Search

Giant knotweeds (Reynoutria spp.) are highly productive and aggressive invaders in riparian wetlands of Europe and North America. We sampled ground-dwelling beetles by pitfall traps from six sites comparing monotypic Reynoutria stands with the invaded native Urtica-dominated stands. Three sites were located in a semi-natural softwood forest and three sites were on a ruderal embankment. The analyses are based on a total of 13,244 individuals from 218 species. Location and site significantly influenced beetle assemblages. Moreover, there were pronounced differences between vegetation stands. The monotypic Reynoutria stands exhibited lower beetle abundance, species richness and rarefaction diversity irrespective of location. However, the negative effect on species richness, abundance and assemblage similarities were stronger on the transformed ruderal embankment than in the semi-natural softwood forest. Reynoutria invasion seems to influence microclimatic conditions. We found a higher abundance of silvicolous and a lower abundance of xerophilous ground beetles in the Reyountria stands than in the Urtica-dominated stands. Feeding guilds reacted differently to Reynoutria invasion that reduced the abundance of predators and herbivores but enhanced that of detritivores. Detritivores assumingly profit from the perennial presence of the large quantities of Reynoutria litter. We conclude that highly productive invaders pauperise the arthropod fauna and alter link strengths in trophic cascades shifting primary producer-based food webs to detritus-based food webs.

Many forest ecosystems have been extensively degraded by acidifying pollutants over the last decades. There is also widespread concern about population decline of a number of songbirds due to acidification-driven calcium limitation. We hypothesize that the carrying capacity of forests decreases with reduced soil calcium content. We analyzed songbird assemblage/habitat relationships by territory mapping at 30 sites in a total of five managed beech forests. The sites harbored 38 songbird species. A canonical correspondence analysis showed that soil acidification, represented by soil calcium content, had a significant influence on the species assemblages of the 14 most frequent songbirds. The vertical complexity of the canopy additionally influenced the assemblages. Multiple regressions revealed that the density of the territories of song thrush (Turdus philomelos) and nuthatch (Sitta europaea) were positively correlated to calcium content. Blackbirds (Turdus merula) seemed to compensate for the negative effect of acidification by selecting breeding sites close to forest edges to forage in less acidified agricultural habitats. In contrast, the territorial density of robin (Erithacus rubecula), chaffinch (Phylloscopus collybita) and coal tit (Parus ater) increased with increasing soil acidification. Contrary to our hypothesis, the overall carrying capacity of songbird was not reduced in forests with acidified soils. However, the nesting success of song thrush and blackbird, as determined by the number of fledglings, was higher in the forest with the highest calcium content when compared to the forest with the lowest calcium content. We conclude that some species are severely affected by acidification, whereas others seem to have evolved successful strategies to meet their calcium demand even in acidified habitats.

The highly invasive giant knotweed (Reynoutria spp.) often displaces nettle (Urtica dioica) dominated stands in European floodplains. Urtica-dominated stands differ from the monospecific Reynoutria stands in plant species richness and stand structure. We thus hypothesize that Reynoutria invasion profoundly alters ecosystem structure and function, with negative effects cascading up through the food chain. We performed a paired sampling design in six sites belonging to two different locations and studied effects on the soil and the litter-dwelling fauna. Reynoutria stands differed in habitat structure and were characterized by decreased soil pH and potassium depletion. The faunal analysis is based on model groups of herbivore generalists (Gastropoda), detritivores (Isopoda and Diplopoda), and predators (Opiliones). The gastropod assemblages from Reynoutria stands were severely impoverished subsets of those from Urtica stands with reduced densities, species richness and diversity. In general, snails were more sensitive to Reynoutria invasion than slugs such as the invasive Arion 'lusitanicus’. Among detritivores, the abundance of the Isopoda decreased, whereas Diplopoda were not affected by Reynoutria invasion. Yet, the relative abundance of detritivores was significantly higher within the Reynoutria stands. Abundance, species richness and diversity of the predatory Opiliones were higher in the relatively sparse Reynoutria stands. We conclude that ecosystem changes associated with Reynoutria invasion are characterized by shifts from a plant-based to a detritus-based food chain and that Reynoutria invasion primarily enhances predators that profit from the simplified vegetation structure.

We investigated the distribution pattern of centipedes (Chilopoda) in four primeval forests of the western Carpathians, central Slovakia. The forests are located in two different mountain ranges (Kremnicke vrchy and Pol’ana Mountains), which are exposed on either the southern (Boky, Rohy) or northern slopes (Pol’ana, Badin). In these forests, the influence of coarse woody debris (CWD) on centipede distribution was studied, by distinguishing sampling sites on the forest floor, close to CWD (c-CWD) and distant from CWD (d-CWD). In total, we collected 2,706 individuals from 20 species of centipedes. Average species richness and number of individuals per forest ranged from 8 to 12 species/m2 and from 244 to 486 individuals/m2. The oak forests on south facing slopes harboured several species, which did not occur in the more northern exposed fir-beech forests. Number of species as well as individuals, however, varied more within than between individual forests. Increase of species number and density was mainly caused by CWD and was more pronounced on the southern slopes (P

