FOR 350 - Lecture 1, What is Silviculture?, Reading: Chapter 1

·  Definition: The art and science of controlling the establishment, composition, structure, and growth of a forest stand to meet the landowners’ objectives on a sustainable basis.

Three parts to the definition, by definition, silviculture involves manipulation of the stand; two, it is for a purpose, to meet the landowners objectives; finally, it must be done in such a manner so that the site is not degraded. Manipulative, objective driven, sustainable.

·  In silviculture, the ‘problem’ at hand is to satisfy landowner objectives by appropriately manipulating the available tree resources and environmental conditions to create and maintain desired values

·  Silviculturists operate in the realm of the biologically possible. However, they also operate under social and economic constraints. Only those solutions that are simultaneously biologically possible, economically feasible, and socially acceptable, will be considered appropriate (and sustainable)

·  To know what is biological possible, one must understand how the forest environment influences individual tree and community establishment and development.

·  Silvics is the study of the biological characteristics of tree species and communities of trees including: 1) how trees establish, grow, and reproduce, 2) how the physical environment influences their physiology and character, 3) how communities of trees influence their physical environment and the interaction between vegetation and physical environment as forests change through time.

Silvics Manual: http://www.na.fs.fed.us/Spfo/pubs/silvics_manual/table_of_contents.htm

·  Steps in planning silvicultural treatment or strategy (Notation 1-1)

·  The Stand

A stand is a contiguous group of trees sufficiently uniform in age or size class distribution, composition, structure, site quality and/or location to be a distinguishable unit. Silviculture is practiced at the stand level. Forest management is primarily concerned with the forest, a collection of stands administered as an integrated unit.

Describing Stand Composition and Structure

Stand Composition:

a.  Pure Stand: A stand in which at least 80% of the trees in the main canopy are of single species.

b.  Mixed Stand: A stand in which less than 80% of the trees in the canopy are of a single species.

Stand Density: The density of stocking expressed in number of trees, basal area, volume, or other criteria, on a per-acre basis.

Stand Form or Age Classification: Stands are usefully described and considered from the standpoint of the age classes of which they are composed. Generally, two stand forms are recognized.

a.  Even-aged stands – Stands in which there exists relatively small age differences between individual trees. Develops following major disturbance.

b.  Uneven-aged stands – Stands in which there exists relatively large age differences between individual trees. At least 3 age classes are present. A similar meaning is all-aged stand. Develops with low intensity disturbance. Typically, individual tree or multiple tree gaps.

c.  Two-aged stands – Stands in which there are two distinct age classes.

Size Class or Tree Size: Trees are conveniently designated by certain size classes through their life development. Those commonly employed are:

Seedling: from germination to the height of 4.5 feet.

Sapling: from 4.5 feet tall to 4 inches diameter at breast height (dbh).

Poletimber: from 4 to 12 inches dbh

Sawtimber: > 12 inches dbh

Mean diameter (dbh) of a stand represents the average tree size found in the stand. It may be expressed by the arithmetic or quadratic mean. The quadratic mean diameter is typically used as it has a stronger correlation to stand volume than does the arithmetic mean. The basal area of a tree with dbh equal to the quadratic mean diameter is equal to the mean basal area of the stand (i.e., dbh of tree of mean basal area).

While mean diameter provides estimate of tree size, a diameter distribution provides a more detailed picture of a stand’s structure (Figure 1-3, Smith 1987)

Site Class or Site Quality: Defined as a designation of the relative production capacity of quality of a site (location or place) with reference to the species employed; volume production at given age or site index is usually used as standard for classification.

Site Index: A measure of actual or potential forest productivity expressed in terms of the average height of dominants and co-dominants in the stand at an index age (usually 50 years for hardwoods and 25 years for southern pine) for a particular species.

Indirect measures of site productivity: soils, landform, indicator species


Lecture 2, The Silvicultural System, Reading: Chapter 2

·  To meet landowner objectives and to create and maintain desired values, silviculturists alter the forest environment by manipulating stand structure. Required environment is influenced by:

·  Primary categories of silvicultural activities

·  The silvicultural system encompasses everything that is done throughout a rotation. In theory, it is unique for each stand. The systems are named for their respective silvicultural methods. The method is how we regenerate the stand (e.g. clearcut, shelterwood, etc…). These are not harvesting methods, they are methods of regeneration. This naming convention identifies the structural character of a stand.

