Experimente zu Biodiversität und Ökosystemleistungen
Hier finden Sie englisch- und deutschsprachige Zusammenfassungen von verschiedenen Veröffentlichungen zu Ergebnissen aus dem Teilprojekt 2 - Experimente zu Biodiversität und Ökosystemleistungen.
Snags, logs, stumps, and microclimate as tools optimizing deadwood enrichment for forest biodiversity
The reduction of deadwood due to forest management threatens saproxylic diversity. Therefore, deadwood needs to be preserved and enriched. While the importance of deadwood tree identity is well investigated, the value of different object types and microclimate for diversity is insufficiently understood. Conservation-oriented forest management, therefore, requires guidelines on how deadwood types under various microclimatic conditions can help to sustain saproxylic diversity. We set up an experiment in sub-montane beech forest to disentangle effects of microclimate (sun vs. shade) and deadwood types (logs, stumps, snags). By surveying beetles, fungal fruiting bodies, and fungal molecular taxa (amplicon sequence variants, ASVs) in early-decomposition stage deadwood, we asked: (i) What is the relative importance of deadwood types vs. microclimate on saproxylic αand β-diversity? (ii) What is the importance of stumps, logs, and snags for saproxylic α- and β-diversity? (iii) Which combinations of microclimate and deadwood type maximize γ-diversity? Deadwood types had a stronger effect on α- and β-diversity of all groups than microclimate, which was not significant in most cases. Among deadwood types, α-diversity was higher on logs than on other deadwood types for beetles and fungal fruiting species. Fungal ASVs reached high α-diversity on snags. Considering effective combinations of deadwood types and microclimate in their contribution to γ-diversity, shaded and sunny logs showed most importance for beetles and fruiting fungi, while sunny snags were important for fungal ASVs. Maintenance of saproxylic diversity is therefore best achieved via enrichment of different deadwood types and by emphasizing logs and snags under variable microclimates.
Uhl, B., Krah, F.-S., Baldrian, P., Brandl, R., Hagge, J., Müller, J., Thorn, S., Vojtech, T., & Bässler, C. (2022). Snags, logs, stumps, and microclimate as tools optimizing deadwood enrichment for forest biodiversity. Biological Conservation, 270, 109569.
A replicated study on the response of spider assemblages to regional and local processes
Understanding species richness variation among local communities is one of the central topics in ecology, but the complex interplay of regional processes, environmental filtering and local processes hampers generalization on the importance of different processes. Here, we aim to unravel drivers of spider community assembly in temperate forests by analyzing two independent data sets covering gradients in elevation and forest succession. We test the following four hypotheses: (H1) Spider assemblages within a region are limited by dispersal; (H2) Local environment has a dominant influence on species composition; and (H3) resources and (H4) biotic interactions both affect species richness patterns. In a comprehensive approach, we studied species richness, abundance, taxonomic composition and trait-phylogenetic dissimilarity of assemblages. The decrease in taxonomic similarity with increasing spatial distance was very weak, failing to support H1. Functional clustering of species in general and with canopy openness strongly supported H2. Moreover, this hypothesis was supported by a positive correlation between environmental and taxonomic similarity and by an increase in abundance with canopy openness. Resource determination of species richness (H3) could be confirmed only by the decrease of species richness with canopy cover. Finally, decreasing species richness with functional clustering indicating effects of biotic interactions (H4) could only be found in one analysis and only in one dataset. In conclusion, our findings indicate that spider assemblages within a region are mainly determined by local environmental conditions, while resource availability, biotic interactions and dispersal play a minor role. Our approach shows that both the analysis of different aspects of species diversity and replication of community studies are necessary to identify the complex interplay of processes forming local assemblages.
Müller, J., Brandl, R., Cadotte, M. W., Heibl, C., Bässler, C., Weiß, I., Birkhofer, K., Thorn, S., & Seibold, S. (2022). A replicated study on the response of spider assemblages to regional and local processes. Ecological Monographs, e1511.
