Relationships between land snail assemblage patterns and soil properties in temperate-humid forest ecosystems

Aim The objectives were to (1) analyse the combined effects of soil pH, Ca content and soil moisture on total density and species richness of land snails in forest ecosystems, (2) explore relationships between the quantitative composition of snail assemblages and habitat characteristics, (3) investigate the relationships between soil pH and density of some of the most frequent species, and (4) compare the data with those from studies conducted in other temperate‐humid regions of Europe. Location Study sites were selected from 15 landscape types including different lithologies within the area of Baden‐Württemberg (35,000 km²), SW Germany. Methods Snails were recorded quantitatively from 83 study sites, with four plots representing a total of 0.25 m² per site. Topsoil samples from each site were analysed for pH, exchangeable Ca, and Ca content of carbonates. Three categories of soil moisture (dry, intermediate and wet) were established and defined according to the (climatic) water balance. Numbers of individuals and species were brought in relation to soil moisture and soil pH. Cluster analyses were conducted to identify groups of quantitatively similar snail species assemblages. Results Topsoil pH (2.7–7.5) and soil Ca contents were closely correlated. On dry soils, total snail density and species richness are generally low and do not change with pH, but clearly increase with increasing pH on intermediate moisture soils and on wet soils. On the latter, numbers of individuals and species are generally much higher compared with intermediate moisture sites at the same value of soil pH. Changes of density in relation to soil pH vary between species. Depending on the species, density increases only in the lower or only in the higher range of pH, is not related to pH, or decreases with increasing pH. Furthermore, these patterns vary within the same species depending on the region. This became evident from comparisons with other studies, particularly between sites in SW Germany and southern Scandinavia. From cluster analyses, subgroups of snail assemblages of high quantitative similarity were identified. Group formation is explained by soil pH to some extent, and one subgroup showed a connection with coniferous woodland sites on acidic soils. No further environmental factors available from our data could explain the clustering of snail assemblages more detailed. Main conclusions Soil moisture is the strongest determinant of snail density and species richness at undisturbed woodland sites, but effects of soil moisture and soil pH on these patterns are closely interrelated on intermediate moisture soils and wet soils. However, the quantitative species composition of the land snail assemblages is related to soil properties to a lower degree than snail density and species richness, and other habitat characteristics such as vegetation or litter quality, can be important for species dominance in addition.     

Forest snail diversity and its environmental predictors along a sharp climatic gradient in southern Siberia

Diversity patterns of forest snail assemblages have been studied mainly in Europe. Siberian snail faunas have different evolutionary history and colonization dynamics than European faunas, but studies of forest snail diversity are almost missing from Siberia. Therefore, we collected snails at 173 forest sites in the Russian Altai and adjacent areas, encompassing broad variation in climate and forest types. We found 51 species, with a maximum of 15 and an average of seven species per site. The main gradient in species composition was related to soil pH, a variable that also positively correlates with snail abundances. The second gradient was associated with climate characteristics of winter. We observed significant differences in both species richness and composition among six forest types defined based on vegetation classification. Hemiboreal continental forests were the poorest of these types but hosted several species characteristic of European full-glacial stages of the Late Pleistocene. A high snow cover in Temperate coniferous and mixed forests, protecting the soil from freezing, allowed the frost-sensitive large-bodied (>10 mm) species to inhabit this forest type. In contrast to most of the European snail assemblages studied so far we found that the factors responsible for the variation in species richness differed from those driving species composition. This may be attributed to the sharp climatic gradient and the presence of the cold-adapted species typical of the Pleistocene cold stages. We suggest that southern Siberian forests hosting these species can serve as modern analogues of full-glacial forests in periglacial Central and Eastern Europe.     

