Riparian Forests

What is a riparian forest?
Riparian forests refer to the areas of forested land adjacent to a body of water, stream, river, marsh, or shoreline which form the transition between the aquatic and the terrestrial environment. Miles of interconnected streams, rivers, wetlands and their riparian areas serve as a “circulatory system” for the Nottawasaga Bay. Forests are the natural riparian vegetation in the Nottawasaga Watershed. Riparian areas play an extremely important role in maintaining the health of the Nottawasaga.

What is a riparian forest buffer?

Riparian forest buffers are areas of trees, shrubs and other vegetation, that are adjacent to a body of water, that are managed for several purposes: to maintain the integrity of stream channels and shorelines; to reduce the impact of upland sources of pollution by trapping, filtering, and converting sediments, nutrients and other chemicals; and to supply food, cover and thermal protection to fish and other wildlife.

The purpose of a riparian buffer is to help control non-point source pollution. Forests are the most effective type of riparian buffer available. These linear strips of trees serve as a stream’s last line of defence against human activities such as agriculture, grazing, and urban development. Unlike most best management practices forest buffers improve habitat for wildlife and fish while improving water quality.

Riparian buffers vary in character, effectiveness and size based on the environmental setting, proposed management, level of protection desired and landowner objectives. A three-zone buffer concept has been proposed to assist technical professionals and landowners with the planning and design of riparian forest buffers. The width of each zone is determined by site conditions and landowner objectives. This three-zone concept provides a conceptual framework in which water quality, habitat, and landowner objectives can be accomplished.

The Benefits of Riparian Forest Buffers:

Riparian forests are integral to the health of the Bay and its rivers for many reasons.

  • Filtering Runoff: Rain that runs off the land can be slowed and infiltrated in the forest, which helps settle out sediment, nutrients and pesticides before they reach streams. Infiltration rates 10-15 times higher than grass turf and 40 times higher than a plowed field are common in forested areas. Studies have shown dramatic reductions of 30 percent to 98 percent in nutrients (nitrogen and phosphorus), sediment, pesticides, and other pollutants in surface and groundwater after passing through a riparian forest. In addition, trees provide deep root systems which hold soil in place, thereby stabilizing stream banks and reducing erosion.
  • Nutrient Uptake: Fertilizers and other pollutants that originate on the land are taken up by tree roots. Nutrients are stored in leaves, limbs and roots instead of reaching the stream. Through a process called “denitrification,” bacteria in the forest floor convert harmful nitrate to nitrogen gas, which is released into the air.
  • Canopy and Shade: Cool stream temperatures maintained by riparian vegetation are essential to the health of aquatic species. Shading moderates water temperatures and protects against rapid fluctuations that can harm stream health and reduce fish spawning and survival. Elevated temperatures also accelerate algae growth and reduce dissolved oxygen, further degrading water quality. In a small stream, temperatures may rise 1.5 degrees in just 100 feet of exposure without trees. The leaf canopy also improves air quality by filtering dust from wind erosion, construction or farm machinery.
  • Leaf Food: Leaves fall into a stream and are trapped on woody debris (fallen trees and limbs) and rocks where they provide food and habitat for small bottom-dwelling creatures (i.e. crustaceans, amphibians, insects and small fish), which are critical to the aquatic food chain.
  • Habitat: Riparian forests offer a tremendous diversity of habitat. The layers of habitat provided by trees, shrubs, and grasses and the transition of habitats from aquatic to upland areas make these areas critical in the life stages of over one-half of all native species. Forest corridors provide crucial habitat for deer. Also, many ecologically important species such as herons, wood ducks, black ducks, as well as amphibians, turtles, foxes and eagles utilize the riparian forest. Streams that travel through woodlands provide more habitat for migratory fish by providing suitable spawning habitat for cold and cool water species. The decline of these species is partly due to destruction of habitat, which for some, like Steelhead and other trout, extends well into small streams. Trees and woody debris provide valuable cover for fish and other aquatic organisms throughout the Nottawasaga. Degradation of any portion of a stream can have profound effects on living resources downstream. While the overall impact of these riparian forest corridors may be greatest in headwaters and smaller order streams, there is a clear linkage all the way to Nottawasaga Bay and Lake Huron.

A riparian buffer is land next to streams, lakes, and wetlands that is managed for perennial vegetation (grass, shrubs, and/or trees) to enhance and protect aquatic resources from adverse impacts of agricultural practices.

  • Stabilize eroding banksProblem: Eroding and collapsing banks can remove valuable agricultural land, particularly if unchecked for many years. Soil from bank erosion becomes sediment in the waterway which damages aquatic habitat; degrades drinking water quality; and fills wetlands, lakes, and reservoirs.Benefit from a buffer: Plant stems absorb the erosive force of flowing water and wave action, while roots hold soil in place.

