Karai Strangegrossman, tea, Mba´eíchapa aprende kuri ahejahangua ajepy´apygui ha ahayhuhagua la ka´akuéra invasadorape

Today’s Post: Dr. Strangegrossman, or, How I learned to stop worrying and love invasive species

I want to take you back a year, to my final months in the United States. At first, garden seeds seemed like the perfect thing to take with me to Paraguay. Seeds are compact and light and it was rumored that certain spices would be hard to find in my new home. Why not grow my own chili peppers? But I was persuaded against the idea by my ecologist friends in Seattle:

“So I think I’ll just bring a few packets of hot pepper seeds.”

Silence. Then one ventures, “But aren’t you afraid of introducing…exotic microbes into the soil.”

Another friend elaborates, “Even if the seeds are of high purity, they may be carrying fungal spores, or soil bacteria!”

So, to avoid contaminating Paraguay’s delicate ecosystems, I left the seeds at home.

I should take a moment now to explain some frequently misinterpreted terms. “Native species” are those groups thought to have evolved in a given region. “Exotic species” are species that have been imported from other regions; they may be harmless, or, if they have been around for awhile, “naturalized”. “Invasive species” are a particular group of exotics – those that wreak environmental havoc after being introduced to a new place. In Seattle, for example, Douglas fir (Pseudotsuga menziesii) is a native species, apples (Malus domestica) are a harmless exotic, and Himalayan blackberries (Rubus armeniacus) are an invasive exotic.

Exotic species cause billions of damage yearly in the United States alone. Numerous examples abound: animals such as zebra mussels (Dreissena polymorpha), plants such as purple loosestrife (Lythrum salicaria) and various morning glories (Ipomoea sp.), and a host of fungal and microbial species. The spread of these invasive species is one form of “biological pollution,” one of the frequently understated outcomes of globalization.

Invasive species constitute a problem for several reasons. By displacing native species, they can diminish biodiversity and outcompete native species. They can reduce the quality and quantity of ecosystem services that humans depend on, either directly (like new pathogens preying on bees) or indirectly (like Phragmites grass making waterways impassable). And they can effect wholesale landscape change, covering grasslands with shrubs, turning wetlands into terrestrial systems, introducing fire into local disturbance regimes, altering rainfall by affecting transpiration, and converting passable fields and forests into walls of non-native vegetation.

As an ecologist and an environmentalist, I abhorred invasive species and vowed to fight them. At Oberlin, a significant component of my field job was attempting to control reed-canary grass (Phalaris arundinacea) and cattail (Typhus sp.) infestations. At the University of Washington, I volunteered at restoration projects where the biggest task was often pulling up Himalayan blackberry and ivy (Hedera helix).

Thus I was shocked to arrive in Paraguay where many exotic and even invasive species are…accepted! Paraguayan yards and gardens are a mishmash of species familiar to Americans. The spider plants and bougainvilleas that we may have to keep inside grow outdoors here, alongside hydrangeas and roses. The tomatoes, peppers, green onions, and potatoes that we plant at home could easily come straight from a Paraguayan garden. My first host family kept dahlias and my current yard is covered in pear trees. But many of these cultivars are harmless exotics that would hardly thrive if left to their own devices.

The fun, however, doesn’t end there. Invasives abound and many are consciously planted by those guardians of the environment…Peace Corps volunteers. So what follows is the story of how one Dr. Strangegrossman learned to stop fearing invasives and started to encourage Paraguayans to plant them. It’s a story of how a confused young ecologist went from carefully dusting himself for grass seeds before leaving the Sky Harbor airport to asking his mother to load up on some Mammoth Russian sunflower seeds before coming to visit. It’s a story of the following invasive species and the Americans and Paraguayans who love them:

Bamboo (species in Bambuseae), which slowly takes over native forests and forms dense clonal “trunks” that defy any efforts at removal, is critical to rural household economies. Bamboo, or takuara/takuarilla is used to make fences (especially for gardens), sheds, screens, tools, posts, roofs, and furniture. It is sometimes sold to be made into paper pulp. Most households have at least one takuarilla tygua (bamboo stand) and the areas without takuara are often hard-pressed for building materials. The alternatives, tree wood and bricks, are often expensive and scarce. Takuara is easy to work with and grows fast. Most families use a variety that produces smooth, large-diameter trunks. But crowding Paraguayan forests and my yard are some other less useful varieties, including a small-diameter one that spreads until it becomes impassable without a machete and a cruel, spiky variety that is impossible to touch or cut without inducing scratches. Normally, bamboo spreads aggressively through vegetative reproduction (a hallmark of invasives), but every few years, all the bamboo in a region goes to seed and then dies, giving the species a chance to spread out over larger distances.

