September 28, 2013

Living on the edge

oakopening

Lately, I've been thinking about tension zones and ecotones.

If you're still with me, you might want to keep reading because these topics are fascinating--especially for gardeners and plant geeks.

We learned about tension zones in my master naturalist courses earlier this summer. An ecological tension zone, anywhere in the world, is where two broad ecological regions meet. Any tension zone is a diverse area--where representative plant and animal species from both zones on either side overlap.

For example, here's a map from the Biota of North America Program (BONAP), showing floristic tension zones throughout the U.S.:

Source: bonap.org

My state, Wisconsin, is split by a diagonal line running from the northwest through the southeast. Two major ecological zones fall on either side, and where they meet, the plant and animal species are more diverse. You can click here to see more information and maps explaining this concept, and to read about the floristic zones in other U.S. regions. (I couldn't find a simple, nonacademic online resource for worldwide tension zones, but if you research your specific country or region, hopefully a similar resource is available.)

I don't live along Wisconsin's tension zone--I'm firmly in the ecological region shared with most of Illinois and parts of Iowa, Minnesota, and Missouri. This region is known for its fertile soil, deciduous forests and Oak savannas.

And then, of course, there are edges on a much smaller scale--for example, where a sandy soil region meets a clay soil region.

forest

Or even smaller areas that you can observe just standing in one spot. For example, ecotones are defined by the Encyclopedia of Earth as transitional areas between two different ecosystems, such as a forest and a grassland. Click here to read about this fascinating topic.

This also ties in with the concepts of permaculture. Appalachian Feet did an excellent post a while back titled, "How to Learn About Permaculture." If you missed the post, it's definitely worth reading.

All of these concepts have significance for gardeners, botanists, biologists, naturalists, and anyone else who studies or simply enjoys nature. Ecotones, for example, are thought to be important ecological indicators of global change. They're thought to be sensitive to changing climates, and many scientists advocate monitoring ecotones to detect patterns of global change.

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My garden resides along a small ecotone. It's a space between an open suburban area and a small forest along a glacial drumlin. The biodiversity is especially evident when the seasons change--when the migrating birds travel into, out of, and through the area, and when the deciduous trees either leaf out or lose their leaves. Back in the days before large-scale agriculture and settlement, this plot of land was probably part of an Oak opening, with less than 50% tree canopy coverage and frequent fires. The part at the top of the drumlin might have had more trees (as it does now) because of its placement on higher ground.

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These concepts of tension zones, ecotones, and Oak openings were becoming common parlance for plant specialists like John Muir at the turn of the 20th century. He describes the uniqueness of Oak openings in "The Story of My Boyhood and Youth":


"When an acorn or hickory-nut [grub] had sent up its first season's sprout, a few inches long, it was burned off in the autumn grass fires; but the root continued to hold on to life, formed a callus over the wound and sent up one or more shoots the next spring. Next autumn, these new shoots were burned off, but the root and calloused head, about level with the surface of the ground, continued to grow and send up more new shoots; and so on, almost every year until very old, probably far more than a century, while the tops, which would naturally have become tall broad-headed trees, were only mere sprouts seldom more than two years old. Thus the ground was kept open like a prairie, with only five or six trees to the acre, which had escaped the fire by having the good fortune to grow on a bare spot at the door of a fox or badger den, or between straggling grass-tufts wide apart on the poorest sandy soil.

The uniformly rich soil of the Illinois and Wisconsin prairies produced so close and tall a growth of grasses for fires that no tree could live on it. Had there been no fires, these fine prairies, so marked a feature of the country, would have been covered by the heaviest forests. As soon as the oak openings in our neighborhood were settled, and the farmers had prevented running grass-fires, the grubs grew up into trees and formed tall thickets so dense that it was difficult to walk through them, and every trace of the sunny 'openings' vanished."



While the "Oak opening" ecotone in my garden is now partially cultivated, it's a fascinating little place teaming with life. Understanding what it was, what it is, and what it can be is helpful to me, as its gardener and caretaker.

