If you’ve already read about the Vancouver Aquarium’s partnership with Earth Rangers, then you know that we are teaming up to help save Oregon spotted frogs (Rana Pretiosa), the most endangered amphibian in Canada. As part of that effort, our two organizations are working together to restore an old wetland site where we can reintroduce this treasured animal, born and bred in human care, back into the wild.
The first step in the process was to identify a good location for the restored wetland. We found a great location in a regional park in Metro Vancouver, Aldergrove Lake Regional Park, and we’re developing a plan to restore a shallow marsh for the Oregon spotted frogs and all the other animals that need wetlands to survive. To accomplish this, we needed a site that fulfilled the following requirements:
1. Was previously a gorgeous wetland. The site needs to be hydrologically suitable; wetlands develop in low-lying areas with lots of water. It’s much more difficult to build a wetland if there is no natural water around.
2. Is within the historic range of the Oregon spotted frog, and free of the invasive American bullfrog.
3. Is on public land where kids (and big kids) can be taken out on field trips for educational purposes.
The second requirement (bullfrog free) is a bit of a problem. American bullfrogs have taken over most of the wetland habitats in the Fraser Valley, and it’s simply not possible any more to find a swamp without them. Instead, we’re going to build a wetland that bullfrogs won’t like very much, but that will be a great home for Oregon spotted frogs. We’ve learned that to make good habitat that isn’t too attractive to bullfrogs, we need to restore a habitat type that is almost completely lost to B.C.’s Lower Mainland: a shallow water marsh.
Most shallow marshes around Vancouver were drained for agriculture in the early 1900s, and very few remain. To restore a marsh, there are two major steps: restore the natural hydrologic regime (water flow) by removing drainage features like ditches and drain tile, and restore a native plant community.
Restoring the hydrologic regime is relatively simple. We need to plug ditches and drain tile, and make sure there’s a good source of water for the wetland. We’ll do this with an excavator. First, though, we need to know how deep the groundwater is and what kind of soils we have (clay? sand? peat? gravel?) under the thick layer of grass. In August, we went on-site with a back-hoe to dig some test pits and install groundwater wells so we could check out the soils and monitor water levels through the winter and next summer.
Restoring the plant community will be a bit more difficult. Invasive reed canary grass has taken over many marshes in B.C., as it was planted as a pasture crop that grew well in wet areas. Our challenge will be to fight back the grass and plant native marsh plants densely enough to stop the grass from coming back in.