Archive for February, 2024

Seed dormancy release and summer temperatures

February 18th, 2024 No comments

In Mediterranean ecosystems, fire breaks the dormancy in many species and stimulates germination in the postfire environment [1]. Both the smoke and the heat of the fire may be responsible for breaking dormancy [1]. Cistaceae species are typical examples of species with this heat-released dormancy [1, 2], together with many legumes. Despite fire is a much more powerful driver of dormancy release than the summer heat (figure 9 in [1] and figure 2 in [2]), there are still people aiming to demonstrate the role of summer temperatures in dormancy release in Cistaceae. A recent research team studied the germination of 12 Cistacea species and compared the effect of fire-type heat in seeds submitted to a summer heat treatment (50/20o C for a month) and in seeds without this summer treatment [3]. They concluded that high summer temperatures are needed for maximum germination in the presence of fire [3]. A reanalysis of their data suggests that not only are summer temperatures inefficient at releasing dormancy, but they also reduce postfire germination [4]. The applied summer heat treatment reduced the germination (%) in the control (H-) and in all fire treatments, and for all species (Fig. 1 below). And for the seeds that germinate, those under summer heat tended to germinate slower than those that did not suffer the summer heat (Fig. 2 below). In conclusion, fire increases the germination of Cistaceae seeds in contrast to summer-type heat, i.e., the great fitness benefits of fire are unmatched by the summer heat [4].

Fig. 1. Germination with no summer heat (x-axis; ~ 20o C for a month) and with summer heat (y-axis, 50/20o C altering for 12 h, and during a month) in 12 Cistaceae species with different fire treatments. All fire heat treatments were 100o C for 10 min applied as follows: H-, no fire heat (black); HB, fire heat before summer (green); HA, fire heat treatment after summer (red); HBA, fire heat before and after the summer (unrealistic scenario; blue). The results suggest that applying a strong summer heat treatment (52/20o C for a month) reduces the germination (%) in the control (H-) and in all fire treatments and for all species. From [4].

Fig. 2. Number of days to the first germination (T0, left) and to reach 50% of the final germination (T50, right) with no summer heat (x-axis, control) and with summer heat (y-axis, treatment), and with different fire treatments (colors; see figure above) for 12 Cistacea species (12 points for each color). The results suggest that summer heat, if any, tends to increase the time to germination.


[1] Pausas J.G. & Lamont B.B. 2022. Fire-released seed dormancy – a global synthesis. Biological Reviews 97: 1612-1639.  [doi | pdf | supp. mat. | data (figshare)]

[2] Moreira B. & Pausas J.G. 2012. Tanned or burned: The role of fire in shaping physical seed dormancy. PLoS ONE 7(12): e51523. [doi | plos | pdf]

[3] Luna B, Piñas-Bonilla P, Zavala G, Pérez B. 2023. Timing of fire during summer determines seed germination in Mediterranean Cistaceae. Fire Ecology 19: 52.

[4] Lamont BB, Burrows GR, Pausas JG 2024. Fire-type heat increases the germination of Cistaceae seeds in contrast to summer heat. Fire Ecology 20:14 [doi | pdf]

More on seed dormancy: A review | a glossary | bet-hedging & best-bet | smoke-released dormancy