In the face of increasing biodiversity loss and ecosystem degradation, ecological restoration is more important than ever. To be more precise: effective and resilient restoration. From an ecological perspective, it is not only important which species are established, but also when and in what order. A recent study by Alonso-Crespo and colleagues, including Vicky Temperton from the Leuphana Institute of Ecology, investigates how the timing of plant arrivals and weather conditions at the start of a restoration shape the long-term dynamics of grassland ecosystems.
The study presents first results of the long-term field experiments on PriOrity Effect Mechanisms (POEM), initiated in 2020 and designed to test how priority and year effects modulate the structure and functioning of dry acidic grassland plant communities over time, both aboveground and belowground.
Info: Priority effects
“Priority effects occur when species that arrive and establish before others can significantly influence the establishment and success of species that arrive later, thus also sometimes influencing ecosystem functioning. Priority effects can lead to alternative vegetation states and thus may play a key role in conservation.”
The POEM Set-up
At a former agricultural field in Niederhaverbeck, Northern Germany, the research team established the POEM field experiment in 2020. It uses a replicated, multi-year design with different plant functional group (PFG) sowing sequences (grasses, forbs, legumes) and compares plots established in different years to capture weather effects. Using transparent tubes called minirhizotrons and a camera system, they tracked root growth over three years – without ever digging up a plant.
Findings that Dig Deep
The first results of the long-term experiment are already exciting. First, the scientists found that the time since establishment was the strongest driver of plant community composition, more than the plant functional group (PFG) order of arrival or the year of initiation. Species richness and diversity were influenced by PFG order of arrival, evolving over time and interacting with the year of sowing. Plots where grasses were sown first had lower diversity, due to their dominance (e.g. Bromus hordeaceus).
While root productivity (overall root biomass/density) did not differ significantly between treatments, the vertical distribution of roots was strongly affected: Communities where forbs or legumes were sown first rooted deeper than those where grasses were planted first. These findings, if generally found in other grasslands, could be a useful way to help create plant communities with deeper roots that are more adapted to droughts. Further research in POEM’s third experiment (being set up in 2025) will test this question. Here, minirhizotrons are installed in the soil and will allow the researchers to test whether there is a repeatable effect of the order of arrival on root distribution. Similar findings in a controlled experiment (Alonso-Crospo et al. 2022 Oikos) are promising, but the researchers need to do the hard work of setting up the same experiment again in the field to know to what extent this finding is generalizable.
Another finding of this study was that aboveground productivity was primarily influenced by year of initiation, with 2020 plots being more productive than those from 2021 — possibly due to more favorable weather in the first year. Thus, the year of sowing, reflecting different weather conditions, greatly impacted early community dynamics.
Implications that Go Beyond the Plot
As restoration becomes an increasingly vital tool for biodiversity and climate issues, nuanced insights and recommendations are critical. The POEM experiment will continue to unravel how ecological history, priority effects, functional traits, and weather variation interact in shaping restoration outcomes.
For practitioners, the experiment has clear takeaways. Among other things, it shows that weather conditions in the establishment year strongly influence productivity. This suggests that restoration projects should time sowing to favorable environmental windows when possible. Deeper rooting from forbs- or legumes-first sowing may promote soil stabilization, water access, and long-term persistence in degraded soils. In the face of increasing drought frequency, these communities will likely be more stable and persistent. Furthermore, deeper roots can contribute more to long-term soil carbon pools, which are more stable than surface biomass, promoting natural climate solutions (NCS).
Ecological experiments like this, which may appear solely scientific at first glance, have a strong practical relevance – especially in our times of overlapping ecological crises.
Want to know more about the study? You can find the paper here: https://onlinelibrary.wiley.com/doi/10.1111/jvs.70026
Are you interested in learning more about priority effects? Then read our article on: Breaking Down Barriers: A Call for Cohesion in Priority Effect Studies – Ecologically speaking – Blog on Ecological Research at Leuphana University Lueneburg
