Changes In Functional Composition Research Articles

Functional Composition Changes of a Subtropical Monsoon Evergreen Broad-Leaved Forest Under Environmental Change

Long-term studies have revealed that forest species composition was shifting under environment change and disturbance induced by loss of large trees. Yet, few studies explicitly analyzed their impacts on composition concurrently. To learn more about impacts of environment change and disturbance on driving forest community, we investigated shifts in functional composition over past 24 years in an old-growth subtropical forest in southern China. We analyzed nine traits that are mainly related to leaf nutrients, photosynthetic capacity, hydraulic conductivity, and drought tolerance of plants and examined hypotheses: (1) The functional composition change over time was directional instead of random fluctuation, (2) drought-tolerant species increased their abundance under soil dryness, (3) both environmental change and disturbance related to changes of functional composition significantly, and (4) initial trait values of quadrats strongly influenced their subsequent change rates in quadrat level (10 × 10 m). We found that species composition had shifted to favor species with high leaf nutrient content, high photosynthesis rate, high hydraulic conductivity, low water-use efficiency, and high drought tolerance traits, which was due to soil dryness and disturbance. These two factors explained 47–58% of quadrats’ trait value changes together. Considering rapidly increasing stem density, this pattern may indicate ecological processes of which disturbance provided numerous recruits of resource-acquisition strategy species and soil dryness conducted a selecting effect on shaping composition in the forest. Additionally, quadrats with initial trait values at the far end of change direction shifted faster in three traits, which also indicated that functional composition changes in quadrats were directional and homogenized. Our results implied that environment change and accompanied disturbance events possibly drove species composition change along a different trajectory in the subtropical forest that experienced high climatic variability.

Environmental effects on community productivity of aquatic macrophytes are mediated by species and functional composition

AbstractEnvironmental variations are rapidly altering plant species and functional composition, which may have consequent influences on ecosystem functioning. We measured species and functional diversity of macrophyte community as well as environmental variables in 1,008 plots in 24 freshwater lakes across Yunnan–Guizhou plateau and Yangtze River in south China. We used generalized multilevel path models to test how the environmental effects on macrophytes productivity directly and indirectly through changes in species and functional diversity. We found distinct species and functional responses to the four groups of environmental variables:water quality, heterogeneity, climate, and topography. Macrophyte communities tended to be high richness and dominated by species with high‐stem dry mass content and long flowering duration at eutrophic, heterogeneous, high altitude, or deepwater habitats. Submersed and annual species with high‐specific leaf area dominated in heterogeneous and high altitude conditions, whereas species with high shoot and leaf dry mass content as well as thin stem and lamina dominated in heterogeneous and low‐altitude conditions. Functional dispersion (FDis) decreased in heterogeneous and high‐altitude habitats and increased at deepwater. These changes in functional composition have subsequently significant influences on community productivity, involving the opposite pathways of positive effects of community‐weighted mean (CWM) traits and negative effects of FDis, ultimately contributing to the observed invariable macrophytes productivity along the tested environmental gradients. Our results provide strong evidences that both species and functional composition mediate the cascading effects of environments on macrophytes productivity.

Community assembly on extensive green roofs: Effects of dispersal‐, abiotic‐ and biotic filtering on the spontaneous species‐ and functional diversity

AbstractQuestionsExtensive green roofs (EGRs) are novel ecosystems and essential tools in mitigating the negative effects of urbanization. However, the extent to which traditional community assembly insights apply to spontaneous plant and trait diversity and composition on EGRs and novel ecosystems in general is unclear: (a) is a dispersal filter present because of EGRs’ fragmented nature (e.g., roof height, urban environment); (b) can we confirm the strong abiotic filtering due to extreme EGR conditions (e.g., limited substrate depth); and (c) does the presence of the planted vegetation lead to biotic filtering?LocationThe Flanders and Brussels region of Belgium.MethodsThe vegetation of 129 EGRs was sampled during a field campaign. Information on local (e.g., substrate, roof height) and regional characteristics (e.g., connectivity indices) were collected and species traits were collected from multiple databases. All data were used to construct (generalized) linear mixed models that tested the effects of the dispersal‐, local abiotic‐ and local biotic filters on plant community formation. Redundancy analysis was used to investigate predictor effects on functional composition and null models were constructed to assess trait divergence/convergence.ResultsOur results show that the spontaneous plant species diversity is not affected by their landscape context (dispersal filtering), while their functional composition is. Additionally, the importance of abiotic filtering is confirmed, as substrate depth and exposure have a strong impact on species diversity and decreasing substrate depth negatively impacts functional diversity. Finally, we show that biotic filtering by increased planted species cover leads to trait divergence, changes in functional composition and reduced cover of spontaneous species.ConclusionsWe find that a broad perspective that includes the regional and local biotic and abiotic environment is needed to assess all factors that influence the vegetation on EGRs. As biotic interactions are present, EGRs should not be considered as static systems.

