Huisman-Olff-Fresco Research Articles

Species–soil relationships across Amazonia: Niche specificity and consistency in understorey ferns

AbstractAimsKnowledge about species niches along environmental gradients is needed to understand community assembly and spatial variation in floristic composition and species richness. In Amazonian rainforests, such knowledge is largely lacking, although ferns have been used to infer overall floristic and edaphic patterns. Here we explore fern species distributions along an important edaphic gradient, how narrow their realised niches are and how sensitive inferences are to species commonness, data quality and the region being sampled.LocationAmazonia.MethodsWe used a large data set (1,215 transects across lowland Amazonia) to explore the realised niches of 54 species of two fern genera (Adiantum and Lindsaea) along a soil base cation concentration gradient. We used weighted averaging to estimate species optima and niche widths, and Huisman–Olff–Fresco modelling to assess species response shapes.ResultsOverall, species optima were rather evenly spread along the soil base cation concentration gradient, but Lindsaea optima were limited to the lower half of the gradient, whereas Adiantum optima were more often in the upper half. Most species had unimodal response curves. Mean niche width was ca. 25% of the observed gradient length for Adiantum and 17% for Lindsaea and was only weakly or not at all related to different aspects of species commonness. Species optima were robust to different modelling approaches and consistent across regional subsets. However, the central Amazonian data contained no transects with high soil base cation concentration, so species with high optima were either absent or obtained a lower optimum than in the NW and SW regions.ConclusionsOur results support niche‐related species sorting as an important process that defines species co‐occurrence, turnover and richness patterns within Amazonian rainforests. All Adiantum and Lindsaea species, including the most abundant ones, had narrow enough realised niches to be considered useful indicators of edaphic and floristic variation within the rainforest.

Beyond salinity: Plants show divergent responses to soil ion composition

AbstractAimIn salt‐affected environments, salinity shapes ecosystem functions and species composition. Apart from salinity, however, we know little about how soil chemical factors affect plant species. We hypothesized that specific ions, most of which contribute to salinity, co‐determine plant niche differentiation. We asked if the importance of ions differs for species with (halophytes) and without (associated species) physiological adaptations to saline soils.LocationCarpatho‐Pannonian region (Central and Eastern Europe).Time period2005–2021.Major taxa studiedVascular plants.MethodsWe recorded species occurrences and collected soil samples in 433 plots in saline habitats. We measured pH, salinity (electrical conductivity), and concentrations of Ca2+, K+, Mg2+, Na+, SO42− Cl−, CO32− and mineral nitrogen (mN) and calculated the sodium adsorption ratio (SAR). For 88 species, we fitted response curves with Huisman–Olff–Fresco (HOF) models. To study ions' effects on species composition and ions' variance, we compared unconstrained and constrained ordinations and performed a principal component analysis. We used random forests to analyse the importance of ions for individual species and created two‐dimensional species niche plots for key ions.ResultsIon concentration niches varied among species and did not necessarily correspond to soil salinity or alkalinity. We frequently observed monotonic, sigmoidal model responses, while skewed unimodal responses were rare. Ions explained a considerable proportion of species compositional variation. Particularly, Na+, SO42−, Cl−, and CO32− contributed to the ions' variance. Na+, followed by SO42−, Cl−, CO32−, Ca2+, Mg2+, and mN, was most important for the occurrence of individual species. Compared to associated species, Na+, SO42−, and mN were significantly less important for halophytes, whereas Cl− and CO32− played a significant role.Main conclusionsWe show that ion composition co‐determines niche differentiation in saline soils, suggesting evolved physiological adaptations in halophytes. Our study calls for incorporating high‐resolution data on soil ion composition in ecological research.

