Competing drivers lead to non-linear native–exotic relationships in endangered temperate grassy woodlands

Evaluating models of expert judgment to inform assessment of ecosystem viability and collapse

Expert judgment underpins assessment of threatened ecosystems. However, experts are often narrowly defined, and variability in their judgments may be substantial. Models built from structured elicitation with large diverse expert panels can contribute to more consistent and transparent decision-making. We conducted a structured elicitation under a broad definition of expertise to examine variation in judgments of ecosystem viability and collapse in a critically endangered ecosystem. We explored whether variation in judgments among 83 experts was related to affiliation and management expertise and assessed performance of an average model based on common ecosystem indicators. There were systematic differences among individuals, much of which were not explained by affiliation or expertise. However, of the individuals affiliated with government, those in conservation and environmental departments were more likely to determine a patch was viable than those in agriculture and rural land management. Classification errors from an average model, in which all individuals were weighted equally, were highest among government agriculture experts (27%) and lowest among government conservation experts (12%). Differences were mostly cases in which the average model predicted a patch was viable but the individual thought it was not. These differences arose primarily for areas that were grazed or cleared of mature trees. These areas are often the target of restoration, but they are also valuable for agriculture. These results highlight the potential for conflicting advice and disagreement about policies and actions for conserving and restoring threatened ecosystems. Although adoption of an average model can improve consistency of ecosystem assessment, it can fail to capture and convey diverse opinions held by experts. Structured elicitation and models of ecosystem viability play an important role in providing data-driven evidence of where differences arise among experts to support engagement and discussion among stakeholders and decision makers and to improve the management of threatened ecosystems.

Wildlife policy, the food system and One Health: a complex systems analysis of unintended consequences for the prevention of emerging zoonoses in China, the Democratic Republic of the Congo and the Philippines

INTRODUCTION

Evolving human-wildlife interactions have contributed to emerging zoonoses outbreaks, and pandemic prevention policy for wildlife management and conservation requires enhanced consideration from this perspective. However, the risk of unintended consequences is high. In this study, we aimed to assess how unrecognised complexity and system adaptation can lead to policy failure, and how these dynamics may impact zoonotic spillover risk and food system outcomes.

METHODOLOGY

This study focused on three countries: China, the Democratic Republic of the Congo (DRC) and the Philippines. We combined evidence from a rapid literature review with key informant interviews to develop causal loop diagrams (CLDs), a form of systems map representing causal theory about system factors and interconnections. We analysed these CLDs using the 'fixes that fail' (FTF) systems archetype, a conceptual tool used to understand and communicate how system adaptation can lead to policy failure. In each country, we situated the FTF in the wider system of disease ecology and food system factors to highlight how zoonotic risk and food system outcomes may be impacted.

RESULTS

We interviewed 104 participants and reviewed 303 documents. In each country, we identified a case of a policy with the potential to become an FTF: wildlife farming in China, the establishment of a new national park in the DRC, and international conservation agenda-setting in the Philippines. In each country, we highlighted context-specific impacts of the FTF on zoonotic spillover risk and key food system outcomes.

CONCLUSION

Our use of systems thinking highlights how system adaptation may undermine prevention policy aims, with a range of unintended consequences for food systems and human, animal and environmental health. A broader application of systems-informed policy design and evaluation could help identify instruments approporiate for the disruption of system traps and improve policy success. A One Health approach may also increase success by supporting collaboration, communication and trust among actors to imporove collective policy action.

Indirect and direct drivers of floristic condition in a threatened temperate woodland

Almost half of Earth's surface is threatened by agriculture, which has extensively degraded ecosystems and resulted in significant biodiversity loss. Remnant ecosystems in fragmented agricultural landscapes are threatened by past and present grazing and land-clearing. Declines in native diversity are common in these ecosystems, and their restoration is a key conservation goal globally. Understanding the drivers of change in floristic condition, reflecting continuity in floristic composition towards native plant communities, is fundamental to inform effective restoration practice. Previous investigations have demonstrated abiotic and biotic drivers of floristic condition independently. However, few consider the combined influence of these drivers on floristic condition, or the interactions between them, which may mediate indirect effects (e.g. plant-soil interactions). Despite this, ecological interactions may underpin changes in floristic condition, and provide critical insights needed to inform restoration. Here, we use structural equation modelling to disentangle the relationships between plants, soils and grass and litter biomass (leaf litter and fine woody debris) to elucidate the direct and indirect drivers of floristic condition in some of the most degraded landscapes globally: the critically endangered box-gum grassy woodlands in south-eastern Australia. We identify divergent plant-soil interactions between native versus exotic plants to key soil properties including soil nitrate and phosphorus. Specifically, native plants were negatively associated with increasing soil fertility, which favored exotic species. We also found evidence of indirect effects on floristic condition, mediated through interactions between litter biomass, soils and the basal area of overstorey trees. Our findings highlight the major role of soils in shaping floristic condition through direct and indirect pathways, and the role of multivariate interactions in mediating these pathways in a highly degraded, critically endangered ecosystem. Effective restoration must therefore consider the multivariate direct and indirect drivers of ecological condition to maximise positive outcomes in these landscapes and those similar.

