Multi-species Grazing Systems in Silvopasture

To this point, we’ve dug a little bit of deeper into grazing methodologies and spent some time talking about the benefits of grazing in a forest setting. We also talked a little bit about the logistical challenges of organizing two seemingly different systems at the same time. In short, it’s not easy, but it’s because we’re trying to rush the clock of ecological succession. And, obviously, time is the one thing we don’t really have right now. So, we gotta do what we gotta do. 

So far, we’ve talked about species utilization and order, as well as some basics around the tree choices that we’ve been interested in, specifically in how that relates to the local ecological conditions of our biomes so that we help accelerate forest succession while adding the benefits of the savannah landscape, which reflects a lot of the indigenous forest management methods across much of the world. Now we’re gonna get a little bit more detail-oriented, so if you haven’t checked out the first silvopasture piece, I’d say check it out.

Big picture, why are we interested in silvopasture at all? The ultimate goal of silvopasture is to create food systems that are more resilient and in alignment with our local ecology. For many of us, that’s a forest setting, which not only traps more carbon than grasslands, in places where forests would occur naturally (more on this nuance in a future piece), and more specifically forests that reflect a diverse landscape of native plants.¹ And we know where those forests would occur naturally from our discussion in the last episode about brittleness.

Further, if we’re talking about managing forests for food systems, and we are aligning our management based on the natural ecosystems around us, then by definition those systems necessitate multiple species. Ultimately, one of the goals of multispecies grazing is to utilize landscape resources more uniformly. And that’s what we want, full cycling of resources within our landscape, to continue to contribute to the local ecology as the energy passes from one species to the next. By the time the last livestock species vacates a paddock, there should be no odd patches of ungrazed plants, and no dropped fruit or nut that hasn’t been nibbled at— within reason, of course. Pastures will generally recover more evenly and require less finish mowing when the utilization of appropriate species has occurred, leading to less work on your part for management— outside of livestock management, of course. Under a tree canopy, where cutting can be a bit more difficult than in a big open grassland, it’s that much more important to make sure all of these are eaten down.

Otherwise, we’ve seen it before, the tall weeds in a field, while the grasses remain short; those foods that aren’t being eaten will eventually take over as they start to seed if we don’t mow them afterward, but using different grazers helps regulate this process, and reflects how nature works. Each species eats different things in order to create specializations and efficiencies, while also having the generalists that fill in the gaps when populations of species ebb and flow. We are trying to mimic this all in a controlled setting. 

So let’s further look at how the pairing of the forest ecology and the prairie together create a uniquely beneficial system for our animals— what we often call a savannah ecosystem. As you might recall, photosynthesis occurs under a fairly narrow band of temperatures, and when grasses are growing in the shade, their leaf temperature is lower than if they were in the full sun. Partially shaded grasses continue to photosynthesize and grow when their full-sun counterparts have shut down to wait for cooler temperatures. Leaf temperatures aren’t the only thing that shuts down photosynthesis in forages— the chlorophyll in a leaf can be thought of as a sponge.

This green sponge soaks up sunlight as fast as it can while some of that sunlight is being used as energy to manufacture basic carbohydrates. Once photosynthesis is happening as fast as it can and reaches its peak efficiency, it can only convert sunlight into simple sugars at that fixed, maximum rate. If more sunlight is striking the leaf than the chloroplasts can use, then that leaf has become “light saturated”.² Some is reflected by the leaf and some is converted into heat which can further slow photosynthesis. Leaf temperatures can become so hot that moisture loss causes wilting and a further reduction in photosynthesis. 

The savanna, with its tree canopy and grassy floor, would produce an even, dappled shade where forages stay in their optimal temperature and light level ranges for longer periods of time while also helping reduce water loss on the soil, assisting these leaves that are light saturated.

