 Our next speaker is Esben Karb. Esben is a PhD student at North Dakota State University. He's co-advised by myself and Tori Hovick. He's a planning colleges with interests in invasive species ecology, statistical ecology and rangeland management. Currently, his research focuses on plant community responses to different management strategies of Kentucky bluegrass invasion in the Northern Plains. Esben's title today is benefits from management are lost after several years in Kentucky bluegrass invaded rangelands. So my name's Esben Karb and before I get started today, I'm gonna give you guys a heads up. My voice puts people to sleep. So if you haven't had your morning copy, go get it. I won't be offended. Otherwise, let's jump into it. So today I'm gonna be talking about how benefits from management in Kentucky bluegrass invaded rangelands are lost after a couple of years. So as you guys might be aware, I probably don't need to tell you this, that rangelands were historically very heterogeneous places, meaning they had a lot of variation in not only the species that inhabited them, but also the structure created by those species. So you had lots of different variation in the height of plant species. However, following European colonization of the area, invasive plants have begun to degrade and homogenize our rangeland, decreasing that structural heterogeneity and basically decreasing native diversity. Now, so here's an example up top where you have Kentucky bluegrass invading an area, creating a very homogenous landscape that's mostly Kentucky bluegrass. And you can see the same thing down below. This is just much more invaded than the one above. Now in the Northern Great Plains, we've got a couple of invasive grasses. It's kind of why we're here this week, such as smooth brome and Kentucky bluegrass, which is the focus of my talk today. And I don't need to tell you this, but Kentucky bluegrass takes fairly diverse areas like you see up top and turns them into that homogenous low diversity mess that you saw before. Now, again, I probably don't need to tell you this, but Kentucky bluegrass is a perennial, cool season invasive grass that decreases native diversity through competition, the accumulation of dense litter layers, and then the resulting process of that litter accumulation, thatch formation. And so thatch is what happens when you have years of dense litter accumulation and that dense litter begins to pile on top of itself, compress and decompose creating a layer that looks something like this between those two dashed lines. Some people will call this duff, others will call it sod. Either way, this thatch layer is a problem because it has unique biological and chemical properties that can suppress native species and enhance Kentucky bluegrass. Now, if you zoom in on like the Kentucky bluegrass profile, you really begin to see how it feels like every single part of this plant is designed to suppress our native species. So let me orient you to this soil profile of Kentucky bluegrass in it. Above ground, you have live plant material and litter. Then you've got your thatch layer, your root mat, and then mineral soil below that. Now, again, it seems like every part of this is designed to suppress native species. You have the live plant material which can outcompete native species. It's great at taking up resources, but it also shades out native species that are trying to grow above ground. The thatch layer, which seems to be the main driver of Kentucky bluegrass invasion, can alter nutrient cycling. So if you guys recall John Hendrickson's talk either yesterday or the day before, this is not necessarily because the thatch layer has a different carbon and nitrogen levels than what was historically present, but you just get so much of it, so much more than you used to, that it ends up altering the amount of soil or the amount of nitrogen and carbon in the soil. Again, going off of what John said earlier, Kentucky bluegrass alters water infiltration and water cycling. So when it's wet, Kentucky bluegrass and it's thatch are a sponge for water, but when it's dry, it repels water and increases runoff. Then additionally, there's some evidence that suggests that Kentucky bluegrass thatch might also decrease seed germination rates. So for example, say seeds are coming into an area via seed rain, those seeds generally need to come into contact with mineral soil to germinate properly. And if they're coming into contact with thatch first, they might never reach that mineral soil. Alternatively, if you have seeds in the seed bank, this thatch layer will kind of alter the soil surface microclimate and make it so those seeds in the seed bank never reach the appropriate germination conditions and they won't germinate either fully or properly. Additionally, the thatch and the roots have been shown to alter soil microbial communities from native soil microbial communities into communities that are favorable for Kentucky bluegrass and only Kentucky bluegrass. There's more. Just like you see above ground with the above ground portion shading out and crowding out native plants, the root and thatch layer of Kentucky bluegrass can crowd out and choke out the roots of native plants. Now, currently a lot of management of Kentucky bluegrass is focused on this