Different tree-ring responses of Norway spruce to air temperature across an altitudinal gradient in the Eastern Carpathians (Romania)

Abstract

A global increase in temperature could potentially increase the trees’ growth at high altitude and decrease at low altitude. Another immediate consequence would be an increase of the altitude threshold where the inversion of tree growth response to temperature occurs. The first network of 18 tree-ring chronologies of Norway spruce (Picea abies) from the Eastern Carpathians (Romania) was studied in relation to the climatic factors and regional patterns in tree growth responses to climate. The sites are distributed along a latitudinal and altitudinal transect. The tree growth reaction to climate variability was analyzed by means of response functions. We used redundancy analysis (RDA) to identify regional patterns in the climatic response. The Norway spruce diameter growth patterns in Eastern Carpathians from Romania correspond to different climatic responses according to three elevation levels: low (≤1000 m a.s.l.); intermediate (1000–1300 m a.s.l.); high (≥1300 m a.s.l.). At high altitudinal level tree growth is strongly limited by summer temperatures. This climatic signal progressively decreases with decreasing altitude and increasing mean temperature. Tree growth at low elevation sites is controlled mainly by summer precipitations and in the intermediate elevation sites there is not any statistically significant correlation with climatic variables. At elevations of 1000–1100 m a.s.l., at a mean temperature of 13–13.5 °C in June and 15.5–16 °C in July, further increases in mean temperature result in an inversion of the relationship between tree-ring growth and temperature (i.e., the response becomes negative). A global increase in temperature could potentially increase the trees’ growth at high altitude and decrease at low altitude. Another immediate consequence would be an increase of the altitude threshold where the inversion of tree growth response to temperature occurs.