Models to predict time since death of Picea abies snags

Number of years since death was estimated by dendrochronological cross-dating of 107 standing dead trees (snags) of Norway spruce [ Picea abies (L.) Karst.] in a submountainous old-growth forest in south-central Norway. Snag characteristics (size, bark cover, branch order present and variables derived from tree-ring analyses) were used in stepwise linear regression procedures to identify variables that explained time since death. Number of branch orders present (where branches growing directly on the stem were branch order 1, branches growing on order 1 branches were order 2, and so on) explained two-thirds of the variation in time since death. Adding other significant variables, such as diameter, relative height of snags, percentage bark cover and average tree-ring width in the final years before death, increased model precision only moderately. The models were validated by the PRESS statistic, which showed that new observations were predicted fairly well with 65-69% of the variation explained.