DOI: 10.5061/dryad.hhmgqnks1
title: Data from: Peeking under the bark: Within-tree densities of the spruce bark beetle (<em>Ips typographus</em>) and its enemies in forest conservation areas

description: The European spruce bark beetle Ips typographus is a major forest pest in
 Europe, with outbreaks intensifying due to climate change-induced weather
 events. In this study, we evaluated within-tree densities of the spruce
 bark beetle and its natural enemies during an outbreak in northern Europe.
 Densities were compared across different forest management types: managed
 forests and two conservation areas (woodland key habitats and nature
 reserves). We assessed beetle colonization density, production,
 reproductive success, predator abundance, and forest characteristics
 through bark sample analysis during four years. Our results indicate that
 spruce bark beetle densities were positively associated with surrounding
 tree mortality, with no significant differences in within-tree densities
 across forest types. Instead, variations in density were more pronounced
 across different outbreak phases and forest conditions, derived from
 remote sensing data. Enemy abundance, particularly Plegaderus spp. and two
 fungivorous insect groups, were generally higher in nature reserves
 compared to managed forests. We conclude that complex interactions between
 forest conditions, outbreak phases, and the occurrence of some specific
 predators play more crucial roles in bark beetle dynamics than whether a
 forest is a conservation area or not. For example, in wetter forests, more
 beetles are needed to overcome defences, while in deciduous forests,
 non-host volatiles may inhibit pheromones. Specifically, we highlight the
 less known clown beetle Plegaderus spp. as an important predator,
 negatively affecting bark beetle reproductive success. These findings
 emphasize the importance of local forest characteristics in managing bark
 beetle infestations, suggesting that outbreak risk assessments should
 focus on these variables rather than on forest conservation status, though
 potential variations at larger scales are beyond the scope of our study.
description: The study was conducted by annual surveys during the autumns
 (Oct-Nov) between 2020 and 2023 in Southern Sweden (Fig.1). We collected
 222 bark samples from M (N=71), WKH (N=72) and NR (N=79), typically in
 spatial triplets (blocks).  In total we used 49 sites in this study (M=16,
 WKH=15, NR=18).  For the existing forest cover around
 our sampled locations, we utilized data from the National Land Cover
 Database (Swedish Environmental Protection Agency 2020). The database
 categorizes Sweden into various land cover classes with a 10-meter
 resolution. Mean soil moisture was extracted from a
 national-scale raster mapping (ranging from 0 to 100, dry to wet, 10-meter
 resolution), based on digital terrain indices and ancillary environmental
 information (Ågren et al. 2021). However, values exceeding 98 were
 excluded as they commonly indicate open fens or bogs and, thus, are
 non-forest areas.
description: # Data from: Peeking under the bark: within-tree densities of the spruce
 bark beetle (*Ips typographus*) and its enemies in forest conservation
 areas **Bark_sample_data_Kärvemo_et_al.xlsx**\ This file contains all
 variables described below, including site information, bark sample
 measurements, insect counts, and environmental variables. ## Description
 of data files | VARIABLES | EXPLANATION | | :------------------- |
 :------------------------------------------------------------------------------------ | | Site | Site name (used as random factor) | | Triplett/Block | The block (used as random factor) | | Management | Forest type (Managed (M), Woodland key habitats (WKH), Nature reserves (NR)) | | Group | Tree group | | Year | Year when the bark sample was taken | | Date | Date when the bark sample was taken | | Diameter | Diameter of sampled tree (cm) | | Sample height | Height of the tree stem where the sample was taken (m) | | Bark length | Bark sample length (cm) | | Bark width | Bark sample width (cm) | | Bark Thickness | Bark sample thickness (mm) | | Bark size | Bark sample size (m2) | | Colonisation density | Number of entrance holes in the bark | | Production | Number of emergence holes + bark beetles in the bark | | Reprod success | (Production/2)/Colonisation density | | Medetera | Number of Medetera larvae | | Thanasimus | Number of Thanasimus larvae | | Plegaderus | Number of Plegaderus spp. | | Staphylinidae | Number of Staphylinidae | | Stratiomyidae | Number of Stratiomyidae | | Sciaridae | Number of Sciaridae | | Rhizophagus | Number of Rhizophagus | | Raphidiidae | Number of Raphidiidae | | Lonchaea | Number of Lonchaea | | Cecidomyiidae | Number of Cecidomyiidae | | Soil moisture 0-100 | Soil moisture index ranging from 0-100 within 100 m from the main tree group | | Soil moisture 0-97 | Soil moisture index ranging from 0-97 within 100 m from the main tree group | | Spruce\_Ha\_100m | Hectares of Norway spruce (&gt;5 m in height) within 100 m from the main tree group   | | Conif\_Ha\_100 | Hectares of coniferous trees (&gt;5 m in height) within 100 m from the main tree group   | | Decid\_Ha\_100m | Hectares of deciduous trees (&gt;5 m in height) within 100 m from the main tree group   |