Why Does Plant Diversity Matter? Help Us Figure It Out!

How important is plant diversity in restored prairies?

Are diverse prairies more resistant to drought and invasive species than less diverse prairies?

How does plant diversity influence invertebrate communities and their ecological functions?

These kinds of questions have been the focus of multiple research projects in our Platte River Prairies over the last decade or so.  We have numerous restored (reseeded) and remnant (unplowed) prairies that provide excellent field sites, and have also established two sets of experimental research plots to help focus specifically on questions related to plant diversity.  Those plots are 3/4 acre (1/3 ha) in size and represent varying levels of plant diversity, allowing us to investigate the functional differences between them.  Researchers from the University of Nebraska, Kansas State University, the University of Illinois, and Simpson College have been involved in data collection efforts so far.

2013 photos from

2013 photos from our experimental research plots.  The plots from left to right were planted to a monoculture (big bluestem), a low diversity mixture (mostly grasses and a few late season wildflowers) and a high diversity mixture (100 plant species).  We are investigating functional differences between these kinds of plant communities.

Craig Allen, Leader of the Nebraska Cooperative Fish & Wildlife Research Unit, and I are hoping to take the next step in these efforts by bringing on either a PhD or Post-Doctoral Research Associate.  We have data to build upon, including some intriguing results regarding invasive species and insect herbivory rates at varying levels of plant diversity, but want to greatly expand upon those data.  If you or someone you know is interested in these kinds of questions, please read below and contact Craig or me with questions.

Here is the official description of the position:

Ph.D. or Post-Doctoral Research Opportunity:  Grassland diversity, restoration and resilience

Ph.D. graduate research assistantship or Post-Doctoral Research Associate.  Available starting in May 2015, to investigate the relationship between grassland restorations and ecosystem services and resilience.  The assistantship (or Post-Doc) is with the Nebraska Cooperative Fish and Wildlife Research Unit, in the School of Natural Resources at the University of Nebraska, working closely with the Nature Conservancy scientists and resource managers.   The research project will include a synthesis of literature to identify prominent knowledge gaps related to the restoration of grasslands and resilience.  In addition to synthesis, field work will occur on a suite of restorations in central Nebraska.  Some questions of interest are listed below, but ultimately, successful candidates will be expected to develop a specific research project(s).  The candidate could approach this project from a broadly ecological, or botanical, or entomological frame.

The successful applicants will be highly motivated, with a strong work ethic, strong and demonstrated writing skills, a passion for field work, and the ability to work in collaboration.  Experience in restoration ecology is helpful, but not required.  Ph.D. applicants should possess a M.S. in Wildlife, Biology, Zoology, Botany, or Entomology, or a related field and have a valid driver’s license.  Post-doctoral applicants should possess a Ph.D.

Interested applicants should send a cover letter, names and emails of 3 references, GPA and GRE scores, and an updated CV as an electronic PDF or Word document to Craig Allen, allencr@unl.edu

Review of applications will begin March 15 and continue until a qualified candidate is identified.  For more information on the Nebraska Coop. Unit and the University of Nebraska-Lincoln please visit us at:

http://snr.unl.edu/necoopunit/default.asp

Applicants should also review:

https://prairieecologist.com/

Specific projects could include all or part of the following:

Relationship between restoration diversity and ecosystem services, such as invasion resistance and herbivory; interactive effects that might mediate some resilience properties; responses to multiple disturbances; how invasions might weaken the ability to cope with disturbance; microbial diversity and ecosystem function and services; response to pulse and press disturbances and mechanisms driving responses; functional trait diversity and redundancy and resilience.

Seeing Past the Ugliness

I’ve spent much of my career restoring prairie, and I gain immense satisfaction from watching bare ground turn into beautiful prairie.  Following the lead of Bill Whitney and Prairie Plains Resource Institute, we have tried to harvest seed from as many plant species as we can for those prairie restoration projects, often collecting from more than two hundred species.  As a result, most of our restored areas are full of color and beauty throughout the growing season.  It’s a pleasure to walk through those areas, photograph them, and take visitors out to see them.

Our restored prairies can be very beautiful.

Our restored prairies can be very beautiful.  Platte River Prairies, Nebraska.

However, not every square foot of our restorations is lush and beautiful.  In fact, some areas are pretty ugly; dominated by weedy species and abundant bare ground.  Those are the areas I don’t usually take visitors to see, and when I walk or drive through our sites, I tend to either avert my eyes or just avoid traveling past them in the first place.

It’s actually not my fault those areas are ugly.  I tried to make them beautiful…  I seeded them with dozens of showy wildflower species, but none of them took.  I re-seeded many of them, but nothing changed.  The alluvial soils beneath our lowland prairies were deposited by old river channels meandering across a broad floodplain, carrying and dropping many layers of sediment.  As a result, our sandy loam soil consists largely of a thin layer of sandy topsoil (4-8” or so) over sand and gravel.  In places, that topsoil may be a little thicker, but in other places, it’s non-existent.  That’s especially true in former cropfields that were scraped flat to aid irrigation, but even in unplowed prairies, there are strips of coarse sand with little or no organic matter – and that’s where my ugly patches are.

weedy patch

This little ugly patch is part of a restoration in its twelfth year of establishment, but it is still dominated by annuals, including annual brome, black medick, and annual sunflower (among others).  This patch is maybe an acre in size. Most of the rest of the planting looks very nice, though there are other ugly patches scattered throughout.