The differences in plant invasion in two types of shorelines under flow regulation of the Three Gorges Reservoir

Riparian zones, crucial for linking fluvial and terrestrial habitats, are among the most diverse ecosystems. However, they are intensively invaded by alien plants, particularly in dam-regulated rivers. Therefore, understanding the mechanisms underlying plant invasion in dam-regulated river systems has become increasingly important, given that over two-thirds of global rivers are artificially regulated. Regulated rivers may flood upland areas or pristine riparian zones, resulting in shorelines developed from pre-upland and pre-riparian areas. However, differences in invasion intensities, adaptive strategies of invasive plants, and native species' resistance (namely the diversity-invasibility relationship) across these shorelines are unclear. To address these uncertainties, we performed field investigations in the Three Gorges Reservoir (TGR) on the upper Yangtze River, where both pre-upland and pre-riparian shorelines are present. Our findings indicate that pre-upland shorelines are more intensively invaded, showing higher relative richness and cover of invasive species. Invasive plants in this area displayed more conservative resource strategies and greater drought tolerance, exhibiting lower community-weighted mean (CWM) specific leaf area, higher CWM leaf dry mass content, and larger CWM seed mass. Pre-upland shorelines' invasibility decreased as the richness and cover of native species increased, a trend not observed in pre-riparian shorelines. The observed variations in plant invasion between the two shoreline types are primarily driven by differences in resident plant presence, soil moisture levels, and hydrological disturbances. This study provides valuable insights for policymakers and practitioners involved in managing invasive plants in regulated river ecosystems.

Identifying thresholds in the impacts of an invasive groundcover on native vegetation

Impacts of invasive species are often difficult to quantify, meaning that many invaders are prioritised for management without robust, contextual evidence of impact. Most impact studies for invasive plants compare heavily invaded with non-invaded sites, revealing little about abundance–impact relationships. We examined effects of increasing cover and volume of the non-native herbaceous groundcover Tradescantia fluminensis on a temperate rainforest community of southern Australia. We hypothesised that there would be critical thresholds in T. fluminensis abundance, below which the native plant community would not be significantly impacted, but above which the community’s condition would degrade markedly. We modelled the abundance–impact relationship from 83 plots that varied in T. fluminensis abundance and landscape context and found the responses of almost all native plant indicators to invasion were non-linear. Native species richness, abundance and diversity exhibited negative exponential relationships with increasing T. fluminensis volume, but negative threshold relationships with increasing T. fluminensis cover. In the latter case, all metrics were relatively stable until cover reached between 20 and 30%, after which each decreased linearly, with a 50% decline occurring at 75–80% invader cover. Few growth forms (notably shrubs and climbers) exhibited such thresholds, with most exhibiting negative exponential relationships. Tradescantia fluminensis biomass increased dramatically at > 80% cover, with few native species able to persist at such high levels of invasion. Landscape context had almost no influence on native communities, or the abundance–impact relationships between T. fluminensis and the plant community metrics. Our results suggest that the diversity of native rainforest community can be maintained where T. fluminensis is present at moderate-to-low cover levels.

Regional climate and local-scale biotic acceptance explain native-exotic richness relationships in Australian annual plant communities

Native and exotic species richness is expected to be negatively related at small spatial scales where individuals interact, and positive at larger spatial scales as a greater variety of habitats are sampled. However, a range of native-exotic richness relationships (NERRs) have been reported, including positive at small scales and negative at larger scales. We present a hierarchical metacommunity framework to explain how contrasting NERRs may emerge across scales and study systems, and then apply this framework to NERRs in an invaded winter annual plant system in southwest Western Australia. We analysed NERRs at increasing spatial scales from neighbourhoods (0.09 m²) to communities (225 m²) to metacommunities (greater than 10 ha) within a multilevel structural equation model. In contrast to many previous studies, native and exotic richness were positively related at the neighbourhood scale and were not significantly associated at larger scales. Heterogeneity in soil surface properties was weakly, but positively, associated with native and exotic richness at the community scale. Metacommunity exotic richness increased strongly with regional temperature and moisture availability, but relationships for native richness were negative and much weaker. Thus, we show that neutral NERRs can emerge at larger scales owing to differential climatic filtering of native and exotic species pools.

Weed abundance is positively correlated with native plant diversity in grasslands of southern Australia

Weeds are commonly considered a threat to biodiversity, yet interactions between native and exotic species in grasslands are poorly understood and reported results vary depending on the spatial scale of study, the factors controlled for and the response variables analysed. We tested whether weed presence and abundance is related to declines in biodiversity in Australian grasslands. We employed existing field data from 241 plots along a disturbance gradient and correlated species richness, cover and Shannon diversity for natives and exotics, controlling for seasonal rainfall, climatic gradients and nutrient status. We found no negative relationships in terms of emergent diversity metrics and occupation of space, indeed, many positive relationships were revealed. When split by land-use, differences were found along the disturbance gradient. In high-moderately disturbed grasslands associated with land-uses such as cropping and modified pastures, positive associations were enhanced. Tolerance and facilitation mechanisms may be involved, such as complementary roles through different life history strategies: the exotic flora was dominated mainly by annual grasses and herbs whereas the native flora represented more diverse growth-forms with a higher proportion of perennials. The positive relationships existing between native and exotic plant species in high-moderately disturbed grasslands of South Australia are most likely due to facilitation through different strategies in occupation of space given that the effect of habitat suitability was controlled for by including environmental and disturbance factors. Consequently, although particular weeds may negatively impact biodiversity, this cannot be generalised and management focusing on general weed eradication in grasslands might be ineffectual.