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46 comments:

  1. When we began this garden, I battled to find any information about gardening in renosterveld. I had high hopes of planting to support local wildlife. Drew a blank, and began to write my garden blog instead. Over the years the Biodiversity in Wine Initiative means that a few wine estates work to conserve their renosterveld remnants. Now, I would find plant lists and renosterveld to hike in at the Hantam Botanical Garden.

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    1. I'm glad to hear the resources are more available now, Diana. Your garden looks like the perfect haven for people and wildlife. I find it fascinating to read about the native plants of South Africa. It's definitely a country I'd like to visit some day.

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  2. My property was logged by the PO and there are just small pockets of the original wild plants left, but I enjoy them and try to spread them around. Good information to consider in property management!

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    1. Thanks, Hannah. I have to admit, I inherited this property since we aren't the original owners, so I don't know how many of the plants were existing and how many were planted by the owners. Obviously, the non-natives were planted, but there are a lot of native plants--particularly in the woods. Frankly, before the neighborhood was residential, the area leading to the glacial drumlin was farmland. And before that...probably prairie.

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  3. Thanks so much for the ecology lesson! I'm a real novice but love to learn.

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    1. Ha! I know, I get a little too enthusiastic about this stuff. But it's so fascinating to know about the origins of places, and how people interact with their surroundings. :)

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    2. you cannot be too enthusiastic for me ;~)
      BushBernie also wrote about her mammoth task clearing invasive aliens
      http://berniesgarden.blogspot.com/2013/05/working-towards-healthy-habitat-chapter.html

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  4. Fascinating stuff. I very much enjoyed reading it and learning from it.

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    1. I'm glad you enjoyed it, Dorothy. I find this stuff fascinating, too. Partly because it tells the stories of the people and the land before we were here.

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  5. Very interesting! It looks like my state, Alabama, has 3 different ecological zones. This doesn't surprise me. Though it is not a particularly large state, Alabama has the third greatest amount of plant and wildlife diversity in the US. Only Texas and California exceed us. I live very close to one of the tension zones. Our soil is clay (acidic) resting upon limestone (alkaline). Our property, which covers 3.5 acres, has 8 different types of oak trees, as well as a variety of other trees including pine, maple, redbud, dogwood, hickory, magnolia, sycamore, cedar, sweet gum, tulip, sourwood, persimmon, wild cherry and others I have not identified. These are all native and do not include decorative trees I have planted! For a long time I took these for granted and did not realize what a treasure we have here.

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    1. Wow--I didn't realize all those things about Alabama! Texas and California don't surprise me, but how interesting that Alabama is No. 3! From your blog posts and your description here, your property sounds like a beautiful place. I know what you mean about taking it for granted--the same thing has happened to me.

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  6. Loved reading this Beth and appreciate the information and links. I will share it with my naturalist group!

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    1. Thank you, Gail. Yes, the topic of "edges" seems to have special significance to naturalists, and I hope your group finds the links useful. Each plot of land has a unique story--on so many different levels!

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  7. This information is so helpful as I live right on one of those tension zones. Though I have not heard is specifically laid out as you have here, I was aware that we straddled regions with the best of both and a little of the worst too. I will
    see if I can find more detail.

    We have an undeveloped plot behind us and I spend time almost weekly exploring the patterns of native plants which have been relatively undisturbed for many years.

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    1. Lucky you! I do remember visiting San Antonio and the "Hill Country," and I can see how that would be a tension zone area--the landscape changes so dramatically and so quickly. Do share if you find out more information about your area, Shirley.

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  8. I looked up ecozones for Canada and my province. There are 3 ecozones in Ontario and I live in the Mixed Wood zone. You can imagine what that means. I have heard of this before but I guess I never paid much attention.

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    1. Ontario is spectacular! I've only been there once--our family camped along the way. One particular campground was among the most peaceful locations I have ever visited. It's a calming influence just thinking about it. And yes, I remember going through some unique zones along the way. The Sudbury area seemed very different from Ottawa, for example.

