Altered Species Composition Research Articles

Does large dam removal restore downstream riparian vegetation diversity? Testing predictions on the Elwha River, Washington, USA.

Large dams and their removal can profoundly affect riparian ecosystems by altering flow and sediment regimes, hydrochory, and landform dynamics, yet few studies have documented these effects on downstream plant communities. Ecological theory and empirical results suggest that by altering disturbance regimes, reducing hydrochory, and shifting communities to later successional stages, dams reduce downstream plant diversity. Dam removal could reverse these processes, but the release of large volumes of sediment could have unexpected, transient effects. Two large dams were removed on the Elwha River in Washington State, USA, from 2011 to 2014, representing an unprecedented opportunity to study large dam removal effects on riparian plant communities. Our research objectives were to determine: (1) whether the Elwha River dams were associated with lower downstream plant diversity and altered species composition across riparian landforms pre-dam removal, and (2) whether dam removal has begun to restore downstream diversity and composition. To address these objectives, we compared plant species richness and community composition in river segments above, below, and between the two dams. Plant communities were sampled twice before (2005 and 2010) and four times after (2013, 2014, 2016, and 2017) the start of dam removal, with 2013 and 2014 sampled while the upstream dam removal was ongoing. Prior to dam removal, native species richness was 41% lower below dams compared with the upstream segment; 6 years after dam removal began, it increased ~31% between the dams, whereas nonnative species richness and cover were not apparently affected by dams or their removal. Deposition caused by large volumes of released reservoir sediment had mixed effects on native species richness (increased on floodplains, decreased elsewhere) in the lowest river segment. Plant community composition was also different downstream from dams compared with the upstream reference, and has changed in downstream floodplains and bars since dam removal. In the long term, we expect that diversity will continue to increase in downstream river segments. Our results provide evidence that (1) large dams reduce downstream native plant diversity, (2) dam removal may restore it, and (3) given the natural dynamics of riparian vegetation, long-term, multiyear before-and-after monitoring is essential for understanding dam removal effects.

Fire Compromises the Recovery of a Managed Forest in Tapajós National Forest, Eastern Amazon, Brazil

Logged forests are more prone to fire, shifts in species composition, and losses in biodiversity. In this work changes in the horizontal structure and species composition of a managed forest in the Tapajós National Forest, Eastern Amazon, Brazil, along 31 years (1981-2012) was evaluated. The disturbances included logging (1982), thinning of non-commercial species (1993/1994), and fire (1997). Data were obtained in 36 0.25-ha permanent plots split in 12 plots per each one of three harvesting treatments. In 1997, 16 plots were reached by an accidental superficial fire. The changes in species composition and diversity between the last measurement after logging and before fire (1995) and the last measurement (2012) were compared. PERMANOVA, considering the relationship between the NMDS axes and the treatment variable (logging / control + unburnt / burnt) differed in species composition, among treatments before fire (1995) and 15 years after fire (2012). The post-hoc test for PERMANOVA showed great similarity among logged forests before and after fire. The forest pre-disturbance conditions were important drivers in forest recovery, since logged forests under heavy thinning presented more losses in basal area and alterations in species composition. Therefore, stronger and more frequent disturbances can compromise the forest resilience.

Fire Compromises the Recovery of a Managed Forest in Tapajós National Forest, Eastern Amazon, Brazil

Logged forests are more prone to fire, shifts in species composition, and losses in biodiversity. In this work changes in the horizontal structure and species composition of a managed forest in the Tapajós National Forest, Eastern Amazon, Brazil, along 31 years (1981-2012) was evaluated. The disturbances included logging (1982), thinning of non-commercial species (1993/1994), and fire (1997). Data were obtained in 36 0.25-ha permanent plots split in 12 plots per each one of three harvesting treatments. In 1997, 16 plots were reached by an accidental superficial fire. The changes in species composition and diversity between the last measurement after logging and before fire (1995) and the last measurement (2012) were compared. PERMANOVA, considering the relationship between the NMDS axes and the treatment variable (logging / control + unburnt / burnt) differed in species composition, among treatments before fire (1995) and 15 years after fire (2012). The post-hoc test for PERMANOVA showed great similarity among logged forests before and after fire. The forest pre-disturbance conditions were important drivers in forest recovery, since logged forests under heavy thinning presented more losses in basal area and alterations in species composition. Therefore, stronger and more frequent disturbances can compromise the forest resilience.

