ECR feature: Costanza Geppert on contrasting native and non-native plants responses

Costanza Geppert is a PhD student at the University of Padua in Italy. She is a conservation ecologist interested in the effects of global change on biodiversity. Here, Costanza shares her recent work on the drivers of plant redistribution in mountainous areas under global change.

Costanza Geppert

Personal links. ResearchGate | GoogleScholar | Research Group Website

Institute. Department of Agronomy, Food, Natural resources, Animals and Environment, University of Padua (Italy)

Academic life stage. PhD student

Major research themes. I have always been interested in the ecological and evolutionary forces shaping community structure and species distributions. In my PhD research, I am studying which biotic and abiotic drivers are redefining the distributional dynamics of native and non-native plants under global change.

Current study system. Plants and herbivores! Plants may seem like static organisms, but they are quite the opposite. My specific interests are related to species’ responses to environmental change, and alpine plants provide an incredible system to understand changes in range margins and community composition in response to global change. In the European Alps, plant species are shifting their range to a higher elevation with a speed of c. 3 – 5 m per year, and non-native species are moving even faster. This large-scale reshuffling of species distributions creates novel interactions among species and across trophic levels that previously did not co-occur. In particular, interactions with herbivores emerged as a fundamental driver of plant community composition.

Team work to install the experiment in Friuli (NE Italy).

Recent JBI paper. Geppert, C., Boscutti, F., La Bella, G., De Marchi, V., Corcos, D., Filippi, A., & Marini, L. (2021). Contrasting response of native and non‐native plants to disturbance and herbivory in mountain environments. Journal of Biogeography, 48(7), 1594-1605

Motivation behind this paper. In temperate mountains, plant diversity is currently under threat by climate warming and human disturbance, while the same drivers promote non-native spread. Although biotic interactions should modulate plant invasions, it is still unclear how invertebrate herbivores can affect non-native spread. Most previous research focused on lab experiments, and we were surprised by the lack of experiments under realistic field conditions investigating the interaction between global change and herbivory in plant invasions. We decided to design such a field experiment. In this paper, we report findings from a large manipulative experiment along an elevational gradient designed to disentangle the effects of climate warming, human disturbance, and herbivory on the establishment dynamics of native and non-native plants.

Experimental set up: after disturbing the soil, we installed in half of the plots cages to exclude herbivores.

Key methodologies. Often studies on plant redistributions disregard biotic interactions. Moreover, research on herbivory and global change is carried out mainly in controlled environments, while the experiments that are under realistic field conditions usually involve transplanting and, thereby, overlook plants’ natural establishments. The novelty of this paper is to consider herbivory and to observe the natural dynamics of plant invasions. We selected fifteen dry semi-natural grasslands along an elevational gradient (0 – 1300 m) in the European Alps. In each grassland, we manipulated soil disturbance, nitrogen deposition, and invertebrate herbivory. Then, we followed the natural establishment under real field conditions of both native and non-native plants for one growing season.

Unexpected challenges. Tilling the soil and installing the 120 herbivory exclusion cages in fifteen sites along the elevational gradient proved to be quite challenging. Together with two enthusiastic MSc students, I planned to install the experiment over a few days, but, on the first day, we ended up exhausted with only two out of the fifteen sites ready. That night we called for backup, and luckily three days later, we were ready to start the experiment.

Philaenus spumarius L., meadow spittlebug, one of the many arthropod herbivores found in our study area (NE Italy). Photo by Francesco Sanna.

Major results. Our findings show that the combination of warm temperatures and human-induced disturbance favoured non-native plant establishments over natives, suggesting that global change will promote the further spread of non-native plants in mountain environments. Moreover, invertebrate herbivores played an important role in invasion dynamics. Natural herbivory pressure from invertebrates might amplify the negative effects of disturbance on resident native species, facilitating the emergence and growth of non-native species. Our experiment is one of the first to elucidate the complex interactions between biotic and abiotic drivers of plant invasions.

Next steps for this research. The next step would be to observe how the novel plant communities were established and developed after our manipulations over a long time. Unfortunately, we had to stop our experiment after one year because of Covid restrictions, but we are continuing to investigate plant distributional changes and plant-herbivore interactions under global change with new observational studies and experiments. In addition, it would be extremely interesting to understand whether functional traits can explain plant community responses to global change and whether we would be able to make predictions based on community traits.

Dry grasslands rich in plant species before tilling the soil in the Italian Alps. Photo by Lorenzo Marini.

If you could study any organism on Earth, what would it be? The story of my fascination with plants and insects goes back to my childhood, but as a conservation ecologist, what is most compelling to me are biotic interactions and species responses to environmental change. After all, I would be curious about any organism!

Anything else to add? This research is part of my PhD thesis, and this experiment would not have been possible without the help of Greta and Vittoria, two MSc students that were motivated enough to carry out with me four 4 months of fieldwork. Also, the collaboration with Francesco, an expert botanist from Udine University, was essential for teaching and helping us identify the 264 plant species even when they were small seedlings.

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