Presence Of Beech Research Articles

Dynamics of soil water potential as a function of stand types in a temperate forest: Emphasis on flash droughts

In the context of a changing climate and the increasing occurrences of extreme events, including droughts, field evidence, and models suggest that cases of forest decline and migration of tree species to more suitable climates will augment in the 21st century. In northeastern North America, an expansion of American beech at the expense of maples has been observed since the 1970s and has been associated to several causes. Through an analysis of time series leveraging thousands of data collected in a temperate forest in southern Quebec, Canada, dynamics of soil water potential were analyzed in interaction with soil temperature, meteorological variables and forest types, including hardwoods (mostly maple) with a large presence of beech trees (hardwood-beech stands), hardwoods (maple and birch) and mixedwoods (maple and fir). During flash drought events with a net precipitation deficit and water stress, the presence of beech led to a decrease in soil temperature and favored the maintenance of low soil water potential and faster restoration of water reserves compared to mixedwoods. Using machine learning-based approaches, distinct critical soil temperature thresholds in regard to water potential were identified for the various forest types, and the temporality in soil water regime changes was more favorable under hardwood-beech stands. The presence of beech appears to render greater resilience in regard to water stress in this forest. A greater capacity of beech to preserve and restore soil water not only offers an additional explanation for its establishment in hardwoods in the last decades, but greater water conservation in the presence of beech, assuming it remains in the landscape, could also help local plant species adapt to climate change and to the predicted increased water deficits, as well as species migrating northward to find more suitable environmental envelopes.

Influence of habitat fragmentation and habitat amount on soil fungi communities in ancient forests

ContextFungi represent a large part of soil biodiversity as well as an essential role for tree hydromineral nutrition, survival, and carbon cycling. While their local diversity has proven to be shaped by abiotic and biotic factors related to soil, climate and vegetation, their response to landscape fragmentation is still debated.ObjectivesIn this paper, we focus on ancient forests characterized by the presence of beech at low elevation, a habitat particularly fragmented in South-West France. We aim to assess the effect of past and present forest fragmentation and quantity on soil fungal and functional group diversity. We expect a negative impact of fragmentation and a positive effect of forest quantity on soil fungal diversity, in addition to an influence of local soil factors.MethodsSoils from 41 1ha ancient forest plots across South-West France were sampled along gradients of past and present forest fragmentation and quantity, before their fungal diversity was characterized by metabarcoding of environmental DNA. Hill numbers have been computed and applied to all fungi, trophic guilds and growth forms.ResultsWe find that past forest fragmentation negatively impacts on soil fungal diversity and in particular for symbiotrophs, while the present forest quantity has a positive impact. In contrast, the species richness of pathotrophic fungi shows a negative correlation with past forest fragmentation. The diversity of fungal groups with lower dispersal abilities (e.g., corticioid, microfungi) is negatively impacted by past forest fragmentation, while the diversity of wind-dispersed fungi (e.g., agaricoid) is not influenced by any landscape descriptors.ConclusionsOur results show the complexity of fungal responses to past and present forest fragmentation and demonstrate the long-lasting effect of past fragmentation as well as the positive impact of recent forest quantity in the landscape on fungal diversity associated with ancient forest soils. Our study also highlights the huge diversity of fungi unraveled by eDNA metabarcoding in this habitat and the potential of such techniques to study the landscape ecology of soil communities.

From the coldest ice age to green carpets of beauty: A 20,000-year vegetation history from the Hyrcanian forest refugium of northern Iran

