ThiRST
Large-scale experimental assessment of pre-commercial thinning to reduce the vulnerability of drought
ThiRST Overview
The ThiRST experiment is a silvicultural trial installed in 2022 to assess the potential of pre-commercial thinning to reduce the vulnerability of white spruce stands to increasing drought. This is of particular interest to the forestry industry as drought frequency and severity are projected to increase in the coming years, which can have negative effects on the growth and productivity of commercial softwoods. Pre-commercial thinning is seen as a potential silvicultural solution to reduce water stress.
Objectives
The project's two main objectives are:
​
-
To assess the vulnerability of white spruce plantations to water deficit.
-
To evaluate the effectiveness of pre-commercial thinning in reducing white spruce stress under water deficit
​
Images above and below show the experiment from 2024. The site (loamy till over limestone bedrock) was planted in 2009 with 90% white spruce and 10% white pine at 9’x6’ spacing.
Data Collection
To track the effectiveness of the drought treatments, we have one complete meteorological station on site, as well as 18 permanent soil moisture sensors (volumetric and matric potential) in two plots within the experiment. In addition, we use a portable moisture sensor biweekly to assess spatial variation in soil moisture in all 18 plot.
Tree response is tracked multiple ways. We have installed electronic dendrometers on 54 trees which monitor radial growth and tree moisture balance continuously. In addition, we have installed manual dendrometer bands on 126 trees to monitor seasonal stem growth. This project is led by Chloe Larstone Hunt, graduate student at University of New Brunswick.
​
Finally, we use multispectral imaging to measure the relationship between drought, crowding, and spectral traits in white spruce tree crowns. This project is led by Taylor Bottoms-Cau, graduate student at University of New Brunswick.
Project Design
​The experiment is made up of 18 plots, each 400m². Each plot receives one of three levels of rain exclusion: 0% (control), 25%, and 50% rain exclusion (or drought). The drought is simulated by large wooden structures which are covered in clear tarps approximately 1-1.5m aboveground. These tarps are connected to culverts between plots, which carry the water out of the site. In addition to the drought treatment, each plot has received one of three pre-commercial thinning treatments: no thinning (2,500 stems/ha), regular PCT (1,500 stems/ha) and high PCT (1,000 stems/ha).
ThiRST is coordinated by Dr. Loïc D’Orangeville at Laval University and funded by NSERC through the Silva21 initiative (ALLRP-556265-20) and the Forest Innovation fund, with significant in-kind support from JDI and Natural Resources Canada.
Contact
Thank you to our partners
