Effects of Three Common Buckthorn Removal Techniques on ......Effects of Three Common Buckthorn...
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ALEX ROTH, SASCHA LODGE, LEE FRELICH AND PETER REICH DEPARTMENT OF FOREST RESOURCES UNIVERSITY OF MINNESOTA NCWSS 2013 Effects of Three Common Buckthorn Removal Techniques on the Regeneration of Understory Vegetation
Transcript of Effects of Three Common Buckthorn Removal Techniques on ......Effects of Three Common Buckthorn...
A L E X R O T H , S A S C H A L O D G E ,
L E E F R E L I C H A N D P E T E R R E I C H
D E P A R T M E N T O F F O R E S T R E S O U R C E S
U N I V E R S I T Y O F M I N N E S O T A
N C W S S 2 0 1 3
Effects of Three Common Buckthorn Removal Techniques on the Regeneration
of Understory Vegetation
Presenter
Presentation Notes
Thank you very much for the introduction. Today, I’ll be discussing some results from a field experiment investigating the effects of different buckthorn removal methods on understory plant regeneration.
Introduction to invasive species Buckthorn
Rationale
Removal Experiment Methods
Results
Conclusions and management implications Application
Considerations
Outline
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I’ll begin by giving a brief introduction to my focal organism, provide some background rationale for the work, move on to present my methods and results for the removal experiment, and wrap up with conclusions and management implications.
Common buckthorn
Rhamnus cathartica L.
From hedgerows to forests and beyond…
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Let’s start with BT. I’m sure everyone here has at least heard of it, but common buckthorn is a tall understory shrub native to Europe and Asia that arrived in the US in the late 1700s as an hedgerow/ornamental and medicinal plant. It can form dense thickets that impede wildlife, changes nutrient cycling through increased decomp, and has negative effects on flowering, growth and survival of flora and neg effects on fauna, as well as serious economic effects through its role as a host for the soybean aphid, and other agricultural pests.
plants.usda.gov
Distribution of Buckthorn in the US and Canada
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USDA map of bthorn. It has spread from its introduction points on the east coast all the way to the west coast and into Canada. It’s pretty ubiquitous throughout North America.
Can we go back?
How do we restore these areas?
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So buckthorn has come to dominate many forest understories, and it’s partly responsible for taking forests from conditions like the one on the left, with high diversity and an in-tact understory, to conditions like the one on the right, with low light, low diversity, and few understory plants. But is it possible to reverse that trend and move back toward forests with diverse understories? Well, there are a lot of considerations here (deer, worms, etc) but let’s just start with the issue of buckthorn.
Removal
“Don’t underestimate the tenacity of buckthorn”
“If you can’t be guaranteed a follow-up, don’t even bother”
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In talking to various managers who’ve dealt with BT, there are a few common themes that they usually mention. First, don’t underestimate the tenacity of buckthorn. People have learned not to cut it down without applying herbicides as it will simply re-sprout. Also, I’ve heard people say “If you can’t be guaranteed a follow-up, don’t even bother. So clearly, the methods people are using aren’t optimal for controlling buckthorn. So the first thing that we need is that we need removal methods that work.
Removal
“Don’t bite off more than you can chew.”
“The seedbank will haunt you.”
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I’ve also heard that when managing BT you shouldn’t bite off more than you can chew. BT management is hard work and agencies often run out of funds to finish projects on large areas. And because of BT’s copious seed production, they mention that the seed bank will haunt you. Managers want to see native plants returning, but they often don’t. So the second thing we need is that we need methods that are easily implementable and encourage re-colonization by native plants, not just buckthorn.
