Like all things this plant seems to be one man's bread and another's poison. I have read that it is indigenous to the West Coast. The State plant of Oregon. People rave about it's beauty and edible and medicinal properties. Not so in Wikipedia. They say it is a bad invasive.
I am researching it for a Permaculture Project that my club is working on at Bristol Community College in Fall River, MA. That's the East Coast.
Any thoughts on the subject?
I noticed a subject here that mentioned day lilies as an invasive. Not me, I use them in many different environments with satisfaction. Back to my opening statement.
First- as to day lilies, the plants referred to as invasive are the ubiquitous (here) orange ones often called "ditch lilies". Are these the ones you grow?
Second- The invasiveness of a plant varies from one part of the country to another, so one needs to research a plant's impact locally. Your local Extension Office should be able (and willing) to provide this information to you. However. here is a link to an evaluation of plants for Massachusetts. http://www.newfs.org/docs/docs/MIPAG040105.pdf . Mahonia is not listed.
Mahonia aquifolium isn't even listed as occurring in the wild anywhere in MA, so it's very unlikely that it would be invasive there. http://plants.usda.gov/java/profile?symbol=MAAQ2&mapType=large&photoID=beaq_001_ahp.tif Also, if you look at the references cited next to the statement in Wiki about it being invasive, they are first of all from southeast states that have a very different climate from MA, and secondly if you actually go to the sites that are referenced, they are talking about other Mahonia species like M. bealei, not M. aquifolium. (FWIW, M. bealei isn't listed as occurring in MA so it also wouldn't likely cause problems for you either, although since it can be a problem elsewhere I'd go with M. aquifolium anyway)