Northern Watershed Project (Report 1). Paradigms for Ecological Management and Practices in Alberta.
Philip Lee and Cheryl Smyth
This report reviewed the qualitative and quantitative data dealing with the ecological retention of treed riparian buffers in timber harvest cutblocks. The review focused primarily on the Boreal and Rocky Mountain ecoregions with applications to Alberta. Studies outside of the Boreal or Rocky Mountain were considered when demonstrating broader concepts or when data was not available for these regions. The report was organized into nine sections with two appendices, but deals with four major issues:
1) defining riparian areas,
2) qualitative and quantitative review for the ecological-basis of riparian buffers,
3) quantitative review of management guidelines for riparian buffers, and
4) natural disturbance-succession model (based on wildfires) for management of riparian.
Definitions for riparian areas reflect their use in administrative or discipline settings. The primary difficulty in defining riparian areas for management is clearly translating the changes in multiple functions, structures, and biota along the gradient, i.e. ecotone, from aquatic to terrestrial upland into administrative boundaries. Currently, the most widely accepted definition is based on a probabilistic delineation. Areas closer to the water’s edge are more likely to be riparian. This definition implies that a hard boundary based on a single criterium may not be appropriate. Rather, impacts should be assessed for their effects across the entire gradient. This definition implies a transverse view of riparian areas moving from aquatic to upland. Longitudinal, i.e. downstream and upstream, and vertical aspects of the riparian are being currently studied but are less well-developed in terms of both conceptual or management models.
A review of the ecological-basis for riparian buffers suggest that their original purpose in preventing pollution and nutrient inputs, and sedimentation and erosion may have given way to provision of aquatic and terrestrial habitat. Buffers are relatively ineffective at mitigating increases in water yield, peak flows, and nutrient yields immediately after disturbance. These are catchment-level effects and are a function of the overall proportion of disturbance in the catchment. Buffers are effective for the reduction of sediment flows into waterbodies from overland flows created by disturbance of the forest floor. They are less effective for sediment transport by channelized flow. Current harvest practices that minimize soil disturbance particularly in low gradient boreal forests may forego the need for wide buffers. At present, most of the sediment transport from harvesting occurs from skid trails, landing areas, and roads.
For aquatic biota and habitats, shade from riparian canopy cover and inputs of allochthonous organic debris into streams are likely the factors that will be most affected by harvesting of treed buffers. In other forested systems, buffer widths of a single tree length (20 - 30 m) were recommended to maintain these features. Western boreal systems lack sufficient short- and long-term X data to evaluate the modification of riparian areas on both water temperature and organic inputs and their subsequent effects on invertebrates and fish communities.
Buffer recommendations for terrestrial biota range from the tens to hundreds of metres wide. However, the current objectives for maintaining terrestrial habitat and biota within riparian buffers after harvest are unclear. Use of riparian buffers can vary from temporary cover in order to prevent cutblock avoidance after harvest to core habitat for long-term sustainability of population. Larger riparian areas are likely required for temporary refugia that will re-colonize disturbed areas or core habitat for long-term population maintenance. Further complicating this issue is our lack of knowledge of which species need the combination of trees and proximity to water as a critical component of their life history. Most of the current research is based on presence/absence data and/or relative density data. Though habitat use can be implied from either data type, the use of buffers as dispersal corridors, temporary refugia, or core habitat cannot. Riparian management plans should contain clear objectives for the maintenance of species. The appropriate use of buffers in combination with upland areas should be used to attain these objectives. Research should be based on these objectives.
The retention of treed riparian buffers in Canada and the United States is the primary management tool applied throughout all reviewed provincial and state jurisdictions (N=60). Canadian jurisdictions have wider riparian buffers for small and large permanent streams, small and large lakes, and water sources than jurisdictions in the United States. Riparian management areas from Boreal jurisdictions are generally wider than all other regions. Rocky Mountain jurisdictions were intermediate in width. Alberta’s riparian buffer widths are comparable or wider than most other jurisdictions for all waterbodies except intermittent streams.
Most jurisdictions use at least one modifying factor to stratify riparian areas. The most common modifying factors were (ordered form highest to lowest); waterbody type, slope, waterbody size, fishbearing, human water supplies/aesthetics, drainage basin area, shoreline forest management, saltwater flow, shoreline vegetation, upstream of fishbearing waters, downstream sediment threat, and flow rates. Jurisdictions that do not have specific guidelines for modifiers (e.g. slope, presence of fish, and human drinking water) usually have wider baseline buffers than jurisdictions with specific guidelines.
