Introduction

Definitions

Resources such as C, H, N, O, P, and S are essential for the construction of new plant tissues. We have just seen in Chapter 3 that habitats with a chronic scarcity of such resources tend to have plants that differ from those in habitats in which resources are more freely available. Shortages of resources will tend to reduce rates of growth, thereby reducing attributes such as shoot size, root length, and allocation to flowers and seeds (Levitt 1980, Grime 1979, Larcher 2003). Stress is therefore defined as any factor that reduces the rate of production of biomass. It is important to understand that stress is different from disturbance, because disturbance, as we shall see in Chapter 6, removes only biomass that has already been produced.

Like any word, the term stress can be used carelessly. Too often, as Harper (1982) observes, it has meant “little more than the observer judging what I don't think I'd like if I was a buttercup, kangaroo, flea, beetle, etc.”