Sanctuary for the Betulaceae

Nestled on the eastern side of the St. Francois Mountains, where the craggy exposures of the Ozarks most ancient rocks begin to subside underneath the Cambrian sandstones laid down over them, lies Hawn State Park – considered by many to be the loveliest of Missouri’s state parks. I have written previously about Hawn – in fact, it was the subject of my very first post on this blog. I have long treasured Hawn for its excellent insect collecting, diversity of plants and habitats, and unbridled beauty. I have hiked the incomparable Pickle Creek and Whispering Pine Trails many times – far more than any other trail in the state, and each time I fall more deeply in love with what, to me, represents the essence of the Missouri Ozarks in their most pristine state.

Lamotte sandstone cutThe charm of Hawn results from a unique combination of geological features. The Lamotte sandstone outcrops that dominate Hawn’s landscape are the oldest sedimentary rocks in the state, formed from coarse sand deposits that were laid down over the Precambrian rhyolites and granites that form the core of the St. Francois Mountains. These sand deposits were themselves buried under limestone and dolomite layers formed at the bottom of vast seas that later covered much of the interior of the continent. Subsequent periods of uplift and erosion once again exposed these sandstones, whose unique ability to hold groundwater has resulted in the formation of spring-fed streams that have cut deep into their soft layers to create canyon-rimmed valleys with tall vertical cliffs. rhyolite shut-ins One of these streams is Pickle Creek, which is fed throughout the year by Pickle Spring and has in some places cut all the way down to the underlying igneous rock to form “shut-ins.” In contrast to the slow, sandy bottomed stretches where Pickle Creek is still cutting through sandstones, the water in these igneous shut-ins rushes through narrow openings in the highly resistant rock. The igneous and sandstone exposures found in Hawn are spectacularly beautiful and support a unique flora due to the acid soils they produce. One group of plants that have taken sanctuary in these moist, acid soils is the Betulaceae, or birch family. Missouri is home to five native species of Betulaceae¹, and while none of them are extraordinarily uncommon they are limited in their occurrence to natural communities with sufficient moisture and exhibit a clear preference for acidic soils. This confluence of conditions occurs perfectly along Pickle Creek, allowing all five native species to grow here side-by-side – a betulaceous “hot spot” that represents not only the full diversity of the family in Missouri, but also the total generic diversity of the family in North America. In fact, only one other genus (Ostryopsis, shrubs related to Corylus and restricted to China) is assigned to the family on a global basis (Furlow 2004).

¹ Dr. George Yatskievych, in his recently published Steyermark’s Flora of Missouri (2006), regarded the presence of Corylus cornuta in Missouri as unlikely despite earlier reports of such. Dr. Yatskievych also recorded a single escape of the European species Alnus glutinosa from Springfield, Missouri.

The Betulaceae are deciduous trees and shrubs that occur primarily in the boreal and cool temperate zones of the Northern Hemisphere, although outposts are also known from high elevations in the Neotropics and, as mentioned above, China. Fossils of this ancient lineage of flowering plants are traceable to the late Mesozoic (upper Cretaceous), and the family appears to form a clade with hamamelidaceous plants. As would be expected from a group with boreal affinities, most species exhibit adaptations for survival in cold climates, such as small stature, shrubby growth habits, and small leaves. Several of Missouri’s species have performed well and gained acceptance as ornamental trees and shrubs, while others are important as sources of hazelnuts (genus Corylus) or ecologically for their ability to fix nitrogen (genus Alnus). My interest in these plants has nothing to do with their economic importance, but rather in their role as host plants for several rarely encountered species of woodboring beetles. Often, insects in this group may be collected on foliage of their hosts during the summer, making host identification fairly easy due to the presence of leaves. This is not always possible, however, due to limited periods of adult activity or low population densities. Rearing these insects from their hosts provides additional opportunity to document their occurrence, and winter is often the best time to collect the dead branches in which they breed, since by that time they have nearly completed their development and will be ready to emerge as soon as temperatures rise during spring. Identifying woody plants without foliage can be a challenge, but the ability to distinguish host plants by non-foliage characters such as bark, growth habit, bud shape, etc. greatly facilitates studies of wood boring beetles through rearing. In the past I have relied heavily on Cliburn and Klomps’ (1980), A Key to Missouri Trees in Winter, which utilizes mostly details of the twigs and buds to discriminate among Missouri’s 160+ species of trees. However, after a certain level of familiarity is gained, one eventually learns to recognize winter trees and even downed logs or fallen branches simply by their “look”.

