Part 9: Collecting Monitoring Data

Dry Weight Rank Method

The Dry Weight Rank Method is used to document species composition by weight. In making this determination, you will observe sites and rank the top three plant species contributing the most weight in the quadrat. As for each method, it is important to have both general view and close-up photos.

A large amount of data can be obtained very quickly using this method. This method provides you with estimates based on standing biomass production, which is very useful when making management decisions. A drawback of this method is that if your ranch is in an area with sparse vegetation (such as some desert landscapes), many quadrats will have only one species, or may be vacant of vegetation. In this case, larger quadrat areas would be necessary to collect data.

To conduct this method, three species in each quadrat are selected and recorded as having the greatest yield for current year’s growth on a dry matter basis. Species are given a rank of 1, 2, or 3; the highest rank as a 1 descending to the lowest rank, 3. These ranks correspond with 70%, 20%, and 10% of biomass, respectively. Species that can be evaluated using dry weight rank include perennial grasses and forbs, annual grasses and forbs, trees and shrubs. This method can be easily coupled with the Frequency Method since the same quadrat frame is used for both methods. If there are fewer than three species in the quadrat, two or even one species may receive more than one rank. For example, if only one species is found in the quadrat, it would be ranked 1, 2, and 3, or 100%. If two species are found, one may be given ranks of 1 and 2 (90%), ranks 1 and 3 (80%), or ranks 2 and 3 (30%), depending on the relative weight for the two species.

Criteria

• Dry weight rank should be assessed in each quadrat within each transect, and quadrats should be placed at each pace along the transect.
• If no vegetation occurs within a quadrat, dry weight rank is not assigned.
• The same size frame that is used for Frequency is usually used to evaluate dry weight rank.

Those conducting dry weight rank need to be able to identify plants of interest (or key species) for your ranch, which is usually about 6-10 species of plants. Common Western rangeland plants are identified in Section 5 of this learning module.

Equipment

• Study location and Documentation Data form (pdf, 13KB)
• Dry Weight Rank Form -- option 1 (pdf, 34KB); option 2 (pdf, 105KB)
• Quadrat frame
• Hammer
• Permanent yellow or orange spray paint
• A ¾ to 1 inch iron stake
• Compass
• Steel post and driver

Conducting the Study and Study Sites

• Slide Show
  

  Conducting the Study/Study Sites

   

   

  Video:

  Quadrats

  Dry weight rank is usually conducted in conjunction with frequency and point intercept methods.
• When selecting key areas for setting up these quadrats, be sure the site is located within a single plant community within a single ecological site.
• Quadrats should be located at each pace along the quadrat.
• This type of study can be conducted using a baseline or a linear study design.
• Be sure to permanently mark the site with a stake.

Study Layout

• At the study site, establish a transect with a distinct marker (stake or landmark) at the opposite end.
• Determine which three species supply the greatest annual yield on a dry matter basis; give the species with the highest yield the rank of 1, the next highest 2, and the third highest 3.
• Record the data on the Dry Weight Rank form (pdf, 34KB)
• This method assumes that a rank of 1 corresponds to 70% composition, rank 2 to 20%, and rank 3 to 10%. If there is only one species present, they are ranked 1,2, and 3 to add up to 100%. If two species are present, rank the most prominent species 1 and 2 (90%), and the second species rank 3 (10%), or rank the prominent species 1 and 3 (80%) and the other species 2 (20%), depending on each species’ occurrence.

Analyzing Data

• Interactive How-to
  

  How to Analyze Data on the Dry Weight Rank form

   

  Using the Dry Weight Rank form
• Multiply species ranked 1, 2, and 3 by 7, 2, and 1, respectively and record appropriately on the form.
• Add the amounts in the weight columns of each species evaluated and record the sum in the “Weighted” column.
• Total the “Weighted” columns for all species. The total of the column will always be ten times the number of quadrats.
• Divide the value recorded for each species in the weighted column by the total of the weighted column to get percent composition for each species. Percent composition should equal 100%.