Final Report – Typha angustifolia and T. x glauca suppression at Mukwonago River Floodplain (TNC Lulu Lake Preserve) Walworth County, WI ∳Integrated Restorations, LLC Ecological Restoration & Land Management Services Integrating Ecological Theory and Research with Restoration Practices Final Report – Typha angustifolia and T. x glauca suppression at Mukwonago River Floodplain (TNC Lulu Lake Preserve) By Craig A. Annen Integrated Restorations, LLC June 2015 228 South Park Street Belleville, WI 53508 (608) 424-6997 (office) (608) 547-1713 (mobile) [email protected] Deliverable final report for contract number 60112-2012028 between The Nature Conservancy, Inc. and Integrated Restorations, LLC Final Report – Typha angustifolia suppression at Lulu Lake Preserve Page 2 Summary 1. A well-established population of Typha angustifolia was present in the Mukwonago River wetland and was found to be spreading at an accelerated rate. This expansion was of immediate management concern and an effective suppression method needed to be developed and empirically tested to protect the biological and ecological integrity of the wetland basin. 2. Both Typha angustifolia and T. x glauca were present in the Mukwonago River floodplain wetland. 3. T. angustifolia covered 4.83 acres of the wetland basin in 2010 (prior to management intervention), equal to 10.9% of the wetland area. T. x glauca occurred sporadically as individual culms throughout the wetland basin. 4. Cumulative species richness of the wetland basin (from 2012 through 2014) was S = 159, with a high proportion of conservative species. Cumulative Floristic Quality (FQI) was estimated at 67.2. 5. Three Wisconsin Special Concern species were detected during the three-year botanical survey: Solidago ohioensis (Ohio goldenrod), Triglochin maritima (bog arrow-grass), and Thelypteris simulata (bog fern). The wetland also supports a small population of Platanthera huronensis (Huron pale green orchid). 6. The Mukwonago River wetland basin has high beta (habitat) diversity, with floristic elements of shrub-carr, southern sedge meadow, bog, fen, wet prairie, aquatic, and riparian emergent wetland types present. 7. The Mukwonago River wetland basin has exceptional natural area quality, and is a high quality natural resource in the Mukwonago River watershed. 8. A single directed cut surface application of imazapyr to T. angustifolia and T. x glauca reduced stem density > 90% for three consecutive growing seasons compared to untreated controls. 9. Plant species density and diversity were similar between treated and non-treated areas, indicating that the suppression technique was methodically selective, even though a non- selective herbicide was used. 10. A variety of sensitive wildlife species were documented within the project area, indicating that the treatment protocol did not elicit any adverse effects to these organisms. 11. Imazapyr application to 1 in 4 cut Typha stems was effective in suppressing the majority of the stand via intra-clonal rhizome translocation, although limited follow up application will be required to suppress immature Typha plants that survived treatments because they were not connected to the rhizome network of the main clone at the time of treatment. 12. This selective approach was effective at reversing the T. angustifolia invasion in this wetland basin. 13. Although absent from control plots, Lythrum salicaria increased in abundance in treated plots following a two-year lag time. Biocontrol should be concurrent with Typha suppression management in the wetlands of the Mukwonago Watershed. Final Report – Typha angustifolia suppression at Lulu Lake Preserve Page 3 Site Description The 40.3-acre project area is bisected by the Mukwonago River, which flows in a west-east direction and empties into Lulu Lake (map 1). Aquatic and emergent wetland vegetation coenoclines occupy the channel and banks of the Mukwonago River, and the wetland also supports diverse assemblages of sedge meadow, fen, bog, and wet prairie herbaceous plant communities within the topographical depressions of the river’s floodplain (map 1). The wetland consists of 29.5 acres of remnant sedge meadow overlying a Marsh (Mf) soil series, with an additional 10.8 acres of the floodplain basin supporting a diverse wet prairie community atop Houghton muck (Ht) soil series (USDA NRCS 2012, Appendix 1). Both the Houghton muck and Marsh organic soils are derived from the decay of herbaceous organic plant material within the wetland and have similar profiles. Both soil types are very poorly drained, occur on slopes of 0 – 2%, have high water holding capacities, intersect the water table at the soil surface, and are prone to frequent ponding. The Houghton muck differs from the Marsh series in that the former is rarely flooded whereas the latter is frequently flooded. The wetland has a history of prescribed burning as a part of ongoing restoration and management within the Lulu Lake Nature Preserve. When this project was initiated, a population of Typha angustifolia had invaded the sedge meadow portion of this wetland and was rapidly expanding; this expansion was of immediate management concern and suppressive intervention was deemed necessary before this species could establish a monoculture to the exclusion of native wetland vegetation. Project Goals 1. Determine the extent of the Typha angustifolia infestation in the wetland basin. 