Methods:- Survival: Counting of germlings on the upper surface of a sandstone, calculation of survival %- Growth rate: Digital images were recorded of 10-15 germlings per experimental population before and after the heat waves. The side-view area was measured by using image J. In each subunit, different groups/ experimental populations were measured. These consisted of different sibling groups (numbers) and different diversity level ("Triplett" = Tx; "Sextett" = Sx)Growth rate: Negative value represents the fact that growth was not pronounced in this group, and that surviving individuals that were measured after the last heat wave event were slighlty smaller than the 15 ones that were measured in the first month of the experiment.