Why is ecology not limited only to the forces of nature?

Ecology is not limited to the forces of nature as it gradually gets modified by human actions. Many seemingly natural features and phenomena associated with the environment are the caused by human activities. For example, the change in climate because of global warming seems to be a natural process, but is an outcome of the human activities. The conservation of soil and water, usage of pesticide, and other man-made materials in agriculture are other examples of human transformation of nature. Artificial environment is prominently visible in cities in the form of built environment made from concrete, cement, brick, stone, glass and tar.