We studied Coleoptera emerging from deadwood in a broadleaved forest that has been managed with nature-oriented forestry since 1990 and in which an accumulation of 10 m3 deadwood/ha has been achieved. We sampled a total of 11 m3 of deadwood from oak and beech trees and yielded 32,477 individuals pertaining to 342 species. The number of species emerging from oak deadwood was significantly higher than that from beech. Significantly more species emerged from deadwood with medium size (15–21 cm) diameter than from smaller (5–7 cm) or larger (40–60 cm) diameters. The stage of decay did not influence the number of species during the first 6 years of decomposition. Species richness strongly increased with the amount of deadwood sampled. Species–area regressions yielded z-values of 0.81 for oak and 0.87 for beech deadwood. The beetle assemblage was characterized by a low number of xylophagous species and a high number of mobile zoophagous species. However, two-thirds of the individuals sampled pertained to nine species of Scolytidae. This is why Shannon–Wiener diversity (H) and evenness-indices (E) greatly decreased with increasing number of scolytids. The species and individuals yielded from the sun-exposed deadwood outnumbered those from shaded areas. Namely the scolytid Taphrorychus bicolor reached remarkably high densities in the sun-exposed beech deadwood (>800 individuals/m2). In contrast, oak deadwood never harboured such high numbers of scolytids. Felling of moribund trees had decreased the number of scolytids but it had also considerably reduced the number of rare and endangered species.

The study area is located in the low mountain range of Central Europe (Eifel) and characterized by a marked relief and high game densities. Especially red deer populations, calculated at 20 ind./100 ha, surpass the carrying capacity of the forests observed. Trampling (by red deer and moufflon) and rooting (wild boar) result in extensive soil disturbances, visible as soil profile mixture and soil erosion.

In April 1996, we collected soil samples in thevicinity of a magnesite plant at Lubenik, southernSlovakia, and screened them for soil microbial biomassand activity. Six investigated sites were chosen alonga transect, with distances ranging from 600 to 8000 mfrom the plant, to represent a gradient ofintoxication. Soil microbial cellulase activity,respiration, biomass, metabolic quotient of the soilmicrobiota, and numbers of platable fungi increasedwith increasing distance from the plant, i.e.decreasing degree of intoxication. The observedgradients of soil microbial characteristics of theinvestigated sites reflect the physico-chemical soilparameters and the floristic characteristics of thesesites, and may be used to predict transitory changesduring amelioration.

In microcosm experiments Porcellio scaber increased litter disappearance of oak and alder litter. Alder litter disappeared at more than twice the rate of oak litter. Soil texture did not influence the disappearance of oak litter; however, disappearance of alder litter was enhanced on silt rather than on sand. P. scaber enhanced microbial communities (i.e. microbial respiration and microbial biomass) on both silt and sand when feeding on either alder or oak. Overall, microbial respiration increased 10-fold when isopods fed on oak litter on sand and 20-fold when isopods fed on alder litter on sand. On silt, the initially high microbial respiration remained constant when isopods fed on oak and doubled when they fed on alder litter. In all treatments without P. scaber there was a decrease in microbial respiration over the 12-week experimental period. The availability of macronutrients (Corg, Ntot, P, K, Mg, Ca) in the topsoil was increased when P. scaber fed on alder litter but less pronounced when P. scaber fed on oak litter. Using sand as a substrate, there was an apparent increase only for Corg, Mg and Ca; on silt, increases in Corg, Ntot and P were measured. Under field conditions the contribution of P. scaber to nutrient fluxes will be higher on sand than on silt.

In einem bewirtschafteten Eichen-Buchenmischwald des Westerwaldes (325 m u. NN) wurde die xylobionte Insektenfauna von 1,7 Fm Totholz mit Eklektoren erfast. Dabei kam Eichen- und Buchen-totholz zur Auswertung. Das frisch eingeschlagene Holz verblieb ein Jahr im Gelande in Sonn- und Schattlagen und wurde wahrend der nachfolgenden Vegetationsperiode besammelt.

Field studies on microbial populations and their activity in soil and litter layers of different sites revealed statistically significant correlations with climatic factors, soil characteristics and the number of terrestrial isopods (Isopoda: Oniscidea). The number of captured Porcellio scaber was negatively correlated with the density of soil microbiota, but positively correlated with both respiration and cellulolytic activity of litter-colonizing microorganisms. By contrast, the number of Oniscus asellus was positively correlated with soil microbial density and respiration, and cellulolytic and respiratory activity of the litter. These interspecific differences were unexpected between species that frequently occur sympatrically, and, thus, probably have similar ecological requirements. Hence, the results suggested species-specific interactions of these species with soil and litter-colonizing microbiota. However, further field studies are required to prove this.