Modeling response curves of European yew (Taxus baccata L.) using HOF models along the environmental gradient in north of Iran

One of the important issues in plant autecology is the analysis and understanding of species-environment relationships and response of species to ecological gradients. Understanding how species respond to environmental variables is useful for predicting the environmental and geographic distribution of species. The main objective of this research is to study the response curve of European yew to identify the most important climatic and physiographic gradient in the northern forests of Iran. In the present study the Huisman–Olff–Fresco function (HOF) was used to study the response curve of the European yew in relation to each of the environmental variables individually and extract the optimum values. In order to select the optimal model, the Akaike Information Criterion (AIC) was used. Based on the results of this study, 41% of the models have either monotonically increasing or decreasing behaviors (models 2 and 3), 27% of the models have a unimodal symmetric behavior and 32% of models have a skewed behavior. European yew in 59% of models has a unimodal response curve. Based on the variables used in the study, it can be said that the European yew is a species that prefers oceanic climates, midlands altitudes, and north-facing slopes for establishment in temperate forests of Iran. Together, these findings advance niche theory about the European yew tree and may be used for generating better predictive models of European yew distributions under future climate change.

Niche breadth and biodiversity change derived from marine Amphipoda species off Iceland.

Understanding the ecological requirements and thresholds of individual species is crucial to better predict potential outcomes of climate change on species distribution. In particular, species optima and lower and upper limits along resource gradients require attention. Based on Huisman‐Olff‐Fresco (HOF) models, we determined species‐specific responses along gradients of nine environmental parameters including depth in order to estimate niche attributes of 30 deep‐sea benthic amphipods occurring around Iceland. We, furthermore, examined the relationships between niche breadth, occupancy, and geographic range assuming that species with a wider niche are spatially more widely dispersed and vice versa. Overall, our results reveal that species react very differently to environmental gradients, which is independent of the family affiliation of the respective species. We could infer a strong relationship between occupancy and geographic range and also relate this to differences in niche breadth; that is specialist species with a narrow niche had a more limited distribution and may thus be more threatened by changing environmental conditions than generalist species, which are more widespread. Given the preponderance of rare species in the deep sea, this implies that many species could be at risk. However, this must be carefully weighed against geographical data gaps in this area, given that many deep‐sea areas are severely undersampled and the true distribution of most species is unknown. After all, our results underline that an accurate taxonomic classification is of crucial importance, without which ecological niche properties cannot be determined and which is hence fundamental for the assessment and understanding of changes in biodiversity in the face of increasing human perturbations.

Modern pollen–climate relationships and their application for pollen-based quantitative climate reconstruction of the mid-Holocene on the southern Korean Peninsula

A modern pollen dataset is a prerequisite for reconstructing quantitative paleoclimate and paleovegetation cover using fossil pollen records. Although multiple modern pollen–climate datasets have been established covering a wide range of climate conditions, such datasets are exceedingly rare for the Korean Peninsula (KP). In this study, we acquired a modern pollen dataset from 198 surface soil samples collected on 37 mountains on the southern KP. Redundancy analysis (RDA) and variation partitioning results identified mean annual temperature (Tann) as the most important climate variable shaping pollen assemblages on the southern KP. Using the pollen–climate relationships inferred from the RDA, we applied the Huisman–Olff–Fresco model and determined that arboreal pollen taxa responded sensitively to the climatic gradient, whereas non-arboreal pollen taxa did not. We applied weighted averaging–partial least squares (WA-PLS) and the modern analog technique (MAT) to the pollen dataset, and a comparison of the results showed that MAT performed better than WA-PLS. A transfer function was applied to fossil pollen records from the areas covered by our dataset; the results confirmed that annual precipitation (Pann) and Tann were modulated by different mechanisms, with Pann strongly affected by El Niño–Southern Oscillation-driven typhoons during the Holocene, whereas Tann was mainly influenced by the Tsushima Warm Current from 7500 to 5100 cal yr BP depending on Kuroshio Current inflow intensity, and subsequently followed by the East Asian winter monsoon during 5100–3400 cal yr BP.

