Grazing effects on woody and herbaceous plant biodiversity on a limestone mountain in northern Tunisia

The First Inventory of Sardinian Mining Vascular Flora

Mining activities and associated waste materials pose significant environmental challenges, including soil, water, and air contamination, along with health risks to nearby populations. Despite the harsh conditions of metal-enriched soils and nutrient-poor substrates, certain plants known as metallophytes thrive in these environments. This study examined the vascular flora of Sardinia's abandoned mining sites, with a focus on identifying metallophytes and their potential role in phytoremediation. A comprehensive floristic checklist was compiled using literature, field surveys, and herbarium samples. Of the 652 taxa identified, 49% were metallophytes, with the majority categorized as facultative species. Notably, 27% of metallophytes were identified as suitable for phytostabilization, while 20% showed potential for phytoextraction. This study also highlighted the presence of endemic and endangered species, emphasizing the need for conservation efforts. The findings suggest that native metallophytes could play a key role in the ecological restoration of mining sites, though careful consideration of invasive species is necessary to avoid ecological disruption. This research provides valuable insights into the biodiversity of Sardinian mining sites and the potential for sustainable remediation strategies using native plants.

Uncovering the multi-fencing effects: Changes in plant diversity across dimensions and spatio, and the relationship between diversity and stability

Plant diversity is fundamental to maintaining grassland ecosystem function. Rangeland managers use fencing as a strategy to enhance plant diversity in degraded grasslands. However, the effects of this natural management approach on grasslands across a wide range of environmental gradients and its spatial pattern remain unclear. This study investigated 37 pairs of fencing and grazing sites along an 1800 km transect of alpine grasslands on the Tibetan Plateau to evaluate the effects of fencing on plant species, functional, and phylogenetic alpha and beta diversity. Fencing increased plant functional and species alpha-diversity, as well as phylogenetic and functional beta-diversity by 0.20%-26.18%, but decreased species beta-diversity by 0.70%. The sensitivity of functional diversity to fencing was higher in alpine meadows than in alpine steppes and alpine desert steppes. Fencing resulted in spatial heterogeneity in plant alpha and beta diversity in alpine grasslands. The beta-diversity of plant communities in the three dimensions across all the alpine grasslands was dominated by turnover components. The response of plant diversity to fencing increased with longitude but declined with latitude and elevation. Consequently, the effects of fencing on plant diversity in Tibetan alpine grasslands are associated with grassland types and climatic conditions. Notably, fencing did not consistently yield positive outcomes for plant diversity, indicating it should be applied selectively for biodiversity restoration. Given the nonlinear relationship between diversity and ecosystem stability, it is recommended that restoration of degraded grasslands should consider not only species selection but also a balanced composition of species with varied functional and phylogenetic traits.

Effects of livestock on arthropod biodiversity in Iberian holm oak savannas revealed by metabarcoding

Increasing food production while avoiding negative impacts on biodiversity constitutes one of the main challenges of our time. Traditional silvopastoral systems like Iberian oak savannas ("dehesas") set an example, where free-range livestock has been reared for centuries while preserving a high natural value. Nevertheless, factors decreasing productivity need to be addressed, one being acorn losses provoked by pest insects. An increased and focalized grazing by livestock on infested acorns would kill the larvae inside and decrease pest numbers, but increased livestock densities could have undesired side effects on ground arthropod communities as a whole. We designed an experimental setup including areas under trees with livestock exclosures of different ages (short-term: 1-year exclusion, long-term: 10-year exclusion), along with controls (continuous grazing), using DNA metabarcoding (mitochondrial markers COI and 16S) to rapidly assess arthropod communities' composition. Livestock removal quickly increased grass cover and arthropod taxonomic richness and diversity, which was already higher in short-term (1-year exclosures) than beneath the canopies of control trees. Interestingly, arthropod diversity was not highest at long-term exclosures (≥10 years), although their community composition was the most distinct. Also, regardless of treatment, we found that functional diversity strongly correlated with the vegetation structure, being higher at trees beneath which there was higher grass cover and taller herbs. Overall, the taxonomic diversity peak at short term exclosures would support the intermediate disturbance hypothesis, which relates it with the higher microhabitat heterogeneity at moderately disturbed areas. Thus, we propose a rotatory livestock management in dehesas: plots with increased grazing should co-exist with temporal short-term exclosures. Ideally, a few long-term excluded areas should be also kept for the singularity of their arthropod communities. This strategy would make possible the combination of biological pest control and arthropod conservation in Iberian dehesas.

Biotic homogenisation and differentiation as directional change in beta diversity: synthesising driver-response relationships to develop conceptual models across ecosystems

Biotic homogenisation is defined as decreasing dissimilarity among ecological assemblages sampled within a given spatial area over time. Biotic differentiation, in turn, is defined as increasing dissimilarity over time. Overall, changes in the spatial dissimilarities among assemblages (termed 'beta diversity') is an increasingly recognised feature of broader biodiversity change in the Anthropocene. Empirical evidence of biotic homogenisation and biotic differentiation remains scattered across different ecosystems. Most meta-analyses quantify the prevalence and direction of change in beta diversity, rather than attempting to identify underlying ecological drivers of such changes. By conceptualising the mechanisms that contribute to decreasing or increasing dissimilarity in the composition of ecological assemblages across space, environmental managers and conservation practitioners can make informed decisions about what interventions may be required to sustain biodiversity and can predict potential biodiversity outcomes of future disturbances. We systematically reviewed and synthesised published empirical evidence for ecological drivers of biotic homogenisation and differentiation across terrestrial, marine, and freshwater realms to derive conceptual models that explain changes in spatial beta diversity. We pursued five key themes in our review: (i) temporal environmental change; (ii) disturbance regime; (iii) connectivity alteration and species redistribution; (iv) habitat change; and (v) biotic and trophic interactions. Our first conceptual model highlights how biotic homogenisation and differentiation can occur as a function of changes in local (alpha) diversity or regional (gamma) diversity, independently of species invasions and losses due to changes in species occurrence among assemblages. Second, the direction and magnitude of change in beta diversity depends on the interaction between spatial variation (patchiness) and temporal variation (synchronicity) of disturbance events. Third, in the context of connectivity and species redistribution, divergent beta diversity outcomes occur as different species have different dispersal characteristics, and the magnitude of beta diversity change associated with species invasions also depends strongly on alpha and gamma diversity prior to species invasion. Fourth, beta diversity is positively linked with spatial environmental variability, such that biotic homogenisation and differentiation occur when environmental heterogeneity decreases or increases, respectively. Fifth, species interactions can influence beta diversity via habitat modification, disease, consumption (trophic dynamics), competition, and by altering ecosystem productivity. Our synthesis highlights the multitude of mechanisms that cause assemblages to be more or less spatially similar in composition (taxonomically, functionally, phylogenetically) through time. We consider that future studies should aim to enhance our collective understanding of ecological systems by clarifying the underlying mechanisms driving homogenisation or differentiation, rather than focusing only on reporting the prevalence and direction of change in beta diversity, per se.