Bramble

An increase of brambles in a tall-herb swamps is not a good sign. Usually, there is an increase of brambles when the damp soil dries out. This is because brambles do not like conditions that are too moist. More intensive mowing can cause bramble dominance to decrease. 

A little bit of bramble certainly can't hurt. In some places, bramble domes are even desirable e.g. for the tree frog, songbirds and butterflies, but brambles should not dominate large parts of the moist shrubland.