Meeting One of North America's Rarest Oaks

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A post (and photos) by Robbie Q. Telfer

“Every species is a masterpiece, exquisitely adapted to the particular environment in which it has survived.”

-- E.O. mothereffin Wilson

One of the perks of working at The Morton Arboretum is you get to see cool lectures on tree science for free. At one such program, Dr. Mary Ashley from the University of Illinois at Chicago was sharing her research on oak pollen and how far it can travel to fertilize female flowers (far). She looked at not only trees in the Chicago region, but also oaks off the coast of California and in the Chihuahuan Desert of west Texas, as well as throughout Mexico. That latter oak was a shrubby species called Quercus hinckleyi or Hinckley oak. It is able to spread pollen over far distances as well, despite the fact that there are only 123 individuals known to be left. IUCN lists it as Critically Endangered.

As she was telling us this, it occured to me that I would be in West Texas soon to visit my sister-in-law, so afterwards I approached Dr. Ashley and asked if there was any way I could have the coordinates of Q. hinckleyi so that I could visit it, take a selfie, and luxuriate in the presence of something so rare. I made it clear to her that I understood just how important it was to keep this information a secret, because the last thing this relict needs is to be uprooted by poachers. Which I wish wasn’t a concern, but it is.

Dr. Ashley put me in touch with her colleague Janet Backs who graciously shared the coordinates. I could see the plants from Google maps satellite view. There they were. I probably waved at the computer screen sheepishly.

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As I waited for my time to bask in the majesty of botanical greatness, I consulted my copy of Oaks of North America (1985) by Howard Miller and Samuel Lamb to see what the entry for hinckleyi said.

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Notably, it mentions that “This is another of the oaks with no specific value, except as a curiosity.” More on that later.

After much anticipation, the time was upon us. I decided to drive out to the plants in my rental first thing in the morning after getting to Texas. The Chihuahuan Desert is an astounding place that my Illinoisan eyes weren’t altogether prepared for. It is perhaps the most biodiverse desert in the world, and compared to our prairies, woodlands, and wetlands, it feels like a different planet. Some of the cooler plants I got to see were tree cholla (Cholla sp.), Havard’s century plant (Agave havardiana), Wright’s cliffbrake (Pellaea wrightiana), and little buckthorn (Condalia ericoides). And also a family of introduced aoudads with TWO adorable babies. I also got to see my first javelina (as roadkill) and all kinds of birds new to me.

Tree cholla ( Cholla  sp.)

Tree cholla (Cholla sp.)

Havard’s century plant ( Agave havardiana )

Havard’s century plant (Agave havardiana)

Wright’s cliffbrake ( Pellaea wrightiana )

Wright’s cliffbrake (Pellaea wrightiana)

Little buckthorn ( Condalia ericoides )

Little buckthorn (Condalia ericoides)

Aoudads in the distance.

Aoudads in the distance.

Finally I got to the coordinates - luckily google preloaded the directions on my phone because there was absolutely no cell service where I was. I parked and walked to the plants. And lo, I present to you, Quercus hinckleyi.

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It’s in the white oak family, which I guess means more than just “has round leaves.” These leaves look like holly, and even the shed ones on the ground still had some stabbiness left in them. It’s quite diminutive - certainly compared to any oak I’ve ever seen and even by shrub standards. I’d pinch its cheeks if that wouldn’t make my fingers bleed. After getting the pics I needed and doing the atheist’s version of saying a prayer over it, I floated back to my car like a cartoon cat in love.

The rest of the trip was great and I can’t wait to go back.

Since returning, I have shown several of my non-plant nerd friends the pics of hinckleyi and they seem politely impressed but not, like, actually impressed. This is totally understandable! If your experience with plants is on the order of what looks best in a planting or what tastes best in your tummy, this shrub is not for you. After all “it’s only value is as a curiosity.”

I don’t know about that. I feel like it’s value is greater than that for humans - it’s a window into the North American continent before the climate shifted 10,000 years ago, it’s an individual member of our vast botanical heritage, it is unique, it is adorbs, and it helped Dr. Ashley, and therefore us, understand more things about the movement of oak pollen.

But beyond what it does for US, what if, and hear me out, what if it has a right to existence on its own, without being displaced by pipelines or aoudads or poachers? It is a member of its ecological community, and just like I feel a loss when a member of my community passes, we don’t have the language to articulate what is felt when a member of an ecosystem winks out forever.

