Forest hydrology: the Canadian experience

Transcription

1 Forest hydrology: the Canadian experience Jim Buttle Department of Geography Trent University, Peterborough, ON

2 Review builds on themes addressed in an earlier review of advances in Canadian forest hydrology (Buttle JM, Creed IF, Moore RD Canadian Water Resources Journal 34: ) Addressed several major issues: 1. Hydrological processes in forest landscapes under natural conditions i. Classification of hydrologic systems ii. Development of hydrology datasets iii. Linkage of hydrologic classification schemes to prediction of system behaviour 2. Hydrological processes in forest landscapes under disturbed conditions i. Emulation of natural disturbance ii. Response to forest management practices iii. Response to natural disturbance and consequent forest management 3. Hydrologic recovery 4. Hydrologic resistance and resilience

3 Classification of hydrologic systems Classification of forest basins in North America using the Budyko framework Creed IF et al. Global Change Biology 20: Examination of effects of climate warming on partitioning of annual P into ET and water yield

4 EI = evaporative index (AET/P) DI = dryness index (PET/P) Blue: cool period; red: subsequent warm period s = static deviation: difference between measured and theoretical evaporative index during cool period d = dynamic deviation: difference between measured and theoretical evaporative index during warm period, following correction for s e = elasticity = range in DI/(max EI residual min EI residual) e > 1 = high elasticity (approximating what Budyko relationship predicts should occur) e < 1 = low elasticity (deviating from what Budyko relationship predicts should occur)

5 Response to forest management practices Harvesting impacts on peak streamflow Effects of forest management practices on snow accumulation and snowmelt Of considerable interest, since most of Canada s forest landscapes experience seasonal snow cover

6 Harvesting impacts on peak streamflow: boreal forest, QC Based on assumption that 50% increase in Q bankfull can significantly modify stream morphology Tested hypothesis that clearcutting < 50% of basin can avoid such increases Also tested hypothesis that clearcutting near stream network (e.g. within riparian buffer) will have greater impact on peak flows than harvesting comparable distal areas Tremblay Y et al Journal of Hydrology 352:

7 Post-treatment regression line Pre-treatment regression line Pre-treatment Q bankfull Non-significant peak-flow increases Q bankfull changes < 50% Greater absolute changes in peak flows for larger flows Harvesting near stream network did not appear to have greater influence on peak flows than harvesting in distal areas of basin

8 Desynchronization of snowmelt: aspect Effects of gap thinning treatments on desynchronization of snowmelt in Rocky Mountain basin (Marmot Cr), southwestern Alberta Forest cover synchronizes melt, regardless of aspect Thinning accelerated snowmelt on south facing slopes primarily through enhanced shortwave radiation, but retarded snowmelt on north facing slopes primarily through reduced incoming longwave radiation Ellis CR et al Water Resources Research 49:

9 Desynchronization of snowmelt: elevation H60 - elevation of the snowline when upper 60% of basin is covered with snow Forest harvesting above H60 generally believed to yield more pronounced impacts on peak flows or high flows in the BC interior 60% of forest harvesting in Willow distributed above H60 only 30% of forest harvesting occurred above H60 in Bowron de-synchronization effects on snowmelt and peak flows expected in Bowron (low-elevation melt precedes high-elevation melt) more synchronization of snowmelt in Willow (greater coincidence between low- and high-elevation melt contributes to less pronounced responses in peak flows to forest harvesting in Bowron relative to Willow Zhang M, Wei X Hydrological Processes 28:

10 Response to natural disturbance and consequent forest management 1. Wildfire Increases of 74% - 118% in wildfire season length, fire severity and area burned in Canadian forests by end of the century (Flannigan et al. 2005) Effects on peak flows, fluxes of suspended sediment and dissolved organic carbon Latter two of particular concern where forested basins serve as source water areas for downstream drinking water supplies (e.g. southern Alberta) 2. Infestation (mountain pine beetle, Dendroctonus ponderosae) Killed more than 9 million ha of pine forest in BC as of 2009 Scenarios predict that 75% of pine forest will be dead by 2015 Response of forest industry in BC: salvage harvest as much timber as possible before it becomes commercially unusable > 50% of forested area in some basins may be logged in future

11 Wildfire Lost Creek fire, 2003 Silins U et al Catena 79:

12 MPB, Fraser R basin, BC Proportion of m cell dominated by saturation overland flow Proportion of m cell dominated by lateral subsurface flow Carver M et al Mountain Pine Beetle Working Paper Natural Resources Canada, Canadian Forest Service, Victoria, BC, 35 p.