Predicting the responses of boreal forests to climate-fire-vegetation interactions in Northeast China

Climate change could alter species composition, with feedback on fire disturbances by modifying fuel types and loads. However, the existing fire predictions were mainly based on climate-fire linkages that might overestimate the probability and size of fire disturbances due to simplifying or omitting vegetation feedback. We applied a model-coupling framework that combines forest succession, climate-fire linkages, and vegetation feedback to predict burned area, aboveground biomass, and species composition of boreal forests in Northeast China under climate change conditions. Results showed that climate change and fire would favor the recruitment of deciduous species, but these species need a long-time to replace the existing coniferous species. Burned area would increase with climate change. Climate change, historical and future fire disturbances affect aboveground biomass by altering tree mortality and regeneration. Further studies should address strategies for altering species composition through forest management practices to adaptation climate change and reduce carbon losses from fire.

Identification and Stratification of Cultured Microorganisms from Wind Cave

Wind Cave National Park in the Black Hills of South Dakota contains many fungal, bacterial, and archaeal organisms. These biotic communities tend to be low in diversity and sensitive to changes in external inputs of organic matter from seasonal snow melts and tourist traffic. Tourist traffic in particular can affect the natural state of the cave environment and alter species composition and population densities of the resident biota. The goal of this project was the molecular identification of the various fungal and bacterial samples between remote and public sites of Wind Cave to better understand the impact of tourist traffic on cave biota. DNA obtained from cultured samples was used to perform PCR‐based sequencing analysis using primers targeting either a specific region of the 16S small ribosomal subunit for identifying bacteria or an internal transcribed spacer (ITS) for identifying fungal lineages. Phylogenetic trees were created of both the fungal and bacterial genra stratified by cave location.

Functional Traits, Species Diversity and Species Composition of a Neotropical Palm Community Vary in Relation to Forest Age

Understanding the factors that shape the diversity and composition of biotic communities in natural and human-modified landscapes remains a key issue in ecology. Here, we evaluate how functional traits, species diversity and community composition of palm species vary in relation to biogeographic variables and forest age in northwest Ecuador. Functional traits capture essential aspects of species’ ecological tradeoffs and roles within an ecosystem, making them useful in determining the ecological consequences of environmental change, but they have not been used as commonly as more traditional metrics of species diversity and community composition. We inventoried palm communities in 965 10 × 10 m plots arrayed in linear transects placed in forests of varying age. Adult palms in forests of younger regeneration stages were characterized by species with greater maximum stem height, greater maximum stem diameter, and solitary stems. The shift in functional features could indicate that shade tolerant palms are more common in old-growth forest. The shift could also reflect the legacy of leaving canopy palms as remnants in areas that were cleared and then allowed to regrow. Moreover, younger forest age was associated with decreased abundance and altered species composition in both juvenile and adult palms, and decreased species richness in adults. These results highlight the importance of retaining intact, old-growth forest to preserve functional and species diversity and highlight the importance of considering multiple aspects of diversity in studies of vegetation communities.

Growth enhancements of elevated atmospheric [CO2] are reduced under drought‐like conditions in temperate eucalypts

Abstract Elevated atmospheric [CO2] (‘eCO2’) may alter species composition within vegetation types by favouring the growth of some species over others. However, other related changes in climate conditions, such as increased frequency and severity of drought, may reduce eCO2 fertilisation effects on plant growth. For many species, it is not known if responses will reflect variability in trait adaptations due to environment. We grew seedlings of nine species of eucalypts indicative of three regional vegetation types (representing a mesic–xeric ecosystem gradient) under two CO2 concentrations (400 parts per million; 640 ppm, i.e. eCO2) and two watering regimes (well‐watered; drought‐like conditions). Elevated CO2 increased biomass accumulation but drought reduced this effect, with mesic species experiencing larger relative reductions. Elevated CO2 increased the size of storage organs used during resprouting, in the absence of drought. Typical drought responses, such as increased leaf mass per unit area and root mass ratio, were more pronounced in xeric species and were reduced under eCO2. Seedling growth and resprouting may be enhanced by eCO2, suggesting continued dominance of resprouting species in disturbance‐prone ecosystems, although severe drought is likely to offset eCO2 fertilisation. Xeric species may cope with drought more effectively under eCO2 than mesic species due to resource acquisition and storage traits that are more responsive. Read the free Plain Language Summary for this article on the Journal blog.