Beetle diversity is higher in sunny forests due to higher microclimatic heterogeneity in deadwood
Microclimate is a crucial driver of saproxylic beetle assemblages, with more species often found in sunny forests than in shady ones. Whether this pattern is caused by a higher detectability due to increased beetle activity under sunny conditions or a greater diversity of beetles emerging from sun-exposed deadwood remains unclear. This study examined whether sun exposure leads to higher microclimatic heterogeneity in deadwood and whether this drives beetle diversity in deadwood logs and at forest stand scale. Saproxylic beetles were sampled at the stand scale using flight-interception traps and at object scale using stem-emergence traps on deadwood logs at the same site. The variability in wood surface temperature was measured on single logs and between logs as a proxy for microclimatic heterogeneity in deadwood. Abundance in sunny forests was higher at the stand scale, and in shady forests at the object scale. The estimated number of species was higher in sunny forests at both scales and correlated positively with temperature variability on single logs and between logs at the stand scale and, albeit weakly, with temperature variability on single logs at the object scale. Gamma-diversity, and thus beta-diversity, across logs at the object scale was higher in sunny forests. These findings indicate that sun exposure promotes saproxylic beetle diversity due to higher microclimatic heterogeneity within and between deadwood logs. Our study therefore corroborates previous research demonstrating the importance of canopy cover and microclimate for forest biodiversity.
Lettenmaier, L., Seibold, S., Bässler, C., Brandl, R., Gruppe, A., Müller, J., & Hagge, J. (2022). Beetle diversity is higher in sunny forests due to higher microclimatic heterogeneity in deadwood. Oecologia, 198(3), 825–834.
Fungal fruit body assemblages are tougher in harsh microclimates
Forest species are affected by macroclimate, however, the microclimatic variability can be more extreme and change through climate change. Fungal fruiting community composition was affected by microclimatic differences. Here we ask whether differences in the fruiting community can be explained by morphological traits of the fruit body, which may help endure harsh conditions. We used a dead wood experiment and macrofungal fruit body size, color, and toughness. We exposed logs of two host tree species under closed and experimentally opened forest canopies in a random-block design for four years and identified all visible fruit bodies of two fungal lineages (Basidio- and Ascomycota). We found a consistently higher proportion of tough-fleshed species in harsher microclimates under open canopies. Although significant, responses of community fruit body size and color lightness were inconsistent across lineages. We suggest the toughness-protection hypothesis, stating that tough-fleshed fruit bodies protect from microclimatic extremes by reducing dehydration. Our study suggests that the predicted increase of microclimatic harshness with climate change will likely decrease the presence of soft-fleshed fruit bodies. Whether harsh microclimates also affect the mycelium of macrofungi with different fruit body morphology would complement our findings and increase predictability under climate change.
Krah, F.-S., Hagge, J., Schreiber, J., Brandl, R., Müller, J., & Bässler, C. (2022). Fungal fruit body assemblages are tougher in harsh microclimates. Scientific Reports, 12(1), 1633.
Fungal Community Development in Decomposing Fine Deadwood Is Largely Affected by Microclimate
Fine woody debris (FWD) represents the majority of the deadwood stock in managed forests and serves as an important biodiversity hotspot and refuge for many organisms, including deadwood fungi. Wood decomposition in forests, representing an important input of nutrients into forest soils, is mainly driven by fungal communities that undergo continuous changes during deadwood decomposition. However, while the assembly processes of fungal communities in long-lasting coarse woody debris have been repeatedly explored, similar information for the more ephemeral habitat of fine deadwood is missing. Here, we followed the fate of FWD of Fagus sylvatica and Abies alba in a Central European forest to describe the assembly and diversity patterns of fungal communities over 6 years. Importantly, the effect of microclimate on deadwood properties and fungal communities was addressed by comparing FWD decomposition in closed forests and under open canopies because the large surface-to-volume ratio of FWD makes it highly sensitive to temperature and moisture fluctuations. Indeed, fungal biomass increases and pH decreases were significantly higher in FWD under closed canopy in the initial stages of decomposition indicating higher fungal activity and hence decay processes. The assembly patterns of the fungal community were strongly affected by both tree species and microclimatic conditions. The communities in the open/closed canopies and in each tree species were different throughout the whole succession with only limited convergence in time in terms of both species and ecological guild composition. Decomposition under the open canopy was characterized by high sample-to-sample variability, showing the diversification of fungal resources. Tree species-specific fungi were detected among the abundant species mostly during the initial decomposition, whereas fungi associated with certain canopy cover treatments were present evenly during decomposition. The species diversity of forest stands and the variability in microclimatic conditions both promote the diversity of fine woody debris fungi in a forest.