The Hyrcanian region is a biogeographic entity of high biodiversity and a centre of Arcto-Tertiary relict flora. A pollen record from the mid-elevation of the Alborz Mountains (northern Iran) reaching back to 20,000 cal BP reveals the Late Quaternary vegetation history of this globally important forest ecosystem. For the period 20,000–14,419 cal BP the pollen record indicates the presence of beech, oak, and birch associated with elm and hornbeam, which indicates the presence of a Weichselian refugium for deciduous tree species. The simultaneous presence of abundant pollen attributable to Artemisia, Amaranthaceae, Apiaceae, and Hippophaë rhamnoides suggests the presence of a dry and cold steppe environment at higher elevations. For the period 16,746–14,419 cal BP, the pollen record indicates a steppe vegetation around the studied peatland (with a predominance of Artemisia, Amaranthaceae and Apiaceae species, along with Eremurus), a slight expansion of oak, and a strong decrease of beech. The period 14,419–12,993 cal BP started with a substantial rise in the values of pollen attributable to Quercus, Carpinus, and Ulmus with the near absence of pollen of dry-growing herbaceous vegetation. For 12,993–11,745 cal BP, a drastic decline of arboreal pollen types, pronounced peaks of NAP types, and constant values of pollen of Ephedra persuasively point to a dry period in the studied region. Towards the end of this period, when the climate apparently became somewhat warmer, deciduous trees expanded around the study site earlier than in other regions, probably because of the site’s proximity to the refugium. After 8600 cal BP, oak declined in importance whereas beech and hornbeam expanded, showing the establishment of the contemporary temperate climate and vegetation. A pronounced expansion of alder and wingnut took place around 4000 cal BP. A remarkable decline of Pterocarya pollen at 1060 cal BP may relate to human impact and/or a cooling/drying climate.

A Least-Cost Dynamic Optimization Approach for Obtaining a Desired Balanced Uneven-Aged Structure

Abstract There has been increasing interest among foresters and landowners in modifying existing even-aged forest structures to multi-aged or uneven-aged structures. Maintaining a continuous forest structure often provides a wider array of forest values over the long term. The conversion process is challenging in regions of the Northeast United States characterized by forests composed of dense diseased beech thickets and low-vigor deformed overstory trees. Abundance of noncommercial beech may result in negative cash flows during the conversion process to achieve a desired balanced uneven-aged structure. The Forest Vegetation Simulator was used to model growth and yield. Given the possibility of negative cash flows, a least-cost dynamic program with a penalty function was used to determine least-cost time paths for two management scenarios, one characterized by the successful removal of beech and the other simulating the continued presence of beech. Incorporating a penalty function allowed creating a continuum of least-cost paths from a zero penalty with the greatest weight given to net revenue goals to the largest penalty with the greatest weight given to ecological goals. Sensitivity analyses revealed least-cost paths were more stable given changes in prices and wages when greater emphasis was placed on the ecological goals associated with the target structure.

Past, present and future distributions of Oriental beech (Fagus orientalis) under climate change projections.

Species distribution models can help predicting range shifts under climate change. The aim of this study is to investigate the late Quaternary distribution of Oriental beech (Fagus orientalis) and to project future distribution ranges under different climate change scenarios using a combined palaeobotanical, phylogeographic, and modelling approach. Five species distribution modelling algorithms under the R-package `biomod2`were applied to occurrence data of Fagus orientalis to predict distributions under present, past (Last Glacial Maximum, 21 ka, Mid-Holocene, 6 ka), and future climatic conditions with different scenarios obtained from MIROC-ESM and CCSM4 global climate models. Distribution models were compared to palaeobotanical and phylogeographic evidence. Pollen data indicate northern Turkey and the western Caucasus as refugia for Oriental beech during the Last Glacial Maximum. Although pollen records are missing, molecular data point to Last Glacial Maximum refugia in northern Iran. For the mid-Holocene, pollen data support the presence of beech in the study region. Species distribution models predicted present and Last Glacial Maximum distribution of Fagus orientalis moderately well yet underestimated mid-Holocene ranges. Future projections under various climate scenarios indicate northern Iran and the Caucasus region as major refugia for Oriental beech. Combining palaeobotanical, phylogeographic and modelling approaches is useful when making projections about distributions of plants. Palaeobotanical and molecular evidence reject some of the model projections. Nevertheless, the projected range reduction in the Caucasus region and northern Iran highlights their importance as long-term refugia, possibly related to higher humidity, stronger environmental and climatic heterogeneity and strong vertical zonation of the forest vegetation.

