Biology subjects

Olff, H.

Publications and source records attributed to Olff, H..

4 recordsLinked to original sources

bioRxiv2026

Experimental Disturbance-Induced Shifts in Benthic Functional Diversity: the importance of marine protected areas in soft-bottom ecosystems

Benthic communities form the foundation of food webs in coastal and shelf seas worldwide. However, these communities face severe threats from anthropogenic bottom-disturbing activities. Marine Protected Areas (MPAs) effectively safeguard benthic communities against such disturbances. Nevertheless, the effectiveness of MPAs for the recovery of benthic communities in highly dynamic soft-bottom areas is much debated, as these communities are thought to be adapted to natural dynamics and therefore resistant to human impacts. In this study, we examine whether MPAs in highly dynamic seas support sensitive communities that are affected by bottom-disturbing fishing gear. Utilising a Before-After-Control-Impact (BACI) experimental design, we investigated the effects of disturbance caused by a shrimp trawl gear on macrozoobenthic communities within MPAs in a dynamic coastal soft-bottom sea over two years. We assessed changes in taxonomic and functional diversity, as well as community composition, across three levels of trawling intensity and frequency (low intensity and high frequency, high intensity and low frequency, and high intensity and high frequency) compared with undisturbed control areas. The study was carried out in the lower dynamic areas of the study system, where we found that, even light trawling gear impacted functional diversity and community assembly of macrozoobenthic communities, leading to shifts in functional groups. Contrastingly, taxonomic diversity metrics were not affected. We found that taxonomic and functional turnover increased stronger over time than the undisturbed control, with the highest turnover in the most frequently disturbed treatments. Long-living species were negatively impacted by disturbance, and the abundance of scavengers and predators increased in trawled areas, with possible radiating effects into undisturbed areas, while suspension feeders declined. Our findings demonstrate that anthropogenic disturbance remains a relevant ecological pressure, even in areas that may appear resilient due to their dynamic nature. MPAs can then provide ecological benefits by protecting sensitive and functionally important species. Article Impact StatementMarine Protected Areas are effective in safeguarding sensitive communities from anthropogenic disturbance.

ecology↗

bioRxiv2024

Long-term non-trophic effects of large herbivores on plant diversity are underestimated

The positive effects of large herbivores on plant diversity in grasslands have so far been mainly attributed to increased light availability or suppressed dominance, and thus to the consequences of aboveground biomass consumption (trophic effects). However, these insights are mainly derived from short-term experiments. Using a 46-year experiment in a salt marsh, comparing cattle grazing, mowing (as a proxy of aboveground consumption) and the ungrazed control, we found that the non-trophic effects (e.g. trampling, deposition of urine and dung) of large herbivores on plant diversity increased over time, exceeding that of the trophic effects after 23 years. This long-term accumulation of non-trophic effects through slow ecosystem-level feedback highlights the sustainability of using low to moderate densities of large herbivores to conserve plant diversity. Our results emphasize the need for the conservation and re-introduction of large herbivores, domestic or wild, to sustain long-term grassland plant diversity.

ecology↗

bioRxiv2023

Understanding woody plant encroachment: a plant functional trait approach

The increase in the density of woody plants threatens the integrity of grassy ecosystems. It remains unclear if such encroachment can be explained mostly by direct effects of soil conditions and hydrology on woody plant growth or by indirect effects on fire regime and herbivory imposing tree recruitment limitation. Here, we investigate whether woody plant functional traits provide a mechanistic understanding of the complex relationships between these direct and indirect effects. We first assess the role of rainfall, soil fertility, texture, and geomorphology to explain variation in woody plant encroachment following anthropogenically-induced fire suppression across the Serengeti ecosystem. Second, we explore trait-environment relationships and how these mediate vegetation response to fire suppression. We find that woody plant encroachment is strongest in areas with high soil fertility, high rainfall, intermediate catenae positions, and fine soil textures. These conditions promote woody plant communities associated with small stature, small seed sizes, and high recruit densities (linked to a recruitment-stature trade-off). The positioning of species along this recruitment-stature axis was found to be the most important predictor of recruitment limitation. Areas that support such plant communities - e.g. mid-catena position - were most sensitive to woody plant encroachment. These findings demonstrate the importance of trait-environment relationships in predicting the impact of human alterations on local vegetation change. Understanding how environmental factors directly (resources) and indirectly (legacy effects and plant traits) determine woody plant encroachment supports the development of process-based ecosystem structure and function models.

ecology↗

bioRxiv2021

Long-term cross-scale comparison of grazing and mowing on plant diversity and community composition in a salt-marsh system

O_LILand abandonment is increasing in recent decades in Europe, usually accompanied by a decline in biodiversity. Whether livestock grazing and mowing can safeguard biodiversity across spatial scales in the long term is unclear. C_LIO_LIUsing a 48-year experiment in a salt marsh, we compared land abandonment (without grazing and mowing) and seven management regimes including cattle grazing, early season mowing, late season mowing, both early and late season mowing, and grazing plus each of the mowing regimes on plant diversity at the local (i.e. plot) and landscape scales (i.e. across plots). Also, we compared their effects on community composition (both in identities and abundances) in time and space. C_LIO_LIUnder land abandonment, plant diversity declined in the local communities and this decline became more apparent at the landscape scale, particularly for graminoids and halophytes. All management regimes, except the late season mowing, maintained plant diversity at these scales. C_LIO_LILocal plant communities under all treatments underwent different successional trajectories, in the end, diverged from their initial state except for that under grazing (a cyclic succession). Interannual composition change remained stable over time under land abandonment and grazing plus early season mowing. It increased over time under grazing and late season mowing, it increased in the second half of the experiment under other treatments. Vegetation homogenized in the landscape over time under land abandonment while vegetation was heterogeneous under all management regimes. C_LIO_LISynthesis. Our experiment suggests that late season mowing may not be sustainable to conserve plant diversity in salt marshes. Other management regimes can maintain plant diversity across scales and vegetation heterogeneity in the landscape in the long term, but local community composition may change over time. C_LI

ecology↗