Short‐term responses in a secondary tropical forest after a severe windstorm event

AbstractQuestionsHow do abiotic conditions, forest structure, as well as taxonomic and functional diversities and composition recover after wind‐generated treefalls? Do young and old‐growth secondary forests differ in their responses?LocationMandai region of the Central Catchment Nature Reserve, Singapore, where extensive treefalls occurred during an unusually powerful windstorm in 2011. Southeast Asia.MethodsSoil nitrogen, phosphorous, potassium, canopy cover, leaf litter depth, coarse woody debris, and woody stems ≥1‐cm diameter were measured and identified in 10 × 10 m plots. Twenty‐six plots were located in treefall areas and 14 plots were located in relatively unaffected areas, with equal numbers in young and old‐growth secondary forest types. The first round of surveys took place within 3–6 months of the windstorm event and yearly re‐surveys were conducted until 2015. Specific leaf area, leaf dry matter content, leaf thickness, woody density, maximum plant height, and seed dry mass were measured or derived from various sources.ResultsThere was a pulse of soil nutrient availability in both affected and unaffected areas 1 year after the wind event. Canopy cover and basal area in the affected areas recovered to similar levels as unaffected areas by the second year, and coarse woody debris by the fourth year. In affected plots, taxonomic and functional diversities increased and overshot that of—and taxonomic composition diverged from—unaffected plots after the second year. Young and old‐growth secondary forest types mainly differed in the taxonomic composition of new recruits. However, there was no evidence of changes in functional composition towards resource‐acquisitive strategies such as lower wood density or higher specific leaf area.ConclusionsAbiotic conditions and basal area recovered rapidly within 2–4 years after the windstorm. Taxonomic composition in young and old‐growth affected forests both diverged from unaffected forests but also from each other over time.

Seasonal dynamics in a cavity-nesting bee-wasp community: Shifts in composition, functional diversity and host-parasitoid network structure.

Ecological communities are composed of species that interact with each other forming complex interaction networks. Although interaction networks have been usually treated as static entities, interactions show high levels of temporal variation, mainly due to temporal species turnover. Changes in taxonomic composition are likely to bring about changes in functional trait composition. Because functional traits influence the likelihood that two species interact, temporal changes in functional composition and structure may ultimately affect interaction network structure. Here, we study the seasonality (spring vs. summer) in a community of cavity-nesting solitary bees and wasps (‘hosts’) and their nest associates (‘parasitoids’). We analyze seasonal changes in taxonomic compostion and structure, as well as in functional traits, of the host and parasitoid communities. We also analyze whether these changes result in changes in percent parasitism and interaction network structure. Our host and parasitoid communities are strongly seasonal. Host species richness increases from spring to summer. This results in important seasonal changes in functional composition of the host community. The spring community (almost exclusively composed of bees) is characterized by large, univoltine, adult-wintering host species. The summer community (composed of both bees and wasps) is dominated by smaller, bivoltine, prepupa-wintering species. Host functional diversity is higher in summer than in spring. Importantly, these functional changes are not only explained by the addition of wasp species in summer. Functional changes in the parasitoid community are much less pronounced, probably due to the lower parasitoid species turnover. Despite these important taxonomic and functional changes, levels of parasitism did not change across seasons. Two network metrics (generality and interaction evenness) increased from spring to summer. These changes can be explained by the seasonal increase in species richness (and therefore network size). The seasonal shift from a bee-dominated community in spring to a wasp-dominated community in summer suggests a change in ecosystem function, with emphasis on pollination in spring to emphasis on predation in summer.