above ground portion, which is totally understandable. It's the most accessible and it's the thing we have the most control over. This is typically done through some combination of fire grazing and herbicide application. And quite truthfully, we've seen a fair bit of success with combining fire grazing and herbicide application and controlling Kentucky bluegrass. But that kind of got us wondering or rather I should say, a lot of advice is that you have to keep hammering Kentucky bluegrass over and over again. But that got us wondering, how long do impacts from management last? So how long do reductions in Kentucky bluegrass last following management and do increases in native species abundance persist following management? So I'm gonna be presenting work from the Central Grasslands Research Extension Center near street or North Dakota. This is a typical northern mixed grass prairie, meaning that it has a healthy abundance of warm and cool season grasses, forbs, legumes, and because it's a typical northern mixed grass prairie, it is very heavily invaded by Kentucky bluegrass. With Kentucky bluegrass in some pastures being between 30 and 40% of the plant community and in others being between 60 and 80% of the plant community. Now I'm gonna be talking about data from eight pastures for which are managed with patch burn grazing where we take our 160 acre pastures and divide them up into 40 acre patches. And then each spring we will burn one patch in that pasture. And then cattle will preferentially graze that recently burned area because that recently burned area is gonna be full of easily accessible, nutritious regrow. Then in subsequent years, we change the patch that's burned. So if we burn that top left patch in the first year, the second year will burn, say the bottom right patch and the cattle will follow the burn because they want that easily accessible, nutritious growth. And then changing this burn patch year after year creates a shifting mosaic of vegetation structure that can not only enhance plant diversity but benefit cattle production and enhance wildlife diversity. Now, as some of you might be aware and painfully so, in the Northern Great Plains, you kind of have a cultural aversion to fire. Also it's just flat out hard to get fire on the ground year after year after year. And so Kevin, Dr. Sedevic came up with kind of a solution or an alternative to that in the form of a heterogeneity-based rotational grazing system, which is a specifically if you're really into cattle grazing, it is a modified twice over rest rotation grazing system. And what that means is that we take our 160 acre pastures and then divide them up using interior fencing, which is different from patch burn grazing because they don't have interior fences. But in this, we divide the pasture into four paddocks using interior fencing. We'll have one paddock that's a rested paddock and will not be grazed within a year. One paddock will be grazed what we call heavily or heavy use achieving between or achieving greater than 60% degree of disappearance, a fully used paddock that achieves between 40 and 60% degree of disappearance and a moderate use paddock that achieves between 20 and 40% degree of disappearance. Cattle turnout in May, cattle will start in this heavy use paddock. They'll spend, I think it's about six weeks there on the first rotation before they're moved into the full use paddock where they'll spend about four weeks and then they'll be moved into this moderate use paddock where they'll spend two weeks. And by this time it's the first week of August. And so at this rotation date, cattle will then be moved back into the heavy use cell and go through the rotation once more. Now, this is all fine and dandy. It creates heterogeneous vegetation structure, but we also want this vegetation structure to shift just like it does in patch burn grazing. So each year we have to change the utilization of each paddock. So heavy paddocks will become rested. Full use paddocks will become heavy. Moderate use paddocks will become full and rested paddocks will become moderate. That way we can achieve that same shifting dynamic. Patch burn pastures were established in 2017 and our heterogeneity-based rotational pastures were established in 2018. All pastures are stocked with roughly equal stocking rate and to achieve about a 30 to 40% degree of disappearance pasture-wide. Now, I should be explicit here and say that these pastures weren't created with the intention of controlling Kentucky bluegrass, rather they were implemented to increase biodeversity and then any effects of controlling Kentucky bluegrass is just icing on the cake. See within each pasture we have eight 60 meter transects where we sample at every other meter for 31 sample points per transect. Within a sample point, we'll collect plant community composition. So we'll identify every plant species in a one meter square frame and take Davenmeyer cover classes. We'll measure litter abundance, litter depth, thatch depth, which is the distance between those two dashed lines. We'll also take measures of grazing intensity and record the time since fire for each transect. And today I'm mostly just gonna be talking about this plant community composition, but later on after this talk is over, you guys wanna talk about the