Plant Stewardship Index
PSI Methodology
Bowman’s Hill Wildflower Preserve offers a free online PSI calculator to groups and individuals interested in monitoring and documenting the landscape.
Once a list of plants on a given site (or portion of a site) are recorded, the online calculator computes several measures of naturalness and disturbance that can be used to track the site’s progress over time.
Site reports can be printed from the website to be included in progress reports and grant applications.
The Calculations Behind the PSI:
1) Compile a plant list of the species within the assessment area.
2) Assign the Coefficient of Conservatism (CC) to each plant documented on the plant list.
3) Calculate the Native Mean Coefficient value by totaling the CC’s and divide the sum by the number of native plant species within the assessed area.
4) OR Calculate the Total Mean Coefficient value by totaling the CC’s and divide by the sum of the total number of plants (native and introduced) within the assessed area.
5) Multiply the Native Mean Coefficient OR the Total Mean Coefficient by the square root of the total of the number of native plant species
FQI = Native Mean C x Sqrt N
PSI = Total Mean C x Sqrt N
Key:
FQI = Floristic Quality Index
PSI = Plant Stewardship Index
N = Number of native species
I = Number of Introduced species
Native Mean C = Sum of Coefficients / N
Total Mean C = Sum of Coefficients / N + I
What does the PSI score tell me?
As the population of native plants increases, the score will go up. As the population of specialist plants increases, the score will go up (the Mean C will increase slightly). As the diversity of plants increases, the score will go up.