Elevated native terrestrial snail abundance and diversity in association with an invasive understory shrub,Berberis thunbergii,in a North American deciduous forest

Invasive terrestrial plants often substantially reshape environments, yet how such invasions affect terrestrial snail assemblages remains understudied. We investigated how snail assemblages in deciduous forest soils with dense Berberis thunbergii (Japanese barberry), an invasive shrub in eastern North America, differ from forest areas lacking the shrub. Leaf litter and soil samples were collected from forest patches with dense B. thunbergii understories and adjacent control areas within two exurban forest tracts in western Pennsylvania, U.S.A. Snails were identified to species and quantified by standard diversity metrics. Contrary to our expectations, snails were significantly more abundant and diverse in B. thunbergii-invaded areas. Despite differences in abundance, the snail community composition did not differ between invaded and control habitats. The terrestrial snail assemblage we observed, which was composed entirely of native species, appears to respond favorably to B. thunbergii invasion and therefore may not be negatively impacted by physicochemical changes to soils typically observed in association with the plant. Such findings could reflect the fact that B. thunbergii likely creates more favorable habitat for snails by creating cooler, more humid, and more alkaline soil environments. However, the snail assemblages we retrieved may consist mostly of species with high tolerance to environmental degradation due to a legacy of land use change and acid deposition in the region.     

Spatial patterns of herbivory by gall-forming insects: a test of the soil fertility hypothesis in a Mexican tropical dry forest

It has been proposed that fertile soils reduce the incidence of gall-forming insect (GFI) species in plant communities. This is known as the soil fertility hypothesis. The main objective of this study was to analyze the spatial distribution of GFI species under different habitats in a tropical dry forest at the Chamela-Cuixmala Biosphere Reserve, Mexico. Eight habitats which differ in soil type, topography, nutrient availability and vegetation were chosen. We found that 38 GFI species specialize on their host plant species. GFI species richness was negatively correlated with phosphorous and nitrogen availability. Using phosphorous as an indicator of soil fertility, we found low frequency and density of GFI on fertile soils. Our study indicates that soil fertility is one of the factors that negatively affects the patterns of spatial distribution of species richness, incidence and abundance of GFI at the community level in two different ways: i) indirectly affecting GFI species richness in plants adapted to infertile soils and ii) directly affecting GFI responses to plant traits of hosts found in a fertility gradient.     

Calcareous forest seepages acting as biodiversity hotspots and refugia for woodland snail faunas

Land-snail species richness has repeatedly been found to increase with the increasing site calcium content and humidity. These two factors, reported as the main drivers of land-snail assemblage diversity, are also among the main habitat characteristics of calcareous seepages. Here we explore local species richness and compositional variation of forest spring-fed patches (i.e. seepages), to test the hypothesis that these habitats might act as biodiversity hotspots and refugia of regional snail faunas. In contrast to treeless spring fens, only little is known about land snail faunas inhabiting forest seepages. Studying 25 isolated calcareous forest seepages, evenly distributed across the White Carpathians Protected Landscape Area (SE Czech Republic), we found that these sites, albeit spatially very limited, can harbour up to 66% of the shelled land-snail species known to occur in this well-explored protected area (in total 83 species). By comparing land snail assemblages of the studied seepages with those occurring in the woodland surroundings of each site as well as those previously sampled in 28 preserved forest sites within the study area, we found the seepages to be among the most species rich sites. Although the numbers of species did not statistically differ among these three systems, we found highly significant differences in species composition. Seepage faunas were composed of many species significantly associated with spring sites, in contrast to the assemblages of both surrounding and preserved forest sites. Our results highly support the hypothesis that calcareous forest seepages might serve as refugia and biodiversity hotspots of regional land snail faunas. Protection of these unique habitats challenges both conservation plans and forest management guidelines as they might act as sources for the recolonization and restoration of forest snail assemblages particularly in areas impoverished by harvesting and clearcutting.     