Weed Wrenching Cut and Paint Basal Bark Application
A Scientific Approach to Removal
Light Litter
~
No Change
No Change
Presenter
Presentation Notes
So we can apply what we know about controls on the colonization and germination of plants to a removal experiment. And that means we have to think about invasive species management a little differently. Not only about the success of the strategy for removing BT, but how the strategy affects the conditions that affect germination and subsequent plant regeneration – things like light availability, litter depth and diversity. So I selected these three removal methods (WW,CP,BB) because they are common, easily implementable, and the results will be applicable for managers. But more importantly, because they may differentially affect those conditions that we know are important to colonizing plants. So WW will increase light but disturb the soil and create bare patches, cut and paint will increase available light, and by leaving standing biomass, BB will create a modified light environment. So the idea is that maybe by managing the abiotic conditions as much as the plant itself, we may be able to affect what comes back and how well BT regenerates versus the native plant species.
6m
6m
4 Sites 12 Plots per site 3 Survey points per plot 2011, 2012 (2), 2013 (2)
720 Survey Points
Removal Experiment
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To do this: removal experiment. We had 4 sites in and around the Twin Cities in Minnesota. At each site, we had 12 6x6m plots, and within each plot, there were three replicate 1m radius plots in which vegetation, light and other characteristics were surveyed. We surveyed these sites in late summer 2011 to get baseline conditions, removed buckthorn in the fall, and then surveyed the sites 4 more times, 2 in 2012 and 2 in 2013.
N = No Removal BB = Basal Bark CP = Cut and Paint WW = Weed Wrench
WW
WW
WW
N
N
N
BB
BB
BB
CP
CP
CP
=6m x 6m
6m
5m
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This is what a single site looks like. We randomly assigned treatments to plots across the site so that there were three replicates of each treatment (BB CP WW) and of the control (no removal) in each site.
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And this shows you what a typical site looked like before removing the buckthorn. All our sites were closed canopy, oak dominated, and buckthorn dominated sites, and you can see that the BT is pretty dense in the understory.
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And at the subplot level, there wasn’t much in the way of other vegetation (though it was there), and buckthorn really dominated almost every vegetation strata.
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And then we had lab workers and volunteers come out and apply these different BT removal techniques. Here’s one of my lab mates (Eli) using a weed wrench and physically pulling buckthorn out of the ground.
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We had others using the cut and paint technique using an herbicide called Garlon.
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And finally others using a basal bark herbicide application of Garlon 4.
Results
Buckthorn
Light
Herbaceous cover
Herbaceous Richness
Time
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Going to run through some quick results about how well the treatments got rid of BT, results about light and the regeneration of herbaceous plant species before wrapping up with some conclusions. For the sake of time, I’m going to mostly focus on one of the sites, but I’ll briefly show trends for all four.
99% Effective Removed over 1,200 buckthorn stems Regeneration from the seedbank
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Once we were finished, the plots are open, surrounded by a wall of buckthorn. There’s a ton more light reaching the ground. We found that each treatment was effective at removing buckthorn. For example in one plot we removed over 1200 stems and were 99 effective at doing so, with resprouts only occurring on a few plots and not limited to any particular treatment type. At all sites we saw cotyledons emerge from the seedbank in the years following removal, but that’s to be expected. Our other sites were 99, 95 and 87% effective.
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So there’s a pretty stark difference between the removal area and the surrounding wall of buckthorn, so you’d expect some differences between the two.
High Light
Low Light
Lig
ht
Ava
ilab
ilit
y
Removal
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So we found that at each of our sites, the 3 treatments (BB, WW, and CP) all saw significantly higher lights levels than the control plots. So if we removed BT in the fall of 2011, you can see that before removal the plots were not significantly different in their light availability, but in the spring following removal, there’s a big difference that holds for the next two years. Proof of concept that our treatments worked.
Spring 2013
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And you can imagine that those light differences and any litter disturbance by the WW would lead to differences in vegetation cover. And what we saw was that some of the plots looked like this a year and even two later, with little vegetation and some bare soil, and others….
Spring 2013
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Looked like this, with almost complete cover of vegetation. So which plots were which?
Removal
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So what did we see. Well for herbaceous species only, the control plots start with roughly 10% cover and really don’t change much throughout the experiment.
