Overcoming biotic homogenization in ecological restoration

Dissimilar forests along the Rio Doce watershed call for multiple restoration references to avoid biotic homogenization

An environmental disaster caused by the rupture of a mining tailings dam has impacted a large area of the Rio Doce watershed in the Brazilian Atlantic Forest, resulting in unprecedented damage at spatial and temporal scales. The Atlantic Forest is one of the world's most important biodiversity hotspots. A long history of land use conversion has resulted in a highly fragmented landscape. Despite numerous restoration initiatives, these efforts have often biased criteria and use limited species assemblages. We conducted a comprehensive synthesis of the plant community in riparian forests along the Rio Doce watershed. Our work detailed vegetation composition (tree and sapling strata) and examined its relationship with edaphic and landscape factors, aiming to inform restoration projects with scientifically robust knowledge. A total of 4906 individuals from the tree strata and 4565 individuals from the sapling strata were recorded, representing a total of 1192 species from 75 families. Only 0.8% of the tree species and 0.5% of the sapling species occurred in all sampled sectors, with over 84% of the species occurring in a single watershed sector for both strata. We observed a high species heterogeneity modulated by turnover (92.3% in the tree, and 92.7% in the sapling strata) among sites. Overall, our research revealed a gradient of soil fertility influencing species composition across different strata. Additionally, we discovered that preserved landscapes had a positive impact on species diversity within both strata. The species exclusivity in the sampled sites and the high turnover rate imply the need to consider multiple reference ecosystems when restoring the watershed to reduce the risk of biotic homogenization. Finally, the reference ecosystems defined here serve as a basis for the selection of locally particular species in the implementation of restoration projects that aim to improve biodiversity, ecosystem services, and water security.

Hierarchical diversity partitioning of microscopic epibiont community on intertidal molluscan shells and inert surfaces over three geographic regions in Japan

Microscopic epibionts on molluscan shells are a component of the biodiversity of intertidal coastal areas. Because molluscan shells are discrete habitats for the epibiont community, and the molluscan basibionts belong to the local community, epibiont diversity can be evaluated hierarchically by basibiont categories including species. To evaluate the structure of epibiont diversity and effects of taxonomic resolution on the evaluation, epibionts on molluscan shells and inert surfaces were investigated at three geographically distant sites in Japan. In total, 94 species-level taxonomic units of epibionts were obtained from 31 basibiont molluscan species and inert surfaces (plastics and rock chips). The density and the species richness at the site of the lowest latitude were significantly lower than those at the other sites. The epibiont community differed between the three sites, although the major portion of the epibionts were diatoms. Between-site diversity contributed most of the total diversity of the species richness and Simpson diversity in the five levels of the hierarchical partitioning: sample (individual basibiont), basibiont species (molluscan species), surface group (bivalves, chitons + limpets, and globose gastropods), site, and the total. The taxonomic resolution did not markedly affect the variability of communities between the three sites, although the taxon richness was reduced to 51 in the genus-level analysis. The lower taxonomic resolution (genus level); however, increased the contribution of the within-sample and decreased the contribution of β diversities at the higher hierarchies, leading to a possible overestimation of biotic homogenization between the communities.

Restoration age affects microbial-herbaceous plant interactions in an oak woodland

In degraded ecosystems, soil microbial communities (SMCs) may influence the outcomes of ecological restoration. Restoration practices can affect SMCs, though it is unclear how variation in the onset of restoration activities in woodlands affects SMCs, how those SMCs influence the performance of hard-to-establish woodland forbs, and how different woodland forbs shape SMCs. In this study, we quantified soil properties and species abundances in an oak woodland restoration chronosequence (young, intermediate, and old restorations). We measured the growth of three woodland forb species when inoculated with live whole-soil from young, intermediate, or old restorations. We used DNA metabarcoding to characterize SMCs of each inoculum treatment and the soil after conditioning by each plant species. Our goals were to (1) understand how time since the onset of restoration affected soil abiotic properties, plant communities, and SMCs in a restoration chronosequence, (2) test growth responses of three forb species to whole-soil inoculum from restoration sites, and (3) characterize changes in SMCs before and after conditioning by each forb species. Younger restored woodlands had greater fire-sensitive tree species and lower concentrations of soil phosphorous than intermediate or older restored woodlands. Bacterial and fungal soil communities varied significantly among sites. Forbs exhibited the greatest growth in soil from the young restoration. Each forb species developed a unique soil microbial community. Our results highlight how restoration practices affect SMCs, which can in turn affect the growth of hard-to-establish forb species. Our results also highlight that the choice of forb species can alter SMCs, which could have long-term potential consequences for restoration success.

