Communication Deadwood, Soil and Carabid Beetle-Based Interaction Networks—An Initial Case Study from Montane Coniferous Forests in Poland Magdalena Kacprzyk 1,*, Ewa Bło ´nska 2 and Tadeusz Wojas 1 1 Department of Forest Ecosystems Protection, University of Agriculture in Krakow, Al. 29 Listopada 46, 31-425 Kraków, Poland; [email protected] 2 Department of Ecology and Forest Silviculture, University of Agriculture in Krakow, Al. 29 Listopada 46, 31-425 Krakow, Poland; [email protected] * Correspondence: [email protected] Abstract: In four study plots located in silver fir and Scots pine stands in Magura National Park (southeastern Poland), the relationships between the occurrence and biomass of epigeic carabids, the volume of deadwood and soil biochemical properties were investigated. Thirteen carabid beetle species from the genera Abax, Carabus, Molops and Pterostichus were captured. Rare epigeic carabid species in the fauna of Poland and Europe, such as Carabus glabratus (Paykull), Carabus sylvestris (Panzer) and Abax schueppeli (Germar), were recorded. The number of carabid individuals and species captured as well as the mean individual biomass index at different elevations and in forests of different tree compositions differed significantly. There were no correlations between deadwood volume, carabid abundance and the mean individual biomass of the carabid beetles. The mean individual Carabidae biomass increased with elevated pH, soil carbon content, soil dehydrogenase activity and the number of stumps. Citation: Kacprzyk, M.; Bło´nska,E.; Wojas, T. Deadwood, Soil and Keywords: dead trees; decomposition degree; epigeic beetles; dehydrogenases Carabid Beetle-Based Interaction Networks—An Initial Case Study from Montane Coniferous Forests in Poland. Forests 2021, 12, 382. The relationship between the occurrence of carabid beetles and deadwood has been https://doi.org/10.3390/f12040382 poorly understood thus far. Few studies have demonstrated positive associations between ground beetle abundance, species richness and diversity and the amount (number and Academic Editor: Zoltán Elek volume of trees) of coarse woody debris [1–3]; however, the extent to which the occur- rence of carabid beetles depends both on the quantity and quality of deadwood remains Received: 6 March 2021 unresolved. Moreover, understanding the changes in carabid biomass, which have not yet Accepted: 22 March 2021 Published: 24 March 2021 been studied, together with species composition as a result of deadwood presence could allow us to expand our knowledge in this area. The individual biomass of carabid beetles Publisher’s Note: MDPI stays neutral (mean individual biomass, MIB) is strongly and positively related to the biomass of the with regard to jurisdictional claims in macrofauna responsible for litter decomposition, which is reflected in the quantity and published maps and institutional affil- quality of organic matter necessary for the proper functioning of forest ecosystems and the iations. nutrient cycle [4–6]. Higher macrofaunal biomass and faster decomposition of the litter layer result in increased carbon (C) content in mineral soil and have positive effects on soil microbial activity. The presence of dead trees in forests stimulates biological activity in soils and the development of soil microorganism populations. Bło´nskaet al. [7] and Piaszczyk et al. [8] Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. proved an increase in dehydrogenases (DHs—enzymes that provide information about This article is an open access article the soil condition and the microorganism activity in the soil; [9,10]) activity in the vicinity distributed under the terms and of stumps and dead trees lying on the ground. The chemical substances that result from conditions of the Creative Commons the death and decomposition of woody tissues reach the organic layer of the soil and Attribution (CC BY) license (https:// contribute to the overall contents of carbon and other nutrients, which are food sources creativecommons.org/licenses/by/ for soil-litter invertebrates and are associated with the occurrence of the prey of predatory 4.0/). carabid beetles [11–14]. The soil organic matter content has a significant impact on carabid Forests 2021, 12, 382. https://doi.org/10.3390/f12040382 https://www.mdpi.com/journal/forests Forests 2021, 12, 382 2 of 9 biomass. Szyszko et al. [15] showed a significant increase in the MIB value of epigeic carabid beetles together with an increase in the carbon content of a forest stand. Changes in soil parameters, and consequently in carabid biomass under the influence of deadwood, may have a relationship with the degree of its decomposition, determined by the form and species composition of a stand and microenvironmental conditions [16,17]. An increase humidity, decrease temperature along an altitudinal gradient may have consequences in decrease of MIB of carabid beetles [18,19]. At the same time climate features (temperature, precipitation), as well as deadwood species and its physical characteristics (density) may