Stasis in forest regeneration following deer exclusion and understory gap creation: A 10-year experiment.

Chronically elevated ungulate browse pressure in temperate forests worldwide often generates ecological legacies characterized by low plant diversity and contributes to the formation of dense, nearly monodominant, and highly recalcitrant layers of understory vegetation. Once established, these recalcitrant layers combined with continued browsing may jointly constrain tree establishment and diversity so completely that understory recovery may be unattainable without mitigating browse pressure, the recalcitrant layer, or both. Here, we investigate the independent and synergistic effects of both white-tailed deer (Odocoileus virginianus) browsing and hay-scented fern (Dennstaedtia punctilobula) competition on tree regeneration in a 10-year experiment. Specifically, we examine how tree seedling establishment, growth, and composition are filtered by fern cover versus fern removal (gaps), browser presence versus absence (exclosures), and their combined effects during 10 years at three hardwood forest sites in Pennsylvania, USA. Fern gaps enhanced establishment for multiple tree species, increasing seedling density and diversity, particularly in the first 3 years post-treatment, and enhancing richness (≤1 species) over the course of the experiment. Excluding deer for a decade increased the height growth of other regeneration and altered species composition, but had no effect on diversity, richness, and density. Notably, we observed higher Prunus serotina seedling densities outside exclosures, possibly due to greater secondary dispersal. We argue that browsing legacies in second growth forests established at the turn of the last century created two conditions inimical to diverse forest regeneration: an overstory dominated by two species, P. serotina and Acer rubrum (86% of basal area), and a dense recalcitrant understory layer dominated by a native fern. The first condition limits propagule supply, the second strongly filters seedling establishment, and both create impoverished forest understories composed of few individuals and species. In undisturbed forest understories, the inertia toward impoverishment was sustained across the decade even where browsing was eliminated. Consequently, stand replacing disturbances (whether natural or anthropogenic) that disrupt the understory layer and reinitiate succession may be necessary to propel forests out of their current stasis and down a pathway leading to greater diversity.

Pathogenic fungus causes density‐ and trait‐mediated trophic cascades in an aquatic community

AbstractPathogens can alter species composition and ecosystem function by causing direct and indirect effects on communities. Zoospores of the chytrid fungus Batrachochytrium dendrobatidis (hereafter, Bd), a pathogen implicated in worldwide amphibian declines, can be consumed by filter‐feeding zooplankton and can damage mouthparts of infected amphibian larvae. Consequently, we hypothesized that this pathogen would affect the abundance of zooplankton and survival and feeding abilities of larval amphibian hosts. In turn, this could affect the algal food resources of zooplankton and tadpoles, which can include phytoplankton and periphyton. We tested these hypotheses by manipulating the presence of western toad (Anaxyrus boreas) larvae and Bd in outdoor mesocosms and quantifying the densities of amphibians, zooplankton, phytoplankton, and periphyton. Bd infections reduced amphibian larval densities, but this only weakly benefitted periphyton (a density‐mediated indirect effect). After controlling for larval densities, mesocosms with Bd‐exposed larvae had significantly more periphyton biomass than mesocosms with larvae but no Bd, consistent with infection‐induced mouthpart damage reducing larval feeding rates on attached algae (a trait‐mediated indirect effect). In fact, the estimated trait‐mediated effect of Bd on periphyton biomass was larger than the density‐mediated effect. However, we did not find evidence that Bd exposure triggered a switch to filter‐feeding phytoplankton. The presence of Bd was associated with increased copepod abundance, consistent with zooplankton consuming chytrid zoospores. These results suggest that Bd has the potential to cause both trait‐ and density‐mediated indirect effects that can alter community composition and perhaps the primary productivity of freshwater ecosystems.

