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Peak flow and water yield responses to mountain pine beetle infested and salvage logged watersheds
Kuras, Piotr K.
British Columbia (BC)?s 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 BC?s 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). ...
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Peak Flow Presentation
Forest Road and Harvesting Impacts...(Abstract)

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