Phragmites Management Look-Up Table

About the Look Up Table

Our team talked with local land managers working to control Phragmites along the Great Lakes coast in Michigan to determine the most commonly used control techniques (what techniques are used alone or in combination, when are those techniques used, and how often?). From the literature, past modeling results, and field experiments, we knew that N loading, hydrology, and propagule pressure (the rate of initial and continuing arrival of invasive plants at a site) can all influence the success and control of Phragmites. To account for this, we did thousands of simulation runs to determine how successful 11 different control techniques are under four levels of N loading, four hydrologic scenarios, and three levels of propagule pressure. We also ran these at long and short growing season lengths to reflect differences between the northern and southern portions of the Great Lakes region.

We developed the interactive Look-Up Table to allow wetland managers and others to explore the wealth of data that came from these thousands of model simulations. The figures will allow you to visualize the simulation results to determine which management technique might best reduce Phragmites and restore native plants, given the ecological context of the wetland, without having to run the model. Please remember that these are only model predictions that involve quite a few assumptions, so results should be viewed more as qualitative predictions than precise quantitative answers. Technical details about these simulations are provided below.

Description of Mondrian Simulation Runs

Phragmites Look Up Table (PhragLUT) was a large set of runs designed to create a look-up table that can be used to recommend the best management options to land managers given a set of site-specific conditions. Below is a summary of the key aspects of the simulation runs that managers might be interested in.

Colonization (1 m² modeling area)

We used 3 levels of invader (Phragmites australis) background propagule pressure (low, medium, high). In these simulations, propagules are rhizomes, which we call individuals or ramets. All 3 invader background propagule pressure scenarios initially seed in 4 cohorts of the three native species (parameterized as Eleocharis smallii, Juncus balticus, and Schoenoplectus acutus), with 65 individuals per species per cohort, with cohorts spaced 2 years apart. Background propagule pressure of the natives is 2 individuals per species per year. The native species stabilize between years 7 and 15. In years 15 and 20, 15 individuals of the invader are seeded in each year. The three levels of invader background propagule pressure (low, medium, high) are then initiated as follows:

· Low: 0.33 propagules per year (stochastic)

· Medium: 1 propagule per year (constant)

· High: 3 propagules per year (constant)

Hydrology

Four hydrological scenarios are modeled using a factorial combination of two values of the hydrograph’s mean stage (0 cm & 30 cm) and either fluctuating or constant stage. Fluctuating hydrographs are modeled as a sine wave, with peak amplitude on January 1 and minimum on July 1. For all four hydrological scenarios, the hydrograph is identical for each year of the model run.

N loading, Growing Season, and other Specifics

· N Loading: 4 (low), 12.5 (medium), 20 (high), 30 (very high) g N · m^-2· y^-1.

· Growing Season: Short = DOY 105-244 (4/15-9/1), Long = DOY 96-253 (4/6-9/10)

o These growing season lengths are based on the University of Michigan Biological Station (UMBS) in the north, and the E.S. George Reserve in the south, where there are 18 more frost-free days than at UMBS.

· Litter is distributed spatially and affects vegetation regeneration and temperature of soil. Atmospheric temperature varies seasonally (sinusoidal) and affects litter and SOM/humus decomposition rates. Light competition and flooding mortality can occur in these simulation runs.

Management Treatments Used

Herbicide only

1. Herbicide (6/1: DOY 152)

2. Herbicide (8/31: DOY 243)

3. Herbicide x 2 (6/1 & 8/31: DOY 152 & 243)

Early Burn and Herbicide

4. Burn (4/30: DOY 120) + Herbicide (6/1: DOY 152)

5. Burn (4/30: DOY 120) + Herbicide (8/31: DOY 243)

Late Burn and Herbicide

6. Burn (12/31: DOY 365) + Herbicide (6/1: DOY 152)

7. Burn (12/31: DOY 365) + Herbicide (8/31: DOY 243)

Early Mow and Herbicide

8. Mow (7/15: DOY 196) + Herbicide (6/1: DOY 152)

9. Mow (7/15: DOY 196) + Herbicide (8/31: DOY 243)

Late Mow and Herbicide

10. Mow (10/1: DOY 274) + Herbicide (6/1: DOY 152)

11. Mow (10/1: DOY 274) + Herbicide (8/31: DOY 243)