Effect of liming on dry matter yield of wheat in pots of low humic gley soil

Summary This experiment was carried out with the aim of verifying the effect of liming on three wheat cultivars, IAC-5, Alondra and Anahuac, in lowland hydromorphic soils (Low Humic Gley) rich in organic matter. The treatments consisted of five levels of liming using two recommended methods. These treatments were: control without liming; liming by the aluminium method and 1/3, 2/3 and 4/3 of the liming recommended by the buffer method of Shoemaker, McLean and Pratt (SMP buffer method). Adequate levels of calcium and magnesium in the plants were obtained with higher doses of calcium than those indicated by the aluminium method. With the aid of curves adjusted to the experimental data it was verified that the maximum yields of dry matter of 15.86, 15.88 and 12.53 g/pot for the cultivars IAC-5, Alondra and Anahuac, respectively, occurred with higher quantities of calcium at 2/3 of liming indicated by the SMP method at pH 6.0 At this rate of liming aluminium levels in the soil were not totally neutralized and the levels of calcium and magnesium adequate for maximum yield were estimated in 4.6, 4.08 and 4.7 meq/100 g of soil.The results indicate that for Low Humic Gley soils with a high level of organic matter, the level exchangeable aluminium does not constitute an adequate criterion for indicating liming requirements for wheat.     

Effect of land-use on the earthworm assemblages in semi-deciduous forests of Central-West Ivory Coast

In this study, the impact of forest disturbance on earthworm assemblages was assessed using monoliths dug out at 5 m intervals along a gradient of land-use intensification. The land-use types comprised primary forest (as a baseline), secondary forest, tree plantation, fallow, perennial and annual crop. Forest disturbance resulted in a significant decrease in soil organic carbon and pH, while earthworm abundance and biomass increased along the gradient of disturbance. Surprisingly, anthropogenic disturbances in semi-deciduous forest areas have not led to the disappearance of native species to the benefit of exotic species as revealed in former studies. As a result, in this study land-use change had no impact on species richness at the landscape level, even if at local scales, recurrent Chromolaena odorata fallows, multispecies tree plantations and 4 year-old teak plantations hosted the highest average species richness. Multiple regression analyses performed between earthworm communities and environmental variables showed that soil organic carbon and pH are potential indicators of earthworm abundance change.     

Effects of liming on phosphate availability in acid soils

Summary The critical factors involved in the plant-soil-phosphorus-lime interaction are outlined and discussed. Conflicting reports suggest that the prior liming of highly weathered acid soils can result in an increase, a decrease, or no change in the availability of applied phosphate. Adsorption of phosphate by amphoteric soil surfaces generally decreases slowly as the pH is raised from 4.0 to 7.0. However, in soils initially high in exchangeable Al³⁺, liming results in the formation of new, highly active, phosphate adsorbing surfaces as the Al³⁺ ions precipitate as insoluble polymeric hydroxy-Al cation species. Thus, if an acid soil is reacted with lime and then phosphate, without intervening air drying, liming can increase phosphate adsorption. If the same limed soil is air dried before reaction with phosphate (e.g. adsorption isotherm studies), liming decreases phosphate adsorption. Apparently, air drying alters the surface characteristics of recently limed soils, probably by promoting the crystallization of the hydroxy-Al cation polymers as gibbsite.An important phenomenon, which is often overlooked, is that liming can increase phosphate availability by stimulating mineralization of soil organic phosphorus. However, at high soil pH values, the precipitation of insoluble calcium phosphates can decrease phosphate availability. Since Al toxicity is characterised by the inhibition of the uptake, translocation and utilization of phosphate by plants, liming often increases the utilization of soil phosphate by plants through amelioration of Al toxicity.When making lime recommendations or interpreting the data collected from lime-phosphate experiments, it is important to consider all the complex interacting soil and plant factors involved.     

