Bringing Trees Back into Agriculture

An introduction to agroforestry systems and why they’re important for farmers

Editor’s note: this is an edited transcription of part of Erik Hagan’s talk from the Acres U.S.A. 2021 Eco-Ag Conference. Erik is the Farm Director of the Savanna Institute’s Spring Green Demonstration and Research Farm Campus, which aims to reintroduce agroforestry practices to the Midwest. 

As we all know, there are a lot of issues within agriculture. I’m not here to belabor that point. We’re all here because we know there are solutions. One way we’re proposing a solution is through agroforestry — adding trees into the landscape to add complexity, biodiversity and ecosystem function. 

American farmers have been doing a lot of work on modifying and refining our agricultural strategy — getting better at grazing, cover cropping, crop rotations, biological systems, etc. But farming still has this protocol, so to speak, of “farming over here” and “nature over there.” This is what’s called “land sparing” — the idea that we do our thing here and we leave some land for the wild over there. 

In agroforestry, we want to share that space. This is called “land sharing” — integrating the processes that we want to see in the wild and regenerating agricultural landscapes within the field: bringing trees and shrubs into the field for their economic and ecosystem service functions, or bringing the same mentality into the forest, where appropriate. 

Agroforestry is a multifunctional solution. It can be very complex and very difficult to describe and, quite frankly, really difficult to know where to start. This isn’t forestry — we’re not talking about something that’s “over there.” It’s not just a woodlot that we go into on our morning walks or where we chop a tree down when we need firewood. Bringing the tree into the field — where you’re driving tractors and moving cows and doing all sorts of stuff on a daily basis — that tree is going to get really annoying if it’s in the wrong spot. Or, 20 years later, if it doesn’t produce a single chestnut.

Ultimately, what we’re trying to do is to remember the way we managed ecosystems before we started to commodify annuals and grazing systems — before we started focusing on industrial cropping systems. Remembering how we managed the field edges; remembering how we used those steep areas on the side of the hill that’s covered in an invasive now because we can’t put a tractor on it. It’s taking a step back and reminding ourselves where we came from — that the original foundation of agriculture was cultivating in and around trees and shrubs. It’s bringing that back into a modern context.

The Four “I’s” of Agroforestry

There are four “I’s” in agroforestry. First of all, agroforestry is intentional. When you’re putting a tree in the way of your tractor, or you’re putting cows into a forest, you have to be very intentional about how you do this. It’s easy to run into problems when you do these things. Most farmers, quite frankly, are chopping their trees down because they’re in the way.

It’s also very intensive. Again, we’re not trying to do “land sparing” — sticking a woodlot over there and calling that agroforestry. We’re trying to mix it all up to keep all the biology and the wildlife habitat within the field — not all around the field. 

Agroforestry is also highly interactive. We’re actively trying to create an ecosystem in the field so we can have the benefits of biological systems. 

And agroforestry is obviously integrated. It’s the integration of trees with crops and livestock. It’s not just forestry. It’s not just having a row of trees over there. That’s an orchard. It’s the integration of trees, livestock and crops. That’s really critical. 

The USDA — and this is more or less globally accepted — defines five main practices of agroforestry: alley cropping, riparian buffers, forest farming, windbreaks and silvopasture. But I don’t like to talk about it in those defined little pockets. Agroforestry is an incredible blend of all those opportunities and options. It’s putting the right tree in the right place at the right time — how you create a system with trees, and work around them, and how they benefit you and benefit your system. 

Ultimately, some people say that a transition to a fully perennial agriculture is the holy grail at the end of the rainbow — the thing they want to achieve — to get away from annual cropping systems. I’m not proposing that entirely. I’m interested in that — that’s something that I think is a possibility within its proper context — but I’m a farmer. I like to grow crops, and I like to raise livestock. I eat a lot of those things. I’m really interested in how to get more perennial — from where I’m at. How do I take my operation — a grazing operation or a cropping operation — and slowly, over time — maybe even multiple generations — shift into a perennial agriculture system. A system where I don’t have to till every year, or I don’t have to do these kinds of landscape modifications every year — these environmental disturbances — to get a crop. 