Interspecific effects between overstorey and regeneration in small-scale mixtures of three late-successional species in the Western Carpathians (southern Poland)

In mixed-species forests, species composition of the overstorey affects regeneration processes through its influence on seed rain intensity and micro-site characteristics. Based on extensive inventory data (1583 sample plots), this study investigated relationships between the percentages of silver fir (Abies alba Mill.), European beech (Fagus sylvatica L.), and Norway spruce (Picea abies (L.) H. Karst.) in the overstorey and in naturally established regeneration (seedlings of a height below 0.5 m). A useful framework for this analysis was the assumption that for a given stand density level expected seedling density increases approximately linearly with the increasing percentage of conspecific trees because of increasing seed supply. The analysis partly disproved this assumption and indicated that the species’ proportions in the overstorey and regeneration change in a nonlinear manner. In the beech–fir and beech–spruce mixtures, a strong tendency for beech regeneration to increase its proportion was found in the stands with similar percentages of the species. Fir regeneration positively responded to the presence of beech and spruce in the overstorey; an over-proportional increase in fir percentage was found in stands with more than 60% of beech and, depending on stand density, in a wide range of mixture variants with spruce. These effects may be viewed as increase-when-rare mechanisms that limit superior competitors and counteract the transformation of mixed-species stands into monocultures of spruce or beech. The analysis indicated that reduced stand density considerably facilitates establishment of spruce regeneration in the mixtures with fir and beech, but decreases the percentage of fir regeneration in the mixtures with beech.

Land snail Acicula parcelineata (Architaenioglossa: Cyclophoroidea: Aciculidae) in Ukraine: distribution, variability, habitat preferences and conservation status

All available data and most of materials on Acicula parcelineata from Ukraine are reviewed. Thirteen areas inhabited by the species are reported for Ukraine, some of which include several known sites. Five of these areas were not reported before. Map of general distribution of A. parcelineata is provided (outside Ukraine based on published data). Habitat preferences of this species are reviewed, it occurs in Ukraine almost exclusively in forests with presence of beech, on altitude 300-1100 m. Conservation status of A. parcelineata in Ukraine is shown to be “Near Threatened” according to IUCN criterions, it is recommended to be included into the next edition of Red Book of Ukraine. Shells’ measurements of A. parcelineata are provided and compared with related Platyla jankowskiana. The later species is discussed; it seems to be possible that it represents large abnormal specimens of A. parcelineata.

Vertical distribution of soil carbon in boreal forest under European beech and Norway spruce

Past forest management decisions have resulted in European beech being replaced with Norway spruce across Europe. Previous studies have revealed variances in soil carbon (C) under different dominating tree species. Yet, there is a scarcity of knowledge about how beech and spruce differ in impact on forest soil C in boreal regions, where beech has its northern distribution limit. We have therefore compared soil C in a natural beech forest (Be) with that of two spruce forests: one planted on former beech forest (SpBe) and the other on former spruce forest (Sp), in South-East Norway. Analyses of biochemical parameters and fungal biomass were performed along fine-scaled soil profiles, covering both the organic and mineral layers. We found no significant difference between the forests when comparing estimates of total C stocks per area. However, throughout the soil profile, the distribution of soil C in Be varied significantly from SpBe, while Sp was intermediate. The distribution of fungal biomass along the soil profile in Be varied significantly from the two other forests. Hence, fungal biomass may drive the observed differences. Soil C, nitrogen (N), and C/N ratios were forest type and soil depth dependent, whereas forest type had an effect on the vertical distribution of condensed tannins and fungal biomass. Our results suggest that the presence of beech or spruce as the dominant tree species in the studied area has an effect on the vertical distribution of soil properties, while there is no major difference when comparing the whole soil profile.