Betula nigra - habit

Betula nigra - habit

Betula nigra - old bark

Betula nigra - old bark

Betula nigra - sapling

Betula nigra - sapling

Betula nigra (river birch) is the only member of this largely boreal genus found in the middle and southern latitudes of the U.S. and, thus, cannot be confused with any of Missouri’s other betulaceous species². It is the largest of the five and, along with the following species, is the most demanding in terms of keeping its “feet” wet. Trees are usually encountered right at the water’s edge, with tall, slender, often twisted or leaning trunks. Young trees and large branches on older trees exhibit gorgeous reddish brown bark peeling in thin, papery sheets, becoming thick and scaly on the main trunks of older trees. Small branches are dark, purplish brown in color with smooth bark and distinctly horizontal lenticels.  I have reared a small jewel beetle from fallen, dead branches of this tree collected at several locations in Missouri – this beetle turned out to be new to science, which I described and named Agrilus betulanigrae in reference to its (then) only known host (MacRae 2003).  I have also reared tremendous series of another jewel beetle, Anthaxia cyanella, which at the time was not known to utilize this host and was considered uncommon.  As it turns out, Betula nigra is its preferred host, and the rearing of large series from many locations resulted in improved knowledge about color forms and variability in this species (MacRae & Nelson 2003).

² The widely planted but dreadfully non-adapted Betula pendula (European white birch) and B. papyrifera (paper birch) can be recognized by their distinctly white bark. These species are limited to urban landscapes where they rarely achieve significant stature before declining and eventually succumbing to insect pests such as Agrilus anxius (bronze birch borer). River birch provides an equally attractive and much more durable choice!

Alnus serrulata - habit

Alnus serrulata - habit

Alnus serrulata - sapling

Alnus serrulata - sapling

Alnus serrulata - old cones

Alnus serrulata - old cones

Alnus serrulata (common alder, hazel alder, smooth alder, tag alder…) also demands to be next to (or even in) the water.  Unlike B. nigra, however, this species rarely reaches true tree status, instead usually forming shrubby thickets along the water’s edge.  Saplings can resemble those of B. nigra due to their smooth brownish bark, but the latter is usually more purplish, and the lenticels of A. serrulata are not distinctly horizontal as in B. nigra. The large purple-red buds also differ from the small brown buds of B. nigra, and during winter A. serrulata is adorned with numerous staminate catkins.  The persistent woody cones also cannot be mistaken for those of any other species of Betulaceae in Missouri. Associated with this plant is the longhorned beetle, Saperda obliqua, which reaches its southwesternmost distributional limit in Missouri on the basis of a single specimen collected some 25 years ago right here along Pickle Creek and given to me by lepidopterist George Balogh. Numerous attempts to find this species here since then have not (yet!) been successful.

Carpinus caroliniana - habit

Carpinus caroliniana - habit

Carpinus caroliniana (blue beech, hornbeam, musclewood) is one of my favorite betulaceous species. The beautifully fluted trunks and smooth, light gray bark are remniscent of the limbs of a sinewy, muscular person – every time I see this tree I cannot resist the temptation to grab and stroke the hard limbs (should I be admitting this?). This character begins to show even in very young trees, making its identification during winter quite easy. These trees also like to be near water, but they are not so demanding to be right at the water’s edge as are the previous two species. They usually form small trees, often in clumps with multiple trunks.  There are some notable insect associations that I’ve found with this plant.  One is a small jewel beetle, Agrilus ohioensis, which I reared from dead branches of this plant collected along Pickle Creek (Nelson & MacRae 1990), and which after more than 20 years still remain the only known Missouri specimens of this species.  Another is the longhorned beetle, Trachysida mutabilis, a single adult of which I reared from a dead (almost rotting) branch of this plant collected not too far from Pickle Creek in Iron Co.  This beetle also is the only representative of its species known from Missouri (MacRae & Rice 2007).

