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De-coupling seasonal changes in water content and dry matter to predict live conifer foliar moisture content

Author(s): William Matt Jolly, Ann M. Hadlow, Kathleen Huguet
Year Published: 2014

Live foliar moisture content (LFMC) significantly influences wildland fire behaviour. However, characterising variations in LFMC is difficult because both foliar mass and dry mass can change throughout the season. Here we quantify the seasonal changes in both plant water status and dry matter partitioning. We collected new and old foliar samples from Pinus contorta for two growing seasons and quantified their LFMC, relative water content (RWC) and dry matter chemistry. LFMC quantifies the amount of water per unit fuel dry weight whereas RWC quantifies the amount of water in the fuel relative to how much water the fuel can hold at saturation. RWC is generally a better indicator of water stress than is LFMC. We separated water mass from dry mass for each sample and we attempted to best explain the seasonal variations in each using our measured physiochemical variables. We found that RWC explained 59% of variation in foliar water mass. Additionally, foliar starch, sugar and crude fat content explained 87% of the variation in seasonal dry mass changes. These two models combined explained 85% of the seasonal variations in LFMC. These results demonstrate that changes to dry matter exert a stronger control on seasonal LFMC dynamics than actual changes in water content, and they challenge the assumption that LFMC variations are strongly related to water stress. This methodology could be applied across a range of plant functional types to better understand the factors that drive seasonal changes in LFMC and live fuel flammability.

Citation: Jolly, W. Matt; Hadlow, Ann M.; Huguet, Kathleen. 2014. De-coupling seasonal changes in water content and dry matter to predict live conifer foliar moisture content. International Journal of Wildland Fire 23(4):480-489.
Topic(s): Weather, Fuels, Fuel Descriptions
Ecosystem(s): Subalpine wet spruce-fir forest, Subalpine dry spruce-fir forest, Montane wet mixed-conifer forest, Montane dry mixed-conifer forest
Document Type: Book or Chapter or Journal Article
NRFSN number: 12959
FRAMES RCS number: 17601
Record updated: Jun 21, 2018