Biology subjects

Hahs, A. K.

Publications and source records attributed to Hahs, A. K..

6 recordsLinked to original sources

bioRxiv2025

The Lawn is Buzzing: Increasing insect biodiversity in urban greenspaces through low-intensity mowing

Greenspaces have become the anvil where stewards and practitioners are forging innovative, evidence-based actions to meet biodiversity targets in urban environments, catalysing a wave of co-designed research/practice projects aimed at assessing the ecological changes brought about by urban greening and generating the evidence that biodiversity objectives are being met. Their full potential often remains unrealised due to entrenched management practices, as best exemplified by high-intensity mowing, which has given rise to the most ubiquitous greenspaces feature worldwide: the turfgrass lawn. Lawns are notoriously deficient at supporting insect communities due to their simplified vegetation structure and low plant diversity, and the compounded effect of frequent mowing on forb growth, which limits their capacity to come into flower and supply floral resources to pollinators and other flower visitors. Addressing these shortcomings can be readily achieved by reducing mowing intensity, resulting in greater vegetation height, flower cover and plant diversity - effectively transforming lawns into a more complex grassland-type ecosystem. This approach is particularly enticing to practitioners pursuing positive, cost-effective biodiversity outcomes while upholding their commitment to core ecological restoration and biodiversity conservation projects. Here, we demonstrate how transitioning a lawn from high-to low-intensity mowing regimes led to pronounced increases in the number of indigenous insect species, evident both for the whole community and on assemblages of functionally similar species, including detritivores, herbivores, predators, parasitoids and pollinators. We further identify a positive effect of vegetation height on the community and species-specific probabilities of occurrence of indigenous species, which was consistently strong for detritivores, herbivores and parasitoids. We also show that the number of indigenous species associated with our low-intensity mowing treatment markedly exceeded that of 43 high-intensity mowed lawns previously surveyed throughout the study area, and that the effect of vegetation height across our field experiment gradient was substantially stronger than that of the existing high-intensity lawns gradient. Our findings provide compelling evidence that reducing lawn mowing intensity yields positive ecological outcomes for functionally diverse indigenous insect communities, charting a course for stakeholders tasked with demonstrating how evidence-based greening actions can be a sound investment to meet local, regional and global biodiversity targets.

ecology↗

bioRxiv2024

Attracting indigenous pollinators to urban greenspaces

Urban greening actions across the world are being carried out to support resident, rare and locally extinct insect pollinators. In parallel, an array of best-practise resources have been designed to support build-environment practitioners and professionals seeking to or tasked with implementing greening actions for pollinators. Three main themes permeate these resources: (1) small greenspaces can provide large ecological benefits; (2) high-quality pollinator habitat should include a large share of indigenous plant species; and (3) considering stakeholders aspirations, motivations, experience, and concerns is critical for designing effective actions. Despite high interest in implementing these actions, few projects have evaluated their ecological benefits or demonstrated achievement of specific objectives. Even fewer have been specifically co-designed by practitioners and researchers to bridge the science-practice gap. Here, we demonstrate the success of a co-designed greening action in attracting indigenous pollinators to an urban greenspace. We compiled a plant-pollinator interactions dataset in a public park, within a densely urbanised municipality, that was purposefully greened with indigenous plant species to support existing and attract new indigenous pollinators. We then assessed: (1) how pollinator species richness and species-specific occupancy varied amongst plant species, and how these metrics compared between the existing greenspace plant species and the new added indigenous ones; (2) the effect of flower cover of the added indigenous plant species on the probabilities of occurrence of indigenous and introduced pollinators; and (3) the effect of the added indigenous plant species on the structure of the greenspace plant-pollinator ecological network. An addition of only six indigenous plant species resulted in a 2.5-fold increase in the number of indigenous pollinator species and other flower-visiting insects observed in the park. The added indigenous plants established interactions with all the indigenous pollinators and remarkably almost half of these were found interacting exclusively with the added indigenous plants. Additionally, the number of indigenous pollinators associated with a given plant species was on average 3.5 times higher for the added indigenous plants than for the baseline ones and the probabilities of occurrence of indigenous pollinators were on average invariable higher in the added indigenous than in the baseline plant species. The plant and insect community changes sparked by the greening action resulted in concomitant changes to the structure of the sites plant-pollinator network. We found an average 4.2-fold increase in the number of interactions linking the greened compared to the baseline network, with almost half of these interactions comprising those between the added indigenous plants and indigenous pollinators. By showing that replacing lawn with indigenous plants leads to positive ecological outcomes for indigenous pollinators and other flower-visiting insects - including increasing the overall greenspace biodiversity by attracting new indigenous insect species to the site - our findings contribute to the evidence base underpinning best-practise resources and provide encouragement to build-environment practitioners and professionals responsible for or endeavouring to support existing or bringing insect pollinators back into our cities. Our study establishes a pathway and acts as a catalyst for researchers and government officials seeking to collaboratively demonstrate that greening is a valuable and sound investment for achieving goals from local, regional and global biodiversity and sustainability plans and policies.