Ostrya virginiana - habit

Ostrya virginiana - habit

Ostrya virginiana - trunk

Ostrya virginiana - trunk

Ostrya virginiana (hop hornbean, American hornbeam) has a form and growth habit very similar to C. caroliniana, but its leaves that persist through the winter make it instantly recognizable from afar.  In Missouri, this habit is most often seen with the oaks (Quercus spp.).  This species can be found even further away from the water than the previous species, and its small stature combines with the orangish, persistent leaves to form a distinctive understory layer during winter.  Also, in contrast to the smooth gray bark of Carpinus, this species exhibits scaly, light reddish brown to brownish gray bark.  I have succeeded in rearing one of the two known Missouri specimens of another jewel beetle, Agrilus champlaini, from O. virginiana collected along Pickle Creek (the other specimen was reared from wood collected at Graham Cave State Park, another site where sandstone bedrocks favor an O. virginiana understory).  Unlike most other jewel beetles, A. champlaini forms galls in small living branches of its host.  I have collected the distinctive swellings during winter on many occasions but managed to rear only these two individuals (plus one ichneumonid parasitoid).  I have also noted similar swellings on Carpinus but have not yet managed to definitely associated them with this beetle.

Corylus americana (hazelnut, American hazelnut) is the smallest of Missouri’s five betulaceous species, always forming shrubs, sometimes in thickets, and never assuming the form of a tree. Its staminate catkins present during winter immediately identify plants of this species as Betulaceae, but the small, globe-shaped buds are unlike the more pointed buds of Ostrya and the elongated, reddish buds of Alnus. This species is the least demanding in terms of being near water and can be found even in upland prairies and glades. I haven’t yet associated any woodboring beetles with this plant in Missouri, but there are several jewel beetles known from the eastern U.S. that utilize Corylus (Agrilus corylicola, A. fulgens, and A. pseudocoryli) and could occur in Missouri.

pine savanna - fire managementThe upland habitats at Hawn are of interest as well. Lamotte sandstones are the dominant bedrock, creating acid soils that support a canopy dominated by Missouri’s only native species of pine, Pinus echinata (shortleaf pine), several species of oak, and a diversity of acid-loving shrubs primarily in the family Ericaceae (including the stunningly beautiful Rhododendron prinophyllum, or wild azalea). Historically, so-called “pine savanna” was prevalent in this area, a natural community in which periodic fires maintained an open structure amongst the fire-adapted pines and allowed a diverse herbaceous layer beneath the open canopy. Much of Hawn has closed up after decades of fire suppression; trail through pine savannahowever, the Department of Natural Resources has implemented a rotational burn management regime to recreate pine savanna habitat within Hawn’s Whispering Pines Wild Area. Evidence of what appeared to be very recent burns could be seen at several places as I hiked along the Whispering Pines Trail, and while many visitors might have been alarmed at the apparent “damage” they were observing, my heart sang with the prospect of seeing mature pine savanna communities taking hold throughout my beloved Hawn. As I stood atop this ridge and looked back down from where I had come, I could almost see Henry Schoolcraft and Levi Pettibone in the distance on horseback, perhaps pausing to gaze at an elk.

REFERENCES:

Cliburn, J. and G. Klomps. 1980. A Key to Missouri Trees in Winter, 2nd edition. Missouri Department of Conservation, Jefferson City, 43 pp. (subsequently revised)

Furlow, J. J.  2004. Betulaceae in Flora of North America @ efloras.org. http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=10101.

MacRae, T. C. 2003. Agrilus (s. str.) betulanigrae MacRae (Coleoptera: Buprestidae: Agrilini), a new species from North America, with comments on subgeneric placement and a key to the otiosus species-group in North America. Zootaxa 380:1–9.

MacRae, T. C., and G. H. Nelson. 2003. Distributional and biological notes on Buprestidae (Coleoptera) in North and Central America and the West Indies, with validation of one species. The Coleopterists Bulletin 57(1):57–70.

MacRae, T. C. and M. E. Rice. 2007. Distributional and biological observations on North American Cerambycidae (Coleoptera). The Coleopterists Bulletin 61(2):227–263.

Nelson, G. H. and T. C. MacRae. 1990. Additional notes on the biology and distribution of Buprestidae (Coleoptera) in North America, III. The Coleopterists Bulletin 44(3):349–354.

