There's life under that grass.

Just off picture, to the right of the yellow hut are a couple of large European Aspen, trembling aspen. They had been growing quite a few years before we moved here, and now they must be around 50 or 60 years old. They have sent their roots out far and wide, gathering in nutrients to the parent tree. However, aspen roots also send up shoots if they find daylight available. Our lawn provides an ideal environment and every year the shoots appear further and further away from the parent. The shoots are now appearing about 30 meters from the parent tree.
So if we didn't cut the grass we'd soon have a large copse of aspen growing here. In the far corner of the field outside our house that is precisely what has happened and there are about 40 trees growing in a tight bunch. Each tree is a part of the collective organism, genetically identical and sharing a common root system. 
The largest such aspen copse so far identified is the Pando organism in Utah.
I cut the grass, and the aspen shoots, and intruding raspberry canes, and even a couple of plum tree suckers trying their luck. Nature is wonderful, and will move in really fast if we're not careful!