Number of Trees Per Acre

1
Number of Trees Per Acre

• To calculate number of trees we must tie number
  of trees to basal area
• Point samples work on basal area per acre
• Number of trees is handled the same way as volume
• Number of trees is tied to basal area through the
  Number-Basal Area Ratio, commonly called the NBAR

2
Number-Basal Area Ratio Calculation

• NBAR is the number of trees required to total one
  square foot of tree basal area.
• Example 10" DBH tree has a basal area slightly
  larger than one-half square foot. Therefore,
  slightly less than two 10" DBH trees will be
  required to total one square foot of basal area.

3
NBAR and basal area per tree

• Tree basal area (sq ft)

R is feet, DBH is inches Divide by 2 to get
radius Divide by 12 to get feet
4
NBAR Calculation

• NBAR
• The basal area of a 10" tree is .545 sq. ft.
  (.005454DBH2)
• therefore the NBAR is 1 divided by .545

5
NBAR

• 1.83 trees with 10" DBH are needed to make one
  square foot of basal area, so NBAR 1.83.
• NBAR will always be 1.83 for 10" DBH trees
  because the basal area of a 10" tree will always
  be .545 square feet.
• Because NBAR by DBH never changes, a table of
  NBARs can be made and used for every point
  sample.

6
NBAR Table
Each value is 1 divided by tree basal area in
square feet.
7
Relative NBAR Sizes
A tree with DBH slightly smaller than 14" has a
basal area of exactly one square foot. Any tree
with DBH 14" or greater will have NBAR less than
one. Any tree with DBH smaller than 14" will
have NBAR greater than one.
8
Tally for one pointTable 4, page 19 in text
9
Sum across height class
Height does not change the NBAR
10
Number of trees per acre BA/Ac NBAR
11
3 Points, BAF 10table 5, page 20 in text
Add across height classes
12
Number of trees per acre BA/Ac NBAR