In Search of Stewartia

Up until a little over a week ago, I had no idea there were native representatives of the family Theaceae other than Franklinia alatamaha in North America. Dr. Mark Whitten was looking for a tree in order to obtain some genetic samples. He showed me a picture and my jaw just about hit the ground.

Fast forward a few days. A friend sent me an email regarding a hike to see Stewartia in the wild. This was an opportunity I was not about to miss. We took the day off and headed into the mountains. We met up with a small group of people whose goal that day was to bask in the glory of the mountain camellia (Stewartia ovata). We were led by local Stewartia expert, Jack Johnston (http://bit.ly/2908lSY).

It wasn't long before we had our first sighting. Just off the trail leading to a campsite was a spindly looking tree that stood roughly 15 feet in height. Without flowers I don't know if I could pick it out of a lineup. Lucky for us, this small tree was covered in large white blossoms. For the second time that week my jaw had to be pulled up off the ground.

The blossoms were absolutely stunning. About the diameter of a softball and with bright white petals, they are impossible to miss. At the center of each flower is a dense cluster of filaments supporting bright yellow anthers. The filaments themselves are quite attractive. They range in color from pure white to deep purple. What's more, any given tree can sport multiple flowers of with different filament colors.

The color did not seem to influence pollination whatsoever. Each flower we saw was crawling with solitary bees. To be fair though, very little research has been done on this species. Aside from some genetic work, the ecology of the mountain camellia remains a bit of a mystery. What we do know about this tree is that it has its roots in Asia. North America is lucky to have two of the 18 - 20 species of Stewartia. The rest are spread around the Asian continent. North America's Stewartia serve as a reminder of an ancient geologic connection North America and Asia once shared.

By the end of our hike we had lost count of the amount of trees we encountered. Despite their abundance, they are by no means common. Though not technically endangered, their limited distribution and low germination rates make it a sensitive component of the Appalachian flora. With tentative introductions into the horticultural trade, the best way to see this species is in the wild. Look for it growing in cool, shaded edge habitats, most often near mountain streams and rivers. It is a sight you will never forget.

 

Further Reading:

http://bit.ly/28ZrctJ

http://bit.ly/28ZtA4g

Why Trees Have Rings (and why they are so useful)

Dendrochronology is a field of study that focuses on tree rings. Though it may not be obvious, the amount of information we gain from looking at these rings is astounding. This research goes far deeper than simply finding out how old a tree was when it died. Dendrochronological data can be used to investigate paleoclimates, paleoecologies, and the archaeological dating of buildings and artwork. It is amazing how a practiced eye can look back in time. To date, we have an unbroken dendrochronological record for the northern hemisphere dating back some 13,900 years!

All of this would not be possible if it were not for tree rings. But what exactly are they and how do they form? The answer is physiological. Essentially tree rings result from patterns in vascular tissues. Early in the spring, before the leaves start to grow, a layer of tissue just under the bark called the cambium begins to divide. In this cool, water-laden time of the growing season the vessels that are produced are large and less dense. This is the beginning of the spring or early wood. Although they are not as strong as vessels that are produced later in the season, they sure can move a lot of water. Things are a bit different for conifers. Because they do not produce vessel elements in their wood, this large cell growth is initiated instead by large amounts of a growth hormone called auxin that is produced by the new buds. This causes the cells of the early wood in conifers to grow large in a similar way to that of the hardwoods. 

As summer heats up, things start to change. The cambium starts producing smaller, thicker cells. The vessels that result from this are much stronger than those of the early wood. This late wood as it is called gives trees much of their rigidity and strength. Late wood is also resistant to what is called cavitation, a process in which water within the tree can literally vaporize, causing a damaging embolism during the hottest months of summer. In conifers, bud growth stops by mid to late summer and with it much of the production of auxin. This results in smaller vessels as well. 

In temperate regions, this cycle of growth occurs over the course of a growing season. As such, each ring demarcates a year in that trees life. Because so much of a trees growth is determined by environmental conditions, the size and shape of the rings can tell a lot about the conditions in which that tree was growing. That is why dendrochronology is such a useful tool. By looking at tree rings from all over the world, researchers can tell what was going on at that point in time. And, though it was long thought that this was a phenomenon restricted to seasonal forests, we are finding that even some tropical trees produce annual growth rings. This is especially true in regions that have a measurable dry season. It just goes to show you that data comes in many shapes, sizes, and forms.

Further Reading:
https://journals.uair.arizona.edu/index.php/radiocarbon/article/view/16947

http://bit.ly/1m9cwvR

http://bit.ly/20COCbI

My oh my, What a Beautiful Magnolia

Magnolia fraseri is, in my opinion, one of the most beautiful trees in our eastern forests. To see this species, one must travel to the Southern Appalachian Mountains where it is endemic. With its whorls of massive leaves, large, cream colored flowers, and smooth gray bark, it is an unmistakeable component of the Appalachian cove forests.