·  Each silvicultural system should (page 22):

·  Even-aged (EA) and Uneven-aged systems (UEA)

  1. one age class vs. at least three age classes in a stand (an age class is defined at 20% of the rotation length)
  2. the three components of a silvicultural system: tending, harvesting, and regenerating are applied at separate times during a rotation in an even-aged stand. They are applied simultaneously at each cutting cycle in an uneven-aged stand
  3. Mature trees are removed all at once in an EA system, periodically in an UEA system. An UEA system maintains continuous canopy cover.

·  Two-aged systems

  1. a hybrid of EA and UEA. Uses EA methodology while maintaining some continual canopy cover.
  2. regeneration is accomplished (in general) two times over a standard rotation.
  3. referred to as: irregular shelterwoods, reserve shelterwoods, or leave tree systems

·  The system has three basic components (I’d argue there are only two a and c should be inseparable) – Figures 2-2 and 2-1

a. 

b. 

c. 

·  Regeneration methods are classified into distinct categories:

a. 

b. 

·  The choice of a method depends on:

·  Modifications of a silvicultural method

  1. Type: apply different kinds of treatments (e.g. burn vs. herbicide)
  2. Intensity: change the intensity of application (e.g. headfire vs. backing fire)
  3. Timing: alter timing of application (e.g. winter vs. summer burn)
  4. Sequence: change the sequence of treatments over time (e.g. control vines before or following harvest)

Modifications often implemented for non-timber considerations:

  1. size of regeneration area
  2. rotation length
  3. kind, size and condition of residuals
  4. species left on site
  5. amount, kind, and frequency of mast production
  6. amount of light to forest floor
  7. kinds of reproduction
  8. coarse woody debris left on site (amount, size, and distribution)
  9. surface disturbance and effect on hydrology

·  Biologic and economic factors that affect silviculture (Notation 2-3)


Lecture 3, Stand Development, Readings: Chapter 15 pages 200-208

·  Four phases of stand development after Oliver and Larson (1996). Nyland (p204-05 in text) Nyland (p204-05 in text) discusses these phases as a reorganization phase, an aggradation phase, a transition phase, and a steady-state phase. Both mean about the same thing. Figure 5.2 Johnson et al. 2002

1.  stand initiation (reorganization phase): rapid increase in the number of stems (establishment)

2.  stem exclusion (aggradation phase): begins at about crown closure, characterized by density dependent mortality and an accumulation of biomass. Phase ends when biomass peaks.

3.  understory reinitiation (transition phase)-permanent understory forms-permanent canopy gaps form-mortality of individuals cannot be closed by adjacent individuals.

4.  old growth (steady-state)-total biomass of system fluctuates around some mean. The structure of the forest is self sustaining. Recruitment and mortality are in balance biomass is stable

·  Each phase of stand development is accompanied by changes in stand structure and species composition.

·  Stand Initiation: rapid increase in the number of stems and biomass (establishment)

·  Structure

  1. Begin vertical stratification of tree crowns
  2. “brushy” stage with herbaceous, shrub, small trees
  3. Invasion continues until all growing space is occupied

·  Follows major disturbances (wind, fire, clearcuts)

·  Regeneration of open space from seed, sprouts, or advance reproduction

·  One cohort or age class

·  Stage ends when canopy becomes continuous and trees begin to compete with each other for light and canopy space

·  Stem Exclusion: begins at about crown closure, characterized by density dependent mortality and an accumulation of biomass. Phase ends when biomass peaks.

·  Canopy continues to have one cohort and canopy too density to allow new trees to grow into canopy

·  Competition is intense and density-dependant “self-thinning” occurs

·  Crowns are small enough so that when a tree dies, others fill the vacant growing space by expanding their crowns

·  Crown differentiation occurs: the biggest trees tend to get bigger, the smaller ones tend to die. In some cases such as in mixed species stratified stands, the slower growing shade tolerant trees fall behind in height growth of faster growing shade intolerant species, but because of their physiology are able to remain alive in the understory or midstory of the stand. Alternatively, some species do not differentiate, stagnation occurs in species like slash or lodgepole pine.

·  Mortality rates are high, especially in intermediate and suppressed crown classes (i.e., the least competitive individuals die).