Shift in community functional composition following nitrogen fertilization in an alpine meadow through intraspecific trait variation and community composition change

In recent years, ecologists have tried to determine the importance of intraspecific trait variation (ITV) versus community composition change (CCC) in shifts in community functional composition. However, results to date have not provided generality. A six-year nitrogen (N) fertilization experiment was conducted in species-rich alpine meadow communities. We focused on five key functional traits (height, leaf dry mass content LDMC, specific leaf area SLA, leaf nitrogen content LNC, and leaf phosphorus content LPC) that belong to three trait categories (whole-plant level trait, leaf morphology trait and leaf chemical trait) and measured biomass of each species in community. A sum of squares decomposition method was used to distinguish the relative contribution of ITV versus CCC to community weighted mean (CWM) traits. Our results showed that N fertilization led to increasing heightCWM and LNCCWM due to light competition intensification and soil nutrient enrichment. However, the responses of community-wide SLA, LDMC and LPC were highly inconsistent and depended on the balance of different opposing processes. Moreover, during short-term fertilization, ITV played a more important role in mediating functional composition changes in all traits, but the effects of CCC overwhelmed ITV and became more important in determining community-wide whole-plant level trait and leaf morphology traits (height, LDMC and SLA) in subsequent fertilization years. On the other hand, ITV always played a more important role than CCC in determining the community-wide leaf chemical traits (LNC and LPC), but CCC had a greater contribution than ITV in terms of explaining shifts in whole-plant traits (height) and leaf morphology traits (LDMC and SLA). In addition, both positive and negative covariations appeared in our study, indicating that community-wide trait shifts due to ITV and CCC may either reinforce or oppose one another, depending on different trait categories. These findings highlight the importance of ITV, CCC and their covariation in mediating community functional composition, and the relative importance of ITV effects and CCC effects depended on fertilization duration and trait category. This study significantly improve our understanding of the mechanisms governing the shifts in community functional composition under N deposition scenarios.

Inside the guts of the city: Urban-induced alterations of the gut microbiota in a wild passerine

Urbanisation represents one of the most radical forms of terrestrial land use change and has been shown to lead to alterations in ecosystem functioning and community dynamics and changes in individual phenotypic traits. While the recent surge in microbiome studies has brought about a paradigm shift by which individuals cannot truly be considered independently of the bacterial communities they host, the role of gut microbiota in organismal response to human-induced environmental change is still scarcely studied. Here, we applied a metabarcoding approach to examine the impact of urbanisation on the gut microbiota of Passer domesticus. We found urbanisation to be associated to lower microbiota species diversity, modifications in taxonomic composition and community structure, and changes in functional composition. The strength of these relationships, however, depended on the spatial scale and season at which they were considered. Such spatio-temporal effect suggests that urbanisation may dampen the natural seasonal variation of the gut microbiota observed in more pristine habitats, potentially influencing the fitness of urban organisms. Our results hence shed light on a hitherto little considered perspective, i.e. that the negative effects of urbanisation on city-dwelling organisms may extend to their microbiomes, causing potential dysbioses.

Contrasting outcomes of species- and community-level analyses of the temporal consistency of functional composition.

Multiple anthropogenic drivers affect every natural community, and there is broad interest in using functional traits to understand and predict the consequences for future biodiversity. There is, however, no consensus regarding the choice of analytical methods. We contrast species- and community-level analyses of change in the functional composition for four traits related to drought tolerance using three decades of repeat censuses of trees in the 50-ha Forest Dynamics Plot on Barro Colorado Island, Panama. Community trait distributions shifted significantly through time, which may indicate a shift toward more drought tolerant species. However, at the species level, changes in abundance were unrelated to trait values. To reconcile these seemingly contrasting results, we evaluated species-specific contributions to the directional shifts observed at the community level. Abundance changes of just one to six of 312 species were responsible for the community-level shifts observed for each trait. Our results demonstrate that directional changes in community-level functional composition can result from idiosyncratic change in a few species rather than widespread community-wide changes associated with functional traits. Future analyses of directional change in natural communities should combine community-, species-, and possibly individual-level analyses to uncover relationships with function that can improve understanding and enable prediction.

Drought-induced mortality patterns and rapid biomass recovery in a terra firme forest in the Colombian Amazon.

