As our results indicated, sometimes the opposite can occur. Such trends in the evaluation data set are difficult to account for, because they cannot simply be corrected by a plot-specific adjustment of the intercept term. Height growth differences in this study ranged from 0.01 to 0.12 m year−1. These results are consistent with similar research. Height increment bias previously reported ranged from 0.01 to 0.30 m year−1 (Sterba et al., 2001 and Härkönen et al., 2010). As with diameter increment, temporal or spatial trends or size effects can occur. Our results indicate that differing height growth patterns can partly be attributed to an incorrect shape

of the site-index function. For example, the particularly good prediction SCH727965 purchase results for spruce in Arnoldstein with the growth model Moses result from a run with the site-index functions of Assmann and Franz (1965). These site-index functions are known to very closely match the height growth patterns in Arnoldstein. In contrast, we did not find any spruce yield table that adequately represents dominant height growth in Litschau. Even though the model run with spruce “Hochgebirge” was better than with any other yield table, bias still remained. Raf activation Another example is Prognaus: comparing the height growth patterns resulting from the Prognaus

height increment model ( Nachtmann, 2006) to the height growth patterns in Arnoldstein and to the yield tables of Assmann and Franz (1965) showed

that the Prognaus height increment pattern was notably too steep at advanced ages, resulting in biased predictions. In contrast, observed and predicted height growth patterns for Prognaus were nearly identical in Litschau, resulting in a good performance. Therefore, an appropriate curve form for a particular region is crucial to correctly predict height growth. Whereas the shape of the site-index curves is routinely examined before the application of a yield table for a region, evaluations of forest growth models so far have mostly focused on overall bias, ignoring shape. In individual-tree growth models that derive potential height increment from yield tables, often only one curve form per species is implemented (e.g. BWIN, and the first version of Moses). The assumption of one OSBPL9 curve shape per species is certainly too stringent, since it is known that the pattern of height growth can vary considerably for different climatic regions, vegetation types, soils, or degrees of competition ( Stage, 1963, Monserud, 1984 and Sterba and Eckmüllner, 2009). Here, a modification that allows for different site-index curves (e.g. Kindermann and Hasenauer, 2005) may help to solve this problem. Site-index functions developed from site factors appear flexible enough to represent different height growth patterns (Prognaus and Silva).