Monday, November 20, 2017

Quercity—Thoughts on Oaks

Coast live oaks, Quercus agrifolia, in the California Coast Range.

Free time has been scarce lately, so I’m offering a short post on oaks, inspired by “Querc-y Characters” at the Lady Bird Johnson Wildflower Center website.

I have a fondness for the Wildflower Center that surfaces at the least provocation, for I once talked plants with Lady Bird! It was 40 years ago, when I was botanist and sole employee of the Wyoming Natural Diversity Database. Jane Sullivan, wife of the governor, invited a small group of botanically-inclined ladies to gather for tea with Mrs. Johnson in Jackson Hole, at the base of the Grand Tetons. Conversation was awkward at first, but Lady Bird had done her homework, and as we introduced ourselves, she responded with what she had heard or read about our work. Soon we were happily discussing plants. Afternoon tea is not my idea of fun in the Tetons—I prefer hiking. But I really enjoyed my time with Lady Bird. She was so gracious and down-to-earth, a wonderful mix.

Now to the oaks …
Bur oak leaves, Dugout Gulch Botanical Area in the Black Hills.
In Wyoming, we have two oaks, both at the edge of their range here. Bur oak, Quercus macrocarpa, is a tree of the eastern and midwestern US that reaches its westernmost extent in northeastern Wyoming, mainly in the Black Hills. Gambel oak, Quercus gambelli, is common in Colorado and the southwestern US, but in Wyoming it grows only in the Sierra Madre, near Colorado. I was going to add “northernmost extent” but when I checked the NRCS PLANTS Database distribution map, I discovered that Gambel oak has been reported from South Dakota! However, there’s no county recorded, and the Forest Service FEIS treatment doesn't mention South Dakota. This would be a major disjunction, and news to me. But it’s an oak matter for another time.
Gambel oak; source.
In a way, we’re lucky we have just two oaks in Wyoming. I worked several winters in southeast Arizona, and struggled with the oak situation there. Apparently it’s even worse in Texas … or better, if you're not obligated to come up with identifications. Texas has more oak species than any other state in the US. Amy McCullough has put together an elegant straightforward guide to four of the common ones in Central Texas: Querc-y Characters, illustrated by Samantha N. Peters. Besides being a work of art, it shows clearly the characters and challenges in oak identification.
If you’re a hardcore oak fan, or looking for a botanical adventure, check out Quercus in the Flora of North America (FNA). There are 90 oak species in North America according to taxonomist Kevin Nixon, who prepared the FNA treatment. The exact number is debatable because oaks hybridize readily. “An astounding number of hybrid combinations have been reported in the literature, and many of these have been given species names, either before or after their hybrid status was known. … Hybridization in most cases results in solitary unusual trees or scattered clusters of intermediate individuals.” Oh dear!!

Even if you’re not up for a Querc-y Mega-Challenge, you might find Nixon’s introduction interesting—a revealing glimpse into the tortured world of oak taxonomists.
“A representative selection of mature sun leaves” is required for oak identification. Shade leaves won’t do. These are leaves of the coast live oak—sun above, shade below.

Monday, November 13, 2017

Boxelder—pest, pleaser, or provider?

Yesterday I went to check on “my” boxelder, the one I’m following. I’m limited to weekend visits, as weekdays belong to the Gustav A. Larson Company, which rents warehouse space next to the tree. Before I show you what I found, have a look at the road construction project en route, now almost a year ahead of schedule! It has been fascinating to watch.
This machine is laying down a bikepath as I write!

Now on to the tree. First, its habitat ...
The boxelder grows in a corner formed by north- and east-facing warehouse walls. The sun has moved far enough south now that it's shaded most (maybe all) of the time. Since last month, it has dropped most of its leaves; just a few dead ones hang on. Another difference: this visit was snow-free. In fact, we’ve been snow-free for almost a week, and it has warmed up enough to feel like fall again. I took advantage of the nice day to examine the boxelder more closely.
Dead leaves: petioles stay on longer than blades. Note opposite branching.
Oppositely arranged buds.
Sucker shoots up against the wall.
Urban habitat wouldn’t be complete without trash. I predict trash composition will change from month to month thanks to our wind. This time I found an inspiring message :-)

Following a tree provides the opportunity to learn about that species. My first stop along the knowledge pathway was the Biodiversity Heritage Library (BHL), “a consortium of natural history and botanical libraries that cooperate to digitize the legacy literature of biodiversity held in their collections and to make that literature available for open access ...” It’s my go-to place for interesting, fun, and often surprising information about plants. I like the emphasis on early pioneering botany, especially accounts by the explorers themselves.

A BHL search on Acer negundo returned 3843 hits. I sorted by date, browsed at the extremes, and found two interesting and contrasting accounts of the boxelder.

