Lesson 5 - Common Cluster Samples in Forestry

Question 1

What is cluster sampling

Answer 1

selecting a group of items for measurement from one location , instead of measuring items at different locations
- two types include fixed area/fixed radius plots and variable radius plots

Question 2

differentiate between fixed radius plots and variable radius plots

Answer 2

fixed area: all items in a fixed area are selected for measurement
variable radius: point on the ground is established and trees are selected for measurement depending on their size and closeness to the point
- several fixed area plots of different sizes are established at each point

Question 3

What attributes are measured in fixed area plots

Answer 3

volume per plot per hectare
stems per plot per hectare
basal area
average age
average volume per tree
average dbh
average tree height
site index
percent decay
growth attributes

Question 4

what are the measurements taken on each tree in a fixed area plot

Answer 4

species, dbh, height, crown class, age, decay indicators, measures of growth

Question 5

what plot attributes are found as a result of analyzing the measurement data

Answer 5

1. volume per plot, per hectare
   - start by calculating volume per tree , then sum tree volumes, then vol per ha (figure out how many plots in a ha)
2. stems per plot, per hectare
   - number of tallied treed
3. basal area per plot, per hectare
4. average age
5. average volume per tree
   - volume per ha / stems per ha
6. average diameter
7. average height
8. site index
9. percent decay
10. growth

Question 6

When combining the calculated attributes of several plots to obtain stand attributes (fixed radius plots) what is N replaced with in the equations?

Answer 6

N is replace with A (the area of the forest in hectares), since the variable of interest is expressed on a per hectare basis

Question 7

what are the steps in establishing variable radius plots

Answer 7

1. establish the plot centre
2. project the critical angle from the plot centre
   - plot size based on a radius equal to the distance from the plot centre of a tree with a dbh that just touches the sides of the angle
   - radius is called the critical distance
3. determine whether trees are “out or in”

Question 8

what devices can we use to measure critical angle

Answer 8

prisms, relascopse, telerelascopes

Question 9

What is a BAF

Answer 9

basal area factor: the basal area per hectare for a given critical angle

BAF = ba{t} x F{t}
where ba is the basal area for tree t and F is the number of stems per hectare represented by each tree (also called tree factor)

Question 10

What is angle constant?

Answer 10

angle constant (k): the relationship between tree dbh and the critical distance for a given angle

Question 11

What is plot radius factor (PRF)

Answer 11

useful for determining the critical distance quickly, so that decisions regarding borderline trees can be made

Question 12

discuss the plot calculations and how to perform them (variable radius plot)

Answer 12

1. volume per hectare and the stock table
   - same as fixed area
   - calculate basal area of the tree, then tree factor (BAF/ba), then volume per ha (vol per tree x Ft)
2. stem per ha and the stand table
   - sum tree factors over all tallied trees
3. basal area per hectare
   - BAF x number of tallied trees
4. average age
5. average volume per tree
   - volume per hectare / stems per hectare
6. average diameter
   - weight each diameter by the Ft
7. average height
   - weighted by Ft
8. site index, percent decay and growth
   - same as for fixed area