Forest Investment Account (FIA) - Forest Science Program
FIA Project M086039

    Peak flow and water yield responses to mountain pine beetle infested and salvage logged watersheds
 
Project lead: Alila, Younes (University of British Columbia)
Contributing Authors: Kuras, Piotr K.; Alila, Younes; Weiler, Markus; Winkler, Rita D.
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Description:
British Columbia (BC)ís forests cover some 60 million hectares, including 14 million hectares of operable lodgepole pine (pinus contorta), which amounts to 1.2 billion m3 of timber (FPB 2004). This proliferation of mature to over-mature pine has spawned several outbreaks of mountain pine beetle (MPB) infestation, the most recent of which started in 1994 and continues today as the largest MPB outbreak in recorded history. The current outbreak has affected about half of BCís interior pine forests, and is expected to kill up to 80% by 2013 (Westfall 2004). Concerns for water quantity, water quality, fisheries resources, and constraints to forest operations have raise questions about the impact of MPB on annual water yield, peak flows, low flows, soil moisture and groundwater levels. Answers to these questions are urgently needed as BC moves towards a large scale timber harvest salvaging strategy that is supposed to minimize economic losses while reducing the potential environmental impacts (Snetsinger 2005). There exists a great deal of literature about the effects of healthy forest and conventional timber harvesting on streamflows from process stand level (e.g. Troendle and Reuss 1997, Winkler et al. 2005), empirical paired watershed (e.g. Stednick 1996, Troendle et al. 2001) and watershed scale modelling (e.g. Schnorbus and Alila 2004, Whitaker et al. 2002, Bowling et al. 2000, Waichler et al. 2005) studies. In the interior pine forest of BC, the winter snow accumulation and spring melt drive the snow dominated hydrologic regime, which in turn is substantially controlled by processes such as canopy interception, evaporation, tree transpiration, melt and groundwater storage. The effects of beetle-kill on these processes, with or without salvage harvesting, is largely unknown and may or may not mimic that of conventional timber harvesting of similar size and extent (Uunilla et al. 2006). Since dead trees do not transpire, the effects of beetle-killed and newly harvested stands on transpiration processes may be the same; however the effects of beetle-kill on interception and melt processes may be different. After beetle attack, trees retain their needles for 2 to 4 years and retain branches and stay standing for many more years. This can potentially affect forest regeneration. Furthermore, beetle-killed stands may retain live understorey vegetation and are not necessarily impacted by road developments, unlike conventional harvested stands. Only few paired watershed studies on the effect of insect infestation (Mitchell and Love 1973, Bethlahmy 1975, Potts 1984) and two others on the effect of salvage harvesting (Cheng 1989 and Moore and Scott 2005) on streamflow characteristics have been reported in the literature. However, the level of disturbance reported in these studies does not exceed 35% of the whole watershed and therefore are not large enough to be of relevance to the larger scale disturbance (i.e. over an entire watershed) questions raised in this study. Only one infested forest stand level investigation had been reported in the literature from the Rocky Mountain of Colorado by Schmid et al. (1991). Their findings indicated that net precipitation under recently infested stands (few years after infestation before trees loosing their needles, so called brown attack) is not significantly different from its respective controls. The authors explained the possible reasons for these findings by the needle retentions of beetle-killed trees and the presence of a young and live understorey that has the potential for mitigating the effects of the beetle-kill. They also suggested that analogues between conventional partial cuts of healthy and beetle-killed forests may be valid, but only in even-aged stands (i.e. without significant understorey) and only after beetle-killed trees have begun to lose their needles. We are not aware of any published study on the so called grey stand (i.e. after the infested stands lose their needles). It is tempting to draw analogues, albeit in an opportunistic ways, between infested (defoliated) conifer stands and healthy (leafless) deciduous stands to take advantage of the wealth of knowledge in the literature on stand level processes in deciduous forest (e.g. Hardy et al. 1998). However, while the forest canopy architecture (tree elements and gaps) of the two forest stands may lead to similar interception and melt processes they would certainly be different in transpiration and its subsequent effects on soil moisture. The effects of forest and forest management on watershed scale functions, such as streamflow, had traditionally been investigated using the paired watershed approach. One of the fundamental conditions in paired watershed studies is that the disturbed (treatment) and undisturbed (control) catchments must be similar in climate and physiography. This condition is better achieved over small catchments, and therefore, a paired watershed approach is a less reliable for studying forest disturbances over larger catchments. A more suitable method is to synergistically supplement experimental results with modelling (Ziemer et al. 1991). A hydrologic model alleviates problems associated with paired watershed studies by acting as a control to filter out the effects of climatic spatial and temporal variability, allows the same watershed to act as its own control, and is useful for integrating stand-level information into a physically or conceptually reasonable description of basin response to forest disturbances. In recent years, and with the advances in computing power, Geographic Information System (GIS), Global Positioning System (GPS), and digital photography technologies, the use of models to quantify the effects of forest management on hydrology has intensified, particularly at heavily instrumented experimental watersheds (Whitaker et al. 2002, Whitaker et al. 2003, Beckers and Alila 2004, Thyer et al. 2004, Schnorbus and Alila 2004a, Bowling et al. 2000, Leung and Wigmosta 1999, Waichler et al. 2005). A numerical modelling approach doesnít require the expensive long-term data collection exercise of a paired watershed study. It uses a shorter period of extensively monitored hydro-climate data to develop and calibrate watershed model applications and uses them subsequently in a long-term simulation exercise to generate time series of watershed hydrologic response for alternative forest disturbance scenarios (Schnorbus and Alila 2004b). We propose in this project a combined field and modelling approach at the already well established and long-standing experimental watersheds in the interior of British Columbia to address four research questions related to streamflows: 1. What would be the effects of leaving the trees to die on the water yield and peak flow regimes (watershed scale hydrologic function)? 2. What would be the effects of total clearcut salvage logging with no retention on the water yield and peak flow regime? 3. What would be the effects of salvage logging with retention in the case of an even-aged and a multi-storied uneven-aged infested forest? 4. How is the magnitude of the impact of MPB infestation and treatment strategies on water yield and peak flow, from questions 1 to 3, affected by physiographic characteristics of the watershed? Our research methods in this project build, and draw heavily, on the experience we have gained over the last decade in experimenting with and applying the distributed physically based hydrologic model called DHSVM of Wigmosta et al. (1994) in scenario analyses at the already well established and long standing experimental watersheds in the interior of BC (namely the Upper Penticton Watershed Experiment in the Okanagan (Thyer et al. 2004), Redfish and Cotton Creek Experimental Watersheds in the Kootenays (Whitaker et al. 2003 and 2002, Schnorbus and Alila 2004a and 2004b), and Carnation Creek Watershed (Beckers and Alila 2004).

    Deliverables:

Extension Note (0.2Mb)
Peak Flow Presentation (2.8Mb)
Forest Road and Harvesting Impacts...(Abstract) (70Kb)

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Updated August 16, 2010 

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