M. fraseri needs canopy gaps to persist. Anywhere that disturbance opens up the canopy and allows light in, M. fraseri is soon to follow. This tree has surely benefitted from the mass die off of eastern hemlock due to the invasive hemlock wooly adelgid. This species flowers in the spring. Magnolias as a whole are an ancient lineage of flowering plants, arising before bees evolved. For that reason, their flowers are pollinated by beetles instead of bees. The large, showy flowers soon give way to your typical magnolia seed pod. As the seeds mature, they are pushed out of their pod and their bright red coloration helps to attract their main seed disperser, birds.

Aside from seed production, the most common form of reproduction for M. fraseri is via stump sprouts. In fact, it is believed that many of the oldest M. fraseri in the Appalachian forest region are stump sprouts that harken back to a time in which forest clearing was more rampant.

The overall appearance of this tree feels tropical. The large leaves are are arranged like an umbrella and these whorls stack themselves all the way up the trunk. Why this species is not cultivated as a native landscape tree is beyond me and I think the following excerpt by Richard E. Weaver Jr. sums it up quite nicely:

 

 

"Many of our fine native plants remain rare in cultivation in our own
country for a variety of reasons. Over-familiarity with them as wild
plants; lack of commercial availability; ignorance as to culture and
propagation; or plain snobbishness. Many are far better appreciated abroad."

Magnolia fraseri was one of the first plants that greeted me upon entering North Carolina. It was growing alongside a pawpaw at a scenic overlook that showcased the hardwood forests that coat these mountains. I never pass up an opportunity to appreciate this tree and indeed I will carry the image of it in my mind wherever I go.

Photo Credit: Jim Dollar (http://bit.ly/1R2Qpjy)

Further Reading:
http://link.springer.com/article/10.1007/BF00346412

http://arnoldia.arboretum.harvard.edu/…/1981-41-2-magnolia-…

http://www.na.fs.fed.us/…/si…/volume_2/magnolia/fraseri.html

Cashews

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I love cashews. I can't seem to get enough of them. Did you know that when you eat a cashew, you are only experiencing part of the fruit? Indeed, cashews are kind of weird and many of us in temperate climates never get a chance to fully appreciate what the cashew has to offer. You may also be surprised to learn that cashews and poison ivy are cousins.

Cashews or Anacardium occidentale as they are known scientifically are large trees belonging to the family Anacardiaceae. This makes them cousins of plants like poison ivy, sumac, pistachio, and mango (just to name a few). Like other members of this family, cashews produce chemicals that can cause severe skin allergies in humans. For cashews, this chemical is known as anacardic acid and is similar in its chemical makeup to urushiol. Because of this, cashews must be roasted before they can be sold. 

As I stated above, the cashew "nut" is only part of the reproductive effort of this species. They are not nuts in the true sense but rather a drupe similar to the pit of a cherry or peach. The drupes themselves hang from the bottom of a much larger accessory fruit called a cashew apple. This pear-shaped pseudocarp is quite juicy and does not ship well. Though it is a delicacy in tropical climates where these trees are cultivated, it rarely makes it to more temperate climates.

Cashews are currently native only to Brazil but fossils found in Eocene deposits from Germany hint at a much wider distribution. It is now believed that the group that gave rise to cashews originated in Africa and subsequently migrated outwards while South America was still attached. Today, the cashew is regaining some of its lost ground thanks to its agricultural importance. 

Speaking of agriculture, cashews are offering an interesting model for more sustainable farming practices. Cashews, like most other crops, are grown in large-scale monocultures. Thousands of gallons of pesticides are used on these crops to stave off pests. However, the pesticides kill more than just unwanted insects. What is interesting about cashews is that they naturally produce extrafloral nectaries (glands that secrete nectar) on their leaves. In the wild these glands attract ants looking for a high energy meal. The ants in turn guard these nectar sources from anything that may interfere with their feeding. As such, many potential pests are driven off by the ants. Research is being done to compare the rates of insect pests between cashew plantations that use pesticides and those that don't. It could be possible that by allowing ants to guard these nectar sources, farmers could avoid the use of pesticides to control insect damage. More work is needed but cashews are certainly a great model for developing such a system. 

www.indefenseofplants.com

Photo Credit: Peter Nijenhuis (http://bit.ly/1A0MmLI)

Further Reading:

http://www.jstor.org/stable/10.1086/520728

http://www.amjbot.org/content/85/6/835.full.pdf

Mangroves

 

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These strangely beautiful flowers are that of a mangrove! A red mangrove in the genus Rhizophora to be more specific. These peculiar trees are known the world over by their stilted appearance and tolerance of salt water. With roughly 110 species worldwide and a lot of erroneous labeling of what it means to be a "mangrove," the taxonomy of this group is a bit messy. 

Mangroves are a tropical species. They form the backbone of saline coastal habitats all around the world. Their real claim to fame is their ability to deal with salt water on a level that would kill pretty much every other plant out there. They do this in a very interesting way. Upwards of 97% of the salt is excluded from the roots by spongy material that acts as a filter. What little salt does make it in ends up in the leaves. In some species, salt gets hyper accumulated in the leaves and then disposed of when those leaves are shed. Some have taken to calling these "sacrificial leaves" but recent evidence suggests that there may be no difference in salt concentrations between leaves on any given tree. Other species excrete salt through special glands, which can be readily seen by turning over the leaves. 

