Design

The design of the NILS programme.

NlLS’ random sampling design makes it possible to collect objective data with the highest precision possible, which is a requirement in order to be able to convey reliable information on national and regional levels.

The composition and structure of the landscape are important elements in NILS and in order to be able to investigate them properly, it is necessary for the random sampling to cover large parts of the landscape. By compromising between need and cost, NILS has chosen landscape squares (5x5 km) for general descriptions with a central kilometer square (1x1 km) for more comprehensive measurements.

In order to carry out the estimates of e.g. landscape structure index, the area of the ground cover and frequency of indicator species, NILS has been designed in the following way:

Strata divisions
Sweden has been divided into ten geographical strata. The divisions provide basis for concentrated random sampling in certain areas, e.g. cultivated land and the alpine region.

Aerial Photo Interpretation
NILS uses aerial photo interpretation in order to describe the composition of the landscape as cost-effective as possible. Comprehensive and detailed interpretations are done in the kilometer square (1x1 km). A method of how to interpret the landscape square (5x5 km) is under development.

Field Inventory
The field inventory is a follow-up to the aerial photo interpretation and adds information that can not be obtained from the aerial photos, for instance species level information. Both comprehensive inventory of the ground cover and land use, as well as detailed description of the vegetation is performed in systematically placed sample plots within the kilometer square. The line intersect inventory, which is performed between the circular plots, provides good estimates of length and quality of linear elements in the landscape (such as roads, hedges and ditches).