Plants can contribute to both chemical and mechanical weathering. The severity of the weathering is dependent on the size of the plant and tree as well as the kind of natural chemicals the plant or tree emits into the environment.
The main cause of fauna-related weathering is due to the roots of the trees or plants. The roots can grow slowly into the rock or concrete and cause mechanical weathering through cracks, splits or even entire structural failure. If a plant creates some sort of waste chemical with any level of acidity, it causes weathering as the chemical is released.