Further, by planting our trees in patterns that are not straight rows, we create windbreaks. We talked about keylines, and these can be a really good way to maximize water access and create natural windbreaks, but you don’t need to do this, and even if you can’t cut in keylines because of stumps, the natural shape can be beneficial for their ability to act as a windbreak. Windbreaks help to prevent desiccation, or dryness, in field crops. They can help prevent wind-generated soil erosion, preserving valuable topsoil.³ Windbreaks can provide shade against the summer heat and shelter from the shivering winter winds. Animals protected from winter winds require less feed to keep warm, reducing feed costs, animal mortality, and headaches. Windbreaks are simple to understand, simple to plant, and simple to care for. 

Let’s talk a little bit about riparian buffers if you have access to a waterway. Riparian zones are the area of land along the edges of bodies of water. The size of a riparian zone depends to a large extent on the size of the water body. The land area affected by the Mississippi River, for example, is much wider than the zone around your half-acre farm pond. Like windbreaks, riparian buffers tend to be linear in nature. In addition to this, these buffers also resemble windbreaks in that they are used to interact with an energy flow. Windbreaks interact primarily with wind patterns whereas riparian buffers primarily interact with water patterns, not the streams themselves, but overland water flow from agricultural fields or flooding from drastic rainfall.

Although riparian buffers don’t prevent the original erosion in the first place, they perform an incredibly useful function as mechanical filters and biological sponges. When runoff encounters the perennial vegetation of a riparian buffer strip the velocity of the water is dramatically decreased. As the water slows down more of it has a chance to soak into the ground. Perennial root systems, rodent burrows, and wormholes provide openings allowing the destructive flow to infiltrate. As the speed of the overland water flow decreases it’s not able to carry along the largest of the soil particulates and they begin to settle out, getting captured and accumulating soil in the riparian buffer. These zones host species such as dogwoods to flowering plants such as American highbush cranberry and lilacs to the twenty-some-odd willows and five or so species of birch — all bring benefits that can be used for food, fuel, and building materials. Water-loving biomass crops such as prairie cordgrass can even be burned directly for fuel and are a perfect fit for riparian zones. 

One of the things that scares some folks away from silvopasture systems, especially if they want to get their trees large enough not to be grazed on before bringing in livestock, is the idea that much of the land will be unproductive for a number of years or even decades. You plant 10 chestnuts, for example, 25 feet apart. Those trees might be 4-foot tall whips, and the rest is left as grass. But, it doesn’t have to be. Probably the simplest agroforestry technique to understand is the practice of alley cropping. Alley cropping is the growing of a row of trees or shrubs (or both) between annual or short-term perennial crop fields. The trees that seem to do the best in alley-cropping systems are trees with taproots. They don’t have a shallow mat of roots to get compacted and damaged by equipment and they don’t steal as much water and nutrients from the crop. 

 Another way to prevent nutrient theft is to drive a subsoiler along the row of trees every year from the very first summer after they are planted. This clips any young roots that attempt to go after the crop nutrients. It keeps roots within the tree row and encourages them to dive deep. If you wait until the tree is older before subsoiling, the tree roots are much bigger and the tree could suffer from all kinds of decay pathogens and generally, it becomes harder for the tree roots to change course. 

Root prune the alley-cropped trees every year beginning in year one. It’s worth also considering the shade density of the mature trees, the number of trees planted per row, and the orientation of the rows. Some studies from the University of Missouri-Columbia have shown that rows of trees oriented east-to-west show slightly greater tree crop yields (measurable, but not statistically significant).⁴ On a square, flat field, it might make sense to orient the tree rows that way, but in most of North America, this doesn’t take into account the prevailing summertime winds or the usual direction of storm winds that might turn the alleys into a wind tunnel. Considering prevailing winds might also be useful if you’re looking to create a windbreak, and of course, if we can work with keylines that would be ideal.