Brabcová, V., Tláskal, V., Lepinay, C., Zrůstová, P., Eichlerová, I., Štursová, M., Müller, J., Brandl, R., Bässler, C., & Baldrian, P. (2022). Fungal Community Development in Decomposing Fine Deadwood Is Largely Affected by Microclimate. Frontiers in Microbiology, 13, 835274.
Saproxylic beetles trace deadwood and differentiate between deadwood niches before their arrival on potential hosts
Deadwood provides a variety of habitats for saproxylic beetles. Whereas the understanding of the drivers promoting saproxylic beetle diversity has improved, the process of deadwood colonisation and beetle's potential to trace resources is poorly understood. However, the mechanisms facilitating deadwood detection by saproxylic beetles appears to be essential for survival, as deadwood is usually scattered in time and space. To investigate whether saproxylic beetles distinguish before their arrival on potential hosts between alive trees and deadwood (lying, stumps, standing), deadwood arrangement (aggregated, distributed) and different heights on standing resources (bottom = 0.5 m, middle = 4–5 m, top = 7.30–11.60 m), we sampled saproxylic beetles with sticky traps in a deadwood experiment. We found on average 67% higher abundance, 100% higher species numbers and 50–130% higher species diversity of colonising saproxylic beetles consistently for all deadwood types compared to alive trees with a distinct community composition on lying deadwood compared to the other resource types. Aggregated deadwood arrangement, which is associated with higher sun-exposure, had a positive effect on species richness. The abundance, species number and diversity, was significantly higher for standing deadwood and alive trees at the bottom section of tree trunks. In contrast to living trees, however, the vertical position had an additional effect on the community composition on standing deadwood. Our results indicate that saproxylic beetles are attracted to potential deadwood habitats and actively select specific trunk sections before arriving on potential hosts. Furthermore, this study highlights the importance of sun-exposed resources for species richness in saproxylic beetles.
Graf M., Lettenmaier L., Müller J., Hagge J. (2021) Saproxylic beetles trace deadwood and differentiate between deadwood niches before their arrival on potential hosts. Insect Conservation and Diversity icad.12534.
Veränderungen der Pflanzendiversität in experimentell gestörten Buchenwäldern
Auf den Flächen des BioHolz-Experiments in der Entwicklungszone des Nationalparks Hunsrück-Hochwald wurden in den Jahren 2017 bis 2019 neben anderen Artengruppen auch die Gefäßpflanzen, Moose und Flechten erfasst. Hierbei wurden Vegetationsaufnahmen fest markierter Kreisflächen (Boden) sowie ausgewählter Einzelobjekte (Bäume, stehendes Totholz, liegende Stämme und Stümpfe) angefertigt. Bisher können nur wenige Veränderungen im Artenspektrum und der Abundanz einzelner Arten nachgewiesen werden. Außerdem sind die in ehemaligen Wirtschaftswäldern gelegenen Flächen sehr viel artenärmer als schon seit Jahrzehnten ungenutzte Buchenwälder vergleichbarer Standorte. Da der Beobachtungszeitraum noch zu kurz war, schlagen wir im Ausblick eine Fortführung der Beobachtungen in regelmäßigen, mehrjährigen Abständen vor. Diese lassen wichtige Erkenntnisse für die Erfolgsaussichten von Entwicklungsmaßnahmen auch in anderen struktur- und totholzarmen Waldbeständen erwarten.
