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.

Life of a Cactus Part 4: Spines

The red, hooked spines of a Barrel Cactus.

Obviously, spines also are a major deterrent to any creature wanting to access the cacti’s rich moisture reservoir.   Many animals still consume cacti anyway.  Prickly pear pads are a staple to javelin.  During extreme drought many animals including packrats and mule deer will consume cacti to obtain water.  I have found entire barrel cacti hollowed out in the inside by rats or chipmunks eating the inside tissue to obtain water during extreme droughts.  Mule deer and javelina supposedly will remove cacti spines with their hooves before eating the tissue.  So under extended dry conditions animals are willing to brave spines and oxalic acid to obtain water.  A few cacti, have such a huge density of spines very few animals ever dare go near them.  The teddy bear cholla is one such example, while the huge density of spines may look fuzzy and attractive like a teddy bear from a distance, one encounter with this cactus will deter you forever.  Teddy bear and jumping chollas both have spines that are microscopically barbed or hooked like fishing hooks.  So it is much easier for these spines to penetrate skin rather than be removed.  I often step on teddy bear cholla joints which isn’t so bad being I have shoes on, but once I accidently bumped a joint on my shoe into the calf of my other leg.  Removing the spines was excruciatingly painful and difficult due to the barbed spines.  Then, the day after, I developed one of the most amazing bruises right were the joint was stuck in my calf.  The bruise changed from blue and black to yellow and green over time, and to say the least I learned my lesson and stay as far away from teddy bear chollas as possible.

Buckhorn Cholla cactus.

Obviously, spines are used to deter animals from eating cacti, but they have a few far less obvious but still very useful functions also.  Spines actually provide a significant amount of shade, helping to cool the plant and therefore prevent water evaporation.  The shade also protects cacti from intense desert sun which could damage the plant.  Spines also provide a sort of shield protecting the cactus from dry desert winds that might “steal” moisture.  Spines can also serve as insulation, preventing freezing temperatures from freezing and damaging the cactus.  Some cacti utilize spines to the extreme.  Teddy bear chollas are so dense with spines nothing can even begin to try and touch the green portions of the plant without first going through the spines.  Small pincushion cacti are also quite dense with spines.  These spines greatly reduce the amount of light reaching the plant, cooling temperatures slightly, as well as slow the wind.  Barrel cacti also have a higher density of spines on their tops where the growing tissue is located.  This protects the growing tissue from intense sun, extreme temperatures, and dehydration so the plant can continue to grow.  Senita cacti also often have a dense almost furry looking accumulation of spines near their tops.  

Close-up of a Buckhorn Cholla.

Desert Ironwood: Olneya tesota

Desert Ironwood flowers.

The Desert Ironwood is a subtle but one of the more interesting desert plants.  Saguaros and other cacti get a lot of attention as hard core desert plants, but the iron like endurance of Ironwoods makes them legendary.  Well at least I think it should, so let me explain.

A few weeks ago the Ironwoods lost most of their leaves in the process of getting ready to bloom.  Nearly every year this happens I fear the lack of rain in past months is killing the tree.  Not so.  Now in mid-May however, Ironwoods in the Sonoran Desert are shows off their stuff with purple blooms that cover the tree.  These flowers are quite beautiful and create quite an array of busyness for several weeks.  When hiking up to a blooming Ironwood this time of year the entire tree appears to be buzzing.  Thousands upon thousands of bees, gnats and other insects swarm the tree, feeding upon the nectar and helping the tree out by pollinating it.  Birds, such as Gnat Catchers and Fly Catchers, also actively feed on this buzzing swarm of insects.  With the minimal amount of rain the desert has received this past winter it is quite amazing that the trees can produce such a spectacular amount of flowers. 

A blooming Ironwood.

How does the Ironwood produce such great displays year after year, even when there is scant rainfall?  As I mentioned earlier, the Ironwood is an iron-like champion of desert conditions.  First off their roots penetrate far deeper than any other Sonoran Desert plant, some say up to 100 or more feet deep.  This allows them access to deep moisture, out of reach of other desert plants and protected from evaporating into the atmosphere.  Access to this highly stable water source is essential to its desert survival.  The problem with this however is that only a very tiny amount of moisture ever penetrates deep into desert soils, nearly all of it only soaks in a foot or two at the most before the heat evaporates it away.  This would make deep roots nearly useless except for one neat little strategy Ironwoods and other deep rooted plants often use.  When rain penetrates only the most shallow layers of soil, Ironwoods use their shallow roots to absorb moisture.  Some of this moisture is of course transported to the leaves to carry out photosynthesis but some of it also is transported downward through the deep roots and deposited into the soil deep below the surface.  Then, when everything drys out above ground the Ironwood reabsorbs and utilizes this moisture stored deep underground, allowing the plant access to water during long periods without rain.