In 2013, Euardo Franceschi and Silvia Boccanelli reported that “spontaneous little forests” (núcleos boscosos espontáneos) of boxelder trees have developed in native Pampean grasslands in J. F. Villarino Park (Santa Fe, Argentina). Boxelder is a non-native and invasive pest species in Argentina, as well as in central Europe, China and Australia. In the Villarino grasslands, it’s clearly thriving. The researchers found overstories often to 40 ft in height (12 m), with boxelder common enough to be a dominant. Seedlings and small saplings were common in the understory, suggesting boxelder is there to stay in the absence of aggressive eradication.

François André Michaux, 1851; source.
At the other end of the BHL time line, I found boxelder in the The North American sylva, or A description of the forest trees of the United States, Canada and Nova Scotia by the pioneering French botanist and explorer François André Michaux (1770-1855). He made several trips to North America to botanize, beginning in 1785. In 1806, following detention in the Bermudas after being captured by the British, Michaux spent three years studying and collecting North American trees. After returning to France, he compiled his monumental work on the North American sylva—three volumes published 1818-1819. It was later translated by Augustus L. Hillhouse; this is the version I found at the BHL.

Below, “Box Elder or Ash leaved Maple” Plate XLVI. Courtesy Linda Hall Library Digital Collections. LHLDC was a great discovery. It provides online access to “significant rare and fragile materials” with free downloads.
Michaux explained that Ash leaved Maple was “a perfectly appropriate denomination,” but that general usage forced him use Box Elder, “though absolutely insignificant of any characteristic property of the tree.” Ash leaved Maple is perfectly appropriate because Acer negundo is indeed a maple, and the leaves are pinnately compound, looking a lot like those of ash trees. As is true for all maples, boxelder leaves are opposite on the stems. “The barren and fertile flowers [male and female] are borne on different trees” (i.e., dioecious).

Michaux found boxelder to be uncommon east of the Alleghenies, but “west of the mountains, on the contrary, it is extremely multiplied,” and abundant on floodplains. Especially interesting was his account of the reception the boxelder received in Europe post-introduction. Apparently humans jump-started its European invasion:
“Subsequently, it has spread into Germany and England, where it is in great request for adorning pleasure grounds, on account of the rapidity of its growth, and the beauty of its foliage, whose bright green forms an agreeable contrast with the surrounding trees.”
There are other reasons to like boxelders. Some botanists note that invasive species like boxelders provide ecosystem services in urban environments. Being an admirer of underdogs and the under-appreciated, I suspect I will become a fan of this tree.

Check out this month's tree-following news, kindly hosted by The Squirrelbasket. And consider joining us ... it's fun!


Franceschi, E., and Boccanelli, S. 2013.  Floristic-structural analysis of spontaneous little forests in the J. F. Villarino park (Santa Fe, Argentina). Bol. Soc. Argent. Bot. 48: 301-314.

Michaux, FA. (translated by Hillhouse, AL). The North American sylva, or A description of the forest trees of the United States, Canada and Nova Scotia ...

Thursday, November 2, 2017

Confronting Original Horizontality on the Poison Spider Road

“I have seen that the earth is composed of layers superimposed on each other at an angle to the horizon.” Nicolas Steno, circa 1671 (all quoted words below are Steno’s)

After communing with ghosts during the total eclipse of the sun, and viewing works by artists now long gone at Castle Gardens, I was happily ensconced in the past as I drove east on the Poison Spider Road. Approaching a rock wall rising abruptly from the plains, I thought of Nicolas Steno. He’s been gone for 331 years now, having died at the age of 48 after a decade of futile ministrations and asceticism in the service of the Catholic Church. But his scientific legacy lives on, in the form of basic principles of geology—for example, the Principle of Original Horizontality.

As luck would have it, the Poison Spider Road passed through the rock wall on a parcel of State land. I stopped for a closer look, and saw that the wall was composed of layers, and the layers were not horizontal. Because they stood at an angle to the horizon, I knew something had happened. Sometime in the past, this part of the Earth had changed.
Tilted stack of rocks (layers delineated with blue lines). Dip is to left (southwest), with youngest rocks on left.
The rocks themselves revealed only a little of their history. Clearly they had been deformed; the strata were far from horizontal. Given the location and context, I concluded they most likely were tilted during the Laramide Orogeny—the major mountain-building episode that created the Rocky Mountains approximately 70-40 million years ago. That’s when the majority of Wyoming’s ranges and basins came to be.