Dittrich, S., & Krautkrämer, O. (2021). Veränderungen der Pflanzendiversität in experimentell gestörten Buchenwäldern. In Nationalparkamt Hunsrück-Hochwald (Ed.), Die Dynamik im Fokus. 5 Jahre Nationalpark Hunsrück-Hochwald – ein wissenschaftlicher Streifzug durch die Forschungslandschaft (Forschungsband 01) (Vol. 01, pp. 82–91). Nationalparkamt Hunsrück-Hochwald.
Effects of disturbance patterns and deadwood on the microclimate in European beech forests
More frequent and severe disturbances increasingly open the forest canopy and initiate tree regeneration. Simultaneously, increasing weather extremes, such as drought and heat, are threatening species adapted to cool and moist climate. The magnitude of the microclimatic buﬀering capacity of forest canopies to mitigate hot and dry weather conditions and its disturbance-induced reduction remains poorly quantiﬁed. Also, the inﬂuence of disturbance legacies (e.g., deadwood) on forest microclimate is unresolved. In a unique manipulation experiment we investigated (i) the microclimatic buﬀering capacity of forest canopies in years with diﬀerent climatic conditions; (ii) the impacts of spatial disturbance patterns on surface light and microclimate; and (iii) the eﬀect of deadwood presence and type on microclimate.
Thom, D., Sommerfeld, A., Sebald, J., Hagge, J., Müller, J. & Seidl, R. (2020). Effects of disturbance patterns and deadwood on the microclimate in European beech forests. Agricultural and Forest Meteorology 291, 108066.
Deadwood retention in forests lowers short-term browsing pressure on silver fir saplings by overabundant deer
Humans have widely extirpated large carnivores and simultaneously promoted overabundance of deer. The intense pressure imposed by these herbivores in forests has led to extremely low rates of natural forest regeneration. In natural old-growth forests, deadwood functions as a key driver of biodiversity and promotes ecosystem functioning, such as water retention and nutrient recycling. An as yet unappreciated function of deadwood is its ability to act as a physical barrier, excluding large herbivores from the obstructed patches and thereby reducing browsing pressure. However, this benefit may be minimized by an increase in rodent herbivory in the sheltered patches. In this study, a field experiment was conducted in a total of 384 plots in which tree crowns (0–4) from logging residuals were used as increasingly dense physical barriers to shelter five newly planted saplings of silver fir (Abies alba Mill.). Generalized linear mixed-effects models were applied to determine whether sapling browsing by roe deer and rodents was differentially affected by these barriers. The probability of roe deer browsing decreased from 26% (no crowns) to 2% (4 crowns) while that of rodent browsing increased from 1% to 17%, respectively, as the number of deadwood crowns used in barrier construction increased. In broadleaf stands, browsing by roe deer and rodents was generally higher than in coniferous stands. In forests with high numbers of visitors, browsing by roe deer was reduced, but browsing by rodents was not influenced. The retention of large amounts of deadwood or active deadwood increments may thus provide an effective barrier to roe deer browsing but promote the browsing activity of rodents. The landscape-level heterogeneity of browsing patterns associated with the presence of deadwood suggests that deadwood shelters in homogenized forests may encourage both natural forest regeneration and forest biodiversity, despite an overabundance of roe deer.
