Factors affecting seed germination of 'Pinus brutia' natural populations in the island of Crete : variation of cone and seed characteristics

Abstract

This study was conducted to investigate any altitudinal variation within two provenances of ‘Pinus brutia’ in Crete and determine whether these provenances can be distinguished, using basic morphological characteristics (seed length, width and weight; ratio of seed length to width; cone's length and width; length of the peduncle; percentage of sound seeds per tree). The germination behaviour of the seeds was also studied. Two types of germination experiments were made - with stratification and with heat treatment. Both experiments were done to both provenances under dry and moist conditions. Cones were collected from 30 trees for both provenances along an altitudinal gradient. For Selakano two types of cones were collected from two separate collections, whereas for Samaria only one type was used. Results show that both provenances are morphologically the same except for the ratio of seed length to seed width. Serotinous cones were distinguished from non-serotinous ones based on the length of the peduncle. No altitudinal variation within the both populations was found. A noteworthy variability was demonstrated in the different germination requirements displayed by the two provenances. Stratification did not have a significant effect on the germination percentages of the two provenances, but only on their germination rate. However there is evidence that the trees in Samaria have become adapted to stratifying their seeds under moist conditions, while seeds from Selakano are adapted to dry stratification. It was also found that the higher the altitude the greater the dependence on stratification for the seeds to germinate. The seeds were found to be resistant to high temperatures until 200°C. Selakano seeds showed two types of behaviour towards heating, whereas Samaria seeds had only one type. The reasons for these different germination behaviours of the two provenances are most probably genetically selected for by wildfires. The results of this investigation also show that ‘Pinus brutia’ are not entirely active pyrophytes, but especially colonisers of open spaces. The release of the canopy seed bank together with the high regenerative capacity of the seeds of some provenances make recolonisation possible for the survival of the local population and genotype.