Later my suspicions were confirmed. The wall—more appropriately a hogback—is part of the west flank of a small anticline (upwarp) associated with the Casper Arch, a Laramide-age uplift separating the Powder and Wind River Basins. The Poison Spider area is complex, with lots of folds and faults. Geologists are still trying to figure out the details, mainly during oil-and-gas exploration.
Poison Spider area west of Casper, Wyoming (Cserna et al. 1983). Arrows mark the long narrow exposure of Teapot Sandstone, and its position in cross-section (click on image to view details).
This striking hogback is made of Teapot Sandstone, a member of the late Cretaceous Mesa Verde Formation. It’s hard and resistant to erosion, which explains why it stands alone on the high desert. Softer adjacent strata have been worn down.

Thanks to geological knowledge accumulated over centuries, I can indulge in informed speculation when I find something of interest. Not so Nicolas Steno. In his day, geology was still in earliest infancy; he had only his observations and amazing mind to guide him.

Steno had observed sediments settling slowly in water, and forming horizontal layered deposits on the bottom of a container. This also would happen in shallow seas, lakes, and such. Furthermore, the rocks that later formed from the sediments—sedimentary rocks—would be horizontal too … unless something had happened. Thus tilted, folded, or fractured sedimentary rocks indicated that the Earth was not always as it is today. The landscape can change radically given enough time.
“… strata either perpendicular to the horizon or inclined to it, were at one time parallel to the horizon.”

Original Horizontality is the second of Steno’s great principles. The first is the Principal of Superposition: “When the lowest stratum was being formed, none of the upper strata existed.” In a stack of sedimentary rocks, the oldest will be at the bottom, the youngest on top; thus the stack is a record of Earth history. Steno's second principal begat today’s stratigraphy.
Partial stratigraphic column (rock stack) for the Poison Spider area tells of advancing and retreating seas.
Steno’s third principle is Lateral Continuity. Sediments are laid down in continuous sheets unless something stands in the way, like an island. The resulting rocks are laterally continuous as well. He developed these principles in the process of deducing and proving that “figured stones” (today’s fossils) began as living organisms. But these principles also revealed what might be Steno's grandest conclusion—that the Earth changes profoundly over time. It's quite possible for sea floors to become mountain tops, replete with shells.

But why does the Earth change? How do mountains rise? Today we know of plate tectonics, through which huge fragments of the Earth’s crust move, jostle, bump, pull, sink, compress and stretch … creating mountain ranges, basins, islands, volcanoes, oceans, and more. But for Steno, back in the 17th century, the Old Testament of the Bible was the only source of explanation, and sometimes it conflicted with his discoveries. Throughout his geological studies, Steno remained religious, as did most scientists of the time; science was considered a way to understand God’s work. But his findings drove him to conclude that the Bible was not to be taken literally, that it was an imperfect work of Man.

Even as he continued studying fossils and Earth history, Steno’s attentions turned increasingly to religion. He had earlier converted to Catholicism, and in 1677, was appointed a titular bishop and sent to Germany to convert Lutherans back to the faith (Counter-Reformation). It was a difficult frustrating mission. Six years later Steno resigned, and spent the last five years of his life as an ascetic, living “devoid of all life’s comforts, lean pale and emaciated” as described by a friend.

From his surviving writings, some have concluded that the great uncertainty that surrounded the cause of change to the Earth led Steno to seek solace in religion and asceticism (see Cutler, chapter 13). But if uncertainty were such a demon, why did Steno speak these now famous words, in his final public talk in 1673?
“Beautiful is what we see. More beautiful is what we understand. Most beautiful is what we do not comprehend.”

I wish that Nicolas Steno’s soul resided in a place where he could watch the centuries unfold. He would see his principles widely accepted, even institutionalized. Stephen Jay Gould would anoint him Founder of Geology, and in 1988, after a 50-year campaign, he would be beatified by Pope John Paul II, who noted his contributions to science (Steno’s feast day is 5 December). And he would be able to rest in peace, comforted by the principles of plate tectonics, which explain how the Earth changes profoundly over time.
Bishop Nicolas Steno; source.

The following books include much more about the amazing life of Nicolas Steno:

Cutler, Alan. 2003. The Seashell on the Mountaintop—a biography of Steno emphasizing his pioneering contributions to geology and paleontology.

Alvarez, Walter. 2009. The Mountains of Saint Francis; discovering the geologic events that shaped our earth. Steno figures prominently in this wide-ranging entertaining account of the history of geology.

Other sources:

Steno's Laws or Principles, by Andrew Alden. March 09, 2017

Deciphering the Layers of Earth, by David Bressan. January 12, 2012

Cserna, EG., Kerns, GJ, and Laraway, WH. 1983. Bedrock geologic map of the Pine Mountain-Oil Mountain area, Natrona County, Wyoming. USGS Open-File Report 83-748.

Steno, N. 1671. The Prodromus to a dissertation concerning solids naturally contained within solids. Laying a foundation for the rendering a rational account both of the frame and the several changes of the masse of the Earth, as also of the various productions in the same. [English translation]