The Deserts and semi-deserts biome includes low to very low biomass ecosystems occurring in arid or semi-arid climates, principally associated with the subtropical high-pressure belts and major continental rain shadows.

Primary productivity is low or very low and dependent on low densities of low-stature photoautotrophs that sustain a complete but sparse trophic web of consumers and predators. Productivity is limited by severe water deficits caused by very low rainfall. Rainfall deficits are exacerbated by extremes of temperature and desiccating winds.

Resources, productivity, and biomass are highly variable in space and time in response to the amount of annual rainfall, the size of individual rainfall events, and the lateral movement of resources from sources to sinks. Landscape heterogeneity and resource gradients are therefore critical to the persistence of desert biota in the context of highly stochastic, unseasonal temporal patterns of rainfall events that drive ‘pulse and reserve’ or ‘boom-bust’ ecosystem dynamics. There may be high rates of erosion and sedimentation due to the lack of surface stability provided by the sparse vegetation cover and this can be amplified by the activities of large mammals and people.

Extreme and prolonged water deficits, punctuated by short episodes of surplus, impose severe physiological constraints on plants and animals, which exhibit a variety of physiological, morphological, behavioural, and life-history traits enabling water acquisition and conservation. The life-history spectra of desert systems are polarised between long-lived drought tolerators with low metabolic rates and opportunistic drought evaders with either high mobility or short-lived active phases and long dormant phases. Mobility enables organisms to track transient resources over large distances. Competitive interactions are weak, although herbivory and predation are more evident in the most productive ecosystems and during the decline in resource availability that follows rainfall events.