The Common Carp, a type of Asian carp, was first introduced to the Great Lakes region in the 1800's. Asian carp are an invasive species
that have devastated marshes by sucking up the bottom sediment to feed on organisms that live in the mud, and it turn, destroy the roots of the vegetation. This has caused a negative impact to the ecosystem by disruption of the food web.
The Christmas Tree Berm project was established to rebuild the mouth of the Grindstone creek which is located within the Grindstone Creek floodplain marsh system in Canada (near western Lake Ontario).Berms were built to follow the natural curve of the creek with adjacent areas to be restored as floodplain ponds, areas for marsh plant growth and fish and wildlife reproduction.
Ecologist Jennifer Bowman leads the project and says that before the berm was built, carp did a lot of damage. The Christmas tree berm acts as a barrier to keep Asian carp out of the marsh. The berm is three feet high and extends nearly 300 yards along the Grindstone Creek.
Discarded Christmas trees used as barrier for Asian carp.
Photo credit: Angelica A. Morrison
Original blog post by project leader, Jennifer Bowman
The Christmas tree barriers at the mouth of Grindstone creek are helping Royal Botanical Gardens (RBG) to rebuild creek channels. Creek channels that have disappeared since carp have been prevalent in Hamilton Harbour. The Common carp, Cyprinus carpio, native to Asia, were introduced to North America in the 1800. Conditions in the Harbour, namely high sediment and nutrient loads, favoured the carp over native fish species. Carp are adapted for living in river mouth habitats with soft substrates. They forage by sucking up portions of the bottom, filtering it through their gill rakers and eating the remaining clams, snails, and insect larva. This activity uproots marsh vegetation, killing it and making it so muddy that other plants can’t grow.
RBG initiated a restoration project in the year 2000 to restore the mouth of the Grindstone by artificially rebuilding the creek channel. Berms were built to follow the natural curve of the creek with adjacent areas to be restored as floodplain ponds, areas for marsh plant growth and fish and wildlife reproduction. The floodplain ponds are fitted with culverts to maintain water flow and a fish structure to allow native fish to pass while blocking non-native carp.
Rebuilding the creek channel has a number of associated benefits to the system. Firstly, it allows the floodplain ponds to be protected from the destructive activity of carp. This facilitates the regrowth of marsh plants creating habitat for native fish and wildlife. At times when the creek has poor water quality (such as following a storm event) the muddy water can flow down the creek leaving the floodplain ponds more or less protected from the dirty waters. The creek channel also helps the creek maintain a healthy channel width and thus a healthy creek depth. The previously impacted creek was extremely wide and shallow essentially acting as a barrier to fish migration at low water levels.
Using recycled Christmas trees was a genius move. The estuary areas are subject to Lake Ontario water levels and remain submerged at the average winter low water mark. This constant saturation of the bottom makes the sediment too unconsolidated to be used in berm construction. Old Christmas trees are an idea building block. They sit on top of the unconsolidated mud without sinking into it, however when they are packed down tight they create a barrier to fish. Tree material creates a soft shoreline feature, the branches help slow the water currents along the berm and accumulate sediment. This sediment in turn can start growing native emergent plants such as cattails and burred, a phenomenon that has occurred in a number of locations along the berms. This creates the conditions similar to the original system, creek channels that are held together by native plants!
As the years go, the old Christmas trees break down and compress further. RBG adds new trees to the top to maintain berm heights that will protect the floodplain ponds during high water levels. Most of the trees obtained are from surplus stock of local stores. This will continue until the creek channels are completely vegetated in. It is a slow process but it is happening already. You can help by donating your Christmas tree. Just be sure to remove ALL of the decorations. Ornaments do not make good habitat features for fish!
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