An Unusually Warm Spring

Ripe Saguaro Cactus fruit a month early.

Warm weather conditions have been present across the Norther Hemisphere this spring.  This has resulted in a lot of unusually early blooming activity.  Here in the Sonoran Desert everything seems to be two weeks to one month ahead of schedule due to the warm weather.  Signs of this started showing up probably in March when I noticed some of the plants blooming quite a bit early.  First, the hedgehog cacti bloomed about four weeks early in mid-March.  Then Buckhorn Cholla bloomed a few weeks earlier than normal.  Cholla flower buds matured so quickly this year that I entirely missed harvesting any buds.  Normally, cholla buds are available to harvest even into the beginning of May but this year the entire harvest was finished towards the end of April.  Saguaro Cacti also began blooming mid-April, a month a head of schedule.  Today, I found quite a few ripe Saguaro Fruit.  Normally this fruit doesn't ripen for another four or five weeks during the hottest part of the summer.  Ironwoods and Palo Verde trees also bloomed weeks ahead of schedule.  

Hedgehog Cactus flowering a month early in the Sonoran Desert.

Other places in North America have also been experiencing early blooms.  In the Midwest, Morel Mushrooms popped up in forests four to six weeks ahead of schedule!  Fruit trees also bloomed six weeks ahead of schedule.  Unfortunately, this extremely early bloom was followed by freezing temperatures that killed the flowers or immature fruits, so fruit harvests will be very poor later this year.  Last week, when I visited the eastern deciduous forest in Missouri the forest looked like it was late June or early July with all the leaves on the trees.  According to weather patterns the farmers also are quite a bit behind schedule, but we really don't know what that will do to crop production this summer if warm weather continues.  There is a possibility that the normally dry late summer will arrive earlier and stay longer, hurting crop production.

Morel Mushroom.

So what is causing all this warm weather that results in early blooms and leaf-outs?  Global warming?  That is a good possibility, but it is hard to point a finger directly at that.  Most likely, global warming is contributing to the warm weather, but it also is probably just an unusually warm year on top of that.  The simple fact that nearly the entire Norther Hemisphere is experiencing such warm temperatures strongly suggests it is more than just an oddly warm year.  Such major and wide spread changes in weather don't just happen unless large changes in overall climate are happening.  It will be interesting to say the least to see how weather and plant and animal patterns change in years to come as the climate warms.  Many of the agricultural problems we see this year are likely small tastes of what is to come as the climate changes.

Life of a Cactus Part 6: Callus

Woodpecker entering a Saguaro "boot" used for nesting.

The last water conserving feature of cacti we will discuss is the abundance of mucilage all cacti produce internally.  If you were to cut open a cactus and touch the internal tissues you would notice the cut surface as being wet.  It would not be a watery wet though, it would be a slightly sticky and slimy wet.  This sliminess, known as mucilage, is a result of polysaccharides, or carbohydrates, produced by the cactus.  This mucilage helps hold on to water, slowing evaporation.  It also functions to form a callus or scab once it is exposed to the air.  This callus functions similar to how scabs function for us.  When we bleed a scab forms to prevent further loss of blood and to prevent infections from entering the body.  When a cactus is damaged it also forms a scab to prevent bleeding of water as well as to prevent infections from entering the cactus.  The scab also hinders predation of the cactus by being a barrier between the cactus flesh and potential predators.  Often the callus can become several millimeters thick.  If you are around cacti at anytime, look for damaged sections of the plant.  The callus will be a tan to black coloration on the damaged portion.

Saguaro boots like this one will often survive long after the cactus decays away.