If you’re working on or planning to develop a site that has first installed a keyline water management system, the rows of trees would parallel the keyline. Instead of straight, rectilinear rows of trees, the trees would sweep gracefully along or near contour and would reveal the natural shape of the landscape as it relates to water. The important thing to note is that the keyline rows of trees would still be parallel, as in, each curving row maintains its distance from the other rows. Their crowns should cast a light shade (between 40 and 60 percent is ideal— again, remember the needs of the grass) across the pastures. Livestock move through the system and are almost always in partial shade. Livestock are kept in one paddock until they’ve eaten their preferred forage, then moved to the next paddock. There are two ways to get to that ideal. One, as previously mentioned, is to plant trees in your pasture. For an already existing rotational grazing paddock system, all that needs to be done is to plant a row of trees alongside the currently existing permanent fence. 

The flipside, which might seem easier, is in many ways more difficult— working with an older forest. Sometimes folks don’t like the idea of cutting down trees in a forest just to plant other trees. It’s worth remembering a very large percentage of the forested land in our agricultural states, is not really a functional forest. The original forest is long since gone, and the trees in existence now are undergrown by invasive species such as honeysuckle, multiflora rose, European buckthorn, garlic mustard, and Japanese barberry. Often, if they are native, they’re homogenous early succession forests filled with fast-growing, low-producing trees. Now there’s nothing wrong with early succession species, but the overwhelming majority of forests today are made up of early succession species, which is the bigger issue.⁵

If any of these modern non-forests were former agricultural fields long since abandoned, they may not have any true forest-dwelling plants in the understory and merely are a collection of opportunistic weeds of various degrees of shade tolerance. Eventually through the ages, hundreds of years perhaps, these places will settle into being a true closed-canopy forest. But for now, they are a tangle of briars producing very few ecological services aside from making oxygen and providing habitat for a few crows, bluejays, and raccoons. Without regular grazing or periodic fires, the underbrush has grown up in these former grasslands, much of its regeneration of the overstorey, which is often trees trapped, unable to progress in the natural forest succession because of previous clearcutting.⁶ As the shade in these sites has increased the once abundant grasses have disappeared and an overabundance of trees has developed. The sites being naturally droughty are not able to support so many trees per acre and the trees grow poorly and slowly. They become increasingly stressed, and in extremely hot and dry summers like that are becoming more and more common, entire sections of forest have died all at once. 

Now, we haven’t spent a TON of time talking about trees, really, unless they are planted in the wrong spots, but sometimes that wrong spot can be a little more specific. And what I mean is really dealing with trees that are dioecious; that is, they only have male or female sexual parts. This could mean you plant five, let’s say, mulberry trees, and only 1 set fruit. It’s pretty unlikely but could happen. Well, if you were doing it for the fruit, you’re in trouble. But, mulberries also have incredibly edible leaves. Cattle, sheep, goats, and pigs all love to eat the leaves of mulberries, and they’re more nutritious than alfalfa and come with a delightful co-product — mulberry fruit. Mulberries are fairly high in protein for a berry, and of course, are high in sugars meaning that they are a high-energy livestock feed.  With male trees that you’re not worried about reducing fruit production, you can trim them back heavily, with fast-growing species like mulberries that can be multiple times a year, while still having the female drop massive amounts of fruit.

Mulberries aren’t the only tree that’s good for tree fodder. Most commonly, willows, alders, and poplars are used, primarily because mature coppice stools or pollards can produce over 20 feet of bushy growth in 1 season. Other plants are perfectly suited as browse and trees such as black locust, honey locust, maples, and birch are all trees that have many other benefits while also being great feed for livestock. Fruiting tree species, nut trees such as pecan and black walnut, and the various hickories and chestnuts are all great options for use in silvopasture systems as well. Of course, it’s important to keep in mind your local ecological conditions and native species, especially keystone species like oaks.

At this point, we have a sense of some of the trees, and the row structure, and the orientation of how the animals graze the site. Our goal is to mature into somewhere between an open and a near closed-canopy forest, depending on the historical and climate-driven future context your site suggests. Grasses and livestock forage require at least 40 percent light in order to thrive, so typically forest farming takes place in forest stands where the shade is less than 60 percent. Grasses, aside from a few rugged sedges, don’t do well in a densely shaded environment, so it’s important to think about how you’ll manage the landscape to allow for the grasses to continue to grow. This goes back to spacing, trimming, and so on. Fortunately, the animals love the trimmed branches.

