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- FG Ökologie (25)
El género Quercus constituye el grupo de especies leñosas más importante del hemisferio norte, con una amplia distribución tanto en España como en México. El estudio de sus rasgos funcionales nos permite conocer su grado de diversificación y su adaptación al medio, así como las limitaciones morfológicas y fisiológicas que restringen su evolución. El principal objetivo del presente estudio es comprender como se segregan los rasgos funcionales foliares dentro del género Quercus, y que factores determinan dicha segregación. Para ello hemos medido cinco rasgos foliares en un total de 28 especies del generó Quercus de España y México a lo largo de un gradiente de evapotranspiración potencial. Nuestros resultados muestran dos dimensiones independientes de variación funcional foliar: por un lado, las especies se distribuyen de acuerdo con el espectro de economía foliar a lo largo del gradiente de humedad edáfica, encontrándose las especies más conservativas en el uso de recursos en regiones con mayor evapotranspiración potencial y las especies más adquisitivas en zonas con menor evapotranspiración. Por otro lado, el tamaño foliar esta principalmente condicionado por el origen geográfico de las especies. Estos resultados sugieren que las variaciones evolutivas dentro de un mismo linaje están asociadas a la variación coordinada de sus rasgos, siendo la humedad un factor clave en la variación funcional del género Quercus. Además, destacar que no se aprecia relación entre la longevidad foliar y el espectro de economía foliar, lo cual podría deberse a que la historia evolutiva del hábito foliar en los robles de ambos países ha sido diferente.
The role of wood anatomical traits in the coexistence of oak species along an environmental gradient
(2021)
Oaks (Quercus) are a dominant woody plant genus in the northern hemisphere, which occupy a wide range of habitats and are ecologically diverse. We analysed the wood anatomical traits, the variables derived and the relative hydraulic conductivity of 21 oak species to identify their performance according to abiotic factors, leaf phenological patterns and phylogenetic restrictions by analysing the interspecific variation along an environmental gradient. First, we determine the causes of anatomical trait variation in the oaks, analysing the functional trade-offs related to distribution along the environmental gradient. We measure the phenotypic plasticity of the anatomical traits to determine the role of environment and geographic distance in the range of phenotypic plasticity. Second, we examined if oaks co-occurred along the environmental gradient. Then we analysed if wood anatomical traits reflect differences among their phylogenetic section, leaf habit and a phylogenetic section/leaf habit category. Last, we tested the phylogenetic signal. Our results showed that vessel diameter, vessel frequency, wood density and relative hydraulic conductivity are the main axes of trait variation in the species analysed among leaf habit categories. The aridity index and seasonal precipitation drive the variation in the analysed traits. Higher environmental distance resulted in a higher relative distance plasticity index among traits. Co-occurrence of oak species with different leaf habits and phylogenetic trajectories may promote complementary resource acquisition. The phylogenetic signal in the oak species studied was low, which implies labile wood traits.
Extensive research efforts are devoted to understand fine root trait variation and to confirm the existence of a belowground root economics spectrum (RES) from acquisitive to conservative root strategies that is analogous to the leaf economics spectrum (LES). The economics spectrum implies a trade-off between maximizing resource acquisition and productivity or maximizing resource conservation and longevity; however, this theoretical framework still remains controversial for roots. We compiled a database of 320 Mediterranean woody and herbaceous species to critically assess if the classic economics spectrum theory can be broadly extended to roots. Fine roots displayed a wide diversity of forms and properties in Mediterranean vegetation, resulting in a multidimensional trait space. The main trend of variation in this multidimensional root space is analogous to the main axis of LES, while the second trend of variation is partially determined by an anatomical trade-off between tissue density and diameter. Specific root area (SRA) is the main trait explaining species distribution along the RES, regardless of the selected traits. We advocate for the need to unify and standardize the criteria and approaches used within the economics framework between leaves and roots, for the sake of theoretical consistency.