Pathways of savannization in a mesic African savanna–forest mosaic following an extreme fire

Abstract Fires in savannas limit tree cover, thereby promoting flammable grass accumulation and fuelling further frequent fires. Meanwhile, forests and thickets form dense canopies that reduce C4 grass fuel loads and creating a humid microclimate, thereby excluding fires under typical climatic conditions. However, extreme fires occasionally burn into these closed‐canopy systems. Although these rare fires cause substantial tree mortality and can make repeat fires more likely, the long‐term consequences of an extreme fire for closed‐canopy vegetation structure and potential to convert to savanna (hereafter ‘savannization’) remain largely unknown. Here, we analysed whether an extreme fire could, alone, alter species composition, vegetation structure and fire regimes of closed‐canopy ecosystems in an intact savanna–forest–thicket mosaic, or whether successive fires after an initial extreme fire were necessary to trigger a biome transition from forest to savanna. We found that forests that only burned once recovered, whereas those that burned again following an initial extreme fire transitioned from closed‐canopy forests towards open, grassy savannas. While thickets had less tree mortality in fires than forests, repeat fires nonetheless precipitated a transition towards savannas. Colonization of the savanna tree community lagged behind the grass community, but also began to transition. Synthesis. Our results suggest that rare extreme fires, followed by repeated burning can indeed result in savannization in places where savanna and forest represent alternative stable states.

Early vegetation recovery of a burned Mediterranean forest in relation to post-fire management strategies

Abstract The risk of wildfires in the Mediterranean region is expected to increase with climate change. Fire is one of the main drivers of plant diversity and composition, triggering succession processes that vary according to the fire regime and species’ regeneration traits. Human management can modulate these processes to promote the recovery of the burned soil-vegetation system, through the application of practices such as salvage logging. Effects of these managements have been studied mostly for coniferous forests, with contrasting results, while little is known about the responses of evergreen broadleaved woodlands. Here, we analysed the 34-month recovery processes of a Quercus ilex forest and an adjacent Pinus pinaster stand in central Italy with respect to their diversity, composition and plant fire-related traits, in relation to three different management strategies applied after fire. These were: (1) no intervention (NT), (2) salvage logging and mulching (SM and SMP for the pine stand), (3) salvage logging, mulching and erosion control measures (e.g. fascines for hill slope stabilization; EC). Overall, the increase of post-fire vegetation cover was negatively affected by SM and EC treatments, while their effects on ɣ- and α-diversity were positive. Species diversity was significantly lower in pine than in broadleaved plots and compositional differences associated with forest type were significant. Abundance of woody species was higher in the unsalvaged sites, except for a few species (e.g. Q. ilex), while herbaceous plants were not affected. Species composition in managed plots was different from control plots after 10 and 22 months, while differences decreased after 34 months. Effects of management strategies on the frequency of resprouters as well as on the proportion of species with persistent vs transient soil seed bank were minor; these traits were mainly driven by forest type. Our findings suggest that non-treatment is the best post-fire management strategy for a fast recovery of woody species in typical Mediterranean broadleaved forests. However, the EC strategy promoted a high diversity level, while not apparently altering species composition compared with the natural post-fire succession process.

Spatial variation in human disturbances and their effects on forest structure and biodiversity across an Afromontane forest

ContextHuman disturbances can have large impacts on forest structure and biodiversity, and thereby result in forest degradation, a property difficult to detect by remote sensing.ObjectivesTo investigate spatial variation in anthropogenic disturbances and their effects on forest structure and biodiversity.MethodsIn 144 plots of 20 × 20 m distributed across a forest area of 750 km2 in Southwest Ethiopia, we recorded: landscape variables (e.g., distance to forest edge), different human disturbances, forest structure variables, and species composition of trees and epiphyllous bryophytes. We then first assessed if landscape variables could explain the spatial distribution of disturbances. Second, we analysed how forest structure and biodiversity were influenced by disturbances.ResultsHuman disturbances, such as coffee management and grazing declined with distance to forest edges, and penetrated at least a kilometer into the forest. Slope was not related to disturbance levels, but several types of disturbances were less common at higher elevations. Among human disturbance types, coffee management reduced liana cover and was associated with altered species composition of trees. The presence of large trees and basal area were not related to any of the disturbance gradients.ConclusionsAlthough most anthropogenic disturbances displayed clear edge effects, surprisingly the variation in the chosen forest degradation indices were only weakly related to these disturbances. We suggest that the intersection between edge effects and forest degradation is very context specific and relies much on how particular societies use the forests. For example, in this landscape coffee management seems to be a key driver.