Varying support for abundance‐centre and congeneric‐competition hypotheses along elevational transects of mammals

AbstractAimWhether species are most abundant at their geographic range centre and increasingly rare towards range limits (the abundance‐centre hypothesis, ACH) has weak empirical support in birds along elevational gradients. This may be due to empirical limitations—most studies do not capture the multi‐faceted nature of elevational gradients or species interactions. We examine the ACH and an alternative that the abundance maximum of elevational sympatric congeners will occur at different elevations along a gradient (the congeneric‐competition hypothesis, CCH).LocationTwelve elevational gradients in Central and Southwest China.TaxonFive small mammal species, including three congeneric species.MethodsThe ACH was tested by fitting abundance patterns to Huisman‐Olff‐Fresco (HOF) models and measuring the relative elevational distance between a species' abundance‐weighted range centre (RCAbu) and its elevational range centre. The CCH was tested by calculating the elevational overlap value of each congeneric pair and the relative elevational distance (RCAbuDiff) between the RCAbus of congeners.ResultsAbundances of each species showed diverse patterns along different gradients. For all species, a unimodal symmetric pattern appeared at most once among the studied gradients and found in only four (8.7%) of the total cases. Most (90.9%) of the Apodemus congeneric pairs had a high elevational overlap (above 75%). For each of the three congeneric pairs, 40.0% to 50.0% of the cases showed RCAbuDiff values > 0.25, suggesting that the congeners’ RCAbus were separated by at least one elevational climate zone.Main conclusionsSpecies' elevational abundance patterns may vary among different elevational gradients in the same geographic region. The elevational abundance patterns of five mammalian species were rarely consistent with the ACH after the spatial variability of the patterns was considered. The abundance patterns of congeneric species showed moderate support for the CCH.

Assessing environmental response of gastropod species in karst springs: what species response curves say us about niche characteristic and extinction risk?

Spring ecosystems are exceptionally threatened and their conservation is often emphasized due to high levels of endemism among the groups inhabiting these ecosystems. This study includes gastropod assemblages of 36 springs situated in the northwestern part of Bosnia and Herzegovina. The aims of this paper were: to determine key factors for distribution of gastropod species on microspatial scale; to define the environmental preferences of gastropod species with respect to the physicochemical properties of water, the hydrological characteristics and the sediment structure; to determine species tolerance ranges and species optimums, with special emphasis on new and endemic species. Moreover the aim was to identify the species with highest extinction risk. The contribution of endangered and rare species to the total density was extremely high (64.6%). Species Response Curves were used to predict the distribution of gastropod species along the environmental gradient in the spring environments for the first time. The most important factors in structuring gastropod spring assemblages were oxygen and temperature. HOF (Huisman–Olff–Fresco) models may determine differences in range of environmental tolerance of species with similar ecological requirements. Our results have shown that two species: Ancylus fluviatilis and A. recurvus may be distinguished by their species response curves. Although there are no data on conservation status of A. recurvus, the extinction risk should be inferred as high, suggesting that IUCN status for this species should be updated to the category Vulnerable. Our study using HOF models revealed the potential gastropod species useful as indicators of karstic springs.

Occupancy patterns and upper range limits of lowland Bornean birds along an elevational gradient

AbstractAimThe traditional view of species’ distributions is that they are less abundant near the edges of their ranges and more abundant towards the centre. Testing this pattern is difficult because of the complexity of distributions across wide geographical areas. An alternative strategy, however, is to measure species’ distributional patterns along elevational gradients. We applied this strategy to examine whether lowland forest birds are indeed less common near their upper range limits on a Bornean mountain, and tested co‐occurrence patterns among species for potential causes of attenuation, including signatures of habitat selection and competition at the periphery of their ranges.LocationMt. Mulu, Borneo.TaxonRain forest birds.MethodsWe surveyed lowland forest birds on Mt. Mulu (2,376 m), classified their elevation‐occupancy distributions using Huisman–Olff–Fresco (HOF) models, and examined co‐occurrence patterns of species pairs for signatures of shared habitat patches and interspecific competition.ResultsFor 39 of 50 common species, occupancy was highest at sea level then gradually declined near their upper range edges, in keeping with a “rare periphery” hypothesis. With respect to habitat selection, lowland species do not appear to cluster together at sites of patchy similar habitat near their upper range limits; neither are most lowland species segregated from potential montane competitors where ranges overlap.Main conclusionsHigh relative abundance at sea level implies that species inhabit “truncated niches” and are not currently near the limits of their fundamental niche, unless unknown critical response thresholds exist. However, indirect effects of increasing temperature predicted under climate change scenarios could still influence lower range limits of lowland species indirectly by altering habitat, precipitation regimes and competitive interactions. The lack of non‐random co‐occurrence patterns implies that patchy habitat and simple pairwise species interactions are unlikely to be responsible for upper range limits in most species; diffuse competition across diverse rain forest bird communities could still play a role.

