Clara Castellano—Understanding the Impact of Rural Abandonment on Ecological Processes in Mediterranean Ecosystems

In this blog post, Clara Castellano—from the Department of Agrarian and Environmental Science at the University of Zaragoza, Huesca, Spain—discusses working on the ARBIO Project in the Middle Ebro River Valley, the joys of fieldwork, and what the future holds.

Profile

I’m interested in ecology in general, and specifically in nature conservation and ecological restoration. Throughout my scientific career, I have studied ecosystem services (i.e., the benefits we obtain from ecosystems) in agricultural landscapes and how ecological restoration can help enhance these services. I have also investigated the role of soil biodiversity in nutrient cycling across a Mediterranean climatic gradient, spanning from the semi-arid lands of the Ebro valley to the subalpine areas in the Pyrenees.

I have been captivated by the beauty and diversity of nature since I was a child. I decided to study biology because I wanted to understand how life functions–from cells to complex ecosystems. During my time at university, I realized that my true passion lay in ecology, specifically in the study of conservation and ecosystem restoration. Throughout history, natural ecosystems have been severely degraded by human activity. Very few places remain undisturbed, with approximately 75% of the Earth’s surface altered.  

My aspiration is to contribute to the field of conservation and ecosystem restoration. The preservation and restoration of natural environments are of vital importance, not only for their remarkable beauty but also for the numerous essential services they provide to humanity. Our existence is intimately intertwined with the well-being of the natural world; we simply cannot live without nature. 

In recent decades, Europe has been experiencing a depopulation process in rural areas driven by socio-economic reasons. This depopulation process is particularly relevant in Mediterranean regions, characterized by high biodiversity, where abandonment directly impacts land use and agricultural landscapes. The abandonment of agricultural practices leads to a process of natural revegetation, altering the landscape and modifying the relationship between human-made and natural habitats. Overall, despite the extensive knowledge about the consequences of land use change on biodiversity, the effect of depopulation itself is not well-studied, even though it compromises the future of services provided by rural areas and is a priority area of interest for policymakers. 

Currently, I am involved in the ARBIO project (BBVA-LEONARDO Programme), which focuses on the effects of rural abandonment on multitrophic biodiversity and ecological processes in Mediterranean ecosystems. We are trying to understand the impact of rural abandonment on biodiversity and ecosystem processes in Mediterranean environments. To achieve this, we are simultaneously considering multiple spatial scales and trophic groups. We aim to contribute to our understanding of rewilding in Mediterranean agricultural systems. This will help enhance the management plans for human activities in depopulated areas of Spain. 

Where in the world are you?

Abandoned crop field in the municipality of Las Pedrosas in the Cinco Villas region © Clara Castellano

We are conducting our research in 40 municipalities in the Middle Ebro River Valley (Aragon, Spain), all of which have experienced depopulation over the past 50 years. Aragon is one of the main hotspots of depopulation in Europe (28 inhabitants/km2), where more than half of its municipalities have experienced depopulation in the last century.  

The climate in the Ebro Valley is Mediterranean continental with significant temperature variations. Winters are cold, with mean temperatures ranging from -1°C to 12°C. Summers are very hot and dry, with mean temperatures ranging from 18°C to over 35°C. Annual precipitation is limited, ranging from 340 mm to 520 mm. The landscape is primarily agricultural, with patches of natural ecosystems such as shrubland, riparian forest, pine forest, and oak forest. 

In each municipality, we selected two sites: one where agricultural activity ceased at least 20 years ago, and another as a control area, which is a natural site with no records of agricultural activity. In each of these areas, we studied biodiversity at three different trophic levels: vegetation, herbivores (grasshoppers), and predators (spiders). We conducted a vegetation inventory in the spring and collected samples of spiders and grasshoppers both in the spring and summer. For the collection of spiders and grasshoppers, we used pitfall traps, which are buried in the ground to collect species with more edaphic habits, and entomological sweep nets to collect species inhabiting shrubs and herbs. 

