Forest management intensity affects aquatic communities in artificial tree holes

Forest management could potentially affect organisms in all forest habitats. However, aquatic communities in water-filled tree-holes may be especially sensitive because of small population sizes, the risk of drought and potential dispersal limitation. We set up artificial tree holes in forest stands subject to different management intensities in two regions in Germany and assessed the influence of local environmental properties (tree-hole opening type, tree diameter, water volume and water temperature) as well as regional drivers (forest management intensity, tree-hole density) on tree-hole insect communities (not considering other organisms such as nematodes or rotifers), detritus content, oxygen and nutrient concentrations. In addition, we compared data from artificial tree holes with data from natural tree holes in the same area to evaluate the methodological approach of using tree-hole analogues. We found that forest management had strong effects on communities in artificial tree holes in both regions and across the season. Abundance and species richness declined, community composition shifted and detritus content declined with increasing forest management intensity. Environmental variables, such as tree-hole density and tree diameter partly explained these changes. However, dispersal limitation, indicated by effects of tree-hole density, generally showed rather weak impacts on communities. Artificial tree holes had higher water temperatures (on average 2° C higher) and oxygen concentrations (on average 25% higher) than natural tree holes. The abundance of organisms was higher but species richness was lower in artificial tree holes. Community composition differed between artificial and natural tree holes. Negative management effects were detectable in both tree-hole systems, despite their abiotic and biotic differences. Our results indicate that forest management has substantial and pervasive effects on tree-hole communities and may alter their structure and functioning. We furthermore conclude that artificial tree-hole analogues represent a useful experimental alternative to test effects of changes in forest management on natural communities.Fil: Petermann, Jana S.. University of Salzburg; Austria. Berlin-Brandenburg Institute of Advanced Biodiversity Research; AlemaniaFil: Rohland, Anja. Friedrich Schiller University; AlemaniaFil: Sichardt, Nora. Friedrich Schiller University; AlemaniaFil: Lade, Peggy. Friedrich Schiller University; AlemaniaFil: Guidetti, Brenda Yamile. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Friedrich Schiller University; AlemaniaFil: Weisser, Wolfgang W.. Friedrich Schiller University; Alemania. Technische Universität München; AlemaniaFil: Gossner, Martin M.. Friedrich Schiller University; Alemania. Technische Universität München; Alemani

Comparison of the canopy fauna of silver fir (Abies alba) and spruce trees (Picea abies)

Natürlicherweise war die Tanne (Abies alba) in den bayerischen Wäldern mit Anteilen von bis zu 20% vertreten (nach ROTHE & BORCHERT 2003). Seit 150 Jahren aber gehen die Tannenbestände in drastischem Ausmaß zurück, was nicht nur auf die wachsende Schadstoffbelastung der Luft, sondern auch auf hohe Wildbestände und die einseitige Waldbewirtschaftung zugunsten der Fichte (Picea abies) zurückzuführen ist. In jüngster Zeit wird seitens der Staatsforstverwaltung angestrebt, der Tanne ihren angestammten Platz in unseren Wäldern wieder einzuräumen (BAYERISCHES STAATSMINISTERIUM FÜR LANDWIRTSCHAFT UND FORSTEN 1993). Es stellt sich die Frage, welchen Beitrag die Tanne zur Biodiversität in Wäldern und speziell in Mischwäldern leistet. Frühere Untersuchungen beschrieben die Tannenfauna als artenarm im Vergleich mit anderen Baumarten (BÖHME 2001, BUCKING 1998), allerdings wurde die Kronenfauna dabei stets vernachlässigt. Da aber 90% eines Hochwaldes über der Reichhöhe eines Menschen liegt (BUßLER et al. 2004), sind Untersuchungen im Kronenraum höheren Straten für eine umfassende Aussage über die Fauna auf Bäumen von großer Bedeutung. Bis jetzt gibt es trotz des generell wachsenden Interesses an der Kronenfauna keine umfassenden Untersuchungen an Tanne (MÜLLER & GOSSNER 2004). Mit dem hier vorgestellten Projekt sollte begonnen werden, die Wissenslücke um die Insektenfauna in Tannenkronen zu schließen. Den xylobionten Käfern galt besondere Aufmerksamkeit, da sie als eine baumartengebundene Insektengruppe für vergleichendeUntersuchungen sehr gut geeignet und sowohl taxonomisch als auch ökologisch gut untersucht sind. Daneben wurden Heteroptera, Neuropterida und Hymenoptera bearbeitet .In the context of forest ecological support programs of silver fir as the “Tree of the year 2004”, the relative contribution of fir and spruce trees to forest insect diversity is compared in present investigation. Previous studies had postulated a species poor community on fir. Insects were sampled by flight-interception traps at 6 different sites in Bavaria in the year 2004. Traps were installed in the centre of the canopy of a total of 30 trees (>100 years) of each species and emptied monthly from April through October. Specimens of Coleoptera, Hymenoptera, Heteroptera and Neuropterida were enumerated. A total of 20.562 specimens was collected, with Coleoptera being the dominant order. The comparison between fir and spruce revealed significant differences in numbers of specimens of Hymenoptera, Heteroptera and Neuropterida. Regarding saproxylic beetle species, a significant difference between fir and spruce was found at one site (Feuchtwangen) only. The Sørensen index values showed a strong similarity between the mountainous sites (Inzell, Reit im Winkel, Nationalpark Bayerischer Wald). Several species in the samples are listed in the German Red Data Book of endangered and threatened species. Most of these were sampled on fir, e.g. Episernus striatellus (RL-D 0) and Euglenes pygmaeus (RL-D 1)

