- September 27, 2016
Shores are ecologically valuable but extremely vulnerable to damage by human activity. Shore zones can have high biodiversity, are structurally complex, and play a critical role in slowing water flow from land into a body of water. This article examines what we know about their ecological functioning in order to make recommendations for design, planting, and management of these specialized zones.
The places where land meets water can look and function very differently depending on how they are managed. People often tidy shore zones, especially those used for recreation or in residential areas. This tidying may involve removal of debris, or terrestrial or aquatic vegetation and the hardening-off of shorelines. Since each of these elements play important ecological roles in the shore zone, it is unsurprising that tidied shore zones have a different ecological structure and function than natural shore zones.
The pond in the image above is heavily managed. Mowed lawn extends right to water’s edge. These tidy, simplified edges are often hardened with rocks or concrete and compress the transitional space between land and open water. This kind of shoreline limits the natural progression of plants from upland to wetland to submerged vegetation and in deeper bodies of water, where the hardened edges drop precipitously into deeper water, it might mean the absence of a littoral zone in that body of water.
The littoral zone is any area of a body of water that is shallow and allows vegetation rooted underwater enough access to sunlight to grow. It is often the areas closest to the shore of a lake or pond. It is shallow, warm, and bright compared to other areas. It is home to a diverse community that includes algae, aquatic plants, snails, clams, insects, crustaceans, fish, and amphibians. The littoral zone is critical for the reproductive cycle of several kinds of wildlife. For instance, dragonflies and frogs lay their eggs here; and, once they hatch the larvae and tadpoles forage in the shallow water as they develop. Ducks, turtles, and snakes also rely on the plants and animals living in this zone to for food and shelter. Fish too rely on such areas for reproduction and shelter from preditors.
Physically complex shore zones often support a richer biota than simple ones. That is, ponds with shorelines with diverse vegetation and debris present also have more species of fish, more fish in general, and those fish tend be larger.
Got Canada Geese problems?
Some research has found that nuisance geese occur almost entirely at sites where lawns abut a body of water. Geese actively select sites where they can forage on a lawn and reach the safety of open water without anything in the way. Sites with more complicated vegetation along the shoreline seem to discourage geese habitation by reducing the forage area for these geese (lawn) and by making it more difficult for the geese to reach the water when they are startled.
Research shows that hardened shorelines often reduce biodiversity at the shore’s edge. Hardened shorelines, like the one pictured above, reduce biodiversity by 23% compared to natural, or soft shorelines. There are 66% fewer kinds of plants, 52% fewer birds, 20% fewer swimming aquatic animals, and 24% fewer organisms living in the substrate (mud or sand). Abundance of all these organisms is reduced by a staggering 45%.
Besides acting as habitat, shorelines provide other valuable ecosystem services. Waves, currents, and wakes may focus enormous amounts of energy onto shore zones. Vegetation may absorb significant amounts of wave energy, thereby reducing erosion along the shore and improving habitat for a diversity of organisms.
Roots of shoreline vegetation reinforce banks along rivers, creeks, ponds, and lakes providing stable ground for other plants, in what would otherwise be a challenging location and stressful to many plant species. If the protective shore zone vegetation is lost, because of a storm event, or because it is physically removed (as is the case to the left with heavy grazing done in this pasture), it can lead to excessive erosion.
Soft edges, where there is a gentle slope rather than a sharp drop, help shoreline vegetation thrive by slowing water rushing towards the water body and buffering the shoreline from the waves generated during storm events. It works in reverse too, vegetation along the shore slows the flow of water during rain events allowing it to be absorbed, and filtered by the plants and soil, before reaching the body of water. Softer shorelines also provide additional habitat among the diversity of plants that take root as the habitable area increases along the gentle slope.
As the surrounding landscape drains into a body of water a large amount of organic matter can be washed in from adjacent ecosystems. In a healthy ecosystem, this includes natural debris like leaves, twigs, bark, moss, fur, feathers and soil. You’ve probably noticed this matter while walking on a beach. It is often “organized” into narrow bands (‘‘wrack’’) along the shore. Wrack is an important source of organic matter to shore zones, acting as a food and shelter for a variety of organisms. The daffodil in the image above is taking advantage of this source of nutrients along a shore in the U.K.. Shore zones play a critical nutrient cycling role by acting as a location for decomposition of this organic matter. These valuable functions can be disrupted if the shore zones are tidied.
You might think that living next to a body of water would alleviate concerns about “where” stormwater ends up since you have an obvious collection point for rainwater that falls on your property. It turns out, however, that people alongside lakes are very concerned with stormwater management since stormwater runoff from developed landscapes is a major source of pollution. Rainwater that falls adjacent to a body of water can travel quickly downhill picking up a number of pollutants ranging from fertilizers to insecticides, which can lead to algal blooms and ecosystem disruptions in the lake. Slowing water and even trapping it in rain gardens (like in the planned rain garden above) gives water time to soak in and take advantage of the natural filtration that plants and the soil itself provide. Any additional vegetation along a shoreline acts as a buffer by slowing and trapping stormwater and pollutants, helping keep that body of water cleaner.
How shorelines look are important to people. Bodies of water are often high-value landscape features. We enjoy being able to see them and have particular expectations about how they look. When landscaping shorelines, it is important to keep aesthetic preferences in mind–including maintaining lines of view and access to the water.
Many of the rules for wild landscaping outlined in our article on the topic apply to landscaping for a wild shoreline as well, with the addition of taking into account the view. This means ensuring you plant lower vegetation, or create open “view lines” towards the water. Plant trees outside these view lines. And, if you are kind neighbor, consider the view lines of your neighbors as well. Having a view doesn’t mean you have to choose lawn, but it does mean reading up on the max-height of any plants you do choose to use.
Above are two creeks, both lovely to look at. One with a natural, soft shoreline, the other with a heavily-managed, hardened shoreline. Both are in residential areas designed to provide residents a focal point in their neighborhood and recreational opportunities; but, one also serves several ecological functions–including nutrient cycling, slowing of runoff during storms, and providing habitat.
How to Map a “Shoreline”
First, map your body of water. It doesn’t matter what it is: pond, lakeshore, creek, river, ocean all utilize the “water” habitat polygon.
Second, set the characteristics for that water polygon.
(Not sure how to set characteristics? Read our detailed article on the topic)
Thanks to Jo Latimore and Erick Elgin from the Score the Shore program for their valuable feedback on this post.