Low Light Availability Associated with American Beech Is the Main Factor for Reduced Sugar Maple Seedling Survival and Growth Rates in a Hardwood Forest of Southern Quebec

Several recent studies have reported a marked increase in American beech dominance (Fagus grandifolia Ehrh.) relative to sugar maple (Acer saccharum Marsh.) in late successional forests of North America. However, many factors have been proposed to explain this sudden shift in tree species composition. We investigated the microsite factors responsible for maple regeneration failure under maple-beech stands, focusing on both light availability and soil conditions. The survival and growth of maple seedlings planted in the natural soil and in pots with enriched soil were monitored for two years, as well as foliar nutrition and herbivory damages of natural seedlings. The results indicate that low light availability associated with the presence of beech is the primary factor leading to maple regeneration failures. Soil nutrient availability and foliar nutrition of natural seedlings did not differ between forest types. Yet, the results indicate that factors such as allelopathy and preferential herbivory on maple seedlings under beech could be superimposed effects that hinder maple regeneration. Under similar forests, a control of beech sapling abundance in the understory followed by selection cutting could be one way to promote and maintain maple populations in the longer term.

Tree size and local neighbourhood affect foliar nutrient content in a mixed plantation of beech (Fagus sylvatica) and maple (Acer pseudoplatanus)

Whereas improved tree mineral nutrition is known to be one driver behind the higher growth in mixed vs pure stands, the effects of stand density and admixture of species with limited functional dissimilarity remain very poorly documented. Our study therefore addresses the impact of local neighbourhood, including density and species composition, on tree nutrition for two species with a limited contrast in traits. We investigated foliar nutrition in a young mixed plantation of beech (Fagus sylvatica L.) and sycamore maple (Acer pseudoplatanus L.), planted along a double gradient of density and species proportion. Target trees of both species were selected over the full diameter range along this double gradient, and neighbourhood (local density, species identity and diversity) was determined in a 3m radius. Using standardized regression analysis, we investigated direct effects of tree size and neighbourhood, and indirect effects of neighbourhood through tree size. Mostly we observed positive tree size effects in both species, be it stronger in beech. For maple, direct positive species identity effects were observed for C, N, P, S, K, Mg, Mn, Zn and Al. For beech, we found indirect negative effects of stand density and diversity. These results were in general agreement with growth data, which suggests that nutrition is one of the driving factors behind complementarity in this stand. We conclude that at this stage the effect of tree size dominates over the neighbourhood effects, including density and diversity. However, the presence of beech reduced intraspecific competition in maple with a positive effect on the foliar nutrient content. As neighbourhood effects are expected to increase as the plantation matures, our findings highlight the potential of admixing tree species with limited dissimilarity in traits for practical use in forestry.

Produire des lames de hache en dolérite au Néolithique en Mayenne. La carrière-atelier de Beulin à Saint-Germain-le-Guillaume

Produire des lames de hache en dolérite au Néolithique en Mayenne. La carrière-atelier de Beulin à Saint-Germain-le-Guillaume

Exploring Factors Influencing Species Natural Regeneration Response Following Harvesting in the Acadian Forests of New Brunswick

In the Acadian Forest Region of northeastern North America, forest managers are under increasing public pressure to restore the forest to a more historic, natural condition by reducing in clearcutting and promoting partial-cut treatments that more closely emulate historic, local natural disturbance regimes. However, although numerous studies on the effects of partial-cutting on forest regeneration response have been conducted in surrounding temperate and boreal forest ecosystems, there are few studies that directly explore responses to various forms of harvesting within the Acadian Forest ecosystem, with its unique mixture of northern hardwoods and boreal forest species. Here, we conducted one of the first retrospective studies on forest regeneration following a variety of harvesting methods in the Acadian Forest using univariate and multivariate regression trees to assess regeneration response in 50 naturally-regenerating, harvested forest sites in New Brunswick, Canada. Our study shows that regeneration was highly influenced by harvest type, overstory composition, and environmental conditions as reflected by ecoregion classification. Canopy opening size (as controlled by harvest method) significantly influenced the dominance of regenerating species. The presence of conspecific overstory trees increased the likelihood of their regeneration following disturbance, supporting the direct-regeneration hypothesis, especially for species with limited seed dispersal (e.g., sugar maple (Acer saccharum Marsh.) and American beech (Fagus grandifolia Ehrh.). Despite reported problems elsewhere in eastern North America, neither American beech nor balsam fir (Abies balsamea (L.) Mill.) constituted significant competition for the desired species on a broad scale, but the presence of beech was a significant deterrent for yellow birch (Betula alleghaniensis Britt.).