Plant species richness in continental southern Siberia: effects of pH and climate in the context of the species pool hypothesis

Aim Many high‐latitude floras contain more calcicole than calcifuge vascular plant species. The species pool hypothesis explains this pattern through an historical abundance of high‐pH soils in the Pleistocene and an associated opportunity for the evolutionary accumulation of calcicoles. To obtain insights into the history of calcicole/calcifuge patterns, we studied species richness–pH–climate relationships across a climatic gradient, which included cool and dry landscapes resembling the Pleistocene environments of northern Eurasia. Location Western Sayan Mountains, southern Siberia. Methods Vegetation and environmental variables were sampled at steppe, forest and tundra sites varying in climate and soil pH, which ranged from 3.7 to 8.6. Species richness was related to pH and other variables using linear models and regression trees. Results Species richness is higher in areas with warmer winters and at medium altitudes that are warmer than the mountains and wetter than the lowlands. In treeless vegetation, the species richness–pH relationship is unimodal. In tundra vegetation, which occurs on low‐pH soils, richness increases with pH, but it decreases in steppes, which have high‐pH soils. In forests, where soils are more acidic than in the open landscape, the species richness–pH relationship is monotonic positive. Most species occur on soils with a pH of 6–7. Main conclusions Soil pH in continental southern Siberia is strongly negatively correlated with precipitation, and species richness is determined by the opposite effects of these two variables. Species richness increases with pH until the soil is very dry. In dry soils, pH is high but species richness decreases due to drought stress. Thus, the species richness–pH relationship is unimodal in treeless vegetation. Trees do not grow on the driest soils, which results in a positive species richness–pH relationship in forests. If modern species richness resulted mainly from the species pool effects, it would suggest that historically common habitats had moderate precipitation and slightly acidic to neutral soils.     

Lizard assemblages in a fragmented landscape of central Chile

We studied lizard assemblages assessing abundance, richness, and nestedness in a fragmented landscape of central Chile including native temperate forest, forest fragments, and commercial pine plantations. Fragmentation and plantations increase the availability of edge habitats triggering both the support of additional lizard species, absent at the continuous forest, and the nestedness of lizard assemblages, where interior habitats of forest and plantations are nested subsets of habitat edges. A vulnerable lizard (Liolaemus tenuis) thrives at fragments in abundance similar to the continuous forest. Therefore, remnants ought to be considered in the conservation of lizard assemblages.     

Decline in snail abundance due to soil acidification causes eggshell defects in forest passerines

On poor soils in the Netherlands an increasing number of great tits, Parus major, and of other forest passerines produce eggs with defective shells and have low reproductive success as a result of calcium deficiency. A similar increase in eggshell defects has been observed in Germany and Sweden. Snail shells are the main calcium source for tits in forests where defective eggshells do not occur, but are very little taken in forests where tits often have eggshell defects. We investigated whether a decrease in snail abundance on poor soils could be responsible for the decline in eggshell quality, and if so, what caused this decrease. Snail density in forests where tits have eggshell defects was much lower than in forests where tits do not have such defects. Snail density correlated with the calcium content and to a lesser extent with pH of the litter layer. Liming of a calciumpoor forest soil with few snails resulted in snail densities comparable to those on calcium-rich soils after 4 years. Snail density has declined on calcium-poor soils over the last two decades, but not on calcium-rich soils. Acid deposition has caused a decline of soil calcium on poor soils. We conclude, therefore, that anthropogenic acidification has caused a decline in snail populations, resulting in an increase in eggshell defects in birds in forests on poor soils.     

The influence of light and nutrient availability on herb layer species richness in oak-dominated forests in central Bohemia

In this study, we examined to what extent the internal site factors (light and soil conditions) are responsible for herb layer diversity in oak-dominated forest stands growing on different substrates in central Bohemia (Czech Republic). We collected data on herb layer diversity, light and nutrient availability at nine oak stands, representing the range of environmental variability for these types of forests in the region. We found that species richness increased with light availability, but only if the site occupied predominantly by fast-colonizing species was excluded from the analysis (P < 0.05). Species richness correlated positively with soil pH and negatively with nitrogen (N) concentration in humus (P < 0.05). The highest species richness was found at sites with not only low N soil concentration, but also simultaneously with high phosphorus (P) soil concentration. Despite this finding, however, herb layer diversity is evidently threatened much more in P-rich soils than in P-poor soils. It seems that the enhancement of N in an ecosystem due to litter accumulation and N deposition generally leads to only a minor increase in N availability at P-poor sites, but a considerable increase at P-rich sites. Therefore, species richness can be exceptionally high at P-rich sites, but only under conditions of strong N limitation.     