With Ellenberg indicator values towards the north: Does the indicative power decrease with distance from Central Europe?

AbstractAimEllenberg indicator values (EIV) are frequently used in regions outside their Central European origin as proxies for environmental conditions, a practice further boosted by the increasing scientific focus on global change. The performance of EIV outside their geographic origin and over long gradients has, however, rarely been tested. The aim of this study was to evaluate if the indicative power of EIV changes over a large geographic gradient and to analyse the potential causes of such changes.LocationSweden.TaxonVascular plants.MethodsWe used data on forest understorey vegetation and soils from >15,000 plots from the Swedish National Forest Inventory to model how the relationship between community mean EIV and measured environmental variables changes along an extensive latitudinal gradient (>15°). We used Generalized Additive Mixed Models to account for the inventory design, and for potential nonlinearities in the relationship between the mean EIV and the environmental variables. Additionally, Huisman–Olff–Fresco (HOF) models were developed for the relationship between the incidence probability and the environmental variables to analyse if the widths of species niches change along the geographic gradient.ResultsOur study shows that EIV for N (nutrients), R (pH) and T (temperature) are useful as far north as the Arctic Circle, while those for K (continentality) showed a much weaker relationship with measured continentality. However, the indicative power of the EIV for N and R gradually became weaker towards the north along with shifts towards larger environmental niche widths of the indicator species.Main conclusionsEIV are useful indicators of soil conditions in boreal forests located far north of Central Europe. However, the drop in indicative power in the northernmost regions due to increasing environmental niche widths needs to be taken into account when applying EIV along long geographic gradients to avoid spatial bias.

The biogeography and ecology of common diatom species in the northern North Atlantic, and their implications for paleoceanographic reconstructions

Abstract Sound knowledge of present-day diatom species and their environments is crucial when attempting to reconstruct past climate and environmental changes based on fossil assemblages. For the North Atlantic region, the biogeography and ecology of many diatom taxa that are used as indicator-species in paleoceanographic studies are still not well known. Using information contained in large diatom-environment calibration datasets can greatly increase our knowledge on diatom taxa and improve the accuracy of paleoenvironmental reconstructions. A diatom calibration dataset including 183 surface sediment samples from the northern North Atlantic was used to explore the distribution and ecology of 21 common Northern Hemisphere diatom taxa. We define the ecological responses of these species to April sea ice concentrations and August sea surface temperatures (aSSTs) using Huisman-Olff-Fresco (HOF)-response curves, provide distribution maps, temperature optima and ranges, and high-quality light microscope images. Based on the results, we find species clearly associated with cold, warm and temperate waters. All species have a statistically significant relationship with aSST, and 15 species with sea ice. Of these, Actinocyclus curvatulus, Fragilariopsis oceanica and Porosira glacialis are most abundant at high sea ice concentrations, whereas Coscinodiscus radiatus, Shionodiscus oestrupii, Thalassionema nitzschioides, Thalassiosira angulata, Thalassiosira nordenskioeldii and Thalassiosira pacifica are associated with low sea ice concentrations/ice-free conditions. Interestingly, some species frequently used as sea ice indicators, such as Fragilariopsis cylindrus, show similar abundances at high and low sea ice concentrations with no statistically significant relationship to sea ice.