Yatskievych, G. 2006. Steyermark’s Flora of Missouri, Volume 2. The Missouri Botanical Garden Press, St. Louis, 1181 pp.

Copyright © Ted C. MacRae 2009

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About Ted C. MacRae

Ted C. MacRae is a research entomologist by vocation and beetle taxonomist by avocation. Areas of expertise in the latter include worldwide jewel beetles (Buprestidae) and North American longhorned beetles (Cerambycidae). More recent work has focused on North American tiger beetles (Cicindelidae) and their distribution, ecology, and conservation.
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17 Responses to Sanctuary for the Betulaceae

  1. From the looks of those pictures, I can see why you love the area Ted. A fascinating look at the tree theres. It is a subject not many people bother to post about. I also like to hear if they have any medicinal properties as so many of them were used by the American Indians. It is a subject I am very interested in too.

    • The leaves and bark of Alnus are rich in tannins and have been used widely in traditional medicine for treatment of infection and inflammation, especially of the skin. I’m not aware of medicinal uses for the remaining genera.

  2. Beautifully written and insightful. I’m hoping there is a book in your future that talks about these inter-relationships among plants and beetles. You make the science so interesting.

  3. Heber says:

    Great post. Recently I’ve been trying to teach myself more about Missouri trees. Little did I suspect I’d find such great information about tree species from an entomologist!

    I’ve been hearing a lot about the Pickle Spring natural area. I’ll have to go hike there soon.

  4. Great ode to a natural area and to a family of plants.

    Thanks Ted!

    • Thanks, Adrian. It didn’t occur to me until this past visit that the totality of Missouri’s Betulaceae were represented in this one spot. It provided me yet another reason to fall in love this place.

  5. Very informative post.

    I would like to be able to identify trees better when taking nature pictures.

    Posts like this help me to learn quickly.

    Thanks

  6. Scott says:

    Great post, Ted. I love boreal relicts…. plant species from a time when the lands we live on were much colder than they are today…. when black spruce and hemlock ranged much further south. We see many of these boreal relicts in Indiana in the cooler soils and in protected ravines.

    Do you think the insects that associate with these species of Betulaceae evolved with these boreal species when Missouri was a much cooler place (not saying that it’s not “cool” now!) and have held on in the few refugia where these species persist, or are their associations more contemporary?

    • Most of the insects I mention above (especially species in the genus Agrilus) show rather high host specificity – thus, their distributions strongly correlate with the distribution of their hosts (or some portion of it). These boreal associates tend to be more commonly encountered further north and east than they are here in Missouri, which seems to be at their southwestern limit of distribution. I suspect these are long-standing associations, and that the beetles were more common here during glacial times when their hosts ranged further south and west than today.

      I love to go to habitats supporting glacial relicts, look at their oak/hickory forests, and visualize spruce, hemlocks, and poplars standing in their place instead. I can almost see a mastodon pushing through the trees in the distance!

  7. Beau says:

    Wonderful how you’ve described Hawn State Park- I’ve intended to go there, and this may be just the year. Of course I may have to bring pack of eager cub scouts along the trail to learn the wonders of the Missouri Ozarks. And I didn’t realize alder grew in Missouri- how silly of me. I loved collecting the cones in WA state along the northwest coast. Thanks for sharing the story of your insect discovery too… I can only wonder what that must be like.

    • Yes, Hawn is a must-see. The 6-mile north loop of the Whispering Pine Trail might be a bit much for cubbies, but the 2-mile Pickle Creek Trail would be easily manageable and a wonderful learning experience for them. If you can get back just by yourself to explore it in silence and solitude you will never forget it. There are a number of places in Missouri that I consider magical, but Hawn has always been at the top of the list.

  8. Dave Bonta says:

    Great addition to the Festival of the Trees — I love learning about tree-insect relationships.

  9. Allison says:

    It’s funny that we have the same favorite park. Awesome pictures and fascinating information, as always. Yes, you should write a book. And yes, we’ve burned thousands of acres there recently. I’m glad the North loop is quiet for you! It’s a backpackers park and a great disservice that it was deemed necessary to put in electric sites. On that grand occasion I actually meet you, remind me to tell you what others in the field think about our management there… we’re “destroying pine.” Glad you’re back in missouri in time for phlox.

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