Native and introduced land snail species as ecological indicators in different land use types in Java

We investigated the effects of different land use types and environmental parameters on the number and abundance of native and introduced land snail species in East Java. 2919 specimens were sampled and assigned to 55 species of which 8 are introduced. Whereas species richness was highest in primary forest, the highest number of introduced species was found in agroforest. The snail assemblages in different habitat types differ much clearer in composition than in total species richness. Plantations and agroforest are dominated by introduced pulmonates with regard to number of individuals, while primary forest is dominated by native prosobranchs. The habitat requirements of the introduced pulmonates differ from those of the native species. In the study area, the abundance of native as well as introduced pulmonate species increased with increasing human impact. However, the abundance of introduced pulmonate species decreased with increasing density of the canopy cover, whereas the abundance of native pulmonate species increased with increasing canopy cover. The abundance of native prosobranch land snails also tends to increase with increasing canopy cover and with the availability of deadwood, but decreased with increasing human impact. Improving the canopy cover and retaining deadwood in plantations and agroforests might help to control the populations of introduced species or even prevent their establishment in these habitats. Land snails are good indicators for the long-term stability of natural habitats, because several species are restricted to undisturbed natural habitats and because of their low dispersal abilities. However, complete inventories of land snail species are costly. Therefore we propose two indices that can be scored with much less effort, namely the percentage of prosobranch individuals and the percentage of individuals of introduced species. Both indices are significantly correlated with the number of native species. Dense plantations and agroforests bordering primary forests may protect the latter from introduced species and help to conserve the native fauna by reducing desiccation and buffering the human impact on the primary forests.     

The diversity of beetle assemblages in different habitat types in Sabah, Malaysia

The diversity of beetle assemblages in different habitat types (primary forest, logged forest, acacia plantation and oil palm plantation) in Sabah, Malaysia was investigated using three different methods based on habitat levels (Winkler sampling, flight-interception-trapping and mist-blowing). The overall diversity was extremely high, with 1711 species recorded from only 8028 individuals and 81 families (115 family and subfamily groups). Different degrees of environmental changes had varying effects on the beetle species richness and abundance, with oil palm plantation assemblage being most severely affected, followed by acacia plantation and then logged forest. A few species became numerically dominant in the oil palm plantation. In terms of beetle species composition, the acacia fauna showed much similarity with the logged forest fauna, and the oil palm fauna was very different from the rest. The effects of environmental variables (number of plant species, sapling and tree densities, amount of leaf litter, ground cover, canopy cover, soil pH and compaction) on the beetle assemblage were also investigated. Leaf litter correlated with species richness, abundance and composition of subterranean beetles. Plant species richness, tree and sapling densities correlated with species richness, abundance and composition of understorey beetles while ground cover correlated only with the species richness and abundance of these beetles. Canopy cover correlated only with arboreal beetles. In trophic structure, predators represented more than 40% of the species and individuals. Environmental changes affected the trophic structure with proportionally more herbivores (abundance) but fewer predators (species richness and abundance) in the oil palm plantation. Biodiversity, conservation and practical aspects of pest management were also highlighted in this study.     