Linking functional composition moments of the sub-Mediterranean ecotone with environmental drivers
(2023)
Leaf structural and nutrient traits are key attributes of plant ecological strategies, as these traits are related to resource-use strategies and plant growth. However, leaf structure and nutrient composition can vary among different habitats, leaf habits or phylogenetic groups. In this study, we measured 13 leaf traits (one structural—leaf mass per area, LMA—and 12 nutrient traits) in 98 Mediterranean woody species growing over a wide range of environmental conditions, with the final aim of discerning the main causes of leaf trait variability. The variance decomposition results show that phylogeny, leaf habit and habitat type affected in several ways the structural and nutrient traits studied. Leaf nutrient concentrations are strongly positively correlated amongst themselves, and negatively correlated with LMA, in accordance with the “leaf economics spectrum”. We found that leaf habit and phylogeny were important causes of variation in LMA and in a broad number of leaf nutrients (i.e., C, N, Mg, S, K), while other micronutrients seemed to be more dependent on the environment (i.e., Cu and Mn). In summary, our study reinforces the existence of the leaf economics spectrum in a broad pool of Mediterranean woody species, and demonstrates the strong influence of phylogeny, leaf habit and environmental context as the main drivers of variability in some leaf structural and nutrient traits.
Background and aimsRoot traits play a critical role inplant resource-use strategies and ecosystem functioning,but there is great controversy regarding their identityand functionality in different dimensions of below-ground functional variation. Here, we explored the levelof covariation among a suite of key root traits (i.e.specific root length, root dry matter content, diameterand density) as well as between them and two above-ground traits related with plant function (leaf nutrientconcentration and specific leaf area). We also evaluatedwhether these patterns of trait covariation were consis-tent at different spatial scales and organisational levels.MethodsWe collected fine root (< 2 mm) samples of 534individuals (of 80 woody species) along a wide regionalrange of environmental conditions in southern Spain.
Iberian oak forests and woodlands are vital providing a variety of ecosystem services. They provide raw materials like cork, wood and fuel, and fodder (acorns) for wild and domestic animals. Oak trees provide a climate regulating service by their capacity to sequester carbon and therefore to mitigate the effects of climatic change. There is an increasing demand for cultural services provided by oak woodlands, mainly for recreation and ecotourism. However, some global-change drivers are negatively affecting oak forests, therefore diminishing their ecosystem services and in consequence undermining human well-being. The main drivers affecting Iberian oaks are: land use changes, introduction of exotic pathogens, air and soil pollution deteriorating oak health, and climatic change, in particular the combined reduction of rainfall and the rise in temperature. In this chapter we focus on the ecology of Iberian oaks and how they are affected by global change. Firstly, we introduce a literature overview of the research conducted on Quercus, analysed by species, countries and topics. Secondly, we review the main biological processes related with the oak responses to global change: i) genetic diversity, climatic refuges and adaptation to climatic change; ii) ecophysiological responses to stress and disturbance, functional diversity, growth patterns, and scaling up from leaf to ecosystem; iii) demographic responses, causes of regeneration failures, spatial patterns of recruitment, drivers of decline and dieback. Thirdly, we review the management strategies in three case studies: the agro-silvo-pastoral systems (dehesas and montados), the cork oak woodlands, and the afforestation of a polluted-land for phytostabilization of contaminants.
The introduction of exotic species to new regions offers opportunities to test fundamental questions in ecology, such as the context-dependency of community structure and assembly. Annual grasslands provide a model system of a major unidirectional introduction of plant species from Europe to North America. We compared the community structure of grasslands in two Mediterranean regions by surveying plots in Spain and in California with similar environmental and management conditions. All species found in Spanish grasslands were native to Spain, and over half of them (74 of 139 species) are known to have colonized California. In contrast, in California, over half of the species (52 of 95 species) were exotic species, all of them native to Spain. Nineteen species were found in multiple plots in both regions (i.e., shared species). The abundance of shared species in California was either similar to (13 species) or greater than (6 species) in Spain. In California, plants considered pests were more likely than non-pest species to have higher abundance. Co-occurring shared species tended to maintain their relative abundance in native and introduced communities, which indicates that pools of exotic species might assemble similarly at home and away. These findings provide interesting insights into community assembly in novel ecosystems. They also highlight an example of startling global and local floristic homogenization.
