Biotic and abiotic controls on the germination of three common forest invaders

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1 Biotic and abiotic controls on the germination of three common forest invaders Alex Roth Department of Forest Resources University of Minnesota FR 8107 Fall 2012 Crowling Arboretum Crowling Arboretum

2 Introduction to Invasive Species Buckthorn Germination Experiment Methods Results Conclusions Management applications Removal Experiment

3 Invasive Species An exotic species is one that is introduced into a location where they do not occur naturally (MDNR) Many exotic species can have beneficial effects on their new environments; not all are harmful. When the exotic species begins to spread and cause ecological or economic problems, they re often called invasive.

4 oregonstate.edu

5 Rhamnus spp. (Buckthorn) Common Buckthorn (R. cathartica) -Leaves dull green, ovate, toothed - Berries Black -Leaves usually sub-opposite Glossy Buckthorn (R. frangula) -Leaves glossy, ovate, entire -Berries usually red -Alternate leaf arrangement plants.usda.gov

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7 Distribution of Buckthorn in the US and Canada plants.usda.gov

8 Does Disturbance Breed Disturbance? Buckthorn has characteristics of early successional species, or species that colonize disturbed areas. These species persist in high disturbance low stress areas Fast growth, high seed production, modest nutritional requirements. May eventually lose out to competition, but certain invasive species persist. Buckthorn and other invasive plants are able to take advantage of increased bare soil and changes in light availability within forest systems (Knight et al. 2007; Luken et al. 1997).

9 Why are they so good at taking over? Because they allocate most of their carbon and nutrients to growth, they are able to quickly limit the amount of light that understory plants receive (McKinney and Goodell 2010). No natural enemies Ability to tolerate sun and shade High seed production High photosynthetic capacity (Knight et al. 2007) Facilitative interactions with earthworms (Heimpel et al. 2010) Distinctive phenology allows them to take advantage of growing conditions before other plants.

10 Buckthorn produces emodin, a toxin that can inhibit the growth of neighboring plants, thus further inhibiting the growth and regeneration of native species (Knight et al. 2007). Emodin prevents fruit and leaf consumption Fruit exudates reduce germination of alfalfa to <1%, leaf exudates to 58% (Steltzner and Eddy 2003). sulis.umn.edu

11 Sketches by Julie Martinez Heimpel et al. 2010

12 So light and litter are important Germination may be an important control point in the establishment of buckthorn and other species. People have looked at factors in isolation, but we need to combine biotic and abiotic factors to get a more real-world experiment. Based on ecological theory, we expected to see higher germination in high light, low litter conditions. As worms are posited to facilitate buckthorn (Heimpel et al. 2010), we expect higher germination in the presence of worms.

13 Introduction to Invasive Species Buckthorn Germination Experiment Methods Results Conclusions Management applications Removal Experiment Preliminary results Conclusions

14 Worms present Low light Med light High Litter Litter absent High Litter Litter absent Medium Litter Medium Litter Six Native Plant Species (3 Functional Groups) Worms absent High light Low light Med light High Litter Litter absent High Litter Litter absent High Litter Litter absent Medium Litter Medium Litter Medium Litter =18 High light High Litter Litter absent Medium Litter

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20 Litter

21 0g, 2.5g, 5g

22 Light

23 Full light, 15% and 3%

24 Worms

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27 Hypothesis #1: All invaders will experience higher germination and have increased biomass in the presence of earthworms. Heneghan et al. 2002; Heneghan et al. 2007; Heimpel et al Nrii.umn.edu

28 Hypothesis #2: Forest invaders will experience higher germination and have increased biomass with increasing light availability and decreasing litter depth. Knight et al. 2007; Luken et al. 1997

29 Introduction to Invasive Species Buckthorn Germination Experiment Methods Results Conclusions Management applications Removal Experiment Preliminary results Conclusions

30 Results

31 Buckthorn Aboveground Hypothesis #1: Biomass (g) Forest invaders will experience higher germination and increased biomass in the presence of earthworms Absent F= , df 1, P=006* Earthworms Present

32 Buckthorn biomass decreases with increasing light 0.1 Litter Level (g) Buckthorn Aboveground Biomass (g) Hypothesis #2: Forest invaders will experience higher germination rates and increased biomass with increasing light availability and decreasing litter depth. Absent Earthworms Buckthorn saw the lowest biomass in high light due to seed Low desiccation. Medium High Light Level

33 In the presence of worms, buckthorn biomass increases with increasing light 0.1 Litter Level (g) 0 Buckthorn Aboveground Biomass (g) Low Medium High Light Level Earthworms Present With worms, buckthorn saw the highest biomass in high light due to earthworm action.