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  9. I too appreciate the information. Where I live there is such a vast difference even in the planting zones.

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    1. That would be interesting to have diversity of planting zones in one small area. Microclimates are challenging enough (but so much fun to figure out)!

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  10. Beth this is fascinating and I am trying to wrap my head around the ecotones and tension zones. I would suspect where I am near the Great Lakes and another lake there must be some interesting info on all this I will find once I look.

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    1. Yes, it does get a bit complicated. The "edges" are the fascinating part for me. It makes sense that these places would have more biodiversity, but it takes a little thought to think about the edges in any given garden or locale. Do let me know when you find out more about your area.

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  11. This is an interesting post! I'm going to go look up the ecozones for my state!

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    1. I'm glad you enjoyed it. Please let me know what you find out about your tension zones, ecozones, and ecotones!

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  12. This was very interesting, Beth, and something I have never heard of before. I've done a little reading about the origins of the prairie and thought John Muir's explanation of the trees being burned and leaving an open area was fascinating. I really should put Muir on my winter reading list!

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    1. I'm sure you would enjoy reading Muir's words, Rose. He was an incredible writer and his writing about his early life describes the Midwest in such a lyrical, warm way. Prairies and Oak savannas are so fascinating--especially when you study them close-up.

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  13. Excellent job explaining one of the things that makes Wisconsin so rewarding for nature lovers. Now that I live in the Chicago area, our more minor edges are hard to detect, except in some natural areas that have been set aside by county forest preserves and so on.

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    1. Thanks, Jason! That's part of the reason the wild edges in the Chicago suburbs and in people's gardens are so important. Keeping habitats for plants and wildlife even in urban settings makes a huge impact. There are some lovely wild areas all throughout the U.S. (and the world, of course). Hopefully we can find ways to retain and reclaim many of them.

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  14. Very interesting, Beth. I feel like you've given me a handle to do research and learn more about the ecology of the land around me. I'm very happy to do master naturalist courses indirectly.

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    1. Thanks, Sue. Of course, once you know a little about something that fascinates, it simply whets the appetite to learn more. I feel like I could study these things for the rest of my life and I would still be a neophyte. But it sure is fascinating!

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  15. Thanks for yet another interesting post from you Beth, I clicked on the link but was a bit disappointed to see the map only covered US. I bet a map over UK would have showed some major ecological zones too, although perhaps not as big diversity as in US, due to the sheer difference in the size of the two countries.

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    1. Thanks, Helene. I did find some local maps for various world regions, but no source seemed to find tension zones throughout the world. But I did find a few links and maps that talk about "biogeographic regions," such as this one: http://schools-wikipedia.org/images/2818/281838.png.htm. I'll keep looking, though. ;-)

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    2. Thanks for the link, I can see UK is just one "biogeographic region" whilst Norway on the other hand is 3 differnt regions. Not sure why as part of Scotland couldn't be more different from where I live in London!

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  16. This is really interesting. I am slowly learning more and more about how climate affects growth and species. Altitude also plays a massive part; I will try to see what I can find about Italy, I imagine England is hundreds of small overlapping zones which is why so many species will grow there happily.

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    1. I'll be curious to read what you find! I'll bet you're right about England--I'm always amazed at the plants UK gardeners blog about!

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  17. A fascinating post. And beautiful photographs too. You've really made me think about where I am now gardening. I was aware of the very different conditions all close together - woodland, clifftop, beach - the variety is one of the things that I really love about living here. Even in my smallish garden there are dramatic differences in soil structure, from very sandy to really moderately heavy clay. It makes me wonder what is going on geologically speaking. And ore generally, I think the borders between places are always really interesting, real melting pots.

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    1. Thanks, Janet. Yes, it makes sense that you would have a wealth of biodiversity in your Wales garden. When I started thinking about "edges" a new magical way of looking at gardening and nature opened up. I guess it's common sense, but I hadn't given it much thought before.

