Last spring a beaver dam at our Hedges Creek Preserve (Tualatin) was breached by vandals, resulting in water levels dropping by a few feet in the beaver pond above. While examining the breach, we noticed several egg masses were exposed and lying in the drying mud. The egg masses were from the Northwestern Salamander, which had never been documented on the site. After contacting a local amphibian expert, we decided to survey the whole marsh and found over 60 egg masses. Surprisingly, most were still healthy even after a week of exposure. Notably, there were no other amphibians or egg masses found on site except for the non-native bullfrog that is infamous for eating native amphibians, fish, birds and even small turtles and mammals.
Amphibians are a key indicator species. When changes occur to an ecosystem, amphibians are often the first to react. Their thin skin makes them incredibly vulnerable to temperature increases, chemical pollutants, disease, and radiation. In the Portland Metro area, everything from mutations of extra legs to the complete absence of native amphibians has been noted. Over the years, we have noticed that very few of our urban preserves have thriving amphibian populations, Surprisingly, Gresham Meadowlands, one of our smallest preserves is the only one with a healthy and diverse amphibian population.
The discovery at Hedges Creek encouraged us to consider the interrelationship between beaver dams and amphibian egg masses. In spring 2015 we will conduct more surveys and better document amphibian presence and absence at our preserves, including cataloguing the habitat and conditions where they are both found and absent.
In tandem with the amphibian monitoring, we will be conducting extensive water quality surveys. Over the next year, data will be collected at, above and below our Nyberg, Hedges Creek, Cedar Mill, Gresham Meadowlands, Minthorn Springs and Hearthwood Preserves. We will also be looking beyond the boundaries of the preserves to better understand and assess the role they play in overall watershed health. .With these new insights we will set goals for desired future conditions and identify new enhancement and restoration opportunities.