Influence of warming on timberline rising: a case study on Pinus peuce Griseb. in Bulgaria
Meshinev, Tenyo; Apostolova, Iva; Koleva, Ekaterina
The Central Balkan Mountain is one of the northernmost localities of the Balkan endemic Pinus peuce Griseb. After 1970 this species made an impressive invasion of the higher mountain slopes from the established timberline at 1760 m up to 2100 m a.s.l. The working hypothesis assumes a possible connection between this phenomenon and climate warming. Average annual temperatures in Bulgaria have marked no major change in the past decades as compared to a 100-year period of observation. After 1971 there was a recorded increase in winter month temperatures throughout the country. The same happened to climate in the studied region. There the trend consistently occurred in the coldest winter month of January. As compared to 1955-1974, in 1975-1998 average monthly, average minimum and average absolute minimum temperatures went up. The greatest increase however was in the minimum temperatures' most frequent value (the mode). Trees' age structure shows that the old timberline had stabilized and had not changed until 1970. Pinus peuce's distribution at an altitude from 1770 to 2100 m is new and appeared after 1970. The species' invasion correlates with winter month temperature growth in the same period. Possible impact of biological and anthropogenic factors is discussed as well as the potential influence of indirect climate warming related changes (i.e. precipitation, snow cover). Evidence of the connection between these impacts and the observed phenomenon is deemed insufficient. Pinus peuce is defined as a good indicator of environment changes.