is a dependable source unless it is sufficiently mature and vigorous to produce seed Seed bearers should be located so that wind or other agencies ensure pollination and proper distribution of seed over the site

33 Essential stages of natural regeneration

Seed supply Not every year is a “good” seed year

Periodicity of cone crop in 4 w. white pine trees from same stand 34 Essential stages of natural regeneration

Seed dispersal Modes of seed dissemination include almost every imaginable mechanism (i.e. animals, wind, water, gravity) Distances of effective dispersal vary widely, but usually no greater than a few times the height of the seed bearers Predators (insects, bats, birds, rodents, etc.) account for some losses

35 Essential stages of natural regeneration

Storage Seeds produced in a “good” year often must survive at least one cold or dry period and be ready to germinate the next growing season (stratification) Varying degrees of dormancy help this process Forest floor conditions usually supply the appropriate conditions of a cool moist period to break dormancy

36 Essential stages of natural regeneration

Germination Adequate amounts of moisture (most critical and variable), heat, and oxygen, sometimes certain wavelengths of red to far red light starts development Depends heavily on the amount of rainfall and conditions right at the spot where the seed fell Species such as oaks with large heavy seeds are generally the only ones that can establish themselves in thick leaf litter – on bare mineral soil, the blunt roots would simply roll them around over the surface without penetrating the soil Light-weight, wind-disseminated species germinate best on or slightly beneath moist seedbeds - bare mineral soil is best 37 Essential stages of natural regeneration

Succulent stage Seedlings are most vulnerable during the first few weeks of life, while stems are still green and succulent Heat injury takes a heavy toll Damping-off, caused by mildly parasitic fungi in shaded conditions also takes its toll

38 Essential stages of natural regeneration

Growth and establishment The key to success is extending roots into the soil quickly enough to maintain contact with portions of the soil where water is available Roots that penetrate below the “capillary fringe” and tops that extend into the turbulent air strata are much less subject to drought and heat injury Once a seedling is established, the ecological and silvicultural rules that govern their lives as trees are quite different

39 Natural Reproduction Triangle

40 Summary Two major methods of regeneration: natural, ‘artificial’ Natural regeneration is affected by type and intensity of ‘disturbance’ Natural Regen initiated in any particular stand through methods deliberately regulating cover is best specified by explicitly stating… Propagule origin Descriptors of site treatment Spatial pattern of operation Vegetation structures remaining 41 Summary (cont’d) Success of natural regeneration depends on the occurrence and timing of of seven (7) essential events Artificial Regeneration requires careful thinking about cost / investment, species, methods Two artificial methods: direct seeding, planting If planting, decisions needed for Stock type Stand density Planting method Planting season Plantation protection 42