Current issue: 56(2)
Under compilation: 56(3)
Silva Fennica Issue 39 includes presentations held in professional development courses in 1935 that were arranged for foresters working in public administration. The presentations focus on practical issues in forest management and administration, especially in regional level. The education was arranged by Forest Service.
This presentation describes different forest inventory methods.
There has been earlier publications on calculating the standard error of the strips. However, they have been calculated with very small amount of data. In the article the confidence of standard error will be examined throughout. The article is a response to the article written by A. Langsaeter on the theme.
A strip survey was performed in the counties of Sahalahti and Kuhmalahti in Häme, situated in Central Finland, to study the condition of the private forests. The forests cover 78% of the total land area of 37,420 hectares. The forest site types were relatively fertile. Scots pine (Pinus sylvestris L.) dominated forest covered 43%, Norway spruce (Picea abies (L.) H. Karst.) 30% and Betula sp. 23% of the forest land. The productivity of the forests could be improved by changing the species so that they suit the site. The volume of the standing crop is 67.2 m3 per hectare. The volume of the growing stock in the area could be 1 million m3 larger if the forests were nearer to the natural state. The annual growth of the forests is low, and could be much improved by correct forest management.
One of the aims of the survey was to study how the distance between survey lines should be adjusted to give acceptably accurate results, in a way that the strip-survey method can be adapted to large areas. The largest distance between the lines that gave results that differed less than 10% from the correct results, varied between 10 and 1.5 kilometres depending on the variables. For instance, to get accurate results for the rarest forest site types required line distance of 1.5 kilometres, but accurate results for the most common forest site types could be achieves with line distance of 10 kilometres.
The PDF includes a summary in German.
The article features a critical observation on used methods for calculating the errors and a trial to improve it. The article describes the calculation method used in Sweden, county of Värmland and another method used by Ilvessalo and developed by Cajanus. The shortcomings of these models are discussed. An improved calculation is presented.