How Well Is the Conservation Status of Alluvial and Lowland Hay Meadows Reflected in Their Plant Functional Composition?

Abstract

Questions

Species-rich grasslands in floodplain landscapes, particularly alluvial and lowland hay meadows, are of high conservation value and are protected under the European Habitats Directive as habitat types 6440 and 6510. Despite being protected, these grasslands often face an unfavourable conservation status. While the conservation status is commonly based on the number of characteristic and habitat-specific species, an unfavourable state might also have functional consequences. Thus, we asked how functional traits at the community scale are related to the community's conservation status and whether they can enhance habitat assessments beyond traditional species-based criteria. We hypothesised that community mean traits and functional diversity can reflect the conservation status, and thus, might complement the traditional assessment criteria based on characteristic species.

Location

River floodplains in Saxony-Anhalt, Germany.

Methods

We compiled vegetation plot records from river floodplains in Saxony-Anhalt from databases, classified them into habitat types and assigned the conservation status to each plot record based on the prevalence of characteristic species. We then linked the grassland's conservation status to its functional identity and diversity, structural variables and Ellenberg indicator values using community-weighted mean values as well as species diversity metrics. From those, we predicted the conservation status, employing multinomial logistic regressions. Furthermore, we used linear discriminant analysis to identify the variables that best differentiate the different levels of conservation status.

Results

Communities with a favourable conservation status displayed a high species richness, a significant presence of endangered species and a low Ellenberg indicator value for nutrient supply. In a multi-criteria approach, dispersal traits, such as ‘Diaspore type: infructescence’ and Ellenberg indicator values for nutrient supply were key discriminators of conservation status, indicating an unfavourable conservation status when these traits attained high values. Although models of both habitat types were insufficiently robust to reliably distinguish between good, poor and bad conservation status, functional diversity clearly tended to increase with better conservation status. We have shown that habitat conservation status can principally be derived from existing vegetation records, originally collected for other purposes, opening up new possibilities in monitoring and restoration.

Conclusions

Our findings demonstrate that functional traits can provide meaningful insights into grassland conservation status, offering supplementary criteria to traditional assessments. Hence, this study provides a framework for integrating functional aspects into conservation assessments, allowing managers to prioritise grasslands suitable for low-impact restoration from those that require more comprehensive restoration methods. As functional criteria reflect both site conditions and management, including them enhances our understanding of the conditions required for preserving vegetation types with priority conservation status and enables us to prioritise restoration efforts for degraded types. However, functional characteristics alone are insufficient measures of the conservation status of alluvial and lowland hay meadows, highlighting the fundamental role of characteristic and habitat-specific species in determining conservation status for a certain habitat type.