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Does diversity tell the whole story?

June 21, 2017 12:00 AM

Jacob Hill Maintaining Iowa’s highly productive agricultural landscape demands high inputs of fertilizer. When fertilizers run off the landscape in rain events or snow melt, negative consequences for water quality may arise due to enrichment by nutrients such as nitrogen and phosphorus. Developing strategies to sustain high levels of agricultural productivity while reducing nutrient runoff and its harmful consequences for water quality is a major concern of conservation science.  

Luckily, conservation measures such as prairie strips offer one strategy to reduce nutrient runoff from row crop fields. Prairie strips are diverse native prairies strategically planted within or at the edge of fields of row crops to slow down water flowing at or within the soil surface, trap and filter out nutrients carried in the flow, and thereby reduce nutrient and soil addition to surface waters. The diversity of these prairie plantings is a primary factor contributing to their success as filters for agricultural runoff, but the impact of individual species (each of which contributes a rib to the umbrella of plant diversity)  planted within strips is less well known. This topic was the focus of a research project I conducted at Iowa State University.     

Over the past year and a half, I’ve been fortunate to be an undergraduate research assistant in the LESEM lab, helping out with some of its various endeavors, including PEWI version testing and STRIPS bird research. I’ve learned much, had fun, and developed great relationships along the way! During this time I was also fortunate to have the opportunity to conduct my own independent research in a topic relevant to the discussion above. In my project, I wanted to know if especially large-growing species commonly planted in prairie reconstructions disproportionately influence the ability of prairie strip plantings varying in diversity to filter out nitrogen from runoff. I conducted this work as a part of a biodiversity-ecosystem function experiment at ISU's Field Extension and Education Laboratory.

In short, I posed the following questions: Is diversity itself sufficient to maximize nitrogen removal of prairie strips? Or do the identities of individual plant species included in plantings factor in as well?

Plants tend to use nitrogen more efficiently when there is little as opposed to a lot of nitrogen available to their roots. This means that when nitrogen is abundant, as occurs in plantings consistently exposed to agricultural runoff, stems and leaves might be expected to have higher nitrogen concentrations than they would with lower nitrogen availability. Therefore, lower nitrogen concentrations in stem and leaf tissue indicate lessavailable nitrogen to plant roots, which suggests that plants are removing nitrogen efficiently from runoff. Put another way, higher nitrogen concentrations in stems and leaves indicate more available nitrogen to plant roots, which suggests that plants are not removing all of the nitrogen from the runoff, and some nitrogen is at risk of being lost from the immediate environment.

With these relationships in mind, I measured the nitrogen composition of a really large prairie species called cup plant and compared it to the nitrogen composition of the other species in prairie strip plantings exposed to nitrate-laden runoff. I expected that as the number of plant species included in prairie strip plantings increased, nitrogen concentrations in plant stems and leaves of both cup plant individually as well as whole prairie strip plantings would decrease, indicating increased removal of nitrogen from runoff.

I unexpectedly found that diversity was not the most important factor influencing nitrogen composition of prairie strip plantings or of cup plant. However, diversity was positively associated with the nitrogen concentration of species other than cup plant. The most important factors explaining patterns in prairie strip nitrogen removal efficiency were the abundance of cup plant and cup plant nitrogen composition, NOT diversity. It appeared as though cup plant overrode the expected positive influence of diversity on prairie strip nitrogen removal from the simulated runoff in this experiment because of its abundance and low requirements for nitrogen relative to other species.

Diversity itself does not tell the whole story.  The relatively high level of diversity in prairie strips is essential to their increased capacity for nitrogen removal, but this effect begs qualification. If the influence of cup plant is any indication, which species to include in prairie strip plantings is an important consideration for conservationists concerned with maximizing the ability of prairie strips to filter out nitrogen from runoff. Separating out the contribution of individuals from the whole prairie strip community may help land managers to construct even more effective prairie strips.            

Jacob Hill grew up on a diversified farm outside of Newton, Iowa and graduated with a B.S. in Environmental Science from Iowa State University in spring 2017. You can find his honors thesis here. He is now an intern at Neal Smith National Wildlife Refuge near Prairie City, Iowa.



Welcome to Dr. Lisa Schulte Moore's lab in the Department of Natural Resource Ecology and Management at Iowa State University. We study human-landscape interactions, and are particularly curious about changing land use and its causes, consequences, and design. Through this research, we hope to improve the scientific basis for decisions that impact people and nature. You can find more information about our members, research, and outreach on this website. Contact us with questions. 