Extreme climatic events affecting the Amazon region are expected to become more frequent under ongoing climate change. In this study, we assessed the responses to the 2010 drought of over 14,000 trees ≥10cm dbh in a 25ha lowland forest plot in the Colombian Amazon and how these responses varied among topographically defined habitats, with tree size, and with species wood density. Tree mortality was significantly higher during the 2010-2013 period immediately after the drought than in 2007-2010. The post-drought increase in mortality was stronger for trees located in valleys (+243%) than for those located on slopes (+67%) and ridges (+57%). Tree-based generalized linear mixed models showed a significant negative effect of species wood density on mortality and no effect of tree size. Despite the elevated post-drought mortality, aboveground biomass increased from 2007 to 2013 by 1.62 Mg ha-1 yr-1 (95% CI 0.80-2.43 Mg ha-1 yr-1 ). Biomass change varied among habitats, with no significant increase on the slopes (1.05, 95% CI -0.76 to 2.85 Mg ha-1 yr-1 ), a significant increase in the valleys (1.33, 95% CI 0.37-2.34 Mg ha-1 yr-1 ), and a strong increase on the ridges (2.79, 95% CI 1.20-4.21 Mg ha-1 yr-1 ). These results indicate a high carbon resilience of this forest to the 2010 drought due to habitat-associated and interspecific heterogeneity in responses including directional changes in functional composition driven by enhanced performance of drought-tolerant species that inhabit the drier ridges.

Modification of Hydrolysis Lignin by Hydrogen Peroxide to Obtain an Effective Adsorbent of Highly Toxic Rocket Fuel

Lignin, a large scale by-product of papermaking and bioethanol production, is applied now in various fields. One of the main areas of use is in the development of different adsorbents, including those intended for detoxification of the spills of 1,1-dimethylhydrazine-based rocket fuel. The present work has shown the possibility of oxidative modification of hydrolytic lignin by hydrogen peroxide to improve the efficiency of the adsorbent. The change in functional composition of the modified adsorbent was studied by IR and NMR spectroscopy. It was shown that the oxidative treatment led to an increase in the content of carbonyl and carboxyl groups, which act as the active adsorption centres for hydrazine molecules. The optimum oxidation conditions were found. An increase in treatment duration from 15 to 120 min and in concentration of hydrogen peroxide from 6 to 30% did not have a significant effect on the functional composition and adsorption properties of lignin.

Climate- and successional-related changes in functional composition of European forests are strongly driven by tree mortality.

Intense droughts combined with increased temperatures are one of the major threats to forest persistence in the 21st century. Despite the direct impact of climate change on forest growth and shifts in species abundance, the effect of altered demography on changes in the composition of functional traits is not well known. We sought to (1) quantify the recent changes in functional composition of European forests; (2) identify the relative importance of climate change, mean climate and forest development for changes in functional composition; and (3) analyse the roles of tree mortality and growth underlying any functional changes in different forest types. We quantified changes in functional composition from the 1980s to the 2000s across Europe by two dimensions of functional trait variation: the first dimension was mainly related to changes in leaf mass per area and wood density (partially related to the trait differences between angiosperms and gymnosperms), and the second dimension was related to changes in maximum tree height. Our results indicate that climate change and mean climatic effects strongly interacted with forest development and it was not possible to completely disentangle their effects. Where recent climate change was not too extreme, the patterns of functional change generally followed the expected patterns under secondary succession (e.g. towards late-successional short-statured hardwoods in Mediterranean forests and taller gymnosperms in boreal forests) and latitudinal gradients (e.g. larger proportion of gymnosperm-like strategies at low water availability in forests formerly dominated by broad-leaved deciduous species). Recent climate change generally favoured the dominance of angiosperm-like related traits under increased temperature and intense droughts. Our results show functional composition changes over relatively short time scales in European forests. These changes are largely determined by tree mortality, which should be further investigated and modelled to adequately predict the impacts of climate change on forest function.

Potential trajectories of old‐growth Neotropical forest functional composition under climate change

Quantifying relationships between plant functional traits and abiotic gradients is valuable for evaluating potential responses of forest communities to climate change. However, the trajectories of change expected to occur in tropical forest functional characteristics as a function of future climate variation are largely unknown. We modeled community level trait values of Costa Rican rain forests as a function of current and future climate, and quantified potential changes in functional composition. We calculated per‐plot community weighted mean (CWM) trait values for leaf area (LA), specific leaf area (SLA), leaf dry matter content (LDMC), leaf nitrogen (N) and phosphorus (P) content, and wood basic specific gravity (WSG), for tree and palm species in 127 0.25 ha plots. We modeled the response of CWM traits to current temperature and precipitation gradients using generalized additive modeling. We then predicted and mapped CWM traits values under current and future climate, and quantified potential changes under a global warming scenario (RCP8.5, year 2050). We calculated the area within the multi trait functional space occupied by forest plots under both current and future climate, and determined potential changes in functional space occupied by forest plots. Overall, precipitation predicted CWM traits better than temperature. Models indicated increases in CWM SLA, N and P, and a decrease in CWM LDMC under climate change. Lowland forest communities converged on a single direction of change towards more acquisitive CWM trait values, indicating a change in forest functional composition resulting from a changed climate. Functional space occupied by forest plots was reduced by 50% under the future climate. Functional composition changes may have further effects on forests ecosystem services. Assessing functional trait spatial‐gradients can help bridge the gap between species‐based biogeography and biogeochemical approaches to strengthen biodiversity and ecosystem services conservation efforts.

