Aim Revisits of non‐permanent, relocatable plots first surveyed several decades ago offer a direct way to observe vegetation change and form a unique and increasingly used source of information for global change research. Despite the important insights that can be obtained from resurveying these quasi‐permanent vegetation plots, their use is prone to both observer and relocation errors. Studying the combined effects of both error types is important since they will play out together in practice and it is yet unknown to what extent observed vegetation changes are influenced by these errors. Methods We designed a study that mimicked all steps in a resurvey study and that allowed determination of the magnitude of observer errors only vs the joint observer and relocation errors. Communities of vascular plants growing in the understorey of temperate forests were selected as study system. Ten regions in Europe were covered to explore generality across contexts and 50 observers were involved, which deliberately differed in their experience in making vegetation records. Results The mean geographic distance between plots in the observer+relocation error data set was 24 m. The mean relative difference in species richness in the observer error and the observer+relocation data set was 15% and 21%, respectively. The mean “pseudo‐turnover” between the five records at a quasi‐permanent plot location was on average 0.21 and 0.35 for the observer error and observer+relocation error data sets, respectively. More detailed analyses of the compositional variation showed that the nestedness and turnover components were of equal importance in the observer data set, whereas turnover was much more important than nestedness in the observer+relocation data set. Interestingly, the differences between the observer and the observer+relocation data sets largely disappeared when looking at temporal change: both the changes in species richness and species composition over time were very similar in these data sets. Conclusions Our results demonstrate that observer and relocation errors are non‐negligible when resurveying quasi‐permanent plots. A careful interpretation of the results of resurvey studies is warranted, especially when changes are assessed based on a low number of plots. We conclude by listing measures that should be taken to maximally increase the precision and the strength of the inferences drawn from vegetation resurveys.

Our paper presents a comparison of historical data concerning the distribution of forest communities in the Sowie Mountains in southwestern Poland in 1968-71 with material collected by the authors between 2009 and 2013. The analyses were performed using geographic information system software. The archival vegetation maps were digitized, and the layer of the current distribution of forest communities was applied afterward. Archival data indicated that, in the study area, spruce monocultures of anthropogenic character predominated, occupying 90% of forest area. The obtained results suggest that regular forest management conducted within the study area has surprisingly contributed to an increase in the area of forest communities of the Querco-Fagetea class from 766 to 1,579 ha (more than 100%) over the last 45 years. The largest rise in the area of studied communities was observed on meso-oligotrophic habitats, and was reflected in the increase of the area of acidophilous beech forests, representing Luzulo luzuloidis-Fagetum association (habitat 9110 protected in the European Union), from 168 ha to1,064 ha. There was a minor decrease in the area of submontane riparian forests Carici remotae-Fraxinetum (habitat 91E0); the area of mesotrophic beech forests Galio odorati-Fagetum (habitat 9130) seems to be stable. Approximately 72% of deciduous forests in the study area have retained their spatial cover for 45 years.The newly created forest communities are deprived of a number of essential elements of the structure, primarily dead wood, including lying trunks and trees. The lack of these features does not allow us to assess the status of these ecosystems as entirely satisfactory. However, the possibility of converting Picea abies monocultures in deciduous forests of the Querco-Fagetea class under regular forest management should be considered beneficial to the conservation status of forest ecosystems of mountain areas of Central Europe.

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