Leucaena (Leucaena leucocephala) is a Central American tree and darling of agroforesters. A legume that grows fast and withstands cold and hot temperatures alike, leaucaena produces abundant animal forage and useful firewood, all while fixing nitrogen in the soil. Agroforesters frequently tout leaucaena as a multi-purpose tree, especially in “cut-and-carry” forage systems: farmers regularly prune the branches and foliage off leaucaena grown in rows and then transport it to waiting animals. This has the added benefit of preventing leucaena from doing what it does best: producing seeds. Left to its own devices, leucaena flowers and fruits all year long, producing thousands and thousands of small brown seeds, encased in pods that easily break open when dry. Today, many people in Prettyview have at least one tree in their yard - the result of gifts from previous extensionists. Most don’t know what it is called or how to manage it, but simply comment “hetaiterei hi’a” (it fruits a lot). The prevalence of unenclosed animals in Prettyview, which I normally lament, has kept the tree from becoming a true pest. Grazing kills immature seedlings before they can fruit. But I’ve already planted a number of leucaena seedlings with families who want to use it as a fodder alternative to sugar cane and grass, so I guess I’m doing my part.

Velvet bean (Mucuna pruriens) or “mucuna” is one of the more commonly used green manures in Paraguay. The insatiable climber is a nitrogen-fixing legume with lush, three-part leaves and large, white seeds. Ideally, one plants corn and then, after it has reached chest height, plants mucuna next to it. The mucuna climbs up the more mature crop and, by the time the corn is ready to be picked, it is covered with mucuna. The mucuna eventually overwhelms the corn, pulling the now-dead stalks to the ground. Then, frost kills the mucuna, leaving behind a mat of dead mucuna and corn stalks, which suppresses weeds and enriches the soil. But what if a mild winter fails to kill the mucuna? Or if it flowers before the frost and its owner doesn’t use a rollo cuchillo (a rotating series of rolling blades pulled by oxen) to kill the plant before itt sets fruit? Some plants may survive to bud anew and mature seeds sprout as soon as the winter comes to an end. Mucuna unmanaged can climb and kill trees and become just as much of a weed as the plants it suppresses. One of my friends has given his fallow fields over to it and invited me to harvest a few bags of mucuna seed. Even trying to vacuum up as many pods as possible, I left behind many, ready to reseed the field next year, and perhaps cross on over to that block of extant forest for a little ride up to the canopy. Nevertheless, I plan on handing out mucuna seeds at my next gardening charla.

I don’t have much to say about the loofah plant (Luffa sp.) because I refuse to have anything to do with it. Certainly, this vine in the squash family produces natural loofahs, a perhaps appealing alternative to synthetic sponges. But each zucchini-like fruit is filled with seeds, which innocently fall out of the sponge as it is dried, cleaned, and then used. The plant itself can pull down a takuara garden fence (invasive versus invasive!) or climb up a tree trunk and compete for light. Although once I run out of leucaena and mucuna seeds, I may get to work on a small business plan for locally produced Prettyview loofahs.

And then there are the gray areas. Hovenia (Hovenia dulcis) is an Asian import, a pretty relative of the pear and apple that starts fruiting in the summer and, as of the following spring, still bears viable seeds (the fruits dry up and fall off the plant, but each contains one to two sweet-smelling, indestructible seeds). Hovenia may be on the way to naturalization. It is a common species in many stands of otherwise native trees and some native species seem capable of competing with it. It loses its leaves in the winter, a holdover from a colder climate, putting it, potentially, at a disadvantage against other, native evergreens. When Hovenia is so widespread, is there a problem with planting more of it? What about the sunflowers and marigolds my family brought from home? A marigold I planted in my garden last fall survived the mild Paraguayan winter unscathed whereas, even in Phoenix, marigolds often emerge from the winter as desiccated piles of brown dust. Are those special “California Reds” – worms meant especially for lombriculture – going to escape and compete with native earthworms? It’s an invasive species truism that you never know the effects until after you’ve introduced the species.

But really, not all invasive species are spread by Peace Corps volunteers. Many of them were here already. One of the reasons that Paraguay has taught me, if not to love invasives, then at least to give them a chance, is that they are so essential to many Paraguayans’ livelihoods. After all, aren’t most crops really just spoiled exotics, one step away from invasiveness? In some ways, the quest for better crops, horticultural varieties, and trees is the quest for a more perfectly invasive species. No natural enemies or diseases? Resistant to drought, heat, and cold? Capable of engineering its own environment through nitrogen fixation? Allelopathic to avoid weeds? Frequently produces lots of large, easy to disperse seeds all throughout the year? Can reproduce vegetatively as well as sexually? Fast growing? Produces lots of organic matter? The same qualities that make plants especially desirable to humans often help them to survive in diverse habitats. Add to this a lax attitude toward biosecurity at Paraguay´s borders, and the country is ripe for an invasion.

The prevalence and lack of anxiety over invasive species in Paraguay also raise uncomfortable questions about relative environmental priorities. Though invasive species can be economically costly, it is hard to generate much concern for the problem when making ends meet requires so much time and energy. A potentially invasive species that puts food on the table (or can be used to build the table itself) is even less likely to encounter opposition. Biological pollution is no more a problem of the affluent than most other environmental issues that are frequently portrayed as such. But it´s a challenge for Peace Corps volunteers and other environmental educators to communicate the issue in a compelling way.

Especially when we keep planting leucaena!