July 26, 1996
Dear Silviculture Foresters:
Re: Checklist to Evaluate Surveys Using the Growth Intercept Method
We have developed the attached checklist to evaluate surveys that use the growth intercept method to determine site index. You may find this useful for quality control on your silviculture surveys.
Please direct questions about determining site index in silviculture surveys and prescriptions to Patrick Martin at (250) 356-0305. Please direct questions about research into methods to estimate site index to Gord Nigh at (250) 387-3093.
Patrick Martin, R.P.F.
Stand Development Specialist
Silviculture Practices Branch
Dr. Gord Nigh, R.P.F.
Biometrician, Growth and Yield
Notes from Field Reviews Silviculture
On April 8th, Shawn Rice, Silviculture Office in Mid-Coast District asked us to check-out a block where the growth intercept method had been used to determine site index during pre-stand tending survey. From this field review, we developed the following checklist that you may find useful to evaluate your own similar surveys. If you would like us to visit a field site with you, to help you with a problem related to site index in silviculture surveys or prescriptions, contact Patrick Martin at 250-356-0305.
To evaluate a survey that used the growth intercept method to determine site index, ask yourself the following 10 questions:
- Were an adequate number of growth intercept sample trees measured?
Ten growth intercept sample trees/stratum will usually produce an
average site index for the stratum that is stable and accurate. You
can further refine required sample size by using procedures outline
in the manual Growth Intercept Method for
- Were the right trees selected as growth intercept sample trees?
The correct growth intercept sample tree is the largest DBH suitable tree of the site index species in a 5.64 m radius plot. A suitable tree is one that a) is dominant or co-dominant and not overtopped by trees or brush, b) has an undamaged stem (no fork, no top dieback, no broken top, etc.), and c) has no evidence of growth slowdown above DBH (a period of tight growth rings or short internodes).
- Were age and height measured accurately on growth intercept sample trees?
Tree total height must be accurately measured -- not occularly estimated. Total height should be recorded to the nearest 0.1 m. Tree age is determined at breast height (1.3 m above tree base on the high side). On small trees, age is most accurately measured by felling the tree and counting rings. When using the increment borer, the core must include the pith. Rings are made more visible by shaving the face of the core or stump with a sharp knife.
- Were the growth intercept tables used correctly?
Check a few of the plot cards to make sure the surveyors used the growth intercept tables correctly. Check that the measured height and age give the recorded site index.
- Did the growth intercept sample plots uniformly cover the entire stratum area?
To make sure that the site index average determined from the survey reflects the average condition on the block, the sample trees should be taken from plots that uniformly cover the entire stratum area. Sample coverage can be checked from the survey plot location map with growth intercept sample plots indicated.
- Were adequate procedures taken to allow for field checking?
For field checks, it is useful to ribbon growth intercept sample trees, record the distance and bearing to growth intercept sample plots, and make sure species, age and height are recorded for growth intercept sample trees on the plot cards.
- Were plot site index values averaged to obtain stratum average site index?
Check that site index was determined for each growth intercept plot. Check that the site index values from all growth intercept plots in the stratum were averaged.
- Was the growth intercept method the most appropriate way to determine site index?
In most surveys, more than one method is available to determine site index. For each stratum, you must select the most appropriate method to use. To select the best method, you need to consider the a) stand condition, b) availability of methods for determining site index for the species on site, c) accuracy required for site index, and d) operational factors such as concerns about destructive sampling and increased survey costs. A decision key has been developed to help you select from the available methods, an appropriate method to determine site index. It can be obtained from Patrick Martin.
- Was an appropriate site index species selected?
In a mixed species stand, growth intercept data is usually collected
on only one species -- the site index species. Site index is required
for both the leading species in the inventory label and the leading
species in the silviculture label. The inventory label leading species
should be the first choice for the site index species. If growth intercept
tables are not available for this species, or if the sample trees
of this species are not suitable for growth intercept sampling, the
first choice for site index species should be the silviculture label
leading species. Then, site index species conversion tables are used
to obtain site index for the leading species in the other label. These
conversion tables are available in the manual Growth
Intercept Method for Silviculture Surveys and from Patrick
- Was the average site index properly carried through to ISIS, MLSIS, 810A, the prescription, etc.?
Check that the average site index was properly carried through to all relevant areas: written into the MLSIS form C, loaded into ISIS or MLSIS, written into the prescription, copied onto the 810A, etc.