Effect of woody plant removal in herb-subshrub communities in preserved and disturbed Brazilian Chaco areas

The impacts caused on Chaco plant communities by the removal of woody species, together with the effects on the composition and functional structure of herbaceous plants, are still unknown. Therefore, this study aimed to assess the effects of anthropization on herb-subshrub communities in preserved and disturbed Chaco areas. Specifically, we examined differences and similarities in species diversity, composition and proportion of life forms in eight areas of Brazilian Chaco. Samples were taken from herb-subshrub communities using 800 1x1m² plots located in disturbed and preserved areas. Among 130 recorded species, 46 were exclusive to disturbed areas. The composition of species differed between preserved and disturbed areas (PERMANOVA; p = 0.001). PCoA ordination analysis showed greater aggregation of the plots in disturbed areas than in preserved areas. In preserved areas, an analysis of indicator species showed Hemicryptophytes species as the most representative life form. In disturbed areas, the proportion of life forms among indicator species was Hemicryptophytes, followed by Therophytes and Chamaephytes. Our study shows evidence that alterations in species composition, structure, and diversity, as well as sets of indicator species, occur in herb-subshrub communities. The removal of trees and bushes leads to a new configuration of this component in Chaco environments.

Future climate and land-use intensification modify arthropod community structure

Climate change and land-use intensification pose increasing threats to biodiversity, with climate change expected to eventually surpass other global environmental change drivers and become the greatest threat to biodiversity in the future. Understanding the combined ecological impacts of multiple global change drivers is crucial to predict future scenarios of biodiversity change. However, experimental evidence for the impacts of land-use intensification under current and future climate scenarios is lacking, even though this is imperative for understanding future trajectories of biodiversity in agricultural landscapes. We experimentally tested for the simultaneous effects of land-use intensification and climate change on arthropod biodiversity in a field-scale grassland experiment known as the Global Change Experimental Facility (GCEF). Specifically, we tested whether future scenarios of climate change are likely to exacerbate impacts of land-use intensification on arthropod diversity and abundance across different trophic levels by sampling aboveground arthropod communities in low and high land-use intensity grasslands under current and future climatic conditions. We found that climate change reduced total abundances of arthropods and increased evenness of the whole community, while only having trophic level-specific effects on detritivore abundance and evenness. Land-use intensification reduced abundance of the whole community, predators and detritivores, but only eroded species richness of the whole community and herbivores, with the magnitude of declines in predator and detritivore abundance depending on the climate scenario. Additionally, both land-use intensification and climate altered species composition of the whole community and within the predator, herbivore, and detritivore trophic levels. We show that climate change and land use intensification cause simultaneous shifts in arthropod abundance, species richness, and species composition across trophic levels. Changes in arthropod communities as a result of climate change and land-use intensification will likely have profound consequences for ecosystem functioning under future environmental conditions.

Litter Flammability of 50 Southeastern North American Tree Species: Evidence for Mesophication Gradients Across Multiple Ecosystems

Widespread fire exclusion and land-use activities across many southeastern United States forested ecosystems have resulted in altered species composition and structure. These changes in composition and structure have been implicated in positive fire-vegetation feedbacks termed “mesophication” where fire spread and intensity are diminished. In forests and woodlands, inherent flammability of different species is the mechanistic driver of mesophication. To date, there has been limited work on documenting the high diversity of flammability among species in the region, limiting the ability to differentiate among species to restore fuels that sustain fire regimes. Here, we coalesce disparate flammability data and add missing species across the spectrum from species that facilitate fire (so called “pyrophytes”) to those that dampen fire (so called “mesophytes”). We present data on 50 important tree species from across the southeast, all burned using identical laboratory methods. We divide our results for four dominant ecosystems: Coastal Plain uplands, oak-hickory woodlands, Appalachian forests, and bottomland forests. Across ecosystems, the most flammable species were American chestnut (Castanea dentata), a suite of pines (Pinus palustris, P. elliottii, P. serotina, and P. rigida), several oaks (Q. laevis, Q. falcata, Q. margaretta, and Q. alba), and sourwood (Oxydendrum arboreum). At the mesophytic end, the least flammable species were Tsuga canadensis, Acer rubrum, and several other hardwoods previously implicated in mesophication. Each of the four ecosystems we studied contained species that spanned the pyrophytic to mesophytic gradient. These data fill in some key holes in our understanding of southeastern fire adaptations, but also provide context for restoration decisions and fire management prioritization efforts to restore and sustain fire-prone ecosystems of the region.