Agroforestry incorporates the foundational practices we need to move in that direction. And its benefits begin right away — in year one. It’s environmentally beneficial. It diversifies farm incomes. It improves biodiversity. It supports healthy rural communities. Once you get started in agroforestry, you are increasing the dynamic nature and complexity of your farm. This is globally recognized and globally supported. A number of organizations all over the world are now starting to focus on agroforestry as that big stopgap measure for climate change issues. 

The U.S. Forest Service has had a National Agroforestry Center for over 30 years. They’ve done phenomenal work. And now, finally, we’re starting to get more and more movement. There are more and more people talking about agroforestry. 

Moving Trees into Agriculture or Agriculture into the Woods

There are basically two ways of going about agroforestry. There’s integrating trees into agriculture and there’s integrating agriculture into trees. The Savanna Institute is a Midwest-based organization, so we focus on moving trees into agriculture. We are in a corn and soy desert, basically. There are very few trees — they’re really only on the edges of fields or in floodplains or wetlands or riparian areas that are too wet to drain. We’re interested in increasing biodiversity within this context. 

But in areas of the country that are more forested — like the Northeast, or the Driftless area in Wisconsin, or in the South — there are many opportunities for increasing the viability of landscapes by introducing agriculture-like systems into trees. 

Alley cropping is simply the integration of crops with trees — rows of trees with rows of crops. Those crops could be perennials or they could be annuals — they could be corn or soy, or even a forage crop. Alley cropping is a more commodified system. It more closely follows our industrial agroforestry model, with linear rows of high-value, high-production trees. These could be timber or they could be chestnuts or hazelnuts, just to name a few.  

The alley in alley cropping is usually as wide as some increment of the width of the equipment you’re using. In an organic system the Savanna Institute manages in Wisconsin, we have 90 feet between tree rows, with 5 feet from the tree row to the crop edge — so 80 feet of an annual alley, because our partner grain farmer is using a 40-foot-wide implement for two passes of cultivation, spraying, seeding and harvest. Alley cropping a highly efficient model of what agroforestry can look like. 

The crop between the trees can also be 100 percent perennial. You can easily utilize a model where everything’s machine harvested. You can plant tree-shrub crops — a polycultural system where you have chestnuts as the tree row and something like blackberries or black currents in the “alleys,” and all of them are machine-harvested. You can have a large-scale system to meet some of the markets that are needed for these crops. 

One of the great things about alley cropping is that it gets implemented in a row-cropping context, where we have a lot of erosion and a lot of concentrated flows in fields. It’s similar to implementing prairie strips — it’s kind of the same thing — except with trees in them that you can harvest from. The trees can be put on contour, or they can be off contour for routing water in a keyline system, or they can be placed in standard crop rotation strips that make sense for your operation. 

One good example of alley cropping is a 20-acre organic field that has Dutch white clover in the understory of chestnut trees set 90 feet apart, with freshly seeded dry beans as that year’s annual alley crop. The farm had a four-inch rainfall event in about an hour at the beginning of the season, where all of the soil was loose from cultivation. Between every alley there was a bit of erosion, but the 10-foot-wide chestnut/clover strip bisected the runoff, effectively mitigating the erosion. Had it been a 100 percent organic dry-crop field, that rain would have caused a lot of erosion across the whole field and into the watershed, with nothing to stop it. 

There does tend to be an interplay with alley cropping and crop yield. There is a slight reduction in crop yield over time. However, the benefits outweigh the cons, especially during drought events. There’s a lot of interesting research that shows that you might get a yield difference — especially as the trees get larger and start to shade the crops in the alleys — but you start to get more nutrient holding capacity or water holding capacity in the field. You actually get a buffering effect. In some years, especially with climatic changes and extreme weather events, alley cropping provides a buffering effect that can pay for itself. 

Alley cropping — and agroforestry in general — stacks functions vertically, and this has an effect on profit per acre. We’re growing crops at ground level, and we’re also growing crops 20 or 30 feet up in the canopy. 

Silvopasture gets us toward the conversation about perennial agriculture. A lot of our green crops are grown for livestock. What does it look like to integrate trees with livestock?

There are basically two forms of silvopasture: silvopasture by addition and silvopasture by subtraction. You might already have a pasture with paddocks. That’s ideal for a silvopasture-by-addition strategy, where you just plant trees along your permanent paddock rows, creating shade, habitat and increased revenue in the same acreage. 

