The Plant Superhighway!

I recently posted a video about the Plant Superhighway. In this video, I am in a weedy field which is turning into a young forest very near a busy highway in Oklahoma. The young forest seems so calm and serene in contrast. But, silent and underground, the plants have superhighways that are just as busy as those built by humans.

For much of my professional life, I considered ecological succession to be a process of shading out: trees such as many oaks in Oklahoma shade out the smaller trees such as honey locust, black locust, and persimmon, which shade out the bushes such as sand plum, which shade out the herbaceous perennials such as goldenrods, which shade out the annual weeds. That was pretty much the story as I told it in three of my books.

As far as this story goes, it is true. But I now realize there is so much more to the story than this. One reason that herbaceous perennials, such as goldenrods, displace the annual weeds is that the annuals have to sprout from seeds, while the perennials have already built up underground reserves and can grow faster in the spring. Bushes shade out herbaceous plants because their stems are higher up in the air; trees, higher yet. But the early-successional weeds, shrubs, and trees have another strategy (in the ecological sense) that promotes their survival and evolutionary fitness. They form underground connections.

When a goldenrod gets established, it not only puts down its roots and stores up food, but it sends out underground stems to new locations, where they become new plants, genetically identical to and connected to the mother plant. Through these underground stems, food can travel from one plant to another. Any plant that happens to be lucky can send nutrients to the less lucky plants, allowing them to form an integrated whole that secures resources for its use. I first learned of this from the research of David Hartnett and Fakhri Bazzaz at the time when I was in their lab at the University of Illinois.

This integration may be absolutely essential to the survival of early-successional plants; at least, most of them do it. In the video, we see goldenrods and false-goldenrods; sand plum bushes; and even trees such as persimmon, black locust, and honey locust that connected into large, integrated systems. It looks, at least, like individual, unconnected early-successional plants do not stand a chance on their own.

There might also be connections among different kinds of plants, via shared mycorrhizal strands. The “wood wide web” of inter-plant connections may be as important of an explanation of ecological succession as the process of one kind of plant shading another (as explained in an earlier essay and video. These connections dampen the variability of light, moisture, and nutrient conditions. They do this by forming underground superhighways.

 

Plants Don't Just Live in Habitats; They Create Them!

I have just posted a video from the scene of the action. I show some clumps of alder (Alnus maritima) growing in the Blue River in south central Oklahoma. One glance and you would say that the river is their habitat. (By the way, that habitat, with its white water emerging from the aquifer, is the nicest place to do field studies in Oklahoma in the summer—in fact, it might be the only nice place to do field studies in an Oklahoma summer.)

But the alders are not just growing in the river. They are creating their own habitat, in four ways.

First, once an alder bush starts growing on a rock in the river, its trunks emerge from the water. (Sometimes floods wash away the trunks; they just grow back, usually within a year.) The trunks slow the water down just a little bit. Dead leaves and stems in the river accumulate at the trunk base, as well as some mineral soil. The alder clumps are creating little islands of soil in the river that would not have been there without them. When these dead tissues decompose, the soil can nurture other plants, such as the sycamore saplings that grow up from the soil.

Second, the roots of the alders have little nodules that are filled with Frankia bacteria. Like the more familiar Rhizobium that grows in legume roots, the Frankia bacteria “fix” nitrogen; that is, they take nitrogen molecules from the air (the little air spaces in the soil) and fix it into ammonium molecules, which act as a fertilizer for the alder. It is a mutually beneficial (symbiotic) arrangement: the alder feeds the bacteria, and even protects them from excessive levels of oxygen gas. In turn, the bacteria produce more ammonium than they need. That is, the alder roots are absorbing nitrogen atoms from the inside, not from the outside. But it goes beyond this: when the alders lose their leaves, stems, and a few roots, the plant tissues have nitrogen atoms in them that came from the bacteria. But when these dead tissues decompose, the nitrogen atoms go into the soil, where it can be used by other plants, such as the walnut saplings that grow up from the soil.

Third, the roots of the alders have mycorrhizal fungi growing in them. This is what makes them fat and orange rather than skinny and brown the way most roots are. The alder feeds the fungi, and in turn the fungi extend their filaments out into the soil and absorb phosphate ions more effectively than could the roots themselves. It is a mutually beneficial (symbiotic) arrangement: the alder feeds the fungi. In turn, the fungi absorb more phosphate than they need. That is, the alder roots are absorbing phosphorus atoms from the inside, not from the outside. But it goes beyond this: when the alders lose their leaves, stems, and a few roots, the plant tissues have phosphorus atoms in them that came from the fungi. But when these dead tissues decompose, the phosphorus atoms go into the soil, where it can be used by other plants, such as the dogwood bushes that grow up from the soil.

But wait, there’s more! Fourth, the mycorrhizae of one alder clump can connect with those of another alder clump, causing the whole alder woodland to form an interconnected whole. They can share nutrients and even send signals to one another. This is the “wood-wide web” that Suzanne Simard first wrote about in 1997. The individual alder clumps create their own individual habitats in three ways, and a collective habitat in a fourth way. How cool is that?

Natural selection does not always favor competition and warfare among species. It can favor cooperation and mutualism. Natural selection favors whatever works: sometimes competition, sometimes cooperation, so long as it enhances the reproduction of the individuals, in this case, the alders. The alders are doing well by doing good.