    Effectiveness: Potentially good on small streams and lakes; poor or ineffective on large unstable streams where bank erosion is severe and rapid.

  • Filter sediment from agricultural land runoffProblem: Sediment in the waterway damages aquatic habitat; degrades drinking water quality; and fills wetlands, lakes, and reservoirs.Benefit from a buffer: Plant stems slow and disperse flow of surface runoff, and promote settling of sediment. Roots stabilize the trapped sediment and hold riparian soil in place.

    Effectiveness: Potentially good, especially for filtering larger-sized sediment such as sand, soil aggregates, and crop residue. Generally less effective for clayey sediments. Periodic removal of sediment from the buffer may be needed to sustain this benefit where sediment loads are high.

  • Filter nutrients, pesticides, and animal waste from agricultural land runoffProblem: High contaminant levels degrade drinking water quality and aquatic habitat. Specifically, nitrate and pesticides can be toxic to humans and aquatic organisms; fecal bacteria and other microbes in animal wastes can cause disease; and phosphate can promote algae blooms which suffocate fish and other aquatic organisms.

    Benefit from a buffer:
    Particulate wastes and sediment-attached contaminants are filtered along with the sediment. Uptake and transformation of soluble contaminants by plants and soil microbes is promoted by improved infiltration of surface runoff and vigorous growth of vegetation. Soluble contaminants may be similarly removed from shallow groundwater. No fertilizers, pesticides, or animal wastes are applied to the buffer zone which could be picked up by runoff. Contaminant-rich runoff from adjacent agricultural land is diluted by rainfall within the buffer zone.Effectiveness: Potentially good for particulate wastes and sediment-attached microbes, nutrients, and pesticides. Generally less effective for dissolved nutrients and pesticides, although excellent nitrate removal from shallow groundwater may be obtained under wetland conditions. Ineffective on contaminants in tile drainage water and drainage ditches that bypass the buffer. Periodic harvesting of vegetation may be required where nutrient loads are high in order to remove the nutrients it contains, maintain vigorous plant growth, and promote additional nutrient uptake. Where sediment loads are high, periodic removal of sediment build-up may help prevent formation of channels which quickly transport contaminant-rich runoff across the buffer without adequate filtering and infiltration.
  • Wildlife habitat

    Problem : Expansive Cultivated cropland may provide insufficient cover and food for upland game, songbirds, and other wildlife, especially in winter.

    Benefit from a Buffer : Perennial vegetation supplies diversity of cover and food for wildlife.

    Effectiveness : Very good for smaller animals and birds, depending on the king of vegetation. Connected stretches of buffers become wildlife corridors, greatly improving habitat for larger animals.

  • Provide shade, shelter, and food for fish and other aquatic organismsProblem: Bare, unshaded, sediment-laden channels are poor habitat for fish and other aquatic organisms.Benefit from a buffer: Shade reduces light intensity and water temperature. Plant litter as well as insects and other invertebrates on plants are food for fish. Larger plant debris and roots can form stable shelter for aquatic organisms.

    Effectiveness: Potentially good for small streams and lakes. Shade is particularly important for cold water fisheries occurring in warmer climates. Water temperature control may depend on extent of buffers within the watershed.

  • Economic products

Problem: Buffers may take land out of cultivated crop production and require additional cost to install.

Benefit from a buffer: Buffers may produce perennial crops, such as lumber and veneer, fibre, hay, nuts, fruit, and berries.

Effectiveness: Variable, depending on markets for products and additional costs associated with managing the crop.

  • Visually diversify a cropland landscape

Problem: Expansive cultivated cropland may have less visual diversity than people would like to see.

Benefit from a buffer: Strips of trees, shrubs, and perennial grasses add visual diversity to a cultivated cropland landscape. Evergreens and deciduous trees and shrubs may provide color diversity at certain times of the year.

Effectiveness: Potentially good. Depends on personal tastes.

  • Protect cropland from flood damage

Problem: Flooding caused by larger storm runoff events can erode valuable cropland, and deposit debris in fields.

Benefit from a buffer: Plant stems reduce floodwater velocity and erosive power, and block stream debris from entering cropland and pastures. Roots hold stream banks and buffer soil in place. Extensive riparian buffers in a watershed may reduce peak flood level.

Effectiveness: Potentially good, depending on the kind of vegetation used and the extent of buffers within the watershed.

Agricultural situations where a buffer should be considered:

  • Cropland, grazing land, livestock enclosures, and pasture
  • Where a landowner wants and/or needs any of the benefits a buffer can provide
  • Where an acceptable level of benefit can be derived at acceptable cost to the landowner and the general public