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There are small wetlands alongside each tributary of Horse Creek within Centennial Park.  These wetlands are covered by shallow water for most of the year and the underlying soil is typically completely saturated.  Specialized plants that tolerate soggy soil conditions (such as cattail and tule) grow in these areas and provide critically-important habitat for a broad diversity of insects and animals.  How did those wetlands get to be here on such small creeks?  Beavers!  Scientists often refer to beavers as “ecosystem engineers” because their activities have dramatic and very significant impacts on their surrounding environment. 

_{Beavers are known as “ecosystem engineers” and they have created several wetlands in Centennial Park. Photo credit: Gerald and Buff Corsi © 2013 California Academy of Sciences}

Beavers need water to be several feet deep to protect the lodges that they build.  Like many other small creeks in California, water levels become quite low in the Horse Creek tributaries during our hot, dry summers.  The beaver’s solution to this problem is to build a long dam made of logs, sticks and mud across the entire creek, backing up the water and creating a semi-permanent wetland.  These dams are known to be as long as 300 feet wide and four feet tall.  In the water ponded behind their dam, beavers construct a conical lodge, made of sticks, vegetation and mud.  These lodges can be up to 8 feet tall and 15 feet wide.  Inside is a hollow chamber which is accessed by a narrow tunnel with an under-water entrance.  These well-made lodges provide excellent shelter, allowing beavers to safely raise their young (called “kits”) and protect them from predators such as bobcats and coyotes. 

_{Beavers strip the cambium layer off trees for food and they gnaw off branches to build their lodges. These lodges cause water to back up and create wetlands. Photo credit: © David Davies}

It is easy to see how beaver-created wetlands benefits beavers and their families, but these wetlands also provide numerous other ecological benefits.  One of these benefits is that water ponded by a beavers’ dams slowly percolates downward, recharging groundwater tables.  In some places where beavers have been removed, farmers have found they have to drill deeper wells to access water.  Another benefit is that sediment-laden water running through creeks slows down as it enters a wetland.  This allows sediments and pollutants to drop out of the water column and settle to the bottom, improving water quality and benefiting all downstream users (both human and animal). 

_{Dragonflies spend most of their lives in wetlands as aquatic nymphs.  They only live as winged adults for a few weeks. Photo credit: © David Davies}

Wetlands also provide excellent habitat for many other kinds of animals including fish (Sacramento blackfish and tule perch), waterfowl (Canada geese and wood ducks), wading birds (great blue herons and snowy egrets), amphibians and reptiles (Pacific tree frogs and western pond turtles), and mammals (mink and river otters) and insects (dragonflies and damselflies).  Dense and varied wetland vegetation provides an abundance of cover and food resources.  For example, it is estimated that 80% of North America’s bird species rely upon wetlands at some point to complete their lifecycle.  Although wetlands occur on less than 5% of the land area in the United States, about half of all animals considered to be endangered are dependent upon wetlands.

_{The colorful wood duck is a common visitor to beaver created wetlands in the Central Valley. Photo credit: © David Davies}

Not only are beavers one of our best-known ecosystem engineers, they are also North America’s largest rodent.  Their large, orange-colored front teeth never stop growing as they are worn down in the process of cutting up branches, saplings and trees used in the construction of lodges.  Most wetland trees are adapted to beaver predation and will re-sprout from the stumps the beavers leave behind.  For food, beavers eat the green cambium layer from tree twigs and small branches as well as the roots and stems of many types of wetland plants.  Beavers’ guts contain specialized bacteria that help them digest cellulose, the primary component of plants.

Beavers are well-adapted to life in the water.  They can stay submerged for up to 15 minutes and can swim a half-mile under water.  Their hind feet are webbed to provide them with extra swimming power, and they can motor along at a rate of four miles per hour. Their large flat tail acts as a rudder, steering them while they swim.  They also use their tail to sound an alarm, smacking the water loudly to alert their family of perceived danger.  Beavers are primarily active during night-time hours so you are most likely to see them close to dawn or dusk.

This information has been provided by the City of Vacaville in partnership with the Solano Resource Conservation District.  It was last updated on May 20, 2020.