There is increasing alarm around the world about how human activities are forcing the pace of change in the environment. A major concern is the effect we are having on plants.

Plants are major regulators of the environment through their ability to capture energy from the Sun and convert it to a form available to other organisms; through their influence on shaping the composition of our atmosphere by removal of carbon dioxide and addition of oxygen during photosynthesis; by their retention, circulation, and evaporation of water below, at, and above the Earth's surface; and in their ability to mine and redistribute mineral elements in soil via their roots, thus contributing to the weathering and breakdown of the surface layers of the planet. All of these critical functions of plants are under threat because of stresses imposed on them through global warming, deforestation, afforestation, agriculture, industrial and domestic pollution, irrigation, drainage, and flooding.

Before the Industrial Revolution began a few hundred years ago, the pace of changes to the Earth was affected by human activities in only limited, localized ways. Chapter 15 is devoted to an examination of this phase of development of our planet, particularly the cycling and recycling of some key chemical elements on which living organisms depend.

As industrialization took hold and grew, the pace of alterations to the Earth's environment began accelerating to what has now become an alarming rate, leading to changes to our land, water, and atmosphere resources, causing an increasingly wide array of stresses on plants.