When we open up thick stands of trees to create silvopasture, our goal is pretty simple: To remove enough tree canopy in order to let sunshine flow through the trees in order to allow grasses, forbs and legumes to grow below. (See previous post on why more open savanna-like landscapes are more the historical norm than open pasture or closed stands of trees.)
Silvopasture is an ancient practice that integrates trees and pasture into a single system for raising livestock. Research suggests silvopasture far outpaces any grassland technique for counteracting the methane emissions of livestock and sequestering carbon under-hoof. Pastures strewn or crisscrossed with trees sequester five to ten times as much carbon as those of the same size that are treeless, storing it in both biomass and soil.Project Drawdown
When we create silvopastures out of thick woods, we leave the best trees, and quite a few of them. Our objective is to remove dying, diseased and dead trees, and we often pile them up to create habitat for ground-dwelling creatures. For the most part, we try to leave the most mature and healthy trees — the opposite of how many forest “thinnings” usually happen, where the most mature trees are harvested for lumber and the understory (mostly genetically inferior stock) is left to regrow. We are selecting for health of the trees, so we want to leave the trees that compete the best for sunlight and resources to propagate more of their own kind.
Most of the trees that we have recently taken out down near the Haw River were not healthy trees. Ideally they would have been thinned over the years with axes, chainsaws and mules, but it is now a much larger job.
How close to the river are you cutting trees? How much land are you opening up?
We are leaving between 165’ to 215’ feet or more from the river untouched by large equipment. The line follows the change in slope and the change in soil type from Piedmont clay to the flood plain’s loamy sand. The flags are set on the topographic change, the vegetative change and the soil change line. Lines in nature are never straight, and we are paying attention to the soil changes rather than a hard-and-fast demarcation.
The total acreage for this project is around 6 acres. A roughly equal amount of land between the site we are working on and the river is going to be left as it is, for the most part. We have plans to collaborate with Hawbridge School students as well as volunteers to hand-remove invasive (non-native) privet bushes to allow the native spice bushes to proliferate.
What are the soils like? Don’t trees get compacted?
Except an area that we initially traversed into the flood plain (the error was ours and not the firm doing the work; we immediately repaired it, see photo below), we are staying off the alluvial soils where high river waters over the centuries have deposited silt and sand. The area where we are taking out trees has the same soil type, Piedmont clay, as our adjacent pastures.
As much as possible, we are leaving mature, healthy trees, and especially trees that provide fodder for livestock and wildlife, such as hickories and oaks. We are staying off the drip line of the trees as much as possible, and not dragging the slash across the bark of the trees that we are leaving. Operators of the equipment company we are working with have listened well to our desire to have as light of a footprint as possible, and to leave the soil surface in place as much as we can.
These types of projects are not common — large machines are usually used to level sites for housing developments and shopping malls — and to their credit, Carroll Contracting has learned quickly what we were after. Instead of grading the site with a bulldozer, they are using logs to level the soil where trees were removed (and fixing old gulleys from where water was not properly managed uphill decades ago, likely because of tilage and row-crop farming). We are keeping as much topsoil in place as we can. I have no desire to lose a precious ounce of it. The whole point of restorative livestock agriculture is to build soil.
Certain trees handle compaction better than others, and we are taking that into account with our selection. Poplars, for example, like compaction less than other trees (primarily because they are heavy consumers of water). They are also faster-growing than oaks, and so all things being equal we will usually elect to keep an oak over a poplar.
Grasses are healing to soil structure, and keeping soil covered is paramount, and to that end we are immediately planting native grasses — and covering the soil with straw loose enough to allow seed emergence. Having the soil covered with vegetative life will help the trees retain moisture through the summer. Covered soils create healthy environments for underground life, which improve water-carrying capacity, fertility and diversity.
Our flood plain is not a wetland
As part of our investigation for this project, we dug with a tile spade for soil classification looking for subsurface water in the alluvial area, which would make the lowland soils less stable. We found no underground water at 40”, the standard test depth for soil classification purposes. We left some Piedmont soil areas in the alluvial flood plain. The 40” hole showed no mottling, thus the soil is technically well-drained, even in the flood plain, although we are not planning to select clear that area except to later remove invasives by hand.
Disturbance is not a perfect process, but healing can and will follow
I will say that cutting trees with a large machine is not a perfect process. Habitat is disturbed. The birds don’t care where our line in the proverbial loamy sand is. We do our best to disturb the area the least, get off the soil quickly and replant. And we’ve already done so on a good portion of the site.
Yet, every one of our choices every day has an impact of a living system. Whether we like it or not, we were designed to eat three meals a day. That food has to come from somewhere. We can choose to buy corn flakes produced thousands of miles away, where no song birds sing anymore because their habitat was destroyed by destructive tillage, herbicides, pesticides and the loss of topsoil and habitat, or we can reconcile ourselves to eat in our foodshed and grapple with the choices therein.
“Solitude is a human presumption. Every quiet step is thunder to beetle life underfoot, a tug of impalpable thread on the web pulling mate to mate and predator to prey, a beginning or an end. Every choice is a world made new for the chosen.”Barbara Kingsolver, Prodigal Summer
The choices are not always simple or easy, and I’m not presuming as much. (Even the device upon which you are reading this is made with minerals that may have been mined by children, at great peril to themselves.) Two-thirds of the earth’s arable land mass cannot grow cultivated crops such as corn, wheat, broccoli and tomatoes because it’s either too steep, too infertile or too far from points of distribution.
If we are going to feed ourselves, we are going to have to come to terms with grass, clover and dandelion leaves as a source of food, and homo sapiens can’t thrive on those alone. We can partner with the mighty dairy cow, whose superpower is turning sunshine into butter through those very plants. Thus, creating a habitat she can dwell in amongst the songbirds, owls, turtles — even coyotes, and hopefully one day again, wolves — is a mighty and worthy task.
Although forests are the lungs of the world, lungs breathe out as well as in, and forests lose their trapped carbon dioxide back to the atmosphere when their leaves decompose. A mixture of trees and grass and herbivores comprise the most ecologically sound and productive ecosystems in the world, more productive and carbon-sequestering than forests, or even grasslands — which may be the only true carbon sinks other than oil left underground.
Grasslands are a net positive carbon sink, as grasses work synergistically with subterranean life to actually sequester carbon and keep it in the ground, provided the soil isn’t repeatedly turned over. Current research points to silvopasture as perhaps the most proven carbon-sequestration ecology.
We estimate that silvopasture is currently practiced on 550 million hectares of land globally. If adoption expands to 720–772 million hectares by 2050—out of the 823 million hectares theoretically suitable for silvopasture—carbon dioxide emissions can be reduced by 26.6–42.3 gigatons. This reduction is a result of the high annual carbon sequestration rate of 2.74 tons of carbon per hectare per year in soil and biomass.Project Drawdown