Back from the dead...again!

Solomon's seal has never been plentiful in the wild in our area, but for many years there was a healthy patch in ash woodland at my nature reserve. Then, about 15 years ago, it started to be harder to find each spring. At least twice since then I've thought we had completely lost it after not seeing it for a couple of years. Today I found two plants, apparently doing well, in the sea of dog's mercury that now dominates the woodland floor. I have a feeling this is part of the problem - the dog's mercury is so dominant now, probably the result of the increased deposition of atmospheric nitrogen. I'm pondering what we can do to keep the solomon's seal going.