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The effect of canopy openness of European beech (Fagus sylvatica) forests on ground‐dwelling spider communities

The composition of spider communities in forests is affected by habitat characteristics, such as canopy openness, vegetation cover or tree species diversity; therefore, we assume that the effect of canopy will differ among tree species. As research in European beech forests has not been conducted, we studied the effect of understory environmental characteristics associated with a gradient of overstory canopy openness in beech forest on ground‐dwelling spider richness, abundance and guild composition in the Western Carpathians, Slovakia. Canopy openness, the cover of understory vegetation and litter, litter thickness and variability and soil reaction were recorded. In total, 17 332 individuals of 174 spider species were trapped during 518 days. We used Generalised Linear Models to explain the effect of environmental characteristics on the assemblages of ground‐dwelling spiders; the unique and shared contributions of the predictors were calculated using variation partitioning. The association of canopy openness with spider species richness was hump‐shaped and displayed positive linear relationship with abundance. Abundance was also affected by soil pH. The composition of spider communities was significantly affected by canopy openness and understory characteristics; a major part of this variation was shared between all variables. The guild composition of the assemblages interacted with canopy openness, as sheet‐web weavers were dominant under the most closed canopy, that below 20% of canopy openness, while ground hunters dominated in the rest of the canopy gradient. The gradient of beech forest canopy openness affected spider species richness, abundance and guild composition and supported distinct assemblages.