Other crops that can be grown in this type of understory are edible crops such as ramps, gooseberries, and currants. Persimmons are partially shade-tolerant as are pawpaws, nannyberries and mayhaws — all of which are sorely underutilized, useful native to me food plants. One of the simplest crops to grow in the shade of a forest are mushrooms. They have forms that are both edible as well as medicinal. Mushrooms also bring us into another phase within the cycle of life and that is the decomposition cycle. Of course, our livestock might have less interest in this, but this is particularly useful in northern parts of your site, where you may have heavier shade, especially if you’re planting your larger species to the north to reduce shading across the rest of the landscape. 

Instead of hunting for the edible species where nature might (or might not have) put it, these types of forest management systems intentionally create the conditions for the crop to thrive and then plants it there. This is the human in its natural environment; it is the quintessential activity of humanity, and it’s exactly what we’re doing in our silvopasture system and all of our land stewardship practices, except with the use of domesticated animals.

Nature might only plant a handful of let’s say, ramps, in a particular area, but a forest farmer might plant intensive beds with thousands of plants per acre. Likewise with mushrooms. Nature might scatter a few puffballs here and there or a patch of morels in profusion, but only for one year out of a dozen years. A forest farmer creates the conditions to produce large quantities in a small space. 

While planting specific species and running domesticated animals that fill natural spaces in ecological systems, how else can we help to, well, be human in our ecology? We can do below the soil similarly to what we do above, and help accelerate and mimic the natural systems. If you want to follow a more natural and cost-effective path, you can simply go to a nearby patch of the trees in question, and gather up some of the soil beneath them, and harvest the bacteria and fungi within this soil in order to spread suitable soil life onto the perennial polyculture crops. You can also choose to make full-blown custom composts to incorporate into the original soil around your new crops. If you are establishing an oak-savanna restoration, you can gather leaves and soil from beneath the oak trees in an oak forest to harvest and add them directly below your recently planted trees. The same could be done for overstory trees of different species. Walnut compost can be made to help establish walnuts, maple compost for new maples, and so on. This practice is commonly referred to as Korean Natural Farming, which we will be covering in a few short chapters

So, what can all of this look like? I think this is where people tend to get overwhelmed; how to put all of this stuff together. There are a lot of things we’re trying to stack here, and it is complicated. That’s why I haven’t gone too deep into specifics because it’s important to get a good handle on the basic fundamentals of what things should look like, what to be aware of, and some of the logistical challenges of grazing in this type of setting.  We can space our trees based on the variety we choose, the site conditions, and what our plan for those trees is. Are we looking for trees that are going to be dropping fruit or nuts mostly for animal feed or is the animal feed just an added perk to something that feeds us? How much tree hay are we cutting? What is the shape of the tree as we cut it, how will it impact the light penetration? For a tighter planting, say, trees 10 feet apart, you might want to shred, which means cutting the sides to keep the tree skinny, in order to increase light penetration. How much work is that for you, and are you afraid of heights? Are you just growing trees and cutting the branches off during the summer, or are you pollarding or coppicing the trees that you’re feeding leaves from? In the following two chapters we’ll be covering this content, so don’t be frustrated if you don’t have those answers yet. But your goals should be around what you want your end results to be. If you want, say, sheep and cows, start with species and foods they’ll eat for trees. 

Of the species that are options, which can you get something from, whether fruit, timber, nuts, or soil building capacity for your site? Which of those aligns with your local biome? Your list of 80 trees will whittle down to less than 15 or so pretty quickly, How large do they get, and are you going to grow them to that size? You’ll have your spacing figured out by what their needs are, and that spacing doesn’t need to be consistent across every tree; it can change with the area on the property and species.