Investigation of the Peninsula Effect Using the Latitudinal Abundance Pattern for Tree Species in Florida

The peninsula effect is a biological diversity pattern found in peninsulas in which the number of species decreases toward the tip of the peninsula. The geometry hypothesis, as one proposed cause of the peninsula effect, attempts to predict this pattern by examining the peculiarities of peninsular geometry. As peninsulas are characterized by their isolated positions, it has been suggested that a decreased immigration-to-extinction rate is the cause of the decrease in species diversity from the base to the tip of a peninsula. We aimed to test the geometry hypothesis on tree species in the Florida peninsula by modeling the latitudinal abundance pattern using sample-based tree inventory data. We postulated that the current abundance distribution of a species is a ramification of past immigration–extinction dynamics in a peninsula, as well as an important indicator of such dynamics in the future. The latitudinal abundance patterns of 113 tree species in Florida in the southeastern United States were simulated with the Huisman–Olff–Fresco (HOF) model using the USDA Forest Service’s Forest Inventory and Analysis (FIA) database. Evidence species for the geometry hypothesis were then selected if the simulated latitudinal abundance pattern was asymmetric with its abundance maxima occurring within the Florida peninsula (i.e., approximately 31.5° latitude or lower). Our HOF model results found that most species (87% of 113 species) did not experience any steep abundance decline along the Florida peninsula when compared with their general trend across the range, suggesting that the observed diversity pattern of tree species in Florida could merely be a continuation of latitudinal diversity gradients in the southeastern United States, independent of peninsular geometry.

A modern pollen–climate dataset from the Darjeeling area, eastern Himalaya: Assessing its potential for past climate reconstruction

Relying on the ability of pollen assemblages to differentiate among elevationally stratified vegetation zones, we assess the potential of a modern pollen-climate dataset from the Darjeeling area, eastern Himalaya, in past climate reconstructions. The dataset includes 73 surface samples from 25 sites collected from a c. 130–3600 m a.s.l. elevation gradient along a horizontal distance of c. 150 km and 124 terrestrial pollen taxa, which are analysed with respect to various climatic and environmental variables such as mean annual temperature (MAT), mean annual precipitation (MAP), mean temperature of coldest quarter (MTCQ), mean temperature of warmest quarter (MTWQ), mean precipitation of driest quarter (MPDQ), mean precipitation of wettest quarter (MPWQ), AET (actual evapotranspiration) and MI (moisture index). To check the reliability of the modern pollen-climate relationships different ordination methods are employed and subsequently tested with Huisman–Olff–Fresco (HOF) models. A series of pollen–climate parameter transfer functions using weighted-averaging regression and calibration partial least squares (WA-PLS) models are developed to reconstruct past climate changes from modern pollen data, and have been cross-validated. Results indicate that three of the environmental variables i.e., MTCQ, MPDQ and MI have strong potential for past climate reconstruction based on the available surface pollen dataset. The potential of the present modern pollen-climate relationship for regional quantitative paleoclimate reconstruction is further tested on a Late Quaternary fossil pollen profile from the Darjeeling foothill region with previously reconstructed and quantified climate. The good agreement with existing data allows for new insights in the hydroclimatic conditions during the Last glacial maxima (LGM) with (winter) temperature being the dominant controlling factor for glacial changes during the LGM in the eastern Himalaya.

Regional differences in soil pH niche among dry grassland plants in Eurasia

Soil pH is a key predictor of plant species occurrence owing to its effect on the availability of nutrients and phytotoxic metals. Although regional differences in realized soil pH niche (‘niche shifts’) have been reported since the 19th century, no study has disentangled how they are influenced by spatial differences in substrate availability, macroclimate, and competitors. We linked plot‐level data on species occurrence and measured soil pH from dry grasslands in eight regions across Eurasia (n = 999 plots), spanning a geographic gradient of 6862 km. We calculated regional shifts in niche optimum (Dopt) and width (Dwidth) for 73 Species × Region 1 × Region 2 combinations (SRRs; 38 study species) using extended Huisman–Olff–Fresco models. Next, we used commonality analysis to partition the contribution of substrate availability, precipitation, and species traits indicative of competitive ability to variation in regional niche shifts. Shifts in optimum were rare (5% of SRRs with Dopt ≥ 1 pH units) but many species did not show optima within regions. By contrast, shifts in niche width were common (22% of SRRs with Dwidth ≥1 pH units) and there were pronounced interspecific differences. Whereas none of the three predictors significantly explained shifts in niche optimum, common and unique effects of substrate availability and precipitation accounted for 85% of variation in niche width. Our results suggest that substrate availability and precipitation could be the driving factors behind species regional shifts in niche width. Studies that address additional factors, such as other edaphic niches, and their variability at the regional and micro‐scale will improve our understanding of the mechanisms underlying species distributions.

