Abstract: Since 1960, 22 species of individually marked, arid-zone perennial plants in the Murchison District and Gibson Desert of Western Australia have been monitored for flowering, fecundity, and survival. The age to which individual species survive was determined in terms of half-life, i.e. the time elapsed for half of the marked sample to die. The estimates ranged from 6.5 to 535 years. Phenology was recorded by observing whether the plants carried buds, flowers, fruits, or any combination of these, or were sterile. Fecundity of each species was measured by recording each year the percentage of the sample trees that carried fruit, by collecting seeds in trays placed beneath the plants and by counting the pods produced by some species. Fecundity was related to seasonal rainfall, most species responding positively to summer rainfall. The concept of mast years, as utilised in the northern hemisphere, was applied to recorded fecundities and some evidence was found that, after a year of high fecundity, the plants responded less vigorously to conditions of high rainfall than they did in the previous year of high rainfall. This suggests that, in years when fecundity is high, it diminishes the resources available within the plants to respond to heavy rainfall the following year or reduces the soil nutrients available to them.