Or you might have a woodlot that’s highly degraded or covered in an invasive species. An example is a farmer outside of Ithaca, New York, who has a black locust woodlot. It’s an invasive species in that area but a highly valuable timber crop. It had a lot of invasives in the understory and was more or less mismanaged for some time, but by slowly integrating cows into the woodlot and thinning the overstory for added sunlight it has now become a multifunctional, productive system. They’re becoming well known for their grass-fed cattle, but they’re also harvesting pole timber from locusts for fence posts and hop yards. It’s certified organic as well.

Sheep are really easy to integrate into silvopasture, as are hogs, but you have to be very careful about using them in silvopasture by subtraction. One of the main benefits of silvopasture for your livestock operation is shade. We all know about the benefits in terms of daily weight gain from shade. A lot of folks are going out and buying very expensive mobile shade units. Moving them daily is a pain, and they tend to blow away in a bad windstorm. Trees can provide that shade, and you’re getting a stacking function — you’re getting an economic value from the overstory, and you’re getting the benefit of the shade and the increased weight gain. You’re also getting enhanced forage quality over time — the trees keep wind off the forage during droughts and keep frost off as well in the late-season rotations. That improves pasture efficiency.

When you do silvopasture by addition, it’s critical to think about how livestock are going to interact with the leaf forage. There’s a lot of good research coming out on the palatability and the nutritional value of tree forages — mulberries or fruit for pigs or chickens, or willow for grazing cattle or sheep — but the options are vast. 

Silvopasture by subtraction is a little bit tricky. It isn’t supported by a lot of the state or federal agencies, for good reason. There’s a lot of work out there about pigs in the forest. That’s good if your forest is degraded and needs pigs — agroforestry is a tool for land management, and your livestock is a tool for land management. They’re managing the understory, and putting pigs in the woods might be good for your bottom line in the short term, but it can actually do a lot of environmental degradation in the long term, if in the wrong context. 

I’ve seen a lot of hog systems, and I’ve done it myself, and there are lot of great systems with hogs and cattle in the woods. I’ve also seen a lot of bad ones. There’s actually a lot of federal policy against livestock in the woods because of this. While much of past conservation work has been about moving away from that, there certainly is a place for being more intentional in these systems, especially in restoration projects. 

Thinning to 30 to 50 percent stand density is a good place to start; you can even start with a little bit less — maybe 60-70 percent. Get the cows in there one day at a time every couple of weeks — something like that. That way you maximize sunlight for forages, and the livestock are in there for a reason. They’re not degrading your trees, soil, etc., but are aiding in the disturbance regime to slowly transition into another system.

Similarly, there’s a concept called living barns. Here in the North there are a lot of old pine plantations — old windbreaks that don’t have a lot of ecological value. But in a grazing context, they could actually be a resource. Folks are starting to keep livestock out all winter, bale grazing in different systems. But in extreme weather events — negative 20, 30, 40 degrees — these pine plantations, these high-density stands, can actually function as a living barn for a day or two — sometimes even longer. An evergreen will provide a microclimate to get through a storm. 

Alley cropping and silvopasture are the two main in-field practices. There are also several edge-of-field practices. 

Windbreaks are obviously put in place to control the wind moving onto a site for controlling microclimate. There’s an engineering strategy to a windbreak. You need to figure out your goals in designing the trees and in spacing to maximize that goal. They also have a place on every farm edge, providing habitat corridors and additional revenue potential from timber and marketable fruits and nuts. 

It’s the same with riparian buffers. These play a big role in phosphorus and nitrogen runoff. Many states have adopted these edge-of-field buffers for this — even above cover crops or other best-management practices. These edge-of-field practices use perennial crops as the most appropriate way to mitigate runoff. 

Finally there’s forest farming. This is a ground management strategy for your woods. It’s primarily focused on medicinals — ginseng, golden seal, etc. — and mushroom production, as well as the canopy fruit or nut.

Ultimately, we want to get to a perennial agricultural system. Agroforestry provides a lot of options that you can slowly integrate into your operation. I’m asking you to add a little bit of complexity to your farm. I know this can be hard to swallow for farmers who for generations have removed trees from fields to get larger and more commodity focused. But many of those systems have proven to have their own suite of challenges. 

Agroforestry provides a time-tested alternative to increase ecological function, increase economic and rural community viability.