Macrophytes as bioindicators of the physicochemical characteristics of wetlands in lowland and mountain regions of the central Balkan Peninsula

The simultaneous monitoring of vegetation, water and sediments was conducted in wetlands of the central Balkan Peninsula due to the lack of available knowledge on the univariate response of macrophytes along environmental gradients. The environmental preferences and bioindicator potential of macrophytes were assessed using Huisman-Olff-Fresco (HOF) models. Bolboschoenus maritimus and Scirpus lacustris subsp. tabernaemontani are valuable bioindicators of slightly saline (electroconductivity of 2000–4000μScm−1 in the sediment) and alkaline habitats that are rich in SO42−. Their ecological niches are partially overlapped. Bolboschoenus maritimus prefers saltier and more alkaline habitats for optimal development. The salinity and alkalinity of habitats are decisive factors in the ecological diversification of the Boloboschoenus species. Bolboschoenus glaucus is adapted to non-saline (400–900μScm−1) and slightly alkaline habitats, unlike Bolboschoenus maritimus. Relatively deep, slightly acid waters which are poor in SO42− (0.30mg/l), and sediments with low values of electroconductivity and K2O (6.8mg/100g sediment) are preferred by Typha angustifolia, Sparganium erectum and Typha latifolia. The abundance of Phalaris arundinacea, Scirpus lacustris, Carex riparia and Eleocharis palustris increases when there is a decrease in the amount of nutrients (NH4+, PO43− and SO42−) in the water. Phragmites australis has low indicative value and regional bioindicator potential. The data obtained in the study may serve as a basis for adjusting the existing indicator values of these species and extending indicator systems by defining the indicator values of species with respect to environmental variables which have not yet been considered.

Acido‐ and neutrophilic temperate forest plants display distinct shifts in ecological pH niche across north‐western Europe

Ecological niches of organisms vary across geographical space, but niche shift patterns between regions and the underlying mechanisms remain largely unexplored. We studied shifts in the pH niche of 42 temperate forest plant species across a latitudinal gradient from northern France to boreo‐nemoral Sweden. We asked 1) whether species restrict their niches with increasing latitude as they reach their northern range margin (environmental constraints); 2) whether species expand their niches with increasing latitude as regional plant species richness decreases (competitive release); and 3) whether species shift their niche position toward more acidic sites with increasing latitude as the relative proportion of acidic soils increases (local adaptation). Based on 1458 vegetation plots and corresponding soil pH values, we modelled species response curves using Huisman–Olff–Fresco models. Four niche measures (width, position, left and right border) were compared among regions by randomization tests. We found that with increasing latitude, neutrophilic species tended to retreat from acidic sites, indicating that these species retreat to more favorable sites when approaching their range margin. Alternatively, these species might benefit from enhanced nitrogen deposition on formerly nutrient‐poor, acidic sites in southern regions or lag behind in post‐glacial recolonization of potential habitats in northern regions. Most acidophilic species extended their niche toward more base‐rich sites with increasing latitude, indicating competitive release from neutrophilic species. Alternatively, acidophilic species might benefit from optimal climatic conditions in the north where some have their core distribution area. Shifts in the niche position suggested that local adaptation is of minor importance. We conclude that shifts in the pH niche of temperate forest plants are the rule, but the directions of the niche shifts and possible explanations vary. Our study demonstrates that differentiating between acidophilic and neutrophilic species is crucial to identify general patterns and underlying mechanisms.

