Seed Sourcing Strategies for a Changing Climate

Years ago, I wrote a blog post comparing prairie restoration to the rebuilding of a city after a major disaster.  I was making the point that our objective with prairie restoration shouldn’t be to create something that looked like it used to or even like the prairie next door.  Instead, we should focus on restoring function to a landscape that had been fragmented and thus degraded.  I ended the post with this sentence, “After all, we’re not building for the past, we’re building for the future.”

I still stand by that, though my thoughts continue to evolve as I learn more about the challenges facing prairies in today’s landscape.  In most places, prairies exist as small and isolated fragments where species and their communities are fighting to survive threats invasive species and other major challenges.  Because the fragmentation of their landscape, many of those species are fighting without the hope of reinforcements from elsewhere.  They’re simply fighting with the troops and ammunition they have on hand. 

Restored prairies don’t have to look a certain way to be effective. In most cases, they should be judged on how well they help stitch a prairie landscape back together. Plant diversity is a key component of that, of course, so restored prairies have to be built and managed so they can sustain that diversity, even as the climate changes.

The rapidly changing climate adds additional stress to those troops by changing the battle conditions – often favoring the enemies.  Many of us have placed hope in the idea that the genetic diversity within species in local prairies will be enough to allow them to adapt and keep fighting.  That’s a big assumption.  What if they’re not equipped to survive a long-term shift in temperature and precipitation conditions? 

If restoration is supposed to bolster the function of fragmented landscapes, how can we best design strategies that decrease stress on isolated prairies and facilitate their need to adapt to changing climate?  For a long time, most of us have stressed the importance of using locally-harvested seed to ensure the plants we grow in restored sites will be adapted to those sites.  In the face of climate change, some have wondered if we should go further afield and gather seeds from places that have the kind of climate that is projected for our restoration sites.

That ‘climate matching’ strategy has some obvious flaws.  If we venture southward, for example, to find plants living under the climate conditions we think will prevail in our restoration sites, those plants will likely to be adapted to different soil types, soil textures, and photoperiods.  Plus, what if today’s climate models are wrong and the future climate is different from current projections?

Here are three photos of prairie larkspur (Delphinium carolinianum) from – left to right – Texas, Kansas, and Nebraska. All three of these photos were taken within a few weeks of each other in 2019. They are all the same species but grow under very different climate conditions.

And yet.  The climate is changing and those isolated armies are already struggling.  If we’re going to provide them with reinforcements and help re-connect currently isolated sites, we want to make sure we recruit the best soldiers we can.  Harvesting local seed just brings in more of the same local genetics we already have.  Climate matching might bring in genetics that won’t fit local conditions.  What do we do?

Fortunately, a team of ecologists led by The Nature Conservancy’s Marissa Ahlering is conducting some experiments that might help solve the conundrum.  Over the last 2 years, they have begun studying the concept of a ‘regional admixture’ approach to prairie restoration seed mixes.  Below, I interview Marissa about the research and what it might mean for the future of prairie restoration.

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PE: First, can you briefly describe your position with The Nature Conservancy?

MA: I am the Lead Prairie Ecologist in Minnesota, North Dakota and South Dakota. The simplest way to explain my job is that I bring science to bear on our grassland conservation issues for the region. Sometimes that means taking the science that exists and applying it to our conservation challenges and sometimes that means collaborating with others to do the science that is needed to fill our knowledge gaps so that we can move our conservation work forward faster.

Marissa Ahlering. Photo by Cara Byington

PE: What do we know about the amount of genetic diversity within plant species living in prairie fragments?  Is it a pretty sure bet that those species are underequipped to deal with climate change?

MA: Honestly, not a lot. Information on genetic diversity and adaptive capacity is lacking for nearly all our native plant species. Work has been done with a very small handful of common prairie plants (e.g., switchgrass, big bluestem, purple prairie clover, and Echinacea angustifolia). For these species, more genetic diversity was found within populations than between populations, and populations closer together are more similar than populations farther apart. This is typical for species with large geographic distributions. Most of this work has been done using parts of the DNA that are not important for the functioning of the plant, so it is somewhat unclear what this means for the adaptive capacity of these species. Genetic techniques can now consider variability across the entire genome and look at parts of the plant’s DNA that might have relevance to characteristics that will help the plant survive better or produce more seeds. In short, there is still a lot to learn, but based on some general principles of population biology and ecology, there are reasons to be concerned.   

