| Summary: | Complete plant inventories of large areas of forests in the moderate and boreal zone have thus far been infeasible and have also not been published. The use of orienteering maps (O-maps) for sampling for inventories was tested. In the sampling method presented herein, the "O-map/way method", O-maps were used for controlled and systematic inspection and sampling, making it possible to carry out successfully complete plant taxon and site inventories of large forest areas (1 to 100 ha). O-maps are much more suitable than the best national or similar topographic maps (NT-maps) for plant inventories in forests; O-maps have many advantages (smaller scale/better resolution, better legibility, internationally standardization, information on vegetation and accessibility), and they contain more small objects, ways (= tracks of any size; roads), and lines and thus have much smaller subareas that allow good orientation and systematic screening for plants. For the example of plant taxon inventories in 6 target areas of 25-85 ha of Swiss midland forests in the moderate/colline zone, the O-map/way method (all accessible areas are screened) was shown to be clearly superior to alternative sampling methods (partial areas screened), such as the NT-map/way method or a plot method, in which only 79.6±6.7% or 34.5±6.6%, respectively, of the taxa found by the O-map/way method were recorded. Taxa detected only by the O-map/way method were shown to be relatively rare at a local as well as at a national scale. The O-map/way method could also be successfully applied to the inventory of plant sites in large forest areas: As shown by the distribution of the sites of five plant species in a target area of 30.1 ha, the great majority of plant sites were detected only by the O-map/way method; but only a few sites were detected by the alternative methods. As O-maps for forests are widely available in many countries, the O-map/way method might allow for complete inventories and other studies in large forest areas.
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