β diversity among ant communities on fragmented habitat islands: the roles of species trait, phylogeny and abundance

Habitat loss and fragmentation reduce biodiversity and alter species composition in local communities. β diversity describes the variation in species composition between or among communities in fragmented landscapes and has two components: species turnover and nestedness. In this study, we assessed β diversity of ant assemblages on 24 island fragments in the Thousand Island Lake, China. We constructed a species‐level phylogenetic tree and measured five morphological traits of all ant species captured. We then assessed taxonomic (both incidence‐based and abundance‐weighted), functional and phylogenetic β diversity and partitioned β diversity into turnover and nestedness (as well as the contributions of particular species and particular islands). Finally, we examined the relationships between β diversity and a suite of geographical variables (i.e. difference in island area, difference in isolation and inter‐island distance) using Mantel tests. We found taxonomic and phylogenetic turnover components dominated overall β diversity whereas the functional turnover and nestedness components contributed equally to overall β diversity. Overall β diversity increased with increasing difference in isolation and inter‐island distance; however, only abundance‐weighted overall β diversity decreased with increasing difference in island size. Our results indicate that species that were abundant on large islands were also abundant on small islands. We conclude that the dispersal limitation of ants likely shapes the pattern of β diversity along isolation and inter‐island distance gradients. Additionally, functional redundancy of species (i.e. different species share similar functional roles) could also explain β diversity patterns among fragmented habitat islands. Our results highlight the necessity of incorporating both incidence‐based and abundance‐weighted community data when examining β diversity in fragmented landscapes. By partitioning β diversity into the contributions of particular species and particular fragments, our study implies that small patches can be valuable for maintaining biodiversity among ant communities.

Long-term vegetation monitoring in the floodplain grasslands of the lower Havel Valley (northeastern Germany) and conclusions for sustainable management practices

As a result of water regulation measures and the subsequent introduction of intensive use practices, riverine floodplains have suffered severe habitat and species losses. With the changed economic conditions and decrease in animal stocking rates after 1990, opportunities arose for the partial restoration of species-rich vegetation areas in East Germany. Sixty permanent plots were established in the lower Havel Valley in the federal state of Brandenburg from 1993 to 1999. We studied the effects of extensification and partial rewetting in this area during a monitoring programme that lasted until 2018. For this purpose, groundwater levels, historical land use, and soil chemical parameters were investigated, and the soil seed bank and phytosociological relevés were sampled. Previous research has shown that an extended period of intensive grassland use eliminates the possibility of success in short- to medium-term natural restoration because of the lack of suitable propagules. Our question was as follows: how does a floodplain grassland respond to extensification and decreased water regulation in an area that experienced a shorter period of intensification in the past, such as the lower Havel floodplain? Tests of soil samples showed a depleted soil seed bank at the beginning of the monitoring period, but the seed bank was less depleted than those in other areas. Using cluster analysis followed by discriminant analysis, we identified water regime parameters and historical land-use intensity as the main drivers of vegetation differentiation. The classification resulted in the differentiation of vegetation into 13 plant communities. Plant communities were combined into 5 main groups based on their location in the ordination diagram of a detrended correspondence analysis. The shift in group centroids over time correlated with increases in the species diversity and moisture level for all groups. The altered species composition as a result of the changed water regime after 1990 influenced the usability of the grassland differently depending on the relief level. At the end of monitoring, vegetation at sites in the mesic moisture range was determined to have the highest fodder quality observed in this study. With increasing mean groundwater levels, the forage quality of the vegetation decreased until it was so low that the vegetation was hardly suitable for use as animal forage. The plant species diversity was negatively correlated with the plant-available P and Ellenberg N indicator value. Plant-available P, K and Mg showed evidence of leaching during the later study period. The abundance of red-listed species and extensive-use indicator species increased over the course of the study period. This positive trend was reversed by the extreme flood event in the summer of 2013. However, the high species richness and the species compositions of the reference communities were not equal in the other communities, even after almost 30 years of extensification. This finding underlines the importance of the few remaining meadows that are rich in typical floodplain species as donor areas of autochthonous seeds. The results of this study are discussed in light of sustainable management practices and global climate change.