ecology↗

bioRxiv2023

Urbanisation generates multiple trait syndromes for terrestrial taxa worldwide

Cities can host significant biological diversity. Yet, urbanisation leads to the loss of habitats and, potentially, to local extinctions. Understanding how multiple taxa respond to urbanisation globally is essential to promote and conserve biodiversity in cities and surrounding landscapes. Using a dataset with site-level occurrence and trait data of 5302 species from six terrestrial fauna taxonomic groups across 379 cities on 6 continents, we show that urbanisation produces taxon-specific changes in trait composition, with traits related to reproductive strategy consistently showing the strongest response. The effect of urbanisation on community trait composition is strongest at the largest spatial scale considered, and more closely linked to landscape composition (% urban) than arrangement (aggregation), although latitude and climatic variables remain a stronger influence. This study did not find evidence in support of a global urban taxa syndrome, but instead we suggest that there are four general urban trait syndromes, with resources associated with reproduction and diet likely to be driving patterns in traits associated with mobility and body size. Functional diversity measures showed a wide range of responses, leading to a shift in trait space that is most likely driven by the distribution and abundance of critical resources, and the urban trait syndrome displayed by individual species within a community. Further research is required to understand the interactions between the four general urban trait syndromes, resource distribution and abundance and changes in functional diversity of taxa at different spatial and temporal scales. Maximising opportunities to support species within taxa groups with different urban trait syndromes should be pivotal in conservation and management programmes within and among cities. This will reduce the likelihood of biotic homogenisation at the taxa level, and helps ensure that urban environments have the ecological capacity to respond to challenges such as climate change, further habitat fragmentation and loss, and other disruptions. These actions are critical if we are to reframe the role of cities in global biodiversity loss.

ecology↗

bioRxiv2022

The City Nature Challenge - A global citizen science phenomenon contributing to biodiversity knowledge and informing local government practices

The bioblitz phenomenon has recently branched into cities, presenting exciting opportunities for local governments to channel participants efforts toward local issues. The City Nature Challenge (CNC) is one such initiative that has been quickly uptaken by hundreds of municipalities worldwide. Despite high participation, we still lack a framework for evaluating how the CNC contributes to local biodiversity knowledge and to inform local government practices. Here, we develop such a tool and present a case study that illustrates its applicability. We demonstrate that the collected records contributed to a better understanding of contemporary, local biodiversity patterns and provided a more realistic representation of understudied groups such as insects and fungi. Importantly, we show that the CNC presented local governments with a cost-effective tool to make informed, evidence-based management and policy decisions, improve education and engagement programs, foster cross-council collaborations, and support a stronger sense of environmental stewardship within the local community.

scientific communication and education↗

bioRxiv2021

Large positive ecological changes of small urban greening actions

The detrimental effects of human-induced environmental change on people and other species are acutely manifested in urban environments. While urban greenspaces are known to mitigate these effects and support functionally diverse ecological communities, evidence of the ecological outcomes of urban greening remains scarce. We use a longitudinal observational design to provide empirical evidence of the putative ecological benefits of greening actions. We show how a small greening action quickly led to large positive changes in the richness, demographic dynamics, and network structure of a depauperate insect community. An increase in the diversity and complexity of the plant community led to, after only three years, a large increase in insect species richness, a greater probability of occurrence of insects within the greenspace, and a higher number and diversity of interactions between insects and plant species. We demonstrate how large ecological benefits may be derived from investing in small greening actions and how these contribute to bring indigenous species back to greenspaces where they have become rare or locally extinct. Our findings provide crucial evidence that support best practice in greenspace design and contribute to re-invigorate policies aimed at mitigating the negative impacts of urbanisation on people and other species.

ecology↗

bioRxiv2020

Indigenous plants promote insect biodiversity in urban greenspaces

The contribution of urban greenspaces to support biodiversity and provide benefits for people is increasingly recognised. However, ongoing management practices still favour (1) vegetation oversimplification, often limiting greenspaces to lawns and tree canopy rather than multi-layered vegetation that includes under and midstorey; and (2) the use of nonnative plant species. These practices likely hinder the potential of greenspaces to sustain indigenous biodiversity, particularly for taxa like insects, that rely on plants for food and habitat. Yet, little is known about which plant species may maximise positive outcomes for taxonomically and functionally diverse insect communities in urban greenspaces. Additionally, while urban environments are expected to experience high rates of introductions, quantitative assessments of the relative occupancy of indigenous vs. introduced insect species in greenspace are rare - hindering understanding of how greenspace management may promote indigenous biodiversity while limiting the establishment of introduced insects. Using a hierarchically replicated study design across 15 public parks, we recorded occurrence data from 552 insect species on 133 plant species - differing in planting design element (lawn, midstorey and tree canopy), midstorey growth form (forbs, lilioids, graminoids and shrubs) and origin (nonnative, native and indigenous) - to assess: (1) the relative contributions of indigenous and introduced insect species and (2) which plant species sustained the highest number of indigenous insects. Our data indicates that the insect community was predominately composed of indigenous rather than introduced species. Our findings further highlight the core role of multi-layered vegetation in sustaining high insect biodiversity in urban areas, with indigenous midstorey and canopy representing key elements to maintain rich and functionally diverse indigenous insect communities. Intriguingly, graminoids supported the highest indigenous insect richness across all studied growth forms by plant origin groups. Taken together, our study emphasise the opportunity posed by indigenous understory and midstorey plants, particularly indigenous graminoids in our study area, to promote indigenous insect biodiversity in urban greenspaces. Our work provides a blueprint and stimulus for built-environment professionals to incorporate into their practice plant species palettes that foster a larger presence of indigenous over regionally native or nonnative plant species, whilst incorporating a broader mixture of midstorey growth forms.

ecology↗