Primary Desert Succession
In
deserts, primary succession could occur on a sand dune or a fresh lava
flow. Bacteria or seeds of colonizing species find a foothold where a
microclimate offers a pocket of increased moisture and protection. These
original colonizers form biofilms and put down roots that stabilize the
upper layer of soil and break down rocks. The improved soil can hold
more moisture and support other plants, which crowd out the original
colonizers. Eventually the ecosystem may be able to support grasses and
finally woody shrubs, if there is enough water.
Secondary Desert Succession
Desert ecosystems can be disturbed by fire, flash flood scouring or land
clearing. After disturbance, succession is set back, but the soil has
already been developed. Secondary succession in deserts is relatively
quick compared to primary succession, but it takes much longer to
establish a desert community than it does in less arid regions. For
example, in the southwestern deserts of North America, it can take 76
years to establish perennial plant cover and 215 years for full
ecosystem recovery. If the disturbance is great enough, secondary
succession may produce an entirely different climax ecosystem.