Taxonomic, Phylogenetic and Functional Diversity Behave Differently Under Disturbance Pressure and Complex Land‐Use History: Assembly Rules in Grassland Communities

TL;DR

This study shows how grazing and land abandonment affect plant diversity in Alpine grasslands, revealing complex patterns in species assembly.

Contribution

The study demonstrates that taxonomic, phylogenetic, and functional diversity respond differently to land-use changes, challenging simple assembly rule paradigms.

Findings

Extensive grazing supports the highest taxonomic and phylogenetic diversity.

Abandoned grasslands show decreasing diversity as succession progresses.

Functional diversity is most influenced by intermediate grazing and recent abandonment.

Abstract

Grazing and land abandonment trigger ecological succession and can affect plant communities by determining the relative importance of ecological assembly rules. A thorough understanding of these processes requires the implementation of taxonomic, phylogenetic, and functional diversity, along with knowledge of how they relate to each other in response to disturbance. We carried out survey on 120 plots and calculated taxonomic, phylogenetic, and functional diversity, the diversity's dimensionality, as well as the community weighted means to detect species functional response to changes in land‐use. Extensive grazing supported highest taxonomic and phylogenetic diversity. Whereas intense grazing had lowest diversity values. Abandoned grasslands resulted in differences between time periods, with past abandonment decreasing in diversity as succession advances. Functional diversity weakly varied among land‐use categories, yet the CWM analysis highlighted an increase in conservative resource‐use strategies through succession, and avoidance mechanisms with an increase in acquisitive traits in grazed communities. The importance of metrics in explaining the variation of the biodiversity space varied according to land‐use categories, where to the diversity of intensive grazing and past abandonment contributed most phylogenetic diversity, for intermediate grazing and recent abandonment the variation was explained mostly by functional diversity, and we found equal contribution between phylogenetic and functional diversity in extensive grazing. Our study suggests that reality is more complex than the simple paradigm that mechanisms of habitat filtering and limiting similarity lead to less and more diverse communities, highlighting the importance to treat the three diversity components as complementary. This knowledge supports management practices in grasslands experiencing grazing intensification or abandonment, especially in protected areas where legislation imposes responsibility for conservation action.

Grasslands in the Alps are undergoing land‐use change triggering ecological succession and affecting community composition. Taxonomic, phylogenetic, and functional diversity are used as complementary information to infer on community assembly processes, supporting conservation practices.

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