1. Many studies have quantified the functional variation of fine root traits to un-derstand the overarching trade-off between maximizing resource acquisition or conservation (root economics spectrum [RES]). However, we know remarkably less on how plant strategies along the RES are actually constrained by the amount of photosynthates required to construct roots (i.e. construction costs, CC) or how below- ground interactions with symbiotic organisms modify root trait patterns and their relationships with CC.2. Our main aim was to quantify CC of fine roots (<2 mm) and their underlying compo-nents (carbon, minerals and organic nitrogen concentrations) in 60 Mediterranean woody species with contrasting symbiotic association types (ectomycorrhizas, ar-buscular and ericoid mycorrhizas and N-fixing bacteria). We examined (a) whether the covariation among fine root traits along the RES was related to the intrinsic cost of producing roots and whether this relationship was dependent on the type of root symbiosis; (b) whether the relationship of each CC component with the RES was dependent on the type of root symbiosis and (c) whether soil water and nutrient availability determined differences in CC across sites.3. According to the RES hypothesis, fine root traits showed a main covariation trend (acquisition vs. conservation), defined by the first PCA axis, which also segregated species by their two main contrasting symbiotic types (arbuscular and ectomycor-rhizal). We found a positive relationship between root CC and the RES (i.e. PCA axis 1) and, interestingly, slopes differed among symbiotic types, in response to the different role of each specific CC component. In addition, independently of symbiotic type, root CC decreased linearly with soil nutrient availability and quad-ratically with plant water availability.4. Synthesis. Our study demonstrates that woody plants display different functional strategies in their root CC, related with their position on the RES, and that CC differ among symbiotic groups. The influence of the root CC components across species varied among symbiotic associations, pointing to a trade-off between structural and metabolic compounds. Root CC were also strongly modulated by soil resource availability (nutrients and water). This study highlights that root CC are fundamental to better understand below- ground resource-use strategies.
Demographic traits improve predictions of spatiotemporal changes in community resilience to drought
(2021)
Communities are increasingly threatened by extreme weather events. The cumulative effects of such events are typically investigated by assessing community resilience, that is, the extent to which affected communities can achieve pre-event states. However, a mechanistic understanding of the processes underlying resilience is frequently lacking and requires linking various measures of resilience to demographic responses within natural communities. Using 13 years of data from a shrub community that experienced a severe drought in 2005, we use generalized additive models to investigate temporal changes in three measures of resilience. We assess whether community-weighted, species-specific demographic traits such as longevity and reproductive output can predict changes in resilience and how the performance of these traits compares to more commonly used plant functional traits such as leaf area or root dry matter content. We find significant spatiotemporal variation in community dynamics after the drought. Overall, demographic traits are better at predicting absolute and relative resilience in total plant cover, but functional traits outperform demographic traits when resilience in community composition is assessed. All resilience measures show nonlinear and context-specific responses to demographic and functional traits; and these responses depend strongly on the severity of initial drought impact.
Synthesis. Our work demonstrates that a full picture of the mechanisms underlying community responses to drought requires the assessment of numerous species-specific characteristics (including demographic and functional traits) and how these characteristics differentially affect complementary measures of community changes through time.
