Forest fires affect the germination of columnar cactus seeds in the Caatinga dry forest

Forest fires have become more common in all Brazilian ecosystems, including the Caatinga, a seasonally dry tropical forest that is threatened by increasing aridity. The aim of this work was to analyze the effects of thermal shock, which simulates forest fires, on the germination of seeds from two columnar cacti in this ecosystem. To simulate the effects of fire, seeds of Cereus jamacaru and Xiquexique gounellei were subjected to the following heat treatments: 80 °C/5 min, 80 °C/10 min, 100 °C/5 min, 100 °C/10 min; and a control (i.e., no heat). After the treatments, the seeds were allowed to germinate at a constant temperature of 25 °C and evaluated daily for 30 days. The statistical design was entirely randomized following a 2 × 5 factorial arrangement (species × heat shock). The heat treatments influenced all the response variables, reducing the viability and vigor of C. jamacaru and X. gounellei seeds as the heat treatment temperature increased. Compared with the control treatment, heat treatment at 100 °C for 10 min caused decreases of 94 and 56% in the germination of C. jamacaru and X. gounellei seeds, respectively. Compared with C. jamacaru seeds, X. gounellei seeds are more tolerant to heat shock, suggesting a relative ability to develop a soil seed bank that can persist after forest fires in the Caatinga and recolonize disturbed areas; thus, understanding these adaptations provides useful insights into conservation strategies.