Abstract Functional traits are commonly used to calculate a wide array of functional diversity indices to infer different mechanisms of community assembly and species coexistence. Recently, the degree of interspecific covariation between multiple functional traits has been suggested as a mechanism influencing both species distributions and abundances in communities. However, empirical assessments of this theory along environmental gradients are still scarce due to the lack of an appropriate method and of sufficiently strong environmental gradients. Here we compare interspecific trait integration (ITI) across plant communities along a marked gradient of copper toxicity in the soil, using new multivariate and bivariate indices. This was achieved using the range of the eigenvalues of a principal component analysis on the traits of the species in a local community (multivariate ITI index) and the correlations between traits in local communities (bivariate ITI index). We show that the plant metal tolerance strategy (i.e. leaf metal content) is relatively independent from leaf economics, while negatively correlated to plant size. In addition, our results indicate a weak support for the expected general patterns of trait syndromes, such as the ‘leaf economics spectrum’ or the ‘leaf–height–seed’, at the whole‐community scale. This arises from an increase in multivariate trait integration along the soil copper gradient. The strongest trait integration is caused by an increase in the degree of association between certain traits on metal‐rich soils. The multivariate trait integration explains species richness better than other commonly used functional diversity indices. Our study highlights the power of ITI, as well as its complementarity to other functional diversity indices, to investigate the variation in functional strategies and their drivers along environmental gradients. The increase in trait integration with soil metal toxicity in plant communities supports that highly constraining environments select increasingly coordinated sets of functional traits, in turn possibly driving the decrease in species richness. Further studies should assess the generality and underlying physiological mechanisms of such ecological patterns.
This specimen-based occurrence dataset was compiled in the framework of the Conservation of Endemic Central African Trees (ECAT) project with the aim of producing global conservation assessments for the IUCN Red List. Funding for the ECAT project was provided by the Franklinia Foundation. The project targets all tree species endemic or sub-endemic to the Central African region comprising the Democratic Republic of the Congo, Rwanda and Burundi. The dataset contains 6363 records with occurrences of 8904 specimens from 337 taxa belonging to 153 genera in 52 families. Many of these taxa have restricted geographic ranges and are only known from a small number of herbarium specimens. As assessments for such taxa can be compromised by inadequate data, we transcribed and georeferenced label information to obtain a more accurate and complete locality dataset. All specimen data were manually cleaned and verified by botanical experts, resulting in improved data quality and consistency. Character encoding: UTF-8 Format name: Darwin Core Archive format Format version: 1.2 Metadata language: English Provided fields: basisOfRecord, occurrenceID, materialSampleID, catalogNumber, recordNumber, recordedBy, occurrenceStatus, associatedReferences, otherCatalogNumbers, occurrenceRemarks, eventDate, year, month, day, habitat, continent, country, countryCode, stateProvince, locality, verbatimElevation, verbatimCoordinates, decimalLatitude, decimalLongitude, geodeticDatum, georeferenceRemarks, identificationRemarks, scientificName, kingdom, phylum, class, order, family, genus, specificEpithet, infraspecificEpithet, taxonRank, taxonRemarks
La restauration ecologique des habitats degrades et des sols nus riches en metaux lourds crees par l'activite miniere est devenue aujourd'hui un enjeu environnemental majeur pour reduire l'erosion de la biodiversite et la degradation des paysages, des sols et de l'eau. Les etudes de restauration ecologique basees sur l'identification des especes sans faire reference aux traits fonctionnels des plantes sont limitees au reservoir regional des especes et rendent difficile les interpretations et les applications dans des contextes ecologiques varies. En comparant les traits fonctionnels des plantes entre l'habitat metallifere non degrade et un gradient de succession d'habitats secondaires, il est possible de definir des traits lies a la capacite de colonisation des sols nus riches en metaux lourds. Cette premiere tentative d'analyse des traits sur les habitats riches en metaux lourds permet ainsi d'identifier les traits candidats pour la phytoremediation. Un des futurs challenges est de creer de nouveaux ecosystemes fonctionnels sur les sols nus contamines par les metaux lourds en
