Invasive Plant Species in Illinois Forests

Findings of Critical Trends Assessment Program –
INHS scientist and EcoWatch volunteer data

The following maps indicate the location and extent of nine common invasive plant species in Illinois forests. They were generated from data collected by the Critical Trends Assessment Program (CTAP), which includes professional scientists at the Illinois Natural History Survey and volunteer citizen scientists with ForestWatch, a component of the EcoWatch Network. While Illinois has more invasive plant species than the nine included here, these nine are the primary invasive indicators surveyed by ForestWatch. The professional scientists collect data on additional invasive species not shown here.

The CTAP professional data, from 131 randomly selected forest sites, were collected between 1997 and 2001. (INHS botanists visit 30 sites in each of three habitats—forests, grasslands, wetlands—once every five years.) The ForestWatch data, from 148 sites (133 for spring ground cover data) were collected between 1998 and 2002. ForestWatch volunteers monitor their sites every other year in the fall and spring, but only the most recent site data were included here. (For example, one site may have three seasons of data, but only the 2002 data were included. Another site may not have been monitored in 2002, so the 2000 data were used.) About 25% of the ForestWatch sites were randomly selected, with the others chosen by volunteers.

Although the professional botanists collect more detailed information, both groups monitor along three 50-meter transects in the interior of each forest patch. The CTAP professional monitoring is conducted at the center of the forest patch, usually with a buffer of at least 40-meters, although the buffer may be slightly less in a few instances. All ForestWatch sites have a 50-meter buffer. Therefore, the maps indicate where invasive species have been found in the interior of the forest and not along the forest edge, where invasive species are more pervasive.

Questions regarding this report can be directed to one of the following:

Brenda Molano – CTAP professional scientists, 217-265-8167

Matt Buffington – ForestWatch data

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