Modeling instream temperature from solar insolation under varying timber harvesting intensities using RPAS laser scanning

Leanna A Stackhouse; Nicholas C Coops; Spencer Dakin Kuiper; Scott G Hinch; Joanne C White; Piotr Tompalski; Alyssa Nonis; Sarah E Gergel

doi:10.1016/j.scitotenv.2023.169459

Modeling instream temperature from solar insolation under varying timber harvesting intensities using RPAS laser scanning

Sci Total Environ. 2024 Feb 20:912:169459. doi: 10.1016/j.scitotenv.2023.169459. Epub 2023 Dec 18.

Authors

Leanna A Stackhouse¹, Nicholas C Coops², Spencer Dakin Kuiper², Scott G Hinch³, Joanne C White⁴, Piotr Tompalski⁴, Alyssa Nonis³, Sarah E Gergel⁵

Affiliations

¹ Department of Forest Resources Management, Faculty of Forestry, University of British Columbia, Vancouver, BC, Canada. Electronic address: leannast@student.ubc.ca.
² Department of Forest Resources Management, Faculty of Forestry, University of British Columbia, Vancouver, BC, Canada.
³ Pacific Salmon Ecology and Conservation Laboratory, Department of Forest Conservation Sciences, University of British Columbia, Vancouver, BC, Canada.
⁴ Canadian Forest Service (Pacific Forestry Centre), Natural Resources Canada, Victoria, British Columbia, Canada.
⁵ Department of Forest and Conservation Sciences, Faculty of Forestry, University of British Columbia, Vancouver, BC, Canada.

PMID: 38123099
DOI: 10.1016/j.scitotenv.2023.169459

Abstract

Stream temperatures are influenced by the amount of solar insolation they receive. Increasing stream temperatures associated with climate warming pose detrimental health risks to freshwater ecosystems. In British Columbia (BC), Canada, timber harvesting along forested streams is managed using riparian buffer zones of varying widths and designations. Within buffer zones, depending on distance from the stream, selective thinning may be permitted or harvest may be forbidden. In this study, we used airborne laser scanning (ALS) point cloud data acquired via a remotely piloted aircraft system (RPAS) to derive forest canopy characteristics that were then used to estimate daily incoming summer and fall solar insolation for five stream reaches in coastal conifer-dominated temperate forests in Vancouver Island, BC, Canada. We then examined empirical relationships between estimated insolation and actual instream temperature measurements. Based on these empirical relationships, the potential effects of timber harvest on instream temperatures were simulated by comparing scenarios of different riparian forest harvest intensities. Our results indicated that modeled solar insolation explained 43-90 % of the variation in observed stream reach temperatures, and furthermore, when a single cold-water stream reach was excluded explained an overall 81 % of variation. Simulated harvesting scenarios generally projected increases in maximum stream reach temperatures 1-2 °C in summer and early fall months. However, in a full clearcut scenario (i.e. where all trees were removed), maximum stream reach temperatures increased as much as 5.8 °C. Our results emphasize the importance of retaining riparian vegetation for the maintenance of habitable temperatures for freshwater-reliant fish with thermal restrictions. In addition, we demonstrate the feasibility of RPAS-based monitoring of stream reach shading and canopy cover, enabling detailed assessment of environmental stressors faced by fish populations under climate warming.

Keywords: Harvesting; Insolation; LiDAR; Simulation model.