Active restoration of degraded areas with multi-purpose tree species has been proposed as a measure to counter the losses from deforestation and mitigate consequences for local human communities. In a restoration project at a former mining site in Ghana, ecosystem services (ES) proxies in an actively restored forest were compared to a local agroforestry system and a natural forest. The results provide information about trade-offs and synergies between proxies of multiple ES(s). ES proxies were assessed according to the following categories: (a) food-tree ES: biomass of food and fodder trees, (b) other trees ES: biomass of fuelwood, medicine or mulch trees, (c) ES-providing arthropods: the number of detritivorous and predaceous arthropods, (d) carbon storage, and (e) tree diversity. Eight replicated plots with sizes of 20 m × 20 m were established in each forest type, and the following ES proxies were quantified: tree diversity was estimated as taxonomic richness of all trees with a diameter at breast height ≥ 10 cm in each plot. Tree species were then classified into ES categories (food, fodder, fuelwood, medicine, or mulch). Ground-dwelling arthropods were sampled for 10 weeks with five pitfall traps in each plot and categorized as decomposers and predators. Tree above-ground biomass was estimated based on the measured tree diameter, height, and specific wood density using an improved allometric equation. The above-ground biomass was later converted into carbon storage by assuming 50% of the above-ground biomass of each tree. ES proxies based on tree biomass were highest in the natural forest. Fodder, medicine, fuelwood, and mulch ES proxies were significantly higher in the restored forest than the agroforestry system. Decomposer arthropods were most dominant in the natural forest, followed by the restored forest and the agroforestry system. Predacious arthropods were more dominant in the restored forest than in the other forest types. Carbon storage was highest in the natural forest, followed by the agroforestry system and the restored forest. The actively restored forest took an intermediate position between the agroforestry system and the natural forest regarding values for all nine ES proxies. Out of the 14 possible relationships between food or fodder and other ES proxies, five were significantly positive (synergies) with no observed trade-offs (significant negative relationships). High fodder production in the restored and natural forests went along with higher values of other biomass ES proxies and numbers of beneficial arthropods, while higher food biomass also correlated positively with numbers of decomposing arthropods. Our results document that active restoration of degraded sites provides a valuable framework to promote ES provision to local communities compared to agroforestry system, but at the cost of lower food and fuelwood biomass and carbon storage compared to natural forests.
Restoration of degraded drylands is urgently needed to mitigate climate change, reverse desertification and secure livelihoods for the two billion people who live in these areas. Bold global targets have been set for dryland restoration to restore millions of hectares of degraded land. These targets have been questioned as overly ambitious, but without a global evaluation of successes and failures it is impossible to gauge feasibility. Here we examine restoration seeding outcomes across 174 sites on six continents, encompassing 594,065 observations of 671 plant species. Our findings suggest reasons for optimism. Seeding had a positive impact on species presence: in almost a third of all treatments, 100% of species seeded were growing at first monitoring. However, dryland restoration is risky: 17% of projects failed, with no establishment of any seeded species, and consistent declines were found in seeded species as projects matured. Across projects, higher seeding rates and larger seed sizes resulted in a greater probability of recruitment, with further influences on species success including site aridity, taxonomic identity and species life form. Our findings suggest that investigations examining these predictive factors will yield more effective and informed restoration decision-making.
Plant functional traits are highly plastic to changes in climatic factors and nutrient availability. However, the intraspecific plant response to abiotic factors and the overall effect on tree growth and productivity is still under debate. We studied forest productivity for 30 Quercus ilex subsp. ballota forests in Spain along a broad climatic gradient of aridity (mean annual precipitation from 321 to 858 mm). We used linear mixed models to quantify the effect of climatic and edaphic (soil nutrients, topography, and texture) factors on tree functional traits (leaf and branch traits), and subsequently, the effect of such functional traits and abiotic factors on the relative growth rate (RGR) of adult trees. We used piecewise structural equation models (SEMs) to determine the causal effect of intrinsic and extrinsic factors on forest productivity. Our results showed that tree functional traits were mainly explained by climatic and edaphic factors. Functional traits and tree biomass explained forest biomass and RGR, respectively, which ultimately explained forest productivity. In conclusion, intraspecific variability of functional traits has a significant effect on plant biomass and growth, which ultimately may explain forest productivity in Quercus ilex forests.