From bottom-up to top-down control of invertebrate herbivores in a retrogressive chronosequence

In the long-term absence of disturbance, ecosystems often enter a decline or retrogressive phase which leads to reductions in primary productivity, plant biomass, nutrient cycling and foliar quality. However, the consequences of ecosystem retrogression for higher trophic levels such as herbivores and predators, are less clear. Using a post-fire forested island-chronosequence across which retrogression occurs, we provide evidence that nutrient availability strongly controls invertebrate herbivore biomass when predators are few, but that there is a switch from bottom-up to top-down control when predators are common. This trophic flip in herbivore control probably arises because invertebrate predators respond to alternative energy channels from the adjacent aquatic matrix, which were independent of terrestrial plant biomass. Our results suggest that effects of nutrient limitation resulting from ecosystem retrogression on trophic cascades are modified by nutrient-independent variation in predator abundance, and this calls for a more holistic approach to trophic ecology to better understand herbivore effects on plant communities

From the South and from the North? – Quilnus marcosi Heiss & Baena and Aradus angularis J. Sahlberg, two flat bug species new for Central Europe (Hemiptera, Heteroptera, Aradidae)

The flat bug fauna of Switzerland is still insufficiently studied. We describe the first records of Aradus angularis J. Sahlberg, 1886 and Quilnus marcosi Heiss & Baena, 2006 (Heteroptera: Aradidae) in Switzerland from a burnt forest area in the canton Valais. These are also the first records for Central Europe. With these new records, the number of Aradidae species recorded in Switzerland increases to 21, and in the canton Valais to 16. A cantonal record list of aradid species in Switzerland and photographs of the two recently new recorded species are provided. The pyrophilous A. angularis shows a disjunct distribution pattern, disconnected from its known distributional range from Fennoscandia to Northeast China, which suggests that the species is a relict of the Ice Age in Central Europe. In contrast, the sub-Mediterranean Q. marcosi seems to have expanded its distributional range to the north-east or has previously gone unnoticed in Switzerland. The host plants of Q. marcosi include Pinus nigra and P. sylvestris

Blue and green food webs respond differently to elevation and land use.

While aquatic (blue) and terrestrial (green) food webs are parts of the same landscape, it remains unclear whether they respond similarly to shared environmental gradients. We use empirical community data from hundreds of sites across Switzerland and a synthesis of interaction information in the form of a metaweb to show that inferred blue and green food webs have different structural and ecological properties along elevation and among various land-use types. Specifically, in green food webs, their modular structure increases with elevation and the overlap of consumers' diet niche decreases, while the opposite pattern is observed in blue food webs. Such differences between blue and green food webs are particularly pronounced in farmland-dominated habitats, indicating that anthropogenic habitat modification modulates the climatic effects on food webs but differently in blue versus green systems. These findings indicate general structural differences between blue and green food webs and suggest their potential divergent future alterations through land-use or climatic changes

Blue and green food webs respond differently to elevation and land use

While aquatic (blue) and terrestrial (green) food webs are parts of the same landscape, it remains unclear whether they respond similarly to shared environmental gradients. We use empirical community data from hundreds of sites across Switzerland and a synthesis of interaction information in the form of a metaweb to show that inferred blue and green food webs have different structural and ecological properties along elevation and among various land-use types. Specifically, in green food webs, their modular structure increases with elevation and the overlap of consumers’ diet niche decreases, while the opposite pattern is observed in blue food webs. Such differences between blue and green food webs are particularly pronounced in farmland-dominated habitats, indicating that anthropogenic habitat modification modulates the climatic effects on food webs but differently in blue versus green systems. These findings indicate general structural differences between blue and green food webs and suggest their potential divergent future alterations through land-use or climatic changes

