In years 2002-2004 eight pairs of experimental surfaces, one from the 3rd and one from the 4th age class, were established in pure pine stands in the Lubin Forest District. In each of these sample plots crown defoliation, the condition of the assimilation apparatus, height increment and shoot vitality of 25 trees of the main stand were assessed. Differences between mean defoliations were compared using for this purpose the standard error of the difference of two means (for P = 0.95). The performed analysis was carried out for each of the experimental surfaces and for the given entire age class during three experimental periods (i.e. years 2002-2003, 2003-2004 and 2002-2004) as well as for pairs of surfaces and age classes in the consecutive three years of observations (2002, 2003 and 2004).

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