When the heat is on: High temperature resistance of buds from European tree species

Abstract

The heat resistance of meristematic tissues is crucial for the survival of plants exposed to high temperatures, as experienced during a forest fire. Although the risk and frequency of forest fires are increasing due to climate change, knowledge about the heat susceptibility of buds, which enclose apical meristems and thus enable resprouting and apical growth, is scarce. In this study, the heat resistance of buds in two different phenological stages was experimentally assessed for 10 European tree species. Cellular heat tolerance of buds was analyzed by determining the electrolyte leakage following heat exposure. Further, the heat insulation capability was tested by measuring the time required to reach lethal internal temperatures linked to bud traits.Our results highlighted differences in cellular heat tolerance and insulation capability among the study species. The phenological stage was found to affect both the thermal stability of cells and the buds' insulation. Further, a good relationship between size-related bud traits and insulation capability was established. Species-specific data on the heat resistance of buds give a more accurate picture of the fire susceptibility of European tree species and provide useful information for estimating tree post-fire responses more precisely.

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

“…However, the analyses of Bär et al . (2021) and the present study use different physical models based on different causal processes. Specifically, Bär et al .…”

“…Specifically, Bär et al . (2021) considered heat conduction within buds, whereas the present study links buoyant plume and convection heat transfer theories to bud necrosis. Thus, our theory identified several additional key bud traits related to plume–bud heat exchange, including the heat transfer coefficient and surface area.…”

“…Our results are consistent with this, with bud volume explaining large proportions of the variation in necrosis heights explained by bud traits. However, the analyses of Bär et al (2021) and the present study use different physical models based on different causal processes. Specifically, Bär et al (2021) considered heat conduction within buds, whereas the present study links buoyant plume and convection heat transfer theories to bud necrosis.…”

“…The fire seasonality hypothesis states that seasonal variation in fire effects are driven by temporal variation in fireline intensity in response to seasonal changes in fuel load, fuel moisture content, and wind speed (Menges & Deyrup, 2001;Thies et al, 2005;Perrakis & Agee, 2006;Knapp et al, 2009;Macias-Fauria et al, 2011). Finally, the trait phenology hypothesis proposes that variation in fire effects originates from the phenology of plant functional traits, as these operate within energy budgets to mediate the fluxes of energy between the fire and the tree (Wade & Johansen, 1986;Harrington, 1987;Michaletz & Johnson, 2007;Bär et al, 2021;Varner et al, 2021). Though all three hypotheses have existed for decades, they have not yet been evaluated within a common mechanistic framework.…”

“…where T n (°C), bud temperature at which necrosis occurs (generally assumed as T n = 60°C, but see Bär et al, 2021). Specifically, the excess temperature ratio θ (dimensionless) formalizes how five bud traits are mechanistically related to the energy budget, temperature dynamics, and heat necrosis of buds (Michaletz et al, 2016), such that:…”