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My favorite aspect of mangrove ecology is their reproduction. Mangroves come about as close as a plant can get to live birth. Their long, pod-like seeds will actually germinate while still attached to the parent tree. Because they are so long and slender, the pods will often spear themselves into the sand when they fall where they will continue to grow. In other cases, the seed can change buoyancy over time. This allows them to float on the surface and travel great distances. Upon germination, the buoyancy of the seed changes, causing it to suspend itself vertically, thus increasing its chances of lodging itself into the mud or sand. In this way, mangroves are excellent long distance colonizers.

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Mangroves are so much more than simple trees. They are ecosystem engineers supremely adapted to harsh environmental conditions. They create habitats that provide breeding grounds for myriad other organisms. Entire economies rely on the bounty these trees provide and yet they are all too often leveled under the guise of economic gain. What's more, their coastal habit provides storm protection that can be counted in the billions of dollars. Sadly, the loss of mangroves often translates into not only a loss of capital for coastal communities but also a collapse in the ecosystems they depend on. Worldwide, mangrove forests have seen a 35% decline over the last few decades. Countries are starting to wake up and realize what they have lost but we still have a ways to go. We ignore species like mangroves at our own peril. 

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Photo Credit: Peripitus, Phil's 1stPix (http://bit.ly/1GTMK41), Holly (http://bit.ly/1wIrC0q)

Further Reading:

http://www.glomis.com/ej/pdf/EJ_8-4.pdf

http://muse.jhu.edu/journals/pacific_science/toc/psc60.3.html

http://www.therakyatpost.com/news/2014/09/15/mangroves-protect-malaysias-coast-also-shield-illegals/

http://www.nhmi.org/mangroves/phy.htm

http://www.botgard.ucla.edu/html/botanytextbooks/worldvegetation/marinewetlands/mangal/index.html

I've Got the Colorado Blues

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You would be hard pressed to find a resident of temperate North America who has never seen a Colorado blue spruce. These iconic trees are a staple of every sapling give-away and can be found in countless landscape plans all over the continent. There is no denying the fact that the blue hues of Picea pungens have managed to tap into the human psyche and in doing so has managed to spread far beyond its relatively limited range. However, despite its popularity, few people ever really get to know this species. Even fewer will ever encounter it in the wild. Today I would like to introduce you to a brief natural history of Picea pungens

Despite its common name, P. pungens is not solely a denizen of Colorado. It can be found in narrow swaths of the Rocky Mountains of Wyoming, Idaho, south to Utah, northern and eastern Arizona, southern New Mexico, and of course, central Colorado. There are also some rumored populations in Montana as well. It has a very narrow range compared to its more common relative the Engelmann spruce (Picea engelmannii). Whereas some authors consider the Colorado blue spruce to be a subspecies of the Engelmann spruce, the paucity of natural hybrids where these two species overlap suggests otherwise. It is likely that Colorado blue spruce split off from this lineage and has since followed its own evolutionary trajectory.

Male cones are short-lived but quite attractive.

Male cones are short-lived but quite attractive.

One of the reasons P. pungens has become such a popular landscape tree is due to its extreme hardiness. Indeed, this is one sturdy tree species. Not only can it handle drought, P. pungens is also capable of surviving temperatures as low as -40 degrees Celsius with minimal foliar damage. Little stands in the way of a well established Colorado blue. In the wild it can be found growing on gentle mountain slopes at elevations of 6,000 to 10,000 feet. It is also a long lived and highly fecund tree. The most highly productive seed years for P. pungens begin at age 50 and last until it reaches roughly 150 years of age. Seeds germinate best on bare soils, which probably keeps this species limited to these mountainous areas in the wild.

The typical female cone of the Colorado blue spruce.

The typical female cone of the Colorado blue spruce.

Another component of its landscape popularity is its characteristic blue color. In reality, not all trees exhibit this coloration. Its blue hue is the result of epicuticular wax deposits on the leaves as they are produced in the spring. Not all trees produce the same amount or consistency of wax and therefore not all look blue. Wax production seems to be controlled by a genetic factor and therefore is often a shared trait among isolated populations. The wax functions as sun screen, reflecting harmful UV rays away from sensitive developing foliage. This is why it is most prominent in new growth. The wax can and often does degrade over the span of a growing season, resulting in duller trees come fall. 

Despite how interesting this spruce is, Picea pungens, in my opinion, represents the epitome of lazy landscaping. Like Norway spruce and Norway maples, P. pungens seems to be an all too easy choice for those looking to save a quick buck. As a result, countless numbers of these trees line streets and demarcate property boundaries. Though P. pungens is native to North America, its narrow home range makes its ecological function elsewhere quite minimal. Though one could certainly do worse than planting this conifer, it nonetheless overshadows more ecologically friendly tree choices. 

Photo Credit: [1] [2] [3]

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