Effects of Alternative Forest Harvesting Strategies on Snowpack Dynamics and Seasonal Soil Moisture Storage in Alberta's Mountain Headwaters

• Author / Creator

  Greenacre, Daniel

• Snowpack accumulation and melt dynamics, and soil moisture storage (SMS) play a critical role in regulating stressed regional water supplies in the southern Alberta Rockies. However, these processes are sensitive to impacts from forest cover losses by timber harvesting and associated land disturbance. While numerous studies have investigated effects of clearcut harvesting, few studies have evaluated the comparative effects of alternative forest-harvesting methods on spatial and temporal snowpack accumulation-melt and subsequent growing season soil moisture dynamics, resulting in a knowledge gap about how current alternative or new/novel strategies influence these key hydrological processes. Spatio-temporal patterns of snowpack accumulation/melt and SMS were assessed from 2016-2018 in the three sub-watersheds located in the Crowsnest Pass, Alberta that were harvested using three different forest-harvesting strategies (clear-cut with tree retention, strip-shelterwood, and partial cut harvesting). Snowpack and SMS were measured in each harvest and adjacent undisturbed forest stands using a series of linear transects. Snow depth and water equivalent (SWE) was measured every 14-21 days from the period of peak snowpack through snow disappearance, and SMS monitored at the same frequency thereafter using time domain reflectometry (TDR) to measure soil water storage at 0-20 cm and 20-60 cm depths. Differences in snowpack accumulation and melt and SMS were evaluated in the context of measured differences in microclimate and modeled solar radiation forcing. Results from this study showed peak snow accumulation increased by 43% in harvested strips, and 28% in the partial-cut relative to corresponding forested reserves, while snowpacks in north and south facing clearcut were either not different or significantly less. Differences in solar radiation due to slope orientation and shading by retained trees produced highly varied patterns of snow accumulation and melt creating within-harvest differences in snow disappearance timing of up to 20 days. Subsequent seasonal SMS was also generally increased by harvesting due to reduced water losses from tree transpiration. However, the duration and magnitude of differences in SMS varied among harvests and soil layer depths over wet and dry years, which was attributed to differences in the ability of specific harvest cutting-patterns to moderate surface soil moisture losses. Across both study years, increased SMS after harvesting was greatest in SS (39%) followed by CC (~25% across both north- and south-facing hillslopes), and PC (~19%) for the two soil layers considered (0-20, and 20-60 cm). Results from this study demonstrate key differences in the comparative ability of specific patterns of tree retention to moderate spatial patterns of snow accumulation and melt and seasonal SMS, and strongly reinforce past research on the importance of interactions between forest cover, slope-orientation, and solar radiation in controlling spatial and temporal water-balance. These findings provide new information on relationships between alternative forest harvesting methods and snowpack and SMS dynamics needed to help evaluate integrated forest-water management strategies in this vital water supply region.

• Subjects / Keywords

  • Snow
  • Water
  • Soil Moisture
  • Watershed
  • Forest Harvesting
  • Timber
  • Hydrology

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-z9rj-hp05

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.