In the middle of our spring tree planting, the Watershed Protection Team had quite the surprise when we spotted evidence of beaver activity in Ashbridge Preserve. A single tree was knocked down along Ridley Creek, with distinctive teeth marks that indicated a beaver had found itself a tasty meal. While it is too soon to tell if the beaver will make a home at Ashbridge, we wanted to take this opportunity to share the history of beavers in the area and the special role they play in stream ecosystems.

Beavers are the largest rodent found in North America, reaching 3 feet in length and weighing between 30 and 60 pounds. They have small faces, stocky brown bodies, and a distinctively hairless, paddle-shaped tail. Their tail allows beavers to be distinguished from groundhogs, which have short, furry tails, as well as muskrats, which have long, hairless tails. Beavers are well-adapted for an aquatic lifestyle; when they dive underwater, their eyes are protected by a set of transparent eyelids and their ears and nose are protected by watertight membranes. They can remain underwater for 15 minutes, and their oily, waterproof fur helps them stay dry. Their webbed feet and rudder-like tail allows beavers to swim at speeds of 5 miles per hour.

Beavers were once abundant throughout North America, from northern Mexico all the way up to the southern Arctic. However, they were heavily hunted for their waterproof pelts by European colonizers, and their numbers dropped rapidly. In Pennsylvania, beavers were wiped out by the beginning of the twentieth century. Reintroduction efforts in the 1920s proved successful, and beaver populations have been stable in Pennsylvania since the 1930s, though they likely are not as abundant as they were before European colonization. There are a few known beaver colonies near Willistown in Ridley and Darby creeks and evidence of beaver activity can occasionally be spotted in Willistown, and most recently at Ashbridge Preserve.

Beavers are perhaps nature’s most effective engineers, changing entire ecosystems to fit their needs. They build their homes, called lodges, almost exclusively in the middle of slow-moving ponds, where the surrounding water acts as a moat that protects them from terrestrial predators. If no such pond can be found, beavers dam streams and rivers to create the perfect pond. To create their dams, beavers cut down trees with their chisel-like teeth, which constantly grow and self-sharpen. They generally prefer trees with diameters of less than 3 inches, but will cut down larger trees if small trees are not readily available. They construct their dam with logs, branches, twigs and grasses and seal everything into place with mud.

Once the dam backs up enough water, beavers build wood and mud lodges in the middle of the pond that can be 6 feet high and up to 40 feet wide. These lodges have 1 or 2 underwater entrances, a ‘living area’ above the water line, and a small air hole in the top to provide ventilation. A lodge houses a colony made of a breeding pair (which mate for life), the current years’ kits, and the surviving offspring from the year before. Before the kits are born, the female drives out the second year young. After the young are driven out from the den, they disperse to find new habitat and form their own colonies.

Beaver settlement causes widespread changes to an ecosystem. The first noticeable change is the clearing of several trees — typically small — that the beaver will use to build its dam. After the dam is built, the creek will start to back up, flooding the adjacent land and forming a small pond. More trees may be felled to build the beaver’s lodge. What was once a wooded valley with a small stream becomes an open pond bordered by wetland vegetation. This new pond supports a host of wetland species that would not otherwise be found in the area — ducks, geese, herons, turtles, fish, frogs, salamanders and more. Even beaver lodges create habitat: the underwater base of the lodge provides shelter for young fish and the top of the lodge can be a nesting area for birds.

Beyond supporting a biodiverse ecosystem, beavers and their dams improve local water quality. Beaver ponds trap and slow down water, reducing downstream flooding during major storm events. By slowing down the flow of water, beaver dams also allow more water to seep through the soil and replenish groundwater resources. As water passes through a beaver pond, fine sediment and pollutants are filtered out, resulting in cleaner water downstream of the dam.

Beavers inhabit a pond until they deplete all nearby food sources, usually after 20 to 30 years. At this point, they abandon their pond and lodge and move on to new habitat. Without constant maintenance, the dam slowly breaks down and eventually breaches. The pond drains and the previously submerged seed bank begins to germinate. Shrubs and trees re-establish in the area and, eventually, the open land turns back into a wooded valley.

By Anna Willig

References

Beaver. (n.d.). Pennsylvania Game Commission. Retrieved May 27, 2021, from https://www.pgc.pa.gov:443/Education/WildlifeNotesIndex/Pages/Beaver.aspx

Beaver. (2016, April 25). Smithsonian’s National Zoo. https://nationalzoo.si.edu/animals/beaver

Beaver | National Geographic. (n.d.). Retrieved May 27, 2021, from https://www.nationalgeographic.com/animals/mammals/facts/beaver

Wohl, E. (2021). Legacy effects of loss of beavers in the continental United States. Environmental Research Letters, 16(2), 025010. https://doi.org/10.1088/1748-9326/abd34e

Few landscape features define American suburbia like the lawn. Drive through a neighborhood anywhere in the US and you are likely to see the same landscape: houses surrounded by a tidy patch of grass, with a few gardens thrown in. Lawn care could be considered a national hobby — the average American spends 70 hours a year tending to their lawn, mowing, clearing, watering and spraying. Lawns are so ubiquitous, so expected, that we rarely consider what the consequences of our tidy little lawn might be.

Although individual lawns do not cover much ground (the average American yard is only 0.19 acres), the summed area of lawns is staggering. Turfgrass, the cropped grass that differentiates a lawn from a field, is the most irrigated crop in the United States, and as of 2005, it covered 40.5 million acres, a number that has only increased since then. To put this number in perspective, if all lawns were put together, they would cover Pennsylvania, Delaware and Maryland combined, with a few acres to spare. 