Hagge, J., Müller, J., Bässler, C., Biebl, S.S., Brandl, R., Drexler, M., Gruppe, A., Hotes, S., Hothorn, T., Langhammer, P., Stark, H., Wirtz, R., Zimmerer, V. & Mysterud, A. (2019). Deadwood retention in forests lowers short-term browsing pressure on silver fir saplings by overabundant deer. Forest Ecology and Management, 451: 117531
Experiments with dead wood reveal the importance of dead branches in the canopy for saproxylic beetle conservation
Vertical gradients of habitats are a typical characteristic of forest ecosystems. Sun-exposed dead wood in the upper canopy, for instance, provides a habitat for saproxylic beetles distinct from that in the more shaded dead wood below the canopy. Canopy research, however, is challenging due to both the limited accessibility and potential confounding eﬀects of temperature on trapping probability when activity traps are used. We studied saproxylic beetle assemblages along a complete vertical gradient without bias caused by temperature eﬀects on activity. Using crane-like constructions attached to the top of large Silver Fir trees (Abies alba), we exposed bundles of freshly cut branches of European Beech (Fagus sylvatica), Silver Fir and Norway Spruce (Picea abies) in three diﬀerent vertical strata (upper canopy, mid-canopy and near the ground). The bundles in the upper canopy were fully exposed to the sun and the bundles in the mid-canopy and near the ground were in the shade. We allowed beetles to colonize the bundles of branches for one growing period and then reared beetles from each bundle over three years. The species composition of saproxylic beetle assemblages diﬀered between bundles in the upper canopy and near the ground; bundles in the mid-canopy had an intermediate assemblage composition. The abundance of saproxylic beetles was higher near the ground than in the upper canopy, whereas the number of species showed the opposite pattern. Overlapping conﬁdence intervals of sample-based rarefaction and extrapolation curves for species diversity indicate that estimated gamma diversity per stratum is similar across the three strata. Our results support earlier studies that revealed the importance of habitat heterogeneity as a driver of the biodiversity of taxa associated with dead wood. As we controlled for wood diameter and tree species diversity, our study suggests that the microclimatic variability within dead wood – and thus habitat heterogeneity for saproxylic beetles – is higher in the upper canopy than near the ground. For biodiversity conservation in forests, our results support a strategy of enhancing the number of trees with microhabitats, particularly those with dead branches in the upper tree crown. Dead branches and standing dead trees should only be removed, e.g. for safety reasons, if no other option is available.
Seibold, S., Hagge, J., Müller, J., Gruppe, A., Brandl, R., Bässler, C., & Thorn, S. (2018). Experiments with dead wood reveal the importance of dead branches in the canopy for saproxylic beetle conservation. Forest Ecology and Management, 409, 564–570. https://doi.org/10.1016/j.foreco.2017.11.052
Independent effects of host and environment on the diversity of wood-inhabiting fungi
- Dead wood is a habitat for numerous fungal species, many of which are important agents of decomposition. Previous studies suggested that wood-inhabiting fungal communities are affected by climate, availability of dead wood in the surrounding landscape and characteristics of the colonized dead-wood object (e.g. host tree species). These findings indicate that different filters structure fungal communities at different scales, but how these factors individually drive fungal fruiting diversity on dead-wood objects is unknown.
- We conducted an orthogonal experiment comprising 180 plots (0.1 ha) in a random block design and measured fungal fruit body richness and community composition on 720 dead-wood objects over the first 4 years of succession. The experiment allowed us to disentangle the effects of the host (beech and fir; logs and branches) and the environment (microclimate: sunny and shady plots; local dead wood: amount and heterogeneity of dead wood added to plot).
- Variance partitioning revealed that the host was more important than the environment for the diversity of wood-inhabiting fungi. A more detailed model revealed that host tree species had the highest independent effect on richness and community composition of fruiting species of fungi. Host size had significant but low independent effects on richness and community composition of fruiting species. Canopy openness significantly affected the community composition of fruiting species. By contrast, neither local amount nor heterogeneity of dead wood significantly affected the fungal diversity measures.
Synthesis. Our study identified host tree species as a more important driver of the diversity of wood-inhabiting fungi than the environment, which suggests a hostcentred filter of this diversity in the early phase of the decomposition process. For the conservation of wood-inhabiting fungi, a high variety of host species in various microclimates is more important than the availability of dead wood at the stand level.