Alberta’s guidelines are relatively simple, mostly focusing on waterbody type (e.g. streams, lakes) and size (e.g. channel width). Alberta’s buffer widths on large streams, small streams, non-fishbearing and fishbearing lakes are wider than other jurisdictions with specific modifiers for presence of fish, human consumption of water, and slope. Most other Boreal jurisdictions have presence of fish as a modifier while Rocky Mountain jurisdictions have presence of fish and slope as modifiers. However, most of the riparian buffers in Alberta areas are equivalent to jurisdictions with modifiers. For Alberta’s riparian guidelines the width of the management area associated with wetlands are poorly developed compared to some other jurisdictions.
Also, Alberta should clarify the criteria requirements for buffers on intermittent streams.
A relatively high percentage of jurisdictions (>80%) permit selective harvest within riparian management areas. Usual rates of harvest were less than 50% of merchantable trees usually with size restrictions to prevent “hi-grade” harvesting, i.e. selection of largest trees. Restrictions were also placed on shoreline harvesting and opening sizes. In many forest types, regeneration of tree species in riparian areas is a problem because of competition with shrubs or grasses.
Given the review of ecological data and guidelines for other jurisdictions, there appears to be no great urgency for changes in the current guidelines. However, there are some long-term changes that may be worth considering (in no particular order):
1. Widths for lakes are larger than other jurisdictions. At these widths, their objectives as habitat for terrestrial biota should be made clear.
2. Further development of riparian management objectives and practices for wetlands and intermittent streams should be considered.
3. Selective riparian harvest should be approached cautiously with an assessment of regeneration problems in riparian areas and changes to terrestrial habitat and biota.
4. Assessment of longitudinal, i.e. upstream and downstream, effects of management actions and incorporation into guidelines, i.e. cumulative watershed approach.
The previous three parts underscores a preservation-protection paradigm attached to the management of riparian areas. Human-caused disturbances in upland areas are to be isolated from the aquatic ecosystem. This traditional management philosophy views treed buffers as an important tool in protecting the riparian ecotone from forestry operations.
An alternative management philosophy argues disturbance-succession as a part of the temporal and spatial dynamics associated with forested landscapes and that riparian zones and aquatic ecosystems are part of those dynamics. For most forest regions in Alberta, this means using the dynamic patterns set by a natural disturbance-succession such as wildfire to set the range of variation for human disturbances such as timber harvest. Under this approach, timber harvest would operate within the dynamic range as natural disturbance-succession. The resultant landscape patterns and dynamics would be similar to natural patterns and dynamics, hence, it would be assumed to maintain natural habitats and biota.
In order to further understand the implications of a disturbance-succession model for riparian management, a single watershed was examined as a case study. We selected the Notikewin River and Rambling Creek watersheds which burned in 1982. The natural disturbance-succession pattern, as measured by the amount of residual or unburned forest, varied with stream type.
Basing riparian management on a natural disturbance-succession model would be quite different than Alberta’s current 1994 guidelines. These differences include: a) removal of streamside forest around large permanent and small permanent streams, b) retention of streamside forest around some intermittent streams, c) retention of forest at distance from stream (i.e. upland) exceeding current buffer distances including large polygon-sized patches, and d) integration of green tree retention patterns between riparian and upland areas.
Further research is required to assess the economic, social, and ecological impacts of using a natural disturbance-succession model for riparian management. Despite being able to produce a similar landscape pattern, there are significant differences in many other aspects of wildfire ecology and timber harvest. These include; deadwood resources, understory communities, soil properties, erosion and sedimentation patterns and nutrient flows. It remains unclear whether similarities in landscape-level patterns retain the sufficient benefits to outweigh differences at the stand-level between wildfire and harvest. Also, it is unclear whether alternative landscape planning scenarios based on other criteria such as old growth or targeted species groups produce more ecologically sustainable landscapes. The lack of clear objectives on the range of acceptable variability and alternative models makes large-scale implementation of the disturbance-succession model unwarranted at this time. For these reasons, we recommend continued exploration and comparison of natural disturbance-succession through sitespecific modeling leading to active adaptive management in the field through pilot projects.