Abstract
AbstractAimThe loss of biodiversity has raised serious concerns about the entailing losses of ecosystem services. Here, we explore the potential of repeated habitat mapping data to identify floristic changes over time. Using one German federal state as a case study, we assessed floristic changes between the 1980s and 2010s. These habitat data have great potential for analysis because of their high spatial coverage while also posing methodological challenges such as incomplete observation data. We developed a modelling approach that accounts for incomplete observations and explored the ability to detect temporal trends.LocationThe Federal State of Schleswig‐Holstein (Germany)MethodsWe compiled plant species lists from the earliest (1980s) and most recent (2010s) habitat mapping survey and aligned differing habitat definitions across mapping campaigns. A total of 5,503 mapped polygons, each with a list of species records, intersected the two surveys. We accounted for underrecorded species by assigning occurrence probabilities, based on species co‐occurrence information across all surveys, using Beals' index and tested the robustness of this approach by simulation experiments. For those species with significant increases and decreases in occurrence probability, we linked these trends to the species' functional characteristics.ResultsWe found a systematic loss of species that are moderately threatened. Species that indicate low nitrogen supply and high soil moisture declined, suggesting a shift towards a more eutrophic and drier landscape. Importantly, assessing specific plant traits associated with losses, we also detected a decrease in species with reddish and blueish flowers and species providing nectar, pointing to a decrease of insect‐pollinated taxa.Main conclusionsThe identified changes raise concerns that plant biodiversity has fundamentally changed over the last three decades, with concomitant consequences for ecosystem services, especially pollination. Given the general lack of historical standardized data, our approach for trend analyses using incomplete observation data may be widely applicable to assess long‐term biodiversity change.
Highlights
The state of nature has become a matter of acute public concern, both internationally and nationally
While expert-based assessment clearly supports the view that biodiversity is declining in Germany (Bundesamt für Naturschutz, 2009– 2016; Bundesamt für Naturschutz, 2019; Nationale Akademie der Wissenschaften Leopoldina, 2018), only a limited number of taxa have been the subject of repeated field sampling (e.g. Hallmann et al, 2017; Meyer et al, 2013; Schuch, Bock, et al, 2012), and all studies have a very limited spatial extent
This situation of heterogeneous biodiversity records applies to many other regions worldwide, which has resulted in considerable uncertainties in the assessment of global biodiversity trends (Díaz et al, 2019)
Summary
The state of nature has become a matter of acute public concern, both internationally and nationally. In addition to different monitoring schemes among federal states, trend analyses are hampered by changes over time in field survey assessment methods, resulting in heterogeneous data sets. Assessing floristic changes based on repeated habitat mapping has so far not been considered feasible One such survey with extensive, if incomplete, species lists, with a focus on the habitat-typical species, is the habitat mapping scheme of the Federal State of Schleswig-Holstein. This would have implications for many other countries, for example those under EU reporting needs for Habitats Directive, as most countries do not have standardized repeated sampling for most taxa. We clearly point out the challenges and limitations in the discussion
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