Forest Investment Account (FIA) - Forest Science Program
FIA Project Y073294

    Forest Management in Interior British Columbia: Moving Beyond Equivalent Cut Area
 
Project lead: Alila, Younes
Imprint: Vancouver, BC : University of British Columbia, 2007
Subject: Forest Investment Account (FIA), Forest Management, British Columbia, Interior
Series: Forest Investment Account (FIA) - Forest Science Program
Description:
Although the relation between Equivalent Cut Area (ECA) and hydro-geomorphology at the watershed scale is not well understood ECA continues to be used to constrain forest management in BC. Until this relation is understood in a quantitative manner we may be unduly restricting forest development at great cost to the industry. The urgency to understand how ECA affects hydro-geomorphology has increased with recent pine beetle epidemics and wildfires that are creating disturbances in watersheds equivalent to 100% ECA. A clear understanding of how forest disturbances affect the hydro-geomorphic regimes of a watershed is necessary if land mangers are expected to make decisions regarding optimal harvesting and sustainable forest management. Traditional long-term paired watershed studies designed to quantify the effects of forest management on hydrology are often contradictory and very few of these studies have addressed the linkages between forest management related hydrologic change and channel (geomorphic) condition. However, the most conservative results of these paired watershed studies are being used to set harvest levels and fuel debate between industry and stakeholders in many BC watersheds. Conclusions regarding forestry impacts on basin-scale hydro-geomorphology from paired watershed studies are difficult to draw from data alone, as illustrated for instance by the debate on connections between forest management and peak streamflows in the maritime region of the Pacific Northwest (Jones and Grant, 1996; Thomas and Megahan, 1998). As well, results from only one or two paired watershed studies are generally of very limited use to forest managers because the magnitude of the impact is a function of not only the physiography and climate of the particular watershed being studied but also the chosen silvicultural system and logging method, the location within the watershed where timber harvesting takes place, and road construction. Issues such as shortness of the hydro-geomorphic records and climate variability are also of concern and, not surprisingly, mixed results have been obtained regarding possible impacts of forest management on watershed hydro-geomorphology (Dunne 1998). A better understanding of cumulative effects of forest management can be accomplished by synergistically supplementing experimental results with numerical modelling (Ziemer et al., 1991). Models can alleviate some of the problems associated with traditional paired watershed studies by acting as a control to filter out effects of climate variability (Bowling et al., 2000) and are useful for linking forest management effects to controlling physical processes (Whitaker et al., 2002). Models can also be used to assess how the ability of roads to affect catchment scale storm response is related to the arrangement of road segments relative to hillslopes and stream network (Wemple and Jones, 2003). Based on these premises, UBC and BC Forest Service scientists have collaborated over the last few years on the use of distributed hydrological models to quantify the effects of forest management on streamflow in BCs experimental watersheds following an approach outlined in Alila and Beckers (2001). This approach does not require a long term data collection but uses few years of intensively monitored hydro-climatic data to calibrate a watershed model and use it subsequently to generate time series of watershed hydrologic response for alternative forest management scenarios. A proxy climate data synthetically generated to reflect the climatic characteristics of the study watershed is used as input to the watershed model. This new approach has been successfully applied in Penticton Creek and Redfish Creek in BC’s southern interior to quantify the long-term effect of forest management on hydrology. For instance, the results at Redfish Creek, a high elevation steep gradient alpine dominated catchment, indicate that the magnitude of the effects on peak flows is not correlated to ECA (Schnorbus and Alila, 2004). A 100% ECA would not increase peak flows by more than 10-15% because the effect of logging is being moderated by the alpine zone and the fact that the lower 60% of the watershed is snow free at time of the annual peak flow. In Penticton Creek, a high elevation catchment with a plateau-like topography, results indicate that 100% ECA would increase peak flows by 40%. In this case, simultaneous melt of the snowpack from all parts of the watershed synchronizes with the effect of harvesting causing larger increases in peak flows. In Penticton Creek there is a strong correlation between the magnitude of the effect on peak flows and ECA (Schnorbus et al. 2004). These studies also determined that canopy removal affects small and large peak flow events in the same way if they are dominantly generated by radiation melt. However, the effect on peak flows decreases with return period if the largest peak flows on record are major rain-on-melting snow events. These findings, which are based on a detailed process based understanding of watershed response involved in peak flow generation, validate the empirically based conjectures of MacDonald and Hoffman (1995) study in the Kootenai National Forest. Our recent research clearly indicates that in many interior watersheds that are either alpine dominated and/or have a high elevation gradient the traditional ECA constraints may be relaxed without affecting hydro-geomorphology. However, in order to widen the scope of applicability of these results to BC interior watersheds with other physiographic and climatic characteristics, we propose a replicate short term research project (i.e. that combines in synergetic ways traditional experimental analysis with innovative numerical modelling) but on a study watershed with physical and climate characteristics between those of Redfish and Penticton. In addition, with this research project we will be making the critical linkage between streamflow response and channel response. The objectives of our research project are to: (i) quantify the effects of forest management on hydrology and channel morphology in a forested, subalpine watershed that experiences both radiation and rain-on-snow driven snowmelt; and (ii) combine the results of this study with previous and future studies to gain an understanding of the influence of basin physiography including topographic relief, size, soil and vegetation attributes on hydrologic and geomorphic response. Cotton Creek, the watershed selected for this study is 22 km2, forested to the headwaters, dendritic with two main sub basins, has existing cut blocks of different age classes and proposed blocks, moderately steep hillslopes and an alluvial channel at the lower reaches. These attributes are typical of many watersheds in the Kootenays. In addition Cotton Creek, which is located in the Moyie Lake area, is an internationally significant fisheries stream in the Yahk – Moyie basin. In summary, the proposed study increases and improves our forest management tools by providing quantitative information on the relation between ECA and hydro-geomorphology in a watershed with an elevation gradient between that of Redfish (alpine) and Penticton (plateau). In addition the results of this study contribute towards our longer-term objective of understanding the influence of watershed physiography on the hydro-geomorphology of forested watersheds. This science-based quantitative information is critical to the forest industry to maintain or enhance economic viability without compromising environmental standards. In other words, this project will deliver answers to such questions as (i) how much timber can we harvest, (ii) how cut blocks should be distributed in space, and (iii) most importantly when can we go back and harvest again (i.e. after hydrologic recovery) without adversely affecting normal watershed functions. Therefore, this project will provide science based guidelines, standards, and criteria at the landscape level that will maximize timber value while minimizing the potential effects of forest practices on watershed processes in southern interior of BC. According to the recommended research topics under the “Sustainability Program” this project falls under Theme 3 “Sustainable Forest Management Indicators, Targets, and Monitoring Systems”. More specifically, this project fits well under topic 3.2 “Indicator targets and functional thresholds of sustainability” which is identified as funding priorities for 05/06 by the FSB of FSP.
Related projects:  FSP_Y051294FSP_Y062294
Contact: Alila, Younes, (604) 822-6058, younes.alila@ubc.ca

Updated August 16, 2010 

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