Au Katanga, Republique Democratique du Congo, les affleurements metalliferes naturels supportent une vegetation et une flore (flore du cuivre) uniques recelant des especes endemiques metallophytes. L'industrie miniere endommage severement les ecosystemes et, au-dela de la perte en biodiversite qu'une telle activite entraine, presente un risque pour la sante publique. De ce fait, la majorite des endemiques metallophytes de la flore du cuivre sont desormais considerees comme des taxa en danger critique d'extinction. Cependant, ces metallophytes representent un patrimoine biologique remarquable, d'autant plus qu'elles sont maintenant considerees comme des elements cles pour le developpement de technologies vertes visant a fixer ou depolluer des sols contamines en metaux. La conservation de la diversite vegetale des sols riches en metaux necessite une comprehension fine des relations sol-plantes a differentes echelles (ecosystemes, communautes et populations) afin de definir des strategies de conservation in situ et ex situ, et mettre en place le cas echeant des projets de restauration et de rehabilitation de la vegetation impactee. Le present chapitre propose une synthese des avancees scientifiques concernant la comprehension des relations sol-plantes operant au niveau des affleurements de roches de Cu et Co, et impliquees dans la conservation de la diversite des communautes, la diversite specifique et la diversite genetique. Les facteurs chimiques du sol (c'est-a-dire Cu, Co, pH, C, N, Ca, Mn et Fe), et les conditions ecologiques qu'ils generent, sont essentiels a la structuration des communautes vegetales, et leur variation est en partie responsable de l'hete-rogeneite de communautes observees a l'echelle d'un affleurement de Cu et Co. Le maintien ou la restauration de ces facteurs du sol est, de ce fait, necessaire et represente un point crucial pour la reconstruction ou la restauration des communautes vegetales des affleurements de cuivre apres exploitation. Chaque affleurement doit faire l'objet d'un plan d'action qui lui est propre de par la specificite des communautes vegetales a l'echelle des affleurements individuels
Background and aims – In Katanga (D. R. Congo), outcrops of bedrocks naturally enriched in Cu and Co ("copper hills"), host unique plant communities. The spatial variation of vegetation has long been attributed almost exclusively to variation in Cu concentration in the soil, but this assumption has not been experimentally tested. We analysed the variation in plant communities and the niches of selected species in relation to edaphic factors within a copper hill. Methods – Forty-eight 1 m 2 plots were sampled for plant community and soil mineral element composition, and classified with Unweighted Pair Group Method with Arithmetic mean (UPGMA) using the Bray-Curtis distance. Plant-edaphic relationships were examined using a Canonical Correspondence Analysis (CCA). Species niches were modelled with Generalized Additive Model (GAM). Mean edaphic factors between the soil of plant communities were compared with one-way Kruskal-Wallis non-parametric ANOVA. Key results – The diversity of communities at the site scale was higher than observed in previous studies at a larger scale. Cu was the most discriminating edaphic factor of plant communities. However, detailed comparisons of mean edaphic factors among communities revealed individual combinations of edaphic parameters for each community, as well as differences in soil Cu content. High covariation appears to be an essential trait of the edaphic factor variation of Katangan Cu-rich soils. This makes it difficult to examine separately the effect of these factors on plant community structures. A bimodal pattern of niche distribution was found for Cu and pH. For physical parameters, niche optima were normally distributed. Conclusions – Global variation in edaphic factors associated with variation in combinations of edaphic parameters generates a highly heterogeneous environment favourable to a high diversity of plant communities over limited areas. Conservation strategies or restoration actions to limit the impact of mining activities on Cu-enriched ecosystems should pay special attention to recreate heterogeneity, taking into account the covariation of edaphic factors.
An accurate description of spatial urban growth is a prerequisite step in order to implement appropriated policies to improve the ecosystem service performance of green spaces in a city. Such information is, however, absent in Lubumbashi, the second metropolis of the Democratic Republic of Congo, despite its high demographic growth rate and an unplanned spatial urban growth. This study was designed to characterize the spatial pattern of green spaces and the extent of changes driven by the urbanization along the urban–rural gradient using a combination of landscape metrics and floristic plots. Our results revealed that the number of patches was directly proportional to the degree of urbanization of the city, whereas the area of the green spaces and the index of the largest patch showed an inverse relationship with the urbanization degree. Urban green spaces were dominated by attached and roadside spaces that are more equipped and present a higher occurrence of cultivated plants. By contrast, peri-urban green spaces were characterized by buffer zones, fields, abandoned areas, and informal spaces, with an elevated proportion of invasive species and natural vegetation. Moreover, it was found that the number of exotic species increased with the degree of urbanization, reaching values considered a threat to the indigenous flora. The current results underline the need for urgent measures oriented both toward increasing the spatial connectivity between green spaces (e.g., by creating new green spaces planted with indigenous species) while reducing the spread of invasive species in the city.
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