Long-term variable distribution of Pinus peuce Griseb. (Macedonian pine) in SW Bulgaria: implications for its future

Background/Question/Methods

The Macedonian pine is a Balkan endemic and a Tertiary relic, and it is one of the commercially most valuable conifer species in SE Europe. One of the largest areas with P. peuce-dominated forests is in the Pirin Mountains (SW Bulgaria). Here, we examine the variability of the present P. peuce communities and the factors that controlled it over the last 18,000 years. We used fossil pollen, spores, non-pollen palynomorphs (algae, fungi, stomata), charcoal, macrofossil remains, LOI, and AMS ¹⁴C dates on 8 lakes (6 previously published and 2 in this study) between 1900 and 2500 m a.s.l.

Results/Conclusions

The macrofossil results reveal that stands of P. peuce grew in the Pirin Mountains at 2000-2200 m a.s.l. during the relatively warm Bølling-Allerød interstadial (14.6-12.6 ka cal. BP). The Macedonian pine occurred in low abundance during the Younger Dryas climatic deterioration (12.6-11.6 ka cal. BP) which is recognized in all pollen diagrams by clear maxima of Artemisia and Chenopodiaceae. The species distribution remained limited during the early Holocene insolation maximum until 7.5 ka cal. BP while Betula alba and Juniperus sp. dominated the upper forest limit. The subsequent expansion of P. peuce, along with Abies and Pinus sylvestris at lower elevation, occurred with a change to cooler and moister climate as summer insolation waned.  P. peuce preserved its dominant role in the upper conifer belt until 4000 ka cal. BP. Its later decline was primarily caused by the expansion of Picea abies and Pinus mugo under the conditions of increased human activities in the mountains through deforestation and burning to increase pasture. The exceptional adaption of P. peuce to severe climatic and edaphic conditions of the Pirin Mountains will allow the species to survive the forecast decrease in precipitation and increase in temperature through expanding at higher elevations, for today we can see single trees at 2600 m a.s.l.