Rhododendrons look lovely, but they can be an invasive species. They shade out smaller plants and the ground around them becomes bare. I know in some places they are removed. Rhododendrons are native to Asia but were imported by plant collectors in the Victorian era. They ‘layer’ themselves to spread, a branch can touch the ground and where it rubs against the soil it will send out roots (or layer). This also happens with other plants. Forest and parkland have to be managed to protect it from invasive species like this and others such as Himalayan Balsam and Japanese Knotweed.