| Abstract/Description or Keywords |
The HyP3 Project (pronounced “hip cubed”) was initiated in 1997 to provide an integrated research approach to the study of pattern, process, and productivity in the hypermaritime forests of north coastal British Columbia. The project has four main goals: • Document the ecology of the blanket bog–upland forest complex of north coastal British Columbia. • Assess the feasibility of managing poorand low-productivity cedar–hemlock forests, which dominate the outer coastal landscape, for timber and fibre production. • Define the extent of these sites and identify the potentially operable portion. • Develop ecologically based management guidelines for these forests. The need for this research was made clear in the 1995 timber supply review for the North Coast Timber Supply Area. This report stated that the Chief Forester required better scientific information before he would consider expanding the operable land base into lower-productivity cedar-dominated (western redcedar [Thuja plicata] and yellow- cedar [Chamaecyparis nootkatensis]) forests. Research was required that would address basic ecosystem function (e.g., watershed and soil hydrology, plant and soil ecology, succession and stand dynamics) and provide practical management guidelines for these forest types. This report presents a synthesis of the HyP3 Project’s 7-year results. It provides an overview of the project to date and summarizes initial results for each of the project components—hydrology and biogeochemistry, ecosystem processes, classification and inventory, and operational trials. The report concludes with a chapter on management interpretations. Chapters 1 and 2 provide the background to the research, including a review of previous studies. These chapters also present descriptions of the north coast landscape and the specific study areas, stand types, and ecosystems targeted for the research. The geographic scope of the project encompasses the Coastal Western Hemlock zone, Very Wet Hypermaritime subzone, Central variant (CWHvh2) within the North Coast and North Island–Central Coast forest districts of the Coast Forest Region. The blanket bog–upland forest complex of the CWHvh2 contains approximately 235 000 ha of lower-productivity cedar-dominated stands that straddle the defined operability thresholds for height class, merchantable volume, and site limitations. As market values for redcedar and yellow-cedar improve, pressure increases to alter the operability thresholds. This has already begun to occur on the north coast, and because this research is now under way, preliminary management guidelines can be in place before operability pressures increase dramatically. From an ecological perspective, the outer coast of British Columbia is a fascinating landscape and a major thrust of the research is simply to gain a better ecological understanding of these hypermaritime forests and wetlands. Chapter 3 describes studies of site and watershed hydrology and biogeochemistry. Water plays a pivotal role in shaping ecosystem function on the outer coast, and thus hydrological studies are an important part of the HyP3 Project. To produce water budgets for small watersheds and predict the potential effects of timber harvesting on these water budgets, watershed-level studies included monitoring of precipitation, interception, throughfall, and streamflow. Site-level studies examined water table dynamics, hydrological linkages between sites, and natural soil drainage mechanisms such as soil pipes. Soil water chemistry across the spectrum of forest and bog ecosystems in the CWHvh2 is also characterized. Hypermaritime watersheds of the CWHvh2 have a relatively low water storage capacity. The shallow, dominantly organic, soils typical of these watersheds have high water retention capacity, and are frequently saturated in this wet climate. The small amount of available water storage capacity in these soils means that significant runoff is generated from relatively small storms. Compared with other locations, rainfall events in the CWHvh2 produce a larger hydrological response. The decrease in canopy interception after harvesting increases the amount of water received on the ground. At the HyP3 study sites, the canopy intercepted 20–25% of the average annual rainfall. If these areas are clear-cut, the amount of water requiring removal by existing hydrological processes can be expected to increase. The possible hydrological consequences of these increased water inputs include faster development and increased volume of peak flows, higher water tables, and increased erosion resulting from overland flow. Organic soils (especially on disturbed sites) have high water retention and low cohesion qualities, and therefore the possibility of increased erosion must be considered. The relatively gentle slopes on which these low-productivity forests occur, however, will result in lower surface water runoff velocities, and thus lower off-site sediment transport than on steeper hillslopes. Using the