About the only place where water penetrates deep into the desert soil is in the numerous dry washes that thread through the landscape.  This deep moisture penetration in dry washes, and the deep roots of the Ironwood, make dry washes a perfect habitat for the Ironwood.  The deep roots do well in the loose sandy soils of washes making Ironwoods one of the more common dry wash plants.  In-fact, they have been labeled as one of the "Big-Four" dry wash plants of the Sonoran Desert.  Even in areas of the desert that receive only four inches of rain, where it is two dry for much of anything to occupy the uplands, Ironwoods will occupy the washes.  These Ironwoods can survive quite well off of the moisture that seeps deep into wash sediments due to infrequent flash floods.

Ironwood actually derives its name from the very nature of its wood, another important desert adaptation.  Like iron, the wood is extremely hard, and is so dense it actually sinks in water.  The hard nature of this wood helps siphon water up from the roots to the leaves even under extreme drought conditions.  Softer wood would cause a breakage of the water column being siphoned up the trunk and to the leaves.

These adaptations make the Ironwood the largest desert tree of the dry uplands.  I have found Ironwoods with trunks three foot in diameter and thirty foot tall.  No other desert tree attains these sizes unless they are along a perennial river.  In the large limbs and trunks I have often found large bee hives or pack-rat middens.  I have also found Kit Foxes hiding high up in the trees.  Other desert trees typically never attain sizes near enough to support these types of things.  Ironwoods also survive cutting being they readily re-sprout from their trunks.  In some areas I have found nearly every Ironwood has been cut sometime in the past by the presence of old stumps.  These stumps however re-sprouted and now support very healthy trees.  It is very rare to find a dead Ironwood, especially in comparison to other desert trees.  I also suspect Ironwoods to be one of the oldest desert plants.  I am sure they can live for several hundred years without problem. 

Saguaro Cactus Flower Bloom

Saguaro Cactus flower.

I know I have been posting a lot about cacti lately, but hey, cacti are some of the coolest plants around.  And one of the coolest cacti around is of course the Saguaro.   Currently this cactus icon of the Sonoran Desert is in full bloom and causing quite a commotion with desert life.  Being cacti are quite the stingy conservatives when it comes to water it is quite unusual to examine a cactus in bloom.  Cacti flowers are very liberal when it comes to water use for flowering.  Much of this water use goes towards producing nectar, which attracts all kinds of desert dwelling organisms.  Saguaros begin flowering at night time and attract Lesser Long-Nosed Bats which feed upon the nectar and transport pollen from one flower to the next.  Once daylight arrives, bees and doves feed on the nectar and pollinate the flowers until afternoon or so when the flowers shrivel-up.   Buzzing swarms of bees and other flying insects quite commonly surround Saguaro blooms in the morning.  These swarms often attract insect eating birds that actively dart around catching their dinner. The simple act of blooming supports several different levels of the food chain.  Once Saguaro blooming is finished up in the next couple of weeks though, this activity will cease and the desert will become quiet until the next, and even bigger annual Sonoran Desert event takes place.  This event is the ripening of the Saguaro fruit which takes place at the end of June.

Blooming Saguaro Cactus next to a blooming Ironwood Tree.

Life of a Cactus Part 3: Rain

Cacti don’t need a lot of water, but sufficient rainfall at least a few times a year is of course desirable.  When soil is soaked by recent rainfall, cacti binge on the soil water.  Water is absorbed faster than the cacti can utilize it and the excess water is stored in succulent tissue.  This stored water ensures the plant remains healthy through periods of drought but generally is utilized within a few seasons of drought.  This is different from some desert shrubs such as creosote that can go three years without any rainfall.  Some cacti are better than others at surviving dry periods.  For example, the eastern prickly pear which grows in the central to eastern United States needs quite a bit of rainfall every year to survive, 25 and upwards to 40 inches annually.  Beaver Tail Prickly Pear and the Teddy Bear Cholla of very hot and dry deserts of the southwestern U.S. on the other hand require only a few inches of rain annually and can go up to a few years without water.  These cacti are the extremes though in North America, most species occupy the slightly wetter deserts were say six to 12 inches of rain fall annually.

In general, cacti also require rain to fall during certain times of the year to ensure success.  Precipitation that falls as snow cannot be used.  Freezing temperatures first of all kill most cacti and cold moisture is not absorbed well.  The Great Basin Desert commonly having snowfall and dry summers, therefore has few cacti.  Cool weather precipitation above freezing can be absorbed and utilized though.  Being warm to hot weather plants, summer precipitation is also well utilized.  As mentioned previously, cacti typically do not endure extended seasons of drought though.  The Mojave Desert of southern California, northwestern Arizona, and southern Nevada has winter rainfall but long hot dry summers and therefore supports few cacti.  The Sonoran Desert of Southern Arizona and northwest Mexico however, has both a winter and summer rainy season and therefore supports an abundance of cacti.  Of course cacti can survive many types of desert conditions but they do generally require evenly dispersed precipitation above freezing to proliferate. 

