GEORGIA DOT RESEARCH PROJECT 13-22 FINAL REPORT

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GEORGIA DOT RESEARCH PROJECT 13-22FINAL REPORTTESTING THE SUCCESS RATE OFESTABLISHING MULTITROPHIC VEGETATIONFOR STREAM BUFFER MITIGATION ACCORDINGTO GEORGIA DOT SPECIFICATIONS ONDIFFERENT SLOPE RATIOSOFFICE OF RESEARCH15 KENNEDY DRIVEFOREST PARK, GA 30297-2534

1.Report No.:FHWA-GA-17-13222. Government Accession No.:3. Recipient's Catalog No.:4. Title: Testing the Success Rate ofEstablishing Multitrophic Vegetation forStream Buffer Mitigation According toGeorgia DOT Specifications on DifferentSlope Ratios7. Author(s): Patrick McCullough, DonnShilling5. Report Date:February 20176. Performing Organization Code:9. Performing Organization Name and Address:University of Georgia1109 Experiment StreetGriffin, GA 3022310. Work Unit No.:12. Sponsoring Agency Name and Address:Georgia Department of TransportationOffice of Research15 Kennedy DriveForest Park, GA 30297-253413. Type of Report and Period Covered:Final; September 2013 – February 20178. Performing Organ. Report No.:13-2211. Contract or Grant No.:PI# 001280314. Sponsoring Agency Code:15. Supplementary Notes:Prepared in cooperation with the U.S. Department of Transportation, Federal HighwayAdministration.16. Abstract: Multitrophic vegetative mitigation is required for stream buffers, wetlands, andretention basins within state waters. Downslopes adjacent to linear road construction aretypically steep, which creates challenges for establishment and erosion control in disturbed areasrequiring vegetation. A field experiment was conducted to test the establishment rate,persistence, and erosion control provided by multitrophic vegetative buffer mitigation plantings.Over the three-year period, native seed mixture was able to establish and persist at all slope ratiostested including 2:1, 2.5:1, 3:1, and 4:1. The increase in slope ratios did not reduce theestablishment of plantings. Topdressing with local soil improved plant establishment by about5% on several dates in the first year, but there was no residual benefit to plant cover or erosioncontrol in the second and third year. The hierarchical rank of erosion levels from high to lowamong slopes evaluated were 2.5:1 2:1 3:1 4:1. The native species that establishedexhibited vegetative growth during the summer and fall, but declined in cover throughout thewinter and spring months. Although the native species were able to establish regardless of slope,agronomists will need to implement management programs to minimize the invasion of weedspecies such as Italian ryegrass and Johnsongrass for long-term culture. Further research isneeded to evaluate the effects of mowing programs, erosion mats, and seeding rates on thecompetition of species established for multitrophic vegetation.17. Key Words: mitigation, slopes, nativespecies, erosion19. Security Classification 20. Security(of this report):Classification (ofthis page):UnclassifiedUnclassified18. Distribution Statement:21. Number ofPages:32ii22. Price:

GDOT Research Project 13-22Testing the Success Rate of Establishing Multitrophic Vegetation for Stream BufferMitigation According to Georgia DOT Specifications on Different Slope RatiosFinal ReportByDr. Patrick McCulloughAssociate ProfessorContract withGeorgia Department of TransportationIn cooperation withU.S. Department of TransportationFederal Highway AdministrationFebruary 2017The contents of this report reflect the views of the author(s) who is (are) responsible forthe facts and the accuracy of the data presented herein. The contents do not necessarilyreflect the official views or policies of the Georgia Department of Transportation or theFederal Highway Administration.This report does not constitute a standard,specification, or regulation.iii

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TABLE OF CONTENTSPageLIST OF TABLES . viLIST OF FIGURES . viLIST OF PICTURES . viiEXECUTIVE SUMMARY . viiiACKNOWLEDGEMENTS . ixINTRODUCTION . 1OBJECTIVE . 3PROCEDURES. 3FINDINGS . 7CONCLUSIONS AND RECOMMENDATIONS . 19REFERENCES . 20v

