BY AKIVA SILVER
Here in upstate NY there are hills everywhere but the ground upon them is flat. The fields of our hillsides are easily mowed and grazed. They were smoothed out a long time ago when they were first cleared and plowed. It did not always look like neat rolling hills here.
Ancient hardwood forests created a ground so uneven, textured, and three dimensional, that it resembled mogul ski runs. These types of forest floors still exist today on the steepest hillsides that have been woods for centuries. Walking in an old forest around here is more like climbing up and down pits and mounds of soil than strolling down a trail. The topography is so intricate that one hillside is actually made up of thousands of micro hills and valleys.
This micro-topography is created when large trees topple over. A giant root mass is lifted into the air, and as it breaks down, it turns into a mound. The place where the root ball used to be is a pit. Pits and mounds, pillows and cradles, don’t sound like much. But they are. What pits and mounds do has far-reaching powerful consequences.
Before I explain exactly why I love the pits and mounds of old forests, lets take a look at a smoothed out hillside (trees or not). The ground is easy to walk on and drive on, it’s easy to get machinery in and out, but other than the convenience of access, I can not see any other benefits. Runoff of rainwater and nutrients is constant, and can be especially severe when the ground is frozen and there is no snow cover. Streams downhill fill up faster than they can handle, eroding their banks, and sometimes flooding.
The soil on my farm is classified as ‘volusia’. It is a dense clay. In the spring, winter, and fall, the soil is saturated. Muddy is probably the best word to describe the soil on our hill for most of the year. During a dry summer, it can be as hard as concrete. Under these anaerobic conditions, trees languish. They grow very slowly, if at all, and they usually have much shorter life spans compared to trees grown in well drained soils.
How did a soil like this once support the massive trees that became the beams of my family's old farmhouse and the collapsed barn nearby? How do volusian soils support the healthy forests all around my fields?
It is true that most of the top soil was lost when the first European settlers first farmed here. They plowed the hillsides to grow annual grains like buckwheat and barley. Gravity and rain took care of everything from there.
When I first began planting trees here, I assumed that by adding compost, topsoil, or mulch that I could improve the soil and bring patches of it back to it’s former greatness.
I would dig a hole, add copious amounts of compost, and apply lots of mulch on top. After a single year, this spot would be exactly the same soil as all the soil surrounding it, wet and muddy. More compost, more mulch, yielded the same results. What was I missing?
The answer is air. As springs bubble from deep within our hillside, the water runs through the soil and completely fills all available pores and capillaries. There is not enough oxygen in a saturated soil for roots to breath, or for certain microbial life to flourish. In some places the soil is so wet, that it smells anaerobic, and has a grey-blue color. Adding compost might work if I added huge amounts, but sooner or later, the anaerobic conditions would triumph over my soil amendments.
I realized the best way to get air into the soil during a walk in the woods. It is hard to describe the beauty of New York’s southern tier. Steep hillsides covered in treesand pastures make up this idyllic landscape. It resembles hobbit country. This is the northern edge of the Appalachians. During my walk, I entered a mature stand of sugar maple. The pits and mounds were so plentiful that there was almost no place that was not a pit or mound. Many of the mounds were taller than me and some of the pits equally deep.
I have spent a lot of time looking at the ground in these types of forests. Trees are almost always growing out of the mounds. The pits fill with water and snow for large parts of the year and dry up in the summer. What this system is, is truly remarkable. It is a network of raised beds and vernal pools.
The raised beds allow drainage to occur. It keeps the crown of tree roots safe from saturation by raising them above the water table. The soil in these mounds is always crumbly, wonderful stuff. And the pits, the pits!, are more than just water storage vessels. They slow water down, give it nowhere to go except to gently infiltrate the soil. They are not deep enough to hold water year round. This seasonality is a big part of what makes them so exceptional.
A pond that holds water 12 months a year, will inevitably become colonized with fish. I did not understand how this could happen until an old friend told me that birds’ legs will carry eggs from one body of water to another.
A pond or pool that dries up every summer will not support fish which can be a great thing from an ecological perspective. I love fish, raise them in my ponds, and have gone fishing my whole life. The thing about fish is that they love to eat. Fish will decimate populations of amphibians and invertebrates in a small pool. The biological diversity of a vernal (seasonal) pool is very high in the absence of fish. These are the places where creatures like salamanders, toads, frogs, and a myriad of insects will lay their eggs and complete life cycles. The forest I was walking through contained thousands of vernal pools in just a few acres.
It also contained thousands of huge mounds that were growing big trees. Trees like red oak that could never grow in the wet field adjacent to this forest. The adjacent field is the same soil series as the forest, ‘volusia’, muddy. The difference is the uneven ground.
With this observation of forest soils, I got to work destroying my fields. They no longer have the smoothed out surface of a hayfield. I began making my own pits and mounds. I started out with a rototiller, I have since moved onto front loaders and plows, but also use a shovel and pick in areas too steep for machines. Without any compost or soil amendments, the trees I planted grew 10 times or 100 times faster than trees I planted into flat ground. The trees I planted in the flat ground never grew more than a couple of inches, but the mounded trees have been very vigorous for the last 4 years. Many chestnuts have been putting on over 2 or 3 feet a year. Chestnuts require excellent drainage to thrive. The field they are growing in has been a wet field with a very high clay content. The trees often have large foot deep puddles next to their mounds. When I first began planting trees on this land, my neighbor declared ‘the only thing you can grow here is frogs!’
Since building pits and mounds, I have moved onto swales and berms. These are built upon the same concept, but take it a step further. A swale is a ditch that is dug along the contour line. A normal ditch carries water downhill, but a swale catches the water and slows it down, holds it in place. The water sits and collects, most of it slowly seeps into the ground. Building a berm instead of a mound allows me to plant many more trees. I can plant long rows of trees with their root crowns elevated above the water table while they have near constant access to water at the same time.
This is an exciting system because it allows me to grow all kinds of trees in a field that formerly could only support a few species. After just a few years, tree roots will extend beyond the mounds or berms. They will find the surrounding ground. This was a big concern of mine when I first started out. So far, I have seen the trees not slow down at this point, but rather they are speeding up as their root systems build strength. I believe this is due to two factors. The first is that their root crowns are the most important part needing drainage. The second is that the surrounding ground is not the same. The water table at the surface has been altered by numerous pits and swales. Water no longer runs unimpeded through the top foot of the soil. There are traps and sinks for it everywhere. The ground below the swales is not as wet as before.
I’m sure that there are many consequences of these types of earthworks that I am unaware of. Using the forest as my example, I believe that uneven ground fosters growth and biodiversity on many levels. I hope that numerous fungi, bacteria, insects, and amphibians are finding the little niche pockets that they need to thrive.
The way forest floors were created is an unbelievably complex and rich system. Automatic mulching in the fall, raised beds, and water storage are just a few benefits of this system. For those of us trying to grow trees in old abused fields, uneven ground can give our trees the boost they sometimes need.