Once water is absorbed into the tissue of a cactus, the plant holds onto it like gold.  Contrary to Hollywood myth, cacti don’t contain a swimming pool of water swishing around inside.  Water absorbed by roots is carried to internal succulent tissues where the cells are filled with and store the water.   Cells swelling with water causes the entire cactus to swell as mentioned before.  Once water is in the cells through it is not easily removed by anything other than the cactus itself.  To remove the water one would literally have to burst billions of microscopic cells.  So extract a glass of water from a cactus would take a lot of work.  It would be much easier simply to eat the cactus and obtain the moisture that way.  Unfortunately, cacti contain oxalic acid, a chemical that can cause kidney stones and tastes bad, and for that reason is a major deterrent to any creature that may want to consume a cactus.  

Life of a Cactus Part 2: Roots

Cactus Roots

Again, as might be expected, the cactus is a highly tuned water preserving organism.  The problem is that first these highly tuned machines must access water they need.  Everything you see above ground on a cacti is designed to hold water in.  The “skin” is thick and contains a waxy layer on top and spines prevent animals from eating the plant to obtain water.  No water enters the cactus from above ground and only the minimal amount necessary is allowed to escape out of the cacti.  Only roots do the job of zealously drinking the latest rainfall.  Nearly all cacti have very shallow root systems, most of which only penetrate no more than one foot underground.  A few cacti such as the saguaro have taproots that penetrate as deep as three feet into the soil.  Even that isn’t very deep compared to some desert shrubs such as creosote brush with roots extending over six feet in depth and Ironwood over 30 feet deep.   But while cacti lack depth of roots they have a vast breadth of shallow roots.  I once examined the root system of a saguaro cactus where most of the soil had been eroded away on one side of it yet left the most of the root system intact and free from soil.  The saguaro’s roots extended twenty plus feet away from the cactus and I couldn’t find a single root deeper than 24 inches into the soil, most were about one foot deep.  Others have traced the saguaro’s root system as far as 50 feet from the trunk.  Most other cacti also have extensively shallow root systems.

Initially, it seems counter intuitive for desert plants to have shallow roots until you realize that only rarely does moisture from rain in the desert penetrate more than two or three feet deep.  Then, once it does rain slumbering cacti roots awaken within hours, sending out tiny rootlets that quickly absorb water.  And when a cactus drinks, it doesn’t just sip, it binges by drinking as much as it can as fast as it can.  In hot deserts roots can’t grow too close to the surface simply because extreme soil temperatures kill the roots, so roots begin about an inch below the surface.  In cooler regions, such as in Colorado, the soil surface doesn’t get extremely hot so cacti roots can grow just millimeters below the surface, greatly increasing their ability to take advantage of every little rainfall.  A scientist once found prickly pear cacti in Colorado with roots only two millimeters below the surface.  This cactus was able to survive on only two millimeters of rain a year owed to the fact of its extremely shallow roots!

Once wet soil activates binge drinking, the cactus absorbs way more water than it is currently using so it must store it somewhere.  Tissue within the stems, pads, or joints absorbs this water and stores it for later use.  As more water is absorbed the stem, pad or joint swells.  Simply by looking at a cactus you can tell how well watered it is.  If it is swollen it is well watered and good to go for months without rain, even in hot weather.  If it is skinny or looking shriveled the cactus needs water.  Cacti are well adapted to swelling and shrinking.  Saguaros and other columnar cacti have palliated or accordion shaped stems that readily expand when swollen with water or compress when water is depleted.  A mature Saguaro can hold thousands of pounds of water by simply expanding its accordion shaped skin.  Pads of prickly pears and joints of cholla, also swell and contract readily, easily doubling or more in size when well watered.

After the desert soil dries out, roots begin to go dormant.  Tiny rootlets that developed in the wet soil dry out and die.  Wet mucilage around the roots also dries out and forms a sheath surrounding the roots preventing the roots from directly contacting the soil.  When this happens, the cactus quits drinking or even attempting to drink water from the soil.  In-fact, the sheath functions as a barrier to prevent any water from leaving the cactus.  This is actually quite unique to the plant world being most plants require their roots to be in contact with at least a little moisture in the soil at all times.  Once the soil dries out however, the cactus must draw from the reserves of water it has stored up in its tissue in order to carry out photosynthesis.  Even so, after a good rainstorm a cactus can absorb enough water to carry it through many months of intense drought.