There are few plant species that can grow in almost pure coarse sand.  During periods of relatively consistent rainfall, seeds can germinate and plants can grow, but when the rain stops, most of those plants wither and die once the last of the soil moisture is used up or drains away.  Plants in these sites tend to grow and bloom during the spring, which is typically our wettest season, and then die or go dormant during the hot summer when rainfall is more sporadic. Our ugly patches are largely dominated by species such as daisy fleabane, annual sunflowers, annual bromes, buffalo bur, black medick, sweet clover, mullein, and “rougher” grasses such as Kentucky bluegrass or tall dropseed. While some of them are exotic species, most of those are either innocuous or already common throughout our sites, so it’s not like the ugly patches are breeding evil invaders.  They’re just ugly.

Ok, hold on a minute…

Ecologically, of course, there’s nothing at all wrong with these areas.  The plants in those coarse sandy soils are exactly the ones that should be there, given the options available.  Just because they are not species often considered to be attractive, or even desirable from some people’s aesthetic viewpoints, they are still the right plants for the job.  Not all are native, but none are problematic in those little patches where very little else can grow anyway.

Hoary vervain (purple) helps trace the outline of this ugly patch, which is also filled with species such as sweet clover, tall dropseed, and Kentucky bluegrass.

Hoary vervain (purple) helps trace the outline of this ugly patch, which is also filled with species such as sweet clover, tall dropseed, and Kentucky bluegrass.

The primary objective for our restoration work is not to create pretty flower gardens; it is to create new prairie habitat that expands and reconnects formerly small and isolated prairies in a fragmented landscape.  To be successful, those restored areas need to be floristically diverse enough to provide for communities of pollinators, herbivores, and other organisms that rely on that kind of diversity.  They must also provide habitat that allows the plants and animals in adjacent prairie fragments to expand their range into, and through, our restored areas.  Larger and more connected habitats facilitate larger and more connected populations of prairie species, making those populations more viable.  We don’t want to precisely replicate the habitat in nearby prairie fragments, we just want our restored habitats to be useable by the species living in those fragments.  In fact, we hope our restored areas provide some complementary conditions – valuable habitat types that might not exist in the prairie fragments.

According to those criteria, our “ugly” patches are perfectly fine.  In fact, they add value to our restored prairies.  A prairie planting that is relatively uniform in plant composition and structure throughout would be much less useful in terms of habitat diversity.  The bare ground in the sparsely-vegetated “ugly” patches provide great places for invertebrates and reptiles to sun themselves.  They are also excellent brood-rearing habitat for quail, prairie chickens, upland sandpipers and pheasants, whose chicks can’t move through dense vegetation but still need overhead cover from predators.  Pollinators probably find our “ugly” patches quite beautiful when they are filled with resource-laden annual sunflower or hoary vervain blossoms, and even less popular species such as daisy fleabane offer food value for at least some insects.

fleabane a

While daisy fleabane is not usually found on lists of species to plant for pollinators, it does provide food for many insects.

Intellectually, I know these rough-looking areas aren’t truly ugly, and I am glad to have them, but my mind doesn’t always think intellectually.  As the person who collected and planted many of the seeds for our restored prairies, I sometimes catch myself thinking of them almost as gardens, or even works of art.  (I imagine architects rarely take visitors to the furnace rooms or utility access areas of the buildings they design, though they certainly appreciate their value.)

Putting ourselves in the role of artist or gardener is a trap many of us can fall into, but it’s a dangerous trap indeed.  The greatest risk is that aesthetics start to guide the way we design and manage restored sites.  We could, for example, devise seed harvest strategies that emphasize greater collection of seeds from big showy plants and minimize harvest of plants with less aesthetic value.  Even worse, its tempting to avoid defoliating prairies during the peak flowering period of our favorite flowers, even though we know periodic mowing or grazing has no long term impact on their populations.  It can also be tempting to spend time removing plants we think are unattractive or undesirable, even though they don’t actually cause any harm (e.g., exotic plants that aren’t truly invasive).  Since I’ve never met a land manager who feels he/she has enough time or resources to deal with the invasive species they have, wasting effort on the removal of non-invasive species is just silly.

Here in the Platte River Prairies, we’ve been very careful to set and follow clear ecological objectives for the restoration and management of all of our sites.  We consider habitat diversity and availability rather than blooming periods of attractive plants as we devise annual management plans, and we harvest seed from every plant species we think can play an important role in our restored prairies (excepting those species we know will colonize on their own).  However, I still find myself tempted to chop down any “ugly” plants I come across while I’m out on musk thistle patrol.  I was also appalled to find that I had almost no photographs of the “uglier” patches among our restorations when I started working on this post (but lots of photos of “pretty” patches).   Clearly, I’m not immune to the gardener/artist mentality – I just resist it the best I can.

P.S. We also have other scattered “ugly” patches in our prairies caused by factors such as high soil nitrogen or grazing/loafing patterns of cattle.  While I don’t often photograph them either, they are just as valuable as the ones featured in this post – they add to the heterogeneity of our prairies.  Next time you stop by, remind me and I’ll show them to you.  That’ll be fun…