13 All pine trees die from MPB attack, no salvage harvesting; change relative to baseline All pine trees die from MPB attack, complete clearcut salvage harvesting of all pine trees; change relative to baseline Carver M et al Mountain Pine Beetle Working Paper Natural Resources Canada, Canadian Forest Service, Victoria, BC, 35 p.

14 Hydrologic recovery Recovery of range of processes (e.g. snow accumulation & melt) at stand scale as well as streamflow at basin scale following disturbance and revegetation (Hudson 2000) White spruce White spruce Hydrologic recovery (%) Hydrologic recovery (%) Maximum height of main canopy (m) Maximum age of main canopy (y) Zhang M, Wei X Hydrological Processes 28: Focus on counter-intuitive outcomes

15 Suspended sediment yield (t km -2 y -1 ) Years following wildfire Reneau et al. (2007) Sheridan et al. (2007) Sheridan et al. (2007) Sheridan et al. (2007) Owens et al. (2013): increased sediment fluxes 3-5 years after wildfire in central BC due to bank erosion and channel migration attributed to loss of root strength and cohesion were able to observe this response in part because of absence of a major driving (precipitation) event during window of disturbance generally-expected pattern of recovery: peak yield following wildfire if major driving (precipitation) event occurs during window of disturbance (Prosser and Williams 1998) decline in suspended sediment yield with recovery of vegetation cover Suspended sediment yield (t km -2 y -1 ) Years following wildfire Reneau et al. (2007) Sheridan et al. (2007) Sheridan et al. (2007) Sheridan et al. (2007) Owens et al. (2013)

16 Lower value of equivalent clearcut area indicates greater hydrologic recovery Clearcut salvage harvesting and planting results in greatest increase in equivalent clearcut area and quickest recovery Full retention of dead stand shows the lowest maximum equivalent clearcut area, but the most prolonged full recovery Greater disturbance to promote faster recovery? Redding et al BC Journal of Ecosystems and Management 9:33 50 (adapted from Huggard and Lewis 2007)

17 Hydrologic resistance and resilience Hydrologic resistance: degree to which runoff is coupled/synchronized with precipitation (Carey et al. HP 2010) Basins that can store water over long time periods (months or years) and release water gradually to the stream have a high resistance, whereas basins that systematically transfer precipitation into discharge have low resistance Hydrological resilience retention of similar form and function under environmental and human pressures (Creed et al. HP 2011) Degree to which a basin can adjust to normal functioning following perturbations from events such as drought or extreme precipitation (Carey et al. HP 2010) Mark Green (Plymouth State U): emphasizes that resilient basins can maintain or quickly regain their hydrologic function following perturbation Carey et al. (2010) hypothesized that basins with high resilience are able to sustain their expected precipitation discharge relations in light of changing inputs, whereas basins with low resilience are sensitive to changes in inputs and exhibit enhanced threshold response behaviour

18 Hydrologic resistance and resilience; Marmot Cr, southwestern Alberta Lower forest snowcourse Alpine snowcourse Harder P et al Hydrological Processes 29:

19 Hydrologic resistance and resilience; Marmot Cr, southwestern Alberta Resilience due to subsurface storage? Harder P et al Hydrological Processes 29:

20 Hydrologic resistance and resilience Feel that there is great potential to incorporate these concepts in our analysis of hydrologic response to natural and human-induced changes in forest landscapes in Canada May assist in understanding why some basins experience marked response to forest disturbance while others show no-or-muted to the same type and intensity of disturbance A major challenge is coming up with metrics that reflect the active component of basin storage