Soil pH limits of forest vascular plants determine range size and threat level

AbstractQuestionsKnowledge about the response curves of species along soil variable gradients is scarce. Because environmental change may force species to live closer to their ecological limits than optima, we examined and compared the importance of response limits, response optima and Ellenberg indicator values for soil pH to determine the regional range sizes and threat levels of species.LocationDeciduous forests in the lowlands and uplands of northern Germany.MethodsWe used Huisman–Olff–Fresco models to examine the species responses of forest vascular plants along a soil pH gradient with a particular focus on rare species. Separately for the two regions, the optima and limits across all species were related to range size, change in regional range size over the past decades and threat level.ResultsLower pH limits showed an aggregation around pH 4, and were consistent across regions, whereas upper pH limits were not clumped and not significantly correlated between regions. In the lowlands, species with relatively large lower pH limits were less widespread, had decreased more over time and were more threatened than species able to grow on very acid soils. Lower limits were more closely related to regional range size and rarity than optima and Ellenberg R values. These patterns were not found for upland species, probably due to a more complex interaction between pH and other soil factors.ConclusionThe results reinforce the importance of soil variables and their interactions for the occurrence of plant species, and suggest that limits may be better predictors of current and future species distributions than optima and Ellenberg indicator values. Still, crucial information is missing even for common species. Therefore, there is an urgent need for more and better species occurrence data relative to edaphic factors in order to identify the species' needs and their potential responses to environmental change.

Eaten but not always beaten: winners and losers along a red deer herbivory gradient in boreal forest

AbstractQuestionsHow does the understorey plant community in a boreal forest respond to variations in red deer herbivory intensity? Do the conclusions depend on the organizational level (taxon, growth form or functional trait) used for the analyses, and does red deer herbivory create more winners or losers?LocationSvanøy, western Norway.MethodsWe modelled the abundance of all understorey plant taxa, growth forms and functional trait categories along a red deer herbivory gradient in old growth pine–bilberry forest by means of Huisman‐Olff‐Fresco (HOF) modelling. The herbivory gradient spanned from zero (deer excluded for 10 yr), via natural variation in plots open to wild red deer, to a maximum in forested parts of a red deer farm.ResultsTwelve taxa had optima at zero to low herbivory intensity (losers), while 25 species had optima at intermediate to high herbivory intensity (winners), with most species peaking at intermediate intensity. The growth forms young trees and dwarf shrubs were losers, and ferns, forbs, bryophytes and juvenile trees were winners. At the functional trait level, woody species were the only losers, whereas clonal, prostrate and non‐palatable species were more abundant towards the high end of the herbivory gradient.ConclusionsWoody species were found to be herbivory losers irrespective of the level of analysis (taxa, growth form or trait category). In contrast, the identities of winners depended on level of analysis: more growth forms and functional trait categories than species peaked at the high end of the gradient. Species analysis gave high resolution and better ecological explanations, while analysis of growth forms and functional traits offered management‐relevant interpretations of herbivory‐driven shifts in the forest ecosystem.

Landscape-scale factors driving plant species composition in mountain streamside and spring riparian forests

Effective sustainable management of riparian forests requires an understanding of both the local physical setting and larger system at the landscape scale. Although site-specific influences on riparian forests are well studied, landscape-scale factors driving species composition are insufficiently recognized, especially regarding forests in spring-fed areas. In this study we ask three questions: (1) What are the main topographic factors driving the species composition in mountain riparian forests at the landscape scale? (2) What are the differences in environmental controls between riparian forests growing along river banks and in spring-fed areas? (3) Are species responses to environmental gradients in streamside and spring-fed environments consistent with plant traits or life history strategies? To address these questions, we used a dataset of vegetation plots sampled along 100 rivers in the Sudetes (southwestern Poland, Central Europe) and GIS-derived topographic variables, including the elevation, slope, topographic wetness index (TWI), stream power index (SPI), potential solar radiation and distance from river source. The significance of the variables was tested by the ordination technique (CCA). In addition, species responses (Huisman–Olff–Fresco models) were analysed for the species that fitted the ordination models best. The results showed that floristic variation in streamside forests is related to distance from the river source, altitude and SPI; while, floristic variation in spring forests is linked to altitude and solar radiation. Moreover, the frequency of particular response curve types varies between streamside and spring forests: the common presence of unimodal responses indicates that streamside forests are much more diverse in terms of community turnover than spring forests. The study highlights different landscape-scale environmental parameters that control the variation in species composition in streamside and spring forests. Streamside forests are the products of their catchments and considerably depend on the conditions that exist within the contributing area, while forests growing in spring-fed areas are mainly controlled by local conditions. We conclude, that effective management and conservation, especially approaches based on emulation of natural disturbances, should take these differences into consideration by developing site-specific management guidelines for both types of riparian forests.