Prairie loss and fragmentation have disrupted the population biology of plant species to varying degrees across the Great Plains. Plants maintain genetic diversity with gene flow, and gene flow happens through the exchange of pollen and the movement of seeds. Dispersal patterns for both pollen and seeds have been disrupted by this prairie loss. The now isolated patches of prairie can no longer exchange pollen or seeds and, therefore, genes. However, most of the plants in our prairies are long-lived individuals. Why does this matter? The persistence of long-lived individuals could mask or delay the eventual impact of reduced seed and pollen dispersal.

I certainly don’t think it is a sure bet that prairie plant species are ill-equipped to deal with climate change, and I also think we can use some general knowledge about population genetics, population dynamics, and life history characteristics to identify populations or species that might be more at risk. Factors that are likely to predict which species will be at risk of reduced genetic diversity, fitness, or adaptive capacity are degree of isolation, population size, mating strategy, and possibly dispersal strategy. For small, isolated sites it is a pretty sure bet that dispersal of new individuals/genes into the site is going to be much more limited. From studies in many other species and ecosystems, we know that generally reduced population sizes decrease genetic diversity. Plants have many different mating systems, and there is some evidence that species that have to mate with other individuals are more prone to genetic diversity loss. Finally, there is also some evidence that insect pollinated species are less likely than wind pollinated species to have gene flow among isolated populations. 

Harvesting Maximilian sunflower seed from a remnant prairie about 6 miles from where it was later planted. We can be confident the plants growing from those seeds will be well-adapted to the site. But will those plants still be well-adapted fifty years from now?

PE: What is the ‘regional admixture’ approach and the case for testing it?

MA: Good question. These terms get used in many different ways. Seed sourcing strategies vary by how far seed comes from and number of different sources used. On one end of the spectrum is a strictly local single source strategy, and on the other end would be a predictive strategy where seed is obtained from sources currently experiencing future conditions. Depending on the models used, predictive sourcing, sometimes called climate-matching, may require seed from fairly long distances. A regional admixture approach falls somewhere between these two extremes. Our approach to this has been mixing seed from multiple geographically close and/or intermediate distances from the restoration site. For our current project, we did not use a specific distance cutoff, but seed was obtained from sites ~5-50 miles from the restoration site. This approach tries to account for local adaptation while increasing adaptive potential.

All seed sourcing strategies have tradeoffs in their risks and benefits. On the strictly local end of the spectrum, it is highly likely seed will be adapted to the current conditions of the site. However, the risk of reduced genetic diversity and adaptive potential is higher, as well as the risk of inbreeding depression. Inbreeding depression occurs when closely related individuals mate resulting in decreased genetic diversity and reduced seed production or plant survival. When fragmentation reduces population sizes, this can alter mating patterns and increase the relatedness of nearby individuals. The current status of inbreeding depression in remnant plant populations is largely unknown. It has been detected for small, isolated populations of Echinacea angustifolia, and decreased survival and/or offspring from inbreeding depression is a well-documented phenomena.

On the predictive sourcing end of the spectrum or sourcing from many different distances from the restoration site, the benefit is high adaptive potential and ability to deal with future conditions. However, the risks here are threefold. The first is if future conditions do not yet occur at the restoration site, initial establishment might be challenging. The second is that environmental factors might be quite different between sites very far apart, which could lead to maladaptation. The last is the risk of outbreeding depression. Outbreeding depression is essentially the opposite of inbreeding depression, when plants produced from the mating of two distantly related individuals have reduced seed production or survival. Contrary to inbreeding depression though, the results of outbreeding are not always negative. Sometimes when distantly related individuals mate their offspring actually do better than their parents. This can especially be true if the parents come from populations with low genetic diversity that is already experiencing inbreeding depression. The challenge with outbreeding is that both outcomes (positive and negative) have been observed in various species and situations so generalizations about the effects of outbreeding are difficult.

We chose a regional admixture approach to balance the benefits and risks. The approach of mixing multiple seed sources locally or regionally captures some of the benefits of local adaptation, increases adaptive potential, and reduces the greatest risks of outbreeding by not sourcing seed from too far from the restoration site. The negative consequences of inbreeding depression are clear while the negative outcomes for outbreeding are less certain, and we reduce the risk of outbreeding depression by not sourcing seed from long-distances.

Many of the seeds being mixed here were harvested locally in our Platte River Prairies, but we also travel into adjacent counties, and sometimes a little further, to find seed.

