Forest Growth and Yield

1
Forest Growth and Yield

• Or Knowing what and how much timber you have,
  how it will change over time and how to manage
  it
• Definitions
• Concepts
• Uses in Management

2
Forest Growth and YieldDefinitions

• Forest yield the volume of timber in a forest
  at a specific point in time
• Forest growth the change in volume over an
  interval of time

3
Forest Growth and YieldDefinitions

• Site quality a loose term denoting the relative
  productivity of a site for a particular tree
  species
• Site index a particular measure of site quality
  based on the average height of the dominant and
  codominant trees at a specified index age (25, 50
  or 100 years usually 50 years)

4
Site Index Curves for Eastern White Pine

• Height and age used as coordinates to determine
  site index
• SI correlated with soil factors and topography
• Curves have been developed for most commercial
  forest tree species

5
Forest Growth and YieldDensity vs Stocking

• Stand density
• Indicates degree of stem crowding within the
  stand
• Stocking
• Refers to whether the stand density meets a
  particular management objective
• These two terms are often interchanged, but they
  have different meanings

6
Forest Growth and YieldDensity vs Stocking

• Stocking chart
• Shows acceptable ranges of basal area for stands
  of different average diameters
• Must first determine the average basal area and
  number of trees per acre
• Use these as coordinates on chart
• If point falls between curves on stocking chart,
  stand is fully stocked
• Point below curve means stand is understocked
  above curve means stand is overstocked

Stocking chart for managed red pine
7
Forest Growth and Yield

• Note
• Height growth is affected by site quality (and
  genetic value) but not much by stand density
  (except at extremes)
• Basal area is affected by stand density but not
  well-correlated with site quality (except at
  extremes)

8
Yield Tables

• Future yields and stand conditions can be
  predicted using growth models and yield tables
• Some models allow for treatments such as thinning

9
Forest Management

• Regulated forest
• Sustained yield
• Allowable cut

10
Regulated forest and sustained yield

• A forest that produces a continuous flow of
  products of about the same size, quality and
  quantity over time is called a regulated forest
• Sustained yield refers to the continuous flow of
  timber products
• Regulated forests, by definition, provide
  sustained yield
• The larger the ownership, the easier it is to
  attain a sustained yield

11
Regulated Forest -Even-aged example

• Assumptions
• 25 years to maturity
• 25-acre forest
• all acres of equal productivity
• Managed as 25 individual even-aged stands - one
  stand harvested each year
• In practice, usually not as simple as example

12
Regulated forest - Uneven-aged example

• Assumptions
• Trees mature at some regular interval (4 years in
  example)
• Need 4 stands to be able to harvest something
  each year

13
Rotation vs cutting cycle

• Rotation age and cutting cycle are both used to
  designate when stands are cut. Note the
  difference between them.
• Rotation age The length of time from final
  harvest cut to final harvest cut in even-aged
  management
• Cutting cycle The length of time between major
  cuts (harvest entries) in uneven-aged management

14
Allowable cut

• The amount of timber considered available for
  cutting during a specified time period, usually
  one year

15
Rotation ageEven-aged management

• Rotation age is determined by first identifying
  the landowners objective
• Is the period of years required to establish and
  grow timber crops to a specific condition of
  maturity (or value) refers to even-aged
  management only

16
Cutting cycleUneven-aged Management

• Idea is to cut a volume of timber equal to the
  growth
• Example shows 5-year cycle
• The forest is regulated by manipulating the
  stands so that an equal volume of timber is due
  for cutting each year
• Concept is equivalent to living off interest
  from money deposited in a savings account at the
  bank

Reserve growing stock
Cutting cycle for a single stand
Cutting cycle for a regulated, uneven-aged forest