Part 9: Collecting Monitoring Data

Comparative Yield Method

Comparative Yield Method is used to estimate total biomass production or the total standing crop at a study site by assigning relative ranks to specific plant species at each quadrat. This method works well for herbaceous vegetation as well as for shrubs and can be used to compare relative production between sites. As with the other methods, be sure to establish a good photo record of the site used in these studies.

Criteria

• It is best if the same observer reads each quadrat throughout the transect to ensure accuracy.
• Include only current years vegetative growth in the reference quadrats.

Equipment Necessary

• Study Location and Documentation Data form (pdf, 16KB)
• Comparative Yield form (pdf, 20KB)
• Five sample quadrats
• Clippers
• Paper bags
• Kilogram weighing scale
• ¾- to 1-inch stake
• Hammer
• Permanent yellow or orange spray paint
• Compass
• Steel post and driver

Conducting the study and study sites

To complete this method, five reference quadrats are established, which represent the range in dry weight of standing crop that can be commonly found during sampling.  Each reference quadrat is subjectively placed. 

• Reference 1 and 5 are placed first, with 1 having the lowest-yielding production on the site and 5 having the highest-yielding production. 
• Reference 3 is then placed as having the average yield, or the halfway between reference 1 and 5. 
• References 2 and 4 are located the same way as being the midpoint yield between references 1 and 3, and references 3 and 5, respectively. 

These reference quadrats are usually clipped, weighed, and then placed again to ensure observer accuracy.

Study Layout

• Start a transect by randomly locating the first quadrat along the transect bearing.
• Read other quadrats randomly located along the transect, usually placed at each pace.
• Quadrats (using a 40 cm x 40 cm frame) are evaluated along the length of an established transect.
• For each quadrat, production is compared to one of five reference quadrats, with relative ranks recorded rather than estimating weight directly. 
• When completed, each reference quadrat is clipped and weighed in the field and “green weight” is recorded. 
• Reference quadrats will be clipped in a vertical projection, which will include tree or shrub canopy. These same samples are then oven-dried, and weighed again for a dry weight. 
• With dry weight, total production (pounds per acre) can be calculated without regard to species.

Data Analysis

1. The number of quadrats tallied for each ranking is totaled and multiplied by the ranking such that

rank X tally = weighted ranking

 

2. Weighted rankings are then summed and divided by the number of total quadrats. This provides the average ranking for the site.
   
   
3. To calculate average yield

 

Total clipped rank	= Average rank of clipped quadrats
Total number of clipped quadrats

 

Total clipped weight	= Average weight of clipped quadrats
Total number of clipped quadrats

 

4. To determine average rank interval

 

Average weight of clipped quadrats	= Average rank interval
Average rank of clipped quadrats

 

5. The average ranking for the site, which is based on the estimated quadrats, is then multiplied by the average rank interval to estimate the average yield per quadrat for the site.
   
   
6. To calculate average yield per quadrat
   
   

Average ranking for the site X Average rank interval = Average yield per quadrat



7. The average yield in gram per quadrat obtained above can be converted to either pounds per acre or kilograms per hectare.