The Merrill W. Linn Land & Waterways Conservancy encouraged the county planning commissions in both Union and Northumberland counties to have Natural Diversity Inventories done. The Linn Conservancy helped to underwrite both studies by securing grants from the Edna Sheary Trust, the Cora Brooks Foundation, and a Huplits from the Sierra Club, in addition to securing financial support from the conservancy itself and other local groups.

Pennsylvania Natural Diversity Inventories (PNDI) have been conducted for both counties by The Nature Conservancy’s science office in Middletown, Pennsylvania. Currently, 24 of Pennsylvania’s 67 counties have had a PNDI done. These in-depth studies combine the results of historic plant and animal habitat studies with current aerial surveys and extensive contemporary on-the-ground fieldwork by specially trained staff. Local expertise has been supplied by members of the Linn Conservancy like the late John G. Clark, botanist; Warren Abrahamsen, biologist and Bucknell professor; and Richard Nickelsen, geologist and Bucknell professor emeritus.

The PNDI for Union and Northumberland counties was completed in 1993 and 2002 respectively and extensive text, maps, and relative ranking on a national, state, and local basis have been made available to the county and township planning commissions of both counties. The PNDI material is updated by The Nature Conservancy approximately every five years. The PNDI forms the basis for registry sites and conservation easements by the Linn Conservancy.