Reforestation: The Miyawaki Method

A popular new method of replanting forests that have been devastated was developed many years ago by a Japanese botanist, Akira Miyawaki (now 93 years old). This method is now being used around the world and is especially popular in the tropical parts of India.

The method is supposedly simple, but of course there are a lot of details. Nevertheless, the basic idea is very simple: plant a thick growth of seedlings of native tree species and let them thin themselves out into a diverse forest. It is the exact opposite of a tree plantation, which consists of a single tree species, each tree spaced out enough that it will probably survive. We have a lot of plantations in Oklahoma, mostly loblolly pines used by Weyerhaeuser Corporation for wood pulp, mostly along State Highway 3 on the east side of the state. Instead, the Miyawaki method is an almost exact replication of natural forest succession, except that it skips the weedy and shrubby stages, going directly to the forest stage. If you use a mixture of native species, they will not only be adapted to local conditions, but will interweave themselves into different layers and roles.

But this is not what I found the most interesting about the method. To me, the most important part was that this method allows nature itself to do the thinning-out of the trees. You know that a lot of them are going to die, but the result will be astonishing.

Plant ecologist K. Yoda found that a thick growth of plants would thin itself out as the bigger plants grew bigger and the smaller ones died. This is hardly surprising in itself. But Yoda found that in a graph in which the average plant weight is a function of density, both on logarithmic scales, the slope of the line was very close to -3/2. The confusing thing about such a graph is that the time axis goes backwards: you have to read the graph from right to left. Or is it backwards? Remember that in Japan they traditionally read right to left. This discovery, like the Miyawaki method, came out of Japan. Here is a recent article about this pattern. Yoda used monocultures (a single species) but it apparently works with polycultures as well.

My message is simple: If you want to restore nature, let nature do it, giving it just a little help.

Resurrection

Last night (March 12, 2016) I went to the Tulsa Symphony production of Gustav Mahler's Second Symphony, the Resurrection Symphony. The Tulsa Symphony, together with the Tulsa Oratorio Chorus, performed magnificently. The conductor was Benjamin Zander, who is also the conductor of the Boston Philharmonic. I have carefully listened to this symphony for thirty years, but I still learned many new things when I actually saw the performance and listened to the conductor explain it.

Most people react to death by not thinking about it: by just going to the funeral and getting it over with. Mahler was not like this. The first movement of his symphony was not a funeral march; the inchoate march was always interrupted when Mahler stopped to agonize, or to appreciate the surprising beauty of life. With excruciating beauty, Mahler wrung out every last insight he could get from the fabric of life, death, and resurrection. Here was neither a facile atheism nor a shallow Christianity.

Mahler's music is not for everybody. I will admit that my writing, too, is not for everybody. I cannot write anything, not even a four-line poem, which does not somehow plumb the meaning of life, revealing both its agony and its beauty, sometimes simultaneously. I am trying to do for the written word what Mahler did for music.

This being a science blog, I am not going to go into any musical details. I just wish to say that, as a scientist, I see resurrection all the time. You have to look for it and think about it, as Mahler did. Here is what I see.

On the cover of a vinyl edition of Bruno Walter's recording of this symphony, there is one simple image: a deep space nebula. A nebula is a resurrection. The old superstar explodes as a supernova and is dead, leaving behind a pregnant cloud of gas and dust. From this cloud, new stars and planets condense, and the second generation of stars ignite. This is where our solar system came from. Our sun is a resurrected sun. And there would be no planets were it not for the engine of creation inside the supernova, the only place in which there is enough temperature and pressure to create the larger kinds of atoms such as iron, phosphorus, and magnesium from which planets and soils are made, and uranium, a radioactive element the decay of which keeps the interior of our planet hot. Our planet is solid and warm-blooded because of the supernova, the death and resurrection, of an earlier generation of star. This is why our sun is only five billion years old, while the universe is over twice that age. Astrophysicists believe in resurrection. It is not the same star, resurrected back to life; it is a different star; but the star-life continues.

I am a botanist and I see resurrection all the time. I don't just mean the opening of tree buds each spring, a process that is in full swing right at this moment. Budburst is not really resurrection; the trees and flowers were just asleep for the winter, and are awakening. But every forest that I walk through is a resurrection. Every forest is one that grew in a place in which an earlier forest was destroyed. Longfellow wrote about "the forest primeval" in Evangeline; but there is no such thing as a primeval forest! Longfellow's "primeval" Acadian forest had not even been there a few thousand years earlier, when the land was covered with glaciers. The forest had grown back after the glaciers melted. A fire or mudslide destroys a forest, and then it goes through a slow process of what ecologists call succession: first weeds, then shrubs, then fast-growing trees such as cottonwood, and finally, after about a century, the slow-growing and long-lived trees such as oaks. This is a resurrection. The original trees are gone; perhaps the new forest is different from the previous forest; but a forest has grown back. It is not a miracle, any more than a nebula is a miracle; it is simply the natural laws of plant growth. To realize this, you have to look closely at the forest, and look at it in four dimensions.

These are the kinds of resurrection that, I think, Mahler believed in. He had a hard time accepting the death of the old, but his faith in the growth of the new was irrepressible.