Statistical modeling of Southern Ocean marine diatom proxy and winter sea ice data: Model comparison and developments

We compare the performance of the modern analog technique (MAT), the Imbrie and Kipp transfer function (IKTF), the generalized additive model (GAM) and weighted averaging partial least squares (WA PLS) on a southern hemisphere diatom relative abundance and winter sea ice concentration training data set. All relevant model assumptions are tested with a random 10-fold cross-validation, whilst a hold out cross-validation tested the explanatory power of each model on spatially independent validation data. We used auto correlograms on model residuals, variance partitioning, and principal coordinates analysis of neighbor matrices (PCNM) to investigate the importance of the spatial structure of our training database. A set of hierarchical logistic regression models (or Huisman–Olff–Fresco models) are used to infer the response of each diatom species along the winter sea ice gradient. Our analyses suggest that IKTF is an inappropriate sea ice estimation approach as its underlying statistical assumptions do not hold and the fit of IKTF to our data under cross-validation was poor. We conclude that MAT may be biased by spatial autocorrelation, and together with IKTF fails to provide unbiased estimates of winter sea ice. We find GAM and WA PLS are more appropriate than IKTF and MAT for the estimation of paleo winter sea ice cover throughout the Southern Ocean. However, as WA PLS is based on a unimodal species response, which is rarely exhibited by diatoms along the winter sea ice gradient, we ultimately advocate the application of GAM. GAM only uses diatoms with a statistically significant association, and ecologically based link, with sea ice. GAM outperformed all other models under cross-validation in terms of performance statistics, the fit of GAM to the training dataset and diagnostic tests for model assumptions. We also demonstrate that GAM provides a more detailed and potentially more accurate (based on a comparison with New Zealand and southeast Australian paleo climatic records) paleo winter sea ice record for the southwestern Pacific Ocean in comparison with IKTF, MAT and WA PLS.

Early dynamics of natural revegetation on roadcuts of the Salamanca province (CW Spain)

In order to reconcile conventional and emergent goals in restoration ecology, the knowledge of community assembly during succession at roadsides is crucial. With a chronosequence design, our study assesses the pathway and speed of vegetation succession on roadcuts under different specific site conditions, relating environmental factors to species cover by means of a combination of multivariate analyses and Huisman–Olff–Fresco (HOF) modeling. We want to ascertain to what extent environmental factors control primary colonization, establishment and early dynamics of vegetation on dry Mediterranean roadcuts. We found that changes in floristic composition during natural succession on roadcuts are mostly determined by the species-pool effect at different scales (landscape, regional, and local); particular site conditions of roadcuts (slope length, steepness) are also influential factors at a local scale. We also found a shift in the dispersal mode of plant species, from anemochory to zoochory, during succession on tertiary sediments and slates, and a tendency for life-form replacement, from pterophytes to hemicriptophytes, during succession on tertiary sediments. Competitive species are primarily circumscribed to tertiary sediments where succession is not so limited by environmental carrying capacity. Natural colonization is less active on granites, and hence succession is slower. Our results indicate that, in a relatively short time, vegetation communities spontaneously installed under roadcut’s environmental harshness are rich in species whether an adjacent seed source is present in remnant patches of natural vegetation. In particular, surrounding woody vegetation favors zoochory dispersion and the early arrival of late-successional species.