helps find the best species mixes.


The Reveg Edge, P.O. Box 361, Redwood City, California 94064

Craig C. Dremann, Research and Co-owner. (650) 325-7333, email

The Reveg Edge has invented a tool to measure plant interactions within natural communities. Other methods only measure species abundance or coverage.The Species Threshold Test measures plant interactions and relationships, and is useful for finding the best species mix when replanting self-sustaining native landscapes.

The Species Threshold Test can also be used to determine the exact densities of desirable species to eliminate weed populations. The test assigns a number to each species indicating the strength of its interaction with other species. Interaction strength rating is level one to level one-hundred, with level one assigned to very weak members of the plant community---plants very easily overtaken by stronger-growing plants. Level one-hundred indicates the most weedy species that are extremely tenacious.

Yellow starthistle is one roadside plant in California with a bad reputation. It is a summer annual accidentally introduced from Europe and now covers over eight million acres. The Species Threshold Test yielded surprising results for this plant:

"According to my test, starthistle turned out not to be an agressive weed," Dremann reports. "It's rating was only a feeble level five, which puts it in the category of the weakest weeds."

The test indicated that starthistle covers the land by default rather than by aggressiveness. Dremann states that, "Starthistle's low Species Threshold rating indicates it is growing where the natural ecosystem has completely collapsed, in areas so poor in species and nutrients that even exotic weed grasses have difficulty surviving. Any improvement in the destroyed habitat would eliminate starthistle."

Dremann's ultimate answer to weed infestation is restoration of functioning native ecosystems. "Otherwise, we're just substituting one element of a destroyed ecosystem for another. We only have solid stands of plants like yellow starthistle because we have allowed our native ecosystems to collapse."

Dremann's test could determine the proper mix of species for a restoration project, and proper densities required to produce a thriving, self-sustaining community. Ecological restorationists replanting native plant communities would have a valuable tool by utilizing Dremann's test.

Contact Craig C. Dremann if you would like help with weeds or roadside vegetation restoration or management, email

Updated April 30, 2016. Back to Craig Dremann's main Contents page