Trait phenology and fire seasonality co‐drive seasonal variation in fire effects on tree crowns

Abstract

Summary The plume of hot gases rising above a wildfire can heat and kill the buds in tree crowns. This can reduce leaf area and rates of photosynthesis, growth, and reproduction, and may ultimately lead to mortality. These effects vary seasonally, but the mechanisms governing this seasonality are not well understood. A trait‐based physical model combining buoyant plume and energy budget theories shows the seasonality of bud necrosis height may originate from temporal variation in climate, fire behaviour, and/or bud functional traits. To assess the relative importance of these drivers, we parameterized the model with time‐series data for air temperature, fireline intensity, and bud traits from Pinus contorta, Picea glauca, and Populus tremuloides. Air temperature, fireline intensity, and bud traits all varied significantly through time, causing significant seasonal variation in predicted necrosis height. Bud traits and fireline intensity explained almost all the variation in necrosis height, with air temperature explaining relatively minor amounts of variation. The seasonality of fire effects on tree crowns appears to originate from seasonal variation in functional traits and fire behaviour. Our approach and results provide needed insight into the physical mechanisms linking environmental variation to plant performance via functional traits.

Cone allometry and seed protection from fire are similar in serotinous and nonserotinous conifers

“…The heat transfer approach used in our study provides a physical process framework for identifying several key functional traits that mechanistically link environmental variation and disturbance to plant functions (Michaletz et al ., 2015, 2016; Kearney et al ., 2021). Such a mechanistic foundation has been largely lacking in both trait‐based ecology (Enquist, 2010; Webb et al ., 2010; Kearney et al ., 2021) and fire ecology (Michaletz & Johnson, 2007; Hood et al ., 2018; O'Brien et al ., 2018; Bar et al ., 2019; Varner et al ., 2021; Bison et al ., 2022). This approach identifies from first principles the governing cone traits and their relationships with fire environment and cone heating variables.…”

Death from hunger or thirst? Phloem death, rather than xylem hydraulic failure, as a driver of fire‐induced conifer mortality

“…winter or beginning of spring; Furze et al ., 2019), mortality could occur faster. Although plant phenological state coupled with fire behavior can impact the magnitude of heat‐induced injuries (Bison et al ., 2022), it is still unclear how tree physiological processes will be affected when plants are exposed to fire in different phenological states. Studies investigating the impacts of fire on plants at different phenological states is extremely important, particularly due to shifts caused by early snowmelt and consequently the greater chances of early fire occurrence (Westerling et al ., 2003).…”

Variation in leaf carbon economics, energy balance, and heat tolerance traits highlights differing timescales of adaptation and acclimation

“…The use of a constant c p,d effectively ‘controls out’ any potential influence of variation in c p,d on variation in τ . This is a common approach (Ball et al ., 1988; Fauset et al ., 2018; Slot et al ., 2021; Bison et al ., 2022), and a suitable first approximation because the specific heat capacity of a fresh leaf primarily reflects that of water ( c p,w ), given that c p,w is ca. double that of dry matter ( c p,d ), and water accounts for the majority of fresh leaf mass (mean of 76% in our data).…”