PE: Is this something you think others should be using now or do you see it more as an experiment and suggest people should wait for the results of your work before implementing it at a large scale?

MA: This approach has been widely recommended in the scientific literature. We have now implemented it across over 900 acres of TNC restorations in Minnesota and the Dakotas. We did set up test plots to evaluate the success of this approach. Obtaining seed from many different sources for all species in a seed mix is extra work in an already time-intensive process, and we wanted to evaluate the impact on outcomes. However, the results from this study won’t come for many years and the effects of climate change and habitat loss are being felt by our prairies now.

I think people need to weigh the pros and cons of the different seed sourcing strategies for themselves and their restoration context. The plea I will make is to make sure you consider the pros and cons of your business as usual seed sourcing strategies as well. All of our actions have risks and benefits, including the use of locally-harvested seed from the site right next to your restoration. Strictly local seed is not without its own drawbacks and risks, and those should be considered alongside the risks and benefits of a new approach.

PE: What else do you want people to know about what you’re working on and what it means?

MA: Connectivity and maintaining large population sizes are generally considered to be the key for species to maintain genetic diversity. In places where connectivity and large populations still exist, mixing of seed sources is likely less of a concern, but in these settings, restoration itself is probably less needed as a conservation strategy. In the fragmented landscapes with limited connectivity where we are doing most of our restoration work, the issues around loss of genetic diversity and the need to boost adaptive capacity in restorations is greater. We are currently using this regional admixture approach to balance the tradeoff between inbreeding and outbreeding depression while increasing genetic diversity and adaptive capacity. Where we ultimately need to get to in the Great Plains is climate informed seed transfer guidelines that incorporate both local adaptation to current condition and adaptive capacity for the rapid pace of climate change. The genomic, modeling, and spatial ecology tools exist to achieve this. We just need to put them to work.

PE: Thanks, Marissa, for all of this thought-provoking information. If anyone would like further information, check out the links below:

Short video on the Prairie DNA project Marissa describes above.

A recorded webinar on this topic.

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About Chris Helzer

Chris Helzer is the Director of Science for The Nature Conservancy in Nebraska. His main role is to evaluate and capture lessons from the Conservancy’s land management and restoration work and then share those lessons with other landowners – both private and public. In addition, Chris works to raise awareness about the importance of prairies and their conservation through his writing, photography, and presentations to various groups. Chris is also the author of "The Ecology and Management of Prairies in the Central United States", published by the University of Iowa Press. He lives in Aurora, Nebraska with his wife Kim and their children.

11 thoughts on “Seed Sourcing Strategies for a Changing Climate

  1. I am the Director of Public Affairs & Development for the Lake County Forest Preserve District in Illinois. Some of my colleagues here, led by our Ecological Services Manager Pati Vitt, PhD, are doing similar work in our region (western side of Lake Michigan immediately south of the Wisconsin/Illinois state line). Here are two recent blogs about our work.

    https://lakecountynature.com/2020/11/30/growing-through-change/
    https://lakecountynature.com/2021/02/11/on-the-path-to-recovery/

    As an aside, I am a native Nebraskan, born in Buffalo County. Since graduate school, I have lived in the greater Chicago metro area, but am leaving the Lake County Forest Preserves at the end of this month after many years here, and will be returning to Nebraska, specifically, Omaha. I look forward to coming west at some point to see the Nature Conservancy operation and the magnificent vistas you profile in your “Prairie Ecologist.”

    Kind regards,

    Katherine Hamilton-Smith

  2. What Marissa is doing has already been done. Most restoration have some limit of distance from which they will accept seed. These are typically 25, 50, and in some cases 100 or more miles. These are not new restorations either. Many are decades old. If people want to see how the regional ‘admixture approach’ is working there are plenty of examples to study.

    What Katherine mentions above is more concerning. Prairies used to be big, really big. One hundred miles away may have been one continuous prairie a few centuries ago. However, moving seed from several hundred miles south will bring in plants adapted to completely different ecosystems entirely.

    The plant from further south will likely do well. However, diversity may not develop since these plants have not co-evolved with all other living things in their newly introduced habitat. In the end, moving seed from the south may not prove to be a solution at all. It may just be another attempt to make us feel better about what humanity has done, and continues to do, to the planet.

  3. Getting seeds from several local/regional remnant prairies is wise (best practice).
    But I can’t really see that anything can mitigate climate change.
    It will be down to survival of the fittest at that point.

