Comparison of four alternative survey methods in assessing dead wood at the stand level

Abstract

Many forestry practitioners need information on the amount of dead wood for various purposes, often at the level of individual stands. Our aim was to compare four simple dead-wood inventory methods of which systematic circular plot inventory is a well-known method, while relascope plot inventory (using the ordinary horizontal angle relascope also for downed trees), diameter class counting and total inventory are new methods. Seven surveyors tested the methods in four stands in southern Finland. All the methods produced rather accurate volume estimates. Mean percent error was the smallest (−5.7%) in total inventory and the largest (−12.4%) in diameter class counting. Precision differed significantly between the methods. Variation among individual measurements, expressed as percentage SD, was 15.9% in total inventory, 24.8% in diameter counting, 36.6% in relascope inventory and 43.0% in circular plot inventory. Diameter counting was by far the fastest method. Relascope inventory and circular plot inventory took about twice as much time, and total inventory over three times as much time as diameter counting. In conclusion, diameter class counting is a cost-effective dead-wood assessment method, if the purpose is to get an estimate of the total volume of dead wood within a forest stand with a reasonable precision.