On the north side of your property, in the northern hemisphere, you’d want to put your largest tree species in order to reduce shading across the property. And, of course, if you can, align your tree rows with your keyline. Otherwise, if you can’t, go crazy and do what makes you happy. Straight rows are slightly more efficient but not something we see in nature, so if you want to work around a pond and take those angles, go for it. Keep in mind the seasons on your site; does water sit all spring long in one area? That might be the spot for your willows, black walnuts, or sugar maples that would do better in more moist conditions.  Lastly, think about your fruit and nut drop periods so that you can move your animals through them so they can harvest the cleanup when unhealthy fruit is dropped before the harvest to reduce infections and pests. Obviously, now you can see how stacking these things, and our understanding of the site conditions on growth capacity, overseeing the site over a full year, and understanding grazing is all necessary in order to understand the bigger picture of what’s going on here.

Now, Mark Shepard also provides an example of one of his systems in his book ‘Restoration Agriculture”. He proposes a 1-acre field as the following:

• 9 rows of edible woody plants with a 23-foot-wide alley between each row.

Those rows would be planted as follows:

• 5 rows of chestnuts planted 12 feet apart within the row. Beneath each chestnut tree would be a row of red currants planted 2 feet apart within the row and one grape vine trellised on each chestnut tree.

• 4 of the 9 rows would be an apple and hazelnut row with apples planted every 24 feet and hazelnuts as an understory planted every 4 feet. Raspberries would be planted on the south side of the entire row every 2 feet and one grape trellised on each apple tree.

This spatial arrangement would result in a total for each acre of:

• 34 apple trees

• 86 chestnut trees

• 120 grape vines

• 208 hazelnut bushes

• 416 raspberry canes

• 520 red currant bushes 

Now, personally, I would do this a little differently, and I’m not a huge fan of the vine suggestion for reasons I’ve covered before, but I want to give you an example of what can be done with an acre. He further makes the case that this example would provide 5.978 million calories per acre, nearly double what a high-yield optimal corn field would produce, which is by far the most calorie-dense mono-crop grown today. That 5.978 million calories is enough to feed 82 people for a year at 2,000 calories a day, while not requiring a drop of insecticide, herbicide, and relying primarily on trees that, once established, will be in place in some cases for hundreds of years. Further, these systems can be put in place on lands that otherwise could not be farmed— steep landscapes, waterlogged areas, and so on, where utilizing the right trees for the right place can not only thrive but provide new diversity for our food systems.

So at this point, I think we’ve got your brain firing on all cylinders, and hopefully all of this is tying everything we have talked about in this podcast into one general cohesive narrative. In the next episode, we’re going to dive into some of the tree management pieces that we’ve been hinting about in this episode, which will help firm up some of the concepts around the utilization of the species we’ve talked about at this point.

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2. Li, Y., Gao, Y., Xu, X., Shen, Q., & Guo, S. (2009). Light-saturated photosynthetic rate in high-nitrogen rice (Oryza sativa L.) leaves is related to chloroplastic CO2 concentration. Journal of Experimental Botany, 60(8), 2351–2360. https://doi.org/10.1093/jxb/erp127

3. Weninger, T., Scheper, S., Lackóová, L., Kitzler, B., Gartner, K., King, N. W., Cornelis, W., Strauss, P., & Michel, K. (2021). Ecosystem Services of tree windbreaks in rural landscapes—a systematic review. Environmental Research Letters, 16(10), 103002. https://doi.org/10.1088/1748-9326/ac1d0d

4. Garrett, G., & Walter, W. D. (2015). Alley cropping: Farming between the trees. Green Horizons, 19(1).

5. https://www.scientificamerican.com/podcast/episode/forests-getting-younger-and-shorter/

6. Sankey, T., & Tatum, J. (2022). Thinning increases forest resiliency during unprecedented drought. Scientific Reports, 12(1). https://doi.org/10.1038/s41598-022-12982-z