2. Ascertain if the model derived by Boers and Zedler (2008) accurately predicted this species' rate of spread. 3. Determine if individuals of both narrow-leaved cattail (Typha angustifolia) and hybrid cattail (T. x glauca) were present in the wetland. 4. Develop a selective and effective Typha suppression technique for use in areas where Typha is commingled with desirable non-target native species. 5. Reduce the distribution and abundance of established Typha angustifolia and T. x glauca stands within the sedge meadow without causing excessive collateral damage to non-target sedge meadow species or disrupting the ecological integrity of the site. 6. Empirically determine if the suppression technique was effective at reducing Typha densities without causing excessive collateral damage to non-target sedge meadow species. 7. Conduct a detailed botanical inventory and Floristic Quality Assessment of the native vegetation communities present within the wetland. Final Report – Typha angustifolia suppression at Lulu Lake Preserve Page 4 Map 1: Vegetation communities of the Mukwonago River wetland basin. Extent of Typha angustifolia invasion In a 2010 baseline survey, we mapped the extent of Typha angustifolia invasion in the Mukwonago River wetland. Where it was abundant enough to be discernible on aerial photos, T. angustifolia covered 4.35 acres of the wetland basin. The majority of T. angustifolia clones were located to the south of the Mukwonago River (map 2). T. angustifolia was intermixed with a diverse assortment of native sedge meadow species within the wetland basin. Boers and Zedler (2008) used a time-series of aerial photographs from 1963 – 2000 to construct a predictive model for T. angustifolia’s rate of spread within the watershed. Boers and Zedler (2008) reported that T. angustifolia dominated 5.3% of the Mukwonago River wetland in 2000, and based upon an analysis of its rate of spread during the 37-year time period they predicted a finite rate of population increase of r = 0.14 per year. Although these authors did not include a linear regression equation of their population growth model in the article, we were able to interpolate an expected value for the extent of T. angustifolia in 2010, the year of our baseline survey, using the linear regression figures they provided. The linear Boers and Zedler model predicted that T. angustifolia would dominate approximately 6.7% of the wetland by 2010. However, Final Report – Typha angustifolia suppression at Lulu Lake Preserve Page 5 our baseline survey (using aerial photos produced in 2010) showed that T. angustifolia actually dominated 10.9% of the wetland, corresponding to a finite rate of increase of r = 0.51 per year, higher than the population growth rate predicted by the Boers and Zedler model. A higher than expected rate of expansion prompted us to consider the possibility that a linear model might not be the best long-term predictor for T. angustifolia population dynamics in the Mukwonago River wetland. State and transition models of community dynamics predict that species invasions increase linearly until they reach a critical mass, or threshold population density, beyond which invasion progresses at an accelerated, nonlinear rate due to internal system feedbacks (Kot 2001; Hobbs and Suding 2009) that can send communities on unpredictable trajectories of change. Accumulation of Typha litter and its secondary effects (such as mulching competing species) is likely one feedback that induces an accelerated expansion rate. Another probable feedback involves the effects of nitrogen and phosphorus loading on biomass production and litter production. Moreover, and perhaps more importantly, the actual life expectancy and duration of reproductive fecundity (under field conditions) of clonal perennial monocots are not well known (Stüfer et al. 2002), and these variables are strong predictors of population dynamics. Although thresholds are difficult to pinpoint empirically and predictive trends involving nonlinear population dynamics are not yet completely understood, we felt there was sufficient evidence to conclude that this population