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Vegetation
Silver maple (Acer saccharinum) trees (some more than a meter and a half in circumference at breast height) are the dominant tree species within the unique floodplain hardwood forest that exists on Sycamore Island. Indeed, the middle region could be referred to as the land of the "Giant Silver Maples" who stand either sentinel or arch over the island's understory in a cathedral-like fashion.
Japanese Knotweed
The northernmost tip of Sycamore Island bears the brunt of
invasive plant species, being inundated with Japanese
Knotweed as the major herbaceous cover (the Japanese
Knotweed is the thick, lime green mat of vegetation in
the foreground). (Click photo for a larger version.)
Related to the dynamic ecology of a river island is the potential for sudden and persistent invasions of invasive species of plants and animals. Controlling or responding effectively to invasives on an island is often quite different from mainland approaches to invasive species management.
A well-documented invasive that has established itself on Sycamore Island is Japanese Knotweed (Polygonum cuspidatum), a problematic plant in many riparian systems of the United States. Previous plans in similar settings have failed to eradicate invasives from islands because of the constant upstream supply of winged seeds and plant parts (rhizomes and stems) that regenerate quickly upon being transported to new locations. Japanese Knotweed spreads quickly to form dense stands that not only crowd out native plants, but also negatively impact the habitat of both terrestrial and aquatic wildlife. This persistent plant is also able to withstand major flooding events and ice scour, thereby competing with desirable, opportunistic native species that tend to settle in dynamic island environments.
Japanese knotweed cover encroaching upon the interior of
the island. (Click photo for a larger version.)
View from beneath the 'canopy' of Japanese knotweed on
Sycamore Island. The knotweed grows upwards of 12'
high on the island, creating a thick, aggressive cover
that suppresses diverse native plant species from
establishing. (Click photo for a larger version.)
Japanese Knotweed can thrive in many different conditions. It is usually found in moist sites, however it has also been known to grow in dry sites. Japanese Knotweed is usually found thriving in sunny sites, but also has been known to grow in part sun to shadier sites, however with frequency and growth of the plant being generally more suppressed in these conditions. It often spreads along the banks of rivers, in wetlands, alongside roads, and in other disturbed areas.
Vegetation Field Inventory
Per the sampling methods outlined in the scope of work for the Sycamore Island Ecological Assessment and Management plan, a preliminary investigation of island vegetation was conducted by AES ecologists on June 22nd through the 24th of 2009. The goals of the investigation included, but were not limited to:
- Characterize more specifically the type of riparian island vegetative community or communities which exist on the island.
- Investigate vegetative diversity and abundance.
- Determine the extent of invasive cover, especially Japanese Knotweed (Polygonum cuspidatum).
- Explore any mitigating factors which may either affect restoration of native species and/or recreational use of the island.
Transects
AES team ecologists conducting the vegetation inventory.
(Click photo for a larger version.)
We photo documented and measured vegetation and floristic diversity from three permanently established transects located in representative areas of the island:
- 50m transect running northeast to southwest through the islands' north end "Japanese Knotweed /rough terrain cover".
- 100m transect through the island's midsection including "invasive/native interface".
- 50m transect through mixed "canopy/understory" area. A portion of this transect also includes a stand of Japanese Knotweed.
The rationale for choosing these areas for transect locations is that they not only represent three superficially distinct community types, which may reveal real distinctions based upon further inquiry and analysis, but that each can be analyzed and crossed referenced for viable native seed banks where invasive cover is a major issue. Thus, these transects informed our inventory by transversing these three distinct phenomena.
Test Plots
Three test plots were established in select loca-
tions on the island in order to test different
invasive species management strategies for
the control of Japanese Knotweed.
(Click photo for a larger version.)
Test plots were positioned over half of each study transect measuring 25m x 50m (Test Plots 1 and 3) and 50m x 50m (Test Plot 2). The Test Plots will serve as future treatment areas for the Japanese knotweed, to be compared against adjacent control areas within each transect. Soil samples were taken from Test Plots 1, 2, and 3. These soil samples have been taken to Taylor Creek Restoration Nurseries at the Applied Ecological Services office in Brodhead, Wisconsin to be grown our and monitored by our ecologists under controlled greenhouse conditions. Seeds can remain viable in soil for years. Through the process of growing out the potential seed bank within each soil sample, we will be able to see what native species may be present in the soil, beneath the suppression of the thick Japanese knotweed cover. The seed bank study will be used to inform our invasive species management recommendations for the Island.
View vegetation images from Sycamore Island.