[alt text: Text that says, “People [say] 'I never see butterflies or lightning bugs in my yard. Their yard: (colon)”. Below the text is a photo of a birds-eye view of a large house with an equally large yard. The lawn is covered in standard turfgrass (probably Kentucky bluegrass) that has been recently mowed.]
The plywood was to provide extra weight for crimping the grasses, which helps to keep them acting as a cover for the next round of grasses and herbaceous plants coming up instead of standing back up. Some operations use a weighted crimper/roller on a tractor, some folks use railroad ties, Ray Archuleta used to use his daughter’s old honda civic… I had leftover plywood from a project.