current watershed assessment procedures for road building and bridge engineering, the management of additional water to a drainage system is possible. By knowing the harvested area and the watershed’s discharge characteristics, the potential increase in peak flows can be identified and accounted for in management plans. Hydrological dynamics differ among forest types. Our study indicates that the cedar-dominated upland scrub forests (i.e., the target stands of the HyP3 Project; CWHvh2/01 sites) will likely have an onsite hydrological response to harvesting that is intermediate between the wetter swamp forests and the more productive upland forests. Water tables are likely to rise slightly depending on specific site and soil characteristics. Compared with the upland scrub forests, the true swamp forests are quite restricted in distribution on the coast. The swamps are more sensitive to harvesting-induced hydrological changes than upland forests; they should not be harvested because of their importance in receiving water and regulating streamflow within a watershed, and their greater potential for rising water tables. Where scrub forests occur on flat or very gently sloping sites, a rise in the water table following timber harvesting is expected and could have negative ecological implications. Smaller rainfall events would saturate these forest soils because of the reduced interception and transpiration following canopy removal. This may hamper regeneration and promote paludification, with the invasion of sphagnum mosses and other wetland plants. As forests regenerate, canopy interception and transpiration begin to increase again, but the time required for hydrological recovery is still uncertain in this hypermaritime environment. Long-term monitoring of current and future operational trials will help answer this question. High water tables and high levels of acidity limit nutrient availability by restricting rooting depth and maintaining anaerobic soil conditions that prevent the oxidization of nutrients to available forms. Our study shows that the highest ion concentrations in soil water occur in well-drained (productive forest) vegetation types, which have deeper water tables and thicker aerobic zones. Naturally formed soil pipes play an important role in draining forests in the hypermaritime north coast. Soil pipes transport stormflow rapidly and efficiently; however, if harvesting damages these pipes, they could become “short-circuited,” decreasing their capacity to route stormflow through the landscape. After harvesting, dissolved organic carbon (DOC) levels could increase along with the greater water inputs to a site. If DOC increases a large amount after harvesting, water quality can be affected. Some evidence from southeast Alaska suggests, however, that peatland streams are better adapted to handle an increase of DOC after harvest than the non-peatland systems. The non-peatland systems are thus more susceptible to changes in stream biology resulting from increased DOC inputs after harvest. Future operational trials in lower-productivity western redcedar–hemlock forests should include a soil water monitoring program. Such a program could better quantify changes in water table levels and DOC and ion concentrations in soil and stream waters associated with harvesting. Chapter 4 describes studies of ecosystem processes, including disturbance and ecological succession, vegetation dynamics, production and decomposition, nutrient cycling, and other aspects of soil ecology. Organic matter dynamics, including rates of forest humus and peat accumulation, is an important ecosystem process on the outer coast, where organic soil layers play a vital role in determining successional trends and site productivity. The many peatlands that characterize the coastal landscape preserve a record of past conditions in their pollen and macrofossil profiles. These profiles provide the data against which we can compare current conditions, and predict future hydrological and related ecosystem responses to natural and human-influenced disturbances. Core sampling at several sites was conducted to reconstruct historical vegetation patterns and rates of peat accumulation. Production and decomposition rates within present-day vascular plant and moss communities were measured to estimate current rates of accumulation. These studies included detailed measurements of annual sphagnum moss productivity and colonization on both disturbed and undisturbed sites. HyP3 research also included studies of bedrock, soil property, and site productivity relationships in both old-growth and second-growth stands across the spectrum of site series, from bog woodland and scrub forest to productive upland forest. From these ecosystem process studies, a simple model of ecosystem development in the CWHvh2 has emerged. In this model, three main factors operate in combination to drive ecosystem development and productivity in this hypermaritime environment: 1. bedrock geology 2. soil drainage 3. disturbance