Interacting ecological filters influence success and functional composition in restored plant communities over time

A trait-based community assembly framework has great potential to direct ecological restoration, but uncertainty over how traits and environmental factors interact to influence community composition over time limits the widespread application of this approach. In this study, we examined how the composition of seed mixes and environment (north- vs. south-facing slope aspect) influence functional composition and native plant cover over time in restored grassland and shrubland communities. Variation in native cover over 4 years was primarily driven by species mix, slope aspect, and a species mix by year interaction rather than an interaction between species mix and slope aspect as predicted. Although native cover was higher on wetter, north-facing slopes for most of the study, south-facing slopes achieved a similar cover (65%-70%) by year 4. While community-weighted mean (CWM) values generally became more resource conservative over time, we found shifts in particular traits across community types and habitats. For example, CWM for specific leaf area increased over time in grassland mixes. Belowground, CWM for root mass fraction increased while CWM for specific root length decreased across all seed mixes. Multivariate functional dispersion remained high in shrub-containing mixes throughout the study, which could enhance invasion resistance and recovery following disturbance. Functional diversity and species richness were initially higher in drier, south-facing slopes compared to north-facing slopes, but these metrics were similar across north- and south-facing slopes by the end of the 4-year study. Our finding that different combinations of traits were favored in south- and north-facing slopes and over time demonstrates that trait-based approaches can be used to identify good restoration candidate species and, ultimately, enhance native plant cover across community types and microhabitat. Changing the composition of planting mixes based on traits could be a useful strategy for restoration practitioners to match species to specific environmental conditions and may be more informative than using seed mixes based on growth form, as species within functional groups can vary tremendously in leaf and root traits.

Achieving zero extinction for land plants

Despite the importance of plants for humans and the threats to their future, plant conservation receives far less support compared with vertebrate conservation. Plants are much cheaper and easier to conserve than are animals, but, although there are no technical reasons why any plant species should become extinct, inadequate funding and the shortage of skilled people has created barriers to their conservation. These barriers include the incomplete inventory, the low proportion of species with conservation status assessments, partial online data accessibility, varied data quality, and insufficient investment in both in and ex situ conservation. Machine learning, citizen science (CS), and new technologies could mitigate these problems, but we need to set national and global targets of zero plant extinction to attract greater support.

Looking back on biodiversity change: lessons for the road ahead

Estimating biodiversity change across the planet in the context of widespread human modification is a critical challenge. Here, we review how biodiversity has changed in recent decades across scales and taxonomic groups, focusing on four diversity metrics: species richness, temporal turnover, spatial beta-diversity and abundance. At local scales, change across all metrics includes many examples of both increases and declines and tends to be centred around zero, but with higher prevalence of declining trends in beta-diversity (increasing similarity in composition across space or biotic homogenization) and abundance. The exception to this pattern is temporal turnover, with changes in species composition through time observed in most local assemblages. Less is known about change at regional scales, although several studies suggest that increases in richness are more prevalent than declines. Change at the global scale is the hardest to estimate accurately, but most studies suggest extinction rates are probably outpacing speciation rates, although both are elevated. Recognizing this variability is essential to accurately portray how biodiversity change is unfolding, and highlights how much remains unknown about the magnitude and direction of multiple biodiversity metrics at different scales. Reducing these blind spots is essential to allow appropriate management actions to be deployed. This article is part of the theme issue 'Detecting and attributing the causes of biodiversity change: needs, gaps and solutions'.

