The other day I got an email from a pastured pork producer in Iowa, someone who is well established and respected in the business, has already established trees on his farm, and wants to continue adding more tree diversity for his pigs, both for shade and for additional feed.
Being that he is in Iowa, he has the benefit of having strong NRCS cost-share for silvopasture through the EQIP program. That program is able to offset much of the cost of establishing trees in a silvopasture. Or, it would, if his application hadn’t been turned down on account of including mulberries in his planting plan, a species that was deemed too invasive to warrant planting. This puzzled me, but it also struck me as a problem that more farmers will face as they look to implement silvopasture or other agroforestry systems that are still uncommon, so I want to break down that statement and analyze it closely. The idea that mulberries or other non-native species should be avoided is a commonly held view, one that is rarely examined with any rigor.
Picture yourself standing at some random point in Iowa. What are you most likely to see? Corn. Corn, corn, and more corn, whole oceans of corn. And if it’s not corn, it’s soybeans. In 2021, Iowa grew 12.9 million acres of corn, and 10.1 million acres of soybeans. To give you some context, the state itself totals roughly 36 million acres. So, cornfields covered 36%, over one third of the entire state, and soybeans covered another 28%. Let that sink in for a second. Just two plants, corn plants and soybean plants, covered 64 percent of the entire state!
Now let’s look back at our mulberry trees. In this case when I say ‘mulberry’, I mean morus alba, the Asian ‘white’ mulberry, or a cross between our native morus rubra (Red Mulberry) and morus alba, a hybrid that is vigorous, productive and very common. Morus rubra in its pure form is now incredibly rare, and so anything planted for high fruit production is going to have alba genetics. Hence, it is indeed a non-native species, and since it likes to spread it is considered an ‘invasive’ species.
Keep in mind that the invasive qualities of a species should be considered on a spectrum, where on the extreme end you have plants that will aggressively dominate ecosystems, and on the other end you have specimens that will only rarely escape cultivation. In my area we have bush honeysuckle, Japanese hops, stiltgrass, knotweed, oriental bittersweet, Tree of Heaven, Bradford pear and mile-a-minute as some of the most aggressive species. I am very familiar with these species as well as others, since invasive species control has been a significant part of my work for years. Other well-known examples are kudzu in the southeast and Himalayan blackberry in the Pacific Northwest. Compared to these, mulberry is quite mild mannered, and will not overpower or dominate native species.
What exactly is so bad about mulberries, other than the fact that you have to weed whack your fencerow and occasionally pull some deep-rooted seedlings from your flowerbed? Probably the main problem opponents will bring up is insects. Native insects are best adapted to feed on native tree species. This should be a real factor for consideration when planting trees, and a great reason to use more native trees when appropriate, whether in landscaping or in agroforestry.
As far as the other ecosystem services provided by mulberries, the fact that they are not a native species changes nothing about the fact that they sequester carbon, provide habitat, slow water in rainstorms, pump out oxygen, etc. While they may not provide food for many native insects, all sorts of vertebrates relish the fruits, leaves and twigs, including deer, opossums, raccoons and squirrels.
Consider for a moment that this particular NRCS proposal was for mulberry to be integrated into a diverse pasture setting as just one tree component alongside a whole suite of other trees, many of them native. Given that pigs are omnivores, they can make use of a wide array of tree crops, including mulberry, persimmon, acorns, chestnuts, hickories, hazelnuts, apples, pears and more. While mulberry cultivars yield heavy enough to compete toe-to-toe with corn for per-acre caloric output, they simply cannot be used alone, since they don’t provide a complete diet, and only drop from June to August or so. They can only ever be used as a portion of a larger, more diverse tree planting, complete with diverse trees, shrubs, grasses, forbs and legumes.
Let’s compare this diverse agroforestry system to the ecological value of all those millions of acres of corn and soybeans. Agroforestry systems will sequester many times more carbon, slow more water, and provide more habitat, hands down. And when we talk about food for native insects, the difference is night and day. Not only are corn and soy both non-native species, the vast majority grown in the United States are genetically modified specifically to be resistant to insects, herbicides or both. Hence, both crops create immense expanses where no other life exists, save for a few mutant bugs and weeds.
It seems that there’s a widely held belief, due to the fact that agroforestry systems for feed production are currently so rare in the United States, that crops are strictly for production, and trees are strictly for conservation. We generally place the two in very stark categories, where we do not expect the production areas to give us ecosystem services, and don’t expect the conservation areas to produce anything salable. This bifurcation allows us to accept the fact that 2/3 of Iowa is utterly devoid of any kind of ecological health or diversity, since crops aren’t supposed to contribute to ecosystem services. Agroforestry challenges that categorization by simultaneously providing both production and abundant ecological health. And certain non-native species can be appropriate for use in agroforestry because they produce something of value, like mulberries dropping fruit in a time when little other fruit is available, or Chinese chestnuts to roast over open fires, or European hazelnuts to make delicious hazelnut spreads. The main difference between these crops and the many other non-native crops that we see every single day (apples, pears, peaches, plums, corn, soybeans, potatoes, tomatoes, wheat, barley, oats, alfalfa, orchardgrass, Kentucky bluegrass, tall fescue, and white clover, just to name a few) is that most folks aren’t yet familiar with them.
Regarding mulberries specifically, here’s how I recommend using them:
- In general, when there’s a native and non-native species that have very similar production capacity, choose the native one, since they provide better habitat for embattled native insects. In this case, morus alba and its hybrids are just vastly more available, and more selected for production, such that in a productive agroforestry system it makes sense for now to go with morus alba. Hopefully someday there will be a robust selection of high-yielding morus rubra cultivars to choose from, but that is likely decades out.
- As with any non-native species, don’t bring mulberries into areas where they haven’t already been introduced. This really isn’t a concern for mulberries, since they can be found throughout the country already.
- Use it as a component of a diverse and complementary system of trees.
In summary, mulberries can offer great food production and ecosystem services as part of diverse silvopasture systems, which will soon start to replace more and more sterile corn and soybean monocultures with rich, vibrant, and highly productive agroecosystems that provide for our needs, and the needs of generations to come.