Saguaro Watch

Why Watch Saguaro's?

     We do not normally think of plants as individuals. A lawn is 'grass' or 'turf', for example; or we may see a cornfield as part of a farm operation but not see unique, individual corn plants. Trees on the other hand can clearly stand above and apart from the other plants in a landscape. A saguaro cactus appearing tall and proud within the harsh environment of the desert truly evokes this feeling within us, a feeling that it must possess extraordinary traits of fortitude, patience, wisdom and experience. We imagine all the years having passed since the minute cactus seed germinated a century or more ago, all the blistering hot days and freezing winter nights that have been endured, and all the lives of neighboring plants, animals, even humans that have come and gone.

     The saguaro cactus is the icon of the Sonoran Desert and indeed it is an ecological keystone species upon which many other Sonoran Desert species depend for food and shelter. Without the saguaro, the Sonoran Desert becomes but a shadow of its glory and function.

     As tough as the Saguaro Cactus is, its survival within parks and preserves is not assured. Although governments within the Sonoran Desert have gone to great lengths to preserve large areas of Sonoran Desert, the preserves are often too small and fragmented to sustain a complete ecosystem. The preserves have become virtual islands of desert within a sea of highways, parking lots, and watered lawns. The mechanisms of island biogeography come into play resulting in restricted gene flow or local extinctions of saguaros or other key species. Consider the chuckwalla, rattlesnake or desert tortoise: it is unlikely that these animals could negotiate the many perils of crossing an Urban Sea.

     Besides these indirect effects of existence on an island, the saguaro cacti within our preserves suffer many direct threats to their survival. Naturally, wildfires do occur in the desert, but only rarely. But now there are many more fires caused by careless people, abrupt changes in animal grazing practices and especially the spread and pervasiveness of exotic weeds. The two most implicated weeds are red brome grass and buffle grass. These grow abundantly during wet periods later to dry into highly inflammable material. A single spark from an automobile, cigarette or lightning is enough to set thousands of hectares ablaze killing most of the saguaros.

     The microclimate of preserves is also affected by the surrounding urbanization. Nighttime low temperatures within the cites are warmer by 10° C or more than during historical times. This phenomenon has come to known as the 'heat island effect'. Then there is air pollution, with ozone being the most detrimental to plant tissues. It is not clear how these will impact the longterm survival of saguaros or other members of the Sonoran Desert ecosystem.

     Vandalism is another, heartbreaking, threat. I have witnessed several saguaros that finally succumbed to repeated rock-throwing attacks. Injuries reduce the photosynthetic area and the injuries can be invaded by secondary infectious rots. Then there is outright thievery. This emblematic icon is sought after for yards and landscapes. There are strict laws against removal of cacti without a permit, but there simply aren't enough cactus-cops on patrol.