Krah, F.-S., Seibold, S., Brandl, R., Baldrian, P., Müller, J., & Bässler, C. (2018). Independent effects of host and environment on the diversity of wood-inhabiting fungi. Journal of Ecology, 106(4), 1428–1442. https://doi.org/10.1111/1365-2745.12939
An experimental test of the habitat - amount hypothesis for saproxylic beetles in a forested region
The habitat-amount hypothesis challenges traditional concepts that explain species richness within habitats, such as the habitat-patch hypothesis, where species number is a function of patch size and patch isolation. It posits that effects of patch size and patch isolation are driven by effects of sample area, and thus that the number of species at a site is basically a function of the total habitat amount surrounding this site. We tested the habitat-amount hypothesis for saproxylic beetles and their habitat of dead wood by using an experiment comprising 190 plots with manipulated patch sizes situated in a forested region with a high variation in habitat amount (i.e., density of dead trees in the surrounding landscape). Although dead wood is a spatio-temporally dynamic habitat, saproxylic insects have life cycles shorter than the time needed for habitat turnover and they closely track their resource. Patch size was manipulated by adding various amounts of downed dead wood to the plots (~800 m³ in total); dead trees in the surrounding landscape (~240 km2) were identified using airborne laser scanning (light detection and ranging). Over 3 yr, 477 saproxylic species (101,416 individuals) were recorded. Considering 20–1,000 m radii around the patches, local landscapes were identified as having a radius of 40–120 m. Both patch size and habitat amount in the local landscapes independently affected species numbers without a significant interaction effect, hence refuting the island effect. Species accumulation curves relative to cumulative patch size were not consistent with either the habitat-patch hypothesis or the habitat-amount hypothesis: several small dead-wood patches held more species than a single large patch with an amount of dead wood equal to the sum of that of the small patches. Our results indicate that conservation of saproxylic beetles in forested regions should primarily focus on increasing the overall amount of dead wood without considering its spatial arrangement. This means dead wood should be added wherever possible including in local landscapes with low or high dead-wood amounts. For species that have disappeared from most forests owing to anthropogenic habitat degradation, this should, however, be complemented by specific conservation measures pursued within their extant distributional ranges.
Seibold, S., Bässler, C., Brandl, R., Fahrig, L., Förster, B., Heurich, M., Hothorn, T., Scheipl, F., Thorn, S. & Müller, J. (2017).An experimental test of the habitat-amount hypothesis for saproxylic beetles in a forested region. Ecology, 98(6):1613–1622
Small-scale positive response of terrestrial gastropods to dead-wood addition is mediated by canopy openness
Terrestrial gastropods can benefit from coarse woody debris, even though they are not saproxylic because dead wood maintains suitable microclimatic conditions and provides food resources and essential nutrients, e.g. calcium. Effects of dead wood on terrestrial gastropods have been studied mostly for coarse woody debris at intermediate and advanced stages of decomposition. However, it remains unclear whether dead wood at an early stage of decomposition and of small diameter has similar positive effects on terrestrial gastropods and how effects of dead wood are mediated by canopy openness. We experimentally exposed different amounts of fresh coarse and fine woody debris on 190 temperate forest plots with either high or low canopy openness and studied terrestrial gastropod activity three years after. Plots with high canopy openness had dense herb layers. Feeding activity of gastropods was higher close than distant to dead wood. This effect was stronger on shady plots. The amount of both fine and coarse woody debris positively affected the feeding activity of gastropods, but only on shady plots. The effect of coarse woody debris amount might be partly due to increased leaf litter accumulation. Our results indicated that dead wood plays a stronger role for terrestrial gastropods in shady than in sunny forests with a dense herb layer and that terrestrial gastropods benefit from both coarse and fine woody debris already at an early stage of decomposition. Thus, conservation strategies that aim at maintaining biodiversity of saproxylic assemblages by retaining or adding dead wood are also beneficial for gastropods, especially in shady forests.
