Field Measurements

Students are divided into 7 groups of 3 to 5.  Have one student be a recorder, the rest are counting and measuring.  The class will collect data for three of each tree species within the plot.  Groups are assigned three trees they will identify and record data for.  Students will confirm identification with instructors before leaving the tree, and the tree will be marked with flagging to ensure no other students measure the same tree.  When students are finished collecting data from the three trees they were assigned they will estimate the number of trees of each of those species found within the plot with and without available browse.  More detailed instructions for each step and plot preparation are below.


Define the plot perimeter (done before class field trip):
Record GPS coordinates in decimal degrees at center of the plot using the NAD 83 datum.  Place 6-8 flags 15 meters from the center of the plot to make an approximate circle for the students to work within.

HINT: Your students may perform this if there is enough time allotted for the field data collection.  If you assign students this task have one group mark the perimeter while other groups start collecting data.  

General Plot Description from each group:

What tree species are present, and how many of each is present in the plot? How many moose fecal pellet groups are present?  To count trees students will walk the plot in a grid counting and identifying all trees they come across in the plot and counting all moose fecal pellet groups.  The easiest way to set up a grid is to have each group hold their 2.4 meter measuring sticks horizontall so that each group's stick are touching but not overlapping.  The group then walks a straight line across the plot counting only the trees and shrubs that their measuring stick comes across.  The class as a whole can determine if the maturity of trees in the plot as sapling, mature or mixed.  (Hint: Have students do this step last.  This should take the least amount of time, and will be more accurate if students have field identified their three trees before completing this step.)

 
 
 

Individual trees data collection

Tree selection
Students find a representative tree of each assigned species within the plot.  If more than one tree is present in the area they should choose trees at random.  (Hint: randomizing selection can be done by one member assigning a number to each tree and another member selects a number without knowing the assignments).  Trees and shrubs sometimes cluster and may in fact be one individual covering a large area.  A tree or shrub is considered an individual (ramet) separate from the surrounding trees and shrubs if you can put your foot between the bases of the two trees.  Groups cannot leave a tree until identification is confirmed by an instructor, and the tree is marked so others will not re-count the tree.  (Hint:  look over data collected from the tree before students leave it.  Does their data look like it makes sense?)

Diameter at chest height (DCH) and tree height
DCH is a measure of the diameter of a tree at approximately 1.2 meters high.  Use calipers to measure the diameter (width) of the main trunk at approximately 1.2 meters high, or height of ones chest. 
Estimate the height of the tree visually.  Exact measurement of height is not necessary.  Use your 3 meter stick graduated every 0.1 meter to guess the height of the tree and determine the DCH.

Tree Browse Intensity description
Broomed- Tree is severely browsed, to the point that its shape resembles that of a broom.  Greater than 50% of available browse is removed.

Browsed- Tree is tall in stature with evidence of browse, such as bitten branches or multiple branches at the base of the tree, however, the noticeable majority of available branches are not browsed.  Less than 50% of available browse is removed.

Un-browsed- tree has no evidence of bite damage to branches, stems or the trunk.

Pictures show browse severity category with image on left depicting broomed shape, image in center depicting browsed in the sense that tree has regular form with more available branches unbrowsed than browsed, and on right is unbrowsed shown as a tree with virtually no available branches.
Browse evidence as broomed on left, browsed in the center, and unbrowsed on right. Center image courtesy Trish Wurtz US Forest Service.

Bark stripping description

Note bark stripping on the tree as one of the following:

Severe- Bark stripping covers the circumference of the tree or is longer than 0.6 meters (2 feet).

Moderate – bark stripping does not circumscribe the trunk or branch stem, and has a length less than 0.6 meters (2 feet).

Minor – Bark stripping length is less than 15.2 centimeters (6 inches) long and appears to be minor.

None- no bark stripping present

Stripped bark on trees showing severity.  Left severe circumscribes tree, middle moderate is greater than six inches, right minor is less than 2 inches long.
Bark stripping, severe on left, moderate in the middle, and minor on the right.

Availability and consumed measures

Browse counts Bite/availabilty 
Current Annual Growth (CAG) count:   Current annual growth is defined as the branch tip followed back to a collar or swelling in the branch.  The collar or swelling is where the previous growing season’s growth began.  2 students in each group count all the twigs attached to the tree that are available for a moose to browse regardless of whether or not they are already browsed.  Average the counts from the 2 students.  Determine if the twigs are available as browse for the moose using the supplied 3 meter stick, and 3 meters as the maximum height for available browse.  Do not count dead branches, and do not count stacked buds which are common in cherry and cottonwood trees.  Stacked buds are not smooth and appear to have multiple spots where a bud formed and is no longer present right next to each other.  Stacked buds do not make good forage.

Bite count: 2 students count the number of twigs attached to the tree that appear to be bitten.  Average the counts from the two students.  Remember not to count rabbit bites or pruning marks.  Both look like flat sharp cuts, and are usually acutely (sharply) angled.

Current annual growth on left has fresh red color and bite mark on right shows broken current annual growth.
Current annual growth on left, notice different fresh colored twigs with a slight collar where current annual growth began. On right is typical sign of browse where the twig was bitten.

CAG and bite diameters
Diameter of current annual growth (CAG) – Measure the diameter of CAG on 10 twigs on the tree.  If there are not 10 twigs that are not bitten beyond the current annual growth (this might happen with willow, aspen and ash) note that and measure the bite diameters so that a total of 10 twig diameters are measured.

Bite Diameter - Measure diameter of twig at the point it was bitten on the twigs that CAG was measured on.  If less than three twigs have bite marks, measure what is available.  If a bite is beyond the CAG circle the measurement to note that on the data sheet.

Download Plot data form

Download Tree and bite data form

Go to Data Analysis

Go to Winter Tree Identification

For more information or to participate e-mail gagraziano@alaska.edu

Back to Top