influence on quantity and quality of soil organic matter and dead wood decomposition rate [20–23]. The aim of this study was to compare carabid beetle assemblages (species compo- sition and richness) and MIB index values in Scots pine and silver fir stands in relation to deadwood stock, decomposition degree and selected chemical soil parameters. The following hypotheses were tested: (1) carabid abundance and biomass will increase with an increasing amount and volume of deadwood; (2) the individual carabid beetle biomass is positively correlated with the biological activity of soils; and (3) deadwood affects soil biological activity and carabid biomass differently in fir and pine forest stands at different elevations (thermal and humidity conditions) as a result of the impact on the quantity and quality of soil organic matter and rate of decomposition. The study was conducted in 2016 in four stands located in Magura National Park in the western Carpathians in southeastern Poland (49◦30000” N, 21◦30000” E). In two of the stands, the dominant tree species was silver fir (Abies alba Mill.), while in the other two stands Scots pine (Pinus sylvestris L.) was the forest-forming tree species. In the pine stands, the species admixture included larch (Larix decidua Mill.), ash (Fraxinus excelsior L.), common beech (Fagus sylvatica L.), European hornbeam (Carpinus betulus L.), maple (Acer spp.), birch (Betula spp.) and rowan (Sorbus aucuparia L.). The fir stand species composition was less varied, with an admixture of common oak (Quercus robur L.) and common beech. For each dominant tree species, two elevations were evaluated: the foothills, between 300 and 450 m above sea level, and the lower montane zone at 600 m a.s.l. The fir stands were 60 years old, while the pine stands were 50 years old. All the stands had a moderate density, i.e., broken canopy closure. The following symbols were assigned to the study sites: SPF—Scots pine stand in the foothill zone; SPLM—Scots pine stand in the lower montane zone; SFF—silver fir stand in the foothill zone; and SFLM—silver fir stand in the lower montane zone. In each of the stands, study plots with area of 25 ares (50 m × 50 m) were established for soil sampling and the inventories of deadwood and carabid beetles were performed within these plots. The adopted inventory procedures of deadwood and soil sampling design were described in detail by Bło´nskaet al. [7]. Carabid beetle monitoring was performed using pitfall traps (9 cm diameter and 0.5 L capacity). In each study plot, six traps were placed at a minimum distance of 20 m from each other. Four traps were arranged within 50 cm of dead prostrate trees (two traps near dead prostrate trees in decay stage III and two traps near dead prostrate trees in decay stage IV), whereas two traps were placed within 50 cm of stumps (one trap near the stump in decay stage III and one trap near the stump in decay stage IV). A 30 m distance from the edge of each study plot for pitfall traps was adopted. A total of 24 pitfall traps were installed. The pitfall trap catch was retrieved at weekly intervals from 30 April to 15 August. All the plots were sampled on the same day. At every turn the beetles were identified to the species level and weighed to the nearest 0.1 mg using an electronic scale (WPE 600, Radwag Balances and Scales). After weighing each beetle, they were released at a distance of 30 m from the study plot. To analyze the beetle assemblages within the biocenosis, an individual dominance in- dex (Di), a quantitative ecological indicator that reflects the percentage share of individuals of one particular species found among the total number of individuals of all species found in the studied ecosystem, was utilized. To compare the forest habitats, the Simpson domi- Forests 2021, 12, 382 3 of 9 nance (c) index, which relates a coefficient of importance for each species (biomass) to the sum of the coefficients of importance, was used [24]. The Shannon diversity index (H’; [25]) was used to evaluate species diversity. Based on carabid biology and ecology [26–28], the beetles were classified into the following ecological groups: (a) Trophic—large zoophages with body lengths greater than 15 mm, small zoophages with body lengths less than 15 mm or hemizoophages (i.e., omnivorous species); (b) Habitat—forest, eurytopic or open area species; and (c) Geographical—Palearctic, Holarctic or European species. Taking into account carabid humidity preferences, we distinguished the follow- ing groups: (d) Hygrophilous species, whose occurrence is related to high water content in the soil; (e) Mesophilous species, which live in areas characterized by moderate soil moisture; and (f) Xerophilous species, which can occur in an environment with low water availability. The carabid nomenclatures were based on de Jong et al. [29]. The effect of elevation and tree stand species composition on the deadwood vol- ume was examined with a Mann–Whitney U test, whereas the differences in the mean values of the soil properties were evaluated by the Kruskal–Wallis test.