Kirchenbaur, T., Fartmann, T., Bässler, C., Löffler, F., Müller, J., Strätz, C. & Seibold, S. (2017). Small-scale positive response of terrestrial gastropods to dead-wood addition is mediated by canopy openness. Forest Ecology and Management, 396: 85-90
Lamprodema maura (Fabricius, 1803) - Erstnachweiß für Deutschland aus dem Nationalpark Bayrischer Wald (Heteroptera: Rhyparochromidae, Megalontini)
Lamprodema maura (FABRICIUS, 1803) has been recorded in Germany for the first time. One female was sampled with a flight-interception trap in 1130m a.s.l. in the Bavarian Forest National Park in July 2015. The site does not match the known habitat requirements of the Mediterranean species well. Thus vital populations of this species are not expected to occur at this site. A spread from nearby populations in Austria or the Czech Republic is likely.
Gossner, M.; Hagge, J. & Seibold, S. (2017). Lamprodema maura (FABRICIUS, 1803) – Erstnachweis für Deutschland aus dem Nationalpark Bayerischer Wald. Nachrichtenblatt der bayerischen Entomologen, 66 (3/4): 93-97
Neue Käfernachweise im Nationalpark Bayrischer Wald im Rahmen von Totholzexperimenten (Insecta, Coleoptera)
Im Rahmen eines Experiments zur Bedeutung von Totholz für die Artenvielfalt wurden im Nationalpark Bayerischer Wald zwischen 2012 und 2014 1675 Käferarten nachgewiesen, davon 622 Arten neu für den Nationalpark. Die hohe Artenvielfalt (1984 Käferarten), darunter viele Rote-Liste Arten und Urwaldreliktarten, unterstreicht denWert derWälder dieser Region.
Seibold, S., Büche, B., Szallies, A. & Müller, J. (2017). Neue Käfernachweise im Nationalpark Bayrischer Wald im Rahmen von Totholzexperimenten (Insecta, Coleoptera). Beiträge zur bayrischen Entomofaunistik, 17: 1-17
Besonnung und Totholzvielfalt - zwei ökologische Schlüsselgrößen
Ein großangelegtes Freilandexperiment in der Randzone des Nationalparks Bayerischer Wald hat ergeben, dass die Artenvielfalt von Totholz bewohnenden Käfern vor allem mit der Vielfalt an Totholz und nicht ausschließlich mit der reinen Menge steigt. Daneben fördert Totholz in Sonne und Schatten völlig andere Artengemeinschaften. In dicken Stämmen ist im Lauf der Zersetzung allerdings immer eine besonders hohe Vielfalt an Totholznischen gegeben. Diese Ergebnisse eröffnen Waldbesitzern effiziente Möglichkeiten, die biologische Vielfalt in ihren Wäldern zu fördern.
Seibold, S., Leibl, F. & Müller, J. (2017). Besonnung und Totholzvielfalt - zwei ökologische Schlüsselgrößen. AFZ - Der Wald, 3: 25-26
Microclimate and habitat heterogeneity as the major drivers of beetle diversity in dead wood
- Resource availability and habitat heterogeneity are principle drivers of biodiversity, but their individual roles often remain unclear since both factors are usually correlated. The biodiversity of species dependent on dead wood could be driven by either resource availability represented by dead-wood amount or habitat heterogeneity characterized by dead-wood diversity or both. Understanding their roles is crucial for improving evidence-based conservation strategies for saproxylic species in managed forests.
- To disentangle the effects of dead-wood amount and dead-wood diversity on biodiversity relative to canopy openness (microclimate), we experimentally exposed different amounts of logs and branches of two different tree species representing a gradient of dead-wood diversity in 190 sunny and shady forest plots. During the 3 years after exposing dead wood, we sampled saproxylic beetles, which are together with fungi the most diverse and important taxonomic group involved in decomposition of wood.
- The composition of saproxylic beetle assemblages differed clearly between shady and sunny forest plots, with higher richness in sunny plots. Both dead-wood amount and dead-wood diversity positively and independently affected species richness of saproxylic beetles, but these effects were mediated by canopy openness. In sunny forest, species richness increased with increasing amount of dead wood, whereas in shady forest, dead-wood diversity was the prevailing factor.