Competition for nitrogen between Fagus sylvatica and Acer pseudoplatanus seedlings depends on soil nitrogen availability.

Competition for nitrogen (N), particularly in resource-limited habitats, might be avoided by different N acquisition strategies of plants. In our study, we investigated whether slow-growing European beech and fast-growing sycamore maple seedlings avoid competition for growth-limiting N by different N uptake patterns and the potential alteration by soil N availability in a microcosm experiment. We quantified growth and biomass indices, 15N uptake capacity and N pools in the fine roots. Overall, growth indices, N acquisition and N pools in the fine roots were influenced by species-specific competition depending on soil N availability. With inter-specific competition, growth of sycamore maple reduced regardless of soil N supply, whereas beech only showed reduced growth when N was limited. Both species responded to inter-specific competition by alteration of N pools in the fine roots; however, sycamore maple showed a stronger response compared to beech for almost all N pools in roots, except for structural N at low soil N availability. Beech generally preferred organic N acquisition while sycamore maple took up more inorganic N. Furthermore, with inter-specific competition, beech had an enhanced organic N uptake capacity, while in sycamore maple inorganic N uptake capacity was impaired by the presence of beech. Although sycamore maple could tolerate the suboptimal conditions at the cost of reduced growth, our study indicates its reduced competitive ability for N compared to beech.

Cryptic no more: soil macrofossils uncover Pleistocene forest microrefugia within a periglacial desert.

Despite their critical importance for understanding the local effects of global climate change on biodiversity, glacial microrefugia are not well studied because they are difficult to detect by using classical palaeoecological or population genetics approaches. We used soil macrofossil charcoal analysis to uncover the presence of cryptic glacial refugia for European beech (Fagus sylvatica) and other tree species in the Landes de Gascogne (southwestern France). Using botanical identification and direct radiocarbon dating (140 (14) C-dates) of macrofossil charcoal extracted from mineral soils, we reconstructed the glacial and postglacial history of all extant beech stands in the region (n = 11). Soil charcoal macrofossils were found in all sites, allowing the identification of up to at least 14 distinct fire events per site. There was direct evidence of the presence of beech during the last glacial period at three sites. Beech was detected during Heinrich stadial-1, one of the coldest and driest intervals of the last glacial period in Western Europe. Together with previous results on the genetic structure of the species in the region, these findings suggest that beech persisted in situ in several microrefugia through full glacial and interglacial periods up to the present day.

Analyzing size-symmetric vs. size-asymmetric and intra- vs. inter-specific competition in beech (Fagus sylvatica L.) mixed stands

In mixed stands, inter-specific competition can be lower than intra-specific competition when niche complementarity and/or facilitation between species prevail. These positive interactions can take place at belowground and/or aboveground levels. Belowground competition tends to be size symmetric while the aboveground competition is usually for light and almost always size-asymmetric. Interactions between forest tree species can be explored analyzing growth at tree level by comparing intra and inter-specific competition. At the same time, possible causes of niche complementarity can be inferred relating intra and inter-specific competition with the mode of competition, i.e. size-symmetric or size-asymmetric. The aim of this paper is to further our understanding of the interactions between species and to detect possible causes of competition reduction in mixed stands of beech (Fagus sylvatica L.) with other species: pine–beech, oak–beech and fir–beech. To test whether species growth is better explained by size-symmetric and/or size-asymmetric competition, five different competition structures where included in basal area growth models fitted using data from the Spanish National Forest Inventory for the Pyrenees. These models considered either size-symmetry only (Reineke’s stand density index, SDI), size-asymmetry only (SDI of large trees or SDI of small trees), or both combined. In order to assess the influence of the admixture, these indices were introduced in two different ways, one of which was to consider that trees of all species compete in a similar way, and the other was to split the stand density indices into intra- and inter-specific competition components. The results showed that in pine–beech mixtures, there is a slightly negative effect of beech on pine basal area growth while beech benefitted from the admixture of Scots pine; this positive effect being greater as the proportion of pine trees in larger size classes increases. In oak–beech mixtures, beech growth was also positively influenced by the presence of oaks that were larger than the beech trees. The growth of oak, however, decreased when the proportion of beech in SDI increased, although the presence of beech in larger size classes promoted oak growth. Finally, in fir–beech mixtures, neither fir nor beech basal area growth were influenced by the presence of the other species. The results indicate that size-asymmetric is stronger than size-symmetric competition in these mixtures, highlighting the importance of light in competition. Positive species interactions in size-asymmetric competition involved a reduction of asymmetry in tree size-growth relationships.