Time lags in functional response to management regimes - evidence from a 26-year field experiment in wet meadows

Questions (i) How does functional composition and diversity respond to different timings and frequencies of mowing or fallow treatment? (ii) To which species assembly and related ecosystem processes do these developments correspond? (iii) What is the time course of these developments, and do they reach a stable state? Location North-western Germany Methods In 1987, a field experiment in nine wet meadow sites formerly exploited as fertilized meadows or pastures was established with four management treatments: (i) mowing twice a year in June/July and in September, (ii) mowing once a year in June/July, (iii) mowing once a year in September, and (iv) leaving fallow except shrub removal. Vegetation was recorded at least every second year and the functional composition (community weighted means) and diversity (Rao's quadratic entropy) were analysed in the course of the experiment. We selected eight plant functional traits (Canopy height, SLA, LDMC, Seed mass, Shoot cyclicity, Clonal Index, Onset of flowering, Leaf distribution) capturing the main plant life strategies. Results Temporal changes, fluctuations and divergences between treatments could be observed in both functional composition and diversity. In particular, the vegetation of the fallow treatment showed strong competition for light and a higher investment into internal nutrient cycling. Over time, all treatments respond towards more stressful conditions due to generally less intensive management compared with the former management and respective nutrient depletion, leading to a more nutrient retentive and patch holding strategy and little investment into competitive seedlings. High competition and loose abiotic filters in the fallow treatment led to a niche separation in foliar traits. Mowing on the other hand enforced a divergence of reproduction mechanisms. Conclusion We detected long-term fluctuations and ongoing changes in functional composition and diversity even after 26 years. Especially early succession was characterized by a transient loss of functional diversity, caused by strong time lags in immigration and extinction of species. Our findings stress the importance of long-term experimental studies to avoid precarious misinterpretations. This article is protected by copyright. All rights reserved.

Bird Responses to Lowland Rainforest Conversion in Sumatran Smallholder Landscapes, Indonesia.

Rapid land-use change in the tropics causes dramatic losses in biodiversity and associated functions. In Sumatra, Indonesia, lowland rainforest has mainly been transformed by smallholders into oil palm (Elaeis guineensis) and rubber (Hevea brasiliensis) monocultures, interspersed with jungle rubber (rubber agroforests) and a few forest remnants. In two regions of the Jambi province, we conducted point counts in 32 plots of four different land-use types (lowland rainforest, jungle rubber, rubber plantation and oil palm plantation) as well as in 16 nearby homegardens, representing a small-scale, traditional agricultural system. We analysed total bird abundance and bird abundance in feeding guilds, as well as species richness per point count visit, per plot, and per land-use system, to unveil the conservation importance and functional responses of birds in the different land-use types. In total, we identified 71 species from 24 families. Across the different land-use types, abundance did not significantly differ, but both species richness per visit and per plot were reduced in plantations. Feeding guild abundances between land-use types were variable, but homegardens were dominated by omnivores and granivores, and frugivorous birds were absent from monoculture rubber and oil palm. Jungle rubber played an important role in harbouring forest bird species and frugivores. Homegardens turned out to be of minor importance for conserving birds due to their low sizes, although collectively, they are used by many bird species. Changes in functional composition with land-use conversion may affect important ecosystem functions such as biological pest control, pollination, and seed dispersal. In conclusion, maintaining forest cover, including degraded forest and jungle rubber, is of utmost importance to the conservation of functional and taxonomic bird diversity.