High-resolution 3D forest structure explains ecomorphological trait variation in assemblages of saproxylic beetles

Climate, topography and the 3D structure of forests are major drivers affecting local species communities. However, little is known about how the specific functional traits of saproxylic (wood-living) beetles, involved in the recycling of wood, might be affected by those environmental characteristics. Here, we combine ecological and morphological traits available for saproxylic beetles and airborne laser scanning (ALS) data in Bayesian trait-based joint species distribution models to study how traits drive the distributions of more than 230 species in temperate forests of Europe. We found that elevation (as a proxy for temperature and precipitation) and the proportion of conifers played important roles in species occurrences while variables related to habitat heterogeneity and forest complexity were less relevant. Furthermore, we showed that local communities were shaped by environmental variation primarily through their ecological traits whereas morphological traits were involved only marginally. As predicted, ecological traits influenced species' responses to forest structure, and to other environmental variation, with canopy niche, wood decay niche and host preference as the most important ecological traits. Conversely, no links between morphological traits and environmental characteristics were observed. Both models, however, revealed strong phylogenetic signal in species' response to environmental characteristics. These findings imply that alterations of climate and tree species composition have the potential to alter saproxylic beetle communities in temperate forests. Additionally, ecological traits help explain species' responses to environmental characteristics and thus should prove useful in predicting their responses to future change. It remains challenging, however, to link simple morphological traits to species' complex ecological niches. Read the free Plain Language Summary for this article on the Journal blog

Functional structure of European forest beetle communities is enhanced by rare species

Biodiverse communities have been shown to sustain high levels of multifunctionality and thus a loss of species likely negatively impacts ecosystem functions. For most taxa, however, roles of individual species are poorly known. Rare species, often most likely to go extinct, may have unique traits and functional roles. Alternatively, rare species may be functionally redundant, such that their loss would not disrupt ecosystem functions. We quantified the functional role of rare species by using captures of wood-living (saproxylic) beetle species, combined with recent databases of morphological and ecological traits, from three regions in central and northern Europe. Using a rarity index based on species' local abundance, geographic range, and habitat breadth, we used local and regional species removal simulations to examine the contributions of both the rarest and the most common beetle species to three measures of community functional structure: functional richness, functional specialization, and functional originality. Both regionally and locally, all three measures declined more rapidly when rare species were removed than under common (or random) species removal scenarios. These consistent patterns across scales and among forest types give evidence that rare species provide unique functional contributions, and their loss may disproportionately impact ecosystem functions. This implies that conservation measures targeting rare and endangered species, such as preserving intact forests with dead wood and mature trees, can provide broader ecosystem-level benefits. Experimental research linking functional structure to ecosystem processes should be prioritized to increase understanding of the functional consequences of species loss and to develop more effective conservation strategies

Insights from regional and short-term biodiversity monitoring datasets are valuable: a reply to Daskalova et al. 2021

Reports of major losses in insect biodiversity have stimulated an increasing interest in temporal population changes. Existing datasets are often limited to a small number of study sites, few points in time, a narrow range of land-use intensities and only some taxonomic groups, or they lack standardised sampling. While new monitoring programs have been initiated, they still cover rather short time periods. Daskalova et al. 2021 (Insect Conservation and Diversity, 14, 1-18) argue that temporal trends of insect populations derived from short time series are biased towards extreme trends, while their own analysis of an assembly of shorter- and longer-term time series does not support an overall insect decline. With respect to the results of Seibold et al. 2019 (Nature, 574, 671–674) based on a 10-year multi-site time series, they claim that the analysis suffers from not accounting for temporal pseudoreplication. Here, we explain why the criticism of missing statistical rigour in the analysis of Seibold et al. (2019) is not warranted. Models that include ‘year’ as random effect, as suggested by Daskalova et al. (2021), fail to detect non-linear trends and assume that consecutive years are independent samples which is questionable for insect time-series data. We agree with Daskalova et al. (2021) that the assembly and analysis of larger datasets is urgently needed, but it will take time until such datasets are available. Thus, short-term datasets are highly valuable, should be extended and analysed continually to provide a more detailed understanding of insect population changes under the influence of global change, and to trigger immediate conservation actions