Summer temperature affects the ratio of radial and height growth of Scots pine in northern Finland

Radial and height growth chronologies from 150-year-old and 50-year old Scots pine stands, both located near to the northern timberline in Laanila, Finland (68 degrees 30' N, 27 degrees 28' E), were cross-correlated with each other and with mean temperatures of various temperature periods defined as months, days or growing-degree-days. The height-growth chronology correlates significantly with radial growth at lags 1 and 2, and radial growth with height growth at lag 2 when the effect of temperature is omitted. On average, low and high growth years represent cool and warm average growing seasons. The summer temperatures (June, July and August) affect most on growth, but height and radial growth do have a different set of effective temperature periods. Furthermore, July temperature variation affects stronger height than radial growth. Those years with low height/radial-growth ratio, i.e. relatively higher current year's radial than next year's height growth, do have lower growth and cooler-than-average July temperature whereas those years with high height/radial-growth ratio do have clearly warmer mid-summer temperatures.