  4. The problem right now is there is no “Ecological Engineering” discipline. There is so much about each plant that we don’t know.

    E.g. I thought all willows were water lovers. No. Many do fine in grasslands, but they can’t compete with grass when young. They take the wetlands because no one else liked the neighbourhood. Willows are “opportunistic” wetland dwellers. March marigolds on the other hand are “obligate” wetland dwellers.

    Pines adaptability to very well drained soils is another opportunistic plant. Anything but soggy.

    We have few native maples in western Canada. Rocky Mountain Maple, and Manitoba Maple are it, as as I know. Turns out that many other maples grow just fine here. I have a sugar maple planted in my poplar bush. It’s 15 years old now.

    So why didn’t maples migrate west as well as north after the last ice age?

    My guess: Fire. Even older maples (with exceptions) are thin skinned, and even a low intensity ground fire can kill them off.

    But this is a guess. No one has done these tests.

    There is a place for citizen science here. Get acreage owners to plant 10 of this or 20 of that, and report back after 1,2,5,10 years on each batch. Part of their report process is to send in a 1 cup soil sample, and a 1 cup subsoil sample.

    Another approach: Make a point of planting things that are one zone too warm for you. I’m getting good success with austrian pine, and ponderosa pine, both nominally zone 4, here in zone 3.

    We’re face with mixed grass prairie moving to short bunch grass prairie in southern Alberta. Aspen Parkland going to mixed grass, Mixed hardwood boreal going to aspen parkland, and no one is guessing yet what will happen to the spruce forests in the provinces north. Soil there is very thin, very acid. Poplar don’t like it except in patches.

  5. In the early days of using native seed for conservation plantings here in Minnesota, there was little commercially available local seed in quantities sufficient for large acreages. So we had to work with whatever we could find. A switchgrass cultivar named Nebraska 28 was used. Over time those stands of switchgrass dwindled, thinned, and declined. The length of the growing season here was too short for that variety to ripen and produce viable seed. So as the original plants died of old age, they were not being replaced with new plants from the seed they produced. The stands died out and were often infiltrated with invasive species such as smooth brome. Luckily more locally grown and adapted native seeds became available and have been much more successful.

    • The climate has changed a lot since the ‘early days.’ It is going to change even more in coming decades. Studies have concluded the native ecotypes won’t be suitable in the future. Sourcing from further south is an idea to mitigate the effects of climate change. Some successes have been reported. However, as with ecological restoration in general, the outcome will never be as rich and diverse as what was present before it was destroyed.

      • I’ve been using a ratio of local ecotype to NE KS with some central KS seed and some western ozark seed from Missouri on a couple of restorations. It’ll be interesting to watch these units over the coming decades.

      • The decline of switchgrass Dave observed is not so much the result of using a non-adapted variety or ecotype as it is from misunderstanding the role of the species. Switchgrass will decline in 10-15 years regardless of which type is planted. It is an early successional species, and never in dense monocultures. In Missouri prairies, switchgrass is commonly found in small colonies where it may persist pretty much as a monoculture because of the poor permeability of the soil. I don’t think any of us know for sure if those colonies move or remain pretty much the same for long periods. If you collect that seed and replant it on disturbed soil such as an old cropfield nearby, it will initially develop a near monoculture similar to a non-local ecotype or cultivar and will likewise decline in time. It’s the role of the species, not the fault of the genetics.

  6. Hi Chris. My name is Rudi Roeslein of Roeslein Alternative Energy
    You can look into my company on our web site and our vision to reconstruct and restore 30 million acres of prairie in 30 years. I find this last blog very timely since we are making decisions on thousands of acres in Northern Mo and southern Iowa this year. I will forward the the discussion I am having with people I have been collaborating with.
    Adam McClain sent me the information on what TNC is promoting and I wanted other opinion and will share them with you. Would love to set up a call to discuss.

    Sent from my iPhone

    • Restoring huge areas of marginal lands with native grasses and prairie plants, and using the sustainably harvested biomass to create renewable natural gas, sounds great.
      However, the worry is that using artificial fertilizers etc. is included to increase commercial production, and that will in fact ruin a natural prairie ecosystem.

  7. Hi there, I am always curious about the possible drawbacks of planting native plants in areas where those same species may grow wild. Obviously we can say that using local ecotype species is best, but is there enough to say that it is bad or dangerous to use nursery grown material?

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