The vertical orientation of cliffs represents the primary (if obvious) difference from other landscape types, but verticality affects the environmental conditions on cliffs in a number of important ways that are not always obvious to ecologists who study the microclimate of level ground or slopes. The function of this chapter is to point out the various ways in which the physical environment of cliffs is distinct from that of horizontal surfaces. Its purpose, therefore, is not to give a complete account of all components of the physical environment. The reader is referred to standard texts, such as Monteith and Unsworth (1990), Arya (1988), Oke (1987) and Gates and Schmerl (1975), for basic information on microclimate and energy balance.

The first subsection briefly outlines the various components of the physical environment that are affected by vertical orientation of the substrate, and shows how these factors are interconnected in a complex way to make the cliff environment drastically different from surrounding level ground. More detail on each of these factors is then provided in the subsections that follow.

The effects of vertical orientation

Vertical orientation affects the total amount of direct radiation a surface receives and the way radiation input varies diurnally, seasonally and latitudinally. It also affects wind speeds on the surface and the amount of direct precipitation received. Radiation, wind and moisture together control the temperature of the rock. Absorption of radiant energy increases rock temperature, while wind speed controls the amount of energy that is dissipated by the heating of air and the evaporation of moisture, thus cooling the cliff surface.