The temporal succession of invasive species in the Goodyear Swamp Sanctuary

Megan Wilckens1

INTRODUCTION

Goodyear Swamp Sanctuary (GSS) is a five-acre property at the northwest end of Otsego Lake belonging to the SUNY Oneonta Biological Field Station (Figure 1). While it is called a swamp, the habitat is technically a marsh, as it is permanently wet (along the edge of Otsego Lake) and is mostly made up of herbaceous plants rather than woody vegetation (Anonymous 2014a). This marsh acts as an ecotone between the lake and the forested upland. The purpose of the GSS is to provide a wildlife refuge to protect unique and native flora and fauna and ensure this wetland complex remains intact. The GSS is home to over 200 species of vascular plants, thousands of invertebrate organisms, waterfowl and other bird species, mammals, amphibians and reptiles which can be seen from the boardwalk that traverses open water areas or the boarder trail that continues into upland portions of the property (Harman et al. 1998).

Figure 1. Goodyear Swamp Sanctuary map showing the main boardwalk and boundary trail. The tree line, end of emergent vegetation and low water levels are also shown.

1 BFS Intern, summer 2014. Current Affiliation: Le Moyne College, Syracuse, NY.

The vegetation present in the GSS ranges from tiny aquatic plants like duckweed to towering oak and ash trees. This study focuses on the emergent wetland vegetation; the plants rooted in the lake bottom along the shoreline with stems that grow above the water’s surface (Anonymous 2014b). Specifically, this study attempted to evaluate the spread of the exotic plants Iris pseudacorus (yellow flag) and Fallopia japonica (Japanese knotweed) found in the Goodyear Swamp Sanctuary over time to determine the area of ground cover currently occupied and the density of patches with the intent of serving as a benchmark for future studies of native and invasive plant dynamics. Will the invasive species present continue to dominate the marsh or will new invasive species take over, as the I. pseudacorus did when the L. salicaria population decreased? Native plants within northeastern wetland habitats are under increasing pressure from invasive plants that are out competing and displacing preexisting species. Without the predators and diseases with which they evolved, invasive plants can flourish in suitable habitat and establish colonies while native species, with no adaptation to the invasive species, are unable to compete for available resources (Gurevitch & Padilla, 2004). Three such invasive species are Lythrum salicaria (purple loosestrife), Iris pseudacorus and Fallopia japonica, all found within Goodyear Swamp Sanctuary. While no formal surveys have been conducted to map plant distribution throughout the property, successive editions of field guides and reports have been used to estimate the change in distribution of these three species over time; these changes are outlined in the paragraphs that follow. Lythrum salicaria is an invasive plant from Europe that spreads about 115,000 ha/year in the U.S. and alters wetlands by dominating the native plants and creating monotypic stands (Pimentel et al. 2005). This invasive species displaces native species of cattails, sedges, bulrushes, willows and horsetails (Blossey et al. 2001). In 1986, when the first GSS self-guided tour pamphlet was made (Harman and Higgins 1986), L. salicaria was present, as well as twelve years later when a revised pamphlet was made. This invasive plant was noted at two particular locations along the Main Trail in 1986 and by 1998 it was noted at three sites; however, photographic interpretations, along with the commencement of a biocontrol study suggest its dominance within the emergent plant community and widespread distribution in the open-canopy areas of the swamp. Since 1998, there have been studies conducted on the percent cover of L. salicaria in the GSS during the spring and fall following the introduction of Galerucella calmariensis and G. pusilla in 1997 as control methods for lessening the competitive ability the invasive species had over the native plants by feeding on their meristematic regions (i.e. Waterfield 2014). Since 2001, there has been a decline in the abundance in L. salicaria in GSS as the G. calmariensis and G. pusilla populations have effectively controlled the rigor and fitness of the plant stands (Waterfield 2014). Iris pseudacorus is another aggressive invasive species that tends to grow densely, forming monotypic patches that are hard to remove. They spread through rhizomatous mats that uplift sediment and alter habitats which in turn reduce the native diversity of a wetland (Thomas 1980). This species’ niche (habitat) is similar to that of native Typha, or cattail, along with sedges and other emergent wetland vegetation and this allows I. pseudacorus to dominate the native species in the marsh that are not adapted to competing with aggressive invasive species. Iris pseudacorus was observed in the GSS in both the 1986 and 1998 self-guided tour pamphlets, suggesting that, while not as aggressive or dense as L. salicaria was, it was established in the

marsh several decades ago and has continued to spread more rapidly. With the decline of L. salicaria over the past decade, I. pseudacorus had been able to thrive and expand its range within the marsh, taking over areas where L. salicaria once grew. Now I. pseudacorus is the dominant invasive species present in the GSS along the Main Trail and is starting to grow along a portion of the Boundary Trail, where it has not been seen growing before. Fallopia japonica spreads similarly through rhizomes, forming monocultures. It has perennating buds that continue to grow underground throughout the winter, allowing it to keep spreading all year long, with woody stocks increasing in mass as the stands age (Beerling et al. 1994). This allows F. japonica to sprout in early spring before native species begin germinating, decreasing biodiversity. This species can also grow new plants from fragments of the stem as small as a node (Aguilera et al 2010). Since F. japonica spreads mainly by vegetative growth, the stems are close together forming thick canopies that block sunlight from reaching the ground layer, shading ground vegetation like skunk cabbage and various fern species, affecting their growth. Fallopia japonica was not recorded in the self-guided tour pamphlets for GSS in 1986 or 1998 so its presence in the marsh and upland areas is relatively new compared to some of the other invasive species. In fact, it had not been noted prior to 2013.