litter responses or anything else I'd be happy to. Now jumping into the results, let me orient you to this graph. On the X axis, we have time since fire zero to four with zero representing the year of a burn and four representing four years post burn. On the Y axis, you have abundance. In this case, it's relative abundance of Kentucky bluegrass. And then you'll see a bunch of dashed lines on here. This represents pre-treatment levels of Kentucky bluegrass. And I should also say that this data is averaged out from the pasture inception to through 2022. And that's because these trends are all the same year after year. It's just the magnitude of the difference changes and where like the relative abundance of Kentucky bluegrass changes year to year. But what we end up seeing is that immediately following a burn, Kentucky bluegrass decreases on average about 5%. But after you get away from that burn, if you don't burn again, Kentucky bluegrass increases quickly and often exceeds pre-treatment levels. When you look at our native functional groups, you see kind of the opposite trends. So in this three panel figure, on the X axis, you have once again have time since fire, zero to four years. On the Y axis, you have abundance. In that left panel, it's abundance of native forbs, abundance of native legumes in the middle and native grasses on the right. And so for all of our native functional groups, specifically forbs and legumes, they increase in abundance following fire, but quickly decrease in subsequent years. And I realize I have forgot to mention that the error bars that you see here represent 95% confidence intervals. That's what they represented on the last graph and will represent it going forward. So if the error bars overlap this dashed line, that means there's no difference between that time point and the pre-treatment levels. If the error bars are entirely above the dashed line, that indicates that there's significantly more abundance of that at that time point. Or if it's entirely below, significantly less at that time point. And so moving into the heterogeneity-based rotational pastures, once again in this graph, you'll have, or not once again, but you'll have grazing intensity in the previous year. So if you grazed heavy, grazing area heavy last year, what's Kentucky bluegrass gonna be like this year? On the Y axis, you once again have Kentucky bluegrass abundance. And that dashed line again is pre-treatment levels of Kentucky bluegrass and the error bars are 95% confidence intervals once again. So Kentucky bluegrass decreases following heavier full grazing in this heterogeneity-based rotational system. But if you graze at a moderate intensity, so between 20 and 40% degree of disappearance, or if you rest a pasture, the following year you're gonna have, or paddocks rather, you're gonna have more Kentucky bluegrass. When you look at our native functional groups, you actually see a much different trend than what you saw before. So once again, on the X axis is that previous grazing intensity. Y axis is the abundance of native forbs, legumes, and grasses. And you'll see these dashed lines represent once again the pre-treatment levels. And so we actually don't ever see on average our native functional groups reaching those pre-treatment levels. This likely is because there's some other plant that's increasing in abundance and swamping out our native plants. It's probably Western Snowberry, truthfully told. But what I really want you to notice is that native plants seem relatively indifferent to grazing pressures in the previous year. And this is likely because these are native plants, meaning that they evolved over hundreds of thousands of years to be robust against different grazing intensities. So it makes sense that they don't vary a whole bunch if they experienced different grazing intensities. The exception being native legumes would see a little bit of variation. So putting it all together, intense disturbances can briefly decrease Kentucky bluegrass abundance, but it quickly recovers after your fire or heavy or full grazing. And so that's kind of seems to be the story for effects of Kentucky bluegrass on the above ground portion. I know like David Toledo and John Hendrickson at the USDA ARS station in Mandan have seen the same thing with their drought experiment where continual drought decreased Kentucky bluegrass abundance. But as soon as they stopped those drought exposures or those rain out shelters, Kentucky bluegrass bounced back really quickly. So, I mean, that's all well and good. That just means that we have to keep hammering Kentucky bluegrass. But what if we kind of shifted our management focus down in the soil profile and targeted that litter and that thatch that really seems to be doing a whole lot to promote Kentucky bluegrass? What happens then? Well, you might be wondering how do you even do that? And I can tell you, there's probably a lot of ways you can do that. Our solution was a giant brush. And so we took a giant brush and use this to remove litter and thatch creating openings in the plant community. And so we did this and set up nine 20 by 10 meter plots within that heterogeneity based rotational grazing system where we would remove litter and thatch from half of the plots, creating a 10 by 10 meter area where