The paper presents the main results of the comprehensive inventory of monumental trees in the Strict Reserve of the Białowieża National Park, which was conducted in years 2002−2017 on an area of ca. 4700 ha and included all live trees with diameter at breast height (dbh) exceeding a minimum threshold value ranging from 60 cm for hornbeam to 120 cm for oak. For every tree fulfilling this condition, species identity, circumference at 1.3 m (measured with tape), geo− graphical coordinates (GPS record) and health status (five classes) were determined. In total, 9190 trees from eleven different species were inventoried. Hornbeam, oak, maple, lime, ash and aspen were the most abundant with their total share in the amount of monumental trees equal to ca. 96%. The average density of monumental trees in the Strict Reserve was approximately 2 ind./ha. The majority (88%) of monumental trees were found in different subassociations of Tilio−Carpinetum community: T−C. calamagrostietosum, T.−C. typicum, T.−C. circaeaetosum alpine, T.−C. caricetosum remotae and T.−C. stachyetosum. As a rule, the fraction of particular species in the amount of monumental trees did not correspond to their fraction in the total pool of trees with dbh5 cm. Particularly high over−representation characterized oak, maple, ash and aspen. On the other hand, such species like spruce and, to a lesser degree, hornbeam, lime, alder and birch played much smaller role in the group of monumental trees than among all trees with dbh 5 cm. The monumental trees of particular species were distinguished by a high diameter differentiation. In this respect, oak clearly prevailed over the other ones. In contrast, the smallest dimensions were typical for hornbeam. The results obtained suggested the need of revision of minimum threshold values of circumference (and of corresponding dbh), used to classify a given individual as a monumental tree. This problem was particularly acute in case of pine, spruce, alder and birch. We suggest that the current minimum values of dbh for these species should be reduced by 10− −20 cm. Further, the comparison of the recorded values of dbh for some species with maximum values of dbh provided in the literature indicated the necessity of correction of the last values, both ‘in plus’ as well as ‘in minus’. For alder, aspen and maple, the current values should be increased by ca. 20−30 cm. On the other hand, for pine, the recent value should be reduced by at least 30 cm. We point out that the definition of large (monumental) tree is, to a large extent, an arbitrary issue. The various growth potential of particular tree species, occurring within a given area, implies that this definition should be used flexibly. It means a necessity of using different thresholds for different species and varied environmental conditions. Also, because of the relative rarity of large trees, the reliable estimation of their density can only be obtained on the basis of sufficiently large sample size. Some high values of density of large trees, which can be found in the existing literature (10−20 trees per hectare and more), may be the result of too small sample sizes.
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