Biology subjects

Hertzog, L.

Publications and source records attributed to Hertzog, L..

4 recordsLinked to original sources

bioRxiv2025

Plant diversity promotes aboveground arthropods and associated functions despite arthropod loss over time

Arthropods comprise the majority of terrestrial biodiversity and play key roles in ecosystem functioning. Biodiverse grasslands support many arthropods, yet such ecosystems have declined due to land conversion and management changes. While restoration aims to conserve species-rich grasslands, long-term effects of plant richness on arthropod communities and associated functions remain underexplored. We addressed this gap by quantifying arthropods, herbivory, and predation over 13 years (2010-2022) across 80 grassland plots with varying plant richness. We examined (1) temporal trends in arthropod communities, herbivory and predation and whether changes depended on plant richness, (2) whether plant richness effects varied or strengthened over time, and (3) whether arthropod changes affected associated functions. Arthropod metrics declined over time across all plant richness levels, with average losses mainly being more pronounced in species-poor mixtures. Plant richness consistently had a positive effect on arthropods and their functions, although this effect varied between years without a consistent temporal trend. Notably, temporal changes in arthropod community metrics did not predict shifts in associated functions. Our findings highlight the dynamic interplay between plant richness and arthropods. From a conservation perspective, we can conclude that diversification in grasslands- the increase in plant diversity- directly supports arthropods and associated functions. Additionally, first trends indicate that the maintenance and protection of diverse semi-natural grasslands over a long period might mitigate the arthropod loss driven by environmental changes. In other words, diverse grasslands may buffer against the ongoing arthropod loss, though this effect may take years to become apparent. This again emphasizes the long-term nature of conservation efforts.

ecology↗

bioRxiv2024

Turning point in forest productivity revealed from 40 years of national forest inventory data

Aim: Global changes, such as changing climate or disruption in biogeochemical cycles, are affecting forest productivity worldwide. Trends in productivity are depending on the focal spatial scale and on the considered time window, stable trends at large spatial scale can mask divergence at smaller scale while short time windows limit the capacity to reveal non-linear trends such as turning points. Capitalizing on 40 years of national forest inventory data from more than 100 tree species we explored trends in forest productivity at the regional level across 4 biogeographical regions. Location: France Time period: 1978-2022 Major taxa studied: 146 tree species Methods: We fitted two classes of models, a first one explicitly estimating temporal trends and a second one including no temporal components but climatic variables reflecting changing temperature and water availability. Results: We find a decrease in productivity in 95% of the regions and a high contrast in trend shapes between regions over the period studied: lowland regions with average temperature above 11.9{degrees}C showed linear negative trends in productivity since 1985 while colder lowland regions showed hump-shaped trends with turning points between 1985 and 2005, followed by declines in productivity. In mountainous regions, average climate did not appear to be a strong mediator of trend shapes. The temporal trends were reconstituted with high fidelity from the model including only climatic variables implying that changes in temperature and water availability are likely drivers of the reported trends. Main conclusion: These results illustrate the progression during the last decades of the adverse effects of climate change on forest productivity over the European forests. They suggest the expected changes over the 21st century that will put further pressure on forest productivity, impacting forest carbon sink potential and reducing sustainable rate of timber extraction.

ecology↗

bioRxiv2021

Losses and gains of fallows drive farmland bird populations over three funding periods of the EU Common Agricultural Policy

O_LIFallow land provides habitat for threatened and declining farmland biodiversity. Policy change under the EUs Common Agricultural Policy (CAP) has been driving the area of fallows over the past decades and influenced trends in farmland biodiversity. C_LIO_LIWe analyzed the relationships between fallow land area across Germany over three CAP funding periods and species richness and abundance of farmland birds. We examined whether the strength of the relationships with fallow land area were moderated by species habitat preferences and landscape configurational complexity (edge density). We combined spatial data on fallow land area from three agricultural censuses in Germany (2007, 2010 and 2016) with country-wide farmland bird monitoring data. C_LIO_LIFarmland bird species richness and the abundance of the majority of the studied farmland bird species were positively related to increases in fallows across three CAP funding periods. The relationship of fallows with bird richness was strongest at intermediate levels of edge density. There was generally little support for a moderating effect of edge density on the relations between fallows and bird abundance. C_LIO_LIWe conclude that the loss of fallows in the period 2007 to 2016 resulted in strong declines of farmland birds. We predict that a future increase of the proportion of fallow land to 4% of the arable land, as envisaged in the German 2023-2027 CAP strategic plans, or to 10%, as foreseen in the EU Biodiversity Strategy, will lead to increases in farmland bird species richness and abundance depending on the landscape context and species-specific habitat preferences. C_LI Policy implicationsIncreasing the proportion of fallow land will likely be a key lever to stabilize and revert negative farmland bird population trends. An increase of fallow area in all but the least complex landscapes will boost farmland bird richness and abundance. Increasing the proportion of fallow land to 4% should bring farmland bird richness and abundance back to the levels observed in 2007 acknowledging that farmland bird populations were already severely depleted in 2007. A more ambitious expansion of fallow land towards 10% should be targeted towards areas that experienced the strongest loss of fallows and towards landscapes with intermediate levels of edge density.

ecology↗

bioRxiv2020

Model-based integration of citizen-science data from disparate sources increases the precision of bird population trends

AimTimely and accurate information on population trends is a prerequisite for effective biodiversity conservation. Structured biodiversity monitoring programs have been shown to track population trends reliably, but require large financial and time investment. The data assembled in a large and growing number of online databases are less structured and suffer from bias, but the number of observations is much higher compared to structured monitoring programs. Model-based integration of data from these disparate sources could capitalize on their respective strengths. LocationGermany. MethodsAbundance data for 26 farmland bird species were gathered from the standardized Common Breeding Bird Survey (CBBS) and three online databases that varied with regard to their degree of survey standardization. Population trends were estimated with a benchmark model that included only CBBS data, and five Bayesian hierarchical models integrating all data sources in different combinations. Across models, we compared consistency and precision of the predicted population trends, and the accuracy of the models. Bird species body mass, prevalence in the dataset and abundance were tested as potential predictors of the explored quantities. ResultsConsistency in predicted annual abundance indices was generally high especially when comparing the benchmark models to the integrated models without unstructured data. The accuracy of the estimated population changes was higher in the hierarchical models compared to the benchmark model but this was not related to data-integration. Precision of the predicted population trends increased as more data sources were integrated. Main conclusionsModel-based integration of data from different sources can lead to improved precision of bird population trend estimates. This opens up new opportunities for conservation managers to identify declining populations earlier. Integrating data from online databases could substantially increase sample size and thus allowing to derive trends for currently not well-monitored species, especially at sub-national scales.

ecology↗