Impact of management type and intensity on multiple facets of grassland biodiversity in the French Jura Mountains
Résumé
Questions: (1) Does grassland vegetation differ in its taxonomic, phylogenetic and functional alpha diversity between strictly grazed parcels (SGP) and mowed-and-grazed parcels (MGP)? (2) Do we observe differences in the responses of functional diversity (reflecting differences in the interspecific varia- tion of a trait in the plant community) and community-weighted mean trait values (CWMs, reflecting the characteristics of the dominant species)? (3) How do diversity and CWM patterns respond to disturbance and fertilization gradi- ents measured by agronomic descriptors in both parcel types?
Location: French Jura Mountains.
Methods: We compared taxonomic, phylogenetic and functional diversities (based on Rao quadratic entropy) and CWMs between the two management types (SGP and MGP). We then used agronomic variables, describing both defo- liation regime and fertilization intensity over the past 10 yrs to explain diversity indices and CWMs in a partial redundancy analysis (pRDA).
Results: Taxonomic and phylogenetic diversities were higher in SGP than in MGP, as well as functional diversity computed for qualitative traits (clonal growth organs and leaf distribution along the stem). Contrary to expectations from literature, we found higher CWM for leaf dry matter content (LDMC) in intensively and regularly cut grasslands compared to only grazed grasslands, which can be explained by the higher dominance of grass species in hay mead- ows. In addition, constrained ordination revealed that taxonomic, phylogenetic and some functional diversity metrics were negatively affected by defoliation intensity (mowing frequency), while most CWMs were mainly influenced by fertilization intensity, either by the available N input or by the role of commer- cial inorganic fertilizers, depending on the trait considered.
Conclusions: Our study revealed consistent patterns between the various facets of biodiversity in grasslands according to the main management regime. Taking agronomic gradients into account suggests the importance of considering both CWMs and functional diversity, which respond variously to agricultural prac- tices. Conservation of high diversity in grasslands, whatever the facet consid- ered, implies keeping some parcels exclusively grazed and limiting N inputs, especially those from inorganic commercial fertilizers.