METHODS

Patches of Iris pseudacorus and Fallopia japonica throughout the marsh were delineated for mapping purposes using the track feature on a Garmin CSx76 GPS unit (Degrees Decimal Minutes, NAD83). Patch density measurements were based on stem counts within 1m x 1m plots which were established in the patches using a collapsible PVC grid. The center of each plot was marked with an Etrex GPS unit (Degrees decimal minutes, NAD83). Small patches were evaluated in a single plot. For larger patches, multiple plots were used (between two and six) depending on the spacing of the plants throughout the patch. All stems within each plot were counted to measure the patch density. Where multiple plots were established in a given patch, average plot density was reported. The second part of this study relates to control methods for the two stands of Fallopia japonica. Manual cutting and removal was deemed the best control option for the GSS; other means of eradication and control were considered (excavation, ground barriers, herbicides), but were found to be too invasive for the sensitivity of the site or cost prohibitive. The larger of the two patches was cut down using pruning shears and machetes. Debris was removed from the Sanctuary in garbage bins (40-gallon); plant material was discarded in the dumpster and landfilled. Mass of F. Japonica removed from the GSS was estimated based on the average air-dry weight per bin.

RESULTS & DISCUSSION

The survey for patches of the target invasive plant species yielded five patches of Iris pseudacorus and two of Fallopia japonica. Patch density was determined based on a total of 17 1m2 plots (Table 1, Figure 2). A summary of the locations and densities of I. pseudacorus and F. japonica patches is provided in Table 2. Mean patch density of I. pseudacorus ranged from 60 stems/m2 to 143 stems/m2 while that of F. japonica ranged from 13 to 21 stems/m2. No attempts were made to remove or control the Iris pseudacorus within the marsh; any changes in patch extent or density in the future compared to the Typha stands will all be the result of natural causes.

Manual harvest of the larger F. japonica patch (Patch F) yielded approximately 25

garbage bins of plant material, or an estimated 283kg of plant material based on the average dry weight per bin (11.3 kg). Immediately following the initial cutting of the Fallopia japonica, sunlight was able to reach the ground layer. Several other species were found in amongst the F. japonica stand, including speckled alder and European hawthorn. Monitoring of the site should be continued in the future. The future extent of the patch will depend on the intensity of control methods employed. Current plans include the use of an herbicide containing glyphosate on new plants (in early spring) over the course of several years. Table 1. Goodyear Swamp Sanctuary I. pseudacorus and F. japonica patches. Average patch densities are separated by shaded rows; mean values rounded to the nearest stem.

Patch Species Plot # Plot Density (stems/m²)

Average Patch Density (stems/m2) Coordinates Date

A Iris pseudacorus 0 80 80 42 48.566'N 74 53.915'W 6/25/2014 B Iris pseudacorus 1 56 ~ 42 48.563'N 74 53.926'W 6/25/2014 B Iris pseudacorus 2 44 ~ 42 48.557'N 74 53.925'W 6/25/2014 B Iris pseudacorus 3 79 60 42 48.548'N 74 53.929'W 6/25/2014 C Iris pseudacorus 4 106 ~ 42 48.549'N 74 53.925'W 7/1/2014 C Iris pseudacorus 5 114 110 42 48.546'N 74 53.924'W 7/1/2014 D Iris pseudacorus 6 104 ~ 42 48.532'N 74 53.902'W 7/1/2014 D Iris pseudacorus 7 69 ~ 42 48.530'N 74 53.899'W 7/1/2014 D Iris pseudacorus 8 67 80 42 48.528'N 74 53.893'W 7/1/2014 E Iris pseudacorus 9 143 143 42 48.510'N 74 53.873'W 7/7/2014 F Fallopia japonica 10 19 ~ 42 48.513'N 74 53.863'W 7/7/2014 F Fallopia japonica 11 10 ~ 42 48.512'N 74 53.859'W 7/7/2014 F Fallopia japonica 12 21 ~ 42 48.516'N 74 53.851'W 7/7/2014 F Fallopia japonica 13 13 ~ 42 48.516'N 74 53.847'W 7/7/2014 F Fallopia japonica 14 42 ~ 42 48.519'N 74 53.849'W 7/7/2014 F Fallopia japonica 15 20 21 42 48.522'N 74 53.863'W 7/7/2014 G Fallopia japonica 16 13 13 42 48.521'N 74 53.907'W 7/7/2014

1cm = 8.5m

A B

C

D

E

F G

Figure 4. Satellite image of Goodyear Swamp Sanctuary from Google Earth. Iris pseudacorus patches indicated with white polygons, F. japonica patches indicated with gray polygons. Plots 0-16 measuring stem densities are labeled and shown with white markers.

CONCLUSION

By the mid-1990s, purple loosestrife was the most prolific invasive species within the Goodyear Swamp Sanctuary; following the control of this plant, the distributions of other common invasive plants have expanded, potentially indicating a succession of invasive species in the marsh. Understanding how species dynamics play out over the long term following control of an invasive species is critical in order to increase the ability of conservationists and resource managers to make informed decisions with limited financial resources.

Invasive species are a threat to many native species found in the northeast. Wetlands such as the Goodyear Swamp Sanctuary marsh are especially at risk because they offer a large niche for invasive species to establish in, which then outcompete native species for available resources. It is important to look for species like Lythrum salicaria, Iris pseudacorus and Fallopia japonica

that are becoming a problem in and around water bodies and, where possible, control or eradicate them to prevent them from spreading. With time and consistent pressure on invasive species, native vegetation and the fauna that depend on them might have a chance at rebounding and restoring ecosystems to their natural state.

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