Low organic matter clay woodland - tree planting designed to increase organic matter under the topso

Good Evening,

Long time lurker.  This is my first post.

I have a lot of poor quality clay soil.  NW MT.  At elevations from 4500 feet down to 3000 ft.  50 acres of high % grade hillside  20-40% varied.  More acreage that is gently sloped, but topsoil is thin with clay underneath.  I must not be using the right search terms on here or generally online.  My question and then more detail below.

Question:  I want to plant native or nativized trees/shrubs that produce a high root density and will provide "speedy" infiltration of organic matter underneath the topsoil in my clay.  Make soil from the bottom up rather than top down.   Plant high density pine/doug fir, irrigate some and then harvest every 5 years, planting new rotation between the rows.  Plant fast growing trees like cottonwood/willow, irrigate, cut down, naturally kill the stumps and then plant again between rows.  The idea is that in 10 years this soil will have XX% of additional organic matter in the top 3 feet of clay.  Am i just describing a christmas tree farm?  I can't quite grasp how to do it right or if it makes any sense at all.

Ultimate Goal:  High quality Silvopasture for some of the property, managed woodland for the rest.  I live here, so I want it to either be pretty or interesting to look at.



More Detail.  

The property was logged 10 years ago.  It was not logged with care in many ways.    

Doug fir dominates, but Western Larch and Ponderosa make up 20% of the upper story trees.  Lots of douglas maple, some other native berry trees.  Lot of randoms.  Ive planted orchard trees.   But over all density of trees on avg is well below what could be supported.

Topsoil is very thin.  

Ive done various "standard" permaculture things like swales, when clearing junk trees I make horizontal on grade piles with a few "stakes" made from junk trees, hugel mounds, appropriate thinning and planting, Ive made single rock height check dams on certain eroded slopes, bunch of other little experiments.

Welcome to the world of posting to the forum!  Love it!

To me planting trees to improve clay soils is a possibility.  What kind of trees would work?

A lot of different aspirations are expressed here.  Which are the best put forward?

Anne Miller wrote:Welcome to the world of posting to the forum!  Love it!

To me planting trees to improve clay soils is a possibility.  What kind of trees would work?

A lot of different aspirations are expressed here.  Which are the best put forward?

Essentially the fastest/best way to put root organic matter in the soil on a 10 year horizon.

Native/nativized trees so I don't have to irrigate after the initial establishment, but could to realize greater growth.  We get around 17 inches of percipitation.  I get a bit more up on the mountain, and the snow remains longer.

Willow and cottonwood would provide more rootmass, but they will coppice rather than die and decay.  More work to kill.

Ponderosa pine or Doug fir would grow more slowly but once cut down the roots would start to die immediately.

I'm interested in the concept! I have clay soil with low organic matter. In one spot, there used to be a pecan tree, but it blew over last year when hurricane winds came through. A mole had dug tunnels around the tree, and I think that weakened some of the roots to make it more susceptible to wind damage. Anyways, I planted a few things in that spot this year -- an elder bush, tomato, green beans, oats, kohl rabi, and watermelon. They're growing so much better than anything in my designated garden, especially the things planted directly over where the tree was. A significant amount of root was left in the ground, so I can only assume that's why the plants are doing so well.

Oak, sweet gum, and wild cherry trees are a large percentage of trees around me. I'm selectively letting a few grow in my food forest area, partly for temporary shade until the others fill in and partly to have their root mass when I'm ready to cut them down.

Counterintuitive as it may seem, if you want to build organic matter deep in the soil, what you want is grass and other prairie vegetation, rather than woody stuff like trees and shrubs.  If you look at a map of the world's soils, the high organic matter soils are usually in places that were originally prairie and not forest.  This is because of several reasons....a typical prairie plant, grass or forb, has a balance between the above and below ground portions of its total biomass that is more equal or even predominantly below ground to start with.  With trees more of it is above ground. Whether living or dead, above ground biomass can be degraded by fungi, by fires, or by browsers....all of which impact organic matter a lot less, or not at all; if it's already deep in the soil.  And grass will also recover from most of these events a lot faster than forest will.  If you are logging the trees, then you are also acting as a biomass reducer.  I think there are even some teachings that state that having animals grazing on the vegetation increases the organic matter even further in the soil, up to the point when the pasture begins to degrade.  Rotational grazing is an attempt to mimic the movement of large herds of something like buffalo across a prairie....Allan Savory gets into this.

If you want to build deep topsoil where there is a clay base, you don't want to use trees. Trees, especially conifers, don't sink deep roots of the type that will build top soil. Look at where rain forest has been cut down and that land then being farmed. It never works.

As already mentioned, grasses are the soil builders, they sink roots up to 3 meters deep, bring mineral nutrients up from the depths, encourage bacteria and other microorganisms to populate, attract mycorrhizae and other fungi to populate. All this is what builds friable topsoil. Other items that build soil depth are broadleaf plants like comfrey, wild sage, sweet grass, etc.

I have lots of information posted in my soil series. I encourage you to read through it to learn methods that are proven to work when building soil.

Redhawk

For clay soils, add lots of leaf mold, wood chips and mushrooms.  Any organic matter helps ...

There is probably a lot of 'it depends' to consider....I've seen deep leafmould in ancient beech woodland over clay, and overgrazed grassland that generates little topsoil at all....   In my tree field the spruce do seem to have very surface roots, but that is still quite a bit of wood returning carbon to the soil, let alone the needle drop that has occurred over the years, already making a deep layer on top of the original soil.
I do understand that some North American grasses have very deep roots, presumably to get them through dry summers....