Growth anomaly in 1965

A network of oak (Quercus robur L.) chronologies established on 49 sites and containing 675 single-tree series was analysed to identify weather variables related to the annual dynamics of ring increment for the area of the southern Sweden (from 55 and 60 N and 12 to 19 E) for the period 1860-2002.

One of the tasks was to establish the point years for southern Swedish oak, that is, years with negative or positive growth anomalies observed in the large number of trees. Accodring to the classical definition of Schweingruber (1988), pointer years (Swedish pekarår) are characterized by tree rings that are particularly narrow and occur in the majority of trees sampled within a site.

The most pronouced pointer year over the 20th century was observed in 1965. In this year ring width was below lower 5% of ring width distribution for the 32% of all trees sampled.

This pointer year was expressed stronger in the western than in south-western and northern parts of the region (Figure 1).

Figure 1. Percentage of trees with ring in 1965 being

below lower 5% of ring-width distribution for a respective tree

Analasys of climate data revealed that the period July 1964 - August 1965 had the following climatic extremes:

Average temp for July below 3.5% of its distribution
Min temp for July - below 0.8% of its distribution
Min temp for March - below 3.4% of its distribution

Mapping the spatial pattern of climatic extremes indicates that cold temperature in March was a likely cause in negative growth anomaly in oak in 1965 (Figure 2).

Figure 2. Mapping of three weather extremes for the period July 1964 - August 1965. Lighter colors indicate areas with lower values of variables.

gridding-ouput-allyears 1965