Treading causes erosion and visual damage to a landscape.
Graffiti is an eyesore, and the spray paint releases toxic gases. The disposal of the aerosol is also a problem.
Cutting trees reduces the number of trees, reducing the earth's capacity to create oxygen and to lock away carbon. It can also lead to soil erosion and loss of habitat for animals, reducing bio-diversity.
Littering is unsightly, and can be hazardous to animals. Things like plastics will exist for an unquantifiably huge amount of time without naturally rotting away.
Fires are not necessarily bad. They are nature's way of renewing an area for new vegetation, but deliberate fires can be fueled by toxic substances.
Dog faeces are hazardous and can cause very serious illness, even blindness.
