Sampling of insect communities is very challenging and for reliable interpretation of results the effects of different sampling protocols and data processing on the results need to be fully understood. We compared three different commonly used methods for sampling forest beetles, freely hanging flight-intercept (window) traps (FWT), flight-intercept traps attached to trunks (TWT) and pitfall traps placed in the ground (PFT), in Scots pine dominated boreal forests in eastern Finland. Using altogether 960 traps, forming 576 sub-samples, at 24 study sites, 59760 beetles belonging to 814 species were collected over a period of a month. All of the material was identified to species, with the exception of a few species pairs, to obtain representative data for analyses. Four partly overlapping groups were used in the analyses: (1) all, (2) saproxylic, (3) rare and (4) red-listed species. In terms of the number of species collected TWTs were the most effective for all species groups and the rarer species the species group composed of (groups 1-2-3-4) the larger were the differences between the trap types. In particular, the TWTs caught most red-listed species. However, when sample sizes were standardized FWTs and TWTs caught similar number of species of all species groups. PFTs caught fewer species of all species groups, whether the sample sizes were standardized or not. In boreal forests they seem to be unsuitable for sampling saproxylic, rare and red-listed species. However, the PFTs clearly sampled different parts of species assemblages than the window traps and can be considered as a supplementary method. The abundance distribution of saproxylic species was truncated lognormal in TWT and pooled material, whereas unclassified material failed to reveal lognormal distribution in all the trap types and pooled material. The results show that even in boreal forests sample sizes of at least thousands, preferably tens of thousands of individuals, collected by a high number of traps are needed for community level studies. Relevant ecological classification of material is also very important for reliable comparisons. Differences in the performance of trap types should be considered when designing a study, and in particular when evaluating the results.
Studie se zabývá pravěkým vývojem oblasti Bezdězska – Dokeska v severních Čechách se zvláštním zřetelem na výzkum laténského sídliště Okna, které je s opatrností připisováno kobylské skupině. Sídliště je posuzováno s ohledem na fakta získaná paleobotanickým, geobotanickým a sedimentologickým výzkumem lokality i celého zkoumaného regionu, který je z velké části tvořen boreálním lesem. Jsou diskutovány možnosti jeho využívání v pravěku a důvody pozdní kolonizace zemědělských půd v jeho bezprostředním okolí, která nastává až v pozdně laténském období a následně ve středověku. Výzkum nivy Robečského potoka zachytil dvě erozní události, které jsou následkem odlesnění a vzniku polí, první v době existence laténského sídliště a druhá nejspíše po založení středověké vsi Okna. and The study deals with the prehistoric development of the Bezděz – Doksy region in Northern Bohemia, with special regard to the excavation of the La Tène settlement at Okna that is cautiously ascribed to the Kobyly group. The settlement is assessed according to the data obtained by palaeobotanic, geobotanic and sedimentologic research of the site as well as the whole studied region which is largely comprised of boreal forest. Its possible use in prehistory and the reasons of late colonization of agricultural lands in its immediate vicinity, which occurs only in late La Tène period and subsequently in the Middle Ages, are discussed. Survey of the alluvial plain of the Robečský brook revealed two erosion events which may be results of deforestation and establishment of fields, first during the existence of the La Tène settlement and the last probably upon foundation of the medieval village of Okna.