Geographic variation of Pinus heldreichii Christ from the Western Balkans based on cone and seed morphology

Pinus heldreichii (Bosnian pine) is a Balkan-Apennine endemic and relict pine species that inhabits high mountains in the Mediterranean and sub-Mediterranean regions. Nineteen populations of P. heldreichii from the Western Balkans encompassing 187 individual trees were examined to evaluate morphological variation, a rarely studied aspect of the species. Univariate and multivariate statistics were applied in order to assess the variation of morphological traits of cones and seeds, evaluate the relationships among the sampled populations and verify geographic differentiation in the Dinaric Alps versus Scardo-Pindic mountains. The observations of P. heldreichii covering the populations from the western margins and the centre of the species distribution range indicated a morphological variation among populations and their geographic structure. In general, the southern populations (Scardo-Pindic group) had lower values for the most of morphological traits than the northern ones (Dinaric group). The observed geographic differences between these populations exhibit a north-western to south-eastern gradient, with a few inconsistencies. The southernmost sampled population, Tomorr in Albania, showed remarkable morphological divergence from the other studied populations and appeared to be a distinct morphological group. The pattern of morphological variation in Bosnian pine most likely resulted from multiple effects of long-term isolation and fragmentation in high mountain systems, adaptation to extreme environments and human disturbances.