·  Crown classification:

  1. Dominant - crown is larger than average and typically above the general upper level of the canopy; receives full top light, considerable side light
  2. Codominant - top of crown is at upper canopy height; receives full top light, little from sides; medium-sized crown, usually somewhat crowded on its sides. Often wide range around “average canopy” tree.
  3. Intermediate - top of crown is below the top of the general canopy; receives some top light from directly above, none from the side; conspicuously narrower, smaller and shorter than the average crown.
  4. Overtopped (suppressed) - crown entirely below some foliage of the upper canopy; receives no direct top light; small, weak crown with low vigor

·  Understory Reinitiation:

·  Mortality of individuals cannot be closed by adjacent individuals

  1. Crowns of trees are now large enough so that when one overstory tree dies, the surrounding trees can not fill the gap

·  Permanent canopy gaps form

·  Permanent understory forms

  1. Tree reproduction becomes re-established beneath parent stand
  2. Factors that influence species composition

·  Light – Degree of shade tolerance

·  Soil moisture

·  Old-Growth/Complex Stage:

·  Natural mortality of large overstory trees produces irregular canopy gaps

·  Mortality and recruitment and are in balance—biomass is stable

·  Stage marks the transition to an even-aged to an uneven-aged stand

·  Figure 9-6 on p204, discuss four phases in relation to biomass.

  1. stand initiation (reorganization phase)-rapid increase in the number of stems (establishment)—lots of stems, very little biomass.
  2. stem exclusion (aggradation phase)-begins at about crown closure; at peak density (TPA), characterized by density dependent mortality and an accumulation of biomass. Phase ends when biomass peaks.
  3. understory reinitiation (transition phase)-permanent understory forms-permanent canopy gaps form-mortality of individuals cannot be closed by adjacent individuals. Biomass declines as smaller individuals replace canopy dominants.
  4. old growth (steady-state)-total biomass of system fluctuates around some mean. The structure of the forest is self sustaining.


Lecture 4, Stand and Tree Growth and Yield, Readings: Chapter 17

·  General growth and yield patterns of even-aged stands

·  Net yield: reflects the amount of yield (volume or biomass) available for removal at any given age, rises throughout stand initiation and stem exclusion phases, can decline during understory reinitiation phase (Nyland figure 9-6)

·  Gross yield: reflects total amount produced on a given site at a given age (volume of living trees + volume of mortality), rises throughout stand development

·  Density: number of trees decrease continuously due to mortality as stand ages

·  Height: height of dominant and codominant trees increases through life of stand, can level off or flatten as stands become decadent

·  Diameter: diameter (dbh) of average tree increases throughout life of a stand as trees growth and as the smaller trees within the stand suffer a disproportionately higher mortality rate.

·  Growth and yield patterns and rotation length Figure 9-5, p 203.

  1. Stage 1: rotation for maximum fiber production ends when mai = pai
  2. Very little volume in small stems; throughout stage 1, mass mortality, but little volume lost in any one stem
  3. Stage 2: rotation for sawtimber production, with exact length determined by economic criteria
  4. Stage 3: understory reinitiation phase (transition phase) where mortality exceeds production, and standing volume declines progressively
  5. The developmental stages of stand dynamics and the stages suggested by the production function—stage 3, or understory reinitiation, you can only economically manage into this stage if a premium is paid for this material or if other byproducts that only occur here are of value (e.g. DDW, CWD, snags, an open canopy).

·  Production, MAI, and PAI (notation 9-3): definition and calculation

·  Production: Net change in stand volume or basal area

  1. p = A + I – M

where, p =production, A = accretion, I = ingrowth, M = mortality

·  Periodic Annual Increment (PAI): net change in production during a specific period

  1. PAI =

where,

Y = production per year during the period of interest

a = initial measurement date or year

n = number of years between successive measurements

·  Mean Annual Increment: Average growth per year a stand has exhibited/experienced to a specified age

  1. MAI =

·  Growth rate of a forest stand largely determined by two factors

  1. Innate productive capacity of the site
  2. The amount and composition of the growing stock present on the site

·  Influence of Site Quality

o  Height growth is primarily dependent on site quality (site index) except at extreme densities

o  As site quality (SI) increases (page 431):

§  Trees grow in height more quickly → stand develops closed canopy more rapidly → quickens time for the beginning competition induced mortality crown differentiation to begin → this results in lower densities, larger average diameter, and more volume at a given age on high quality sites when compared to low quality sites.