Changes of Frost Damage and Treeline Advance for Swiss Stone Pine in the Calimani Mts. (Eastern Carpathians, Romania)

Abstract

Checking the tree-ring structure of 39 living and 9 crossdated dead samples of Swiss stone pine (Pinus cembra L.) collected from the upper timberline of the CalimaniMts. we have identified 59 frost rings over the past 250 years. We found concentrated occurrence of frost events in three decades: in the 1790s, 1810s and 1910s. No frost ring was observed in two bidecadal periods: 1750-1770 and 1850-1870. Out of the analysed interval 1963-2004 is the longest period without frost ring occurrence. After 1920 both frequency and severity of frost events seem to decrease compared to the prior 170 years. We determined the altitude of highest growing stone pine individuals in the Bradului Ciont–Pietrosu region in June, 2006. Individuals were sorted into tree-form or bush-like morphological groups. Mean elevation data of the groups were corrected by an estimated constant bias of GPS measurements (-30 m). Comparing the corrected values to early 20th century inventory data 65 m and 95 m upward migration was determined for treeline and boundary of bush-like occurence, respectively. The parallel results suggest that the 20th century advance of the upper forest limit was due to the decrease of frost stress at the zone of timberline.