In late July or August, after the saguaro cactus has fed and housed countless species of insects, birds and mammals, its seeds fall finally to the desert floor where they wait for monsoon rains. The season’s activity began back in February when Gila Woodpeckers and Gilded Flickers excavated holes in saguaros in preparation for nesting season. Once the wounds in the giant cacti sealed, forming “boots”, many different types of birds moved into the cozy cavities, laying eggs and raising families.
Flower buds formed on the ends of the saguaro stems in May, creating fashionable hats on the stately plants. Creamy white flowers brimming with nectar nourished bees, flies, beetles, bats, White-winged doves, Gila Woodpeckers, finches, ravens and more.
By June the ripe fruits had split open, providing about the only moist food available to desert animals during the hottest, driest time of year. Birds feasted on the juicy fruits, knocking some to the ground where rodents, coyotes and javelinas profited. Everyone had nutrient dense food for their babies, thanks to the saguaros.
Nearly every creature in its range is tied in some way to the towering cacti. When a saguaro falls, due to disease or old age, even more critters gain food, shelter and precious moisture, as the plant slowly decomposes.
Saguaros can live 200 years or more. Depending on soils and rainfall, some grow arms when they are between 50-100 years of age. Waxy skin protects the water they hold in their interior tissues – a fully hydrated stem is 90% water. Expanding pleats allow the plant to accommodate maximum moisture. This store of water insulates and protects saguaros from extreme temperatures. In summer the cacti’s moisture absorbs daytime heat and radiates it back out in the relative cool of night.
With July or August monsoon rains, the saguaro seeds germinate. Those that have been deposited by birds under trees such as ironwood or Palo Verde have the best chance at survival. Sheltering nurse plants provide shade and a more humid environment. Very few seedlings will grow to adulthood. Too small to hold ample water for insulation, they are vulnerable to heat and frost. And, the tiny cactis’ soft spines don’t always deter predators. Survival requires a nurse plant, some luck, and several consecutive years of milder temperatures and above average rainfall. If you look across the desert, cohorts of equal sized saguaros illustrate the rare providence of perfect conditions, often many decades apart.
This year there have been no monsoon rains, and record high day and night temperatures over many weeks have stressed desert life, including the mighty saguaros. Scientists believe the cacti are already beginning to migrate to higher elevations and north facing slopes, in a slow march to survive climate change.