Introduction

The physical environment is the ultimate determinant of where organisms can live, the resources that are available to them, and the rate at which their populations can grow. Therefore, an understanding of the physical environment is key to understanding all ecological phenomena, from the outcome of interactions between bacteria and fungi in the soil, to the exchange of carbon dioxide between the biosphere and the atmosphere.

The physical environment includes climate, which consists of long-term trends in temperature, wind, and precipitation. Radiation from the sun ultimately drives the climate system, as well as biological energy production. Another aspect of the physical environment is the chemical composition of air and water, which includes salinity (concentrations of dissolved salts), acidity, and concentrations of gases in the atmosphere and dissolved in water. Soil is an important component of the physical environment because it is a medium in which microorganisms, plants, and animals live. Soil also influences the availability of critical resources, particularly water and nutrients. This chapter will focus on climate and the chemical environment; we will cover soil development and nutrient supply in Chapter 22.

This chapter will provide a framework for characterizing the physical environment, including its variability, at a variety of spatial and temporal scales. We will begin by exploring the processes that create the climate patterns we see at global to regional scales.