Freezing and Heating Tolerance of Pinus nigra Seedlings from Three South to North Balkan Provenances

To meet the restoration and reforestation goals in the changing environment, the translocation of genotypes and species northward and upward need to be considered to a great extent. Pinus nigra is a genetically diverse, drought sensitive species, with cold hardiness comparable to other tree species under the same climatic conditions. This study tested frost hardiness (whole plant freezing test—WPFT, and electric conductivity—EC test), and heat tolerance (heat tolerance test) of P. nigra seedlings from two southern Greek provenances (Kalamata and Grevena) and one northern Serbian provenance (Šargan) to better understand the potential of seed transfer from the south to the north of the species distribution in the Balkan peninsula. The results showed that, that for all studied provenances, the damage was great; the index of injury (Ii) at −18 °C was ranged from 49 to 54.5 (measured by the EC method) and the percentage of injured tissues ranged from 80–90% (measured by visual observation). For all studied provenances, a sharp increase in damages was observed with the fall of temperature from −5 and −18 °C and the time after exposure. The WPFT results showed that the highest tolerance to freezing (−18 °C) was presented by seedlings from the northern (Šargan) provenance; however, no significant differences were statistically detected among the studied provenances. The heat and drought-treated seedlings, from both provenances, presented significantly highler foliar damages than only drought-treated ones. For seedlings from both contrasting provenances (Grevena and Šargan), exposure to moderate heat (45 °C) and short drought did present damages but without significant difference between them. Considering freezing and heating tolerance, Greek provenances of P. nigra (i.e., Grevena region) can be successfully used in Serbian forestation and restoration programs. The present study makes a contribution towards P. nigra reforestation with practical implications for abiotic stress (frost, heat drought) tolerance among southern and northern provenances and could be valuable to determine the suitable provenances for reforestation programs and assisted population migration under climatic change scenarios.