Planting, seeding, and sediment impact restoration success following dam removal

Large dam removals effectively restore geomorphic and hydrologic processes, but little is known about subsequent vegetation recovery and the role of active restoration. We studied whether planting and seeding affected vegetation recovery in a dewatered reservoir, and whether effects differed on landforms composed of fine or coarse‐textured sediments. The dewatered reservoir is behind the former Glines Canyon Dam, which was removed from the Elwha River in Washington State (U.S.A.) in 2011–2014. We measured bare ground in 2013–2017, and species richness, relative frequency of non‐native species, woody stem density, and species composition in 2016. Sediment texture affected all response variables. Several years after seeding, bare ground was reduced on coarse sediments and non‐native species frequency was reduced on both textures. Planting increased species richness. Seeding and planting altered species composition on both textures, with stronger effects on coarse sediments. High densities of riparian woody plants naturally established on fine sediments, reaching a mean of 34,000 stems/ha 5 years after dam removal began; density was only a fraction of this (5,000 stems/ha) on coarse sediments. Future dam removals should incorporate sediment texture into their revegetation plans. Seeding and planting can be valuable strategies for minimizing non‐native species frequency, increasing species richness, and establishing desirable target species after dam removal, particularly on landforms composed of coarse sediments.

Comparison of biofouling on 3D-printing materials in the marine environment

3D printing has an increasing variety of applications in the marine environment for customized or replaceable components of instrumentation and infrastructure. Because marine biofouling can interfere with the performance of such applications and plays an important role in species dispersal, there is a need to understand biofouling dynamics on the materials used. This study compared biofouling on common 3D-printing polymers printed by common methods - polycaprolactone (PCL) printed by fused deposition modelling, VisiJet® SL Clear printed by stereolithography, and VeroClear™ printed by PolyJet, as well as the comparison materials polydimethylsiloxane (PDMS, used in many experimental biofouling studies) and glass - and related fouling to material properties. Bacterial assemblages in 2- and 4-week old biofilms were similar on all materials, dominated by cyanobacteria and proteobacteria. The extent of macrofouling after 12 weeks differed significantly among materials, with the greatest coverage on glass (98.4%) and the least on PCL (86.8%). Macrofouler assemblages differed significantly, with 3D-printing polymers generally having less microalgae and more encrusting bryozoans than PDMS and glass. PCL was the most extreme of the 3D-printing materials in having the least microalgae and most bryozoans (arborescent and encrusting combined). Macrofouling coverage was not significantly related to material hydrophobicity, elastic modulus, hardness, or roughness. In contrast, macrofouler assemblage structure had a statistically significant relationship to hardness and a marginally significant relationship to hydrophobicity (explaining 19.0% and 8.6% of the variation in the assemblages, respectively). The reduced biofouling coverage and altered species composition on PCL may be advantageous for using PCL in marine applications of 3D printing, although other factors should be considered such as material degradation over time.

Effects of land‐use change on avian taxonomic, functional and phylogenetic diversity in a tropical montane rainforest

AbstractAimAlthough land use change is a leading cause of biodiversity loss worldwide, there is scant information on the extent to which it has affected the structure and composition of bird communities in the Afrotropical region. This study aimed to quantify the effects of habitat transformation on taxonomic, functional and phylogenetic diversity in Afrotropical bird communities.LocationNyungwe landscape, a montane rainforest with adjoining farmland in south‐west Rwanda.MethodsData on bird occurrence, abundance and functional traits were collected in 2017/18 using point counts. We also collected data on habitat and morphological traits for all bird species recorded. We quantified bird diversity using a range of metrics, including the inverse Simpson index, functional dispersion and the standardized effect size of mean nearest taxon distance.ResultsIn comparison with primary forest areas, even low levels of land use change altered species composition and reduced species diversity. Although overall functional diversity and phylogenetic diversity were similar across land use types, we found a significant contraction of trophic and locomotory trait structures of bird communities in restored areas and cultivated areas, respectively. Soil moisture, elevation and lower vegetation height were major factors influencing taxonomic, functional and phylogenetic dimensions of bird communities, although their effects varied across these dimensions.Main conclusionsThe sensitivity of forest species to minor habitat disturbance emphasizes the value of conserving primary vegetation. Long‐term conservation of bird communities in Afromontane ecosystems requires halting wide‐scale destruction of primary forest, promoting vegetation heterogeneity in the ecological restoration of degraded habitats and adopting wildlife‐friendly agricultural practices. Our results suggest that monitoring and conservation in these landscapes can be refined using taxonomic, functional and phylogenetic diversity metrics to provide complementary information about the current and likely future impacts of land use change.