Fire-embracers possess higher shoot flammability, lower litter flammability and a more acquisitive strategy than fire-tolerators in Pinus yunnanensis.

Abstract

Plants in fire-prone environments have evolved traits to survive recurrent fires. Some traits enable plants to survive under crown fires (fire-embracer strategy), while others support persistence under surface fires (fire-tolerator strategy). Although plant fire survival strategies have been extensively studied, the manner in which they interact with other complementary survival strategies, such as flammability strategy and plant economic strategy, to facilitate plant coexistence with wildfires remain poorly investigated. Pinus yunnanensis, a fire-adapted species native to southwest China, has diversified into three distinct varieties: var. yunnanensis, var. pygmaea and var. tenuifolia. We examined the variations in fire-adaptations traits, shoot flammability, litter flammability, and plant economics traits across 21 populations from their three varieties. The relationships across these traits were also investigated to better understand their interplay. We found that P. yunnanensis has developed distinct fire survival strategies. Specifically, var. pygmaea survives wildfire as fire-embracers due to its high serotiny level, low crown height and thin bark; var. tenuifolia survives wildfire as fire-tolerators characterized by low serotiny level, high crown and thick bark, while the original var. yunnanensis exhibits the intermediate values in these fire-adaptions. Populations exhibiting fire-embracer strategy possess higher shoot flammability, lower litter flammability and a more acquisitive strategy compared to those with fire-tolerator strategy. Our study elucidated the divergent evolutionary trajectories among P. yunnanensis varieties to survive wildfires, and uncovered how the interplay among flammability attributes, fire-adaptations and economic traits facilitated the coexistence of P. yunnanensis with wildfires.