An assessment of rainfall modification in mountainous ecosystems dominated by Fagus sylvatica L. and Picea abies (L.) Karst. (Western Balkans, Bulgaria) by multivariate analyses

Bulk precipitation, throughfall, and stemflow samples were collected in Petrohan site (Western Balkan, Bulgaria), operating in the framework of the Long-Term Ecological Research network, during a 6-year period (1995–2000). This mountain area is characterized by the presence of beech and spruce forests (Fagus sylvatica L. and Picea abies (L.) Karst.) and is utilized for drinking water supply. All samples were analyzed for pH and major inorganic anions (Cl−, NO3 −, and SO4 2−) and cations (Ca2+, K+, Mg2+, Na+, and NH4 +). Results show that bulk precipitation in this region is mainly acidic (pH = 5.1), and the dominant neutralization components in the rainwater are Ca2+ and NH4 +. As for Ca2+, K+, Mg2+, Cl−, and SO4 2−, they are not originated by marine source. Cluster analysis and principal component analysis were used for investigating the possible sources contributing to the chemical composition of the bulk precipitation and its possible modifications during the passing through beech and spruce stands. Results highlight that local and long-range transport-related anthropogenic sources and natural sources contribute to the anion and cation content of the bulk precipitation. The enrichment of the solution through the foliage made up of dry depositions is significant in both stands, but canopy leaching processes are much greater in the spruce forest, especially for Ca2+. As for the stemflow, it follows the same pattern as the throughfall, but N uptake and a strong K+ and Mg2+ leaching are observed mainly in the spruce stand.

Tree identity surpasses tree diversity in affecting the community structure of oribatid mites (Oribatida) of deciduous temperate forests

The role of tree diversity and identity as determinants of soil animal community structure is little understood. In a mature deciduous forest dominated by beech we identified clusters of one, two and three tree species of beech, ash and lime allowing to investigate the role of tree species diversity and identity on the density and community structure of oribatid mites. To relate oribatid mite community structure to environmental factors we measured leaf litter input, fine root biomass, mass of organic layers, topsoil pH and C and N content. We expected oribatid mite density to increase with increasing tree diversity, but we expected the effects of tree species identity to override effects of tree diversity. Further, we hypothesized the density of oribatid mites to be reduced by the presence of beech but increased by the presence of lime and ash. As expected tree diversity little affected oribatid mite communities, whereas tree species identity strongly altered density and community structure of oribatid mites. However, in contrast to our expectations the density of oribatid mites was highest in presence of beech indicating that many oribatid mite species benefit from the presence of recalcitrant litter forming thick organic layers. Especially Oppioidea benefited from the presence of beech presumably due to an increased availability of food resources such as fungi and nematodes. Lower density of oribatid mites in monospecific clusters of lime and ash suggests that oribatid mites did not benefit from high quality litter of these species. Notably, large and strongly sclerotized oribatid mite species, such as Steganacarus magnus and Chamobates voigtsi, benefited from the presence of ash and lime. Presumably, these large species better resist harsh microclimatic conditions in shallow organic layers.