While this vast area of lawn may not seem like an environmental problem — after all, it’s still a green area, taking in carbon dioxide and releasing oxygen — the consequences of our obsession with lawns are hard to overstate. Most turfgrasses are not native to the United States (even the famed Kentucky Bluegrass is native to Europe, Asia and Northern Africa), meaning that nearly every one of those 40.5 million acres of lawn is devoid of native plant species. Instead of a biodiverse landscape that can sustain a complex ecosystem, we maintain acres and acres of ecological desert.

Starting at the base of the food chain, lawns provide little habitat and few food sources for insects. Lawns are often devoid of leaf litter, which provides crucial habitat for benign and beneficial insects, including our beloved fireflies. Small wildflowers are often removed as weeds, depriving bees and other pollinators of crucial food sources. Without this food source, insects move elsewhere or die off. Once the insects are gone, there is little to sustain the birds, frogs and other small animals that rely upon insects as a food source.

In addition to lacking food and habitat that insects and wildlife need to survive, many lawns are poisoned with pesticides. A 2012 report from the EPA on pesticide use found that, annually, homeowners spend $3.3 billion on pesticides and apply 59 million pounds of pesticide to their lawns. As these numbers do not include pesticide use by lawn care companies, the true amount of pesticides applied each year on lawns is even higher.

Pesticides used on lawns can devastate organisms they were never supposed to impact. Many pesticides, particularly insecticides, are indiscriminate, killing not only target insects such as mosquitos, but also beneficial insects such as butterflies and bees. Insects are not the only victims—birds, frogs or turtles that eat insects with pesticides in their system ingest these pesticides as well, often with deadly results.

Pesticides applied to lawns readily runoff into aquatic systems, impacting the entire waterway. The use of pesticides is so extensive that they are commonly found in urban waterways and, increasingly, in groundwater. Due to the prohibitively high costs of long-term ecological studies, we do not know how the presence of low levels of pesticides in waterways alters aquatic ecosystems.

In addition to impacting aquatic organisms, the presence of pesticides in waterways also impacts humans. A CDC biomonitoring program that samples human blood for a range of environmental contaminants has found some type of pesticide in nearly every blood sample, suggesting that most, if not all, Americans have low-levels of pesticides in their blood. The persistence of many pesticides is of particular concern: though DDT has been banned in the US for nearly 40 years, it is not uncommon to detect DDT and its degradation products in humans today. Just as we do not understand the impacts of chronic, low-level pesticide exposure on ecosystems, we do not understand these impacts on human health.

In addition to applying millions of pounds of pesticides to lawns, homeowners also apply millions of pounds of fertilizers to lawns. Though fertilizers pose fewer immediate health concerns to humans than pesticides, their overuse can also devastate ecosystems. Fertilizers enter streams and rivers through runoff and ultimately end up in estuaries, lakes, and bays. The resulting increase of nutrients in these systems can cause massive blooms of algae. Algae blooms rapidly deplete the oxygen in the water, causing massive ‘dead zones’ such as those found in the Chesapeake Bay and the Gulf of Mexico. In some areas, the algae bloom can even release a neurotoxin dangerous to humans and pets.

While the problems caused by lawns are far-reaching, many can be addressed by simply doing less to care for our lawns. Here are 10 ways you can have a more eco-friendly yard:

1. Before any expected rainfall, avoid applying pesticides and fertilizers to reduce runoff of pesticides and fertilizers into waterways.
2. Test your soil! This can tell you exactly what kind and how much fertilizer you might need for your lawn, reducing the risk of overuse (and saving you money!).
3. Before applying pesticides, contact your County Extension Services Office to determine if you actually have a pest problem that needs to be treated.
4. Avoid using lawn services that apply pesticides on a regularly scheduled basis. Many of the pesticides used are long-lasting, meaning that any application after the initial application is unnecessary. Only re-apply if you have determined you have a problem that needs to be treated.
5. Consider eliminating the use of pesticides in your lawn. Many pests, especially insects, have natural predators that can thrive in your lawn and control your pests for you.
6. Raise the blade of your lawnmower. Taller grass has a longer root system, allowing it to soak up more water and reduce runoff into waterways,
7. Mow less frequently, especially in early spring. A study found that lawns that were not mowed for the month of May had five times more bees, which are crucial pollinators, than lawns that were regularly mowed. Mowing less frequently also reduces greenhouse gas emissions from lawnmowers.
8. Allow your lawn to become a little messy. Weeds and small wildflowers increase the biodiversity of your lawn, providing more food sources and creating more habitat for insects and other wildlife. Grass clippings and leaf litter provide habitat for insects and nutrients for your lawn, reducing the need for fertilizer.
9. Consider replacing some of your lawn with a native wildflower garden or, if you have space, a meadow filled with native grasses and wildflowers. Native plantings provide far more habitat for insects and birds than lawns and often require less care after the initial establishment. They also capture more runoff and prevent pollutants from reaching waterways.
10. Reach out to local neighborhood groups or homeowners’ associations to advocate for greener lawn care! Reducing pesticide and fertilizer use at a neighborhood scale can have a massive impact on local waterways and ecosystems.

Remember that you can make a difference! Every acre of the 40.5 million acres of lawn represents an acre of habitat that is yet to be created. Making small changes in your backyard can make a world of difference for local wildlife and waterways, and at a quicker rate than you might expect. Small actions can add up to big results, and it is far better to make some changes than no changes at all.

By Anna Willig

Resources

To learn more about the extent of lawns: https://earthobservatory.nasa.gov/features/Lawn/lawn.php

To learn more about the benefits of converting lawns to meadows: https://conservationtools.org/guides/151-from-lawn-to-meadow#_ednref1

To learn more about proper fertilizer use: https://www.epa.gov/nutrientpollution/what-you-can-do-your-yard

To learn more about proper pesticide use:

https://extension.psu.edu/are-you-thinking-about-using-pesticides