LIST OF TABLESTablePage1.Standard errors of the means presented in figures . 18LIST OF FIGURESFigure1.PageGround cover of the multitrophic mixture planted on fourslopes in a field experiment, 2014-2017, Griffin, GA 132.Erosion levels following the plantings of multitrophic plant mixtureson four slopes in a field experiment, 2014-2017,Griffin, GA . 17vi

LIST OF PICTURESPicturePage1.The construction of the plots on March 13, 2015 in Griffin, GA . .52.A replication in the experiment consisting of the four slope ratiosevaluated . . 53.The plot area before plant establishment on March 15, 2014. . .64.Seedlings of native species that established in May 2014 . . 125.Native vegetation growth on May 26, 2015 on a plot sloped at 2.5:1 . 146.Native vegetation growth on May 26, 2015 on a plot sloped at 4:1 . .157.Erosion on May 20, 2014 after establishment on the 4:1 slope ration .16vii

EXECUTIVE SUMMARYMultitrophic vegetative mitigation is required for stream buffers, wetlands, and retentionbasins within state waters. Downslopes adjacent to linear road construction are typicallysteep, which creates challenges for establishment and erosion control in disturbed areasrequiring vegetation. A field experiment was conducted to test the establishment rate,persistence, and erosion control provided by multitrophic vegetative buffer mitigationplantings. Over the three-year period, native seed mixture was able to establish andpersist at all slope ratios tested including 2:1, 2.5:1, 3:1, and 4:1. The increase in sloperatios did not reduce the establishment of plantings.Topdressing with local soilimproved plant establishment by about 5% on several dates in the first year, but there wasno residual benefit to plant cover or erosion control in the second and third year. Thehierarchical rank of erosion levels from high to low among slopes evaluated were 2.5:1 2:1 3:1 4:1. The native species that established exhibited vegetative growth duringthe summer and fall, but declined in cover throughout the winter and spring months.Although the native species were able to establish regardless of slope, agronomists willneed to implement management programs to minimize the invasion of weed species suchas Italian ryegrass and Johnsongrass for long-term culture. Further research is needed toevaluate the effects of mowing programs, erosion mats, and seeding rates on thecompetition of species established for multitrophic vegetation.viii

ACKNOWLEDGEMENTSSpecial thanks Seth Williams, Jialin Yu, Bill Nutt, and Henry Jordan for technicalsupport with this research. We would also like to thank Davie Biagi from the GeorgiaDOT for the opportunity to work on this project and for all of her assistance with helpingplan and conduct this research.ix

INTRODUCTIONThe Georgia Department of Transportation (GDOT) is responsible for mitigatingdisturbances where road construction impacts buffers of state waters. These areas aretypically beyond the 50-foot exemption for a drainage structure variance. The GeorgiaEnvironmental Protection Division typically requires establishment of a multitrophicvegetative planting, which includes large canopy native trees, understory species, and anative riparian seeded ground cover mix. In areas within the clear zone, areas within thestructural boundaries of sediment basins, or areas within power line easements, only thenative riparian ground cover species are required. Multitrophic vegetative mitigation isrequired for stream buffers, wetlands, and retention basins. Downslopes adjacent tolinear road construction are typically quite steep, which creates challenges forestablishment and erosion control in disturbed areas requiring vegetation.Multitrophic native species have potential for succession growth and forimproving the aesthetics of stream buffer mitigation projects. In previous research, thepotential of 29 native grass and forb species to establish was investigated for seeded,native riparian ground cover mitigation projects for Georgia roadsides (Georgia DOT 700- Grassing specifications). These species, which include grasses and forbs, are adapted tosoils and climates of Georgia that may allow for long-term growth and competition withweeds. Several of these species, such as black-eyed Susan (Rudbeckia hirta) andlanceleaf coreopsis (Coreopsis lanceolata), established in fall and spring despitecompetition with annual weeds (Johnston et al. 2015).One of the challenges for successful multitrophic vegetation establishment is thedifferential slope gradient that affects soil stabilization after planting.1Removing