Amazonian Dark Earth Shapes the Understory Plant Community in a Bolivian Forest

Amazonian Dark Earths (ADE) are the result of human modification of the Amazonian landscape since pre‐Columbian times. ADE are characterized by increased soil fertility compared to natural soils. In the Amazonian forest, soil fertility influences understory herb and fern species composition. However, little research has been done to evaluate the effect of ADE on the composition of the understory community. We evaluated the effects of ADE and soil in 36 plots (150 m × 4 m) established in a Bolivian moist forest (La Chonta). For each plot, we determined soil nutrients, and the composition, richness, and abundance of terrestrial fern, angiosperm herb, and understory palm species. We found that the presence of ADE created a gradient in soil nutrients and pH that affected the understory species composition especially of ferns and palms. Additionally, the higher nutrient concentration and more neutral soil pH on ADE soils caused a decrease of ferns species richness. We therefore conclude that the current composition of the understory community in this particular Bolivian forest is a reflection of past human modifications of the soil.     

Neighborhood-Scale Analyses of Non-additive Species Effects on Cation Concentrations in Forest Soils

Trees affect soil chemistry and nutrient availability via a broad range of processes. Effects can vary dramatically among species, whose distinctive spatial “footprints” can vary for different nutrients. Potentially overlapping effects of neighboring trees in mixed-species stands make footprint shape and interspecific interactions important: If interactions are non-additive, then not only abundance but also spatial configuration influence tree species’ effects on ecosystem properties. We used spatially explicit neighborhood-scale data on tree distributions to fit maximum likelihood models of exchangeable calcium, magnesium, and potassium in surface soils of four sites in northern hardwood forests in northwestern Connecticut, USA. The models incorporated parent material, site, and tree species or functional group configuration to predict availability of the three cations. Site had a stronger effect than species for all cations (there was no species effect for potassium), even after accounting for variation in parent material. Species’ spatial footprints extended further from the stem for calcium than magnesium, which is consistent with the relative importance of litterfall versus stemflow transfer of these nutrients. The magnitude of species effects on calcium and magnesium varied widely. Functional groups made up of species with positive or negative effects provided parsimonious models for magnesium and calcium, and the best model for calcium included a non-additive, antagonistic effect whose strength varied by site. This non-additive effect suggests that the degree of intermingling of tree species from negative- and positive-effect functional groups may influence stand-level availability of calcium, a key nutrient for forest health in these ecosystems.     

The role of calcium in buffering soils

Abstract. Calcium is the soluble cation that occurs in largest amount in most soils. It does not take part directly in the proton transfer reactions involved in pH-buffering, but it provides the cation charge balance for these reactions. It is also the complementary cation in formulations of chemical potential for many other ions in soils. The presence of free calcium carbonate in calcareous soils. The presence of free calcium carbonate in calcareous soils ensures a very high soil buffer capacity; d AB/ d pH ≃ 1000 Eq. m⁻³.
In acid mineral soils, dissolution and precipitation of aluminium ions contribute to the buffering processes, but most of the buffering in non-calcareous soils is caused by specific ion adsorption at variable-charge sites, in particular those associated with the dissociation of humus acids. Typical buffer capacity values of non-calcareous soils vary from 10 Eq. m⁻³ for sandy soils to 100 Eq. m⁻³ for peats. The pH changes associated with buffering are produced by leaching of calcium from soil, or by adding calcium to soil in liming materials.     

Use of habitat resources by scarab dung beetles in an savanna

In the Queen Elizabeth National Park, Uganda, we compared the scarab beetle assemblages in the dung of three wild ungulates (African buffalo, a ruminant foregut fermenter; hippopotamus, nonruminant foregut fermenter; and warthog, nonruminant hindgut fermenter). Dung was collected from two sandy-clay soils with different percentage of coarse sand. We aimed at investigating habitat resource selection by dung beetle species within a savanna natural contest with abundant and diverse food availability. Analyses were performed to detect differences for dung beetle assemblages in abundance, diversity, functional groups. Species richness in the three dung types and in the two soil types was similar. However, warthog dung and sandy-rich soil appeared the preferred habitat resources, in terms of abundance and biomass, while hippopotamus dung hosted the lowest values for these parameters. The analysis of functional groups revealed that slow-burying tunnellers held the major role, both in terms of abundance and biomass, and were mainly found in warthog dung.