Dissertation Defence: How Forest Landscape Pattern Modulates Hydrology
August 27 at 9:00 am - 1:00 pm
Ming Qiu, supervised by Dr. Adam Wei, will defend their dissertation titled “How Forest Landscape Pattern Modulates Hydrology: Linking Stand-level Processes to Watershed-scale Impacts” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Earth and Environmental Sciences.
An abstract for Ming Qiu’s dissertation is included below.
Examinations are open to all members of the campus community as well as the general public. Registration is not required for in-person exams.
Abstract
Escalating forest disturbances threaten water security, yet watershed management traditionally prioritizes total forest cover over spatial configuration. Although policies increasingly favour spatially explicit planning, the underlying scientific foundation remains underdeveloped. This dissertation investigates how forest landscape patterns, primarily characterized by edge density (ED), modulate hydrological responses (water yield, flow regimes, and water quality) following forest disturbance. A multi-scale framework (stand, watershed, and global) bridges mechanistic validation with broad-scale generalization.
At the stand scale, transect monitoring across forest–cutblock edges in the Okanagan Valley reveals edges as active hydrological zones with enhanced evapotranspiration. Increased light, temperature, and vapour pressure deficit drive soil moisture depletion, creating a U-shaped moisture gradient extending into the forest interior with edge zones representing the driest conditions.
At the watershed scale, stable water isotope (δ¹⁸O and δ²H) analysis was applied across two specific watersheds (Duteau and Peachland), demonstrating that higher cutblock ED significantly reduces young water fraction (Fyw) and line-conditioned excess (lower values reflect evaporative enrichment) in streamflow. Remote sensing analyses further show that ED increases local annual evapotranspiration, with longitudinal (north–south) edges amplifying this effect compared to latitudinal (east–west) edges. Complementing this, distributed hydrological modelling reveals that increased ED redistributes snowpack energy, suppressing rapid spring melt and reducing peak flows, while preserving snowpack to sustain warm-season low flows.
Globally, a meta-analysis shows that higher patch and edge densities significantly degrade water quality via enhanced edge-mediated nutrient deposition, with nitrogen parameters exhibiting a particularly pronounced response compared to other chemical variables. Regarding water yield, another global synthesis highlights that landscape patterns non-linearly interact with total forest cover to modulate streamflow Fyw. In sparsely forested landscapes, large canopy openings sustain enhanced evapotranspiration, returning recent precipitation to the atmosphere before it contributes to rapid streamflow.
Ultimately, this work establishes post-disturbance landscape patterns as a complementary control on hydrology, beyond the total disturbed area. Stand-scale forest edge effects emerge as the central mechanism, accumulating spatially to predictably influence broader-scale hydrological processes. Optimizing these spatial patterns offers a critical pathway to mitigate adverse hydrological impacts and safeguard water security.