All cacti form calluses, which may be helpful to the cactus but an annoyance to any animal that may want to feed on cactus flesh.  A lot of birds though find cactus calluses quite useful.  In large columnar cacti such as saguaros, woodpeckers will remove the spines and peck a hole.  Gila woodpeckers and flickers are the most common birds that do this in the Sonoran Desert.  These woodpeckers will excavate a hole large enough to nest in.  Of course, excavating a hole in a cactus will cause it to bleed but a callus will in short time line the hole.   Typically, this causes little harm to the plant itself in the long-run.  These callused holes are called “boots” and will remain for the entire lifespan of the cactus.  Once the boot is abandoned by the woodpecker, an assortment of other birds will also use it for nesting being it is warmer in the winter and cooler in the summer.  Birds using saguaro boots for nesting include elf owls, kestrels, ash-throated flycatchers, and purple martins.  In-fact several species of birds can be found nesting in the same large cactus if it has many different boots.  This is why saguaros have been called by some a “cactus hotel”.  Oddly, these boots are so durable that, years after a saguaro dies and most all remnants of the cactus have decayed, the boot still remains lying on the ground.

A callused hole in a Saguaro cactus.

Life of a Cactus Part 5: CAM Photosynthesis

This is a microscopic image of the surface of a cactus stem.  The oval shaped objects with dark areas in the middle are stomata, the pores through which cacti and other plants breath.

Once water is stored inside of the cactus water conservation does not stop.  Microscopic pores called stomata cover the green tissue of all plants, allowing them to “breathe” and carry out photosynthesis.  Through these stomata, all plants “exhale” water vapor and oxygen and “inhale” carbon dioxide.  The exhaled oxygen is a waste product of photosynthesis.  Inhaled carbon dioxide, along with water stored in the plant, are converted into sugar and starches by use the sun’s rays through photosynthesis.  Water vapor is passively lost through the stomata whenever they are open to inhale and exhale carbon dioxide and oxygen.  Even when the stomata are closed a small amount of water vapor is lost.  Nearly all plants open their stomata to carry out this breathing process during the day.  As a result, most plants are opening their stomata when it is hottest and are therefore releasing huge amounts of water through evaporation.  In areas where there is plenty of water this really isn’t much of a problem, if you have water to spare you have water to waste and can afford to use it quite liberally.

Crested Saguaro Cactus.

 In the desert, there is no water to spare and to waste.  The cactus therefore does the exact opposite of what almost all plants do; it opens its stomata to “breath” during the night and closes them during the day.  By closing stomata when it is hottest and opening them when it is cooler the cactus conserves huge amounts of water.  The problem with this is cacti still need a constant input of carbon dioxide in order to carry out photosynthesis during the day, and without the stomata open there is no direct supply.  To overcome this, cacti absorb huge amounts of carbon dioxide at night time when their stomata are open.  They do not absorb this carbon dioxide like a balloon would though.  Instead, they convert it to a chemical called malic acid, in which form the carbon dioxide can be stored until day light.  Once daylight appears the, malic acid is then converted back to carbon dioxide needed to carry out photosynthesis.  Plants only need to breathe when it is daylight and photosynthesis is being carried out.  So in the dark no photosynthesis is being carried out and there is no reason for the plant to breathe.  This is why most plants only open their stomata and breathe during the day, and because day temperatures are warmer, more water is lost through the stomata.  As said before, cacti open their stomata at night to breath, storing the carbon dioxide as malic acid for later use when daylight appears.  Once daylight appears, the cactus closes its stomata and sort of holds its breath, converting the malic acid back into carbon dioxide for use in photosynthesis.  By only opening their stomata in the cool of night, far less water is lost.

Cacti stomata not only open and close in an ideal fashion to conserve water, they are also specifically designed to conserve water.  Most plants have large amounts of relatively small stomata all over their green tissues.  Relatively small cells also open and close these stomata.  Cacti however have far fewer stomata but the stomata they do have are much larger.  Overall though, this decreases the amount of water that can evaporate through the stomata.  Cacti also locate their stomata is a shallow pit as opposed to directly on the surface of green tissue.  This protects the stomata from drying winds.  Lastly, the cells that open and close the stomata are huge in comparison to the typical plant.  This allows the cacti to firmly close their stomata so water vapor does not accidentally leak out.