Anthropogenic impacts on multiple facets of macroinvertebrate α and β diversity in a large river-floodplain ecosystem

Anthropogenic disturbances have become one of the primary causes of biodiversity decline in freshwater ecosystems. Beyond the well-documented loss of taxon richness in increasingly impacted ecosystems, our knowledge on how different facets of α and β diversity respond to human disturbances is still limited. Here, we examined the responses of taxonomic (TD), functional (FD) and phylogenetic (PD) α and β diversity of macroinvertebrate communities to human impact across 33 floodplain lakes surrounding the Yangtze River. We found that most pairwise correlations between TD and FD/PD were low and non-significant, whereas FD and PD metrics were instead positively and significantly correlated. All facets of α diversity decreased from weakly to strongly impacted lakes owing to the removal of sensitive species harboring unique evolutionary legacies and phenotypes. By contrast, the three facets of β diversity responded inconsistently to anthropogenic disturbance: while FDβ and PDβ showed significant impairment in moderately and strongly impacted lakes as a result of spatial homogenization, TDβ was lowest in weakly impacted lakes. The multiple facets of diversity also responded differently to the underlying environmental gradients, re-emphasizing that taxonomic, functional and phylogenetic diversities provide complementary information on community dynamics. However, the explanatory power of our machine learning and constrained ordination models was relatively low and suggests that unmeasured environmental features and stochastic processes may strongly contribute to macroinvertebrate communities in floodplain lakes suffering from variable levels of anthropogenic degradation. We finally suggested guidelines for effective conservation and restoration targets aimed at achieving healthier aquatic biotas in a context of increasing human impact across the 'lakescape' surrounding the Yangtze River, the most important being the control of nutrient inputs and increased spatial spillover effects to promote natural metasystem dynamics.

How cougars and feral donkeys change desert wetlands: Novel interactions between native predators and non-native megaherbivores shape trophic cascades in the Anthropocene

Research Highlight: Lundgren, E. J., Ramp, D., Middleton, O. S., Wooster, E. I. F., Kusch, E., Balisi, M., Ripple, W. J., Hasselerharm, C. D., Sanchez, J. N., Mills, M. & Wallach, A. D. (2022) A novel trophic cascade between cougars and feral donkeys shapes desert wetlands. Journal of Animal Ecology, (91, 2010-2022). https://doi.org/10.1111/1365-2656.13766. Despite being absent from most regions of the contemporary world, megafauna species dominated the dynamics of ecological communities until the late Pleistocene. Trophic rewilding is a promising approach to restoring megafauna interactions, their functional roles and the consequent trophic cascades. Unintentional rewilding with large non-native herbivores, such as equids, offers outstanding opportunities for ecologists to understand the outcomes of using replacement species to restore the ecological functions of extinct native megafauna. In this context, it is relevant to understand the extent to which extant native predators can impose top-down control on non-native megaherbivores and how trophic cascades arising from novel predator-prey interactions influences biodiversity and ecosystem functions. In Death Valley National Park (United States), Lundgren et al. depict a natural experiment showing compelling evidence of native cougars overcoming ecological naïveté-that is, the mismatches between predator and prey species that do not share a common evolutionary history-and are now successfully preying on younger individuals of feral donkeys. These non-native donkeys, whose growing wild populations threaten the native biota, became cougars' most frequent dietary item in that region. In areas with cougars, donkeys changed their spatiotemporal foraging patterns, becoming diurnal and less active. On the other hand, donkeys remain more active and forage throughout the day and night in areas without cougars. The cougar-donkey interaction triggered a behaviourally mediated trophic cascade emerging from a 'landscape of fear', that is, from the perception of spatial heterogeneity in predation risk by donkeys. Areas with cougars have less trampled ground, fewer donkey trails, and much more canopy cover and vegetation around water. Donkeys concentrate their activity mostly in topologically plain terrains lacking proper sites for the ambush behaviour of cougars and with more intense human presence, likely acting as a shield against the predators. Lundgren et al. present a promising model system for studying the effects of fearful grazers on community structure in the context of novel ecological interactions being established in the Anthropocene. Whether the emerging cascade is transient or persistent, the relative roles of consumptive and non-consumptive effects as underlying mechanisms, and their consequences for food web structure, functioning and stability, are questions of general interest. Addressing them can help us to elucidate the costs and benefits of using non-native megaherbivores in the functional restoration of permanently invaded ecosystems.