How to find the rare trees in the forest -: New inventory strategies for culturally modified trees in boreal Sweden

Culturally modified trees (CMTs) in northern forests are rare traces of past human activity that provide unique information on past land use and the relationship between people and forests throughout history. There is an apparent need to provide probability sampling methods for these traces. This article describes the simulation and evaluation of circular plot sampling and strip surveying for estimating the density of culturally modified trees in 25 ha of a forest reserve in northern Sweden. CMTs were surveyed, documented, and prepared for use in simulator software and the bias, precision, and cost of different inventory strategies were calculated. For a given level of precision circular plot sampling was found to be more efficient than strip surveying for estimating the abundance frequencies of all CMTs. For smaller subpopulations of scarce CMT types, the strip-surveying method was superior. Probability sampling would be an important tool for examining larger areas and gaining more CMT information at a lower cost. The results are important for studies of cultural history in sparsely populated forested regions in northwestern North America, northern Scandinavia, and northern Russia, but there are also implications for finding other rare objects in forest ecosystems.