Understanding Plant (Soil) Succession

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The term “plant progression” or “plant succession” is frequently used when considering revitalizing or remediating a plot of land. So what exactly is plant progression? And why did I include “soil succession”?

If we look at the earliest phase of soil formation, it begins with mountains rising from the oceans either through the action of volcanoes (Hawaii for example) or from colliding tectonic plates (Rockies). These mountains begin as large boulders or sheets of cooled lava brought up from the depths of the earth.

Wind, rain and the freeze/thaw cycle of water begin breaking little pieces of rock away to create pebbles and stones. Moss, algae and lichen attach to rocks and provide a habitat for microbes to begin mining minerals from rock to feed themselves and the moss, algae or lichen too.

Slowly, boulders become pebbles, pebbles become sand, silt and clay in ever decreasing size of rock particles. Lichens, moss and algae in conjunction with ever growing population and diversity of mostly bacteria and diatoms at this stage begin the basic formation of soil. As moss, lichen and algae die, their organic structures of mostly carbon, oxygen, hydrogen and nitrogen provide food for a larger diversity of bacteria, diatoms, tardigrades, and insects. In the case of moss and algae which use photosynthesis there are sugars produced as well. Sugars (in particular glucose) is the main energy source for life on earth. These sugars are quickly consumed by microbe life and insects, microbes die, insects die and their remains are again recycled for their glucose and minerals. Soon there is enough food to support ruderal plant life (most of what we call weeds). These first higher plants are able to grow in hard, compacted and shallow soil with a low organic matter. They often have long taproots that writhe their way into the tiniest of cracks in rock and push through very compacted mineral particles all the while offering glucose in the form of root exudates to microbes; in exchange for retrieving other needed nutrients and minerals.  Microbes make minerals and nutrients available to the plants, the plants lift those nutrients to their leaves and seeds above the surface to produce proteins, more glucose and ultimately seeds to ensure survival of the species. Like all life, weeds die, the remains of the weeds now have minerals and nutrients (including glucose) on the surface of the earth. As nature always does these minerals, nutrients and glucose are recycled by microbes. Now however there are strands of primarily carbon compounds called cellulose and lignins. The bacteria and other microbes present up to now aren’t adept at reusing lignin and cellulose- enter the fungi.

Fungi slowly begin the process of recycling cellulose, with the help of  bacteria and other microscopic life start to form small balls of soil called aggregates. With aggregate formation there are air spaces between aggregates for finer, smaller roots to penetrate. With the presence of fungi begins the appearance of grasses and a lessening of weeds. Eventually as fungi population increases more, grasses are replaced by shrubby bushes, and eventually trees.

Every stage results in more and more organic matter being dropped and recycled. With more organic matter comes more fungi and a greater diversity of life (both microbes and larger creatures like insects, arthropods, and  earthworms on up to mammals).

Many people refer to this as plant progression or succession. I personally prefer to think of it as soil progression even though they’re tightly knit together. We can engineer a succession of soil without waiting for plant prgression by adding organic matter as mulch and/or composts and planting the appropriate plants to provide the root exudates to feed the organisms those plants require.

By looking at the plants growing in our plot to be revitalized or remediated we can, with experience (or the correct tools and knowledge) get a starting point on engineering the soil type our desired crop requires.

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