Effect of Strip Roads on the Growth and Yield of Young Spruce Stands in Southern Finland

1990

36 S.

12 Abb., 13 Tab., zahlr. Lit. Ang.

Bandaufführung

37269

Folia Forestalia ; Nr. 756, 36 S.

The aim of this study was to investigate the effects of average strip roads on the growth and yield of Norway spruce stands after the first thinning. The study material consisted of 20 well-growing spruce stands from Southern Finland, with thinning and the opening of strip roads 6-11 years before measurements. The total area of the sample plots was 17 735 m2 and the total length of the investigated strip roads was 773 m. The analysis of radial increment was made for each sample-plot-tree (n = 1734). The number of felled sample trees was 420. To determine the width of the strip roads, four concepts of width were created. The notion of external "outside width" meant the average width of the strip road restricted by edge trees. This was considered to represent the strip road available for transport and logging machines. The abstraction "target width" was considered to approximate the minimum space necessary required for machines. In the study material the mean value of the outside width was 5.1 m and the target width slightly less than 4 metres. The remaining two concepts were considered to represent the internal "production width" of a strip road. Their average share of the outside width was only about 50 per cent. The strip roads constructed at the standard distance of 30 metres and available for forwarders of medium size represented 17 per cent of the total area of the stand. Thus, only 8 percent of the total area of the stand was estimated to remain nonproductive. The edge trees of the strip roads showed a recreation resulting from asymmetrically increased growing space even during the first growing season after thinning. The additional growth of the edge trees reached its maximum, about 25 per cent, by the fifth growing season and continued at the same level still 10 years after thinning. In several stands, the effects of strip roads were notable also in the "second edge trees" i.e. the trees growing behind but at less than three metres' distance fromthe actual edge trees bordering the strip road. Further into the forest the effects of strip roads were not observable. The total production loss caused by the strip roads in the Norway spruce stands was estimated to be approximately 10 m3/hectare during a period of 15 years. the 4 metres wide strip roads are supposed to be opened at a standard distance of 30 metres. In addition, it is assumed that the remaining edge stands are even and without injuries nor any other special treatments.