34 Buckthorn biomass decreases in the high litter treatment 0.1 Light Level Low Medium High Buckthorn Aboveground Biomass (g) Absent Earthworms Buckthorn saw the lowest biomass in high litter due to separation from the soil and shading Litter Level (g)

35 In the presence of worms, buckthorn biomass increases with increasing litter 0.1 Light Level Low Buckthorn Aboveground Biomass (g) Medium 0.1 High With worms, buckthorn saw the highest biomass in high 0 litter due to 2.5 earthworm action. 5 Litter Level (g) Present Earthworms

36 Buckthorn Aboveground Biomass Model R 2 = 0.40 P<001

37 Interaction between light and earthworms Seeds mixed into soil Low High Buckthorn Aboveground Biomass (g) LS Means Too dry; seeds desiccate Absent Earthworms Present

38 Interaction between litter and earthworms Buckthorn Aboveground Biomass (g) LS Means Seeds don t reach soil or are shaded Absent Present Seeds reach soil, litter is eaten away 0 5 Earthworms

39 biomass (g) Invasive species biomass (g) Monoculture Two species Six species Native (g) Native species biomass (g) Worms absent (open symbols), MANOVA: F = 4.52, df 2, 66, p=145 Worms present (filled symbols), MANOVA: F = 5.26, df 2, 66, p = 08 Difference between worm treatments, MANOVA: F = 35.78, df 2, 135, p<001

40 Conclusions Forest management that leaves an intact litter layer helps prevent invasive germination High light may cause desiccation of seeds Worms are the key! They reverse the normal ecological trends and increase overall invasive germination With earthworms, deep litter led to higher germination With earthworms, seeds were able to germinate even in high light Diverse communities resisted invasive germination and growth

41 Introduction to Invasive Species Buckthorn Germination Experiment Methods Results (Focus on buckthorn) Conclusions Management applications Removal Experiment

42 3 Common Buckthorn Treatments Weed Wrenching/Mechanical Removal Cut and Paint Basal Bark Application Weed wrenching creates a disturbed soil environment The cut and paint technique creates a high-light environment Basal bark application creates a moderate light environment

43 Removal Experiment Plots where buckhorn has been removed using these methods. Pre- and post-removal surveys of vegetation and abiotic characteristics How does each treatment affect these abiotic characteristics, native species regeneration, and re-invasion? 6m 6m

44 Acknowledgements UMN Forest Ecology Lab Group: Sascha Lodge, Dr. Peter Reich, Dr. Lee Frelich, Dr. Tim Whitfeld, Cindy, Buschena, Susan Barrott, Dr. Kevin Mueller, Dr. Nico Eisenhauer, Rachael Nicoll Lab student workers Volunteers Summer field assistants: Kayla Altendorf and Yasha Horstman Funding was provided by: LCCMR, NSF ISG-IGERT, Dayton Fund of the Bell Museum of Natural History, GAPSA Travel Grants

45 Literature Cited Heimpel, G.E., Frelich, L.E., Landis, D.A., Hopper, K.R., Hoelmer, K.A., Sezen, Z., Asplen, M.K., Wu, K. (2010) European buckthorn and Asian soybean aphid as components of an extensive invasional meltdown in North America. Biol Invasions 12 (9): Heneghan, L., Clay, C., Brundage, C. (2002) Rapid decomposition of Buckthorn litter may change soil nutrient levels. Ecol Restor 20: Heneghan, L., Steffen, J., Fagen, K. (2006) Interactions of an introduced shrub and introduced earthworms in an Illinois urban woodland: Impact on leaf litter decomposition. Pedobiologia 50: Knight, K.S., Kurylo, J.S., Endress, A.G., Stewart, J.R., Reich, P.B. (2007) Ecology and Ecosystem Impacts of Rhamnus cathartica: A review. Biol Invasions 9: McKinney, A.M., Goodell, K. (2010) Shading by invasive shrub reduces seed production and pollinator services in a native herb. Biol Invasions 12(8): Luken, J.O., Kuddes, L.M., Tholemeier, T.C. (1997) Comparative responses of Lonicera maackii (Amur honeysuckle) and Lindera benzoin (spicebush) to increased light. Am Mid Nat 138 (2): Pimentel, D, Zuniga, R, Morrison, D (2005) Update on the environmental and economic costs associated with alien-invasive species in the United States. Ecol Econ 52:

46 Questions?