nothing happened in a 10 by 10 area where that had no litter and thatch or less litter and thatch. And we did it within the heterogeneity based rotational system particularly because that way we could make sure to place them in paddocks in the different pastures that would receive roughly the same grazing intensity within a year. So within a year, all nine of these split plots would receive say moderate grazing. Then the next year they would all receive full grazing and heavy grazing the year after. Within each of these halves, we set up a five by five meter grid made up of 25 one meter squared cells. Within those cells, we then sampled the plant community composition starting in July of 2020 and have continued through July of 2022 and will continue into the future. And so what do we see when we did this? Well, first off, I can tell you if you really want to brush your range land and get rid of litter and thatch, you can do just that. So on the X axis here, you've got time since that brushing or that removal event in months, 12 and 24 on the X axis on the left panel, you have litter depth and centimeters and thatch depth and centimeters on the right panel. These lines and then color coded to correspond with removal or control, green being removal or brush plots and tan being control plots. And basically Kentucky bluegrass litter and thatch can be reduced using a rotary brush if you really want to. But what this ended up doing to Kentucky bluegrass is this. So again, on the X axis, you have the time since that removal event on the Y axis Kentucky bluegrass relative abundance. And what we ended up seeing is that Kentucky bluegrass abundance remained decreased 24 months after litter and thatch removal. There is, as you can see, kind of a convergence in 2021 or that 12 month time period. I can tell you this is July of 2021, which is I'm sure most of you are aware as one of the worst droughts North Dakota has ever occurred. And because this is relative abundance, what likely happened is that Kentucky bluegrass started growing in both plots in the early season, kept growing the drought hit and then none of those native warm season plants that would grow up in the control plots started growing. They couldn't grow because of the drought basically. And so Kentucky bluegrass relative abundance stayed high just because there was nothing else that could grow to drown it out. When you look at our native functional groups, you see a very happy trend in the opposite direction. So again, on the X axis, you have time since that removal event on the Y you have abundance of native Forbes, native Graminoids or grasses and native legumes. And so all native plant functional groups increased in abundance following reductions in litter and thatch, specifically native Forbes and legumes were increased for at least 12 months and then have since converged at this 24 month time period. That might just be due to slight variation or it might be true convergence when we're losing those effects, only time will tell. However, the native grasses are still very, and very clearly and presently increase in abundance over the control plots. And so what does that all mean? Well, targeted removal of Kentucky bluegrass, litter and thatch can then reduce Kentucky bluegrass abundance for at least 24 months following removal events. That removal of thatch and litter promotes native plants for at least 24 months, specifically native grasses following that removal. However, I have to be very, very clear here. I am not advocating you go out and brush your range land. It's very impractical, expensive and time consuming. Instead, what you should probably be doing is looking for management that can reduce that litter and thatch layer over time. This is likely some combination of fire and grazing. And there's room for discussion on about like, you might have to continually apply fire and grazing for a number of years, and then you finally hit a threshold and you can have some breathing room once again, provided that you're persistent for several years. Putting it all together, so where do we go from here? Well, benefits from management of Kentucky bluegrass seem to be lost over time. However, management that targets the mechanisms that promote Kentucky bluegrass invasion, so management that targets litter and thatch accumulation seem to be more effective in controlling Kentucky bluegrass longterm than kind of broad sweeping management, like just fire and grazing or increasing grazing intensity alone. Moving forward, a deeper understanding of the mechanisms that underlie Kentucky bluegrass invasion are needed to develop more efficient management that can decrease Kentucky bluegrass longterm, increase native species and give us, as practitioners and land managers, kind of some breathing room. So we don't have to hammer the damn thing year after year after year. Specifically what I'm advocating for is that we try and understand how all of these parts of Kentucky bluegrass impact both the ecosystem and ecosystem functions and find out what is most important to Kentucky bluegrass invasion and how we can target it to more effectively control Kentucky bluegrass. I'd like to thank my advisors, my co-authors, C-GREC for hosting it, my funding from the USDA. And with that, I'll take any questions.