Populations of spur-thighed tortoises (Testudo graeca欧洲陆龟), a species classified as vulnerable and at risk of extinction¹, can withstand fires if outbreaks occur once every three decades or more. However, the youngest tortoises are more vulnerable, and disappear after each fire. These are the results of a study by Spanish researchers, who analysed the impact of a 2004 forest fire in the Sierra de la Carrasquilla mountains in Murcia (Spain) on these reptiles². "Tortoises can withstand high temperatures, but this does not mean their shells are completely fire proof", Ana Sanz-Aguilar, lead author of the study, tells SINC. Currently a postdoctoral scholar at the Centre for Functional³ and Evolutionary⁴ Ecology in Montpellier, France, she collaborated⁵ with the Miguel Hernández University (UMH) and the Mediterranean⁶ Institute for Advanced Studies (IMEDEA-CSIC) for this research.

One such forest fire occurred on 1 August 2004 in the Sierra de la Carrasquilla mountains in Murcia, Spain, which incinerated（烧成灰） a 250-hectare area that was home to a large population of these reptiles. The researchers have been studying the behaviour of more than 1,000 of the animals over the past decade.

The study, published in the journal Biological Conservation, shows that the tortoises' response to fire varied⁷ greatly according to their age, with the fire killing⁸ 100% of the animals aged⁹ under four and causing increased mortality rates of 62% in sub-adults (aged from 4 to 8) and 12% in adults (over 8 years of age).

"For the dynamics¹⁰ of this species, a 12% increased mortality rate among adults is more serious than the disappearance¹¹ of all the young tortoises", says Sanz-Aguilar.

According to the study, the viability¹² of populations of these animals depends on low mortality rates and longevity¹³ among adult individuals. Any factor that causes an increase in adult mortality, such as greater vulnerability to forest fires in rocky environments, "increases the likelihood of a population becoming extinct", the authors explain.

However, when fires occur every 30 years (a frequency similar to the natural cycle in Mediterranean environments), medium-large populations of spur-thighed tortoises will not become extinct, according to models designed by the researchers. "Above this limit, the likelihood of extinction increases exponentially（以指数方式地） ", the experts warn.

None of the youngest tortoises were able to survive the passage of fire in any kind of terrain¹⁴（地形，地势） , because of the type of shelter they choose – below vegetation or in very shallow holes. They are also less able to withstand high temperatures, since their shells are not yet ossified¹⁵.