Durch waldbauliche Masnahmen, die vor etwa 80 Jahren im Sauener Forst (Brandenburg) erfolgten, wurden Kiefernwalder auf Sanderflachen in Kiefern-Buchen-Walder (Zweistufenwald) und Kiefernwalder auf Grundmoranen in Kiefern-Eichen-Buchen-Walder (Dreistufenwald) umgewandelt. Im naturnahen, laubbaumdominierten Dreistufenwald waren Streuzersetzung und C-Mineralisation im Vergleich zum Kiefernwald signifikant erhoht (p≤0,01), das C/N-Verhaltnis (O1- und Ah-Horizont) im Jahresgang fast immer signifikant erniedrigt (p≤0,001). Steigerungen im Gehalt an pflanzenverfugbaren Nahrstoffen (K+, Mg++, Ca++, P2O5) waren besonders deutlich, der Gehalt an Al3+-Ionen lag bei durchschnittlich 1/3 der Vergleichswerte (p≤0,001). Der Dreistufenwald enthielt eine hohere Biomasse an Bodenmikroorganismen. Die Zunahme der mikrobiellen Biomasse war nach Plattierungsversuchen auf eine erhohte Pilzbesiedlung zuruckzufuhren. Bodenatmung (µg CO2-C/g*h), spezifische Bodenatmung (µg CO2-C/mg Cmic*h) und C-Mineralisation (µg CO2-C/mg Corg*d) waren wahrend der gesamten Vegetationsperiode signifikant erhoht (p≤0,01). Daruber hinaus war die Besiedlungsdichte der Bodenfauna im Vergleich zum nadelbaumdominierten Wirtschaftswald angestiegen. Dies galt sowohl fur die Makrofauna (Lumbricidae) als auch fur die Mesofauna (Enchytraeidae, Collembola, Oribatei). Bei den Regenwurmern waren die Artenzahl und die Biomasse fur alle Lebensformtypen (Oberflachenbewohner, Mineralbodenbewohner, Tiefengraber) erhoht. Im Zweistufenwald waren Verbesserungen der Bodenqualitat nicht nachweisbar. Die Streuzersetzung war im Vergleich zu der nadelbaumdominierten Flache vermindert (p≤0,001), der Al3+-Gehalt sogar zumeist erhoht (p≤0,001). Mikrobielle Biomasse und Atmung waren im Zweistufenwald nur geringfugig erhoht, die C-Mineralisation haufig herabgesetzt (p≤0,05), ein Biomasseanstieg der Bodenfauna meistens nicht nachweisbar (p>0,05). Veranderungen im Streuabbau konnten bei varianzanalytischer Betrachtung (ANOVA) wesentlich durch das Bodensubstrat und die Interaktion von Boden × Bestockung erklart werden. Boden und Bestockung hatten gleichermasen auf alle erfasten Kenngrosen der Mikroorganismen sowie fur die Biomasse von Collembola und Oribatei einen signifikanten Einflus (p≤0,001). Veranderungen in der Besiedlungsdichte der Enchytraeidae wurden nur durch den Boden und die Interaktion Boden × Bestockung, Veranderungen bei der Besiedlung mit Regenwurmern ausschlieslich durch den Boden erklart (p≤0,001). Kovarianzanalysen liesen die grose Bedeutung der Bodenfauna an der Erhohung der mikrobiellen Atmung, der spezifischen Bodenatmung und der C-Mineralisation erkennen. Bodenfauna und Bodenmikroorganismen beeinflusten das C/N-Verhaltnis, die Gehalte an pflanzenverfugbaren Nahrstoffen (K+, Mg++, Ca++, P2O5) und den Gehalt an Al3+-Ionen. Bemerkenswert ist der deutliche Zusammenhang zwischen der hohen biotischen Aktivitat, einem Anstieg der pH-Werte und einer Verringerung im Gehalt an Al3+-Ionen in dem naturnahen, laubbaumdominierten Dreistufenwald.

In the common woodlouse Porcellio scaber different parts of the gut were observed with respect to microbial counts, cellulose activity, and degradation of cellulose. Cellulose is mainly digested in the anterior part of the hindgut, as was indicated by the distribution of cellulolytic activity and the decrease of cellulose content inside the gut. The cellulases woodlice utilize for the degradation of litter are mainly produced by endosymbiotic bacteria in the hepatopancreas rather than by microorganisms ingested with the food. Microorganisms ingested with the litter are digested in the anterior part of the hindgut and may provide an important food source. In the posterior hindgut, bacterial proliferation ensures microbial colonization of feces.

Population parameters (mortality of females, reproductive success, longevity of juveniles) of the common woodlouse, Porcellio scaber (Isopoda, Oniscidea), were examined with respect to the influence of varying leaf litter attributes: pH level, microbial cellulase activity, microbial dehydrogenase activity, protein content, nitrogen content, water content, tannin content, total phenol content and toughness of the leaves. These attributes were combined by using Principal Component Analysis. We obtained three Principal Components (PC) that were defined as “acidification,”“microorganisms” and “tree species.” The PCs explained 85% of the variance of leaf litter attributes. The PC “acidification” mainly influenced the mortality of females (P