history. Although these same factors influence ecosystem development to some degree in most other terrestrial environments, their influence is especially dramatic in the CWHvh2. The scarcity of glacial till in this coastal environment highlights the importance of bedrock geology. Most soils develop directly from the weathering of bedrock or colluvial material. This contrasts with many other areas where a mantle of glacial till of mixed lithology masks the influence of bedrock. In addition, sharp contrasts in bedrock type occur on the outer coast, from the hard, slowly weathering granodiorites with relatively low amounts of available nutrient elements, to the much softer, easily weathered metamorphic rocks and limestone with more nutrientrich lithologies. These different bedrock types manifest themselves in dramatic differences in plant communities and forest productivity. Excess soil water is the rule in this hypermaritime environment, and subtle variations in slope or internal soil drainage result in significant differences in forest productivity. In contrast to the majority of other subzones in the province (where moisture deficits are common), the most freely drained sites in the CWHvh2 are the most productive sites for trees. Even these “drier” sites are fresh to moist in absolute terms, and as long as soil water is moving, rather than stagnant, tree productivity will remain moderate to high. The tendency for organic matter to accumulate on sites that have not been disturbed by landslides, windthrow, or fluvial disturbances for hundreds (or thousands) of years is also dramatic in the CWHvh2. As soil organic matter accumulates, soils become wetter and tree roots become more confined to surface organic horizons. Although the nutrient capital in these organic horizons is considerable, nutrient availability is relatively low because of the wet, acidic conditions and low rates of nitrogen mineralization. Better-drained sites, which often have a history of natural disturbance, especially where soil organic and mineral horizons are mixed, exhibit higher forest productivity. Although models are inherently simplistic, ecosystem development and forest productivity on the majority of sites on the outer coast are largely driven by bedrock geology, soil drainage, and disturbance history working in combination. The model presented in Chapter 4 can also be used to guide forest management investments and activities, and to help define and understand the limits of operability in the CWHvh2. For example, marginally productive sites occurring on metamorphic rock will exhibit higher second-growth productivity following harvesting and site treatments compared with a similar site on granodiorites. Two variations of the model are presented—one emphasizing forest productivity, and one emphasizing biomass allocation. As indicated by the soil ecology, moss productivity, and succession studies, a switch in biomass allocation from trees to mosses (and other understorey vegetation) occurs as sites paludify and tree productivity declines. Bogs and bog forests are often referred to as “low productivity.” They are, however, highly productive if one considers the annual rates of total biomass accumulation in these ecosystems. Chapter 5 presents the classification and inventory component of the HyP3 Project, which serves as the link between the hydrology and ecosystem process components and the application of results across the north coast. The project has used the Biogeoclimatic Ecosystem Classification (BEC) system as the framework to make ecologically based forest management recommendations. BEC uses the site series to classify forests for management purposes. Ecosystem classification is invaluable for choosing appropriate sites for in-depth studies, and for extrapolating the results to other similar sites on the north coast. We conducted sampling to collect baseline information on tree growth and site productivity throughout the range of forested site series in the CWHvh2. These data show that estimates of site productivity from old-growth stands significantly underestimate second-growth site potential. On CWHvh2/01 (upland scrub forest) sites, for example, western redcedar site index at breast height age 50 years, averages 18 m in second-growth stands, but estimates of 10 m or less are derived from old-growth stands. Past timber supply analyses have used the old-growth productivity estimates from the forest cover inventory database to model the growth and yield of regenerating stands. This suggests that potential yields of second-growth CWHvh2/01 sites, as well as other currently operable sites, are underestimated. HyP3 results clearly indicate that second-growth productivity of these scrub forests is high enough to consider them as potentially operable, subject to the assessment of other site limitations. At each of the HyP3 study sites, timber cruising was carried out to quantify stand structure, species composition, and gross and merchantable volume. Several forest mensuration attributes