Competition for nitrogen sources between European beech (Fagus sylvatica) and sycamore maple (Acer pseudoplatanus) seedlings

To investigate the short-term consequences of direct competition between beech and sycamore maple on root N uptake and N composition, mycorrhizal seedlings of both tree species were incubated for 4 days (i.e. beech only, sycamore maple only or both together) in an artificial nutrient solution with low N availability. On the fourth day, N uptake experiments were conducted to study the effects of competition on inorganic and organic N uptake. For this purpose, multiple N sources were applied with a single label. Furthermore, fine roots were sampled and analysed for total amino acids, soluble protein, total nitrogen, nitrate and ammonium content. Our results clearly show that both tree species were able to use inorganic and organic N sources. Uptake of inorganic and organic N by beech roots was negatively affected in the presence of the competing tree species. In contrast, the presence of beech stimulated inorganic N uptake by sycamore maple roots. Both the negative effect of sycamore maple on N uptake of beech and the positive effect of beech on N uptake of sycamore maple led to an increase in root soluble protein in beech, despite an overall decrease in total N concentration. Thus, beech compensated for the negative effects of the tree competitor on N uptake by incorporating less N into structural N components, but otherwise exhibited the same strategy as the competitor, namely, enhancing soluble protein levels in roots when grown under competition. It is speculated that enhanced enzyme activities of so far unknown nature are required in beech as a defence response to inter-specific competition.

Leaf diversity influences in‐stream litter decomposition through effects on shredders

Summary1. The functioning of many aquatic ecosystems is controlled by surrounding terrestrial ecosystems. In a view of growing interest in linking biodiversity to ecosystem‐level processes, we examined whether and how leaf diversity influences litter decomposition and consumers in streams.2. We tested experimentally the hypothesis that the effects of leaf diversity on decomposition are determined by the responses of leaf consumers to resource–habitat heterogeneity. Leaves from three common riparian trees, beech (Fagus sylvatica), hazel (Corylus avellana) and ash (Fraxinus excelsior), were exposed alone and in all possible mixtures of two and three species in a stream. We analysed individual leaf species for decomposition rate, microbial respiration and mycelial biomass, and we determined the species composition, abundance and biomass of shredders in leaf bags.3. We found that the decomposition of the fastest decomposing leaves (hazel and ash) was substantially stimulated (up to twofold higher than single species leaf packs) in mixtures containing beech leaves, which are refractory. In contrast, the decomposition of beech leaves was not affected by leaf mixing. Such species‐specific behaviour of leaves in species mixtures has been overlooked in previous studies that examined the overall decomposition of litter mixtures.4. The effects of leaf diversity on decomposition varied with the abundance and biomass of shredders but not with microbial parameters. Beech leaves alone were less attractive to shredders than leaf packs made of hazel, ash or any mixture of species. Moreover, the presence of beech leaves in mixtures led to higher shredder abundance and biomass than we had expected from data from single species exposed alone. Lastly, we found that early instars of the caddisfly Potamophylax (the dominant shredder in terms of biomass) almost exclusively used the toughest material (i.e. beech leaves) to construct their cases.5. Leaf pack heterogeneity may have altered shredder‐mediated decomposition. Shredders colonising diverse leaf packs benefited from the stable substratum provided by beech leaves, whereas ash and hazel leaves were primarily used as food. Thus, our findings provide strong evidence for an intimate linkage between the diversity of riparian vegetation and aquatic communities.

Soil aggregation in a laboratory experiment: Interactions between earthworms, woodlice and litter palatability

Summary Interactions between soil invertebrate functional groups are still poorly understood. In this study, the effect of the soil dwelling earthworm Aporrectodea caliginosa and the woodlouse Porcellio scaber (litter inhabitant), alone or in combination, on soil aggregation was investigated in laboratory microcosms with litter of different quality (Quercus robur and Fagus sylvatica). After 4 months of incubation, the aggregate size distribution was measured using a dry-sieving method. A. caliginosa played an important role in the formation of large aggregates (>2 mm), whereas P. scaber greatly influenced litter disappearance. A. caliginosa individuals formed a greater number of large aggregates when fed with beech leaves compared to oak leaves even though they preferred the latter. In the presence of beech and P. scaber, A. caliginosa produced significantly fewer large aggregates than expected.