Janet Backs told me that she heard of someone who was trying to poach acorns from a subpopulation of hinckleyi and that the landowners where that shrub is actually chased those folks for miles and miles down the road. I love that. I wish every single threatened species/subpopulation had someone who understood its value beyond what it does for humans enough to chase people, possibly with a gun, for miles and miles.

I have had a paltry bucket list for most of my adult life - boring stuff like meeting my heroes or getting to a 7th bowl of never-ending-pasta. But despite their apparent lack of reverence for Q. hinckleyi I think a pretty good guiding list for me would be to visit each of the 77 oaks of North America in their native habitats. I know they won’t all be as special as this experience, but what better way to visit the corners of this continent and its myriad ecological communities, than by visiting each of its oaks? I currently can’t think of any, and would invite anyone to, if not fund me, join me.

Meet the Ocotillo

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I love the ocotillo (Fouquieria splendens) for many reasons. It is an impossible plant to miss with its spindly, spine-covered stems. It is a lovely plant that is right at home in the arid parts of southwestern North America. Beyond its unique appearance, the ocotillo is a fascinating and important component of the ecology of this region.

My first impression of ocotillo was interesting. I could not figure out where this plant belonged on the tree of life. As a temperate northeasterner, one can forgive my taxonomic ignorance of this group. The family from which it hails, Fouquieriaceae, is restricted to southwestern North America. It contains one genus (Fouquieria) and about 11 species, all of which are rather spiky in appearance.

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Of course, those spines serve as protection. Resources like water are in short supply in desert ecosystems so these plants ensure that it is a real struggle for any animal looking to take a bite. Those spines are tough as well. One manged to pierce the underside of my boot during a hike and I was lucky that it just barely grazed the underside of my foot. Needless to say, the ocotillo is a plant worthy of attention and respect.

One of the most striking aspects of ocotillo life is how quickly these plants respond to water. As spring brings rain to this region of North America, ocotillo respond with wonderful sprays of bright red flowers situated atop their spindly stems. These blooms are usually timed so as to take advantage of migrating hummingbirds and emerging bees. The collective display of a landscape full of blooming ocotillo is jaw-droppingly gorgeous and a sight one soon doesn't forget. It is as if the whole landscape has suddenly caught on fire. Indeed, the word "ocotillo" is Spanish for "little torch."

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Flowering isn't the only way this species responds to the sudden availability of water. A soaking rain will also bring about an eruption of leaves, turning its barren, white stems bright green. The leaves themselves are small and rather fragile. They do not have the tough, succulent texture of what one would expect out of a desert specialist. That is because they don't have to ride out the hard times. Instead, ocotillo are what we call a drought deciduous species, producing leaves when times are good and water is in high supply, and dropping them as soon as the soil dries out.

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This cycle of growing and dropping leaves can and does happen multiple times per year. It is not uncommon to see ocotillo leaf out up to 4 or 5 times between spring and fall. During the rest of the year, ocotillo relies on chlorophyll in its stems for its photosynthetic needs. Interestingly enough, this poses a bit of a challenge when it comes to getting enough CO2. Whereas leaves are covered in tiny pours called stomata which help to regulate gas exchange, the stems of an ocotillo are a lot less porous, making it a challenge to get gases in and out. This is where the efficient metabolism of this plant comes in handy.

All plants undergo respiration like you and me. The carbohydrates made during photosynthesis are broken down to fuel the plant and in doing so, CO2 is produced. Amazingly, the ocotillo (as well as many other plants that undergo stem photosynthesis) are able to recycle the CO2 generated by cellular respiration back into photosynthesis within the stem. In this way, the ocotillo is fully capable of photosynthesis even without leaves.

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Through the good times and the bad, the ocotillo and its relatives are important components of desert ecology. They are as hardy as they are beautiful and getting to see them in person has been a remarkable experience. They ad a flare of surreality to the landscape that must be seen in person to believe.

Further Reading: [1] [2] [3] [4] [5]

The Wild World of the Creosote Bush

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Apart from the cacti, the real rockstar of my Sonoran experience was the creosote bush (Larrea tridentata). Despite having been quite familiar with creosote as an ingredient, I admit to complete ignorance of the plant from which it originates. Having no familiarity with the Sonoran Desert ecosystem, I was walking into completely new territory in regard to the flora. It didn’t take long to notice creosote though. Once we hit the outskirts of town, it seemed to be everywhere.