Context‐dependent changes in the functional composition of tree communities along successional gradients after land‐use change

Summary Land‐use change can modify the functional composition of tree communities, which is an essential determinant of the ecosystem functions. The lack of consensus about the functional responses of tree communities to land‐use change is a major uncertainty in the assessments of human impacts on terrestrial ecosystem functions. In this study, we applied a machine‐learning method to a large data set consisting of 2574 tree communities across Japan to examine changes in the functional composition of tree communities after land‐use change while considering contexts including successional trajectories, forest types and the presence of gymnosperms. Specifically, we hypothesized that functional changes along successional gradients after land‐use change can be different in different contexts. Effects of two successional variables (stand age and basal area) on functional composition were highly significant throughout the study region. Changes in functional composition with changes in the two successional variables differed greatly, and the effects of basal area often outweighed those of stand age. Tree communities with small basal area were generally characterized by functional traits related to the resource‐acquisitive strategy, that is short adult stature, low leaf mass per unit area, small seeds, low wood density and large leaves, especially when gymnosperms were excluded from the analysis. Decreasing basal area but not decreasing stand age often led to a considerable loss in functional diversity. Despite these general trends, functional changes along successional gradients after land‐use change were not necessarily parallel and the opposite patterns were sometimes observed among forest types, traits and taxonomic groups. Synthesis. As a whole, our analyses demonstrate that the functional changes in tree communities after land‐use change are highly evident in a given context but can be different under different contexts. These changes in functional composition can trigger variable changes in ecosystem functions such as carbon and nutrient cycling that depend on the context.

Elevation, Topography, and Edge Effects Drive Functional Composition of Woody Plant Species in Tropical Montane Forests

AbstractTropical montane forests comprise heterogeneous environments along natural gradients of topography and elevation. Human‐induced edge effects further increase the environmental heterogeneity in these forests. The simultaneous effects of natural and human‐induced gradients on the functional diversity of plant leaf traits are poorly understood. In a tropical montane forest in Bolivia, we studied environmental gradients associated with elevation (from 1900 m to 2500 m asl), topography (ridge and gorge), and edge effects (forest edge vs. forest interior), and their relationship with leaf traits and resource‐use strategies. First, we investigated associations of environmental conditions (soil properties and microclimate) with six leaf traits, measured on 119 woody plant species. Second, we evaluated changes in functional composition with community‐weighted means and functional structure with multidimensional functional diversity indices (FRic, FEve and FDiv). We found significant associations between leaf traits and soil properties in accordance with the trade‐off between acquisition and conservation of resources. Functional composition of leaf traits shifted from the dominance of acquisitive species in habitats at low altitudes, gorges, and forest interior to the dominance of conservative species in habitats at high altitudes, ridges, and forest edges. Functional structure was only weakly associated with the environmental gradients. Natural and human‐induced environmental gradients, especially soil properties, are important for driving leaf traits and resource‐use strategies of woody plants. Nevertheless, weak associations between functional structure and environmental gradients suggest a high redundancy of functional leaf traits in this tropical montane forest.

Changing gears during succession: shifting functional strategies in young tropical secondary forests.

Adaptations to resource availability strongly shape patterns of community composition along successional gradients in environmental conditions. In the present study, we examined the extent to which variation in functional composition explains shifts in trait-based functional strategies in young tropical secondary forests during the most dynamic stage of succession (0-20 years). Functional composition of two size classes in 51 secondary forest plots was determined using community-weighted means of seven functional traits, which were intensively measured on 55 woody plant species (n = 875-1,761 individuals). Along the successional gradient in forest structure, there was a significant and consistent shift in functional strategies from resource acquisition to resource conservation. Leaf toughness and adult plant size increased significantly, while net photosynthetic capacity (A(mass)) decreased significantly during succession. Shifts in functional strategies within size classes for A(mass) and wood density also support the hypothesis that changes in functional composition are shaped by environmental conditions along successional gradients. In general, 'hard' functional traits, e.g., A(mass) and leaf toughness, linked to different facets of plant performance exhibited greater sensitivity to successional changes in forest structure than 'soft' traits, such as leaf mass area and leaf dry matter content. Our results also suggested that stochastic processes related to previous land-use history, dispersal limitation, and abiotic factors explained variation in functional composition beyond that attributed to deterministic shifts in functional strategies. Further data on seed dispersal vectors and distance and landscape configuration are needed to improve current mechanistic models of succession in tropical secondary forests.

Inferring resilience to fragmentation-induced changes in plant communities in a semi-arid Mediterranean ecosystem.

