Step outside this afternoon and the balmy air ensures the big freeze of 2013 is over. Yes, ever so rarely the Sonoran Desert is visited by an arctic air mass. The past few days I’ve been wearing two layers of pants and a fleece coat – inside the house!
I’d crack open a shutter and peek outside to observe the yard redecorated as a graveyard, misty and frosted, with plants draped in sheets, their colors erased and their forms smudged. Even beneath protective covering the leaves of plants from basil and lettuce to citrus and ficus shriveled and turned black. What about native species?
Saguaro cacti suffer from a hard freeze. Depending on the time of year, the length of the freeze, the age and microclimate of the individual plant, these cacti may die from the cold. Generally the largest and the smallest of the saguaros are most vulnerable. The freeze kills the outer tissue on portions of the body of the cactus. These injured areas scab over with brown patches that no longer contribute to photosynthesis, causing the plant to slowly starve. Saguaros generally do not grow on valley floors where cold air pools and successful seedlings flourish in the shelter of nurse plants.
In December of 1978 a polar air mass swept into the Sonoran desert and sent night time temperatures into the teens while day time temperatures remained below 30 degrees Fahrenheit for four consecutive days. This caused widespread damage to saguaros as well as mesquites and brittle bush. This week’s cold snap pales in comparison.
The hummingbird is another desert species vulnerable to cold. The amped up metabolisms of these tiny birds require constant fuel, and keeping warm through a freezing night is too much to ask. Rather than resisting, hummingbirds react to extreme cold with a survival technique known as torpor. They hunker down in sheltered thickets with their heads pulled in and their beaks pointed to the sky, while allowing their feathers to lift, releasing body heat. The hummers’ temperatures drop, while heartbeats and breathing slows to a near stop. When the sun rises hummingbirds have the miraculous capacity to ramp back up to seek food and energy.
As we wimpy humans recoil from frigid breezes and hide indoors, wild plants and animals utilize hardship as another evolutionary nudge toward adaptation to the rigors of life.