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  18. This is very interesting, I had no idea that these zones existed, or were named.

    I am going to be looking at the area around us so differently from now on.

    Jen

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    1. It was fun learning about my own state, and then I wanted to find out more about all the U.S. zones. Then I started thinking about places outside the U.S. and how "edges" are important no matter where your garden is located. I imagine your region has a lot of biodiversity, too, Jen.

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  19. I live in a rural area and my house is located essentially in the middle of 20 acres of fields that are surrounded by 35 acres of woodland or wetland. When we had an Audubon assessesment of our woods this spring, our guide noted our transition areas with pleasure, but reminded us that they need to be managed or the field would eventually be total woodland. We do not want that.

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    1. How wonderful! It's a nature-lover's playground! My little (quarter-acre) plot is challenging enough, so I can just imagine the challenges you have. The "edges" are fascinating, though, aren't they?

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  20. What a fascinating post. I've often thought about the diverse plant communities on this property.

    With its steep slopes we have some very marked differences in the types of plants a particular slope is populated with. Most of the woodland here is relatively new, not much more than a century old. The area was stripped from logging old growth redwood, followed by raging wildfire, but since the turn of the 20th Century it's been relatively untouched. The landscape has changed much though. What was traditionally predominantly redwood is now mostly Douglas Fir, Oak, Bay Laurel, and Madrone. The sentence that probably best describes the more heavily wooded areas here is "...and every trace of the sunny 'openings' vanished". We've tried to remedy some of that since living here, removing diseased trees and shrubs, and amazing how quickly the forest floor springs back to life.

    However, our much of our woodland is so dense, that in dry years like this one, I worry about what a wildfire would do. Not just burning the plants, but the fuel load is so heavy that I wonder what plant communities would be capable of returning. Much is being written at the moment about wildfires in the west burning much hotter than they used to due to the abundance of fuel, and that many seeds that may have been stimulated by fire, are destroyed, slowing the return of plant communities after fire.

    However, we're also fortunate here to be very close to a unique sand hill ecotone, which is in the process of being restored, after much of it was exploited for a gravel quarry for decades, and much of the rest paved over, the community has finally seen value in its preservation. It's been fascinating to learn about the unique plants, and animals, that are found nowhere else, but with climate change, they are at especially high risk of being lost, forever.

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    1. How lovely--and your description reveals how diverse your property is. I know what you mean about the fuel load! Although our little forest is much smaller than yours, I was worried for weeks and weeks last summer during the terrible drought here. A forest fire in a suburban neighborhood would have been tragic for so many reasons! The sand ecotone you describe would be a fascinating place to witness. I also think often about the huge wildfires out west--they seem to be evidence of how some ecosystems have gotten out of balance.

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    2. Such an interesting topic you have introduced to me... I look forward to exploring it further. You live in a beautiful corner of the earth.

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    3. Thanks, Carolyn. I know you live along a beautiful edge, too--with a grand mountain view! Lucky you!

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  21. Hi Beth, i was a bit late here. This is very interesting topic, I remember we touched about it in ecology and landscape ecology classes. Maybe the transitions of ecozones are more easily seen in big continents like the US, but in our case in the Indo-Malayan or Southeast Asian Regions these are not very distinct. Our warm humid tropics produced by convergence of continental drifts, tectonic plates convergence or separations, etc, etc, produced the most biodiversity. We see only our transitions in vegetation when we climb mountains, because of species suited to certain temperatures; we get lowlands, grasslands, dipterocarp forest, mossy forest as we climb the peaks. This is a very interesting but also difficult subject matter.

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    1. Thanks, Andrea. The biodiversity in the tropics is incredible, of course! I can only imagine. And the transitions between the ecosystems you mention must be incredible! I would think the transitions from valleys to mountains in the tropics would be especially fascinating. I can't seem to get ecological "edges" off my mind. ;-)

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