Predicting the capacity of ecosystems to absorb impacts from disturbance events (resilience), including land-use intensification and landscape fragmentation, is challenging in the face of global change. Little is known about the impacts of fragmentation on ecosystem functioning from a multi-dimensional perspective (multiple traits). This study used 58 500-m linear transects to quantify changes in the functional composition and resilience of vascular plant communities in response to an increase in landscape fragmentation in 18 natural scrubland fragments embedded within a matrix of abandoned crop fields in Cabo de Gata-Níjar Natural Park, Almería, Spain. Changes in functional community composition were measured using functional diversity indices (functional richness and functional dispersion) that were based on 12 plant traits. Resilience was evaluated using the functional redundancy and response diversity from the perspective of plant dispersal, which is important, particularly, in fragmented landscapes. Scrubland fragmentation was measured using the Integral Index of Connectivity (IIC). The functional richness of the plant communities was higher in the most fragmented scrubland. Conversely, the functional dispersion (i.e., spread) of trait values among species in the functional trait space was lower at the most fragmented sites; consequently, the ecological tolerance of the vegetation to scrubland fragmentation decreased. Classifying the plant species into four functional groups indicated that fragmentation favoured an increase in functional redundancy in the ‘short basal annual forbs and perennial forbs’ group, most of which are species adapted to degraded soils. An assessment based on the traits associated with plant dispersal indicated that the resilience of ‘woody plants’, an important component in the Mediterranean scrubland, and habitat fragmentation were negatively correlated; however, the correlation was positive in the ‘short basal annual forbs and perennial forbs’ and the ‘grasses’ groups.

Effect of Aging on Adhesion Properties of Asphalt Mixtures with the Use of Bitumen Bond Strength and Surface Energy Measurement Tests

The interaction between asphalt binder and aggregate is fundamental to ensure adequate performance of asphalt mixtures, mainly in the presence of water. The work of adhesion generated between both materials directly affects the resistance of asphalt mixture to moisture damage, because it measures the ease with which water can displace asphalt binder from the aggregate surface. The objective of this study was to characterize the bond strength between asphalt and several aggregate sources. A PG 64-22 neat binder was modified with several additives to determine the effect on adhesion: polymers, nanomaterials, and adhesion promoters. To measure the strength of adhesion, the bitumen bond strength (BBS) test and contact angle measurements between asphalt binder and the aggregate surface by means of goniometry were used. The surface energy of the asphalt and the aggregate, with and without the presence of water, was estimated also. Testing was performed on all binders and on each binder–aggregate combination after ( a) rolling thin-film oven (RTFO) aging and ( b) RTFO and pressure aging vessel aging. The BBS results identified differences in bond strength as a result of moisture conditioning and aging. The differences depended on the aggregate source and binder type. Different failure modes were also observed (i.e., cohesive, adhesive). The results also indicated an increase in strength of adhesion associated with the aging process: the main resistance gain was observed after RTFO aging. Finally, changes in bond strength were compared with functional composition changes associated with the aging process and related to changes in performance.

Biomass-based targets and the management of multispecies coral reef fisheries.

The failure of fisheries management among multispecies coral reef fisheries is well documented and has dire implications for the 100 million people engaged in these small-scale operations. Weak or missing management institutions, a lack of research capacity, and the complex nature of these ecosystems have heralded a call for ecosystem-based management approaches. However, ecosystem-based management of coral reef fisheries has proved challenging due to the multispecies nature of catches and the diversity of fish functional roles. We used data on fish communities collected from 233 individual sites in 9 western Indian Ocean countries to evaluate changes in the site's functional composition and associated life-history characteristics along a large range of fish biomass. As biomass increased along this range, fish were larger and grew and matured more slowly while the abundance of scraping and predatory species increased. The greatest changes in functional composition occurred below relatively low standing stock biomass (<600 kg/ha); abundances of piscivores, apex predators, and scraping herbivores were low at very light levels of fishing. This suggests potential trade-offs in ecosystem function and estimated yields for different management systems. Current fishing gear and area restrictions are not achieving conservation targets (proposed here as standing stock biomass of 1150 kg/ha) and result in losses of life history and ecological functions. Fish in reefs where destructive gears were restricted typically had very similar biomass and functions to young and low compliance closures. This indicates the potentially important role of fisheries restrictions in providing some gains in biomass and associated ecological functions when fully protected area enforcement potential is limited and likely to fail. Our results indicate that biomass alone can provide broad ecosystem-based fisheries management targets that can be easily applied even where research capacity and information is limited. Of particular value, is our finding that current management tools may be used to reach key ecosystem-based management targets, enabling ecosystem-based management in many socioeconomic contexts.