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Teach your children well

January 20, 2014 12:00 AM

Family of four "What's the action of greatest impact?"

This is the question I have taped to the top of my computer screen. As a scientist, educator, and mom concerned with the fate of our planet, it’s something I contemplate on a daily basis. I recently had the opportunity to plumb the depths of my mind regarding this question while on a 500 mile solo road trip through arguably one of the planet’s most altered regions: the U.S. Corn Belt. One of the answers I came up with was to teach my children well, especially regarding the laws of nature and human interactions with them. I try to do so through our everyday activities—some spontaneous, and some planned—in the great outdoors of our local community.

We’re lucky enough to live in a pretty ideal urban setting when it comes to nature: next to a large public park with a substantial area devoted to wildness in addition to the usual manicured picnic area and ball field. We’re literally over there every day. Trips with the kids (ages 4 and 2) regularly include stream stomping, rock turning, and leaf picking (“Oh, watch out for THAT one! It will make you itchy.”). In so doing we learn about species diversity and that some flora and fauna are more common than others (“Why Mama?”). When we find trash -- little of which makes for good habitat -- we pick it up.

As the kids grow older and more capable, we’ve started to engage in more structured volunteer activities, furthering our human-nature education. We began participating in the Great Backyard Bird Count when my kids were 3 and almost 1. For a few days each February, we catalog the birds that frequent our feeder, as well as those we see in the park. We learn how to identify birds common in Iowa, their adaptations to winter, and differences between habitat specialists versus generalists. Last year we found black-capped chickadees, dark-eyed juncos, and blue jays wherever we went. We didn't see house sparrows in the more remote areas of the park, but they were the most abundant species in our yard, choosing to roost in our discarded Christmas tree. Surprisingly, we saw two bald eagles (“Why are they bald, Mama?”). We found them flying down the stream corridor in the park, but never saw them anywhere else. 

Over the last two summers we've also volunteered as "goat checkers" for a local conservation organization. Story County Conservation uses goats to keep woody plants from encroaching on a native prairie remnant at one of their high quality preserves, Robison Wildlife Acres. Goat checking involves weekly trips to the preserve to make sure the goats are all there, the electric fence surrounding them is still intact, and they have plenty of water to drink. My older son, Freddy, particularly enjoys pulling over the encroaching trees and shrubs for the goats to munch on (my, how they come running!). And so we connect with a local organization that’s doing good work while also learning about preferred forage and a prairie’s need for periodic disturbance to remain intact.

My husband also signed us up as IOWATER volunteers. IOWATER is a statewide citizen-based water quality monitoring program in which we periodically sample water and record the characteristics of two streams: the one in our neighborhood park and a country stream located about 20 minutes from our home. We like to guess what values we'll observe before we make measurements of dissolved oxygen and water clarity, or what critters we might find. Thus, we teach the kids about making predictions, hypothesis tests, and data collection, which, when you really stop to think about it, expand beyond science skills to key life skills (“There are dark clouds in the western sky; I predict it’s going to rain later today so I’ll bring my raincoat with me”). We also talk about the critical issue of where our water comes from and where it goes.

These family educational activities give us loads of healthy outdoor fun, cost us little-to-nothing, and provide fantastic family bonding experiences – I hope the pictures I’ve included provide good evidence of this. But we aren’t really doing much besides making observations, picking up the occasional piece of trash, and learning for our own sakes, so how could they be considered "actions of greatest impact? I believe our impact is much greater than you might think, and here’s why:

  • The goats are only working on a couple acre patch of prairie, but Robison Wildlife Acres is a demonstration site that other landowners and conservation organization in the region are watching. If they like what they see in terms of prairie response and cost effectiveness, they might adopt the practice. And in a state that now hosts less than one-tenth of a percent of its native prairie ecosystem, even small gains can be huge.

Finally, if we scale up these small efforts to also include your family, my neighbors' families, your siblings’ families, their neighbors’ families, and so on, these kinds of undertakings could result in something immense: generations of people more connected to the soil, water, flora, fauna, and people they depend on. I posit this would be the greatest impact of all. So, cheers to the New Year! I hope you to get your kids outside, teach them well, and share your experience.

This blog entry was also posted on Ecological Society of America's EcoTone blog.