are summarized from these data for each of the CWHvh2 site series studied. Rare, or otherwise threatened or imperiled ecosystems of the CWHvh2 are also reviewed to examine the potential effects of expanding forestry operations into the lower productivity forest types. A predictive ecosystem mapping (PEM) model was developed for the outer coast. The resulting maps identify the site series most likely associated with each forest cover polygon. These maps help to establish the extent and location of potentially operable low-productivity cedar–hemlock forest types. Site series productivity data can also be combined with these maps to aid in growth and yield analysis. Chapter 6 describes the HyP3 operational research trials at Port Simpson and Oona River. The trial near Port Simpson, north of Prince Rupert, was established in 1990 to examine second-growth productivity in the poor cedar–hemlock forest type. Initially funded by South Moresby Forest Replacement Account (SMFRA) research funds, this study was taken over by the HyP3 Project in 1999. The Port Simpson trial focused on the effect of mounding on the survival and growth of planted seedlings and on some of the ecological impacts of site treatments. The Oona River operational trial is located on Porcher Island, south of Prince Rupert. This is a more expansive trial and was established in 1998 to test some of the management ideas gained from both the Port Simpson trial and the multitude of research studies undertaken on CWHvh2/01 sites around Prince Rupert. The Oona River trial examines several ecological and operational aspects of forest management activities on the low productivity cedar–hemlock sites. Results from the Port Simpson trial suggest that site preparation, including soil mixing and mounding, improves regeneration success and tree growth and nutrition on poor cedar–hemlock sites. Care must be taken, however, to avoid creating conditions (e.g., pools beside mounds) that facilitate sphagnum moss growth and paludification. Monitoring of planted and natural regeneration, as well as moss and vascular plant succession, at this site will continue into the future. Block layout, harvesting, site treatments, planting, and initial regeneration surveys are complete at the Oona River trial. Planted western redcedar survival and growth results are very encouraging and reinforce the belief that CWHvh2/01 sites have significant forest management potential. Long-term monitoring of this trial will take place to ensure that early trends continue and management interpretations remain current and realistic. Chapter 7 presents management interpretations resulting from the first 7 years of HyP3 research and operational trials. The HyP3 Project focuses primarily on the ecological and operational feasibility of sustainable forest management practices on the CWHvh2/01 sites. The economics of the operations were not examined because the value of western redcedar is quite variable, and subtle changes will significantly affect the economic viability of managing these sites. Low-productivity sites in the CWHvh2 belong primarily to the Western redcedar – Western hemlock – Salal site series (CWHvh2 /01). These sites typically have between 200 and 300 m3/ha merchantable volume. The vast majority of these sites are currently outside the operable land base. At the upper end of the productivity spectrum for these site series, soil and vegetation conditions become transitional to the Western hemlock – Sitka spruce – Lanky moss site series (CWHvh2/04), which is currently included in the operable land base (merchantable volumes typically greater than 400 m3/ha). At the lower extremes of productivity for the CWHvh2/01 site series, conditions are transitional to the Western redcedar – Yellow-cedar – Goldthread site series (CWHvh2/11), in which merchantable wood volumes (typically less than 150 m3/ha) are well below current and projected operability limits. Historical ecosystem classification data were used to develop better descriptions of these hypermaritime ecosystems, especially for the lower-productivity forest types of interest in this study. By combining this information with HyP3 Project results, we have defined a set of criteria to identify those CWHvh2/01 sites with the greatest potential for sustainable forest management. These criteria include: depth and nature of mineral and organic soil horizons, bedrock geology, overstorey and understorey composition, and stand volume. Other information, such as location and access, should be used in combination with these site factors to determine overall operability on a site-specific basis. We will further refine these operability criteria as we gain more experience in these forest types. Specific recommendations are provided on block layout, harvesting methods, site preparation treatments, and planting on CWHvh2/01 sites. Chapter 7 concludes with a summary of the future research required to further develop and test our current management recommendations for these hypermaritime ecosystems. |