Plant functional traits are useful in tracking changes in the environment, and play an important role in determining ecosystem functioning. The relationship between plant functional traits and ecosystem functioning remains unclear, although there is growing evidence on this relationship. In this study, we tested whether the functional structure of vegetation has significant effects on the provision of ecosystem services. We analysed plant trait composition (specific leaf area, leaf carbon and nitrogen ratio, isotopic carbon fraction, stem dry matter content, seed mass and plant height), soil parameters (nutrients, pH, bulk density) and proxies of ecosystem services (carbon stock, decomposition rate, invertebrate activity) in twenty-four plots in three tropical ecosystems (active restored and natural forests and an agroforestry system) in Ghana. For each plot, we measured above-ground biomass, decomposition rates of leaves and invertebrate activity as proxies for the provision of ecosystem services to evaluate (i) whether there were differences in functional composition and soil properties and their magnitude between ecosystem types. We further aimed to (ii) determine whether the functional structure and/or soil parameters drove ecosystem functions and multifunctionality in the three ecosystem types. For functional composition, both the leaf economic spectrum and seed mass dimension clearly separated the ecosystem types. The natural forest was more dominated by acquisitive plants than the other two ecosystem types, while the non-natural forests (agroforest and restored forest) showed higher variation in the functional space. The natural forest had higher values of soil properties than the restored forest and the agroforestry system, with the differences between the restored and agroforestry systems driven by bulk density. Levels of ecosystem service proxies and multifunctionality were positively related to the functional richness of forest plots and were mainly explained by the differences in site conditions. Our study demonstrated the effects of functional forest structure on ecosystem services in different forest ecosystems located in the semi-deciduous forest zone of Ghana.
The phylogenetic diversity (PD) can be used as a proxy for measures of functional diversity (FD); this relationship between PD and FD is premised on the reasonable assumption that evolutionary diversification has generated trait diversification, which in turn may result in greater niche complementarity. Functional traits have been used in various applications, from assemblage ecology looking at the relationship between functional diversity, environmental filtering, and assemblage structure. We used a trait-based approach, quantifying variations in the leaf-height-seed (LHS) scheme and functional and phylogenetic indices in semi-arid communities from three different habitats (grasslands, shrubland, and mixed habitats). To do so, three functional traits including specific leaf area (SLA), vegetation height (VH), and seed mass (SM) were measured in three habitats. We calculated at the plot scale, community weighted means (CWM) for each trait, species richness, Faith’s phylogenetic diversity index (PD), functional richness (Frich), functional and phylogenetic mean pairwise dissimilarities (MPD), and nutrient concentration. The results showed that the first Soil_PCA axis (explaining 37.1% of the total variance) showed a high loading of soil nutrients (N, P, K, OM) and pH, while the second axis (which explained 22.1% 224 of the variance) exhibited a high loading of pH at the top and K at the bottom. Also, the higher soil nutrient concentration and pH were significant and positively related with species and functional richness and Faith’s phylogenetic diversity.
The ongoing global deforestation resulting from anthropogenic activities such as unsustainable agriculture and surface mining threatens biodiversity and decreases both soil carbon and above-ground biomass stocks. In this study, we assessed soil properties and below- and above-ground biomass attributes in a restored former gravel mine area in Ghana two decades after active restoration with potted plants and fresh topsoil. We compared conditions to four alternative land-use types (unrestored abandoned gravel mine, arable land, semi-natural forest, and natural forest) representing pre- and post-disturbance as well as natural reference states. We hypothesized that soil properties and related levels of below- and above-ground biomass in the restored area share similarities with the natural reference systems and thereby are indicative of a trajectory towards successful restoration. Eight replicated subareas in each land-use type were assessed for a set of soil parameters as well as below- and above-ground biomass attributes. The soil properties characteristic for the restored area differed significantly from pre-restoration stages, such as the abandoned gravel site, but did not differ significantly from properties in the natural forest (except for bulk density and base saturation). Above-ground biomass was lower in the restored area in comparison to the reference natural forests, while differences were not significant for below-ground biomass. Silt and effective cation exchange capacity were closely related to above-ground biomass, while below-ground biomass was related to soil organic carbon, bulk density, and potassium concentration in soils. Our results suggest that major steps towards successful restoration can be accomplished within a relatively short period, without the wholesale application of topsoil. Improving soil conditions is a vital tool for the successful development of extensive vegetation cover after surface mining, which also affects carbon sequestration by both above- and below-ground biomass. We emphasize that the use of reference systems provides critical information for the monitoring of ecosystem development towards an expected future state of the restored area.
