Short- and mid-term fire effects on the giant cactus Trichocereus terschekii: drivers of survival and growth

Cacti are ecologically significant in American fire-prone dry ecosystems but understudied regarding fire effects. We evaluated how fire impacts survival and resprouting of Trichocereus terschekii , a key arborescent cactus in northwestern Argentina. We assessed fire effects in three situations: A) one year post-fire (n = 151); B) five years post-fire (n = 151); and C) unburned control (n = 101), and analyzed their relationship with plant size, fire severity and microenvironment. Survival differed between the control (79 %) and burned sites (20 % in situation A and 23% in situation B; p < 0.001), but not between the latter ( p = 0.58), indicating that fire's main impact occurs within the first post-fire year. Plant size positively influenced survival in burned sites ( p < 0.0001), while fire severity had a negative influence ( p < 0.0001). In situation A, charred vegetation percentage ꟷa measure of fire severityꟷ was negatively correlated with remaining green epidermis (Spearman's ρ = −0.62; p < 0.001; N = 151). In turn, resprouting in situation B was positively related to green epidermis ( p = 0.0022; N = 34), but not to plant size ( p = 0.80), indicating dependence on photosynthetic tissue, rather than underground reserves. Microenvironment influenced survival ( p < 0.004), with patterns differing between burned sites. This study contributes to understanding post-fire dynamics of cacti and to designing appropriate conservation and restoration strategies. • T. terschekii post-fire survival is low, influenced by plant size and fire severity. • Microenvironment affects survival, but relationships change over post-fire time. • Post-fire growth depends on fire damage to the photosynthetic tissue, not plant size.