Sunday, June 26, 2011

Saguaro natural history and fruit harvesting

Saguaro fruits ripening on the ends of some saguaro arms. 
As mentioned in a previous post, the month of June can be pretty slow in the month of June.  Slow that is until the Saguaro (Carnegiea gigantea) fruits ripen and begin bursting open.  If it wasn't for this fruit the normally 110 plus degree temperatures and scorching sun would keep everything wishing they were in the mountains or hibernating somewhere far away.  Ripe Saguaro fruit wake many animals up from the lazy month of June. Due to these fruits these organisms are more willing to brave the extreme heat and will often hyper-actively gorge themselves for several weeks.  These juicy fruits are not simply an abundant food source, they are also an abundant water source during the hottest driest time of year.  When the fruit is ripe it bursts open, exposing the edible pulp to the outside world.  Bugs of all types will swarm around these fruits, eating the sweet contents.  Even ants will climb to the top to find the food.  Many types of birds will also go from Saguaro to Saguaro eating their fill of fruit or bugs.  Much of the fruit also falls to the ground where rodents, deer, and javelina can consume them.  As you can probably see, without the Saguaro not nearly as many animals could inhabit the Sonoran Desert through the summer.  This is part of the reason Saguaros are considered "keystone" species.  Keystone species are organisms that play a critical role in determining ecosystem structure and what organisms live there.
Dove sitting atop a Saguaro consuming ripe fruit.
Conveniently and purposely, Saguaro fruit ripening is timed only a few weeks prior to the summer monsoon rainy season.  Saguaro fruit pulp is loaded with tiny black round seeds that are eaten up by anything that eats the fruit.  Oddly, this is actually a very good thing.  As long as the seeds are not chewed they will pass through the entire digestive tract unharmed.  In-fact, partial digestion of the seed coat may actually help seed germination.  Being saguaro fruits are so high in the air, birds are the primary consumers and carrier of the seeds.  When undigested seeds pass unharmed through the digestive tract, they are often deposited under a bush or small tree such as the Palo Verde (Parkinsonia microphylla) that the bird perched in.  These nurse plants (the bush or tree) create an ideal microclimate with increased moisture and nutrients, and decreased sun and temperature.  This microclimate is ideal for the saguaro seed to germinate and grow to adulthood.  Even so, only a tiny fraction of seed actually germinate, and an even tinier fraction grow to maturity.  And by tiny fractions I mean tiny fractions of one percent, the remaining seeds or seedlings die in the unforgiving desert environment.  This is absolutely normal, and for a Saguaro population to maintain itself only one Saguaro needs to reach maturity for each Saguaro already in existence.  That is, each plant only needs to produce one out of millions of seeds that germinates and grows to maturity.  To help ensure germination of these seeds the plant produces all its seeds every year just before the summer rains.

Two Saguaro fruits.  The black part at the top of the fruits in the old flower.  
Humans also have been active Saguaro fruit harvesters and consumers for many millenniums.  The process is quite easy if you have a long stick, 10 foot or so, and are willing to brave the heat.  In Arizona there is no law that I know of that prohibits non-commercial fruit harvesting, but the laws are obscure.  To be safe, harvest with someone, or an organization that has a permit, or on private land.  Also don't harvest very much.  Land managers have told me it is OK to do within reason.  It is however illegal to collect from a crested saguaro.  According to the laws, as long as you are not damaging or removing the plant it is "legal", again the law is obscure and incomplete when it comes to fruit harvesting.  But again, collect with an organization with a permit or on private land, do not harm the plant, and limit how much you collect.

Saguaro fruit cut in half.  The soft red pulp in the middle is what can be eaten.  The green and white wall should not be eaten.
Saguaro fruit is collected by knocking the fruit off the cactus with a long stick and then picking the fruit up off of the ground.  If you want to, you can try catching the fruit in a bag or basket.  Fruit harvesting is best done early in the morning before the scorching sun and 110 plus degree temperatures roast you.  Once a fruit is harvested simply cut it in half and scoop out the soft pulp and eat it.  Do not eat the surrounding wall of the fruit, it contains slightly toxic substances in it and does not taste good at all.  It is extremely good and refreshing in the summer heat.  Native Americans have also dried the pulp in the sun to make a sort of fruit leather.

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