Functional segregation among species in a community depends on their mean trait values (i.e. functional distinctiveness), and the range of trait attributes exhibited by each species (i.e. functional diversity). Previous evidence suggests that invasive plants tend to display traits related to a more acquisitive resource-use strategy than natives. However, the contribution of intraspecific trait variation to functional diversity has received little attention in community ecology, and might provide interesting information about community processes. In this study, we used eight plant traits related to carbon and nutrient acquisition of coexisting dominant native and invasive plants in eight communities across the Mediterranean-climate biome to determine sources of functional segregation between native and invasive species. We found three major axes of functional variation, related to leaf economics, resource-use efficiency, and plant height. Invasive species across communities had leaf traits related to an acquisitive resource-use strategy in contrast to native species, whereas differences in the second and third axes were community dependent. Invasive species were more functionally diverse than native species across the dataset and in four out of the eight communities. Intraspecific variance accounted for 11%–27% of total trait variation and was on average greater in invasive species, and especially important in the axis related to resource use efficiency. These results, although dependent on the trait and community considered, offer interesting insights to the sources of functional trait diversity of native and invasive species within communities, indicating that intraspecific variation might not be equally distributed between native and invasive species.
From biodiversity to health: Quantifying the impact of diverse ecosystems on human well-being
(2023)
A major aim in invasion ecology is to understand the role of exotic species in plant communities. Whereas most studies have explored the traits of exotic species in the context of the introduced community, functional comparisons of entire assemblages of species in their native and introduced communities have rarely been analysed. Taking advantage of the unidirectional invasion of plant species of European origin (i.e. colonizers) into California, this study aims to investigate the relative importance of plant traits, environmental factors and invasion status in biological invasions.We compared the functional structure (i.e. trait composition and diversity) along resource availability gradients in recipient and native Mediterranean grassland communities in California and Spain, respectively. Traits were related to resource use in above-ground and below-ground organs and reproductive strategy. We also investigated how niche differences vary along environmental gradients between coexisting colonizer and native species assemblages within communities.There were clear differences in the functional structure of Mediterranean grassland communities between regions, which were associated with the resource availability gradient. Paradoxically, the most acquisitive communities occurred in resource-poor sites, highlighting that rapid acquisition and use of resources permit species to cope with environmental stress through stress avoidance. In Spain, colonizer species had greater specific leaf area than non-colonizers. Yet, differences between colonizer and non-colonizer species in Spain for other traits were mostly absent and did not change along the gradient. This might be a result of the greater native species richness as a consequence of the agricultural practices that have taken place in Europe for millennia and reflect that the entire species pool of grasslands is adapted to agricultural landscapes. In comparison, in California, colonizer species were more acquisitive in their use of resources than natives under favourable conditions, but functionally converged in resource-limited sites.Synthesis. These results underscore that the importance of niche differences between native and colonizer species as a community assembly mechanism is strongly subjected to the influence of habitat filtering. Trait comparisons are context dependent, and a correct interpretation of filtering processes in community assembly requires a regional perspective.
Respiratory costs of producing and maintaining stem biomass in eight co-occurring tree species
(2019)
BACKGROUND AND AIMS: Leaf litter decomposition is an important process controlling nutrient cycling in most terrestrial ecosystems. We evaluated the relationships among traits of green leaves and decomposition rates of leaf litter (k) at different environmental scales and organisational levels (species and community). We also assessed the relationships at community level between k and the Leaf Economic Spectrum (LES) and between k and different soil variables. METHODS: We measured leaf traits in 38 woody species distributed in nine sampling sites along a topographic gradient in southern Spain. Leaf litter was collected for each species in each sampling site and incubated in a microcosm experiment with soil collected from the top 20 cm of each site. RESULTS: We found positive relationships between k and specific leaf area (SLA), leaf N, K and P and negative relationships with leaf dry matter content (LDMC) and leaf C isotopic composition (δ¹³C), both at species and community levels. Decomposability was positively related with the first PCA axis describing the LES and the relationships were consistent across all sites and within different zones or topographic positions. In addition, community weighted mean values of leaf traits (LESCWM) were stronger predictors of litter decomposition than soil variables. CONCLUSIONS: A major finding of the present study is the main role that leaf traits, and the covariation among them (LES), play on decomposition process in Mediterranean ecosystems both at the species and community levels. In summary, our results support the idea that the suites of leaf traits have a strong control on the pace of C cycling, being the best drivers of decomposition processes under similar climatic conditions.