Large-scale variations in radial tree growth in Norway

Published Date
Applied Geography
April 1998, Vol.18(2):153–168, doi:10.1016/S0143-6228(98)00003-4

An application of median polish for spatial trend detection

Author 
Geir-Harald Strand 
Norwegian Institute of Land Inventory, PO Box 115, N-1430 Ås, Norway

Revised 19 September 1997. Available online 6 January 1999.

Abstract

Radial growth was measured on 11,452 Norway spruce (Picea abies) trees on a systematic random sample of 1492 forest inventory sites in Norway. The data were decomposed using median polish and examined for spatial trends. Radial growth was higher than average in the far south and lower than average in the north. This latitudinal trend followed a linear gradient in the eastern, continental parts of the country. A similar but less smooth gradient was also found in the western, coastal region. Summary points were used to characterize and compare the two gradients. Radial tree growth in the western region was consistently lower than in the eastern region, but the shapes of the two gradients were almost identical. These may be explained as an effect of a climatic gradient shared by the two regions, with high radial growth broadly corresponding to a warmer climate and a longer growing season. Norway spruce is at the limit of its geographical range near the western coast of Norway, which may explain the generally lower growth rate here. The results do not support the hypothesis that widespread forest decline is taking place in Norway, but surprisingly high growth in the extreme south of the country may be related to the fertilizing effect of airborne nitrogen deposition. Median polish of geographical data was found to perform well as an alternative technique for spatial trend detection.

Keywords

air pollution

forest growth

median polish

Norway spruce

spatial trends

---

Fig. 1.

Fig. 2.

Fig. 3.

 Table 1

Table 1.

Fig. 4.

Fig. 5.

Fig. 6.

Fig. 7.

.

• *
  Corresponding author. Fax: +47 64 94 97 86; E-mail: ghs@nijos.no

Copyright © 1998 Elsevier Science Ltd. All rights reserved.

For further details log on website :
http://www.sciencedirect.com/science/article/pii/S0143622898000034