- The stepwise analysis of abundance and species richness, however, indicated that effects of both factors supported only the habitat-heterogeneity hypothesis, as the positive effect of high amounts of dead wood could be explained by cryptic variability of dead-wood quality within single objects.
Synthesis and applications. As canopy openness and habitat heterogeneity seem to be the major drivers of saproxylic beetle diversity in temperate forests, we recommend that managers aim to increase the heterogeneity of dead-wood substrates under both sunny and shady forest conditions. Intentional opening of the canopy should be considered in anthropogenically homogenized, dense forests. Specifically in temperate mixed montane forests, dead wood should be provided in the form of large logs in sunny habitats and a high diversity of different dead-wood substrates should be retained or created in shady forests.
Seibold, S., Bässler, C., Brandl, R., Büche, B., Szallies, A., Thorn, S., Ulyshen, M. D. & Müller, J. (2016). Microclimate and habitat heterogeneity as the major drivers of beetle diversity in dead wood. Journal of Applied Ecology, 53(3): 934–943
Dead-wood addition promotes non-saproxylic epigeal arthropods but effects are mediated by canopy openness
Restoring dead-wood amounts in forests is an increasingly and successfully applied conservation measure to counteract negative effects of intensive logging on biodiversity of saproxylic taxa. By contrast, if and how dead-wood addition benefits the vast number of non-saproxylic forest taxa, and how this varies with contextual factors like canopy openness, remains poorly understood. To enhance dead-wood addition strategies, it is thus important to understand how dead wood affects entire forests communities, not just saproxylic taxa. To untangle effects of dead-wood addition and canopy openness on non-saproxylic epigeal arthropods, we exposed different amounts of logs and branches on 190 0.1-ha plots located in sunny or shady mixed montane forests and sampled epigeal arthropods over three years. Canopy openness was a major driver of species assemblage composition and clearly mediated the effects of dead wood on epigeal beetles, spiders/harvestmen and springtails. Most species groups responded positively to the addition of dead wood. All groups decreased in number with increasing distance to dead wood. Dead wood affected taxa of both lower and higher trophic levels directly and taxa of higher trophic levels benefitted also indirectly owing to bottom-up effects. Our results indicate that increasing the amount of dead wood for conservation of saproxylic taxa benefits also non-saproxylic epigeal arthropods and thus, a larger number of forest species than commonly assumed. Because of the strong effects of canopy openness, similar to those found for saproxylic taxa, dead wood in both sunny and shady forest stands is needed.
Seibold, S., Bässler, C., Baldrian, P., Reinhard, L., Thorn, S., Ulyshen, M. D., Weiß, I. & Müller, J. (2016). Dead-wood addition promotes non-saproxylic epigeal arthropods but effects are mediated by canopy openness. Biological Conservation, 204: 181–188
Short-distance attraction of saproxylic Heteroptera to olfactory cues
- As dead wood is ephemeral, saproxylic insect species must be able to effectively locate new resources via, e.g. olfactory cues.
- Although saproxylic flat bugs feed on fungal mycelia, published evidence points to their use of dead wood-specific volatile cues rather than fungal-specific cues for long-distance orientation towards new habitat patches.
- To evaluate which olfactory cues saproxylic flat bugs use for short-distance orientation, we tested the attraction of Aradus obtectus (Vasarhelyi) to fresh wood, fungal mycelia and fungal fruiting bodies using an olfactometer.
- Aradus obtectus individuals were attracted only to fungal mycelia but not to wood or fungal fruiting bodies.
Our results and those of our earlier field experiment testing long-distance attraction (Seibold et al., 2014) together suggest that A. obtectus uses cues emitted by dead wood to locate potential resources over long distances, but relies on olfactory cues emitted by mycelia of its host species to locate suitable short-range microhabitats.
Koban, M. B., Goßner, M. M., Müller, J., Steidle, J. L. M., Bässler, C., Hothorn, T., Unsicker, S. B., & Seibold, S. (2016). Short-distance attraction of saproxylic Heteroptera to olfactory cues. Insect Conservation and Diversity, 9(3), 254–257.