Effects of high temperatures and ash on seed germination of two iberian pines (Pinus nigra ssp salzmannii, P sylvestris var iberica)

Abstract

The effect of high temperatures and ash on seed germination of two Iberian pines (Pinus nigra ssp salzmannii and P sylvestris var iberica) has been studied. These two pines are widely distributed in the oromediterranean and supramediterranean bioclimatological belts of the eastern half of the Iberian Peninsula. Our results are clearly very similar for both pines. Seed cover protects embryos up to 70 °C (germination percentage above 90%), which is a very low temperature for a wildfire, catastrophically failing when this temperature is surpassed. Addition of ash solutions did not modify this trend. As has been previously reported, both pines have photophillous seeds, which indicates that they can regenerate rapidly after disturbance, except wildfires, as our results illustrate. These results confirm the field observations after very large fires in extensive and homogeneous pine forests (> 10 000 Ha), in the sense that recruitments of both pines are extremely rare after disturbance. At a community level, our results seem to indicate that pine formations must be naturally confined to the oromeditenanean belt or at permanent stands in spurs, crests or steep rocky slopes where density is very low and wildfires do not become catastrophic. The existense of formations in the supramediterranean belt must be man-induced (landscape changes) and driven, not necessarily planted, and can be rapidly substituted by oak formations after intense wildfires.