Pitfall trap © Clara Castellano

Hugo using an entomological net to capture arthropods
© Clara Castellano

I was surprised by the quantity and diversity of spiders and grasshoppers we managed to capture. While I have some vegetation studies experience, I had never participated in arthropod sampling and was unsure if it would be easy to collect grasshoppers and spiders. In the pitfall traps, we collected a wide variety of arthropods, but what surprised me even more was the abundance of insects (and other arthropods) we gathered using the entomological sweep net (stick insects, praying mantises, caterpillars, ladybugs, etc.).

Our study area has been characterized by high agricultural pressure since the 1940s. In some municipalities, it was challenging to find a control area near the abandoned crop. We relied on satellite images from 1957, 2000 and now. The images from the ’50s were sometimes unclear. Mainly, we had to ensure that the abandoned crop had been left uncultivated for at least 20 years, and then locate a suitable control area. 

Although we have not yet analyzed the data, our field observations suggest that nature is recovering relatively quickly despite the harsh climate conditions. However, in some municipalities where control areas from which propagules disperse (to recolonize the abandoned zones) appear scarce, the process is slower. There also seems to be a high diversity of arthropods. However, we still need to analyze the data, and it’s important to differentiate between local-level and landscape-level biodiversity. While an increase in biodiversity can be observed at the local level after fields are abandoned, landscape-level biodiversity is typically higher in landscapes composed of patches of different ecosystem types. Additionally, it’s important to consider that even though nature may recolonize disturbed areas, it’s difficult for these areas to return to their original state. The effects of disturbances persist for many years, and a new equilibrium is often reached which differs from the original one. 

Spiders observed with the binocular microscope for identification:
Thomisus onustus (right) and Argiope lobata (left).
© Clara Castellano

Tips for fieldwork  

We do field sampling in spring and summer. During that time, it can get very hot in our study area. One day, the car thermometer even reached over 45°C! You must come prepared with a hat, sunscreen, and plenty of cold water. Additionally, besides the arthropods we’re interested in, there are many mosquitoes and ticks in the Middle Ebro Valley. The only thing we can do against this is to spray ourselves with a strong repellent and thoroughly check our entire body when we get home. Fortunately, I was only bitten by one tick, even though we saw many of them! 

In addition, we had some issues with pitfall traps because sometimes when we returned to collect them, we found that they had been pulled out of the ground. We think it was sometimes animals and other times people. We were able to partially solve this by leaving them in the field for fewer days. On the other hand, the Ebro Valley is famous for its strong wind, known as cierzo. On cierzo days, it was very difficult to use the entomological sweep net to capture spiders and grasshoppers. It was important to check the weather forecast before planning our fieldwork days. Nevertheless, we had to be flexible because sometimes the forecast was wrong, and if it was too windy, it was best to go back home and try our luck another day.  

I love working outdoors, surrounded by nature. Sometimes the conditions can be a bit challenging, but they’re offset by the beautiful views and surprises like seeing foxes, deer, and birds of prey. Additionally, during fieldwork days, you spend a lot of time with your colleagues, and it can be very enjoyable, fostering closer relationships among team members. 

We always talk about our research with local residents, including the mechanic who fixed our car (twice) on the field. We also try to get university students involved in research, so we bring them to the field and explain our work. Finally, the most relevant results will be communicated to the Department of Agriculture, Livestock, and Environment, as well as to the Commissioner for the Fight against Depopulation of the Government of Aragón.  

The Future

During my participation in the ASBIO project from 2020 to 2022, I had the opportunity to work in the Pyrenees, studying the role of soil biodiversity in key ecosystem processes. I absolutely loved the experience; the Pyrenees are a mountain range with a spectacular landscape. I would like to return to work in the Pyrenees, perhaps studying what we are currently researching, the effects of agricultural abandonment on biodiversity. The Pyrenees have also experienced a significant rural exodus. On the other hand, during my doctoral studies, I had a research stay at the University of Bern. During my time there, I fell in love with the Alps, so I would also be eager to conduct field studies in those magnificent mountains. 

For now, we still have a lot of work ahead of us. We need to finish identifying the spiders and grasshoppers we’ve captured and analyse the data we’ve collected. The project’s principal investigator, Hugo Saiz, has secured additional funding, so in the future, the project’s research will continue, but the study area will be expanded to include more municipalities in the Ebro Valley. As for what I’ll work in the long term, I’m not sure yet, but my dream is to continue dedicating myself to ecology, conservation, and the study of biodiversity.