As demonstrated by Roschak (1998), a management
demonstration and referencing plot may be used to obtain
empirical data about forest dynamics. The resulting
forest and tree models provide the basis for silvi-cultural decision-making. They are developed from
empirical data which may be obtained in field experiments.
Considering the time horizon, three types of trials
have been used. Permanent growth trials are established
and remeasured, usually at regular intervals, for
long periods of time, resulting in high maintenance
cost and long wait for data. Temporary plots may provide
a quick solution in a situation were nothing is
known about forest dynamics. They are measured only
once, but cover a wide range of ages and growing sites,
assuming some “normal” or representative silviculture.
This method has been used extensively during the 19th
century (see, for example Kramer 1988, p. 97; Assmann
1953; Wenk et al. 1990 p. 116). The main limitation
of the temporary plots is the fact that they do not
provide information about change rates. Thus, most of
the contemporary modelling techniques cannot be applied.
Interval plots, measured twice and spread over a
range of growing sites, development stages and silvicultural
treatment categories, combine the advantages
of the permanent plot, – change information, – and the
temporary designs, minimum wait for data. The interval
between two successive measurements should be
sufficiently long to absorb the short-term effects of abnormal
climatic extremes.