Removal
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But you can see that after BT removal, the WW plots increase from an average of 10 to 60% cover, sitting around 50% in the fall of 2013. This huge increase is due in part to the available light, but also likely to the WW treatment disturbing the soil and uncovering the seedbank. So we’re seeing that the treatment worked to encourage the re-vegetation of the plot.
Removal
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The BB plots lose cover after BT removal, but start to recover somewhat and surpass the control plots in 2013.
Diversity and Cover
Removal
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The same general pattern is true for the CP plots. But what’s neat to see is that the cover of both the CP and BB plots slowly starts to rebound. We seem to have gotten some residual kill of the native vegetation, which then took longer to rebound than in the WW plots where no herbicide was used.
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So here I’m just showing you that the patterns are similar for all four of our sites. We’re still seeing these initial increases in the WW plots, and temporary declines in the CP and BB plots that eventually start to recover. Each site behaves a little differently, but the main trends are still present.
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But is this mess of vegetation just made up of one or two species, or are we actually seeing a diversity of species come back?
Removal
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We see the same general trends in species richness. For herbaceous species, the control plots start with roughly 6 species and actually gain species throughout (potentially because of what’s going on in the other plots).
Removal
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But you can see that by the spring after removing buckthorn, the WW plots have about double the number of herbaceous species. This number increases and then levels off around and average of 16 in 2013.
Removal
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BB plots started with slightly higher species richness by chance, but lost over half their species, likely due to the suppressive effects of the herbicide. But slowly but surely they’ve continued to increase in richness, ending just about where the WW plots do, and at a higher level than the control plots.
Removal
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The same pattern is true for the CP plots, which actually start to recover soon and ultimately reach the highest species richness of any of the treatments. So not only are we bringing cover back, but we’re bringing back a diversity of species, up to 20 in some cases.
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So again, here’s the trends for all four of the sites, and again you see those initial increase for the WW plots, whereas the CP and BB plots have temporary declines in richness. Again, each site behaves a little differently but the main trends are still there.
Early Successionals
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Some plots dominated by species like Motherwort and Stickseed, which some people consider weedier species but are normal components of forest understories.
Later successional species
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But also plenty of later successional species like bedstraw, asters, sedges, nightshade, and ferns. So we’re actually seeing a lot of really good species coming back into the plots.
Conclusions and implications
We can apply the experimental evidence in the field Encourage diversity, light, and litter cover
Weed-wrench saw the most re-vegetation Uncovering the seedbank
Plots with herbicide saw less re-vegetation Herbicide may have suppressive effects
Presenter
Presentation Notes
So what can we take from this experiment? Well first we can make invasive plant management more scientific and use what we know about controls on germination and growth to get better results and ultimately encourage native plant diversity and cover, which as has been shown in previous studies, might help resist future buckthorn invasion. WW saw the most re-vegetation due to uncovering the seedbank. Herbicide may have suppressive effects, and while it’s recovering, it pays to be careful when applying.
Conclusions and implications
Vegetation is recovering A mix of early successionals and later successional plants
Will this suppress buckthorn? Paired with local propagule management
Time and money constraints? Small scale projects may work best
Picking the right method is site/situation dependent
Presenter
Presentation Notes
But the good news is that the vegetation is coming back in all plots. A future step will be to assess how well these differences will suppress buckthorn, but for management purposes, that will ultimately depend on management of the local seed source to prevent more buckthorn from reaching the site. And finally, the applicability of these results will depend on the scale of the project and on the specific site. So while WW might encourage re-vegetation the fastest, it may not be practical on a large scale, so applying this will be site and situation dependent.
Acknowledgements
UMN Forest Ecology Lab Group Tim Whitfeld, Cindy Buschena, Rachael Nicoll, Yasha
Horstman et al.
Summer field assistants
Volunteers
Lab Student Workers Funding was provided by: LCCMR, NSF ISG-IGERT,
Dayton Fund of the Bell Museum of Natural History
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With that I’d like to thank a few people: lab for ideas and encouragement, and everyone who helped me remove buckthorn, my sources of funding. And thanks to you all coming. I’ll take questions.
Questions?
