protecting ground bees
The Marion County Master Gardeners are becoming involved with the Marion County Soil and Water Conservation District in a Backyard Habitat Improvement Program. One aspect of the program is about converting lawn area to something more beneficial, like native plants. A standard recommendation for how to do this, as in Eileen Stark’s Real Gardens Grow Natives on page 124, is to lay down newspaper or cardboard and cover that with some sort of mulch. How much of a problem is this for ground bees? What needs to be done to accommodate the ground bees?
I am glad to learn of this initiative from Marion County Master Gardeners. Hurrah!
Part of Oregon's new pollinator health Strategic Plan specifies the need to come up with backyard certification programs with recommendations for pollinators.
I would encourage you to reach out to the Oregon Bee Project and see if there is someway to partner as its in their mandate to be supporting initiatives such as yours.
Weed control is the most important feature of establishing pollinator habitat. I think there are not many great ways to both control weeds and maintain ground nesting habitat at the same time, particularly when mulch is involved. My suggestion is to maintain some area (and you don't need much) that is not mulched. These might include rock garden features or pathways. Although there is a great variety of soil preferences by ground nesting bees (preferences that are notwell understood), my experience is that many species like a hard packed soil that you would have around a pathway and rock garden (although we have also seen early spring miner bees build nests right into the lawn).
A few alternatives to consider beside taking lawn out are more diverse lawn seed blends that contain clovers, micro clovers and yarrow. Also incorporating spring blooming bulbs into lawn (that bloom before mowing begins) may be an easy strategy that enables people to build pollinator habitat that a broader group of people would be willing to adopt:
Converting lawn to pollinator habitat can have immense challenges and certainly using a barrier and mulch can be a good strategy.
But depending on the weeds that are present, even this approach will require maintenance over time.
Two good videos outlining strategies for establishing habitat with pollinators can be viewed here
Quick guide to establishing wildflower plantings: https://www.youtube.com/watch?v=jJSGXb81xbM&t=69s
There has been some good research on the use of solarization iat OSU. Here is a link to that work: