INTRODUCTION
Next to mountains, water is the predominant feature of BC's geography. The ocean, lakes, rivers and wetlands are significant forces of change and diversity across the landscape of the province. The interaction between the water environment and the terrestrial surroundings is profound for both ecosystems.
Where land and aquatic ecosystems meet, the area of influence is called a riparian ecosystem or zone. The name comes from the Latin word Ripa - meaning bank or shore. These zones provide habitat for many species of fish, wildlife, plants and other organisms such as frogs and salamanders. Such areas create important links between land and water based ecologies. The influence of the water on the land is as significant as the influence of the land on the water.
Riparian areas are rich in plant and animal diversity and are sensitive to disturbance. The effects of development, agriculture, road building or forestry can be detrimental to both the aquatic and shore ecosystems. In this article we will be exploring the biological and physical nature of riparian ecosystems, how forestry can impact these zones and what measures are being taken to conserve and manage these special areas.
RIPARIAN ECOSYSTEMS
Our society treasures the many values produced by riparian ecosystems, such as drinking water, fish and wildlife habitat and recreational opportunities. In British Columbia the goal is to manage these ecosystems sustainably. This requires sound ecological knowledge. The nature of riparian ecosystems is complex. These ecosystems have both aquatic and land components with intricate connections between the two. Streams have characteristics that control the level of water quality and fish habitat, but the land also has strong influences on these processes. In turn, the land near streams is strongly affected by the aquatic environment. For example, soil productivity, shaped in part by water processes, will direct the plant and animal communities that develop.
Stream Characteristics
Every stream has a set of characteristics based on the nature of its streambed, the shape of its channel, its gradient and the quality of its water. Under certain conditions, these characteristics will produce important products like fish habitat and domestic water supply. There are a number of physical and chemical processes that affect these features, and therefore the products they produce. Many of the processes that can alter stream attributes are linked to changes in the watershed that a stream drains. There are 4 key processes explored below.
Water flow is one of these stream processes. The flow rates will change naturally through the seasons with rainfall and snowmelt. Flowing water moves both rock and sediment, and so the character of the stream will change as the rates change. Faster flows can carry larger rocks and so cause greater erosion of stream banks. Faster flows can also remove large logs or woody debris that would otherwise have provided important fish habitat.
Sedimentation is another stream process. The amount of sediment coming from the watershed into a stream will vary with rainfall and snow melt as well. An increase in the sediment supply can cause streams to become wider and shallower. Sediments can also cover the gravel required for spawning or cause a reduction in oxygenation of the stream leading to the suffocation of fish eggs.
A third stream process is water temperature. Water flow and amounts of shade affect the water temperature. Slower flows expose the water to more heating, affecting salmon which require cold water. Shading from streamside vegetation is an important factor in keeping water temperatures low.
Another important process is chemical inputs. The chemistry of the water depends on materials brought into the stream from rain, snow, weathering of rock and nutrients from plants and animals. In developed watersheds, the chemicals in fertilizers, pesticides, and sewage are unwanted additions. Streamside vegetation can act as a filter for some of this material.
Flow rates, sedimentation, water temperatures and chemical/nutrient input are all processes that define and control the character of a stream. All four of these processes are affected by both natural and human disturbances within the watershed. Urban development, agriculture, logging or road building can influence these processes dramatically, leading to changes in stream characteristics. Further, since streams feed lakes and estuaries, the quality of these water resources is also related to these stream characteristics. Any changes to the stream will directly affect the quality of fish habitat and drinking water produced.
The lands influence on the water
The strips of land next to streams, lakes and wetlands provide a number of important functions in regards to water quality and fish habitat. The shore vegetation plays a significant role in influencing stream flows, sedimentation, water temperature and chemical inputs. Overhanging plants and trees directly link with fish habitat through the various inputs into the water system.
The vegetation in these riparian areas is critical for enhancing water quality. The roots of the plants help to stabilize the stream bank, reducing erosion and therefore sedimentation. The vegetation also acts as a filter, removing sediments and cleansing runoff water before it enters the stream. The forest canopy intercepts rain and snow, helping to control water flow at peak times and slowing the erosion of soil from rainfall. Vegetation can also modify stream flow more directly. For example, the occasional tree falling into a stream acts to slow water flows and reduce erosion. Shade production from trees and shrubs help modify water temperature. Vegetation's direct connection to water quality makes it a key factor in producing both drinking water and fish habitat.
Water quality is one key factor necessary for good fish habitat. Some of the other factors required come from streamside vegetation. Insects and other organic debris that fall into streams from overhanging branches are important food sources. Shade from these trees helps to keep water temperatures cool in the summer and warmer in the winter. Fallen trees form pools and areas for fish to rest and hide.
The water's influence on the land
The presence of rivers and streams exert a strong influence on the character of the forest ecosystem and thus shapes the wildlife habitat and recreational opportunities that ensue. Streams contribute to the development of the soil, which shapes the plant communities and the resulting wildlife habitat. The overall aesthetics or ambiance that arises in these riparian areas produces a range of recreation opportunities.
Streams are directly involved in the controlling the levels of the soil moisture and nutrients in riparian areas. Land near rivers and floodplains has an abundant source of moisture. Recurring floods deposit silts and sands, which contain nutrients to enrich the soil. The fluctuating water table provides sub-surface irrigation for root systems. This rich soil and abundant moisture provides excellent growing conditions for many plants. The richness of these riparian zones is clear when comparing the great height and size of floodplain red cedar or Sitka spruce to the smaller trees grown in upland conditions. Due to the highly productive growing conditions produced by this land-water interaction, riparian areas frequently contain the highest number of plant species in the forest.
The rich plant communities found in riparian areas provides a wide range of food and shelter opportunities for animals. Not surprisingly, riparian areas have a higher number of animal species than anywhere else in the natural forest. Wildlife trees are often more abundant in these zones. These dead or deformed trees are important for more than ninety species of birds, mammals and amphibians in British Columbia. The presence of so many key habitat components such as drinking water, the variety of structure provided by wildlife trees and a rich, diverse plant community make these crucial areas for wildlife management.
Riparian ecosystems contain a very high percentage of the non-timber resources found in the forest. Ecologically they provide fish and wildlife habitat and so are important for biodiversity. Riparian areas also provide a crucial linkage throughout the forest landscape. They connect hilltops and valley bottoms. This ecological network is important for animal movement, and serves as a repository for plants. For people these areas often hold a high value for recreation and can be important aesthetically for viewscapes.
Understanding the complexity of riparian ecosystems is the first step in sustainable management. The stream processes and all of the land-water influences that characterize riparian areas are sensitive to disturbance. Once the natural connections are understood, the impacts of disturbances such as forestry can be evaluated and steps can be taken to protect and manage these special ecosystems.
FORESTRY IMPACTS ON RIPARIAN ECOSYSTEMS
The complex interactions between water and land processes create the productive and diverse biology found in riparian ecosystems. This high level of productivity is also attractive in terms of logging, as the trees are often larger and more valuable. As well, the flat land occurring where streams meet lakes or the ocean makes logging easier and cheaper. These facts explain why, historically, riparian areas were often the first places logged. Unfortunately, riparian areas are very sensitive to any activity that impacts the soil or vegetation in a watershed. Forestry activities can have dramatically negative effects on both of these elements and therefore, on the associated streams. Forest practices that result in soil disturbance, windthrow, logging debris and the removal of streamside vegetation must be examined. The key to avoiding damage is to develop a clear understanding of how forestry activities affect the function of and processes in these ecosystems.
Erosion
Stream banks are sensitive to erosion. Large heavy machines crossing banks or dragging logs increases erosion and sedimentation. Poor road building and maintenance can also lead to gully formation and erosion. The steeper the slope, the more severe the erosion and ensuing sedimentation problem. Improper use of skidders and other heavy machines can lead to accelerated surface erosion, sedimentation and changes to the timing of peak water flows.
Debris and Windthrow
Logging can produce large amounts of debris such as bark, branches and rotten logs. Although debris does play a role in nutrient recycling, it can cause serious problems for streams. Too much debris can make fish passage difficult and in some cases can act as a dam. Windthrow, or uprooting of trees by the wind, can occur as a result of logging. The removal of trees changes the wind's patterns and force on remaining trees. Windthrow into a stream can be beneficial, as streams need large woody debris to help form pools and resting places for fish. However, too much windthrow acts the same as debris, choking the stream and making fish passage impossible.
Loss of Vegetation
Removing streamside vegetation will affect stream bank stability as well as increase water temperatures and sedimentation. Without a streamside forest, there will be no future logs to form pools and rest spots for fish. Removal of the riparian vegetation will obviously have a dramatic effect on the plant and animal habitat and ecological connectivity for a number of years.
Understanding the linkages between forestry practices and detrimental results such as erosion, debris and windthrow is step one in damage prevention. Evaluating various practices based on their impact on riparian areas will lead to new procedures. The goal is to ensure that forestry practices plan for these special areas and find new ways to work sustainably in and around riparian ecosystems.
PROTECTING AND MANAGING RIPARIAN AREAS
In British Columbia the regulations in the Forest Practices Code (1996) govern all aspects of forest management including managing riparian areas. The goal of the code is to ensure that the management of all forest resources is sustainable. This includes conserving biological diversity, soil, wildlife, water and fish. The regulations and guidebooks concerning riparian areas are comprehensive. The planning strategy for protecting and managing riparian areas includes stream classification, the assignment of special management areas and reserves which restrict forest practices, and modifications to forest practices in order to meet riparian protection goals.
Stream Classification / Riparian Management Areas
In order to do any planning around streams and riparian areas, information needs to be gathered about each stream. Inventory crews find each stream, map it, take measurements and carry out a fish inventory. Once data is collected the stream can be classified. The purpose of classifying is to define important areas that require special treatment. There are 6 stream riparian classes based on the
- presence of fish,
- occurrence in a community watershed
- average channel width
As stream characteristics vary greatly over their course, one stream will often have different classifications for different sections or reaches.
Lakes and wetlands are also classified. Management levels will vary based on this classification, with critical areas receiving more protection. For example, fish and community watershed streams will have more restrictions to logging activities than the other classes. This means that the initial classification is a critical process that will determine the level of future forestry practices for each area.
The next step is to establish a Riparian Management Area (RMA) along rivers, streams, lakeshores and the margins of wetlands. The goal of these Riparian Management Areas is to minimize the impact of forest practices on stream characteristics, water quality and fish and wildlife habitat. Within these zones there will be constraints to forest practices. Some of these RMA's will also include a reserve zone immediately adjacent to the stream, which is basically a no harvest area. The RMA size, and the presence of a reserve zone, varies with the level of class assigned.
The planning process starts with the gathering of data, followed by the classification of streams and then the delineation of RMA's and reserves. The process continues with the identification of any other sensitive zones which are critical for fisheries, such as side channels, swamps and estuaries. Further, there is also the identification of habitat components crucial to fish and wildlife, such as coarse woody debris and wildlife trees. These key ecological factors are identified and protected in the various levels of planning.
Changes to Forest Practices
Forest practices have evolved over time as silvicultural and ecological knowledge has expanded. Working within the constraints of a Riparian Management Area requires further modification to standard practices in order to avoid the negative impacts that some practices can produce in these sensitive areas (see above section on Forestry Impacts). The forest practices within the RMA should be designed to
- retain vegetation along the banks in order to provide shade, maintain channel and bank stability, provide coarse woody debris and retain any attributes important to wildlife, and
- reduce the risk of windthrow to the reserve zone and avoid depositing debris into the stream
The main activities that require modified practices are road building, harvesting, and silvicultural practices. There are strict guidelines governing these practices within RMA's.
Road building has been responsible for the majority of stream damage caused from forestry practices. In order to minimize impacts, there are now clear guidelines for the building of roads within the RMA. Such guidelines include narrower road widths, end hauling (removing any excavated material from the roadside), and deactivating (or unbuilding) roads after harvest. Regulations for temporary or permanent stream crossings now consider fish habitat, fish life histories and passage. After harvest is complete, all temporary structures must be removed, stream-bank armouring must be completed (if required), and streamside vegetation must be re-established. There are no road building activities within a reserve zone.
Harvesting practices within RMA's are designed to avoid erosion and debris problems.
All falling and yarding should be away from or parallel to the stream or lake. This will prevents any logs from hitting or dragging across the bank. This procedure protects the stream-bank and any natural large woody debris structures in the channel.
Designing harvests with patches of trees retained or using selective harvesting practices are more common today, especially in RMA's. Reserves may exclude harvesting altogether.
Any silvicultural work such as site preparation, forest health or weeding treatments must limit ground and vegetation disturbance and maintain natural levels of woody debris. Woody debris plays an essential role in nutrient cycling, animal habitat and stream structure. "Brush free" requirements for conifer growth are generally waived for streamside areas to avoid any weed control methods using herbicides.
SUMMARY
The record of fish / forestry interactions in British Columbia has been poor. Erosion and degradation of fish streams has occurred for a variety of reasons. Over the years increasing public and political concern as well as increased knowledge has led to changes in regulations and attitudes. The intrinsic value of these areas is now acknowledged and respected. Research into riparian ecology and management has provided essential knowledge in understanding these critical areas. Improved inventory data collection and the development of new harvesting and silvicultural techniques have also added to the evolution of new management systems for riparian areas.
References
- Olympic National Forests Web Site
Stream Processes - Ministry of Forests Website:
Protecting BC's Rivers
Riparian Management Area Guidebook Forest Development Plan Guidebook Fish- Stream Identification Guidebook Guidebook Summary Coast Watershed Assessment Gully Assessment Procedures