Nutrient addition, but not predator exclusion, shapes arthropod communities and herbivory in a temperate forest

Plants support diverse arthropod communities, and arthropod herbivores respond differently to plant traits, nutritional content, and defences, which influence their host plants selection, survival and performance (bottom-up control). At the same time, arthropod herbivores are affected by their interactions with predators (top-down control). Investigating how these forces interact, and how they are affected by nutrient availability, is crucial for understanding the mechanisms driving herbivore populations and their impact on ecosystems.
We investigated how predator exclusion and fertilisation affect arthropod densities, sizes, and herbivory on two temperate forest tree species. Using a factorial design, we compared fertilised and unfertilised trees with and without the exclusion of flying vertebrate predators in the forest understory during September 2020 and 2021. We collected and identified arthropods into feeding guilds.
Fertilisation, but not predator exclusion, increased herbivory d..., Arthropod survey
We used beating sheets to collect all arthropods from each of the trees. We measured all arthropods (to the nearest mm) and identified them into morphospecies, assigned them to an order or family if necessary for their assignment to one of the following four feeding guilds: predator, leaf chewer, leaf sucker, and as having “no relationship” (i.e., arthropod with no consumptive relationship with other arthropods or plants). Considering that the adult arthropod may belong to a different feeding guild than the juvenile, the developmental stage was considered in the guild assignment. 
Herbivory damage survey
Individual leaves with a piece of cm-scale were scanned (EPSON, 600 dpi, colour tiff format) within 12 hours after collection. To analyse herbivory, we first outlined the missing part of the leaves based on the expected shape in Photoshop® (following Sam et al., 2020). Then we calculated the remaining area (a) and the full expected area of each leaf (b, both in cm2..., , # **Nutrient addition, but not predator exclusion, shapes arthropod communities and herbivory in a temperate forest**

Dataset DOI: [10.5061/dryad.5dv41nsh2](10.5061/dryad.5dv41nsh2)

**Description of the data and file structure**

This dataset was collected in a riparian forest (*Alnion incanae*) near Čejkovice, Czech Republic, as part of a study investigating the effects of nutrient addition and predator exclusion on arthropod communities and herbivory in a temperate forest. Using a fully factorial field experiment, we manipulated fertilization levels (fertilized, non-fertilized) and access to flying vertebrate predators (birds and bats) on two tree species: *Tilia cordata* and *Alnus glutinosa*.

Over two years (2020–2021), we surveyed arthropods on experimental trees by collecting individuals and classifying them into morphospecies and feeding guilds (chewers, sap-suckers, predators, and arthropods with no direct relationship to plants or other arthropods). We measured arthropod den...,