vegetation during roadside construction is a major contributor to soil degradation andsubsequent erosion (Castillo et al. 1996; Mohammad and Adam 2010; Hacisalihoglu2007). The establishment of native species on various slope gradients for erosion controlis a function of root system architecture and soil characteristics (Reubens et al. 2007; Fanand Lai 2014). Grasses and forbs that establish on sloped areas buffer the soil againstsediment losses for erosion control (Chuanwei et al. 2008; Zhilin et al. 2005). Collins etal. (2004) modeled the effects of erosion on landscape evolution.A model wasdeveloped that quantified vegetation-erosion dynamics that consisted of plant growth,plant death, and rigidity on plants to resist erosion. In some instances, plants with moresusceptibility to erosion may enhance topography steepening and reduced drainagedensity to make some erosion events more extreme. The susceptibility to erosion forspecies evaluated in riparian mixtures for the Georgia DOT could influence the sloperatio that is appropriate for construction in these areas.The rate of establishment for seeded multitrophic species can be an importantfactor for mitigating slope erosion on roadsides. Gray (1994) found that herbaceousvegetation that includes grasses and forbs were most effective for improving theresistance to erosion, whereas woody vegetation was more effective for the prevention ofshallow mass wasting.The rate of vegetation establishment on hillslopes will alsoinfluence the mass stability of the soil by root reinforcement. Kinnell (1999) foundsediment concentration flow due to erosion was linearly related to the intensity of rainfalland slope gradients. These effects on erosion are associated with the increased velocityof water flow as slope increases (Changxing 1996; Zhilin et al. 2005; Woo and DiCenzo1997).2

Native vegetation enhances soil water storage, growth, and infiltration to reduceerosion (Ludwig et al. 2005). Runoff also increases on disturbed hillslopes withoutvegetation compared to slopes that were not disturbed. The erosion intensity oftendepends on the intensity of rainstorms and type of topography, soils, and vegetationpresent (Duley and Hays 1932). Most work in riparian seed establishment research hasbeen conducted on level ground, but undulations or variability in slopes could affect seedestablishment and subsequent soil stabilization.Road designers have traditionallydefaulted to the maximum 2:1 slopes with erosion control blankets and other structuralbest management practices. However, these areas often have poor plant establishmentand unacceptable levels of erosion.Further research is warranted to evaluate theestablishment rate of multitrophic plantings on different slope ratios to improve theGeorgia DOT Special Provision 700-Grassing and Georgia DOT 702-Vine, Shrub, andTree Planting specifications for disturbed areas.OBJECTIVEThe objective of the proposed research is to develop new slope recommendationsfor establishing multitrophic vegetative buffer mitigation plantings at four slopes of clayloam soils during the required dormant planting season.PROCEDURESThe experiment was conducted at the Research and Education Gardens at theUniversity of Georgia Griffin Campus. The soil was a clay loam (42% sand, 20% silt,38% clay) with a 5.4 pH and 2.6% organic matter. The plots were constructed from3

March 13 to 15 in 2014. A backhoe was used to remove existing grasses and soil (Picture1). The soil was then prepared using a leveler to determine the appropriate slope and thesoil was rolled to firm the surface. The plots were graded to one of four slope ratiosincluding 2:1, 2.5:1, 3:1, and 4:1 (Pictures 1 and 2).Plots were then seeded on March 24, 2014 according to GDOT 700 and 702specifications. Each plot was established in bare root seedlings of red maple (Acerrubrum L.) and elderberry (Sambucus nigra L.) spaces 8 feet on center, underplantedwith a native riparian seed mix of Canadian rye (Elymus canadensis L.), purpletop(Tridens flavus (L.) Hitchc.), switchgrass (Panicum virgatum L.), black