What is the Plant Stewardship Index?

The Plant Stewardship Index (PSI) is a "thermometer" reading of the ecological quality of open land by seeing what plants live there. PSI is designed to assist in answering two questions:

- What is the naturalness of any site? 

-  How have land management practices (or their absence) affected that naturalness over time?

How does the PSI work?

The index is calculated based on averaging numbers assigned to each plant by a group of leading botanists and ecologists in the state. These numbers are referred to as "CC" or coefficients of conservatism.

They range from 0 to 10 with zero being those "generalist" plants that can be found in any area (including parking lots, plowed fields and other highly disturbed land sites) to ten being "specialist" plants that the botanists have agreed can be found naturally in very specific habitats. Many (although not all) of our threatened and endangered plants have been assigned a 10 because they are so specialized and their required habitats are disappearing.

The average of all these numbers is called the Mean C. The calculation also takes in to account the total diversity of plants on a site.

Is the methodology new?

No, it has been used effectively since the 1970's in the Chicago region and was developed by Swink and Wilhelm known as the Floristic Quality Assessment Index (FQAI) and it is required by the Army Corps of Engineers in Illinois under law. 

Dr. Wilhelm has been an active adviser to the PSI program and has assisted and guided the assignment of the numbers by the botanists in PA and NJ. There are more than a dozen states in the US currently utilizing the methodology. The EPA is funding the assignment of numbers by botanists in the Northeast state. To learn more about FQAI, click here.

What is required to use the PSI?

A baseline assessment requires a day of a plant survey (dependent on area to be covered) by a botanist. The best time for surveys is late June (particularly for sedge rich sites) and July-September.

Because the "thermometer" is based on a statistical average, it does not require ALL plants at a site to be identified, but the sampling should be representative (i.e. not skipping nonnatives, grasses or trees).  BHWP offers expert PSI site surveys for PA and NJ that creates a report, interpretation as well as account for the client.

How do I obtain more information on my results and also see what others are doing?

Our online PSI database makes available site survey results to the public. The addresses and owners are private and are identified by zipcode. The sites are also distinguished between restoration/planted sites as well as natural sites. You can print out your own report as well as other sites.

In addition to the site information you can also freely access the list of all native and introduced plants as well as assigned numbers compiled by the botanists.