If you are in the Mojave, Sonoran, and Chihuahuan Deserts of western North America, you are never far from a creosote bush. They are medium sized, slow growing shrubs with sprays of compact green leaves, tiny yellow flowers, and fuzzy seeds. Apparently what is thought of as one single species is actually made up of three different genetic populations. The differences between these has everything to do with chromosome counts. Populations in the Mojave Desert have 78 chromosomes, Sonoran populations have 52 chromosomes, and Chihuahuan have 26. This may have to do with the way in which these populations have adapted to the relative amounts of rainfall each of these deserts receive throughout the year, however, it is hard to say for sure.

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Regardless, creosote is supremely adapted to these xeric ecosystems. For starters, their branching architecture coupled with their tiny leaves are arranged so as to make the most out of favorable conditions. If you stare at these shrubs long enough, you may notice that their branches largely orient towards the southeast. Also, their leaves tend to be highly clustered along the branches. It is thought that this branching architecture allows the creosote to minimize water loss while maximizing photosynthesis.

Deserts aren’t hot 24 hours per day. Night and mornings are actually quite cool. By taking advantage of the morning sun as it rises in the east, creosote are able to open their stomata and commence photosynthesis during those few hours when evapotranspiration would be at its lowest. In doing so, they are able to minimize water loss to a large degree. Although their southeast orientation causes them to miss out on afternoon and evening sun to a large degree, the benefits of saving precious water far outweigh the loss to photosynthesis. The clustering of the leaves along the branches may also reduce overheating by providing their own shade. Coupled with their small size, this further reduces heat stress and water loss during the hottest parts of the day.

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Creosote also secrets lots of waxy, resinous compounds. These coat the leaves and to some extent the stems, making them appear lacquered. It is thought that this also helps save water by reducing water loss through the leaf cuticle. However, the sheer diversity of compounds extracted from these shrubs suggests other functions as well. It is likely that at least some of these compounds are used in defense. One study showed that when desert woodrats eat creosote leaves, the compounds within caused the rats to lose more water through their urine and feces. They also caused a reduction in the amount of energy the rats were able to absorb from food. In other words, any mammal that regularly feeds on creosote runs the risk of both dehydration and starvation. This isn’t the only interesting interaction that creosote as with rodents either. Before we get to that, however, we first need to discuss roots.

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Creosote shrubs have deep root systems that are capable of accessing soil water that more shallowly rooted plants cannot. This brings them into competition with neighboring plants in intriguing ways. When rainfall is limited, shallowly rooted species like Opuntia gain access to water before it has a chance to reach deeper creosote roots. Surprisingly this happens more often than you would think. The branching architecture of creosote is such that it tends to accumulate debris as winds blow dust around the desert landscape. As a result, the soils directly beneath creosote often contain elevated nutrients. This coupled with the added shade of the creosote canopy means that seedlings that find themselves under creosote bushes tend to do better than seedlings that germinated elsewhere. As such, creosote are considered nurse plants that actually facilitate the growth and survival of surrounding vegetation. So, if recruitment and resulting competition from vegetation can become such an issue for long term creosote survival, why then do we still so much creosote on the landscape?

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The answer may lie in rodents and other burrowing animals in these desert ecosystems. Take a look at the base of a large creosote and you will often find the ground littered with burrows. Indeed, many a mammal finds the rooting zone of the creosote shrub to be a good place to dig a den. When these animals burrow under shallowly rooted desert plants, many of them nibble on and disturb the rooting zones. Over the long-term, this can be extremely detrimental for the survival of shallow rooted species. This is not the case for creosote. Its roots run so deep that most burrowing animals cannot reach them. As such, they avoid most of the damage that other plants experience. This lends to a slight survival advantage for creosote at the expense of neighboring vegetation. In this way, rodents and other burrowing animals may actually help reduce competition for the creosote.

Barring major disturbances, creosote can live a long, long time. In fact, one particular patch of creosote growing in the Mojave Desert is thought to be one of the oldest living organisms on Earth. As creosote shrubs grow, they eventually get to a point in which their main stems break and split. From there, they begin producing new stems that radiate out in a circle from the original plant. These clones can go on growing for centuries. By calculating the average growth rate of these shrubs, experts have estimated that the Mojave specimen, affectionately referred to as the “King Clone,” is somewhere around 11,700 years old!

The ring of creosote that is King Clone.

The ring of creosote that is King Clone.

For creosote, its slow and steady wins the race. They are a backbone of North American desert ecosystems. Their structure offers shelter, their seeds offer food, and their flowers support myriad pollinators. Creosote is one shrub worthy of our respect and admiration.

Photo Credit: [1] [2]

Further Reading: [1] [2] [3] [4]