The new planning concept in the canton of Grisons, consisting of regional development plans and local management plans, affects information needs and thus the previous inventory method. Information on forest condition and forest dynamics is needed both at the regional and at the management level. Where the management level is concerned, the information needed is gained by means of a detailed description of each stand.
To support the decision on the future inventory method at the regional level, a pilot inventory was conducted, using the method of the second National Forest Inventory (NFI 2).
The given cost framework enabled a survey in a sample grid of 500 x 500 m to be conducted. The software and the recording equipment of the NFI 2 were used. The variable list of the NFI 2, however, was reduced according to the needs of the canton. In order to reduce the costs, no tariff sample trees were assessed.
The field work for assessing one plot required 8.4 person hours or CHF. 680.–. These values are within the expected range. For the entire area, the costs amounted to CHF. 27.30 per hectare.
The standard error for the total forest area was between 6.0% (Schanfigg) and 6.8% (Val Müstair) and thus rather high. The standard error for the growing stock, the most important variable, was 7.0% and thus within the desired range. The pilot inventory also gave satisfactory results for the growing stock of the main tree species. Based on the sample grid of the NFI 1, the increase in growing stock could, already with the first regional inventory, be determined more reliably than by the use of the previous sampling design with temporary plots.
The pilot inventory also showed that, with the conditions prevailing in the canton of Grisons, an additional interpretation of aerial photographs is only useful if the variables assessed on the photographs enable a better stratification than the variable tree height class alone.
The experience and the results gained from the pilot inventory are positive. From now on, the canton of Grisons will conduct an inventory on permanent plots in a 500 x 500 m grid, and drop the surveys of temporary sampling plots.