Part 9: Collecting Monitoring Data

Frequency

Frequency is a quantitative expression of the presence or absence of individuals of a species in a population. It is defined as the percentage of occurrence of a species in a series of plots of uniform size. It is not a direct count of the number of a particular species in the monitoring area, but simply an indication that the plant is present or not present in each plot. Frequency reflects the density and distribution of plant species and is the probability of encountering a particular species in a defined study area.

Measuring frequency is a principle method used to document change in vegetation over time. Having an understanding of the abundance and distribution of vegetation on your ranch is especially useful as you collect data for your monitoring program year after year. You will need several years’ worth of data before you can start to make a determination of meeting, or moving in the direction of meeting, management objectives.

Some things to consider when determining plant frequency on your ranch:

• Plant species frequency depends on the size of your monitoring plot. If you have a large plot you are usually more likely to see the presence of a particular plant species than if you have a small plot.
• To best compare frequency over time, the species should be present in at least 20% but no more than 80% of your quadrats.
• Be sure to use the same size plot each time you monitor.
• You may want to record seedlings separate of your count of established plants. Then, if seedlings do not become established, they will not interfere with the validity of your data collected over many years.
• Frequency must be interpreted for each species encountered; it cannot be combined into one overall value for the plant community.
• Frequency cannot be estimated.