The Strangest Maple

I love being humbled by plant ID. Confusion usually means I am going to end up learning something new. This happened quite recently during a trip through The Morton Arboretum. Admittedly trees are not my forte but I had spotted something that seemed off and needed further inspection. I was greeted by a small tree with leaves that screamed "birch family" (Betulaceae) yet they were opposite. Members of the birch family should have alternately arranged leaves. What the heck was I looking at?

It didn't take long for me to find the ID tag. As a plant obsessed person, the information on the tag gave me quite the thrill. What I was looking at was possible the strangest maple on the planet. This, my friends, was my first introduction to Acer carpinifolium a.k.a the hornbeam maple.

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The hornbeam maple is endemic to Japan where it can be found growing in mountainous woodlands and alongside streams. Maxing out around 30 feet (9 m) in height, the hornbeam maple is by no means a large tree. It would appear that it has a similar place in its native ecology as other smaller understory maples do here in North America. It blooms in spring and its fruits are the typical samaras one comes to expect from the genus.

It probably goes without saying that the thing I find most fascinating about the hornbeam maple are its leaves. As both its common and scientific names tell you, they more closely resemble that of a hornbeam (Carpinus spp.) than a maple. Unlike the lobed, palmately veined leaves of its cousins, the hornbeam maple produces simple, unlobed leaves with pinnate venation and serrated margins. They challenge everything I have come to expect out of a maple. Indeed, the hornbeam maple is one of only a handful of species in the genus Acer that break the mold for leaf shape. However, compared to the rest, I think its safe to say that the hornbeam maple is the most aberrant of them all. 

Not a lot of phylogenetic work has been done on the relationship between the hornbeam maple and the rest of its Acer cousins. At least one study suggests that it is most closely related to the mountain maple of neartheastern North America. More scrutiny will be needed before anyone can make this claim with certainty. Still, from an anecdotal standpoint, it seems like a reasonable leap to make considering just how shallow the lobes are on mountain maple leaves.

Regardless of who it is related to, running into this tree was truly a thrilling experience. I love it when species challenge long held expectations of large groups of plants. Hornbeam maple has gone from a place of complete mystery to me to being one of my favorite maples of all time. I hope you too will get a chance to meet this species if you haven't already!

Photo Credits: [1] [2] [3]

Further Reading: [1] [2]

 

Maples, Epiphytes, and a Canopy Full of Goodies

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The forests of the Pacific Northwest are known for the grandeur. This region is home to one of the greatest temperate rainforests in the world. A hiker is both dwarfed and enveloped by greenery as soon as they hit the trail. One aspect of these forests that is readily apparent are the carpets of epiphytes that drape limbs and branches all the way up into the canopy. Their arboreal lifestyle is made possible by a combination of mild winters and plenty of precipitation. 

Weare frequently taught that the relationship between trees and their epiphytes are commensal - the epiphytes get a place to live and the trees are no worse for wear. However, there are a handful of trees native to the Pacific Northwest that are changing the way we think about the relationship between these organisms in temperate rainforests.

Though conifers dominate the Pacific Northwest landscape, plenty of broad leaved tree species abound. One of the most easily recognizable is the bigleaf maple (Acer macrophyllum). Both its common and scientific names hint at its most distinguishing feature, its large leaves. Another striking feature of this tree are its epiphyte communities. Indeed, along with the vine maple (A. circinatum), these two tree species carry the greatest epiphyte to shoot biomass ratio in the entire forest. Numerous species of moss, liverworts, lichens, and ferns have been found growing on the bark and branches of these two species.

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Epiphyte loads are pretty intense. One study found that the average epiphyte crop of a bigleaf maple weighs around 78 lbs. (35.5 Kg). That is a lot of biomass living in the canopy! The trees seem just fine despite all of that extra weight. In fact, the relationship between bigleaf and vine maples and their epiphyte communities run far deeper than commensalism. Evidence accumulated over the last few decades has revealed that these maples are benefiting greatly from their epiphytic adornments.

Rainforests, both tropical and temperate, generally grow on poor soils. Lots of rain and plenty of biodiversity means that soils are quickly leached of valuable nutrients. Any boost a plant can get from its environment will have serious benefits for growth and survival. This is where the epiphytes come in. The richly textured mix of epiphytic plants greatly increase the surface area of any branch they live on. And all of that added surface area equates to more nooks and crannies for water and dust to get caught and accumulate.

When researchers investigated just how much of a nutrient load gets incorporated into these epiphyte communities, the results painted quite an impressive picture. On a single bigleaf maple, epiphyte leaf biomass was 4 times that of the host tree despite comprising less than 2% of the tree's above ground weight. All of that biomass equates to a massive canopy nutrient pool rich in nitrogen, phosphorus, potassium, calcium, magnesium, and sodium. Much of these nutrients arrive in the form of dust-sized soil particles blowing around on the breeze. What's more, epiphytes act like sponges, soaking up and holding onto precious water well into the dry summer months.

Now its reasonable to think that nutrients and water tied up in epiphyte biomass would be unavailable to trees. Indeed, for many species, epiphytes may slow the rate at which nutrients fall to and enter into the soil. However, trees like bigleaf and vine maples appear to be tapping into these nutrient and water-rich epiphyte mats.

A subcanopy of vine maple ( Acer circinatum ) draped in epiphytes.

A subcanopy of vine maple (Acer circinatum) draped in epiphytes.

Both bigleaf and vine maples (as well as a handful of other tree species) are capable of producing canopy roots. Wherever the epiphyte load is thick enough, bundles of cells just under the bark awaken and begin growing roots. This is a common phenomenon in the tropics, however, the canopy roots of these temperate trees differ in that they are indistinguishable in form and function from subterranean roots.

Canopy roots significantly increase the amount of foraging an individual tree can do for precious water and nutrients. Additionally, it has been found that canopy roots of the bigleaf maple even go as far as to partner with mycorrhizal fungi, thus unlocking even more potential for nutrient and water gain. In the absence of soil nutrient and water pools, a small handful of trees in the Pacific Northwest have unlocked a massive pool of nutrients located above us in the canopy. Amazingly, it has been estimated that mature bigleaf and vine maples with well developed epiphyte communities may actually gain a substantial fraction of their water and nutrient needs via their canopy roots.

 

Photo Credits: [1] [2]

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